Positive electrode active material, method for preparing the same, and rechargeable lithium battery including the same

Abstract

Provided are a positive electrode active material, a method of preparing the same, and a rechargeable lithium battery including the same. The positive electrode active material includes: a first positive electrode active material including a lithium nickel-based composite oxide and including secondary particles formed by aggregating a plurality of primary particles and a cobalt coating portion on a surface of the secondary particles; and a second positive electrode active material including a lithium nickel-based composite oxide and including single particles and a cobalt coating portion on a surface of the single particles, wherein the second positive electrode active material has an uneven surface having a concave-convex and a flat surface having no concave-convex.

Description

Technical Field

[0001] Exemplary embodiments of this disclosure relate to positive electrode active materials for rechargeable lithium batteries, methods for preparing the same, and rechargeable lithium batteries including the same. Background Technology

[0002] Portable information devices such as cell phones, laptops, and smartphones, as well as electric vehicles, already use rechargeable lithium batteries with high energy density and portability as their power source. Recently, research has been actively underway to use rechargeable lithium batteries with high energy density as a power source or energy storage source for hybrid or electric vehicles.

[0003] Various cathode active materials have been studied for application in rechargeable lithium-ion batteries. Among them, lithium nickel oxides, lithium nickel manganese cobalt composite oxides, lithium nickel cobalt aluminum composite oxides, and lithium cobalt oxide are mainly used as cathode active materials. However, these cathode active materials exhibit structural collapse or cracking during repeated charging and discharging, resulting in long-term cycle life degradation and increased resistance in rechargeable lithium-ion batteries, thus exhibiting unsatisfactory capacity characteristics. Accordingly, there is a need to develop new cathode active materials that ensure long-term cycle life characteristics and achieve high capacity and high energy density. Summary of the Invention

[0004] A positive electrode active material for rechargeable lithium batteries with improved cycle life and safety while achieving high capacity is provided, along with a method for its preparation and a rechargeable lithium battery including the material.

[0005] In an embodiment, the positive electrode active material for a rechargeable lithium battery includes: a first positive electrode active material comprising a lithium-nickel composite oxide and including secondary particles formed by aggregating a plurality of primary particles and a cobalt coating portion on the surface of the secondary particles; and a second positive electrode active material comprising a lithium-nickel composite oxide and including a single particle and a cobalt coating portion on the surface of the single particle, wherein the second positive electrode active material has an uneven surface with irregularities and a flat surface without irregularities.

[0006] In another embodiment, a method for preparing a positive electrode active material for a rechargeable lithium battery includes: mixing a first nickel hydroxide and a lithium raw material and performing a first heat treatment to prepare a first nickel oxide in the form of secondary particles formed by aggregating a plurality of primary particles; mixing a second nickel hydroxide and a lithium raw material and performing a second heat treatment to prepare a second nickel oxide in the form of individual particles; and mixing the first nickel oxide, the second nickel oxide, and a cobalt raw material and performing a third heat treatment.

[0007] In another embodiment, a rechargeable lithium battery is provided, comprising: a positive electrode including a positive electrode active material, a negative electrode, and an electrolyte.

[0008] The positive electrode active material for rechargeable lithium batteries prepared according to the embodiments, and the rechargeable lithium batteries including the present invention, exhibit excellent charge / discharge efficiency, cycle life characteristics, and safety, while achieving high capacity and high energy density. Attached Figure Description

[0009] Figure 1 A schematic diagram illustrating a rechargeable lithium battery according to an embodiment.

[0010] Figure 2 This is a scanning electron microscope image of the second positive electrode active material in Example 1.

[0011] Figure 3 This is a scanning electron microscope image of the second positive electrode active material after cobalt coating and before the third heat treatment in Example 2.

[0012] Figure 4 This is a scanning electron microscope image of the second positive electrode active material in Example 2.

[0013] Figure 5 A scanning electron microscope image of the second positive electrode active material of Comparative Example 1.

[0014] Figure 6 A scanning electron microscope image of the second positive electrode active material of Comparative Example 2.

[0015] Figure 7 A photograph of cobalt element obtained by SEM-EDS (scanning electron microscopy-energy dispersive spectroscopy) analysis of the second positive electrode active material according to Example 1.

[0016] Figure 8 A photograph of cobalt element obtained by SEM-EDS analysis of the second positive electrode active material according to Comparative Example 1.

[0017] <Symbol Description>

[0018] 100: Rechargeable lithium battery; 112: Negative electrode

[0019] 113: Separator 114: Positive electrode

[0020] 120: Battery casing; 140: Sealing component Detailed Implementation

[0021] Specific implementations will be described in detail below so that those skilled in the art can readily implement them. However, this disclosure may be embodied in many different forms and is not to be construed as limited to the exemplary implementations set forth herein.

[0022] The terminology used herein is for descriptive purposes only and is not intended to limit this disclosure. Unless the context clearly indicates otherwise, singular expressions include plural expressions.

[0023] As used herein, “combinations thereof” refers to mixtures, laminates, composites, copolymers, alloys, blends, and reaction products, etc.

[0024] In this document, it should be understood that terms such as “comprises,” “includes,” or “have” are intended to indicate the presence of specific features, quantities, steps, elements, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, quantities, steps, elements, or combinations thereof.

[0025] In the accompanying drawings, for clarity, the thicknesses of layers, films, panels, areas, etc., are enlarged, and the same reference numerals are used throughout the specification to label the same elements. It will be understood that when an element, such as a layer, film, area, or substrate, is referred to as being "on" another element, it may be directly on the other element, or an intervening element may be present. In contrast, when an element is referred to as being "directly on" another element, no intervening element is present.

[0026] In addition, the term "layer" in this article includes not only shapes that form across the entire surface when viewed from a plan view, but also shapes that form on a portion of the surface.

[0027] Alternatively, the average particle size can be measured using methods well known to those skilled in the art, for example, by a particle size analyzer, or by transmission electron microscopy or scanning electron microscopy. Optionally, the average particle size value can be obtained by measuring using a dynamic light scattering method, performing data analysis, counting the number of particles in each particle size range, and thereby calculating. Unless otherwise defined, the average particle size may mean the diameter (D50) of particles that constitute 50% of the total volume in the particle size distribution.

[0028] In this article, "or" is not interpreted as exclusive; for example, "A or B" is interpreted as including A, B, and A+B, etc.

[0029] Positive electrode active material

[0030] In one embodiment, the first positive electrode active material comprises a lithium-nickel composite oxide in the form of secondary particles formed by aggregating multiple primary particles, and includes a cobalt coating portion on the surface of the secondary particles. The second positive electrode active material comprises a lithium-nickel composite oxide in the form of a single particle, and includes a cobalt coating portion on the surface of the single particle. The second positive electrode active material has both an uneven surface with irregularities and a flat surface without irregularities. This positive electrode active material exhibits improved cycle life characteristics while achieving high capacity and high energy density.

[0031] First positive electrode active material

[0032] The first positive electrode active material has a polycrystalline form and includes secondary particles formed by the aggregation of two or more primary particles.

[0033] The first positive electrode active material according to an embodiment includes a cobalt coating portion on the surface of the secondary particles. The cobalt coating portion may be disposed on the entire surface or at least a portion of the surface of the secondary particles. The first positive electrode active material is coated with cobalt, and thus effectively suppresses structural collapse due to repeated charging and discharging, and accordingly improves room temperature and high temperature cycle life characteristics.

[0034] The cobalt coating portion includes a cobalt-containing compound. The cobalt-containing compound may be, for example, cobalt oxide, cobalt hydroxide, cobalt carbonate, composites thereof, or mixtures thereof, and these may further include lithium and / or nickel. For example, the cobalt-containing compound may be lithium cobalt oxide.

[0035] Based on the total amount of the first positive electrode active material, the amount of the cobalt coating portion in the first positive electrode active material can be from about 0.01 mol% to about 7 mol%, for example, from about 0.01 mol% to about 6 mol%, from about 0.1 mol% to about 5 mol%, from about 0.5 mol% to about 4 mol%, from about 1 mol% to about 5 mol%, or from about 2 mol% to about 5 mol%, and can also be from about 0.01 atomic% to about 7 atomic%, from about 0.1 atomic% to about 5 atomic%, or from about 0.5 atomic% to about 4 atomic%. In this case, the rechargeable lithium battery including the first positive electrode active material can achieve excellent room temperature and high temperature cycle life characteristics.

[0036] The thickness of the cobalt coating portion in the first positive electrode active material varies depending on the firing temperature during coating, and cobalt can infiltrate into the active material, and is coated and / or doped according to the firing temperature. Accordingly, the thickness of the cobalt coating portion can be, for example, about 1 nm to about 2 μm, about 1 nm to about 1.5 μm, about 1 nm to about 1 μm, about 1 nm to about 900 nm, about 1 nm to about 700 nm, about 1 nm to about 500 nm, about 1 nm to about 300 nm, about 5 nm to about 100 nm, or about 5 nm to about 50 nm. In this case, the rechargeable lithium battery including the first positive electrode active material can exhibit excellent room temperature and high temperature cycle life characteristics.

