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

Abstract

The invention relates to a positive electrode active material, a method for preparing the same, a positive electrode, and a rechargeable lithium battery. The positive electrode active material includes: a core particle including a lithium cobalt-based composite oxide; and a coating layer on a surface of the core particle and including a lithium iron phosphate-based compound and aluminum. The positive electrode active material according to some embodiments has long cycle life characteristics and improved stability even at high voltages. When the positive electrode active material is applied to a rechargeable lithium battery, appropriate high initial charge capacity / discharge capacity and efficiency can be achieved under high-voltage operating conditions, and appropriate long cycle life characteristics can be achieved under high-voltage and high-temperature conditions.

Description

Technical Field

[0001] One or more aspects of embodiments of the present disclosure relate to a positive electrode active material, a method for preparing the same, a positive electrode including the positive electrode active material, and a rechargeable lithium battery including the positive electrode. Background Art

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

[0003] Various positive electrode active materials have been studied to realize rechargeable lithium batteries applied to the above uses. Among them, lithium nickel-based oxides, lithium nickel manganese cobalt composite oxides, lithium nickel cobalt aluminum composite oxides, and lithium cobalt-based oxides are generally used as positive electrode active materials. However, although the demand for large-sized, high-capacity, high-voltage, and / or high-energy density rechargeable lithium batteries has increased significantly recently, the stability of driving rechargeable lithium batteries at an appropriate high voltage is still inappropriately weak (or difficult). For example, it is necessary or desirable to improve the stability of the positive electrode active material and develop a positive electrode active material that can reduce heat generation even when operating at a high voltage (for example, when operating at a high voltage). Summary of the Invention

[0004] One or more aspects of embodiments of the present disclosure provide a positive electrode active material, a method for preparing the same, a positive electrode including the positive electrode active material, and a rechargeable lithium battery including the positive electrode. The positive electrode active material includes a surface-coated lithium cobalt composite oxide, and has an appropriate high capacity, appropriate long cycle life characteristics, and improved stability even at a high voltage. Other aspects will be set forth in part in the following description, and in part will be obvious from the description, or may be learned by practice of the presented embodiments of the present disclosure.

[0005] In some embodiments, the positive electrode active material includes: a core particle including a lithium cobalt composite oxide; and a coating located on the surface of the core particle and including a lithium iron phosphate compound and aluminum.

[0006] In some embodiments, a method for preparing a positive electrode active material includes: (i) dry-mixing a lithium cobalt composite oxide, a lithium iron phosphate compound, and an aluminum raw material to prepare a mixture; and (ii) firing the mixture in a nitrogen atmosphere or an inert gas atmosphere.

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

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

[0009] The positive electrode active material according to some embodiments has appropriate long cycle life characteristics and improved stability even at high voltages. If the positive electrode active material is applied to a rechargeable lithium battery (for example, when the positive electrode active material is applied to a rechargeable lithium battery), appropriate high initial charge capacity / discharge capacity and efficiency can be achieved under high voltage operating conditions, and long cycle life characteristics can be achieved under high voltage and high temperature conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figures 1 to 4 FIG. is a schematic diagram showing a rechargeable lithium battery according to some embodiments.

[0011] Figure 5 and Figure 6 are each a scanning electron microscope (SEM) image of the positive electrode active material according to Comparative Example 1.

[0012] Figure 7 and Figure 8 are each an SEM image of the positive electrode active material according to Example 1.

[0013] Figure 9 is a graph of the heat flow according to temperature of the positive electrode active material according to Example 1 and Comparative Example 1 measured by differential scanning calorimetry.

[0014] <Reference Numerals>

[0015] 100: Rechargeable lithium battery 10: Positive electrode

[0016] 11: Positive electrode lead tab 12: Positive electrode terminal

[0017] 20: Negative electrode 21: Negative electrode lead tab

[0018] 22: Negative electrode terminal 30: Separator

[0019] 40: Electrode assembly 50: Housing

[0020] 60: Sealing member 70: Electrode tab

[0021] 71: Positive electrode tab 72: Negative electrode tab DETAILED DESCRIPTION

[0022] Hereinafter, example embodiments will be described in more detail so that those of ordinary skill in the art can easily implement them. However, the present disclosure can be implemented in many different forms and is not to be construed as limited to the example embodiments set forth herein.

[0023] The terms used herein are for the purpose of describing embodiments only and are not intended to limit the present disclosure. Unless the context clearly indicates otherwise, singular expressions include plural expressions.

[0024] As used herein, "a combination thereof" refers to a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of components.

[0025] In this document, it should be understood that terms such as "comprises", "includes" and / or "has" are intended to denote the presence of a specific feature, quantity, step (e.g., action or task), element or combination thereof, but do not preclude the presence or addition of one or more other features, quantity, steps (e.g., action or task), elements or combination thereof.

[0026] In the drawings, for clarity, the thickness of layers, films, panels, regions, etc. is exaggerated, and the same reference numerals are used throughout to denote the same elements, and their repeated description may not be provided in the specification. It will be understood that if an element (such as a layer, film, region or substrate) is referred to as being "on" another element (such as a layer, film, region or substrate) (e.g., when an element (such as a layer, film, region or substrate) is referred to as being "on" another element (such as a layer, film, region or substrate)), it can be directly on the other element (such as a layer, film, region or substrate), or there may also be an intervening element (such as a layer, film, region or substrate). In contrast, if an element is referred to as being "directly on" another element (such as a layer, film, region or substrate) (e.g., when an element is referred to as being "directly on" another element (such as a layer, film, region or substrate)), there is no intervening element (such as a layer, film, region or substrate).

[0027] A "layer" herein includes not only a shape formed on the entire surface as observed in a plan view (e.g., a shape formed on the entire surface when observed in a plan view), but also a shape formed on a partial surface.

[0028] Furthermore, in this specification, the phrase "in a plane" or "plan view" means observing the target part from the top, and the phrase "in a cross-section" means observing a cross-section formed by vertically cutting the target part from the side.

[0029] The average particle size (D 50 ) can be measured by methods applicable to those skilled in the art, for example, by a particle size analyzer, or by transmission electron microscope images and / or scanning electron microscope images. In one or more embodiments, the average particle size value can be obtained by measuring using the dynamic light scattering method, performing data analysis, counting the number of particles in each particle size range, and thus performing calculations. Unless otherwise defined, the average particle size (D 50 ) can refer to the diameter of the particles with a cumulative volume of 50% by volume in the particle size distribution. As used herein, if no other definition is provided (e.g., when no other definition is provided), the average particle size (D 50 ) refers to the diameter of the particles with a cumulative volume of 50% by volume in the particle size distribution obtained by randomly measuring the sizes (diameter or major axis length) of about 20 particles in a scanning electron microscope image.

[0030] As used herein, "or" is not interpreted in an exclusive sense. For example, "A or B" is interpreted to include A, B, A + B, etc.

[0031] As used herein, "metal" is interpreted to include the concepts of ordinary metals, transition metals, and metalloids (semi-metals).

[0032] It will be understood that although terms such as first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. Thus, without departing from the teachings of the present invention, the first element may be referred to as the second element. Similarly, the second element may be referred to as the first element.

