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

Abstract

The present disclosure relates to a positive electrode active material, a method of preparing the same, a positive electrode including the positive electrode active material, and a rechargeable lithium battery. The positive electrode active material includes: a positive electrode active material including a lithium nickel-based composite oxide and having a form of secondary particles in which a plurality of primary particles aggregate, in which an average size of the primary particles measured by electron backscatter diffraction (EBSD) analysis of a cross-section of the secondary particles is about 1.05 [mu] m to about 1.5 [mu] m, the standard deviation of the size of the primary particles is less than or equal to about 0.3 [mu] m, and the average aspect ratio of the primary particles is less than or equal to about 1.7.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority and benefit to Korean Patent Application No. 10-2024-0107774, filed on August 12, 2024, with the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] According to one or more embodiments, this disclosure relates to positive electrode active materials, methods for preparing the same, positive electrodes including positive electrode active materials, and rechargeable lithium batteries. Background Technology

[0004] Because of their high portability and high energy density, rechargeable lithium batteries are widely used as power sources for mobile information terminals such as smartphones and laptops. Recently, there has been active research into rechargeable lithium batteries with relatively high capacity, long cycle life, and high output for use as power sources in hybrid or electric vehicles, or as energy storage.

[0005] Lithium-nickel composite oxides, used as positive electrode active materials, offer the desired high capacity. These oxides can be polycrystalline, with multiple primary particles agglomerating to form secondary particles. While smaller primary particles provide improved charge / discharge efficiency, output characteristics, etc., they also have a larger surface area, making them more susceptible to undesirable reactions with the electrolyte, which can degrade stability or cycle life.

[0006] To meet expectations or requirements, attempts have been made to explore the application of coated particles and single crystals with increased particle size in industrial applications. However, these approaches have limitations in improving the degree of high output.

[0007] Accordingly, there is a desire or need for positive electrode active materials that include lithium-nickel composite oxides but still achieve high capacity, long cycle life, and high output. Summary of the Invention

[0008] One or more aspects involve positive electrode active materials that can provide (ensure) high capacity, long cycle life and high output.

[0009] Other aspects will be set forth in part in the description which follows and in part will be obvious from the description or may be learned by practice of the embodiments presented in this disclosure.

[0010] According to one or more embodiments, the positive electrode active material includes secondary particles comprising lithium-nickel composite oxides and having a secondary particle form in which a plurality of primary particles are aggregated, wherein the average size of the primary particles can be measured by electron backscatter diffraction (EBSD) analysis of the cross-section of the secondary particles, and the standard deviation of the size of the primary particles is less than or equal to about 0.3 μm in the range of about 1.05 μm to about 1.5 μm, and the average aspect ratio of the primary particles is less than or equal to about 1.7.

[0011] According to one or more embodiments, a method for preparing a positive electrode active material includes: mixing a nickel-based composite oxide with a lithium feedstock (to provide a mixture); and heat-treating (the mixture) to obtain the positive electrode active material described herein.

[0012] According to one or more 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.

[0013] According to one or more embodiments, a rechargeable lithium battery includes the aforementioned positive electrode, negative electrode, and electrolyte.

[0014] According to some example implementations, the positive electrode active material can be advantageous in providing (ensuring) high capacity, long cycle life and high output. Attached Figure Description

[0015] The accompanying drawings are included to provide a further understanding of this disclosure, and are incorporated in and form a part of this specification. The drawings illustrate embodiments of this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0016] Figures 1-4 A schematic diagram illustrating a rechargeable lithium battery according to some example embodiments.

[0017] Figure 5 This is a scanning electron microscope (SEM) image of the cross-section of the positive electrode active material prepared in the example.

[0018] Figure 6 This is a scanning electron microscope (SEM) image of the cross-section of the positive electrode active material prepared in the comparative example.

[0019] Figure 7 The image shown is an electron backscatter diffraction (EBSD) image of the cross-section of the positive electrode active material prepared in the example.

[0020] Figure 8 Electron backscatter diffraction (EBSD) image of the cross-section of the positive electrode active material prepared in the comparative example.

[0021] Figure 9 The curve shows the aspect ratio distribution of primary particles in the cross-section of the positive electrode active material prepared in the examples.

[0022] Figure 10 A curve showing the aspect ratio distribution of primary particles in the cross-section of the positive electrode active material prepared in the comparative example.

[0023] Figure 11 for Figure 9 and Figure 10 A combination diagram.

[0024] Figure 12 Through analysis Figure 9 and Figure 10 The curve obtained is the aspect ratio distribution curve of the primary particles.

[0025] Figure 13 To illustrate the high-rate performance evaluation curves of the rechargeable lithium batteries prepared in the examples and comparative examples.

[0026] Explanation of reference numerals in the attached figures

[0027] 100: Rechargeable lithium battery; 10: Positive electrode

[0028] 11: Positive electrode lead connector 12: Positive electrode terminal

[0029] 20: Negative electrode 21: Negative electrode lead connector

[0030] 22: Negative electrode terminal; 30: Diaphragm

[0031] 40: Electrode assembly; 50: Housing

[0032] 60: Sealing component; 70: Electrode terminal piece

[0033] 71: Positive electrode connector; 72: Negative electrode connector Detailed Implementation

[0034] The following detailed description of specific embodiments of this disclosure will enable those skilled in the art to implement it. To fully understand the layout and effects of this disclosure, one or more embodiments of this disclosure are described with reference to the accompanying drawings. However, this disclosure may be implemented in many different forms and is not to be construed as limited to the exemplary embodiments set forth herein.

[0035] The terminology used herein is for descriptive purposes only and is not intended to limit this disclosure. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0036] As used herein, “combinations thereof” refers to mixtures, laminates, complexes, copolymers, alloys, blends, reaction products, etc. of the components.

[0037] Here it should be understood that terms such as “comprises”, “includes”, “has”, “comprising”, “including”, “having”, “comprise”, “include” and / or “have” are intended to indicate the presence of a feature, quantity, step, element or combination thereof, but this does not preclude the possibility of the presence or addition of one or more other features, quantities, steps, elements or combinations thereof.

[0038] In the accompanying drawings, for clarity, the dimensions (e.g., thickness) of layers, films, panels, areas, etc., are enlarged, and the same reference numerals are used throughout the specification to denote the same elements. It will be understood that when an element (such as a layer, film, area, substrate, etc.) is referred to as being "on" another element (such as a layer, film, area, substrate, etc.), it may be directly on the other element (such as a layer, film, area, substrate, etc.), or an intermediary element may be present. In contrast, when an element (such as a layer, film, area, substrate, etc.) is referred to as being "directly on" another element (such as a layer, film, area, substrate, etc.), no intermediary element is present.