[0037] The average particle size of the first positive electrode active material, i.e., the average particle size of the secondary particles, can be from about 7 μm to about 25 μm. For example, the average particle size of the first positive electrode active material can be from about 9 μm to about 25 μm, from about 10 μm to about 25 μm, from about 15 μm to about 25 μm, or from about 10 μm to about 20 μm. The average particle size of the secondary particles of the first positive electrode active material can be equal to or greater than the average particle size of the second positive electrode active material having the form of individual particles, which will be described later. The positive electrode active material according to the embodiment can be in the form of a mixture of the first positive electrode active material (as polycrystalline and large particles) and the second positive electrode active material (in the form of individual particles and small particles), thereby improving the mixture density and providing high capacity and high energy density.

[0038] In this paper, the average particle size, or D50, refers to the diameter of the particles that constitute 50% of the total volume in the particle size distribution. The average particle size can be measured using electron microscopy, such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM). For example, in a SEM of the first positive electrode active material, 30 particles are randomly selected as secondary particles, their dimensions (particle diameter or length of the major axis) are measured to obtain the particle size distribution, and D50 is calculated to obtain the average particle size of the first positive electrode active material.

[0039] The first positive electrode active material is a nickel-based positive electrode active material, and includes lithium-nickel composite oxides (or first nickel oxides). Based on the total amount of elements other than lithium and oxygen, the nickel content in the lithium-nickel composite oxide can be greater than or equal to about 30 mol%, for example, greater than or equal to about 40 mol%, greater than or equal to about 50 mol%, greater than or equal to about 60 mol%, greater than or equal to about 70 mol%, greater than or equal to about 80 mol%, or greater than or equal to about 90 mol% and less than or equal to about 99.9 mol%, or less than or equal to about 99 mol%. For example, the nickel content in the lithium-nickel composite oxide can be higher than the content of each of other metals such as cobalt, manganese, and aluminum. When the nickel content meets the above range, the rechargeable lithium battery including the first positive electrode active material can exhibit excellent battery performance while achieving high capacity.

[0040] Specifically, the first positive electrode active material may include a lithium-nickel composite oxide represented by chemical formula 1.

[0041] [Chemical Formula 1]

[0042] Li a1 Ni x1 M 1 y1 M 2 1-x1-y1 O2

[0043] In chemical formula 1, 0.9 ≤ a1 ≤ 1.8, 0.3 ≤ x1 ≤ 1, 0 ≤ y1 ≤ 0.7, and M 1 and M 2 Each of the following is independently Al, B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr or a combination thereof.

[0044] In chemical formula 1, 0.4≤x1≤1 and 0≤y1≤0.6, 0.5≤x1≤1 and 0≤y1≤0.5, 0.6≤x1≤1 and 0≤y1≤0.4, 0.7≤x1≤1 and 0≤y1≤0.3, 0.8≤x1≤1 and 0≤y1≤0.2, or 0.9≤x1≤1 and 0≤y1≤0.1.

[0045] The first positive electrode active material may include, for example, a lithium-nickel composite oxide represented by chemical formula 2.

[0046] [Chemical Formula 2]

[0047] Li a2 Ni x2 Co y2 M 3 1-x2-y2 O2

[0048] In Chemical Formula 2, 0.9 ≤ a2 ≤ 1.8, 0.3 ≤ x2 < 1, 0 < y2 ≤ 0.7, and M 3 is Al, B, Ba, Ca, Ce, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, or a combination thereof.

[0049] In Chemical Formula 2, 0.3 ≤ x2 ≤ 0.99 and 0.01 ≤ y2 ≤ 0.7, 0.4 ≤ x2 ≤ 0.99 and 0.01 ≤ y2 ≤ 0.6, 0.5 ≤ x2 ≤ 0.99 and 0.01 ≤ y2 ≤ 0.5, 0.6 ≤ x2 ≤ 0.99 and 0.01 ≤ y2 ≤ 0.4, 0.7 ≤ x2 ≤ 0.99 and 0.01 ≤ y2 ≤ 0.3, 0.8 ≤ x2 ≤ 0.99 and 0.01 ≤ y2 ≤ 0.2, or 0.9 ≤ x2 ≤ 0.99 and 0.01 ≤ y2 ≤ 0.1.

[0050] The first positive electrode active material may include, for example, a lithium nickel-based composite oxide represented by Chemical Formula 3.

[0051] [Chemical Formula 3]

[0052] Li a3 Ni x3 Co y3 M 4 z3 M 5 1-x3-y3-z3 O2

[0053] In Chemical Formula 3, 0.9 ≤ a3 ≤ 1.8, 0.3 ≤ x3 ≤ 0.98, 0.01 ≤ y3 ≤ 0.69, 0.01 ≤ z3 ≤ 0.69, M 4 is Al, Mn, or a combination thereof, and M 5 is B, Ba, Ca, Ce, Cr, Cu, F, Fe, Mg, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, or a combination thereof.

[0054] In chemical formula 3, 0.4≤x3≤0.98, 0.01≤y3≤0.59, and 0.01≤z3≤0.59, 0.5≤x3≤0.98, 0.01≤y3≤0.49, and 0.01≤z3≤0.49, 0.6≤x3≤0.98, 0.01≤y3≤0.39, and 0.01≤z3≤0.39, 0.7≤x3≤0.98, 0.01≤y3≤0.29, and 0.01≤z3≤0.29, 0.8≤x3≤0.98, 0.01≤y3≤0.19, and 0.01≤z3≤0.19, or 0.9≤x3≤0.98, 0.01≤y3≤0.09, and 0.01≤z3≤0.09.

[0055] Meanwhile, the maximum surface roughness of the first positive electrode active material can be, for example, about 3 nm to about 100 nm, about 5 nm to about 50 nm, about 3 nm to about 15 nm, or about 3 nm to about 10 nm; the average roughness can be about 0.2 nm to about 10 nm, about 0.5 nm to about 3 nm, about 0.2 nm to about 1.5 nm, or about 0.2 nm to about 1 nm; and the root mean square roughness can be about 0.5 nm to about 10 nm, about 0.7 nm to about 3 nm, about 0.5 nm to about 2 nm, or about 0.5 nm to about 1.5 nm. Details regarding the meaning and measurement methods of maximum roughness, average roughness, and root mean square roughness will be described later in the section on the second positive electrode active material.

[0056] Second positive electrode active material

[0057] The second positive electrode active material can be in the form of a single particle, where a single particle means that a single particle exists independently without grain boundaries on its interior; or it can be a monolithic or non-aggregated particle with an integral structure, where the particles do not aggregate but exist as an independent phase from a morphological perspective and can be, for example, a single crystal. Rechargeable lithium batteries including the second positive electrode active material according to embodiments can exhibit improved cycle life characteristics while achieving high capacity and high energy density by including the second positive electrode active material.

[0058] There are no particular limitations on the shape of the second positive electrode active material; it can have various shapes, such as polyhedrons, ellipses, plates, rods, and irregular shapes. The single-crystal second positive electrode active material according to the embodiment can have a polyhedral structure with two or more surfaces.

[0059] The second positive electrode active material according to the embodiment includes a cobalt coating portion on the surface of individual particles. Because the second positive electrode active material is coated with cobalt, structural collapse due to repeated charging and discharging is effectively suppressed, thus improving room temperature and high temperature cycle life characteristics.

[0060] The cobalt coating portion includes a cobalt-containing compound. The cobalt-containing compound may be, for example, cobalt oxide, cobalt hydroxide, cobalt carbonate, composites thereof, or mixtures thereof, and may further include lithium and / or nickel. For example, the cobalt-containing compound may be lithium cobalt oxide, etc.

[0061] The method for preparing the positive electrode active material according to the embodiments, as described later, can be carried out by mixing a first nickel oxide and a second nickel oxide with a cobalt raw material and performing a third heat treatment to simultaneously coat (or simultaneously fire) the materials, rather than coating the first and second nickel oxides separately. According to this method, cobalt is effectively coated only on a portion of the crystal surface of the single-crystal second positive electrode active material, and an uneven surface is formed in this portion. Accordingly, a single particle of the second positive electrode active material includes both an uneven surface with a rough shape due to the specific shape of the uneven surface and a flat or smooth surface. It is understood that cobalt is effectively coated only on the crystal surface where lithium ions can easily enter and exit, thus creating the uneven surface. The surface roughness of the second positive electrode active material increases the specific surface area, and the second positive electrode active material and the positive electrode active material including it can have an increased specific surface area. Rechargeable lithium batteries including such positive electrode active materials can have improved initial discharge capacity, charge / discharge efficiency, and cycle life characteristics.