[0033] As used herein, the terms "use", "using", and "used" may be regarded as synonymous with the terms "utilize", "utilizing", and "utilized", respectively.

[0034] As used herein, expressions such as "at least one of...", "one of...", and "selected from...", when before / after a list of elements, modify the entire list of elements and do not modify a single element of the list. For example, "at least one selected from a, b, and c" and "at least one of a, b, and c" can indicate only a, only b, only c, both a and b (e.g., a and b simultaneously), both a and c (e.g., a and c simultaneously), both b and c (e.g., b and c simultaneously), all of a, b, and c, or variants thereof.

[0035] As used herein, the term "and / or" includes any and all combinations of one or more of the related listed items.

[0036] Further, when describing embodiments of the present disclosure, the use of "may" refers to "one or more embodiments of the present disclosure".

[0037] For ease of description, spatially relative terms, such as "beneath", "below", "lower", "above", "upper", "bottom", "top", etc., may be used herein to describe the relationship of one element or feature to another element or feature as illustrated in the figures. It will be understood that, in addition to the orientation depicted in the figures, spatially relative terms are intended to encompass different orientations of the device in use or operation. For example, if the device in the figures is turned over, an element described as "below" or "beneath" other elements or features will then be oriented "above" or "over" the other elements or features. Thus, the term "below" can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations), and the spatially relative descriptors used herein should be interpreted accordingly.

[0038] As used herein, the terms "substantially", "about" and similar terms are used as approximate terms and not as terms of degree, and are intended to account for the inherent variations in measured or calculated values that would be recognized by a person of ordinary skill in the art. As used herein, "about" or "approximate" includes the recited value and means within an acceptable deviation range determined by a person of ordinary skill in the art considering the measurement in question and the errors associated with the measurement of a particular quantity (i.e., the limitations of the measurement system). For example, "about" can mean within one or more standard deviations of the recited value, or within ±30%, ±20%, ±10% or ±5% of the recited value.

[0039] Any numerical range set forth herein is intended to include all sub-ranges of the same numerical precision falling within the set forth range. For example, the range "1.0 to 10.0" is intended to include between the minimum value of 1.0 and the maximum value of 10.0 set forth (and including 1.0 and 10.0), i.e., all sub-ranges having a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 10.0, such as, for example, 2.4 to 7.6. Any maximum numerical limit set forth herein is intended to include all lower numerical limits falling therein and any minimum numerical limit set forth in this specification is intended to include all higher numerical limits falling therein. Accordingly, the applicant reserves the right to modify this specification (including the claims) to expressly recite any sub-ranges falling within the ranges expressly set forth herein.

[0040] Given the entirety of the present disclosure, those of ordinary skill in the art will recognize that each suitable feature of the various embodiments of the present disclosure can be partially or fully combined with each other, and can be interlocked and operated technically in various suitable ways, and each embodiment can be implemented independently of each other or in combination with each other in any suitable way unless otherwise stated or implied.

[0041] Positive electrode active material

[0042] In some embodiments, the positive electrode active material includes: a core particle including a lithium cobalt composite oxide; and a coating located on the surface of the core particle and including a lithium iron phosphate compound and aluminum.

[0043] Since the lithium cobalt positive electrode active material (i.e., the positive electrode active material including a lithium cobalt composite oxide) is in the form of single particles, the lithium cobalt positive electrode active material has excellent or suitable density characteristics, but may have a problem of poor stability if operated in a high voltage range (e.g., when operating in a high voltage range). Accordingly, in some embodiments, a coating including a lithium iron phosphate compound and aluminum is formed on the surface of the lithium cobalt positive electrode active material, thereby not only improving the high voltage and high temperature cycle life characteristics of the battery, but also improving the initial charge capacity / discharge capacity and efficiency of the battery.

[0044] Core particle

[0045] The core particle according to some embodiments includes a lithium cobalt composite oxide, and the lithium cobalt composite oxide can be represented by, for example, Chemical Formula 1:

[0046] Chemical Formula 1

[0047] Li a1 Co x1 Al y1 Mg z1 M 1 w1 O 2-b1 X b1 .

[0048] In Chemical Formula 1, 0.9 ≤ a1 ≤ 1.8, 0.8 ≤ x1 ≤ 0.99, 0 ≤ y1 ≤ 0.1, 0 ≤ z1 ≤ 0.1, 0 ≤ w1 ≤ 0.1, 0.9 ≤ x1 + y1 + z1 ≤ 1.1 and 0 ≤ b1 ≤ 0.1, M 1 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn and Zr, and X is one or more elements selected from F, P and S.

[0049] In Chemical Formula 1, 0.9 ≤ a1 ≤ 1.5 or 0.9 ≤ a1 ≤ 1.2. In one or more embodiments, 0.8 < x1 ≤ 0.99, 0.82 ≤ x1 ≤ 0.99, 0.84 ≤ x1 ≤ 0.99, 0.86 ≤ x1 ≤ 0.99, 0.88 ≤ x1 ≤ 0.98 or 0.9 ≤ x1 ≤ 0.97; 0 < y1 ≤ 0.1, 0.01 ≤ y1 ≤ 0.09, 0.01 ≤ y1 ≤ 0.05, 0.01 ≤ y1 ≤ 0.03 or 0.01 ≤ y1 ≤ 0.02; 0 < z1 ≤ 0.1, 0.001 ≤ z1 ≤ 0.09, 0.001 ≤ z1 ≤ 0.05, 0.005 ≤ z1 ≤ 0.03 or 0.005 ≤ z1 ≤ 0.01; 0 < w1 ≤ 0.1, 0.001 ≤ w1 ≤ 0.075, 0.001 < w1 ≤ 0.05 or 0.001 < w1 ≤ 0.025.

[0050] In some embodiments, the lithium cobalt composite oxide may further include aluminum, magnesium, or a combination thereof. For example, aluminum and magnesium may be dopants, and if the lithium cobalt composite oxide is doped with aluminum, magnesium, or a combination thereof (e.g., when the lithium cobalt composite oxide is doped with aluminum, magnesium, or a combination thereof), the capacity characteristics and cycle life characteristics of the battery when operating at high voltages can be improved.

[0051] If the lithium cobalt composite oxide includes aluminum, based on 100 mol% of the metals other than lithium in the lithium cobalt composite oxide, the aluminum content (e.g., amount) may be about 1 mol% to about 3 mol%, for example, about 1.5 mol% to about 2.5 mol%. If the aluminum content (e.g., amount) satisfies any one of the above ranges, the high voltage characteristics of the positive electrode active material can be further improved.

