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

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 layered lithium-nickel-manganese-based composite oxide having a nickel content of 60 mol% or more based on 100 mol% of total metals other than lithium in the layered lithium-nickel-manganese-based composite oxide; and a coating layer on a surface of the core particle and including Al, in which an Al content is 20-33 at% based on a total of 100 at% of Ni, Mn, and Al on a surface of the positive electrode active material.

Description

Technical Field

[0001] The present application discloses a positive electrode active material, a preparation method thereof, a positive electrode including the same, and a rechargeable lithium battery. Background Art

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

[0003] Various positive electrode active materials have been studied to realize rechargeable lithium batteries for these purposes. Among them, lithium nickel oxides, lithium nickel manganese cobalt composite oxides, lithium nickel cobalt aluminum composite oxides and lithium cobalt oxides are mainly used as positive electrode active materials. However, despite the recent rapid increase in interest in large-size, high-capacity and / or high-energy-density rechargeable lithium batteries, the supply of positive electrode active materials containing cobalt (a rare metal) is expected to be in serious shortage. Because cobalt is expensive and there is not much remaining reserves, there is interest in developing positive electrode active materials that do not contain cobalt or reduce its content. Summary of the invention

[0004] Some embodiments of the present disclosure provide a positive electrode active material including a lithium nickel manganese composite oxide, which realizes a high-concentration aluminum coating of uniform thickness to improve the performance of a rechargeable lithium battery at high temperature and high voltage, initial charge / discharge capacity characteristics (hereinafter also referred to as capacity), initial charge / discharge efficiency (hereinafter also referred to as efficiency), and high temperature cycle life characteristics.

[0005] In some embodiments, the positive electrode active material includes: a core particle including a layered lithium nickel manganese composite oxide, the nickel content of the layered lithium nickel manganese composite oxide being greater than or equal to 60 mol% based on 100 mol% of total metals other than lithium in the layered lithium nickel manganese composite oxide; and a coating on the surface of the core particle and including Al, wherein the Al content is 20 atomic % to 33 atomic % based on a total of 100 atomic % of Ni, Mn and Al on the surface of the positive electrode active material.

[0006] In some embodiments, a method for preparing a positive electrode active material includes: (i) preparing core particles, the core particles including a layered lithium nickel manganese composite oxide, the nickel content of the layered lithium nickel manganese composite oxide being greater than or equal to 60 mol% based on 100 mol% of total metals other than lithium in the layered lithium nickel manganese composite oxide, (ii) adding aluminum sulfate and the core particles to an aqueous solvent and mixing them together to prepare a mixed solution, and (iii) removing the aqueous solvent from the mixed solution, drying the resulting product, and heat treating at a temperature range of 730°C to 800°C to obtain the positive electrode active material.

[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 aforementioned positive electrode active material.

[0008] In some embodiments, a rechargeable lithium battery includes a positive electrode, a negative electrode, and an electrolyte.

[0009] The positive electrode active material according to some embodiments can maximize or increase the capacity while minimizing or reducing the production cost to ensure long cycle life characteristics and improve high voltage characteristics and high temperature storage characteristics. If the positive electrode active material is applied to a rechargeable lithium battery, a high initial charge / discharge capacity and initial charge / discharge efficiency can be achieved under high voltage operating conditions, a long cycle life characteristic can be achieved, and the amount of gas generated due to high voltage and high temperature operation can be effectively suppressed or reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The accompanying drawings, together with the specification, illustrate embodiments of the presently disclosed subject matter, and, together with the description, serve to explain principles of embodiments of the presently disclosed subject matter.

[0011] Figure 1 is a cutaway perspective view schematically illustrating a rechargeable lithium battery according to some embodiments.

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

[0013] Figure 3-4 is a perspective view schematically illustrating a rechargeable lithium battery according to some embodiments.

[0014] Figure 5 This is a scanning electron microscope (SEM) image of the surface of the positive electrode active material of Comparative Example 1.

[0015] Figure 6 This is a SEM image of the surface of the positive electrode active material of Example 1.

[0016] Figure 7 This is a SEM image of the surface of the positive electrode active material of Example 2.

[0017] Figure 8 This is a SEM image of the surface of the positive electrode active material of Example 3.

[0018] Fig. 9 This is a SEM image of the surface of the positive electrode active material of Example 4.

[0019] Fig.10 This is a SEM image of the surface of the positive electrode active material of Comparative Example 4.

[0020] Fig.11 is a SEM image of a cross section of the positive electrode active material of Comparative Example 1 cut using a focused ion beam (FIB).

[0021] Fig.12 To highlight Fig.11 Energy dispersive X-ray spectroscopy (EDS) analysis image of the Al element in the sample.

[0022] Fig.13 This is a SEM image of a cross section of the positive electrode active material of Example 1 cut using FIB.

[0023] Fig.14 To highlight Fig.13 EDS analysis image of the Al element.

[0024] Fig.15 The energy distribution energy dispersive X-ray spectroscopy (EP-EDS) analysis results of the positive electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 4 are shown, and the ratio of the Al content (atomic %) on the surface of the secondary particles to the total amount of Ni, Mn and Al of 100 atomic % (Al / (Ni+Mn+Al)) is shown.

[0025] Fig.16 FIG. 1 is a transmission electron microscope (TEM) image showing an enlarged cross section of a primary particle located at the outermost portion of a secondary particle in the positive electrode active material prepared in Example 1. FIG.

[0026] Fig.17 Show Fig.16 The results of EDS line profile analysis from the particle surface to the particle interior are shown in FIG.

[0027] Description of Reference Numerals

[0028] 100: Rechargeable lithium battery 10: Positive electrode

[0029] 11: Positive electrode lead lug 12: Positive electrode terminal

[0030] 20: Negative electrode 21: Negative electrode lead lug

[0031] 22: Negative electrode terminal 30: Separator

[0032] 40: electrode assembly 50: shell

[0033] 60: Sealing member 70: Electrode terminal piece

[0034] 71: Positive electrode terminal tab 72: Negative electrode terminal tab DETAILED DESCRIPTION

[0035] Hereinafter, example embodiments will be described in more detail so that those skilled in the art can easily implement them. However, the subject matter of the present disclosure may be embodied in many different forms and is not to be construed as limited to the example embodiments set forth herein.

[0036] The terms used herein are for describing the embodiments only and are not intended to limit the scope of the present disclosure. A singular expression includes a plural expression unless the context clearly indicates otherwise.

[0037] As used herein, "combinations thereof" means mixtures, laminates, composites, copolymers, alloys, blends, reaction products, etc. of the components.

[0038] In this document, it should be understood that terms such as "comprising", "including" or "having" are intended to indicate the presence of specified features, quantities, steps, elements or combinations thereof, but do not exclude the possibility of the presence or addition of one or more other features, quantities, steps, elements or combinations thereof.

[0039] In the accompanying drawings, the size (e.g., thickness) of layers, films, panels, regions, etc. may be exaggerated for clarity, and throughout the specification, the same reference numerals represent the same elements, and a repeated description thereof may not be provided in the specification. It will be understood that if an element (such as a layer, film, region, and / or substrate) is referred to as being "on" another element (such as a layer, film, region, and / or substrate), it may be directly on the other element (such as a layer, film, region, and / or substrate), or there may also be intervening elements. In contrast, if (for example, when) an element (such as a layer, film, region, and / or substrate) is referred to as being "directly on" another element (such as a layer, film, region, and / or substrate), there are no intervening elements.

[0040] In the embodiments, the “layer” herein includes not only a shape formed on the entire surface if viewed from a plan view but also a shape formed on a partial surface.

[0041] The average particle size can be measured by any suitable method commonly used in the art, for example, by a particle size analyzer, and / or by a transmission electron microscopic image and / or a scanning electron microscopic image. In an embodiment, the average particle size value can be obtained by measuring using a dynamic light scattering method, performing data analysis, counting the number of particles in each particle size range, and calculating therefrom. Unless otherwise specified, the average particle size (D 50 ) may refer to the diameter of particles having a cumulative volume of 50% by volume in a particle size distribution. As used herein, if otherwise defined, the average particle size (D 50 ) refers to the diameter of particles accounting for 50% by volume of the cumulative volume in a particle size distribution obtained by randomly measuring the sizes (diameters or lengths of major axes) of about 20 particles in a scanning electron microscope image.