[0062] The unevenness on the surface can be linear or irregular. Furthermore, an uneven surface can be defined as a shape in which a cobalt-containing compound is linearly or irregularly attached, or a shape in which the cobalt-containing compound covers the surface of a single particle in an irregular shape. This shape differs from traditional island-type coatings.

[0063] A single particle of the second positive electrode active material may include an uneven surface with high surface roughness and a flat surface with low surface roughness. That is, in the second positive electrode active material, the uneven surface has high surface roughness. Maximum roughness (R) max The peak height and maximum roughness depth can be the vertical distance between the highest peak and the lowest valley within the reference length of the roughness cross-sectional curve (roughness curve diagram).

[0064] The average roughness (R) of the surface roughness a Also known as centerline average roughness, it is obtained as the arithmetic mean of the absolute values ​​of the ordinates (length from the center to the peak) over a reference length on a roughness graph. Root mean square roughness (Rm) q The roughness can be the root mean square (rms) of the vertical value within the reference length of the roughness curve. For the parameters and measurement methods specified in KSB 0601 or ISO 4287 / 1, please refer to these standards.

[0065] The uneven surface of the second positive electrode active material may have a maximum roughness (R0) greater than or equal to about 18 nm, for example, greater than or equal to about 20 nm, about 18 nm to about 100 nm, about 18 nm to about 80 nm, about 19 nm to about 60 nm, or about 20 nm to about 40 nm. max (Peak height). In this case, rechargeable lithium batteries including a second positive electrode active material exhibit high energy density and high capacity, and achieve excellent charge / discharge efficiency and cycle life characteristics.

[0066] The uneven surface of the second positive electrode active material may have an average roughness (R0) greater than or equal to about 1.9 nm, for example, greater than or equal to about 2.0 nm, about 1.9 nm to about 10 nm, about 1.9 nm to about 8.0 nm, about 1.9 nm to about 6.0 nm, about 1.9 nm to about 5.0 nm, or about 2.0 nm to about 10 nm. a In this case, rechargeable lithium batteries including a second positive electrode active material can exhibit high energy density and high capacity, and can achieve excellent charge / discharge efficiency and cycle life characteristics.

[0067] The uneven surface of the second positive electrode active material may have a root mean square roughness (Rm) greater than or equal to about 2.3 nm, for example, greater than or equal to about 2.4 nm, about 2.3 nm to about 10 nm, about 2.3 nm to about 8 nm, about 2.3 nm to about 6 nm, about 2.3 nm to about 5 nm, or about 2.4 nm to about 10 nm. q In this case, rechargeable lithium batteries including a second positive electrode active material exhibit high energy density and high capacity, and achieve excellent charge / discharge efficiency and cycle life characteristics.

[0068] On the other hand, the flat surface of the second positive electrode active material can exhibit a lower surface roughness than that of a non-flat surface. For example, the flat surface of the second positive electrode active material can have a maximum roughness (R0) of less than or equal to about 15 nm, for example, from about 0.1 nm to about 14 nm, or from about 1 nm to about 13 nm. max Additionally, the flat surface of the second positive electrode active material may have an average roughness (R0) of less than or equal to about 1.8 nm, for example, about 0.1 nm to about 1.8 nm, or about 0.5 nm to about 1.7 nm. a The flat surface of the second positive electrode active material may have a root mean square roughness (Rm) of less than or equal to about 2.2 nm, for example, about 0.1 nm to about 2.2 nm, or about 0.5 nm to about 2.1 nm. q ).

[0069] As mentioned above, the second positive electrode active material, which includes both uneven and flat surfaces, can have a stable structure that will not collapse due to repeated charging and discharging of the battery. Furthermore, rechargeable lithium batteries that include the second positive electrode active material exhibit excellent cycle life characteristics while achieving high capacity and high energy density.

[0070] Based on the total amount of the second positive electrode active material, the content of the cobalt coating portion in the second positive electrode active material can be from about 0.01 mol% to about 10 mol%, for example, from about 0.05 mol% to about 9 mol%, from about 0.1 mol% to about 8 mol%, from about 0.5 mol% to about 7 mol%, or from about 1 mol% to about 6 mol%, and can also be from about 0.01 atomic% to about 10 atomic%, from about 0.1 atomic% to about 8 atomic%, or from about 0.5 atomic% to about 6 atomic%. In this case, the rechargeable lithium battery including the second positive electrode active material can achieve excellent room temperature and high temperature cycle life characteristics.

[0071] The ratio of the uneven surface to the total surface area of ​​the second positive electrode active material can be from about 40% to about 80%, for example, from about 45% to about 80%, or from about 50% to about 75%. Alternatively, the ratio of the flat surface to the total surface area of ​​the second positive electrode active material can be from about 20% to about 60%, for example, from about 20% to about 55%, or from about 25% to about 50%. The second positive electrode active material includes both uneven and flat surfaces at these ratios, and therefore, rechargeable lithium batteries incorporating the second positive electrode active material can achieve high capacity while simultaneously exhibiting improved cycle life characteristics.

[0072] The thickness of the cobalt coating in the second positive electrode active material can be from about 1 nm to about 2 μm, for example, from about 1 nm to about 1 μm, from about 1 nm to about 900 nm, from about 1 nm to about 700 nm, from about 1 nm to about 500 nm, from about 1 nm to about 300 nm, from about 5 nm to about 100 nm, or from about 5 nm to about 50 nm. In this case, the rechargeable lithium battery including the second positive electrode active material can exhibit excellent room temperature and high temperature cycle life characteristics. The thickness of the cobalt coating can be measured by electron micrograph of the second positive electrode active material.

[0073] On the other hand, the second positive electrode active material may have sides with different cobalt contents. In other words, within a single particle, the second positive electrode active material may have a side with a high cobalt content and another side with a low cobalt content. For example, based on the total content of all metals except lithium, the cobalt content of the side with the high cobalt content may be 30 atomic% to 70 atomic% or 35 atomic% to 65 atomic%. Based on the total content of all metals except lithium, the cobalt content of the side with the low cobalt content may be about 1 atomic% to about 30 atomic%, or about 3 atomic% to about 25 atomic%. Furthermore, the ratio of the side with the high cobalt content in a single particle may be about 20% to about 50%, and the ratio of the side with the low cobalt content in a single particle may be about 50% to about 80%. This second positive electrode active material can improve the capacity characteristics and cycle life characteristics of the battery.

[0074] The average particle size of the second positive electrode active material, i.e., the average particle size of a single particle, can be from about 0.05 μm to about 10 μm, for example, from about 0.1 μm to about 8 μm, from about 0.1 μm to about 7 μm, from about 0.1 μm to about 6 μm, from about 0.1 μm to about 10 μm, or specifically from about 1 μm to about 5 μm. The average particle size of the second positive electrode active material can be the same as or smaller than that of the first positive electrode active material, and thus can further increase the density of the positive electrode active material. In this document, the average particle size, i.e., D50, refers to the diameter of the particles that accumulate to 50% of the volume in the particle size distribution. For example, in a scanning electron microscope image of the second positive electrode active material, 30 particles are randomly selected as individual particles, their dimensions (particle diameter or length of the major axis) are measured to obtain the particle size distribution, and D50 is calculated to obtain the average particle size of the second positive electrode active material.

[0075] The BET specific surface area of ​​the entire positive electrode active material, including the first and second positive electrode active materials, can be approximately 0.2 m². 2 / g to approximately 0.6m 2 / g, for example, about 0.3m 2 / g to approximately 0.5m 2 / g, or approximately 0.3m 2 / g to approximately 0.4m 2 / g. In this case, the positive electrode active material achieves excellent charge / discharge efficiency and cycle life characteristics. The BET specific surface area can be measured using, for example, the ASAP 2020 specific surface area measurement device manufactured by Micromeritics via nitrogen gas adsorption. Specifically, approximately 0.4g of the positive electrode active material sample is filled into a tank, pretreated by heating to 220°C, cooled to the temperature of liquid nitrogen, and subjected to saturation adsorption with a gas of 30% nitrogen and 70% helium, and then heated to room temperature to measure the amount of desorbed gas. From the obtained results, the specific surface area can be calculated using the conventional Brunol-Emmett-Taylor (BET) method.

[0076] The second positive electrode active material includes lithium-nickel composite oxides (or second nickel oxides) as the nickel-based active material. Based on the total amount of elements other than lithium and oxygen, the nickel content in the lithium-nickel composite oxide can be greater than or equal to about 30 mol%, for example, greater than or equal to about 40 mol%, greater than or equal to about 50 mol%, greater than or equal to about 60 mol%, greater than or equal to about 70 mol%, greater than or equal to about 80 mol%, or greater than or equal to about 90 mol% and less than or equal to about 99.9 mol%, or less than or equal to about 99 mol%. For example, the nickel content in the lithium-nickel composite oxide can be higher than the individual contents of other transition metals such as cobalt, manganese, and aluminum. When the nickel content meets the above range, the positive electrode active material can exhibit excellent battery performance while achieving high capacity.