[0052] The positive electrode active material is in the form of particles, and the average particle diameter (D 50 ) may be, for example, about 1 μm to about 30 μm. If the average particle diameter (D 50 ) of the core particles satisfies the above range, appropriate high capacity and long cycle life can be achieved, and according to some embodiments, it may be beneficial for forming a coating. As an example, the positive electrode active material may be (e.g., may include) large particles with an average particle diameter (D 50 ) of about 9 μm to about 25 μm, or may be (e.g., may include) small particles with an average particle diameter (D 50 ) of about 0.5 μm to about 8 μm, and the large particles and small particles can be appropriately or suitably mixed. The average particle diameter (D 50 ) of the large particles may be, for example, about 10 μm to about 20 μm or about 12 μm to about 18 μm, and the average particle diameter (D 50) can be, for example, from about 1 μm to about 6 μm or from about 2 μm to about 5 μm. In this specification, when the particles are spherical, "diameter" indicates the average particle size (D 50 ), and when the particles are non-spherical, "diameter" indicates the major axis length. Also, if the positive electrode active material includes a mixture of large particles and small particles, the amount of large particles that can be included is from about 60 wt% to about 95 wt% or from about 70 wt% to about 90 wt%, and the amount of small particles that can be included is from about 5 wt% to about 40 wt% or from about 10 wt% to about 30 wt%. If the large particles and small particles are mixed within the above content (e.g., amount) range, the cycle life characteristics can be improved while maximizing or increasing the capacity and energy density. As used herein, if no other definition is provided (e.g., when no other definition is provided otherwise), the average particle size (D 50 ) refers to the diameter of the particle at which the cumulative volume is 50% by volume in the particle size distribution obtained by randomly measuring the sizes (diameter or major axis length) of about 20 particles in the scanning electron microscope image of the positive electrode active material.

[0053] The shape of the core particles can be irregular, spherical, etc.

[0054] Coating

[0055] The positive electrode active material according to some embodiments includes a coating located on the surface of the core particles and including a lithium iron phosphate-based compound and aluminum. When a coating is formed on the core particles, the cycle life characteristics and / or capacity characteristics at high voltages can be further improved. Since the core particles have been described above, no repeated definition thereof will be provided, and the coating will be described.

[0056] The lithium iron phosphate-based compound can include, for example, lithium iron phosphate, lithium manganese iron phosphate, or a combination thereof, and the lithium iron phosphate-based compound can be represented by Chemical Formula 2 or Chemical Formula 3.

[0057] Chemical Formula 2

[0058] Li a2 Fe (1-x2) M 2 x2 PO4.

[0059] In Chemical Formula 2, 0.90 ≤ a2 ≤ 1.5, 0 ≤ x2 ≤ 0.4, and M 2 can be Al, Ca, Ce, Cr, Cu, La, Mg, Mn, Mo, Nb, Ni, Sn, Sr, Ti, V, W, Y, Zn, Zr, or a combination thereof.

[0060] The compound represented by Chemical Formula 2 may be lithium iron phosphate. In Chemical Formula 2, for example, 0.90 ≤ a2 ≤ 1.2 or 0.95 ≤ a2 ≤ 1.1, and 0 ≤ x2 ≤ 0.3, 0 ≤ x2 ≤ 0.2, 0 ≤ x2 ≤ 0.1 or 0 < x2 ≤ 0.05. For example, if a2 = 1 and x2 = 0 (for example, when a2 = 1 and x2 = 0), Chemical Formula 2 may be represented by LiFePO4.

[0061] Chemical Formula 3

[0062] Li a3 Mn x3 Fe (1-x3-y3) M 3 y3 PO4.

[0063] In Chemical Formula 3, 0.90 ≤ a3 ≤ 1.5, 0.1 ≤ x3 ≤ 0.9, 0 < x3 + y3 < 1, and M 3 may be Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, Ti, V, W, Y, Zn, Zr, or a combination thereof.

[0064] The compound represented by Chemical Formula 3 may be lithium manganese iron phosphate. In Chemical Formula 3, for example, 0.90 ≤ a3 ≤ 1.2 or 0.95 ≤ a3 ≤ 1.1; 0.2 ≤ x3 ≤ 0.8, 0.3 ≤ x3 ≤ 0.7 or 0.4 ≤ x3 ≤ 0.6. The compound represented by Chemical Formula 3 may be, for example, LiMn 0.9 Fe 0.1 PO4, LiMn 0.8 Fe 0.2 PO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.5 Fe 0.5 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.3 Fe 0.7 PO4, LiMn 0.2 Fe 0.8 PO4 or LiMn 0.1 Fe 0.9 PO4.

[0065] For example, lithium iron phosphate compounds may include LiFePO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.5Fe 0.5 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.2 Fe 0.8 PO4, LiMn 0.1 Fe 0.9 PO4, LiMn 0.3 Fe 0.7 PO4 or a combination thereof.

[0066] Based on the total weight of 100 wt% of the positive electrode active material, the content (e.g., amount) of the lithium iron phosphate-based compound in the coating can be about 0.1 wt% to about 5 wt%, e.g., about 0.5 wt% to about 4 wt% or about 1 wt% to about 3 wt%. The content (e.g., amount) of the lithium iron phosphate-based compound in the coating can be measured by, for example, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) of the surface or cross-section of the positive electrode active material. If the content (e.g., amount) of the lithium iron phosphate-based compound in the coating satisfies any of the above ranges, the cycle life characteristics and / or stability at high voltage can be further improved.

[0067] The coating included in the positive electrode active material according to some embodiments includes a lithium iron phosphate-based compound and aluminum. The core particles including the lithium cobalt composite oxide may have a low specific surface area (e.g., an inappropriately low specific surface area), making it difficult to uniformly (e.g., substantially uniformly) coat the surface of the core particles with only the lithium iron phosphate-based compound. However, according to some embodiments, by coating the core particles with a lithium iron phosphate-based compound and aluminum and applying the coating methods and conditions described below herein, the surface of the core particles can be uniformly (e.g., substantially uniformly) coated with the lithium iron phosphate-based compound. Due to the appropriate high phase stability, the lithium iron phosphate-based compound can improve the structural stability of the lithium cobalt composite oxide under high voltage and high temperature conditions and improve the battery cycle life characteristics. In one or more embodiments, by coating the surface of the core particles with the lithium iron phosphate-based compound in a substantially uniform form, the resistance can be reduced, the initial charge capacity / discharge capacity and efficiency can be improved, and the high temperature cycle life characteristics can be improved. In one or more embodiments, the aluminum in the coating not only improves the cycle life characteristics by improving the structural stability of the core particles, but also acts as a fluoride scavenger (F scavenger) to remove (or substantially reduce) fluoride in the electrolyte, thus suppressing or reducing the erosion of hydrofluoric acid (HF) on the positive electrode surface. Accordingly, the side reaction between the positive electrode and the electrolyte can be suppressed or reduced, the interface can be stabilized or improved, and the deterioration of the positive electrode active material can be effectively suppressed or reduced.

[0068] Based on the total metal of 100 wt% other than lithium in the positive electrode active material, the aluminum content (e.g., amount) in the coating can be from about 0.01 wt% to about 2 wt%, for example, from about 0.01 wt% to about 1.5 wt%, from about 0.05 wt% to about 1 wt%, or from about 0.04 wt% to about 0.05 wt%. This only refers to the aluminum content (e.g., amount) contained in the coating and does not include the aluminum contained inside the core particles. The aluminum content (e.g., amount) in the coating can be measured by, for example, SEM-EDS analysis of the surface or cross-section of the positive electrode active material. If the aluminum content (e.g., amount) in the coating meets any of the above ranges, a substantially uniform and appropriate thin coating may be formed, the resistance of the positive electrode active material may not be increased (or may not be inappropriately increased), the side reaction with the electrolyte can be effectively or appropriately suppressed or reduced, and the lithium iron phosphate compound can be effectively or appropriately coated, thereby improving the cycle life characteristics of the rechargeable lithium battery under high voltage and high temperature conditions.