[0042] In this document, “or” is not interpreted as being exclusive. For example, “A or B” is interpreted as including A, B, A+B, etc.

[0043] The term "metal" is interpreted as a concept including common metals, transition metals and metalloids (semimetals).

[0044] Positive electrode active material

[0045] In some embodiments, the positive electrode active material includes: a core particle including a layered lithium nickel manganese composite oxide, the layered lithium nickel manganese composite oxide having a nickel content greater than or equal to 60 mol% based on 100 mol% of total metals other than lithium in the layered lithium nickel manganese composite oxide; and a coating layer on the surface of the core particle and including Al. Based on a total of 100 atomic % of Ni, Mn and Al on the surface of the positive electrode active material, the Al content is 20 atomic % to 33 atomic %.

[0046] The Al content on the surface of the positive electrode active material can be measured by energy distribution energy dispersive X-ray spectroscopy (EP-EDS).

[0047] Since the price of cobalt (rare metal) has risen sharply recently, there is interest in developing positive electrode active materials that do not contain cobalt or reduce the cobalt content. Among them, positive electrode active materials with olivine crystal structure (such as lithium iron phosphate (LFP), lithium manganese phosphate (LMP), lithium manganese iron phosphate (LMFP), etc.) or spinel crystal structure (such as lithium manganese oxide (LMO), etc.) have limitations in achieving high capacity due to the small amount of available lithium in their structure. Layered lithium nickel manganese positive electrode active materials have excellent capacity and efficiency characteristics due to the high effective lithium capacity in the structure, making them suitable as materials for high-capacity batteries. However, due to the removal of cobalt, which plays a key role in the layered structure, the structural stability is reduced, the impedance (e.g., resistance) increases, and it becomes difficult to ensure long cycle life characteristics. Layered nickel manganese positive electrode active materials that do not contain cobalt may have the problem of accelerating the side reaction with the electrolyte under high voltage and high temperature conditions, resulting in increased gas generation and deterioration of cycle life characteristics.

[0048] In some embodiments, the surface of the lithium nickel manganese-based positive electrode active material is uniformly (or substantially uniformly) coated with aluminum, and the Al concentration on the surface is optimized or improved, thereby providing a method that can strengthen the particle surface, maintain a stable structure even at high voltage, achieve high capacity and long high temperature cycle life characteristics, and improve storage characteristics.

[0049] If the surface of the secondary particles of the positive electrode active material including the layered lithium nickel manganese composite oxide is coated with aluminum, the aluminum has a strong tendency to diffuse into the interior of the secondary particles, so it is not easy to actually achieve a uniform (or substantially uniform) coating of high-concentration aluminum in the form of a shell on the surface of the secondary particles. In some embodiments, a coating method that is most suitable for the characteristics of the layered lithium nickel manganese composite oxide is provided, and a condition for coating a high concentration of Al on the surface of the secondary particles with a uniform (or substantially uniform) and thin thickness without increasing impedance (e.g., resistance) is provided. Accordingly, the Al concentration on the surface of the secondary particles, for example, the ratio of Al / (Ni+Mn+Al) is confirmed to be 20 atomic % to 33 atomic %, and a method for actually achieving this concentration is provided. It is confirmed that the rechargeable lithium battery using the positive electrode active material according to some embodiments has improved initial charge / discharge capacity and initial charge / discharge efficiency under high voltage conditions, while (e.g., synchronously) improving high temperature cycle life characteristics and improving high temperature storage characteristics.

[0050] Nuclear particles

[0051] The core particles include layered lithium nickel manganese composite oxides. Based on 100 mol% of the total metals other than lithium in the layered lithium nickel manganese composite oxide, the nickel content of the layered lithium nickel manganese composite oxide may be greater than or equal to 60 mol%, such as 60 mol% to 80 mol%, 65 mol% to 80 mol%, 70 mol% to 80 mol%, 60 mol% to 79 mol%, 60 mol% to 78 mol% or 60 mol% to 75 mol%. If the nickel content meets the above range, even if the cobalt content is reduced, high capacity can be achieved and structural stability can be increased.

[0052] The manganese content of the layered lithium nickel manganese composite oxide may be, for example, greater than or equal to 10 mol%, such as 15 mol% to 40 mol%, 15 mol% to 35 mol%, 15 mol% to 30 mol%, or 20 mol% to 30 mol%, based on 100 mol% of the total metals other than lithium in the layered lithium nickel manganese composite oxide. If the manganese content satisfies the above range, the positive electrode active material can improve structural stability while achieving high capacity.

[0053] The layered lithium nickel manganese composite oxide may be a layered lithium nickel manganese aluminum composite oxide further including aluminum in addition to nickel and manganese. If the layered lithium nickel manganese composite oxide includes aluminum, it is beneficial to maintain a stable layered structure even if the cobalt element is excluded from the structure. Based on 100 mol% of the layered lithium nickel manganese composite oxide, the aluminum content of the layered lithium nickel manganese composite oxide may be greater than or equal to 0.1 mol%, greater than or equal to 0.5 mol%, or greater than or equal to 1 mol%, such as greater than 0 mol% and less than or equal to 3 mol%, such as 1 mol% to 3 mol%, 1 mol% to 2.5 mol%, 1 mol% to 2 mol% or 1.5 mol% to 2.5 mol%. If the aluminum content meets the above range, even if cobalt is excluded, a stable layered structure can be maintained, and the problem of structural collapse caused by charging and discharging can be suppressed or reduced, and the long cycle life characteristics of the positive electrode active material can be achieved.

[0054] According to some embodiments, the concentration of aluminum in the core particle may be uniform (or substantially uniform). In an embodiment, the uniform concentration of aluminum in the core particle means that there is no aluminum concentration gradient from the center to its surface in the core particle, or the aluminum concentration in the interior of the core particle is neither higher than nor lower than the aluminum concentration of the surface portion, and the aluminum in the core particle is uniformly distributed. This can be a structure obtained by using an aluminum raw material in the precursor production process, and not additionally doping aluminum in the synthesis of the core particle, thereby using a nickel-manganese-aluminum composite hydroxide as a precursor to synthesize a nickel-manganese-aluminum composite oxide. The core particle may be in the form of a secondary particle in which a plurality of primary particles are aggregated, and the aluminum content inside the primary particle may be the same or similar, regardless of the position of the primary particle. In an embodiment, if a primary particle is selected at a random position in the cross section of the secondary particle, and the aluminum content is measured inside the primary particle rather than at its interface, regardless of the position of the primary particle, for example, whether the primary particle is close to the center of the primary particle or close to the surface, the aluminum content may be the same / similar / uniform. In this structure, even if cobalt is not present or is present in a very small amount, a stable layered structure can be maintained, and no (or substantially no) aluminum byproducts or aluminum aggregates are produced, thereby simultaneously improving the capacity, efficiency and cycle life characteristics of the positive electrode active material.

[0055] The layered lithium nickel manganese-based composite oxide may be represented by Chemical Formula 1.

[0056] Chemical formula 1

[0057] Li a1 Ni x1 Mn y1 Al z1 M 1 w1 O 2-b1 X b1

[0058] In Chemical Formula 1, 0.9≤a1≤1.8, 0.6≤x1≤0.8, 0.1≤y1≤0.4, 0≤z1≤0.03, 0≤w1≤0.3, 0.9≤x1+y1+z1+w1≤1.1, and 0≤b1≤0.1, M 1 is one or more elements selected from B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y and Zr, and X is one or more elements selected from F, P and S.

[0059] In Chemical Formula 1, 0.9 ≤ a1 ≤ 1.5, or 0.9 ≤ a1 ≤ 1.2. In an embodiment, Chemical Formula 1 may include aluminum, in which case, it may satisfy 0.6 ≤ x1 ≤ 0.8, 0.1 ≤ y1 ≤ 0.39, 0.01 ≤ z1 ≤ 0.03, and 0 ≤ w1 ≤ 0.29. For example, 0.6 ≤ x1 ≤ 0.8, 0.1 ≤ y1 ≤ 0.39, 0.01 < z1 ≤ 0.03, and 0 ≤ w1 ≤ 0.29.