[0077] The second positive electrode active material may include, for example, a lithium-nickel composite oxide represented by chemical formula 11.

[0078] [Chemical Formula 11]

[0079] Li a11 Ni x11 M 11 y11 M 12 1-x11-y11 O2

[0080] In chemical formula 11, 0.9 ≤ a11 ≤ 1.8, 0.3 ≤ x11 ≤ 1, 0 ≤ y11 ≤ 0.7, M 11 and M 12 Each of the following is independently Al, B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr or a combination thereof.

[0081] In Chemical Formula 11, 0.4 ≤ x11 ≤ 1 and 0 ≤ y11 ≤ 0.6, 0.5 ≤ x11 ≤ 1 and 0 ≤ y11 ≤ 0.5, 0.6 ≤ x11 ≤ 1 and 0 ≤ y11 ≤ 0.4, 0.7 ≤ x11 ≤ 1 and 0 ≤ y11 ≤ 0.3, 0.8 ≤ x11 ≤ 1 and 0 ≤ y11 ≤ 0.2, or 0.9 ≤ x11 ≤ 1 and 0 ≤ y11 ≤ 0.1.

[0082] The second positive electrode active material may include, for example, a lithium nickel-based composite oxide represented by Chemical Formula 12.

[0083] [Chemical Formula 12]

[0084] Li a12 Ni x12 Co y12 M 13 1-x12-y12 O2

[0085] In Chemical Formula 12, 0.9 ≤ a12 ≤ 1.8, 0.3 ≤ x12 < 1, 0 < y12 ≤ 0.7, and M 13 is Al, B, Ba, Ca, Ce, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, or a combination thereof.

[0086] In Chemical Formula 12, 0.3 ≤ x12 ≤ 0.99 and 0.01 ≤ y12 ≤ 0.7, 0.4 ≤ x12 ≤ 0.99 and 0.01 ≤ y12 ≤0.6, 0.5 ≤ x12 ≤ 0.99 and 0.01 ≤ y12 ≤ 0.5, 0.6 ≤ x12 ≤ 0.99 and 0.01 ≤ y12 ≤ 0.4, 0.7 ≤ x12 ≤ 0.99 and 0.01 ≤ y12 ≤ 0.3, 0.8 ≤ x12 ≤ 0.99 and 0.01 ≤ y12 ≤ 0.2, or 0.9 ≤ x12 ≤ 0.99 and 0.01 ≤ y12 ≤ 0.1.

[0087] As a specific example, the second positive electrode active material may include a lithium nickel cobalt composite oxide represented by Chemical Formula 13.

[0088] [Chemical Formula 13]

[0089] Li a13 Ni x13 Co y13 M 14 z13 M 15 1-x13-y13-z13 O2

[0090] In chemical formula 13, 0.9 ≤ a13 ≤ 1.8, 0.3 ≤ x13 ≤ 0.98, 0.01 ≤ y13 ≤ 0.69, 0.01 ≤ z13 ≤ 0.69, M 14 It is Al, Mn or a combination thereof, and M 15 It is B, Ba, Ca, Ce, Cr, Cu, F, Fe, Mg, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr or combinations thereof.

[0091] In chemical formula 13, 0.4 ≤ x13 ≤ 0.98, 0.01 ≤ y13 ≤ 0.59, and 0.01 ≤ z13 ≤ 0.59; 0.5 ≤ x13 ≤ 0.98, 0.01 ≤ y13 ≤ 0.49, and 0.01 ≤ z13 ≤ 0.49; 0.6 ≤ x13 ≤ 0.98, 0.01 ≤ y13 ≤ 0.39, and 0.01 ≤ z13 ≤ 0. 0.39, 0.7≤x13≤0.98, 0.01≤y13≤0.29, and 0.01≤z13≤0.29, 0.8≤x13≤0.98, 0.01≤y13≤0.19, and 0.01≤z13≤0.19, or 0.9≤x13≤0.98, 0.01≤y13≤0.09, and 0.01≤z13≤0.09.

[0092] In the positive electrode active material according to the embodiment, based on the total amount of the first positive electrode active material and the second positive electrode active material, the amount of the first positive electrode active material included can be from about 50 wt% to about 90 wt%, and the amount of the second positive electrode active material included can be from about 10 wt% to about 50 wt%. Alternatively, the amount of the first positive electrode active material included can be, for example, from about 60 wt% to about 90 wt%, or from about 70 wt% to about 90 wt%, and the amount of the second positive electrode active material included can be, for example, from about 10 wt% to about 40 wt%, or from about 10 wt% to about 30 wt%. When the amounts of the first and second positive electrode active materials are as described above, the rechargeable lithium battery including the positive electrode active material can achieve high capacity, improve mixture density, and exhibit high energy density.

[0093] Methods for preparing positive electrode active materials

[0094] In one embodiment, a method for preparing a positive electrode active material for a rechargeable lithium battery includes: mixing a first nickel hydroxide and a lithium raw material and performing a first heat treatment to prepare a first nickel oxide; mixing a second nickel hydroxide and a lithium raw material and performing a second heat treatment to prepare a second nickel oxide; and mixing the first nickel oxide and the second nickel oxide with a cobalt raw material and performing a third heat treatment to prepare a final positive electrode active material comprising the first positive electrode active material and the second positive electrode active material.

[0095] In this document, the first nickel oxide and the first positive electrode active material are in the form of secondary particles formed by the aggregation of multiple primary particles, and the second nickel oxide and the second positive electrode active material are in the form of single particles. The first positive electrode active material may be a material with a first nickel oxide coated with cobalt on its surface, and the second positive electrode active material may be a material with a second nickel oxide coated with cobalt on its surface.

[0096] In one embodiment, the first and second positive electrode active materials can be prepared by first mixing the first nickel oxide and the second nickel oxide and then simultaneously coating them, instead of coating the first and second nickel oxides separately. Accordingly, the cobalt-coated single-crystal second positive electrode active material has both an uneven surface and a smooth flat surface, and therefore exhibits high surface roughness and specific surface area. Consequently, the positive electrode active material for a rechargeable lithium battery including this second positive electrode active material can exhibit a high specific surface area, and thus the rechargeable lithium battery including this positive electrode active material achieves excellent capacity and cycle life characteristics.

[0097] The first and second nickel hydroxides are precursors to the positive electrode active material, and can be nickel hydroxide, nickel complex hydroxide containing elements other than nickel, or nickel-transition element complex hydroxide containing transition metals other than nickel, respectively.

[0098] For example, the first nickel hydroxide and the second nickel hydroxide can each be represented independently by chemical formula 21.

[0099] [Chemical Formula 21]

[0100] Ni x21 M 21 y21 M 22 1-x21-y21 (OH)2

[0101] In chemical formula 21, 0.3 ≤ x21 ≤ 1, 0 ≤ y21 ≤ 0.7, M 21 and M 22 Each of the following is independently Al, B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr or a combination thereof.

[0102] The first nickel hydroxide may have an average particle size of about 7 μm to about 25 μm, for example, about 10 μm to about 25 μm, about 15 μm to about 25 μm, or about 10 μm to about 20 μm. The second nickel hydroxide may have an average particle size of about 0.05 μm to about 10 μm, for example, about 0.1 μm to about 9 μm, about 0.5 μm to about 8 μm, or about 1 μm to about 7 μm. Here, the average particle size of the first nickel hydroxide is analyzed by a particle size analyzer using a laser diffraction method, and may refer to, for example, D50.

[0103] The lithium raw material is the lithium source for the positive electrode active material, and may include, for example, Li2CO3, LiOH, their hydrates or combinations thereof.

[0104] When the first nickel hydroxide and the lithium feedstock are mixed, the ratio of the number of moles of lithium in the lithium feedstock to the number of moles of the metal included in the first nickel hydroxide may, for example, be greater than or equal to about 0.8, greater than or equal to about 0.85, greater than or equal to about 0.9, greater than or equal to about 0.95, or greater than or equal to about 1.0 and less than or equal to about 1.8, less than or equal to about 1.5, less than or equal to about 1.2, less than or equal to about 1.1, or less than or equal to about 1.05.

[0105] The first heat treatment can be performed in an oxidizing gas atmosphere, such as an oxygen atmosphere or an air atmosphere. Alternatively, the first heat treatment can be performed at about 600°C to about 900°C or about 600°C to about 800°C, for example, for about 5 hours to about 20 hours, or for example, 5 hours to 15 hours. The first nickel oxide obtained by the first heat treatment may be referred to as a first lithium nickel oxide.