[0039] In some implementations, the term "layer" as used herein includes not only shapes formed across the entire surface when viewed from a plan view, but also shapes formed on a portion of the surface.

[0040] The average particle size can be measured by 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 images. Optionally, the average particle size value can be obtained by measuring using a dynamic light scattering method, performing data analysis, counting particles for each particle size range, and calculating therefrom. Unless otherwise specified, the average particle size (D) is... 50 The particle size distribution may refer to the diameter of particles that constitute 50% of the total volume. As used herein, unless otherwise specified, the average particle size (D) refers to the diameter of particles that constitute 50% of the total volume. 50 The diameter refers to the diameter of particles that constitute 50% of the total volume in a particle size distribution obtained by randomly measuring the size (diameter or major axis length) of approximately 20 particles in a scanning electron microscope image.

[0041] Here, "or" is not interpreted as exclusive. For example, "A or B" can be interpreted as including A, B, A+B, etc.

[0042] The term "metal" is defined as encompassing common metals, transition metals, and quasi-metals (semi-metals).

[0043] It will be understood that although the terms “first,” “second,” “third,” etc., may be used herein to describe one or more appropriate elements, components, areas, layers, and / or portions, these elements, components, areas, layers, and / or portions should not be limited by these terms. These terms are used only to distinguish one element, component, area, layer, or portion from another. Therefore, without departing from the teachings set forth herein, a first element, component, area, layer, or portion described herein may be referred to as a second element, component, area, layer, or portion.

[0044] As used herein, the term “and / or” includes any and all combinations of one or more related enumerated items. Expressions such as “at least one of…”, “one of…”, and “selected from…” modify the entire list of elements, not individual elements, if they appear before / after a list of elements. For example, the expressions “at least one of a to c”, “at least one of a, b, and c” can indicate only a, only b, only c, both a and b (e.g., simultaneously), both a and c (e.g., simultaneously), both b and c (e.g., simultaneously), all a, b, and c, or variations thereof.

[0045] Spatial relative terms such as “below,” “under,” “down,” “above,” and “above” may be used herein to readily describe the relationship between one element or feature and another. It will be understood that, in addition to the orientations illustrated in the figures, spatial relative terms are intended to encompass different orientations of the device in use or operation. For example, if (e.g., when) the device in the figures is flipped, an element described as being “below” or “under” other elements or features will be oriented “above” other elements or features. Thus, the example term “below” may (e.g., simultaneously) encompass both the above and below orientations. The device may be oriented in other ways (rotated 90 degrees or otherwise), and the spatial relative terms used herein may be interpreted accordingly.

[0046] The terminology used herein is for the purpose of describing particular embodiments and is not intended to limit this disclosure. Unless otherwise defined, all terms used herein (including chemical, technical, and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It will be further understood that terms (such as those defined in commonly used dictionaries) should be interpreted as having the meaning consistent with their meaning in the relevant field and in the context of this disclosure, and will not be interpreted in an ideal or overly formal sense.

[0047] The term "may" will be understood to refer to "one or more embodiments of the present disclosure", where some embodiments include the described element and some embodiments exclude the element and / or include alternative elements. Similarly, optional language such as "or" refers to "one or more embodiments of the present disclosure" that each include the respective listed item.

[0048] Positive electrode active material

[0049] In one or more embodiments, the positive electrode active material includes: secondary particles including a lithium nickel-based composite oxide, the secondary particles having a form in which a plurality of primary particles are aggregated (e.g., in the form of secondary particles), wherein the average size of the primary particles measured by electron backscatter diffraction (EBSD) analysis of a cross-section of the secondary particles is in the range of about 1.05 micrometers (μm) to about 1.5 μm, the standard deviation of the size of the primary particles is less than or equal to about 0.3 μm, and the average aspect ratio of the primary particles is less than or equal to about 1.7.

[0050] The lithium nickel-based composite oxide can be represented by Chemical Formula 1.

[0051] Chemical Formula 1

[0052] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1

[0053] In Chemical Formula 1, 0.9 ≤ a1 ≤ 1.2, 0.8 ≤ x1 < 1, 0 < y1 ≤ 0.2, 0 ≤ z1 ≤ 0.2, 0.9 ≤ x1 + y1 + z1 ≤ 1.1, and 0 ≤ b1 ≤ 0.1, M 1 and M 2 may each independently be at least one element selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y, and Zr, and X may be at least one element selected from F, P, and S.

[0054] In one or more embodiments of Chemical Formula 1, 0.85 ≤ x1 < 1, 0 < y1 ≤ 0.15, and 0 ≤ z1 ≤ 0.15.

[0055] The lithium nickel-based composite oxide can be represented, for example, by Chemical Formula 2 or Chemical Formula 3.

[0056] Chemical Formula 2

[0057] Li a2 Ni x2 Coy2 M 3 z2 O 2-b2 X b2

[0058] In Chemical Formula 2, 0.9 ≤ a2 ≤ 1.2, 0.8 ≤ x2 < 1, 0 < y2 ≤ 0.2, 0 ≤ z2 ≤ 0.2, 0.9 ≤ x2 + y2 + z2 ≤ 1.1, and 0 ≤ b2 ≤ 0.1. M 3 may be at least one (e.g., one or more) element selected from Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y, and Zr, and X may be F, P, S, or a combination thereof.

[0059] In one or more embodiments of Chemical Formula 2, 0.8 ≤ x2 ≤ 0.99, 0.01 ≤ y2 ≤ 0.1, and 0 ≤ z2 ≤ 0.1. <00002​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Lithium-nickel composite oxides may include high concentrations of nickel. For example, in lithium-nickel composite oxides, based on 100 mol% of total metals other than lithium, the amount (e.g., content) of nickel may be greater than or equal to about 80 mol%, and in other examples, it may be greater than or equal to about 81 mol%, greater than or equal to about 82 mol%, greater than or equal to about 83 mol%, greater than or equal to about 84 mol%, or greater than or equal to about 85 mol%, and less than or equal to about 100 mol%, less than or equal to about 99 mol%, less than or equal to about 95 mol%, less than or equal to about 90 mol%, less than or equal to about 89 mol%, or less than or equal to about 88 mol%.

[0065] Because high-capacity lithium-nickel composite oxides are polymorphic secondary particles in which multiple primary particles aggregate, smaller primary particles can provide improved efficiency and output characteristics. However, smaller primary particles have a larger surface area, which increases the reaction area with the electrolyte, making them more susceptible to undesirable reactions that can lead to deterioration in stability and cycle life. To address these challenges, one or more exemplary embodiments provide a positive electrode active material having substantially uniform and substantially spherical primary particles.