[0069] The coating according to some embodiments can be in the form of islands and / or films. For example, the coating can be in the form of a film continuously surrounding the surface of the core particles, or, for example, the coating can be in the form of a shell surrounding the entire surface of the core particles. According to some embodiments, the coating can be formed to be very (e.g., substantially or appropriately) thin and have a substantially uniform thickness, so that the positive electrode active material may not increase (e.g., inappropriately increase) the resistance or reduce (e.g., inappropriately reduce) the capacity, the structural stability can be improved, the side reaction with the electrolyte can be effectively or appropriately suppressed or reduced, the amount of gas generated under high voltage and high temperature conditions can be reduced, and long cycle life characteristics can be achieved.

[0070] The coating according to some embodiments can have a thickness of from about 30 nm to about 500 nm, for example, from about 30 nm to about 450 nm, from about 30 nm to about 400 nm, from about 30 nm to about 350 nm, from about 30 nm to about 300 nm, from about 30 nm to about 250 nm, from about 30 nm to about 200 nm, from about 30 nm to about 150 nm, from about 50 nm to about 500 nm, from about 80 nm to about 500 nm, or from about 100 nm to about 500 nm. If the coating meets any of the above thickness ranges, the structural stability of the positive electrode active material can be improved without (or substantially without) increasing the resistance or reducing the capacity due to the coating, and the side reaction with the electrolyte can be effectively or appropriately suppressed or reduced. The thickness of the coating can be measured by, for example, time-of-flight secondary ion mass spectrometry (TOF-SIMS), X-ray photoelectron spectroscopy (XPS), and / or energy-dispersive X-ray spectroscopy (EDS) analysis, and in some embodiments, the thickness range of the coating can be measured by transmission electron microscopy energy-dispersive X-ray spectroscopy (TEM-EDS) line profiles.

[0071] Method for preparing positive electrode active material

[0072] In some embodiments, the method for preparing positive electrode active material includes: (i) dry-mixing a lithium cobalt composite oxide, a lithium iron phosphate compound, and an aluminum raw material to prepare a mixture; and (ii) firing the mixture in a nitrogen atmosphere or an inert gas atmosphere.

[0073] Since the lithium cobalt composite oxide and the lithium iron phosphate compound have been described above, a repetitive description thereof will not be provided, and the aluminum raw material will be described.

[0074] The aluminum raw material may include, for example, aluminum nitrate, aluminum sulfate, aluminum carbonate, aluminum hydroxide, aluminum oxide, or a combination thereof, and may include, for example, aluminum hydroxide, and may be, for example, Al(OH)3.

[0075] In step (i) (e.g., action or task) of dry-mixing the lithium cobalt composite oxide, the lithium iron phosphate compound, and the aluminum raw material, based on the total weight of 100 wt% of the lithium cobalt composite oxide, the lithium iron phosphate compound, and the aluminum raw material (e.g., the total weight of the mixture), the amount of the lithium cobalt composite oxide included may be about 90 wt% to about 99.8 wt%, the amount of the lithium iron phosphate compound included may be about 0.1 wt% to about 9.9 wt%, and the amount of the aluminum raw material included may be about 0.01 wt% to about 2 wt%. For example, based on the total weight of 100 wt% of the mixture, the amount of the lithium cobalt composite oxide included may be about 94 wt% to about 99.4 wt% or about 96 wt% to about 98 wt%, the amount of the lithium iron phosphate compound included may be about 0.5 wt% to about 5 wt% or about 1 wt% to about 3 wt%, and the amount of the aluminum raw material included may be about 0.01 wt% to about 1 wt% or about 0.05 wt% to about 0.1 wt%. If these content (e.g., amount) ranges are satisfied, a positive electrode active material in which a coating containing a lithium iron phosphate compound and aluminum is coated on core particles including a lithium cobalt composite oxide with a substantially uniform thickness can be obtained, thereby improving the initial charge capacity / discharge capacity, efficiency, and high-temperature cycle life characteristics of a rechargeable lithium battery, and also improving the thermal safety of the rechargeable lithium battery.

[0076] In step (e.g., action or task) (i), dry mixing can be performed at a rotational speed of about 2,000 rpm or higher, e.g., about 2,000 rpm to about 3,000 rpm or about 2,000 rpm to about 2,500 rpm. The dry mixing can be carried out for about 1 minute to about 60 minutes, e.g., about 1 minute to about 30 minutes or about 1 minute to about 10 minutes. If the dry mixing meets the above conditions, if the mixing is completed (e.g., when the mixing is completed), the mixture can be maintained at a temperature of about 45 °C or higher for about 3 minutes or longer. Correspondingly, the lithium iron phosphate compound and aluminum can be uniformly (e.g., substantially uniformly) coated on the surface of the core particles including the lithium cobalt composite oxide.

[0077] When dry mixing is completed at a rotational speed of about 2,000 rpm or higher for a set or predetermined time, the mixture can meet a temperature of about 45 °C or higher, e.g., about 45 °C to about 80 °C, about 45 °C to about 50 °C or about 40 °C to about 45 °C, and these temperatures (e.g., this temperature) can be maintained for about 3 minutes or longer, e.g., about 3 minutes to about 10 minutes or about 3 minutes to about 5 minutes. It is considered that due to these conditions, the lithium iron phosphate compound can be uniformly (e.g., substantially uniformly) coated on the surface of the core particles containing the lithium cobalt composite oxide with a relatively small specific surface area. The method for preparing the positive electrode active material according to some embodiments may further include maintaining the mixture prepared in step (e.g., action or task) (i) at a temperature of about 45 °C or higher for about 3 minutes or longer.

[0078] In step (e.g., action or task) (ii), the mixture is fired. Compared with the case where the mixture itself is not fired and used as the positive electrode active material, the positive electrode active material prepared by firing the mixture under set or predetermined conditions exhibits an appropriate high initial charge capacity / discharge capacity, appropriate high efficiency, and further improved high-temperature cycle life characteristics. The firing can be carried out in a nitrogen atmosphere or an inert gas atmosphere. If the firing is carried out, for example, in an oxygen atmosphere or in air instead of in a nitrogen atmosphere or an inert gas atmosphere, compared with the firing in a nitrogen atmosphere or an inert gas atmosphere, since the components and / or properties on the surface of the positive electrode active material are changed, the initial charge capacity / discharge capacity, efficiency, and high-temperature cycle life characteristics are significantly deteriorated.

[0079] The firing can be carried out in a temperature range of about 300 °C to about 500 °C, e.g., about 350 °C to about 450 °C, about 370 °C to about 430 °C or about 390 °C to about 410 °C. If the firing is carried out within any of the above temperature ranges, the lithium iron phosphate compound and aluminum can be appropriately firmly coated on the surface of the core particles including the lithium cobalt composite oxide to ensure appropriate high capacity and long cycle life characteristics, and improve the stability at high voltages.