[0106] When the second nickel hydroxide and the lithium feedstock are mixed, the ratio of the number of moles of lithium in the lithium feedstock to the number of moles of the metal included in the second nickel hydroxide can be, for example, greater than or equal to about 0.8, greater than or equal to about 0.85, greater than or equal to about 0.9, greater than or equal to about 0.95, or greater than or equal to about 1.0 and less than or equal to about 1.8, less than or equal to about 1.5, less than or equal to about 1.2, less than or equal to about 1.1, or less than or equal to about 1.05.

[0107] The second heat treatment can also be carried out in an oxidizing gas atmosphere, such as an oxygen atmosphere or an air atmosphere. Alternatively, the second heat treatment can be carried out, for example, at about 800°C to about 1100°C, or about 900°C to about 1000°C, for example, for about 5 hours to about 20 hours or about 5 hours to about 15 hours. The second nickel oxide obtained by the second heat treatment can be referred to as a second lithium nickel oxide.

[0108] The second nickel oxide exists in the form of individual particles, which can be obtained by adjusting the conditions of the second heat treatment, such as temperature and time, or by adjusting various conditions during the synthesis of the second nickel hydroxide in the co-precipitation method.

[0109] A method for preparing positive electrode active materials for rechargeable lithium batteries may further include: mixing a second nickel hydroxide and a lithium raw material, followed by a second heat treatment, and then pulverizing the resulting product to obtain a single-crystal second nickel oxide. Pulverization can be performed using various pulverizing devices, such as jet mills. In this paper, the pulverization of the obtained product is a process for obtaining single-crystal active materials, which differs from the crushing of ordinary active materials.

[0110] When the first nickel oxide and the second nickel oxide are mixed, the first nickel oxide and the second nickel oxide may have a weight ratio of about 9:1 to about 5:5, for example, about 9:1 to about 6:4, or about 8:2 to about 7:3. When the first nickel oxide and the second nickel oxide are mixed within the aforementioned ranges, the rechargeable lithium battery including the obtained positive electrode active material can exhibit high capacity, high energy density, and high electrode plate density.

[0111] Subsequently, the first and second nickel oxides are mixed with the cobalt raw material, and then a third heat treatment is performed for cobalt coating. Cobalt coating can be carried out by dry or wet methods. For example, the first nickel oxide, the second nickel oxide, and the cobalt raw material are mixed without solvent, and then a third heat treatment is performed for dry coating.

[0112] Cobalt raw materials can be, for example, cobalt sulfate, cobalt oxide, and cobalt nitrate.

[0113] The cobalt raw material can be mixed in amounts based on the total amount of metals other than lithium in 100 molar parts of a first nickel oxide and a second lithium oxide, including cobalt in amounts of about 0.01 molar parts to about 7 molar parts, about 0.01 molar parts to about 5 molar parts, or about 0.1 molar parts to about 4 molar parts.

[0114] In this paper, when adding cobalt raw materials, lithium-containing compounds such as lithium hydroxide can be added. Based on the total metal content of 100 moles of positive electrode active material, the amount of lithium-containing compound added can be from 0.01 moles to 5 moles, or from 0.1 moles to 3 moles. Based on 1 mole of cobalt raw material added together, the amount of lithium-containing compound added can be from 1 mole to 4 moles, for example, from 1.5 moles to 3 moles. That is, the amount of lithium raw material added can be 1 to 4 times, or 1.5 to 3 times, the amount of cobalt raw material.

[0115] Optionally, the first and second nickel oxides can be added to a solvent such as distilled water for washing and mixing, and cobalt raw material can be added dropwise for wet coating, followed by a third heat treatment. In this document, when adding cobalt raw material, lithium-containing compounds such as lithium hydroxide and / or pH control agents such as sodium hydroxide can be added.

[0116] The amount of lithium-containing compound is the same as described above. Based on 1 mole of cobalt raw material, the amount of added pH control agent can be from 0.5 moles to 5 moles. The cobalt coating portion according to the embodiment can be effectively formed by using lithium-containing compound or pH control agent, etc.

[0117] The third heat treatment can be performed in an oxidizing gas atmosphere, such as an oxygen atmosphere or an air atmosphere. For example, the third heat treatment can be performed at a temperature of about 650°C to about 900°C or about 650°C to about 800°C. Depending on the heat treatment temperature, the third heat treatment can be performed for different durations, such as about 5 hours to about 30 hours or about 10 hours to about 24 hours.

[0118] Subsequently, upon completion of the heat treatment, the heat-treated product is cooled to room temperature to prepare the aforementioned positive electrode active material for a rechargeable lithium battery according to the embodiment. The prepared positive electrode active material is in a state in which a first positive electrode active material comprising secondary particles formed from aggregated primary particles and a second positive electrode active material having the form of individual particles are mixed, wherein the first and second positive electrode active materials are respectively coated with cobalt, and the second positive electrode active material includes both uneven and flat surfaces.

[0119] positive electrode

[0120] The positive electrode for a rechargeable lithium battery may include a positive electrode current collector and a layer of positive electrode active material on the positive electrode current collector. The positive electrode active material layer may include a positive electrode active material and may further include a binder and / or a conductive material.

[0121] The binder improves the bonding characteristics between the positive electrode active material particles and the bonding characteristics between the positive electrode active material particles and the positive electrode current collector. Examples of binders include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic styrene-butadiene rubber, epoxy resin, and nylon, but are not limited to these.

[0122] Based on the total weight of the positive electrode active material layer, the binder content in the positive electrode active material layer can be from about 1 wt% to about 5 wt%.

[0123] Conductive materials are included to provide electrode conductivity. Any conductive material may be used as a conductive material unless it causes a chemical change. Examples of conductive materials may include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, and carbon nanotubes; metallic materials including metal powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0124] Based on the total weight of the positive electrode active material layer, the content of conductive material in the positive electrode active material layer can be from about 1 wt% to about 5 wt%.

[0125] Aluminum foil can be used as a positive electrode current collector, but is not limited to this.

[0126] negative electrode

[0127] The negative electrode for a rechargeable lithium battery includes a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector. The negative electrode active material layer may include a negative electrode active material and may further include a binder and / or a conductive material.

[0128] The negative electrode active material may include materials that can reversibly insert / deintercalate lithium ions, lithium metal, lithium metal alloys, materials that can be doped / dedoped with lithium, or transition metal oxides.

[0129] Materials capable of reversibly inserting / deintercalating lithium ions may include, for example, crystalline carbon, amorphous carbon, or combinations thereof as carbon-based anode active materials. Crystalline carbon may be shapeless, or in the form of flakes, scales, spherical or fibrous natural or artificial graphite. Amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbonization products, and calcined coke, etc.

[0130] Lithium metal alloys include alloys of lithium with metals selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0131] Materials capable of lithium doping / de-doping can be Si-based or Sn-based anode active materials. Si-based anode active materials can include silicon, silicon-carbon composites, and SiO₂. x(0 < x < 2), Si-Q alloy (where Q is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, Group 15 element, Group 16 element, transition metal, rare earth element, and combinations thereof, but not Si), and the Sn-based negative electrode active material may include Sn, SnO2, Sn-R alloy (where R is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, Group 15 element, Group 16 element, transition metal, rare earth element, and combinations thereof, but not Sn). At least one of these materials may be mixed with SiO2. The elements Q and R may be selected from 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.

[0132] The silicon-carbon composite material may be, for example, a silicon-carbon composite material including: a core including crystalline carbon and silicon particles, and an amorphous carbon coating provided on the surface of the core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. The amorphous carbon precursor may be coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, or a polymer resin such as phenolic resin, furan resin, or polyimide resin. In this case, based on the total weight of the silicon-carbon composite material, the content of the silicon particles may be about 10 wt% to about 50 wt%. Additionally, based on the total weight of the silicon-carbon composite material, the content of the crystalline carbon may be about 10 wt% to about 70 wt%, and based on the total weight of the silicon-carbon composite material, the content of the amorphous carbon may be about 20 wt% to about 40 wt%. Additionally, the thickness of the amorphous carbon coating may be about 5 nm to about 100 nm. The average particle size (D50) of the silicon particles may be about 10 nm to about 20 μm. The average particle size (D50) of the silicon particles may preferably be about 10 nm to about 200 nm. The silicon particles may exist in an oxidized form, and in this case, the atomic content ratio of Si:O indicating the degree of oxidation in the silicon particles may be about 99:1 to about 33:67. The silicon particles may be SiO x particles, and in this case, SiO x in which the range of x may be greater than about 0 and less than about 2.

[0133] The Si-based negative electrode active material or the Sn-based negative electrode active material may be mixed with the carbon-based negative electrode active material. When the Si-based negative electrode active material or the Sn-based negative electrode active material is mixed with the carbon-based negative electrode active material and used, the mixing ratio may be a weight ratio of about 1:99 to about 90:10.

[0134] In the negative electrode active material layer, the amount of negative electrode active material included, based on the total weight of the negative electrode active material layer, can be from about 95 wt% to about 99 wt%.