[0066] By adjusting the average size and standard deviation of the primary particle size to their respective appropriate ranges, basic uniformity of the primary particles can be provided (ensuring).

[0067] According to some example embodiments, the average size of the primary particles is in the range of about 1.05 μm to about 1.5 μm. The average size of the primary particles may, for example, be greater than or equal to about 1.05 μm, greater than or equal to about 1.1 μm, greater than or equal to about 1.15 μm, or greater than or equal to about 1.2 μm, and less than or equal to about 1.5 μm, less than or equal to about 1.45 μm, less than or equal to about 1.4 μm, less than or equal to about 1.35 μm, less than or equal to about 1.3 μm, or less than or equal to about 1.25 μm. The size of the primary particle may refer to the size of the primary particle observed in a cross-section of one of the secondary particles, and can be measured by electron backscatter diffraction (EBSD) of the cross-section of the secondary particle. The size of the primary particle can be calculated by measuring the area of ​​each primary particle in the EBSD image of the cross-section of the secondary particle, deriving a circle having an area equal to the measured area (the same area as the measured area), and thus determining the diameter of the derived circle. In this document, the average size of the primary particles can be the arithmetic mean (average) of the sizes of about 10 primary particles. Positive electrode active materials with an average primary particle size of about 1.05 μm to about 1.5 μm can be prepared by appropriately selecting (controlling) the raw materials (such as using nickel-based composite oxides) and also by selecting (adjusting) the preparation conditions. For example, by employing a preparation method according to one or more example embodiments as described in more detail herein. If (e.g., when) the average size of the primary particles is within the aforementioned range, not only can the charge / discharge capacity, efficiency, and cycle life characteristics be enhanced or improved, but the output characteristics can also be increased.

[0068] The standard deviation of the primary particle size according to one or more example embodiments may be less than or equal to about 0.3 μm. The standard deviation of the primary particle size may, for example, be less than or equal to about 0.25 μm or less than or equal to about 0.2 μm. The standard deviation of the primary particle size can be calculated as the standard deviation of the average size of the primary particles relative to the EBSD image obtained through a cross-section of the secondary particles. Positive electrode active materials with a standard deviation of primary particle size less than or equal to about 0.3 μm can be prepared by appropriately selecting (controlling) raw materials (such as using nickel-based composite oxides during the preparation of the positive electrode active material). A standard deviation of primary particle size within this range indicates that the primary particle size is substantially (very) uniform, which can help increase the battery's output characteristics and improve the battery's charge / discharge capacity, efficiency, and cycle life characteristics.

[0069] By selecting (controlling) the average aspect ratio of the primary particles within an appropriate range, the sphericity of the primary particles can be provided (ensured).

[0070] According to some example implementations, the average aspect ratio of the primary particles may be less than or equal to about 1.7. The average aspect ratio of the primary particles refers to the average aspect ratio of a cross-section of one of the primary particles observed in a cross-section of a secondary particle, which can be measured by an image analysis program in electron backscatter diffraction (EBSD) analysis of the cross-section of the secondary particles. For example, the secondary particles can be cut with a focused ion beam (FIB) to obtain an image of the cross-section of the secondary particles using electron backscatter diffraction (EBSD). In the EBSD image of the cross-section, after outlining the primary particles using Image J (an image analysis program), the aspect ratio of the outlined primary particles can be measured using the Image J program. The aspect ratio of a cross-section of one of the primary particles can be measured by one or more suitable image programs (e.g., the Image J program). Image J is software developed by the National Institutes of Health and can be downloaded from https: / / imagej.net / ImageJ. More information can be found at sites such as https: / / en.Wikipedia.org / wiki / ImageJ.

[0071] The aspect ratio of a primary particle can be determined as follows: A primary particle is randomly selected in an EBSD image, and two parallel lines are drawn such that the primary particle forms a sandwich shape with the parallel lines. The longest distance between the parallel lines (major axis, width, long side) is called "x", and the length perpendicular to it (minor axis, height, short side) is called "y". In this document, the aspect ratio of the primary particle refers to the ratio of x to y, i.e., x / y. In some embodiments, the average aspect ratio of the primary particles can be expressed as the average aspect ratio of the primary particles in a secondary particle.

[0072] The average aspect ratio of the primary particles can be, for example, less than or equal to about 1.7, less than or equal to about 1.6, less than or equal to about 1.5, less than or equal to about 1.4, or less than or equal to about 1.3, and greater than or equal to about 1, greater than or equal to about 1.1, greater than or equal to about 1.2, greater than or equal to about 1.3, greater than or equal to about 1.4, or greater than or equal to about 1.5. Positive electrode active material with an average aspect ratio of less than or equal to 1.7 (using nickel-based composite oxides as raw materials) can be prepared by appropriately selecting (controlling) the preparation conditions of the positive electrode active material (such as removing the hindering effect of hydrate evaporation during the reaction with lithium), thereby improving the reaction of the lithium raw material (e.g., LiOH) with water. If, for example, the average aspect ratio of the primary particles meets the aforementioned range, sphericity and uniformity can be enhanced or improved, the output characteristics of the battery can be enhanced, and the charge / discharge capacity, efficiency, and cycle life characteristics of the battery can be improved.

[0073] According to one or more exemplary embodiments, in the cross-section of a secondary particle, the proportion of primary particles with an aspect ratio of about 1.2 to about 1.7 may be greater than or equal to about 50% of the total number of primary particles. For example, the proportion of primary particles with an aspect ratio of about 1.2 to about 1.7 may be, for example, greater than or equal to about 50%, greater than or equal to about 60%, greater than or equal to about 70%, greater than or equal to about 80%, or greater than or equal to about 90%.

[0074] In one or more embodiments, the proportion of primary particles with an aspect ratio of about 1.2 to about 1.7 can be obtained, for example, by the following method: Primary particles are plotted in an EBSD image of a cross-section of secondary particles cut with a focused ion beam (FIB) using the ImageJ program. The aspect ratio of all plotted primary particles is measured to analyze the aspect ratio distribution. The proportion of primary particles with an aspect ratio of about 1.2 to about 1.7 can then be estimated.