[0080] Positive electrode

[0081] In some embodiments, the positive electrode includes a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material according to the present embodiment. In addition to the aforementioned positive electrode active material, the positive electrode active material layer may further include other types (or kinds) of positive electrode active materials. In some embodiments, the positive electrode active material layer may optionally further include a binder, a conductive material, or a combination thereof.

[0082] According to some embodiments, the loading level of the positive electrode active material layer may be about 10 mg / cm 2 ~ about 40 mg / cm 2 , for example, about 10 mg / cm 2 ~ about 30 mg / cm 2 or about 10 mg / cm 2 ~ about 20 mg / cm 2 . Additionally, the density of the positive electrode active material layer in the finally compressed positive electrode (also referred to as the positive electrode density) may be about 3.3 g / cc to about 3.7 g / cc, for example, about 3.3 g / cc to about 3.6 g / cc or about 3.4 g / cc to about 3.58 g / cc. When applying a positive electrode active material according to some embodiments, it is beneficial to implement such loading levels and positive electrode densities, and positive electrodes that meet the loading levels and positive electrode densities within the above ranges are suitable for implementing high-capacity, high-energy density rechargeable lithium batteries.

[0083] Binder

[0084] The binder improves the binding characteristics of the positive electrode active material particles to each other and the binding characteristics of the positive electrode active material particles to the positive electrode current collector. Examples of the binder may include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate esterified styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon, but are not limited thereto.

[0085] Conductive material

[0086] It includes a conductive material to provide (or improve) the conductivity of the electrode, and any suitable conductive material can be used as the conductive material, unless it causes an undesired chemical change in the battery. Examples of the conductive material can include carbonaceous materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube), etc.; metallic materials including metal powders or metal fibers such as copper, nickel, aluminum, silver, etc.; conductive polymers (such as poly(phenylene) derivatives); or mixtures thereof.

[0087] Based on 100 wt% of the positive electrode active material layer, the contents (e.g., amounts) of the binder and the conductive material can each independently be about 0.5 wt% to about 5 wt%.

[0088] The positive electrode current collector can include Al foil, but the present disclosure is not limited thereto.

[0089] Rechargeable lithium battery

[0090] Some embodiments provide a rechargeable lithium battery, including the positive electrode, negative electrode, and electrolyte of the present embodiment. As an example, the rechargeable lithium battery can include a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and an electrolyte.

[0091] Depending on the shape, the rechargeable lithium battery can be classified as cylindrical, prismatic, pouch-shaped, coin-shaped, etc. Figures 1 to 4 Respectively are schematic diagrams showing a rechargeable lithium battery according to some embodiments, wherein Figure 1 is a cylindrical battery, Figure 2 is a prismatic battery, and Figure 3 and Figure 4 are pouch-shaped batteries. Referring to Figures 1 to 4 , the rechargeable lithium battery 100 includes an electrode assembly 40 and a housing 50 that houses the electrode assembly 40. The electrode assembly 40 has a separator 30 inserted between the positive electrode 10 and the negative electrode 20. The positive electrode 10, negative electrode 20, and separator 30 can be impregnated with an electrolyte. As Figure 1 shown, the rechargeable lithium battery 100 can include a sealing member 60 that seals the housing 50. Additionally, as Figure 2 shown, the rechargeable lithium battery 100 can include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As Figure 3 and Figure 4 shown, the rechargeable lithium battery 100 can further include an electrode tab 70 that serves as a circuit path for guiding the current formed in the electrode assembly 40 to the outside, including a positive electrode tab 71 and a negative electrode tab 72.

[0092] The rechargeable lithium battery according to some embodiments can be rechargeable at high voltages or can be suitable for driving at high voltages. For example, the upper limit voltage for charging the rechargeable lithium battery can be greater than or equal to about 4.45 V, about 4.45 V to about 4.7 V, about 4.45 V to about 4.6 V, or about 4.45 V to about 4.55 V, etc. By applying the positive electrode active material according to some embodiments, even when charging at high voltages (e.g., when charging at high voltages), the rechargeable lithium battery can significantly reduce the amount of gas generated and can achieve appropriate high-capacity and long cycle life characteristics.

[0093] Negative electrode

[0094] The negative electrode may include a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector, and the negative electrode active material layer may include a negative electrode active material and may further include a binder, a conductive material, or a combination thereof.

[0095] Negative electrode active material

[0096] The negative electrode active material may include a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / dedoping lithium, and / or a transition metal oxide.

[0097] The material that reversibly intercalates / deintercalates lithium ions may include, for example, crystalline carbon, amorphous carbon, or a combination thereof as a carbon-based negative electrode active material. The crystalline carbon may be amorphous, flaky, sheet-like, spherical, and / or fibrous (e.g., in fiber form) natural graphite and / or artificial graphite. The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbonization product, calcined coke, etc.

[0098] The lithium metal alloy includes 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.

[0099] 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), an Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements (excluding Si), Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, e.g., 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 / or combinations thereof) or a combination thereof. The Sn-based negative electrode active material can be Sn, SnO x (0 < x ≤ 2) (e.g., SnO2), an Sn alloy, or a combination thereof.

[0100] The silicon-carbon composite can be a composite of silicon and amorphous carbon. The average particle size (D 50 ) can be, for example, from about 0.5 μm to about 20 μm. According to some embodiments, the silicon-carbon composite can be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, the silicon-carbon composite can include secondary particles (cores) in which silicon primary particles are aggregated and an amorphous carbon coating (shell) on the surface of the secondary particles. Amorphous carbon can also be present between the silicon primary particles, e.g., the silicon primary particles can be coated with amorphous carbon. The secondary particles can be dispersed in the amorphous carbon matrix.

[0101] The silicon-carbon composite can further include crystalline carbon. For example, the silicon-carbon composite can include: a core including crystalline carbon and silicon particles and an amorphous carbon coating on the surface of the core. The crystalline carbon can be artificial graphite, natural graphite, or a combination thereof. The amorphous carbon can include soft carbon, hard carbon, mesophase pitch carbonization products, and / or calcined coke.

[0102] When the silicon-carbon composite includes silicon and amorphous carbon, based on 100 wt% of the silicon-carbon composite, the content (e.g., amount) of silicon can be from about 10 wt% to about 50 wt%, and the content (e.g., amount) of amorphous carbon can be from about 50 wt% to about 90 wt%. In one or more embodiments, if the composite includes silicon, amorphous carbon, and crystalline carbon (e.g., when the composite includes silicon, amorphous carbon, and crystalline carbon), based on 100 wt% of the silicon-carbon composite, the content (e.g., amount) of silicon can be from about 10 wt% to about 50 wt%, the content (e.g., amount) of crystalline carbon can be from about 10 wt% to about 70 wt%, and the content (e.g., amount) of amorphous carbon can be from about 20 wt% to about 40 wt%.