[0135] In an embodiment, the negative electrode active material layer further includes a binder and optionally further includes a conductive material. Based on the total weight of the negative electrode active material layer, the binder content in the negative electrode active material layer can be from about 1 wt% to about 5 wt%. Alternatively, when further including a conductive material, the negative electrode active material layer may include about 90 wt% to about 98 wt% of negative electrode active material, about 1 wt% to about 5 wt% of binder, and about 1 wt% to about 5 wt% of conductive material.

[0136] The binder is used to bond the negative electrode active material particles together effectively, and also to bond the negative electrode active material to the negative electrode current collector. The binder may be a water-insoluble binder, a water-soluble binder, or a combination thereof.

[0137] Examples of water-insoluble adhesives include polyvinyl chloride, carboxylated polyvinyl chloride, fluorinated polyethylene, ethylene oxide-containing polymers, ethylene-propylene copolymers, polystyrene, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0138] Water-soluble adhesives may include rubber adhesives or polymeric resin adhesives. Rubber adhesives may be selected from styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. Polymeric resin adhesives may be selected from polyethylene oxide, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0139] When a water-soluble binder is used as a negative electrode binder, it may further include a thickener, such as a cellulose compound capable of imparting viscosity. As a cellulose compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and their alkali metal salts may be mixed and used. As an alkali metal, Na, K, or Li may be used. Based on 100 parts by weight of the negative electrode active material, the amount of thickener used may be from about 0.1 parts by weight to about 3 parts by weight.

[0140] Conductive materials are included to provide electrode conductivity. Any conductive material can be used as a conductive material unless it causes a chemical change. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, and carbon nanotubes; metallic materials including metal powders or fibers of copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0141] The negative electrode current collector may include one selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0142] Rechargeable lithium battery

[0143] Another embodiment provides a rechargeable lithium battery, including: a positive electrode, a negative electrode, a separator between the positive and negative electrodes, and an electrolyte.

[0144] Figure 1 A schematic diagram illustrating a rechargeable lithium battery according to an embodiment. (Reference) Figure 1 According to an embodiment, a rechargeable lithium battery 100 includes: a single cell including a positive electrode 114, a negative electrode 112 facing the positive electrode 114, a separator 113 between the positive electrode 114 and the negative electrode 112, and an electrolyte (not shown) for a rechargeable lithium battery impregnating the positive electrode 114, the negative electrode 112 and the separator 113; a battery casing 120 housing the single cell; and a sealing member 140 sealing the battery casing 120.

[0145] Electrolytes include non-aqueous organic solvents and lithium salts.

[0146] Non-aqueous organic solvents are used as media for transporting ions involved in the electrochemical reactions of a battery. Non-aqueous organic solvents can be carbonates, esters, ethers, ketones, alcohols, or proton-inert solvents. Examples of carbonate solvents include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene glycol carbonate (EC), propylene glycol carbonate (PC), and butylene glycol carbonate (BC). Examples of ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolactone, valerate, mevalonolactone, and caprolactone. Ether solvents can be dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran, and ketone solvents can be cyclohexanone, etc. In addition, alcohol solvents may be ethanol, isopropanol, etc., and proton inert solvents may be nitriles such as R-CN (where R is a C2 to C20 straight-chain, branched or cyclic hydrocarbon group and may include double bonds, aromatic rings or ether bonds), amides such as dimethylformamide, dioxolane such as 1,3-dioxolane and sulfolane, etc.

[0147] It can be used alone or in mixtures with non-aqueous organic solvents. When using organic solvents in mixtures, the mixture ratio can be controlled according to the desired battery performance.

[0148] Alternatively, in the case of carbonate solvents, a mixture of cyclic carbonates and chain carbonates can be used. In this case, the electrolyte exhibits excellent performance when the cyclic carbonates and chain carbonates are mixed in a volume ratio of about 1:1 to about 1:9.

[0149] In addition to carbonate solvents, non-aqueous organic solvents may further include aromatic hydrocarbon organic solvents. In this case, carbonate solvents and aromatic hydrocarbon organic solvents can be mixed in a volume ratio of about 1:1 to about 30:1.

[0150] As an aromatic hydrocarbon organic solvent, aromatic hydrocarbon compounds represented by chemical formula I can be used.

[0151] [Chemical Formula I]

[0152]

[0153] In chemical formula I, R 4 To R 9 They may be the same or different, and are selected from hydrogen, halogens, C1 to C10 alkyl, C1 to C10 haloalkyl and combinations thereof.

[0154] Specific examples of aromatic hydrocarbon solvents can be selected from benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, and fluorotoluene. 2,3-Difluorotoluene, 2,4-Difluorotoluene, 2,5-Difluorotoluene, 2,3,4-Trifluorotoluene, 2,3,5-Trifluorotoluene, Chlorotoluene, 2,3-Dichlorotoluene, 2,4-Dichlorotoluene, 2,5-Dichlorotoluene, 2,3,4-Trichlorotoluene, 2,3,5-Trichlorotoluene, Iodotoluene, 2,3-Diiodotoluene, 2,4-Diiodotoluene, 2,5-Diiodotoluene, 2,3,4-Triiodotoluene, 2,3,5-Triiodotoluene, Xylene and combinations thereof.

[0155] The electrolyte may further include vinylene carbonate or ethylene glycol carbonate compounds of formula II in order to improve the cycle life of the battery.

[0156] [Chemical Formula II]

[0157]

[0158] In chemical formula II, R 10 and R 11 The same or different, and selected from hydrogen, halogen, cyano, nitro and fluorinated C1 to C5 alkyl groups, under the condition that R 10 and R 11 At least one of them is selected from halogen, cyano, nitro and fluorinated C1 to C5 alkyl groups, but R 10 and R 11 Not all of them are hydrogen.

[0159] Examples of ethylene glycol carbonate compounds may be difluoroethylene glycol carbonate, chloroethylene glycol carbonate, dichloroethylene glycol carbonate, bromoethylene glycol carbonate, dibromoethylene glycol carbonate, nitroethylene glycol carbonate, cyanoethylene glycol carbonate, or fluoroethylene glycol carbonate. The amount of additives used to improve cycle life may be used within appropriate limits.

[0160] Lithium salts dissolved in non-aqueous organic solvents supply lithium ions in the battery, ensuring the basic operation of the rechargeable lithium battery and improving the transport of lithium ions between the positive and negative electrodes.

[0161] Examples of lithium salts include at least one supported salt selected from the following: LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide, LiFSI), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2 (where x and y are natural numbers, for example, integers ranging from 1 to 20), lithium difluoro(bis(oxalate)phosphate), LiCl, LiI, LiB(C2O4)2 (lithium bis(oxalate)borate, LiBOB) and lithium difluoro(oxalate)borate (LiDFOB).

[0162] Lithium salts can be used at concentrations ranging from about 0.1 M to about 2.0 M. When lithium salts are included in the above concentration range, the electrolyte exhibits excellent performance and lithium-ion mobility due to optimal electrolyte conductivity and viscosity.

[0163] Separator 113 separates the positive electrode 114 and the negative electrode 112 and provides a transport channel for lithium ions. It can be any commonly used separator in lithium-ion batteries. In other words, separator 113 can have low resistance to ion transport and excellent impregnation properties with the electrolyte. Separator 113 can include, for example, glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or combinations thereof, and can be in the form of non-woven or woven fabric. For example, in lithium-ion batteries, polyolefin polymer separators such as polyethylene and polypropylene separators can be used primarily. To ensure heat resistance or mechanical strength, coated separators including ceramic components or polymer materials can be used. Optionally, it can have a single-layer or multi-layer structure.

[0164] Based on the presence of a separator and the type of electrolyte used, rechargeable lithium batteries can be classified into lithium-ion batteries, lithium-ion polymer batteries, and lithium polymer batteries. Rechargeable lithium batteries can have various shapes and sizes, including cylindrical, prismatic, coin-shaped, or pouch-shaped batteries, and can be thin-film batteries or quite large in size. The structures and manufacturing methods for lithium-ion batteries disclosed herein are well known in the art.

[0165] The rechargeable lithium battery according to the embodiments can be used in electric vehicles (EVs), hybrid electric vehicles such as plug-in hybrid electric vehicles (PHEVs), and portable electronic devices because it achieves high capacity and has excellent storage stability, cycle life characteristics, and high rate capability at high temperatures.

[0166] The following describes embodiments and comparative examples of the present invention. However, it should be understood that the embodiments are for illustrative purposes and are not intended to limit the invention.

[0167] Example 1

[0168] 1. Preparation of primary nickel oxides in the form of secondary particles

[0169] The first nickel hydroxide (Ni) obtained by co-precipitation method 0.95 Co 0.04 Mn 0.01 (OH)₂) and LiOH are mixed to make the molar ratio of lithium to the total amount of transition metal 1.04, and the mixture is subjected to a first heat treatment at about 750°C for 15 hours in an oxygen atmosphere to obtain a first nickel oxide (LiNi). 0.95 Co 0.04 Mn 0.01 The first nickel oxide obtained has an average particle size of about 13.8 μm and is in the form of secondary particles in which primary particles aggregate.