[0075] According to one or more exemplary embodiments, the ratio of the number of primary particles with an aspect ratio greater than or equal to about 4 in the cross-section of a secondary particle to the total number of primary particles may be less than or equal to about 10%. The proportion of primary particles with an aspect ratio greater than or equal to about 4 may, for example, be less than or equal to about 10%, less than or equal to about 8%, less than or equal to about 6%, less than or equal to about 5%, less than or equal to about 4%, less than or equal to about 2%, or less than or equal to about 1%, and may be greater than or equal to about 0.2%, greater than or equal to about 0.4%, greater than or equal to about 0.6%, or greater than or equal to about 0.8%.

[0076] If, for example, the primary particles exhibit the aforementioned aspect ratio distribution, the number of primary particles with a circular shape increases, making it possible to provide (ensure) primary particles with substantially high sphericity, and accordingly, the positive electrode active material can provide (ensure) high capacity, long cycle life and high output.

[0077] The average particle size of secondary particles (D) 50 The size of the secondary particles can be approximately 8 μm to approximately 20 μm, approximately 8 μm to approximately 18 μm, or approximately 10 μm to approximately 15 μm. Here, the average particle size (D) of the secondary particles is... 50 The particle size distribution can be obtained by measuring the size (particle diameter or major axis length) of approximately 20 secondary particles in the SEM image of the positive electrode active material, and taking the size of the secondary particles with a cumulative volume of 50% as the average particle diameter.

[0078] Methods for preparing positive electrode active materials

[0079] In one or more embodiments, a method for preparing a positive electrode active material includes: mixing a nickel-based composite oxide with a lithium raw material, and performing heat treatment to obtain the positive electrode active material.

[0080] The nickel-based composite oxide can be represented by Chemical Formula 4.

[0081] Chemical Formula 4

[0082] Ni x4 M 6 y4 M 7 z4 O 2-b4 X b4

[0083] In Chemical Formula 4, 0.8 ≤ x4 < 1, 0 < y4 ≤ 0.2, 0 ≤ z4 ≤ 0.2, 0.9 ≤ x4 + y4 + z4 ≤ 1.1, and 0 ≤ b4 ≤ 0.1; M 6 and M 7 can each independently be at least one element selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y, and Zr; and X can be at least one (e.g., one or more) element selected from F, P, and S.

[0084] In one or more embodiments of Chemical Formula 4, 0.85 ≤ x4 < 1, 0 < y4 ≤ 0.15, and 0 ≤ z4 ≤ 0.15.

[0085] The nickel-based composite oxide can be represented by exemplary Chemical Formula 5 or Chemical Formula 6.

[0086] Chemical Formula 5

[0087] Ni x5 Co y5 M 8 z5 O 2-b5 X b5

[0088] In Chemical Formula 5, 0.8 ≤ x5 < 1, 0 < y5 ≤ 0.2, 0 ≤ z5 ≤ 0.2, 0.9 ≤ x5 + y + z5 ≤ 1.1, and 0 ≤ b5 ≤ 0.1; M 8 can be at least one (e.g., one or more) element selected from Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y, and Zr; and X can be F, P, S, or a combination thereof.

[0089] In Chemical Formula 5, 0.8 ≤ x5 ≤ 0.99, 0.01 ≤ y5 ≤ 0.1, and 0 ≤ z5 ≤ 0.1.

[0090] Chemical Formula 6

[0091] Nix6 Co y6 M 9 z6 M 10 w6 O 2-b6 X b6

[0092] In chemical formula 6, 0.8 ≤ x6 ≤ 0.98, 0.01 ≤ y6 ≤ 0.19, 0.01 ≤ z6 ≤ 0.19, 0 ≤ w6 ≤ 0.19, 0.9 ≤ x6 + y6 + z6 + w6 ≤ 1.1, and 0 ≤ b6 ≤ 0.1; M 9 It can be Al, Mn, or a combination thereof, M 10 It may be selected from at least one (e.g., one or more) element selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y and Zr, and X may be F, P, S or a combination thereof.

[0093] In one or more embodiments of chemical formula 6, 0.8 ≤ x6 ≤ 0.95, 0.01 ≤ y6 ≤ 0.15, 0.01 ≤ z6 ≤ 0.05, and 0 ≤ w6 ≤ 0.05.

[0094] Nickel-based complex oxides can be oxides containing a high concentration of nickel. For example, in nickel-based complex oxides, based on 100 mol% of total metal, the amount (e.g., content) of nickel can be greater than or equal to about 80 mol%, and in other examples, it can be greater than or equal to about 81 mol%, greater than or equal to about 82 mol%, greater than or equal to about 83 mol%, greater than or equal to about 84 mol%, or greater than or equal to about 85 mol%, and can be less than or equal to about 100 mol%, less than or equal to about 99 mol%, less than or equal to about 95 mol%, less than or equal to about 90 mol%, less than or equal to about 89 mol%, or less than or equal to about 88 mol%.

[0095] Nickel-based complex oxides can be obtained by purchasing commercially available products, or they can be prepared using nickel-based complex hydroxides. For example, nickel-based complex oxides can be prepared by heat-treating nickel-based complex hydroxides prepared by a co-precipitation method in an oxidizing atmosphere at a temperature of less than or equal to about 500°C for less than or equal to about 6 hours.

[0096] According to one or more exemplary embodiments, a method for preparing a positive electrode active material includes: mixing a nickel-based composite oxide with a lithium feedstock, and heat-treating the nickel-based composite oxide with the lithium feedstock. The method may include performing heat treatment at a lower temperature than that used when (e.g., when) the lithium feedstock is mixed with a conventional nickel-based composite hydroxide and the lithium feedstock is heat-treated with a conventional nickel-based composite hydroxide. The method may include selecting (controlling) the size (e.g., average size), standard deviation, aspect ratio (e.g., average aspect ratio), etc., of the primary particles of the positive electrode active material within the aforementioned ranges, thereby providing a positive electrode active material capable of providing (ensuring) high capacity, long cycle life, and high output.

[0097] Lithium feedstocks are, for example, Li₂CO₃, LiOH, their hydrates, or combinations thereof.

[0098] Lithium feedstock can be mixed in proportions of approximately 0.9 mol to approximately 1.2 mol of lithium feedstock per mole of total metal in nickel-based composite oxides. Lithium feedstock can be mixed in proportions greater than or equal to approximately 0.9 mol, greater than or equal to approximately 0.95 mol, greater than or equal to approximately 1 mol, or greater than or equal to approximately 1.04 mol of lithium feedstock per mole of total metal in nickel-based composite oxides, and lithium feedstock can be mixed in proportions less than or equal to approximately 1.2 mol, less than or equal to approximately 1.15 mol, less than or equal to approximately 1.1 mol, or less than or equal to approximately 1.06 mol of lithium feedstock.