[0103] The thickness of the amorphous carbon coating can be from about 5 nm to about 100 nm. The average particle size (D 50) can be from about 10 nm to about 1 μm or from about 10 nm to about 200 nm. The silicon particles can exist as silicon alone, in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon can be represented by SiO x (0 < x ≤ 2). At this time, the atomic content ratio of Si:O indicating the degree of oxidation can be from about 99:1 to about 33:67. As used herein, if no other limitation is provided (e.g., when no other limitation is provided otherwise), the average particle size (D 50 ) indicates the diameter of the particles in which the cumulative volume in the particle distribution is about 50% by volume.

[0104] The Si-based negative electrode active material and / or the Sn-based negative electrode active material can be mixed with the carbon-based negative electrode active material. When the Si-based negative electrode active material and / or the Sn-based negative electrode active material are mixed with the carbon-based negative electrode active material and used as a mixture, the mixing ratio can be a weight ratio of from about 1:99 to about 90:10 (e.g., in wt%).

[0105] Binder

[0106] The binder is used to appropriately bond the negative electrode active material particles to each other and is also used to bond the negative electrode active material particles to the negative electrode current collector. The binder can include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0107] The non-aqueous binder can include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0108] The aqueous binder can include styrene-butadiene rubber, (meth)acrylate esterified styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, epichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, or a combination thereof.

[0109] If the aqueous binder is used as the binder in the negative electrode active material layer (e.g., when the aqueous binder is used as the negative electrode binder), a cellulose-based compound capable of imparting viscosity can be further included. As the cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and their alkali metal salts can be mixed and used. The alkali metal can be Na, K, and / or Li.

[0110] The dry binder can be a polymer material capable of being fibrillated and can be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride - hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0111] Conductive material

[0112] A conductive material is included to provide (or improve) the conductivity of the electrode, and any suitable conductive material can be used as the conductive material, unless it causes an undesirable chemical change in the battery. Examples of conductive materials include carbon - based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube), etc.; metal - based materials including metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers (such as polyphenylene derivatives); or mixtures thereof.

[0113] Based on 100 wt% of the negative electrode active material layer, the content (e.g., amount) of the negative electrode active material can be about 95 wt% to about 99.5 wt%, and based on 100 wt% of the negative electrode active material layer, the content (e.g., amount) of the binder can be about 0.5 wt% to about 5 wt%. In another embodiment, the negative electrode active material layer can include about 90 wt% to about 99 wt% of the negative electrode active material, about 0.5 wt% to about 5 wt% of the binder, and about 0.5 wt% to about 5 wt% of the conductive material.

[0114] Negative electrode current collector

[0115] The negative electrode current collector can include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof, and can be in the form of a foil, sheet, and / or foam. The thickness of the negative electrode current collector can be, for example, about 1 μm to about 20 μm, about 5 μm to about 15 μm, or about 7 μm to about 10 μm.

[0116] Electrolyte

[0117] For example, the electrolyte for a rechargeable lithium battery can be an electrolyte that can include a non - aqueous organic solvent and a lithium salt.

[0118] The non - aqueous organic solvent serves as a medium for transporting ions participating in the electrochemical reaction of the battery. The non - aqueous organic solvent can include carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, or a combination thereof.

[0119] Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. In one or more embodiments, ketone solvents may include cyclohexanone, etc. Alcohol solvents may include ethanol, isopropanol, etc., and aprotic solvents may include nitriles (such as, R-CN, where R is a C2 to C20 straight-chain hydrocarbon group, branched-chain hydrocarbon group or cycloalkyl group, and may further include double bonds, aromatic rings or ether bonds, etc.); amides (such as, dimethylformamide); dioxolanes (such as, 1,3-dioxolane, 1,4-dioxolane, etc.); sulfolane; etc.

[0120] The non-aqueous organic solvents may be used alone or in a mixture of two or more types (or species), and if two or more types (or species) of non-aqueous organic solvents are used in a mixture (for example, when two or more types (or species) of non-aqueous organic solvents are used in a mixture), the mixing ratio may be appropriately or suitably adjusted according to the desired or appropriate battery performance, which should be understood by those skilled in the art.

[0121] When using carbonate solvents, cyclic carbonates and chain carbonates may be mixed and used, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of about 1:1 to about 1:9.

[0122] The non-aqueous organic solvents may further include aromatic hydrocarbon organic solvents. For example, carbonate solvents and aromatic hydrocarbon organic solvents may be mixed and used in a volume ratio of about 1:1 to about 30:1.

[0123] The electrolyte may further include vinylene ethylene carbonate, vinylene carbonate and / or ethylene carbonate compounds to improve the battery cycle life.

[0124] Examples of ethylene carbonate compounds may include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate and cyanoethylene carbonate.

[0125] Lithium salts dissolved in non-aqueous organic solvents supply lithium ions in a battery, ensuring (or contributing to facilitating) the basic operation of rechargeable lithium batteries and improving the transport of lithium ions between the positive electrode and the negative electrode. Examples of lithium salts may include at least one selected from LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide, LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+ 1SO2) (where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluoro bis(oxalate) phosphate (LiDBOP), and lithium bis(oxalate) borate (LiBOB).

[0126] The concentration of the lithium salt may be in the range of about 0.1 M to about 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate or suitable ionic conductivity and viscosity, so excellent or appropriate performance can be achieved, and lithium ions can move effectively or appropriately.

[0127] Separator

[0128] Depending on the type or kind of rechargeable lithium battery, a separator may be present between the positive electrode and the negative electrode. The separator may include a polyethylene separator, a polypropylene separator, a polyvinylidene fluoride separator, a multilayer film of two or more of its layers (such as, a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, etc.).

[0129] The separator may include a porous substrate and a coating including an organic material, an inorganic material, or a combination thereof on the surface of the porous substrate (e.g., one or two surfaces (e.g., both surfaces simultaneously) (e.g., opposite surfaces)).

[0130] The porous substrate may be a polymer film formed of a polymer (e.g., any one) selected from polyolefins (such as polyethylene and / or polypropylene), polyesters (such as polyethylene terephthalate and / or polybutylene terephthalate), polyacetals, polyamides, polyimides, polycarbonates, polyether ketones, polyaryl ether ketones, polyetherimides, polyamideimides, polybenzimidazoles, polyethersulfones, polyphenylene ethers, cycloolefin copolymers, polyphenylene sulfides, polyethylene naphthalate, glass fibers, and polytetrafluoroethylene (Teflon TM ).), a copolymer and / or mixture of two or more of them.

[0131] The porous substrate may have a thickness of about 1 μm to about 40 μm, for example, about 1 μm to about 30 μm, about 1 μm to about 20 μm, about 5 μm to about 15 μm, or about 10 μm to about 15 μm.

[0132] The organic material may include a (meth)acrylic copolymer, the (meth)acrylic copolymer including a first structural unit and a second structural unit, the first structural unit being derived from (meth)acrylamide, and the second structural unit including at least one selected from the group consisting of a structural unit derived from (meth)acrylic acid or (meth)acrylate and a structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof.