[0060] In Chemical Formula 1, for example, 0.6 ≤ x1 ≤ 0.79, 0.6 ≤ x1 ≤ 0.78, 0.6 ≤ x1 ≤ 0.75, 0.65 ≤ x1 ≤ 0.8, or 0.7 ≤ x1 ≤ 0.79; 0.1 ≤ y1 ≤ 0.35, 0.1 ≤ y1 ≤ 0.30, 0.1 ≤ y1 ≤ 0.29, 0.15 ≤ y1 ≤ 0.39, or 0.2 ≤ y1 ≤ 0.3; 0.01 ≤ z1 ≤ 0.025, 0.01 < z1 ≤ 0.02, or 0.01 < z1 ≤ 0.019; and 0 ≤ w1 ≤ 0.28, 0 ≤ w1 ≤ 0.27, 0 ≤ w1 ≤ 0.26, 0 ≤ w2 ≤ 0.25, 0 ≤ w1 ≤ 0.24, 0 ≤ w1 ≤ 0.23, 0 ≤ w1 ≤ 0.22, 0 ≤ w1 ≤ 0.21, 0 ≤ w1 ≤ 0.2, 0 ≤ w1 ≤ 0.15, 0 ≤ w1 ≤ 0.1, or 0 ≤ w1 ≤ 0.09.

[0061] For example, the layered lithium nickel manganese composite oxide may not contain cobalt or may contain a small amount of cobalt, and based on the total metals other than lithium in the layered lithium nickel manganese composite oxide at 100 mol%, the cobalt content may be 0 mol% to 0.01 mol%.

[0062] The core particle may be in the form of a secondary particle made by aggregating a plurality of primary particles. The secondary particle may be spherical, elliptical, polyhedral, and / or irregular in shape, and the primary particle may be spherical, elliptical, plate-shaped, or a combination thereof.

[0063] If the battery operates under high voltage or high temperature conditions, the core particle is vulnerable to chemical erosion by the components in the electrolyte, and thus may undergo many side reactions with the electrolyte, resulting in an increase in the amount of gas generated, thereby deteriorating the battery cycle life and safety. However, these problems can be solved by introducing a coating according to some embodiments, and the coating will be further described below.

[0064] Coating

[0065] The positive electrode active material according to some embodiments includes an Al-rich coating on the surface of the core particles. Based on a total of 100 atomic % of Ni, Mn and Al, the Al content measured on the particle surface of the positive electrode active material may be 20 atomic % to 33 atomic %. For example, the positive electrode active material particles may be secondary particles made by aggregating a plurality of primary particles, and in an embodiment, it may refer to the Al content measured on the surface of the secondary particles.

[0066] The Al content on the surface of the positive electrode active material particles, for example, Al / (Ni+Mn+Al), may be, for example, 21 to 32 atomic % or 22 to 31.5 atomic %. The content of each element on the surface of the positive electrode active material particles (for example, Al content) can be measured by EP-EDS.

[0067] Based on 100 mol% of the total metal other than lithium in the positive electrode active material, the Al content of the coating may be 0.5 mol% to 1.5 mol%, such as 0.6 mol% to 1.4 mol%, 0.7 mol% to 1.3 mol% or 0.8 mol% to 1.2 mol%. The aforementioned content refers to the content of aluminum included in the coating alone, separate from the aluminum contained in the core particles. The Al content of the coating in the entire positive electrode active material can be measured, for example, by SEM-EDS analysis of the surface and / or cross-section of the positive electrode active material. If the aluminum content in the coating satisfies the above range, the coating may have a uniform (or substantially uniform) and thin thickness, which does not increase the impedance (e.g., resistance) of the positive electrode active material, and effectively inhibits or reduces side reactions with the electrolyte, thereby improving the cycle life characteristics of the rechargeable lithium battery under high voltage and high temperature conditions. For example, if the aluminum content of the coating is too high, a uniform (or substantially uniform) coating may not be formed, or impedance (e.g., resistance) may increase, which may reduce initial charge / discharge efficiency and high-temperature cycle life characteristics, and if the aluminum content of the coating is too low, a coating of an appropriate or suitable thickness may not be formed, and the effect of suppressing or reducing side reactions with the electrolyte may be reduced.

[0068] In some embodiments, the Al content of the coating is adjusted to 0.5 mol% to 1.5 mol% based on 100 mol% of the total metals other than lithium in the entire positive electrode active material, and the coating method and conditions are adjusted so that the Al / (Ni+Mn+Al) ratio on the surface of the positive electrode active material can satisfy 20 atomic% to 33 atomic% based on a total of 100 atomic% of Ni, Mn and Al on the surface of the positive electrode active material. The Al-containing coating can improve the structural stability of the layered lithium nickel manganese composite oxide and improve the high voltage characteristics.

[0069] The coating according to some embodiments may be in the form of a film that continuously surrounds the surface of the core particle, for example, or may be in the form of a shell that surrounds the entire surface of the core particle. The aforementioned structure is different from a structure that only partially coats a portion of the surface of the core particle. According to some embodiments, the coating may be formed to completely cover the surface of the core particle, and may be formed to have a very thin and uniform thickness (or substantially uniform), so that the positive electrode active material does not increase impedance (e.g., resistance) or reduce capacity, improve structural stability, effectively inhibit or reduce side reactions with the electrolyte, reduce the amount of gas generated under high voltage and high temperature conditions, and achieve long cycle life characteristics.

[0070] The coating may have a thickness of 5nm to 200nm, such as 5nm to 150nm, 5nm to 100nm, 5nm to 80nm, 5nm to 50nm or 10nm to 50nm. If the coating satisfies the above thickness range, the structural stability of the positive electrode active material can be improved without increasing impedance (e.g., resistance) or reducing capacity due to the coating, and the side reaction with the electrolyte can be effectively suppressed or reduced. The thickness of the coating can be measured by, for example, SEM, TEM, TOF-SIMS, XPS and / or EDS analysis, and, for example, can be measured by EDS line profile analysis of a cross section of the positive electrode active material.

[0071] The coating according to some embodiments has a thin and uniform (or substantially uniform) thickness of several nanometers to several hundred nanometers. For example, the deviation of the coating thickness in a positive electrode active material particle may be less than or equal to 20%, less than or equal to 18%, or less than or equal to 15%. In this article, the deviation of the coating thickness refers to the deviation of the coating thickness in a positive electrode active material particle. For example, the deviation of the coating thickness can be calculated by measuring the thickness of about 10 points in the electron microscope image of the cross section of a single positive electrode active material particle to calculate the arithmetic mean, and then the absolute value of the difference between one measurement data and the arithmetic mean is divided by the arithmetic mean and multiplied by 100%. The fact that the deviation or standard deviation of the coating thickness meets the above range means that a coating of uniform (or substantially uniform) thickness is formed in the form of a good film on the surface of the core particle of the positive electrode active material. Accordingly, the structural stability of the positive electrode active material is improved, the side reaction with the electrolyte can be effectively suppressed or reduced, and the impedance (e.g., resistance) increase or capacity reduction caused by the coating can be minimized, or the impedance (e.g., resistance) increase or capacity reduction caused by the coating can be reduced.

[0072] The coating may include, for example, a layered aluminum compound, such as aluminum oxide, lithium aluminum oxide (eg, LiAlO 2 ), or a combination thereof.

[0073] In addition to aluminum, the coating may further contain nickel, manganese or a combination thereof.

[0074] According to some embodiments, the average particle size (D 50 ) is not particularly limited, but may be, for example, 1 μm to 25 μm, 5 μm to 25 μm, 10 μm to 25 μm, 11 μm to 20 μm, or 12 μm to 18 μm. As used herein, if no definition is otherwise provided, the average particle size (D 50 ) means the diameter of particles with a cumulative volume of 50% by volume in a particle size distribution obtained by randomly measuring the size (diameter or major axis length) of 20 particles in a scanning electron microscope image of a positive electrode active material. If the average particle size of the positive electrode active material satisfies the above range, high capacity and long cycle life can be achieved, and forming a coating according to one or more embodiments can be beneficial.