[0099] To prepare polycrystalline materials using nickel-based composite oxides or nickel-based hydroxides containing a high concentration of nickel, the heat treatment temperature can (should) be increased. However, since structural instability can occur if (e.g.) the heat treatment temperature is increased, there are limits to the increase in heat treatment temperature. However, the method for preparing positive electrode active materials according to one or more example embodiments uses nickel-based composite oxides as raw materials, so that even when preparing positive electrode active materials containing a high concentration of nickel, the heat treatment temperature can be appropriately selected (controlled), and positive electrode active materials that can provide (ensure) high capacity, long cycle life, and high output can be prepared.

[0100] The heat treatment can be performed in the range of about 600°C to about 800°C. The heat treatment can be performed, for example, at a temperature greater than or equal to about 650°C, greater than or equal to about 700°C, or greater than or equal to about 750°C, and can be performed at a temperature less than or equal to about 790°C, less than or equal to about 780°C, or less than or equal to about 770°C.

[0101] In some example implementations, the heat treatment includes a heating step and a holding step. For example, the heating time may be about 1 hour to about 3 hours, and the holding time may be about 6 hours to about 8 hours. Depending on the circumstances, the heating time and holding time may be adjusted appropriately, and the heating time may be longer than the holding time.

[0102] positive electrode

[0103] The positive electrode of a rechargeable lithium battery may include a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material and may further include a binder, a conductive material, or a combination thereof.

[0104] The binder is used to bond the positive electrode active material particles well together and also to bond the positive electrode active material well to the positive electrode current collector. Examples of binders include, but are not limited to: 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, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylate resin, polyester resin and / or nylon.

[0105] In the positive electrode active material layer, based on 100 wt% of the positive electrode active material layer, the amount of binder can be about 1 wt% to about 5 wt%.

[0106] Conductive materials are included to provide electrode conductivity, and 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, carbon nanofibers, carbon nanotubes, etc.; metallic materials, including metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0107] In the positive electrode active material layer, based on 100 wt% of the positive electrode active material layer, the amount of conductive material can be about 1 wt% to about 5 wt%.

[0108] The positive electrode current collector may include, but is not limited to, aluminum foil.

[0109] Rechargeable lithium batteries

[0110] One or more example implementations provide a rechargeable lithium battery including a positive electrode, a negative electrode, and an electrolyte.

[0111] Rechargeable lithium batteries include a positive electrode and a negative electrode, which include positive electrode active materials, thereby providing (ensuring) high capacity, long cycle life and high output.

[0112] Rechargeable lithium batteries can be, for example, rechargeable lithium batteries comprising a positive electrode, a negative electrode, a separator between the positive and negative electrodes, and an electrolyte, wherein the electrolyte may be in the form of a liquid or a gel polymer. In one or more embodiments, a rechargeable lithium battery may be an all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte, or a semi-solid-state battery comprising a positive electrode, a negative electrode, and a semi-solid electrolyte. Semi-solid may refer to a state comprising both solid and liquid components, or a state that is primarily solid but includes some liquid components. All-solid-state batteries and semi-solid-state batteries exclude the separator. The positive electrode active material according to some example embodiments can provide high capacity while providing substantially high charge / discharge efficiency and high-temperature cycle life, depending on its shape, and is therefore suitable for use in the types of batteries mentioned herein and exhibits appropriate or superior performance in each type of battery.

[0113] Based on their shape, rechargeable lithium batteries can be classified into cylindrical, prismatic, pouch, and coin-shaped types. Figures 1-4 To illustrate a schematic diagram of a rechargeable lithium battery according to some exemplary embodiments, wherein... Figure 1 It is a cylindrical battery. Figure 2 It is a prismatic battery, and Figure 3 and Figure 4 Each is a pouch-type battery. (Reference) Figures 1-4 The rechargeable lithium battery 100 may include an electrode assembly 40 (with a separator 30 between the positive electrode 10 and the negative electrode 20) and a housing 50 therein housing the electrode assembly 40. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). Figure 1 As shown, the rechargeable lithium battery 100 may include a sealing member 60 of a sealed housing 50. Additionally, in Figure 2 In this context, the rechargeable lithium battery 100 may include a positive electrode lead connector 11, a positive electrode terminal 12, a negative electrode lead connector 21, and a negative electrode terminal 22. For example... Figure 3 and Figure 4 As shown, the rechargeable lithium battery 100 includes an electrode terminal 70, which may be a positive electrode terminal 71 and a negative electrode terminal 72, serving as an electrical path to conduct the current generated in the electrode assembly 40 to the outside.

[0114] negative electrode

[0115] 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 includes negative electrode active material, and may further include a binder, a conductive material, or a combination thereof.

[0116] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, a lithium metal alloy, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0117] The material capable of reversibly intercalating / deintercalating lithium ions may be a carbon-based negative electrode active material.

[0118] The carbon-based negative electrode active material may include crystalline carbon, amorphous carbon, or a combination thereof. The crystalline carbon may be irregular or flaky, sheet-like, spherical, or fibrous natural graphite or artificial graphite. The amorphous carbon may be soft carbon, hard carbon, a mesophase pitch carbonized product, calcined coke, etc. Soft carbon refers to a graphitizable carbon material and is a material that is easily graphitized by heat treatment at a high temperature (about 2800 °C). Hard carbon is a non-graphitizable or slightly graphitized carbon material by heat treatment.

[0119] In addition to the carbon-based negative electrode active material, the negative electrode active material layer may further include other types (species) of negative electrode active material, and may further include, for example, lithium metal, a lithium metal alloy, and a material capable of doping and dedoping lithium.

[0120] 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.

[0121] The material capable of doping / dedoping lithium may be a Si-based negative electrode active material 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, for example, SiO2), a Si-Q alloy (where Q is 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), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO x (0 < x ≤ 2, for example, SnO2), a Sn-based alloy, or a combination thereof.

[0122] The silicon-carbon composite can be a composite of silicon and amorphous carbon. According to some example 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 may include secondary particles (cores) aggregated with primary silicon particles and an amorphous carbon coating (shell) on the surface of the secondary particles. Amorphous carbon may also be present between the primary silicon particles, such that, for example, the primary silicon particles may be coated with amorphous carbon. And the secondary particles may be dispersed within an amorphous carbon matrix.

[0123] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core comprising crystalline carbon and silicon particles, and an amorphous carbon coating on the surface of the core.

[0124] Si-based and / or Sn-based negative electrode active materials can be mixed with carbon-based negative electrode active materials. The mixing ratio of Si-based and / or Sn-based negative electrode active materials to carbon-based negative electrode active materials can be approximately 1:99 to approximately 90:10 by weight.