[0133] The inorganic material may include inorganic particles selected from the group consisting of Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof, but the present disclosure is not limited thereto. The average particle diameter (D 50 ) may be about 1 nm to about 2000 nm, for example, about 100 nm to about 1000 nm or about 100 nm to about 700 nm.

[0134] The organic material and the inorganic material may be mixed in one coating, or coatings including the organic material and coatings including the inorganic material may be stacked.

[0135] The thickness of the coating may be about 0.5 μm to about 20 μm, for example, about 1 μm to about 10 μm or about 1 μm to about 5 μm.

[0136] Embodiments and comparative examples of the present disclosure are described in more detail below. However, the following embodiments are merely examples of the present disclosure, and the present disclosure is not limited to the following embodiments.

[0137] Example 1

[0138] 1. Preparation of the positive electrode active material

[0139] Co 0.985 Al 0.015 O2 and Li2CO3 were mixed such that the molar ratio of (Co + Al):Li was 1:1.03, and then heat-treated at 1050 °C in an air atmosphere for 8 hours to prepare a composition of Li 1.03 Co 0.985 Al 0.015 O2 and an average particle diameter (D 50) is a lithium cobalt composite oxide of about 17 μm. Based on the total weight of 100 wt% of the mixture of lithium cobalt composite oxide, LiFePO4 and Al(OH)3, 98.95 wt% of lithium cobalt composite oxide, 1.0 wt% of LiFePO4 and 0.05 wt% of Al(OH)3 are added to the reactor and dry mixed by stirring at about 2,400 rpm for about 5 minutes to prepare a mixture. When the mixing is completed, the mixture sample is maintained at a temperature of 45 °C or higher for about 3 minutes. The prepared mixture is fired in a nitrogen atmosphere at 400 °C to prepare the final positive electrode active material.

[0140] 2. Manufacture of rechargeable lithium battery cells

[0141] 98.5 wt% of the positive electrode active material, 1.0 wt% of polyvinylidene fluoride binder and 0.5 wt% of carbon nanotube conductive material are mixed to prepare a positive electrode active material layer slurry, and the positive electrode active material layer slurry is coated on an aluminum foil current collector, and then dried and compressed to manufacture a positive electrode.

[0142] 97.5 wt% of graphite negative electrode active material, 1.5 wt% of carboxymethyl cellulose and 1 wt% of styrene-butadiene rubber are mixed in an aqueous solvent to prepare a negative electrode active material layer slurry. The negative electrode active material layer slurry is coated on a copper foil current collector, dried and compressed to manufacture a negative electrode.

[0143] Subsequently, a rechargeable lithium battery cell is manufactured by a method well known to those of ordinary skill in the art using a positive electrode, a negative electrode and a polytetrafluoroethylene separator, and an electrolyte prepared by dissolving 1 M LiPF6 in a mixed solvent of ethylene carbonate and dimethyl carbonate in a volume ratio of 3:7.

[0144] Example 2

[0145] The positive electrode active material and the rechargeable lithium battery cell are manufactured in substantially the same manner as in Example 1, except that the positive electrode active material is prepared using 97.95 wt% of lithium cobalt composite oxide, 2.0 wt% of LiFePO4 and 0.05 wt% of Al(OH)3.

[0146] Example 3

[0147] The positive electrode active material and the rechargeable lithium battery cell are manufactured in substantially the same manner as in Example 1, except that the positive electrode active material is prepared using 96.95 wt% of lithium cobalt composite oxide, 3.0 wt% of LiFePO4 and 0.05 wt% of Al(OH)3.

[0148] Comparative Example 1

[0149] The positive electrode active material and the rechargeable lithium battery cell were manufactured in substantially the same manner as in Example 1, except that the lithium cobalt composite oxide was used alone as the final positive electrode active material.

[0150] Comparative Example 2

[0151] The positive electrode active material and the rechargeable lithium battery cell were manufactured in substantially the same manner as in Example 1, except that the positive electrode active material was prepared by dry-mixing 99.0 wt% of the lithium cobalt composite oxide and 1.0 wt% of LiFePO4, i.e., Al(OH)3 was not added, and the mixture was prepared by stirring at 1,200 rpm for about 5 minutes but not fired.

[0152] Comparative Example 3

[0153] The positive electrode active material and the rechargeable lithium battery cell were manufactured in substantially the same manner as in Comparative Example 2, except that the stirring was carried out at 2,400 rpm for about 5 minutes.

[0154] Comparative Example 4

[0155] The positive electrode active material and the rechargeable lithium battery cell were manufactured in substantially the same manner as in Example 1, except that the positive electrode active material was prepared by dry-mixing 99.95 wt% of the lithium cobalt composite oxide and 0.05 wt% of Al(OH)3, i.e., LiFePO4 was not added, the mixture was prepared, and then the mixture was not fired.

[0156] Comparative Example 5

[0157] The positive electrode active material and the rechargeable lithium battery cell were manufactured in substantially the same manner as in Example 1, except that the positive electrode active material was prepared without firing the mixture.

[0158] Comparative Example 6

[0159] The positive electrode active material and the rechargeable lithium battery cell were manufactured in substantially the same manner as in Example 1, except that the firing was carried out in an air atmosphere instead of a nitrogen atmosphere.

[0160] The manufacturing methods of Examples 1 to 3 and Comparative Examples 1 to 6 are summarized in Table 1.

[0161] Table 1

[0162]

[0163] Evaluation Example 1: Surface analysis of the positive electrode active material

[0164] The positive electrode active materials according to Example 1 and Comparative Example 1 were compared by taking images with a scanning electron microscope. Figure 5 andFigure 6 To show the SEM image of the particle surface of the positive electrode active material according to Comparative Example 1, and Figure 7 and Figure 8 To show the SEM image of the particle surface of the positive electrode active material including LiFePO4 and aluminum according to Example 1. Referring to Figures 5 to 8 , compared with Comparative Example 1, in the positive electrode active material of Example 1, LiFePO4 and aluminum are uniformly (e.g., substantially uniformly) coated on the surface of the positive electrode active material particles.

[0165] Evaluation Example 2: Evaluation of Initial Charge Capacity / Discharge Capacity and Efficiency

[0166] The rechargeable lithium battery cells of Examples 1 to 3 and Comparative Examples 1 to 6 were charged at a constant current of 0.2C to an upper limit voltage of 4.55V at 25°C, and then charged at a constant voltage to 0.05C and discharged at 0.2C to a cut-off voltage of 3.0V for initial charge and discharge. In Table 2, the initial charge capacity, the initial discharge capacity, and the ratio of the initial discharge capacity to the initial charge capacity as efficiency are provided.

[0167] Evaluation Example 3: High Temperature Cycle Life Characteristics

[0168] After the initial charge and discharge in Evaluation Example 2, in the voltage range of 3.0V to 4.55V at 45°C, the rechargeable lithium battery cells were repeatedly charged and discharged at 1.0C for 50 times or more to calculate the ratio of the discharge capacity of the 50th cycle to the initial discharge capacity, and the results are shown as the high temperature cycle life in Table 2.