[0075] In some embodiments, another positive electrode active material can be characterized as being sodium-free. Generally speaking, sodium ions can be used in the preparation process of the positive electrode active material, but according to the preparation method described further, core particles having a stable structure and a coating layer of uniform (or substantially uniform) thickness can be formed without using sodium ions.

[0076] Method for preparing positive electrode active material

[0077] In some embodiments, a method for preparing a positive electrode active material includes: (i) preparing core particles, the core particles including a layered lithium nickel manganese composite oxide, the nickel content being greater than or equal to 60 mol% based on 100 mol% of the total metals other than lithium in the layered lithium nickel manganese composite oxide, (ii) adding aluminum sulfate and the core particles to an aqueous solvent and mixing them together to prepare a mixed solution, and (iii) removing the aqueous solvent from the mixed solution, drying the resulting product, and performing a heat treatment at a temperature range of 730° C. to 800° C. to obtain a positive electrode active material. The aforementioned positive electrode active material can be manufactured by the above method.

[0078] In (i), the layered lithium nickel-manganese composite oxide can be prepared, for example, by mixing a nickel-manganese composite hydroxide and a lithium raw material together and performing a first heat treatment. The nickel-manganese composite hydroxide can be a precursor of a core particle, and can be in the form of a secondary particle in which a plurality of primary particles are aggregated. The nickel-manganese composite hydroxide can be prepared by a general coprecipitation method.

[0079] Based on 100mol% of total metal in the nickel-manganese composite hydroxide, the nickel content in the nickel-manganese composite hydroxide is greater than or equal to 60mol%, for example, 60mol% to 80mol%, 65mol% to 80mol% or 70mol% to 80mol%, 60mol% to 79mol%, 60mol% to 78mol%, 60mol% to 75mol%. If the nickel content meets the above range, even if the cobalt content is reduced, high capacity can be achieved and structural stability can be increased.

[0080] The manganese content in the nickel-manganese composite hydroxide may be greater than or equal to 10 mol%, for example, 15 mol% to 40 mol%, 15 mol% to 39 mol%, 15 mol% to 35 mol%, 15 mol% to 30 mol% or 20 mol% to 30 mol%, based on 100 mol% of total metals in the nickel-manganese composite hydroxide.

[0081] In an embodiment, if the nickel-manganese composite hydroxide further contains aluminum, the content of aluminum may be greater than or equal to 0.1 mol%, greater than or equal to 0.5 mol%, or greater than or equal to 1 mol%, for example, 1 mol% to 3 mol%, 1 mol% to 2.5 mol%, 1 mol% to 2 mol%, or 1 mol% to 1.9 mol%, based on 100 mol% of the total metal in the nickel-manganese composite hydroxide. If the manganese and aluminum contents of the nickel-manganese composite hydroxide meet the above ranges, high capacity can be achieved, while the structural stability of the positive electrode active material can be increased, and the production price can be reduced to increase economic efficiency.

[0082] In the method for preparing the positive electrode active material according to some embodiments, in the preparation of the core particles, aluminum may not be additionally doped, but an aluminum raw material may be used to prepare a precursor, so that a nickel-manganese-aluminum composite hydroxide in which aluminum is uniformly (e.g., substantially uniformly) dispersed in the structure may be used as a precursor. If such a precursor is used, the positive electrode active material may stably maintain a layered structure without containing cobalt despite repeated charging and discharging, and may not form aluminum byproducts or aluminum aggregates, improving the capacity and efficiency characteristics of the positive electrode active material and high temperature cycle life characteristics.

[0083] Based on 100 mol% of total metals in the nickel-manganese composite hydroxide, the cobalt content in the nickel-manganese composite hydroxide may be less than or equal to 0.01 mol%, less than or equal to 0.005 mol%, or less than or equal to 0.001 mol%. The nickel-manganese composite hydroxide may be economical because it avoids the increase in unit cost caused by cobalt, maximizes or increases capacity, and improves structural stability.

[0084] As an example, the nickel-manganese-based composite hydroxide may be represented by Chemical Formula 2.

[0085] Chemical formula 2

[0086] Ni x2 Mn y2 Al z2 M 2 w2 (OH)2

[0087] In Formula 2, 0.6≤x2≤0.8, 0.1≤y2≤0.4, 0≤z2≤0.03, 0≤w2≤0.3, and 0.9≤x2+y2+z2+w2≤1.1, and M 2 It is one or more elements selected from B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y and Zr.

[0088] In Chemical Formula 2, for example, 6≤x2≤0.8, 0.1≤y2≤0.39, 0.01≤z2≤0.03, and 0≤w2≤0.29.

[0089] The nickel-manganese composite hydroxide is in the form of particles, and the average particle size (D 50 ) can be 1μm to 25μm, 5μm to 20μm, 10μm to 20μm, 11μm to 18μm or 12μm to 15μm.

[0090] The nickel-manganese composite hydroxide and the lithium raw material can be mixed together in a molar ratio of 1:0.9 to 1:1.8, for example, 1:0.9 to 1:1.5 or 1:0.9 to 1:1.2. The first heat treatment can be carried out under an oxygen atmosphere, for example, at a temperature range of 750°C to 950°C, 780°C to 900°C or 810°C to 890°C for 2 hours to 20 hours or 4 hours to 12 hours. By heat treatment, a layered lithium nickel-manganese composite oxide can be obtained. The obtained layered lithium nickel-manganese composite oxide is substantially the same as the layered lithium nickel-manganese composite oxide described for the core particles in the positive electrode active material portion.

[0091] Because the layered lithium nickel manganese composite oxide may have a significantly different residual lithium content on the particle surface from oxides having different compositions (e.g., lithium nickel cobalt manganese composite oxides, lithium nickel cobalt aluminum composite oxides, lithium cobalt oxides, etc.), and various properties different from oxides having different compositions (e.g., lithium nickel cobalt manganese composite oxides, lithium nickel cobalt aluminum composite oxides, lithium cobalt oxides, etc.), it is considered impossible to form a suitable or satisfactory coating in the form of a uniform film in a conventional coating method. In one or more embodiments, a method is proposed that the surface of the layered lithium nickel manganese composite oxide particles can be coated with a high concentration of Al at a very uniform (or substantially uniform) thickness.

[0092] In (ii), the aqueous solvent may include distilled water, an alcohol solvent, or a combination thereof.

[0093] Aluminum sulfate may be an appropriate or optimal raw material for forming a coating according to some embodiments. Based on 100 mol% of the total metal other than lithium in the final positive electrode active material (i.e., the sum of 100 mol% of the total metal other than lithium and aluminum sulfate in the core particles), the Al content in aluminum sulfate may be designed to be 0.5 mol% to 1.5 mol%, for example, 0.6 mol% to 1.4 mol%, 0.7 mol% to 1.3 mol% or 0.8 mol% to 1.2 mol%. If the Al content of the coating is designed within the above range, the coating may be formed to have a thin and uniform (or substantially uniform) thickness of several nanometers to several hundred nanometers, reducing the amount of gas generated by the rechargeable lithium battery under high voltage or high temperature operating conditions, and improving high capacity and long cycle life characteristics.

[0094] In some embodiments, the core particles may be added to an aqueous solvent and mixed together, and then aluminum sulfate may be added to prepare a mixed solution. The foregoing is a wet coating method, and may be referred to as a post-addition method in which a coating raw material is added after the core particles are added.

[0095] In some embodiments, the coating solution can be prepared by first adding aluminum sulfate to an aqueous solvent and mixing, and then adding the core particles to the coating solution and mixing together to prepare a mixed solution. This is a salt-dissolving wet coating method and can be referred to as a pre-addition method in which the salt as a coating raw material is first completely dissolved and then the core particles are added.

[0096] In the pre-addition method, aluminum sulfate is added to the aqueous solvent and mixed together for 1 minute to 60 minutes, for example, 3 minutes to 30 minutes or 5 minutes to 10 minutes. In an embodiment, mixing is performed at a speed of 100rpm to 800rpm, for example, 200rpm to 600rpm or 250rpm to 500rpm. Under the aforementioned conditions, aluminum sulfate is completely dissolved in the aqueous solvent to obtain a colorless and transparent coating solution, and the coating solution can be used to effectively form a uniform (or substantially uniform) aluminum coating according to some embodiments. The coating solution completed by mixing may have, for example, a pH of 1.5 to 3.5, for example, 2.0 to 3.4, 2.5 to 3.3, 2.7 to 3.3 or 2.9 to 3.2.