[0125] In the negative electrode active material layer, based on a 100wt% negative electrode active material layer, the amount of negative electrode active material included can be approximately 95wt% to approximately 99wt%.

[0126] In some example embodiments, the negative electrode active material layer may optionally further include a binder, a conductive material, or a combination thereof.

[0127] The binder is used to bond the active material particles of the negative electrode to each other effectively, and also to bond the active material of the negative electrode to the negative electrode current collector. The binder may be a water-insoluble binder, a water-soluble binder, or a combination thereof.

[0128] Water-insoluble adhesives may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, ethylene propylene copolymers, polystyrene, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0129] Water-soluble adhesives may include rubber-based adhesives or polymeric resin-based adhesives. Rubber-based adhesives are selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and / or combinations thereof. Polymeric resin-based adhesives are 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 / or combinations thereof.

[0130] If (for example, when) a water-soluble binder is used as a binder in the negative electrode active material layer, it may further include a cellulose-based compound capable of imparting viscosity. As a cellulose-based compound, one or more types (species) may be mixed and used, such as carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be Na, K, and / or Li.

[0131] Conductive materials may be included to provide electrode conductivity, and any conductive material may be used as a conductive material unless it causes a chemical change. Examples of conductive materials may include: carbonaceous materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, and carbon nanotubes; metallic materials in the form of metal powders or metal fibers including copper, nickel, aluminum, and silver; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0132] Based on a 100wt% negative electrode active material layer, the amount of binder in the negative electrode active material layer can be 1wt% to 5wt%, and based on a 100wt% negative electrode active material layer, the amount of conductive material in the negative electrode active material layer can be 1wt% to 5wt%.

[0133] The negative electrode current collector is selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and / or combinations thereof.

[0134] electrolytes

[0135] In one or more embodiments, the electrolyte for the rechargeable lithium battery may be an electrolyte comprising a non-aqueous organic solvent and a lithium salt.

[0136] Non-aqueous organic solvents are used as media for transporting ions that participate in the electrochemical reactions of the battery.

[0137] Non-aqueous organic solvents may include carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, or combinations thereof.

[0138] 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), butyl carbonate (BC), etc.

[0139] Ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonate lactone, caprolactone, etc.

[0140] Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. In some embodiments, ketone solvents may include cyclohexanone, etc. Alcohol solvents may include ethanol, isopropanol, etc., and aprotic solvents may include: nitrile solvents (such as R-CN (where R is a C2-C20 straight-chain, branched, or cyclic hydrocarbon group, and may include double bonds, aromatic rings, or ether groups, etc.)); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane, 1,4-dioxolane, etc.; sulfolane, etc.

[0141] Non-aqueous organic solvents can be used alone or in mixtures of two or more substances.

[0142] If (for example, when) a carbonate solvent is used, cyclic carbonates and chain carbonates can be mixed and used, and cyclic carbonates and chain carbonates can be mixed in a volume ratio of about 1:1 to about 1:9.

[0143] Lithium salts dissolved in non-aqueous organic solvents supply lithium ions in batteries, ensuring basic operation of rechargeable lithium batteries and improving lithium ion transport between the positive and negative electrodes. Examples of lithium salts may include those 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 difluorobis(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB).

[0144] diaphragm

[0145] Depending on the type of rechargeable lithium battery, the separator may be present between the positive and negative electrodes. The separator may include polyethylene separator, polypropylene separator, polyvinylidene fluoride separator, or a multilayer film of two or more layers thereof (such as polyethylene / polypropylene double-layer separator, polyethylene / polypropylene / polypropylene triple-layer separator, polypropylene / polypropylene / polypropylene triple-layer separator, etc.).

[0146] The diaphragm may include a porous substrate and a coating on one or both (e.g., opposite) surfaces of the porous substrate, the coating comprising an organic material, an inorganic material, or a combination thereof.

[0147] The porous substrate may be a polymer film formed from any one or more copolymers or mixtures of the following polymers: polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene ether, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, and polytetrafluoroethylene (e.g., ).

[0148] Organic materials may include polymers such as polyvinylidene fluoride or (meth)acrylic acid polymers.

[0149] Inorganic materials may include, but are not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite and combinations thereof.

[0150] Organic and inorganic materials can be mixed in a coating, or coatings containing organic materials and coatings containing inorganic materials can be stacked.

[0151] Terms such as “substantially,” “about,” and “approximately” are used as relative terms rather than terms of degree and are intended to encompass the inherent biases of measured or calculated values ​​that would be recognized by a person skilled in the art. They may include the stated value and a range of acceptable deviations as determined by a person skilled in the art considering the limitations and errors associated with the measurement of that quantity. For example, “about” may refer to one or more standard deviations, or ±30%, ±20%, ±10%, or ±5% of the stated value.

[0152] The numerical ranges disclosed herein include and are intended to include all subranges containing the same numerical precision. For example, the range “1.0 to 10.0” is intended to include all subranges (such as, for example, 2.4 to 7.6) where the minimum value is equal to or greater than 1.0 and the maximum value is equal to or less than 10.0. Therefore, the applicant reserves the right to amend this specification (including the claims) to expressly describe any subranges included within the ranges expressly described herein.

[0153] Embodiments and comparative examples of this disclosure are described herein. However, the following embodiments are merely examples of this disclosure, and this disclosure is not limited to these embodiments.

[0154] Example

[0155] Example

[0156] (1) Preparation of positive electrode active material

[0157] 100 moles of Ni as a nickel-based complex oxide 0.88 Co 0.105 Al 0.015 O2 was mixed with 100 moles of LiOH, and then heat-treated at 750°C for 8 hours under an oxygen atmosphere by uniformly increasing the temperature for 2 hours to 750°C. This yielded a lithium-nickel composite oxide (LiNi). 0.88 Co 0.105 Al 0.015 O2 (the final positive electrode active material).

[0158] The lithium-nickel composite oxide exists as secondary particles aggregated from multiple primary particles. The primary particles have an average size of approximately 1.24 micrometers (μm) and a standard deviation of approximately 0.17 μm, as measured by electron backscatter diffraction (EBSD) analysis of the cross-section of the secondary particles; and the secondary particles have an average particle size of approximately 13 μm, as measured by scanning electron microscopy (SEM) images. 50 ).