[0170] 2. Preparation of second nickel oxides in the form of single particles

[0171] [Coprecipitation process]

[0172] Nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O) were dissolved in distilled water as a solvent to prepare a mixed solution. To form a complex, ammonia water (NH4OH) and sodium hydroxide (NaOH) were prepared as precipitating agents. Subsequently, the mixed solution of the metal raw materials, ammonia water, and sodium hydroxide were separately placed into reactors. The reaction was carried out for approximately 20 hours with stirring. The slurry solution in the reactor was then filtered, washed with high-purity distilled water, and dried for 24 hours to obtain a second nickel hydroxide (NiSO4·6H2O). 0.94 Co 0.05 Mn 0.01 (OH)2) powder. The second nickel hydroxide powder obtained had an average particle size of about 4.0 μm and a particle size of about 15 μm as measured by the BET method. 2 Specific surface area per g.

[0173] [Oxidation Process]

[0174] The obtained second nickel hydroxide was mixed with LiOH to satisfy Li / (Ni+Co+Mn) = 1.05 and placed in a furnace, where it underwent a second heat treatment at 910°C for 8 hours under an oxygen atmosphere. Subsequently, the obtained product was pulverized for approximately 30 minutes and then separated / dispersed into multiple second nickel oxides with individual particle structures. The second nickel oxide (LiNi) was formed as individual particles. 0.94 Co 0.05 Mn 0.01 O2) has an average particle size of approximately 3.7 μm.

[0175] 3. Cobalt coating and preparation of the final positive electrode active material

[0176] The first nickel oxide and the second nickel oxide were mixed in a weight ratio of 7:3, and the mixture was washed with water in a 1:1 weight ratio in a stirrer and dried at 150°C. In this paper, based on the total amount of metals other than lithium in 100 moles of the first and second nickel oxides, 5 moles of lithium hydroxide and 2.5 moles of cobalt oxide were added and then placed in a furnace for a third heat treatment at approximately 710°C for 15 hours under an oxygen atmosphere. Subsequently, the furnace was cooled to room temperature to obtain the final positive electrode active material, in which the first and second positive electrode active materials were mixed.

[0177] The final positive electrode active material is a mixture of a first positive electrode active material in the form of secondary particles coated with cobalt and a second positive electrode active material in the form of individual particles.

[0178] Figure 2 Scanning electron microscope (SEM) images of particles corresponding to the second positive electrode active material in the final positive electrode active material prepared according to Example 1. Reference Figure 2 The second positive electrode active material, as a single particle, has an uneven surface and a flat surface formed on the surface.

[0179] 4. Manufacturing of the positive electrode

[0180] A slurry of the positive electrode active material was prepared by mixing 95 wt% of the final positive electrode active material, 3 wt% of polyvinylidene fluoride binder, and 2 wt% of carbon nanotube conductive material in an N-methylpyrrolidone solvent. The positive electrode active material slurry was applied to an aluminum foil current collector, dried, and then compressed to fabricate the positive electrode.

[0181] 5. Preparation of coin-type half-cells

[0182] A coin-shaped half-cell was manufactured by placing a separator with a polyethylene-polypropylene multilayer structure between a manufactured positive electrode and a lithium metal counter electrode, and injecting an electrolyte in which 1.0 M of LiPF6 lithium salt was added to a solvent in which ethylene glycol carbonate and diethyl carbonate were mixed in a volume ratio of 50:50.

[0183] Example 2

[0184] The positive electrode active material, positive electrode, and coin-shaped half-cell were manufactured according to essentially the same method as in Example 1, except that the cobalt coating was performed using a wet process in "3. Cobalt Coating and Preparation of the Final Positive Electrode Active Material" of Example 1. The cobalt coating process is as follows: A first nickel oxide and a second nickel oxide were mixed at a weight ratio of 7:3, and then placed in distilled water and washed with it while mixing. Subsequently, based on the total amount of metals other than lithium in 100 moles of the first and second nickel oxides, 2.5 moles of cobalt sulfate (CoSO4) were slowly added to perform cobalt coating. In addition, sodium hydroxide (NaOH) was slowly added. The resulting product was then dried at 150°C for 12 hours. Figure 3 Scanning electron micrographs of a second nickel oxide containing individual particles in a dried material, showing the formation of uneven and flat surfaces on its surface.

[0185] Subsequently, the dried material was placed in a furnace and subjected to a third heat treatment at approximately 710°C for 15 hours in an oxygen atmosphere. The furnace was then cooled to room temperature to obtain the final positive electrode active material, which contains a mixture of the first and second positive electrode active materials.

[0186] Figure 4 This is a scanning electron microscope image of particles containing a single-crystal second positive electrode active material in the obtained final positive electrode active material. (Reference) Figure 4 An uneven surface and a flat surface were formed on the surface of the second positive electrode active material. The second positive electrode active material has an average particle size of approximately 4 μm.

[0187] Comparative Example 1

[0188] The positive electrode active material, positive electrode, and coin-shaped half-cell are manufactured according to the same method as in Example 1, except that instead of first mixing and then coating the first and second nickel oxides, they are coated separately and then mixed in "3. Cobalt Coating and Preparation of the Final Positive Electrode Active Material" in Example 1.

[0189] Cobalt coating was performed as follows. Based on the total amount of metals other than lithium in 100 moles of the first nickel oxide, 5 moles of lithium hydroxide and 3 moles of cobalt oxide were mixed with the first nickel oxide. The mixture was then placed in a furnace and subjected to a third heat treatment at approximately 700°C for 15 hours under an oxygen atmosphere. After cooling to room temperature, a first positive electrode active material was obtained. Additionally, based on the total amount of metals other than lithium in 100 moles of the second nickel oxide, 5 moles of lithium hydroxide and 3 moles of cobalt oxide were mixed with the second nickel oxide. The mixture was then placed in a furnace and subjected to a third heat treatment at approximately 850°C for 15 hours under an oxygen atmosphere. After cooling to room temperature, a second positive electrode active material was obtained. The cobalt-coated first positive electrode active material and the cobalt-coated second positive electrode active material were mixed at a weight ratio of 7:3 to prepare the final positive electrode active material according to Comparative Example 1.

[0190] Figure 5 A scanning electron microscope image of the second positive electrode active material prepared according to Comparative Example 1. Reference Figure 5 The surface of the second positive electrode active material in Comparative Example 1 is smooth and flat, without any bumps or depressions.

[0191] Comparative Example 2

[0192] The positive electrode active material, positive electrode, and coin-shaped half-cell were manufactured using essentially the same method as in Comparative Example 1, except that the second nickel oxide was subjected to a third heat treatment at approximately 700°C for 15 hours in an oxygen atmosphere.

[0193] Figure 6 A scanning electron microscope image of the second positive electrode active material prepared according to Comparative Example 2. Reference Figure 6 In Comparative Example 2, the surface of the second positive electrode active material is not uneven, but smooth and flat.

[0194] Evaluation Example 1: Evaluation of the surface roughness of the second positive electrode active material

[0195] The surface roughness of the second positive electrode active material in the positive electrode active materials according to Examples 1 and 2 and Comparative Examples 1 and 2 was measured using a surface roughness meter of an atomic force microscope (scanning speed: 0.25 μm / s, non-contact mode range: 250 nm × 250 nm, DME UHV AFM). The results are shown in Table 1. In Table 1, the unit of each value is nm.

[0196] Table 1

[0197]

[0198] Evaluation Example 2: Evaluation of Specific Surface Area

[0199] The specific surface area of ​​the positive electrode active materials of Examples 1 and 2 and Comparative Examples 1 and 2 was measured, and the results are shown in Table 2. The specific surface area was measured using physical and chemical adsorption phenomena and the BET method. In other words, after measuring the weight of the active material, nitrogen gas was absorbed onto the surface of the active material, and the amount of absorbed nitrogen gas was measured and used to obtain the specific surface area using the BET method.

[0200] Table 2

[0201] <![CDATA[BET specific surface area (m 2 / g)]]> Example 1 0.3856 Example 2 0.3652 Comparative Example 1 0.2575 Comparative Example 2 0.2521

[0202] Referring to Table 2, the positive electrode active materials, including the first and second positive electrode active materials according to Examples 1 and 2, exhibit an increased specific surface area compared to the positive electrode active materials of Comparative Examples 1 and 2.