[0097] In the process of adding the core particles to the prepared coating solution, the core particles are added to the coating solution while stirring it to increase the coating quality.

[0098] In an embodiment, the amount of time spent adding the core particles to the coating solution may be 30 seconds / 500g to 2 minutes / 500g, for example, 30 seconds / 500g to 1.5 minutes / 500g, etc. The speed of adding the core particles may be appropriately or suitably adjusted to control the pH of the supernatant after the coating is completed, thereby inducing the effective formation of a uniform (or substantially uniform) Al-containing coating according to some embodiments. If the speed of adding the core particles is too fast, the pH of the supernatant may increase and become alkaline after the coating is completed, resulting in no uniform coating. If the speed of adding the core particles is too slow, the pH of the supernatant may decrease and become more acidic, and still no uniform coating is formed.

[0099] After all the core particles are added to the coating solution, stirring can be performed for 15 to 60 minutes, for example, 20 to 50 minutes or 30 to 45 minutes. The time spent from starting to add the core particles to the coating solution to completing stirring, for example, the coating reaction time can be adjusted within 1 hour.

[0100] In some embodiments, if the addition of the core particles to the coating solution and mixing are stopped, for example, after the mixing or coating is completed, the pH of the supernatant may be in the range of 5.5 to 7.5. If the pH of the supernatant is less than 5.5, the acidity may become strong and a uniform coating may not be formed, and if the pH is greater than 7.5, the alkalinity may become strong, making it difficult to form a uniform Al-containing coating.

[0101] In (iii), after removing the aqueous solvent from the mixed solution, the resulting product can be dried, for example, at 40°C to 240°C, 100°C to 220°C or 150°C to 200°C and, for example, under vacuum conditions, and a suitable or satisfactory coating product can be obtained under the aforementioned conditions.

[0102] The dried product after removing the aqueous solvent from the mixed solution may be referred to as a coating product. The coating product includes a core particle and an Al-containing coating on the surface of the core particle. For example, the Al-containing coating may include a fiber shape, for example, a grid-like or spider-web-like structure. Such a grid-like structure may be provided continuously over the entire surface of the core particle. The grid-like coating may wrap the core particle with a very thin and uniform (or substantially uniform) thickness to strengthen the surface of the positive electrode active material and improve structural stability, thereby enhancing high temperature and high voltage characteristics.

[0103] After the nickel-manganese-based composite hydroxide and the lithium raw material are mixed together, the heat treatment of the mixture may be referred to as a first heat treatment, while the heat treatment of the coated product may be referred to as a second heat treatment.

[0104] In some embodiments, the second heat treatment temperature range is set to 730°C to 800°C. The second heat treatment temperature range may be, for example, 740°C to 800°C, 750°C to 800°C, 750°C to 780°C, or 750°C to 775°C. If the second heat treatment temperature is set to the above range, the tendency of aluminum to diffuse into the secondary particles can be reduced, and aluminum is mainly retained on the surface of the secondary particles, and at the same time, the surface of the secondary particles can be coated in the form of a very thin and uniform (or substantially uniform) thickness shell. If the heat treatment range is adjusted to the above range, based on a total of 100 atomic % of Ni, Mn and Al on the surface of the secondary particles, the Al content ratio on the surface of the secondary particles, for example, Al / (Ni+Mn+Al), can be controlled to be 20 atomic % to 33 atomic %.

[0105] If the second heat treatment temperature exceeds 800°C, the tendency of aluminum to diffuse into the secondary particles increases, making it difficult to form a high-concentration Al-rich coating on the surface, and accordingly, the initial charge / discharge capacity and initial charge / discharge efficiency characteristics at high voltage may be reduced, the cycle life characteristics at high voltage and high temperature may be reduced, and the amount of gas generated during high-temperature storage may increase. If the second heat treatment temperature is lower than 730°C, the tendency of aluminum to diffuse into the secondary particles may be reduced, but some aluminum will aggregate or be unevenly distributed on the surface of the secondary particles, resulting in reduced cycle life characteristics under high temperature and high voltage conditions, and if stored at high temperature, the amount of gas generated increases.

[0106] The second heat treatment may be performed, for example, in an oxygen atmosphere for 2 to 20 hours or 3 to 10 hours.

[0107] The obtained positive electrode active material includes: a core particle, including a layered lithium nickel manganese composite oxide, the nickel content of the layered lithium nickel manganese composite oxide being greater than or equal to 60 mol% based on 100 mol% of total metals other than lithium in the layered lithium nickel manganese composite oxide; and a coating on the surface of the core particle and including aluminum oxide, lithium aluminum oxide or a combination thereof.

[0108] Positive electrode

[0109] In some embodiments, the positive electrode includes a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, wherein the positive electrode active material layer includes the aforementioned positive electrode active material. In addition to the aforementioned positive electrode active material, the positive electrode active material layer may further include other types (or types) of positive electrode active materials. In an embodiment, the positive electrode active material layer may optionally further include a binder, a conductive material (e.g., a conductive material) or a combination thereof.

[0110] According to some embodiments, the loading level of the positive electrode active material layer may be 10 mg / cm 2 ~40mg / cm 2 , for example 10mg / cm 2 ~30mg / cm 2 or 10mg / cm 2 ~20mg / cm 2 . In an embodiment, the density of the positive electrode active material layer in the final pressed positive electrode may be 3.3 g / cc to 3.7 g / cc, for example, 3.3 g / cc to 3.6 g / cc or 3.4 g / cc to 3.58 g / cc. If the positive electrode active material according to some embodiments is applied, it is beneficial to achieve such a loading level and density of the positive electrode active material layer, and the positive electrode satisfying the loading level and density of the positive electrode active material layer within the above range is suitable for realizing a high-capacity, high-energy-density rechargeable lithium battery.

[0111] Binder

[0112] The binder improves the bonding properties of the positive electrode active material particles to each other and 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, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon, but are not limited thereto.

[0113] Conductive Materials

[0114] The conductive material is included to provide electrode conductivity (e.g., electrical conductivity), and any suitable conductive material may be used as the conductive material unless it causes chemical changes (e.g., undesirable changes in a rechargeable lithium battery). Examples of the conductive material may 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 (e.g., conductive polymers) such as polyphenylene derivatives; or mixtures thereof.

[0115] Each of the binder and the conductive material may be included in an amount of 0.5 wt % to 5 wt % based on 100 wt % of the positive electrode active material layer.

[0116] The positive electrode current collector may include Al foil, but is not limited thereto.

[0117] Rechargeable lithium battery

[0118] Some embodiments provide a rechargeable lithium battery including the aforementioned positive electrode, negative electrode, and electrolyte. As an example, the rechargeable lithium battery may include a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and an electrolyte.

[0119] Rechargeable lithium batteries may be classified into cylindrical batteries, prismatic batteries, pouch batteries, coin batteries, etc., depending on the shape. Figure 1 to Figure 4 is a schematic diagram showing a rechargeable lithium battery according to one or more embodiments, wherein Figure 1 A cylindrical battery is shown, Figure 2 A prismatic cell is shown, and Figure 3 and Figure 4 A pouch cell is shown. Figure 1 to Figure 4 , the rechargeable lithium battery 100 includes an electrode assembly 40 and a case 50 in which the electrode assembly 40 is accommodated, and the electrode assembly 40 includes a separator 30 between a positive electrode 10 and a negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte. Figure 1 As shown in , the rechargeable lithium battery 100 may include a sealing member 60 that seals the housing 50. Figure 2 In the embodiment, the rechargeable lithium battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. Figure 3-4 As shown in FIG. 1 , the rechargeable lithium battery 100 includes an electrode tab 70 ( Figure 4 ), that is, the positive electrode tab 71 and the negative electrode tab 72 ( Figure 3 ).