[0159] (2) Preparation of the positive electrode

[0160] The obtained positive electrode active material, polyvinylidene fluoride as a binder, and carbon nanotubes as a conductive material were mixed in a weight ratio of 97.7:1.0:1.3 to prepare a positive electrode active material composition. The positive electrode active material composition was dispersed in N-methylpyrrolidone solvent to prepare a slurry for forming the positive electrode active material layer. The slurry for forming the positive electrode active material layer was coated onto aluminum foil to form an electrode plate. The electrode plate was dried at 135°C for 3 hours, then pressed and vacuum dried to prepare the positive electrode.

[0161] (3) Preparation of rechargeable lithium battery cells

[0162] A coin half-cell (rechargeable lithium battery cell) was prepared by using a positive electrode with a lithium metal counter electrode as the negative electrode. A separator (approximately 16 μm thick) formed of a porous polyethylene membrane was arranged between the positive electrode and the lithium metal counter electrode, and an electrolyte was injected into it. The electrolyte was prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:5 to prepare a mixed solvent, and dissolving 1.1 molar concentration (M) of LiPF6 therein.

[0163] Comparative example

[0164] (1) Preparation of positive electrode active material

[0165] 100 moles of Ni as a nickel-based complex hydroxide 0.88 Co 0.105 Al0.015 (OH)₂ was mixed with 100 moles of LiOH, and then heat-treated at 750°C for 8 hours under an oxygen atmosphere by uniformly increasing the temperature for 2 hours to 750°C, to obtain a lithium-nickel composite oxide (LiNi). 0.88 Co 0.105 Al 0.015 O2 (the final positive electrode active material).

[0166] The lithium-nickel composite oxides exist as secondary particles aggregated from multiple primary particles. The primary particles have an average size of approximately 1.01 μm and a standard deviation of approximately 0.14 μm, as measured by EBSD analysis of cross-sections of the secondary particles, and the secondary particles have an average particle size (D) of approximately 13 μm, as measured by SEM images. 50 ).

[0167] (2) Preparation of positive electrode and rechargeable lithium battery cell

[0168] The positive electrode and rechargeable lithium battery cell were prepared in essentially the same manner as in the examples.

[0169] Evaluation Example 1: Analysis of the cross-section of the active material in the positive electrode

[0170] Figure 5 This is a scanning electron microscope (SEM) image of a cross-section of the positive electrode active material prepared in the example by focused ion beam (FIB) cutting, and Figure 7 for Figure 5 The image depicts the electron backscatter diffraction (EBSD) pattern of the primary particles.

[0171] Figure 6 This is a scanning electron microscope (SEM) image of the cross-section of the positive electrode active material prepared in the comparative example by FIB cutting, and Figure 8 for Figure 6 The image depicts the electron backscatter diffraction (EBSD) pattern of the primary particles.

[0172] refer to Figure 7 and Figure 8 Compared with the primary particles of the positive electrode active material according to the comparative example, the primary particles of the positive electrode active material according to the embodiment are not only relatively larger and relatively more uniform, but also have an aspect ratio closer to 1, which confirms the spherical shape.

[0173] In this document, the secondary particles of the positive electrode active material of the embodiments and the secondary particles of the positive electrode active material of the comparative examples both (for example, simultaneously) have an average particle size of about 13 μm.

[0174] Evaluation Example 2: Evaluation of the mean and standard deviation of primary particle size

[0175] The cross-sections of the positive electrode active materials of the Examples and Comparative Examples were characterized using electron backscatter diffraction (EBSD) images. Ten points were randomly selected from the EBSD images, and the size of the primary particles at each of the ten points was measured using an image analysis program (Image J). The mean and standard deviation were calculated using the size of the primary particles at the ten points. The results are shown in Table 1, where the numbers 1 to 10 in the first column represent any ten points selected from each of the EBSD images of the cross-sections of the positive electrode active materials according to the Examples and Comparative Examples.

[0176] Table 1

[0177]

[0178] Evaluation Example 3: Aspect Ratio Analysis of Primary Particles

[0179] When using Figure 7 and Figure 8 When the images were analyzed using an image analysis program (Image J) to determine the aspect ratio distribution of the primary particles in the embodiments and comparative examples, the primary particles in the embodiments had an average aspect ratio of 1.58, while the primary particles in the comparative examples had an average aspect ratio of 1.82. (Reference) Figure 7 and Figure 8 It was confirmed that the primary particles of the embodiment were closer to spherical and more uniform than the primary particles of the comparative example, while the primary particles of the comparative example were arranged relatively radially.

[0180] Figure 9 and Figure 10 The aspect ratio distribution of primary particles in the cross-sections of the positive electrode active materials prepared in the examples and comparative examples are shown respectively. Figure 9 and Figure 10 In the figure, the horizontal axis represents the aspect ratio of the primary particles, and the vertical axis represents the cumulative proportion of primary particles with the aspect ratio corresponding to the horizontal axis (area weight fraction (%)).

[0181] refer to Figure 9 and Figure 10 In the cross-section of the positive electrode active material of the embodiment, the primary particles mainly have an aspect ratio of less than 4, but in the cross-section of the positive electrode active material of the comparative example, some primary particles have an aspect ratio greater than or equal to 4. In some embodiments, reference is made to... Figure 11 Compared with the aspect ratio distribution curve of the primary particles of the positive electrode active material in the comparative example, the aspect ratio distribution curve of the primary particles in the cross section of the positive electrode active material of the embodiment shifts to the left, confirming that the primary particles with an aspect ratio of 1 to 2 in the embodiment have a higher cumulative number ratio.

[0182] Figure 12 To analyze Figure 9 The graph obtained is a distribution curve of the aspect ratio of the primary particles, and the number (%) of primary particles in the aspect ratio range of the secondary particles in each cross section of the positive electrode active material of the examples and comparative examples is shown as a bar graph by analyzing the aspect ratio of the primary particles in the secondary particles of each example and comparative example. Figure 12 The data is shown in Table 2.

[0183] Table 2

[0184]

[0185] refer to Figure 12 According to Table 2, it was confirmed that the proportion of primary particles with an aspect ratio greater than or equal to about 4 in the cross-section of the positive electrode active material of the embodiment was 0.8%. Conversely, since it was confirmed that the proportion of primary particles with an aspect ratio greater than or equal to about 4 in the cross-section of the positive electrode active material of the comparative example was 1.51%, it was confirmed that the primary particles of the positive electrode active material of the embodiment had appropriate or superior uniformity compared to the primary particles of the positive electrode active material of the comparative example.