[0169] Table 2

[0170]

[0171] Referring to Table 2, according to the present embodiment, by adding LiFePO4 and aluminum hydroxide, and then stirring and firing under specific conditions, Examples 1 to 3 including LiFePO4 and aluminum on the surface of the positive electrode active material exhibit excellent or appropriate efficiency and high temperature cycle life characteristics.

[0172] In contrast, Comparative Examples 1 to 4 without added LiFePO4 and / or aluminum hydroxide exhibit deteriorated high-temperature cycle life characteristics compared to the Examples. In particular, Comparative Examples 1 to 3 without added aluminum hydroxide exhibit further deteriorated high-temperature cycle life characteristics compared to other Comparative Examples. In one or more embodiments, compared to the Examples, Comparative Example 5 (wherein LiFePO4 and aluminum hydroxide are coated together without firing) and Comparative Example 6 (wherein LiFePO4 and aluminum hydroxide are coated together by firing in an air atmosphere) exhibit deteriorated high-temperature cycle life characteristics. Accordingly, the positive electrode active material of the Examples prepared by dry-mixing core particles containing a lithium-cobalt composite oxide with a lithium iron phosphate compound and aluminum under set or predetermined conditions and heat-treating the mixture under set or predetermined conditions exhibits improved initial charge capacity / discharge capacity and efficiency, and also exhibits improved high-temperature cycle life characteristics.

[0173] Evaluation Example 4: DSC

[0174] The thermal stability of the positive electrode active materials of Example 1 and Comparative Example 1 was evaluated by measuring the heat flow according to temperature by differential scanning calorimetry (DSC), and the results are shown in Figure 9 . The measurement was carried out using a differential scanning calorimeter (SENSYS evo, SETARAM), and specifically, 15 mg of each positive electrode was charged to 4.55 V (versus Li / Li + ), and it was added to 20 μL of the electrolyte solution, and then the temperature was raised to 400 °C at a rate of 10 °C per minute.

[0175] Reference Figure 9 , compared to the positive electrode active material of Comparative Example 1, Example 1 including LiFePO4 and aluminum on the surface of the positive electrode active material exhibits a delayed peak appearance and a peak appearing at a higher temperature, which confirms that the DSC measurement shows reduced exothermicity and, accordingly, improved thermal stability.

[0176] Although the present disclosure has been described in connection with what are presently considered to be example embodiments, it is to be understood that the disclosure is not limited to the disclosed embodiments. It will be understood that the description of each feature or aspect in each embodiment is generally to be considered available for other similar features or aspects in other embodiments, unless otherwise described. Thus, as will be apparent to those of ordinary skill in the art, unless otherwise specifically indicated, the features, characteristics, and / or elements described in connection with a particular embodiment may be used alone or in combination with features, characteristics, and / or elements described in connection with other embodiments. Accordingly, it is to be understood that the foregoing disclosure is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the claims and their equivalents.

Claims

1. A positive electrode active material, comprising: A core particle, comprising a lithium cobalt composite oxide; And A coating, disposed on the surface of the core particle and comprising a lithium iron phosphate compound and aluminum.

2. The positive electrode active material according to claim 1, wherein The lithium cobalt composite oxide is represented by Chemical Formula 1: Chemical Formula 1 Li a1 Co x1 Al y1 Mg z1 M 1 w1 O 2-b1 X b1 and In Chemical Formula 1, 0.9 ≤ a1 ≤ 1.8, 0.8 ≤ x1 ≤ 0.99, 0 ≤ y1 ≤ 0.1, 0 ≤ z1 ≤ 0.1, 0 ≤ w1 ≤ 0.1, 0.9 ≤ x1 + y1 + z1 ≤ 1.1 and 0 ≤ b1 ≤ 0.1, M 1 is one or more selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more selected from F, P, and S.

3. The positive electrode active material according to claim 1, wherein The average particle size D of the nuclear particles 50 is 1 μm to 30 μm.

4. The positive electrode active material according to claim 1, wherein The lithium iron phosphate compound is represented by Chemical Formula 2 or Chemical Formula 3: Chemical Formula 2 Li a2 Fe (1-x2) M 2 x2 PO4, In Chemical Formula 2, 0.90 ≤ a2 ≤ 1.5, 0 ≤ x2 ≤ 0.4, and M 2 is Al, Ca, Ce, Cr, Cu, La, Mg, Mn, Mo, Nb, Ni, Sn, Sr, Ti, V, W, Y, Zn, Zr, or a combination thereof, Chemical Formula 3 Li a3 Mn x3 Fe (1-x3-y3) M 3 y3 PO4, In Chemical Formula 3, 0.90 ≤ a3 ≤ 1.5, 0.1 ≤ x3 ≤ 0.9, 0 < x3 + y3 < 1, and M 3 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, Ti, V, W, Y, Zn, Zr, or a combination thereof.

5. The positive electrode active material according to claim 1, wherein The lithium iron phosphate compounds include LiFePO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.5 Fe 0.5 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.3 Fe 0.7 PO4, LiMn 0.2 Fe 0.8 PO4, LiMn 0.1 Fe 0.9 PO4, or a combination thereof.

6. The positive electrode active material according to claim 1, wherein Based on the total weight of 100 wt% of the positive electrode active material, the content of the lithium iron phosphate compound in the coating is 0.1 wt% to 5 wt%.

7. The positive electrode active material according to claim 1, wherein Based on the total metal of 100 wt% other than lithium in the positive electrode active material, the content of the aluminum in the coating is 0.01 wt% to 2 wt%.

8. The positive electrode active material according to claim 1, wherein The thickness of the coating is 30 nm to 500 nm.

9. A method for preparing a positive electrode active material, the method comprising: (i) Dry-mixing a lithium cobalt composite oxide, a lithium iron phosphate compound, and an aluminum raw material to prepare a mixture; And (ii) Firing the mixture in a nitrogen atmosphere or an inert gas atmosphere.

10. The method according to claim 9, wherein In (i), the dry-mixing is performed at a rotation speed of 2,000 rpm or higher.

11. The method according to claim 9, wherein The aluminum raw material comprises aluminum nitrate, aluminum sulfate, aluminum carbonate, aluminum hydroxide, aluminum oxide, or a combination thereof.

12. The method according to claim 9, wherein Based on the total weight of 100 wt% of the mixture of the lithium cobalt composite oxide, the lithium iron phosphate compound, and the aluminum raw material, 90 wt% to 99.8 wt% is the lithium cobalt composite oxide, 0.1 wt% to 9.9 wt% is the lithium iron phosphate compound, and 0.01 wt% to 2 wt% is the aluminum raw material.

13. The method according to claim 9, wherein The method further comprises holding the mixture prepared in (i) at a temperature of 45 °C or higher for 3 minutes or longer.

14. The method according to claim 9, wherein When firing the mixture in (ii), the firing temperature is 300 °C to 500 °C.

15. A positive electrode, comprising: A positive electrode current collector, and A positive electrode active material layer on the positive electrode current collector, Wherein the positive electrode active material layer comprises the positive electrode active material according to any one of claims 1 to 8 or the positive electrode active material prepared by the method according to any one of claims 9 to 14.

16. A rechargeable lithium battery, comprising: The positive electrode according to claim 15; A negative electrode; And An electrolyte.

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