[0120] According to some embodiments of the rechargeable lithium battery can be rechargeable at a high voltage, and / or can be suitable for driving at a high voltage. For example, the charging voltage of the rechargeable lithium battery can be greater than or equal to about 4.45V, about 4.45V to about 4.7V, about 4.45V to about 4.6V, or about 4.45V to about 4.55V. By applying the positive electrode active material according to one or more embodiments, even (for example, when) charging at a high voltage, the rechargeable lithium battery can significantly reduce the amount of gas generated, and can achieve high capacity and long cycle life characteristics.

[0121] Negative electrode

[0122] The negative electrode may include a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector and including a negative electrode active material, and the negative electrode active material layer may further include a binder, a conductive material (eg, an electrically conductive material), or a combination thereof.

[0123] Negative electrode active material

[0124] 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.

[0125] The material that reversibly intercalates / deintercalates lithium ions may include, for example, crystalline carbon, amorphous carbon, or a combination thereof as a carbonaceous negative electrode active material. The crystalline carbon may be amorphous, and / or flaky, sheet-like, spherical, and / or fibrous natural graphite and / or artificial graphite. The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbonization product, calcined coke, etc.

[0126] Lithium metal alloys include alloys of lithium with a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0127] The material capable of being doped / undoped with lithium may be a Si-based negative electrode active material and / or a Sn-based negative electrode active material. The Si-based negative electrode active material may include silicon, a silicon-carbon composite, SiO x(0 < x ≤ 2), Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements (excluding Si), Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, such as Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof) or a combination thereof. The Sn-based negative electrode active material can be Sn, SnO x (0 < x ≤ 2) (for example, SnO2), Sn alloy, or a combination thereof.

[0128] The silicon-carbon composite can be a composite of silicon and amorphous carbon. The average particle size (D 50 ) of the silicon-carbon composite particles can be, for example, 0.5 μm to 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. For example, the silicon primary particles can be coated with amorphous carbon. The secondary particles can be dispersed in the amorphous carbon matrix and exist.

[0129] The silicon-carbon composite can further include crystalline carbon. For example, the silicon-carbon composite can include a core containing 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 and / or hard carbon, mesophase pitch carbonized products, and / or calcined coke.

[0130] If the silicon-carbon composite includes silicon and amorphous carbon, based on 100 wt% of the silicon-carbon composite, the content of silicon can be 10 wt% to 50 wt% and the content of amorphous carbon can be 50 wt% to 90 wt%. Additionally, if the silicon-carbon composite includes silicon, amorphous carbon, and crystalline carbon, based on 100 wt% of the silicon-carbon composite, the content of silicon can be 10 wt% to 50 wt%, the content of crystalline carbon can be 10 wt% to 70 wt%, and the content of amorphous carbon can be 20 wt% to 40 wt%.

[0131] In an embodiment, the thickness of the amorphous carbon coating can be 5 nm to 100 nm. The average particle size (D 50 ) of the silicon particles (primary particles) can be 10 nm to 1 μm or 10 nm to 200 nm. The silicon particles can exist in the form of elemental silicon, silicon alloy, and / or oxidized form of silicon. The oxidized form of silicon can be SiO x(0 < x ≤ 2). In an embodiment, the atomic content ratio of Si:O indicating the degree of oxidation may be from about 99:1 to about 33:67. As used herein, unless otherwise provided with a definition, the average particle size (D 50 ) indicates the diameter of the particles with a cumulative volume of about 50% by volume in the particle size distribution.

[0132] The Si-based negative electrode active material and / or the Sn-based negative electrode active material may be mixed with the carbon-based negative electrode active material. If the Si-based negative electrode active material and / or the Sn-based negative electrode active material and the carbon-based negative electrode active material are mixed and used, the mixing ratio may be a weight ratio of 1:99 to 90:10.

[0133] Binder

[0134] The binder is used to bond the negative electrode active material particles to each other well and is also used to bond the negative electrode active material to the negative electrode current collector. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0135] The non-aqueous binder may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0136] The aqueous binder may include styrene-butadiene rubber, (meth)acrylate esterified styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, poly(ethylene oxide), polyvinylpyrrolidone, polyepichlorohydrin, 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.

[0137] If the aqueous binder is used as the binder in the negative electrode active material layer, a cellulose-based compound capable of imparting or increasing viscosity may be further included. As the cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and their alkali metal salts may be mixed and used. The alkali metal may be Na, K, or Li.

[0138] The dry binder may be a polymer material capable of becoming fibers (e.g., capable of fibrillating), and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, poly(ethylene oxide), or a combination thereof.

[0139] Conductive material

[0140] The conductive material is included to provide electrode conductivity (e.g., electrical conductivity), and any suitable conductive material can be used as the conductive material unless it causes chemical changes (e.g., undesirable chemical changes in a rechargeable lithium battery). Examples of the conductive material 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 and / or metal fibers of copper, nickel, aluminum silver, etc.; conductive polymers (e.g., conductive polymers) such as polyphenylene derivatives; or mixtures thereof.

[0141] Based on 100wt% of the negative electrode active material layer, the content of the negative electrode active material may be 95wt% to 99.5wt%, and based on 100wt% of the negative electrode active material layer, the content of the binder may be 0.5wt% to 5wt%. For example, the negative electrode active material layer may include 90wt% to 99wt% of the negative electrode active material, 0.5wt% to 5wt% of the binder, and 0.5wt% to 5wt% of the conductive material.

[0142] Negative electrode current collector

[0143] The negative electrode current collector may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li) and / or alloys thereof, and may be in the form of foil, sheet and / or foam. The thickness of the negative electrode current collector may be, for example, 1 μm to 20 μm, 5 μm to 15 μm or 7 μm to 10 μm.

[0144] Electrolytes

[0145] For example, the electrolyte for a rechargeable lithium battery may be an electrolyte that may include a non-aqueous organic solvent and a lithium salt.

[0146] The non-aqueous organic solvent is used as a medium for transporting ions participating in the electrochemical reaction of the rechargeable lithium battery. The non-aqueous organic solvent may include a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, an aprotic solvent, or a combination thereof.

[0147] Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl 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, decanoic acid lactone, mevalonate lactone, 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 an embodiment, ketone solvents may include cyclohexanone, etc. Alcohol solvents may include ethanol, isopropanol, etc., and aprotic solvents may include nitriles (such as R-CN (wherein R is a C2-C20 straight chain hydrocarbon group, a branched hydrocarbon group or a cyclic hydrocarbon group, and may include a double bond, an aromatic ring and / or an ether bond, etc.)); amides (such as dimethylformamide); dioxolanes (such as 1,3-dioxolane, 1,4-dioxolane, etc.); cyclopentane sulfone, etc.

[0148] The non-aqueous organic solvent may be used alone or as a mixture of two or more types (or species), and if used as a mixture of two or more types (or species), the mixing ratio may be appropriately or suitably adjusted according to appropriate or desired battery performance, which is widely known to those skilled in the art after referring to the present disclosure.

[0149] If a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed and used, and the cyclic carbonate and the chain carbonate may be mixed together in a volume ratio of about 1:1 to about 1:9.

[0150] The non-aqueous organic solvent may further include an aromatic hydrocarbon organic solvent. For example, a carbonate-based solvent and an aromatic hydrocarbon organic solvent may be mixed together in a volume ratio of 1:1 to 30:1 and used.

[0151] The electrolyte may further include vinyl ethylene carbonate, vinylene carbonate and / or ethylene carbonate-based compounds to improve the battery cycle life.

[0152] Examples of the ethylene carbonate-based compound may include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0153] The lithium salt dissolved in the non-aqueous organic solvent supplies lithium ions in the battery, ensures the basic operation of the rechargeable lithium battery, and improves the transport of lithium ions between the positive electrode and the negative electrode. 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) (wherein x and y are integers of 1 to 20), at least one of lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP) and lithium bis(oxalato)borate (LiBOB).

[0154] The concentration of the lithium salt may be in the range of about 0.1 M to about 2.0 M. If the concentration of the lithium salt is within the above range, the electrolyte has appropriate or suitable ion conductivity and viscosity, and thus excellent performance may be achieved, and lithium ions may be efficiently moved.

[0155] Diaphragm

[0156] Depending on the type (or kind) of the rechargeable lithium battery, the 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, or a multilayer film of two or more layers thereof, such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, etc.

[0157] The separator may include a porous substrate and a coating on one surface or both surfaces (eg, two opposite surfaces) of the porous substrate, the coating including an organic material, an inorganic material, and / or a combination thereof.