[0186] Evaluation Example 4: High-Rate Capacity Assessment

[0187] At 25°C, the rechargeable lithium-ion battery cells of the examples and comparative examples were initially charged and discharged: charged at a constant current / constant voltage under conditions of 1.0C (1C), 4.25V, and 0.05C cutoff (0.05CC / O), and allowed to stand for 10 minutes; discharged at a constant current / constant voltage under conditions of 1C and 3V cutoff (3V C / O), and allowed to stand for 10 minutes. Subsequently, the C-rate (cycle rate) was changed to 2.0C (2C), 3.0C (3C), 4.0C (4C), 5.0C (5C), and 1C to repeatedly charge and discharge the battery cells.

[0188] Figure 13 The diagram shows the discharge capacity for each cycle, from which the ratio of the discharge capacity of each C-rate cycle to the discharge capacity of the initial 1C cycle (discharge capacity retention rate) is calculated, and the results are shown in Table 3.

[0189] Table 3

[0190] 1.0C 2.0C 3.0C 4.0C 5.0C 1.0C (after recovery) Example 100％ 96.9％ 91.0％ 83.2％ 65.2％ 97.0％ Comparative example 100％ 96.5％ 88.5％ 76.1％ 56.3％ 97.3％

[0191] Reference Figure 13 The rechargeable lithium battery cells of the embodiments exhibit improved or better discharge capacity retention at all C-rates (especially at high rates of 4C and 5C) compared to the rechargeable lithium battery cells of the comparative examples, and exhibit excellent discharge capacity retention even at the last 1C rate, which confirms excellent or appropriate capacity recovery.

[0192] Summarize

[0193] The positive electrode active material of the embodiment, prepared by mixing a nickel-based composite oxide obtained by heat-treating a nickel-based composite hydroxide raw material with a lithium raw material and then heat-treating the mixture, has the same average particle size of secondary particles as the positive electrode active material of the comparative example, prepared by mixing a nickel-based composite hydroxide raw material with a lithium raw material and then heat-treating the mixture. An unexpected beneficial effect provided by the difference in raw materials is that the primary particles of the embodiment have a relatively larger average size than the primary particles of the comparative example, but with a small standard deviation of less than or equal to 0.3 μm and an average aspect ratio of less than or equal to 1.7. These results confirm that the primary particles of the embodiment are relatively uniform and spherical.

[0194] Conversely, the preparation process of the comparative example confirmed that it provides primary particles with a relatively large aspect ratio and a more radially distributed structure.

[0195] In some embodiments, when compared to the positive electrode active material of a comparative example in which the primary particles are relatively smaller and have a non-uniform (e.g., significantly non-uniform) aspect ratio and are more radially arranged, the positive electrode active material of an embodiment in which the primary particles are relatively large, relatively uniform, and spherical exhibits appropriate or superior discharge capacity retention and capacity recovery.

[0196] Accordingly, compared with the positive electrode active materials of the comparative examples, the positive electrode active materials of the embodiments of the present disclosure, having relatively large, uniform, and spherical primary particles, exhibit appropriate or superior battery performance.

[0197] Those skilled in the art, considering the disclosure in its entirety, will recognize that various suitable features of embodiments of the disclosure may be combined in part or in whole, or combined with one another, and may be technically interlocked and operated in one or more suitable ways, and that various embodiments may be implemented independently of each other or in any suitable combination with one another, unless otherwise stated or implied.

[0198] Although this disclosure 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 one or more suitable modifications and equivalent arrangements included within the spirit and scope of the claims and their equivalents.

Claims

1. A positive electrode active material, comprising: This includes secondary particles of lithium-nickel composite oxides, wherein the secondary particles are in the form of aggregates of multiple primary particles. The average size of the primary particles was measured by electron backscatter diffraction analysis of the cross-section of the secondary particles, and the average size was 1.05 μm to 1.5 μm. The standard deviation of the size of the primary particles is less than or equal to 0.3 μm, and The average aspect ratio of the primary particles is less than or equal to 1.

7.

2. The positive electrode active material according to claim 1, wherein, The lithium-nickel composite oxide is represented by chemical formula 1: Chemical Formula 1 Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 In chemical formula 1, 0.9≤a1≤1.2， 0.8≤x1<1， 0<y1≤0.2， 0≤z1≤0.2， 0.9≤x1+y1+z1≤1.1, 0≤b1≤0.1， M 1 and M 2 Each element is independently selected from at least one element chosen from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y, and Zr. X is at least one element selected from F, P, and S.

3. The positive electrode active material according to claim 1, wherein, In the lithium-nickel composite oxide, based on 100 mol% of total metals excluding lithium, the amount of nickel is greater than or equal to 80 mol%.

4. The positive electrode active material according to claim 1, wherein, In the cross-section of a secondary particle, the ratio of the number of primary particles with an aspect ratio of 1.2 to 1.7 to the total number of primary particles is greater than or equal to 50%.

5. The positive electrode active material according to claim 1, wherein, In the cross-section of a secondary particle, the ratio of the number of primary particles with an aspect ratio greater than or equal to 4 to the total number of primary particles is less than or equal to 10%.

6. The positive electrode active material according to claim 1, wherein, The average particle size D of the secondary particles 50 The size ranges from 8μm to 20μm.

7. A method for preparing a positive electrode active material, comprising: Mixing nickel-based composite oxides with lithium raw materials; and Heat treatment is performed to obtain the positive electrode active material according to any one of claims 1 to 6.

8. The method according to claim 7, wherein, The nickel-based composite oxide is represented by chemical formula 4: Chemical Formula 4 In x4 M 6 y4 M 7 z4 SHE 2-b4 X b4 In chemical formula 4, 0.8≤x4<1， 0<y4≤0.2， 0≤z4≤0.2， 0.9 ≤ x⁴ + y⁴ + z⁴ ≤ 1.1 0≤b4≤0.1， M 6 and M 7 Each element is independently selected from at least one element chosen from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y, and Zr. X is at least one element selected from F, P, and S.

9. The method according to claim 7, wherein, In the nickel-based composite oxide, the amount of nickel is greater than or equal to 80 mol% based on 100 mol% total metal.

10. The method according to claim 7, wherein, The mixing of the nickel composite oxide with the lithium raw material comprises: mixing the lithium raw material with a ratio of 0.9 to 1.2 moles of lithium relative to 1 mole of total metal in the nickel composite oxide.

11. The method according to claim 7, wherein, The heat treatment is carried out at a temperature of 600℃ to 800℃.

12. A positive electrode, comprising: Positive electrode current collector, and The positive electrode active material layer is located on the positive electrode current collector. The positive electrode active material layer comprises the positive electrode active material according to any one of claims 1 to 6 or the positive electrode active material prepared by the method according to any one of claims 7 to 11.

13. A rechargeable lithium battery, comprising a positive electrode, a negative electrode, and an electrolyte as described in claim 12.

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