[0203] Evaluation Example 3: Evaluation of Surface Cobalt Content

[0204] Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) was performed on the surface of the single-crystal second positive electrode active material in the positive electrode active materials according to Example 1 and Comparative Example 1 to measure the cobalt content (atomic %) on the surface, i.e., Co / (Ni+Co). Figure 7 The SEM-EDS image of the second positive electrode active material according to Example 1 is shown, in which the cobalt content at positions 1 to 4 was measured, and the results are provided in Table 3. Figure 8 Based on the SEM-EDS image of the second positive electrode active material of Comparative Example 1, the cobalt content at positions 5 to 8 was measured, and the results are provided in Table 4. Here, considering that the manganese content is very small, for convenience, the cobalt content is calculated as the cobalt content relative to the total amount of nickel and cobalt.

[0205] Table 3

[0206]

[0207] Table 4

[0208]

[0209] refer to Figure 7 As shown in Table 3, the second positive electrode active material in Example 1 has a side with a low cobalt content of 19.4 atomic% and also has a side with a high cobalt content of 40 to 60 atomic%.

[0210] refer to Figure 8As shown in Table 4, in Comparative Example 1, the first and second positive electrode active materials were coated with cobalt. The second positive electrode active material exhibited a cobalt content on its surface ranging from approximately 8 atomic% to 16 atomic%, with almost no difference between crystal planes. Furthermore, the cobalt content on its surface was lower than that on the surface of Example 1.

[0211] Evaluation Example 4: Charge / Discharge Efficiency and Cycle Life Characteristics

[0212] The coin-type semi-single cells of Examples 1 and 2, and Comparative Examples 1 and 2, were charged under constant current (0.2C) and constant voltage (4.25V, 0.05C cutoff) conditions to measure the charging capacity, and then discharged to 3.0V under constant current (0.2C) conditions for 10 minutes to measure the discharging capacity. The ratio of discharging capacity to charging capacity is shown as the charge / discharge efficiency. The results are shown in Table 5.

[0213] In addition, the coin-type half-cell was initially charged and discharged, and then charged and discharged 50 times at 1C at 45°C to measure the discharge capacity of the 50th cycle. The ratio of the discharge capacity of the 50th cycle to the initial discharge capacity is expressed as the capacity retention rate (%), i.e., the capacity retention rate of 50 cycles in Table 5.

[0214] Table 5

[0215]

[0216] Referring to Table 5, compared with Comparative Examples 1 and 2, in which the first and second positive electrode active materials were separately coated and fired with cobalt, Examples 1 and 2 showed increased discharge capacity and improved charge / discharge efficiency, and also showed improved high-temperature cycle life characteristics.

[0217] Although both the first and second positive electrode active materials are coated with cobalt, the cobalt is only effectively coated on some surfaces of the second positive electrode active material as individual particles, resulting in an uneven surface and thus increasing the specific surface area, etc. When a single cell is manufactured by applying the positive electrode active material, it improves characteristics such as initial discharge capacity, charge / discharge efficiency and cycle life.

[0218] Although the invention has been described in conjunction with exemplary embodiments now regarded as practice, it should be understood that the invention is not limited to the disclosed embodiments. Rather, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A positive electrode active material for a rechargeable lithium battery, comprising: The first positive electrode active material comprises a lithium-nickel composite oxide and includes secondary particles formed by aggregating multiple primary particles and a cobalt coating portion on the surface of the secondary particles. The second positive electrode active material comprises a lithium-nickel composite oxide and includes individual particles and a cobalt coating portion on the surface of the individual particles. The second positive electrode active material has an uneven surface with irregularities and a flat surface without irregularities. The uneven surface of the second positive electrode active material has an average roughness of 1.9 nm or greater, and the flat surface of the second positive electrode active material has an average roughness of 1.8 nm or less.

2. The positive electrode active material for a rechargeable lithium battery according to claim 1, wherein... The uneven surface of the second positive electrode active material has a maximum roughness of 18 nm or more.

3. The positive electrode active material for a rechargeable lithium battery according to claim 1, wherein... The uneven surface of the second positive electrode active material has a root mean square roughness of 2.3 nm or greater.

4. The positive electrode active material for a rechargeable lithium battery according to claim 1, wherein... The flat surface of the second positive electrode active material has a maximum roughness of less than or equal to 15 nm.

5. The positive electrode active material for a rechargeable lithium battery according to claim 1, wherein... The flat surface of the second positive electrode active material has a root mean square roughness of less than or equal to 2.2 nm.

6. The positive electrode active material for a rechargeable lithium battery according to claim 1, wherein... The ratio of the uneven surface of the second positive electrode active material to the total surface area of ​​the second positive electrode active material is 40% to 80%.

7. The positive electrode active material for a rechargeable lithium battery according to claim 1, wherein... The positive electrode active material for the rechargeable lithium battery, comprising the first positive electrode active material and the second positive electrode active material, has a 0.2 μm... 2 / g to 0.6 m 2 / g BET specific surface area.

8. The positive electrode active material for a rechargeable lithium battery according to claim 1, wherein... The first positive electrode active material has an average particle size of 7 μm to 25 μm, and The second positive electrode active material has an average particle size of 0.05 μm to 10 μm.

9. The positive electrode active material for a rechargeable lithium battery according to claim 1, wherein... Based on the total amount of the first positive electrode active material and the second positive electrode active material, the amount of the first positive electrode active material included is 50 wt% to 90 wt% and the amount of the second positive electrode active material included is 10 wt% to 50 wt%.

10. The positive electrode active material for a rechargeable lithium battery according to claim 1, wherein... The first positive electrode active material comprises a lithium-nickel composite oxide represented by chemical formula 1, and The second positive electrode active material includes a lithium-nickel composite oxide represented by chemical formula 11: [Chemical Formula 1] Li a1 Ni x1 M 1 y1 M 2 1-x1-y1 O2 in, In chemical formula 1, 0.9 ≤ a1 ≤ 1.8, 0.3 ≤ x1 ≤ 1, 0 ≤ y1 ≤ 0.7, and M 1 and M 2 Each of the following elements independently consists of Al, B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, or combinations thereof. [Chemical Formula 11] Li a11 Ni x11 M 11 y11 M 12 1-x11-y11 O2 In chemical formula 11, 0.9 ≤ a11 ≤ 1.8, 0.3 ≤ x11 ≤ 1, 0 ≤ y11 ≤ 0.7, and M 11 and M 12 Each of the following is independently Al, B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr or a combination thereof.

11. A method for preparing a positive electrode active material for a rechargeable lithium battery according to any one of claims 1 to 10, comprising: A first nickel hydroxide and a lithium raw material are mixed and subjected to a first heat treatment to prepare a first nickel oxide in the form of secondary particles formed by aggregating multiple primary particles. A second nickel hydroxide and a lithium feedstock are mixed and subjected to a second heat treatment to prepare a second nickel oxide in the form of individual particles; and The first nickel oxide, the second nickel oxide, and the cobalt raw material are mixed and subjected to a third heat treatment.

12. The method of claim 11, wherein The first nickel hydroxide and the second nickel hydroxide are each independently represented by chemical formula 21: [Chemical Formula 21] No x21 M 21 y21 M 22 1-x21-y21 (OH)2 in, In chemical formula 21, 0.3 ≤ x21 ≤ 1, 0 ≤ y21 ≤ 0.7, and M 21 and M 22 Each of the following is independently Al, B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr or a combination thereof.

13. The method of claim 11, wherein The mixing of the first nickel hydroxide and the lithium raw material is carried out at a ratio of greater than or equal to 0.9 and less than or equal to 1.2 of the molar number of lithium in the lithium raw material to the molar number of metals included in the first nickel hydroxide. The mixing of the second nickel hydroxide and the lithium raw material is carried out at a ratio of greater than or equal to 0.9 and less than or equal to 1.2 of the number of moles of lithium in the lithium raw material to the number of moles of metals included in the second nickel hydroxide.

14. The method of claim 11, wherein The first heat treatment is carried out at a temperature of 600°C to 900°C for 5 to 20 hours.

15. The method of claim 11, wherein The second heat treatment is carried out at a temperature of 800°C to 1100°C for 5 to 20 hours.

16. The method of claim 11, wherein The preparation of the second nickel oxide involves mixing the second nickel hydroxide and the lithium raw material, performing a second heat treatment on the mixture, and pulverizing the result to obtain the second nickel oxide as individual particles.

17. The method of claim 11, wherein The mixing of the first nickel oxide and the second nickel oxide is performed by mixing the first nickel oxide and the second nickel oxide in a weight ratio of 9:1 to 5:

5.

18. The method of claim 11, wherein The mixing of the first nickel oxide, the second nickel oxide, and the cobalt raw material is carried out such that the total amount of metals other than lithium in 100 molar parts of the first nickel oxide and the second nickel oxide, including the amount of cobalt included in the cobalt raw material, is from 0.01 molar parts to 7 molar parts.

19. The method of claim 11, wherein The third heat treatment is carried out at a temperature of 650°C to 900°C for 5 to 30 hours.

20. A rechargeable lithium battery, comprising: A positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises a positive electrode active material according to any one of claims 1-10 or a positive electrode active material prepared by any one of claims 11-19.

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