[0158] The porous substrate may be a polymer film formed from any one or a copolymer or mixture of two or more selected from the following: polymer polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyacetals, polyamides, polyimides, polycarbonates, polyether ketones, polyaryletherketones, polyetherimides, polyamideimides, polybenzimidazoles, polyethersulfones, polyphenylene oxides, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fibers, and polytetrafluoroethylene (e.g., Teflon).

[0159] The porous substrate may have a thickness of 1 μm to 40 μm, for example, 1 μm to 30 μm, 1 μm to 20 μm, 5 μm to 15 μm, or 10 μm to 15 μm.

[0160] The organic material may include a (meth)acryl-based copolymer, which includes: a first structural unit derived from (meth)acrylamide; and a second structural unit including at least one of a structural unit derived from (meth)acrylic acid or (meth)acrylate and a structural unit derived from (meth)acrylamide sulfonic acid or its salt.

[0161] The inorganic material may include inorganic particles selected from the group consisting of Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof, but is not limited thereto. The average particle size (D 50 ) may be 1 nm to 2000 nm, for example, 100 nm to 1000 nm or 100 nm to 700 nm.

[0162] The organic material and the inorganic material may be mixed together in one coating layer, or may exist in the form of a stack of a coating layer including an organic material and a coating layer including an inorganic material.

[0163] The coating may have a thickness of 0.5 μm to 20 μm, for example, 1 μm to 10 μm or 1 μm to 5 μm.

[0164] Examples and comparative examples of the present disclosure are described below. However, the following examples are merely examples of the present disclosure, and the present disclosure is not limited to the following examples.

[0165] Example 1

[0166] 1. Preparation of positive electrode active material

[0167] Ni 0.75 Mn 0.23 Al 0.02 (OH)2 and LiOH were mixed together in a molar ratio of 1:1.05, and then a first heat treatment was performed at 845°C in an oxygen atmosphere for 8 hours to prepare a Li 1.05 Ni 0.75 Mn 0.23 Al 0.02 The composition and average particle size of O2 (D 50 ) is a layered lithium nickel manganese composite oxide in the form of secondary particles of about 14 μm.

[0168] 500 g of layered lithium nickel manganese composite oxide and 600 g of distilled water were added to a 1 L reactor, and aluminum sulfate was added thereto while stirring the mixture for 1.5 minutes, and then stirred for 45 minutes. In this article, aluminum sulfate is designed to have an aluminum content of 1.0 mol% based on 100 mol% of total metals other than lithium in the final positive electrode active material.

[0169] After removing the solvent from the mixed solution by using an aspirator and a filter press, a coated product was obtained by vacuum drying at 190°C.

[0170] The coated product was subjected to a second heat treatment at 750° C. for 8 hours under an oxygen atmosphere to obtain a final positive electrode active material.

[0171] 2. Manufacturing of rechargeable lithium battery cells

[0172] 98.5 wt% of the positive electrode active material, 1.0 wt% of the polyvinylidene fluoride binder and 0.5 wt% of the carbon nanotube conductive material were mixed together to prepare a positive electrode active material layer slurry, and the slurry was coated on an aluminum foil current collector, then dried and pressed to manufacture a positive electrode. In this paper, the loading level of the positive electrode active material layer was 10 mg / cm 2 , and the density of the positive electrode active material layer in the final pressed positive electrode was 3.4 g / cc.

[0173] 97.5 wt% of graphite negative electrode active material, 1.5 wt% of carboxymethyl cellulose and 1 wt% of styrene butadiene rubber were mixed together in an aqueous solvent to prepare a negative electrode active material layer slurry. The negative electrode active material layer slurry was coated on a copper foil current collector, then dried and pressed to make a negative electrode.

[0174] A rechargeable lithium battery cell was manufactured in a conventional method using a polytetrafluoroethylene separator and using an electrolyte prepared by dissolving 1M LiPF6 in a mixed solvent of ethylene carbonate and dimethyl carbonate in a volume ratio of 3:7.

[0175] Example 2

[0176] A positive electrode active material and a 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 first adding aluminum sulfate and distilled water to a reactor and mixing them together for 5 minutes while stirring at 350 rpm to prepare a coating solution, then adding 500 g of the layered lithium nickel manganese composite oxide according to Example 1 to the coating solution while continuously stirring for 1.5 minutes, and then stirring the obtained mixture for 45 minutes.

[0177] Example 3

[0178] A positive electrode active material and a rechargeable lithium battery cell were manufactured in substantially the same manner as in Example 2, except that the second heat treatment was performed at 775°C.

[0179] Example 4

[0180] A positive electrode active material and a rechargeable lithium battery cell were manufactured in substantially the same manner as in Example 2, except that the second heat treatment was performed at 800°C.

[0181] Comparative Example 1

[0182] A positive electrode active material and a rechargeable lithium battery cell were manufactured in substantially the same manner as in Example 1, except that the second heat treatment was performed at 825°C.

[0183] Comparative Example 2

[0184] A positive electrode active material and a rechargeable lithium battery cell were manufactured in substantially the same manner as Comparative Example 1, except that the aluminum content of aluminum sulfate was designed to be 1.5 mol % based on 100 mol % of total metals excluding lithium in the final positive electrode active material.

[0185] Comparative Example 3

[0186] A positive electrode active material and a rechargeable lithium battery cell were manufactured in substantially the same manner as Comparative Example 1, except that the aluminum content of aluminum sulfate was designed to be 2.0 mol % based on 100 mol % of total metals excluding lithium in the final positive electrode active material.

[0187] Comparative Example 4

[0188] A positive electrode active material and a rechargeable lithium battery cell were manufactured in substantially the same manner as in Example 2, except that the second heat treatment was performed at 725°C.

[0189] For better understanding, the design details of the embodiments and comparative examples are briefly shown in Table 1.

[0190] Table 1

[0191]

[0192] Evaluation Example 1: SEM Analysis

[0193] Figure 5 is a SEM image of the surface of the positive electrode active material of Comparative Example 1, Figure 6 is a SEM image of the surface of the positive electrode active material of Example 1, and Figure 7 This is a SEM image of the surface of the positive electrode active material of Example 2.

[0194] refer to Figure 5 , regarding Comparative Example 1, since aluminum diffuses into the positive electrode active material secondary particles, Comparative Example 1 shows that the secondary particle surface is smooth, but Figure 6 Example 1 and Figure 7 Example 2 shows that the Al-containing coating is confirmed on the surface of the secondary particles. Figure 6 In Example 1, micrometer-sized island-type coatings were observed, and Figure 7 In Example 2, a nano-sized Al-containing coating was observed.

[0195] Figure 8 is a SEM image of the surface of the positive electrode active material of Example 3, and Fig. 9 This is a SEM image of the surface of the positive electrode active material of Example 4. Figure 8 and Fig. 9 , an Al-containing coating was observed on the surface of the secondary particles.

[0196] Fig.10 This is a SEM image of the surface of the positive electrode active material of Comparative Example 4. Fig.10 An uneven coating was observed on the surface of the secondary particles within the white circles.

[0197] Evaluation Example 2: EDS Mapping Analysis

[0198] Fig.11 is a SEM image of a cross section of the positive electrode active material of Comparative Example 1 cut by FIB, and Fig.12 To highlight Fig.11 EDS analysis image of Al element in . Fig.12 , in Comparative Example 1, Al-coated regions were observed not only on the surfaces of the secondary particles but also at the internal grain boundaries of the particles.

[0199] Fig.13 is a SEM image of a cross section of the positive electrode active material of Example 1 cut by FIB, and Fig.14 To highlight Fig.13 EDS analysis image of Al element in . Fig.14 Regarding Example 1, because Al is uniformly coated on the surface of the secondary particles at a high content instead of diffusing into the internal boundaries of the secondary particles, Example 1 exhibits a thicker and more uniform Al-rich coating on the surface of the secondary particles than the Al-rich coating of Comparative Example 1.

[0200] Evaluation Example 3: TEM Analysis

[0201] On the other hand, as a result of HR-TEM (high resolution transmission electron microscopy) analysis of the cross section of the positive electrode active material according to Example 1, a layered structure was observed even in the Al-containing coating on the surface of the secondary particles and inside the secondary particles, and accordingly, the coating was shown to include layered lithium aluminum oxide, such as LiAlO2.

[0202] Evaluation Example 4: EP-EDS

[0203] The positive electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 4 were subjected to EP-EDS analysis to calculate the ratio of the Al content (atomic %) on the surface of the secondary particles to the total content of Ni, Mn and Al (Al / (Ni+Mn+Al)) of 100 atomic %. The results are as follows: Fig.15 shown.

[0204] refer to Fig.15 , the examples show an Al content ratio of 22 atomic % to 31.3 atomic %. Compared with Comparative Example 1 fired at 825°C, Examples 1 and 2 fired at 750°C on the surface show a higher Al content on the surface. Example 3 (775°C) and Example 4 (800°C) show a much higher Al content on the surface than the Al content on the surface of Comparative Example 1. Compared with Examples 1 to 4, Comparative Examples 2 and 3, which are fired at 825°C like Comparative Example 1 but with an increased Al content of the coating, show a lower Al content on the surface of the secondary particles. In this article, even if the coating amount increases, if fired at 825°C, because Al tends to diffuse more into the secondary particles, Comparative Examples 2 and 3 show a lower Al content of the coated surface coating compared with Examples 1 to 4, and thus, the initial charge / discharge capacity and initial charge / discharge efficiency of the battery are poorer than those of Examples 1 to 4.

[0205] Evaluation Example 5: TEM and EDS Line Profile Analysis

[0206] Fig.16 A TEM image showing a cross section of a primary particle located at the outermost portion of a secondary particle in the positive electrode active material in Example 1. Fig.16 EDS line profile analysis was performed from the particle surface to the particle interior, and the results are shown in Fig.17 Reference Fig.17 , an Al-rich coating is formed on the surface of the secondary particles with a thickness of about 10 nm.

[0207] Evaluation Example 6: Evaluation of the initial charge / discharge capacity and initial charge / discharge efficiency of a battery cell, high-temperature cycle life characteristics, and high-temperature gas generation

[0208] The rechargeable lithium battery cells of Examples 1 to 4 and Comparative Examples 1 to 4 were charged to an upper voltage limit of 4.45V at a constant current of 0.2C and charged to 0.05C at a constant voltage at 25°C, and then discharged to a cutoff voltage of 3.0V at 0.2C to perform initial charging and discharging. Table 2 shows the initial charging capacity, the initial discharging capacity, and the ratio of the initial discharging capacity to the initial charging capacity as efficiency.

[0209] Subsequently, the charge and discharge cycle at 1.0 C was repeated 25 times or more at 45° C. in the voltage range of 3.0 V to 4.45 V to calculate the ratio of the 25th cycle discharge capacity to the initial discharge capacity, which is provided in Table 2 as the high temperature cycle life.

[0210] On the other hand, the rechargeable lithium battery cells of Examples 1 to 4 and Comparative Examples 1 to 4 that completed initial charging were stored at 90° C. for 4 hours, and then the amount of gas generated therefrom was measured, and the results are shown in Table 2.

[0211] Table 2

[0212]

[0213] Compared with Examples 1 to 4, Comparative Example 1 fired at 825°C exhibited poor high temperature cycle life characteristics, and the amount of gas generated by Comparative Example 1 during high temperature storage was greater than that of Examples 1 to 4. Compared with Examples 1 to 4, Comparative Example 2 fired at 825°C and with the Al coating content increased to 1.5 mol% exhibited deteriorated initial discharge capacity and high temperature cycle life characteristics, and the amount of gas generated by Comparative Example 2 was greater than that of Examples 1 to 4. Compared with Examples 1, 2, and 4, Comparative Example 3 fired at 825°C and with the Al coating content increased to 2.0 mol% exhibited deteriorated initial charge capacity, initial discharge capacity, and efficiency, and the amount of gas generated by Comparative Example 3 was greater than that of Examples 1 to 4.

[0214] Comparative Example 4 fired at 725° C. had non-reactive substances remaining on the secondary particle surfaces due to the low temperature, and exhibited a large amount of gas generated during high-temperature storage and deteriorated cycle life characteristics at high temperatures.

[0215] Examples 1 to 4 in which a high-concentration Al-rich coating with a uniform thickness is formed on the surface of the secondary particles of the positive electrode active material show improved initial charge / discharge capacity, efficiency, and high-temperature cycle life characteristics, and in addition, the amount of gas generated under high-temperature storage is reduced. On the other hand, in the examples, the capacity characteristics are more improved according to the heat treatment temperature, for example, compared with Example 3 (775°C) and Example 4 (800°C), Examples 1 and 2 in which the firing temperature is 750°C show more excellent initial charge / discharge capacity and initial charge / discharge efficiency.

[0216] Although the subject matter of the present disclosure has been described in conjunction with what are presently considered to be practical example embodiments, it should be understood that the present disclosure should not be limited to the disclosed embodiments. Instead, the present 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 layered lithium nickel manganese composite oxide, wherein the layered lithium nickel manganese composite oxide has a nickel content of greater than or equal to 60 mol % based on 100 mol % of total metals other than lithium in the layered lithium nickel manganese composite oxide, and a coating on the surface of the core particle and comprising Al, The Al content is 20 to 33 atomic % based on 100 atomic % in total of Ni, Mn and Al on the surface of the positive electrode active material.

2. The positive electrode active material according to claim 1, wherein: The Al content of the coating layer is 0.5 mol % to 1.5 mol % based on 100 mol % of total metals excluding lithium in the positive electrode active material.

3. The positive electrode active material according to claim 1, wherein: The coating is in the form of a film that continuously surrounds the surface of the core particle, wherein the coating has a thickness of 5 nm to 200 nm, A deviation in thickness of the coating layer in one of the positive electrode active material particles is less than or equal to 20%.

4. The positive electrode active material according to claim 1, wherein: The coating includes LiAlO2.

5. The positive electrode active material according to claim 1, wherein: The coating further comprises nickel, manganese or a combination thereof, Wherein in the layered lithium nickel manganese composite oxide of the core particle, the nickel content is 60 mol% to 80 mol% based on 100 mol% of total metals excluding lithium in the layered lithium nickel manganese composite oxide, and the manganese content is greater than or equal to 10 mol%.

6. The positive electrode active material according to claim 1, wherein: The layered lithium nickel manganese-based composite oxide of the core particle further includes aluminum based on 100 mol% of total metals other than lithium in the layered lithium nickel manganese-based composite oxide, and the aluminum content in the core particle is greater than 0 mol% and less than or equal to 3 mol%, The concentration of aluminum in the core particles is uniform.

7. The positive electrode active material according to claim 1, wherein: In the layered lithium nickel manganese-based composite oxide of the core particle, the cobalt content is 0 mol % to 0.01 mol % based on 100 mol % of total metals excluding lithium in the layered lithium nickel manganese-based composite oxide.

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

9. The positive electrode active material according to claim 1, wherein: The core particle is a secondary particle formed by aggregating a plurality of primary particles, and The average particle size D of the positive electrode active material 50 1μm~25μm.

10. A method for preparing a positive electrode active material, the method comprising: preparing a core particle, the core particle comprising a layered lithium nickel manganese composite oxide, the layered lithium nickel manganese composite oxide having a nickel content greater than or equal to 60 mol%, based on 100 mol% of total metals other than lithium in the layered lithium nickel manganese composite oxide; adding aluminum sulfate and the core particles to an aqueous solvent and mixing them together to prepare a mixed solution, and The aqueous solvent is removed from the mixed solution, and the resultant product is dried and heat-treated at a temperature ranging from 730° C. to 800° C. to obtain a positive electrode active material.

11. The method of claim 10, wherein: The heat treatment is performed at a temperature in the range of 750°C to 775°C.

12. The method of claim 10, wherein: In the layered lithium nickel manganese composite oxide, based on 100 mol% of total metals other than lithium in the layered lithium nickel manganese composite oxide, the nickel content is 60 mol% to 80 mol%, the manganese content is greater than or equal to 15 mol%, the aluminum content is 0 mol% to 3 mol%, and the cobalt content is 0 mol% to 0.01 mol%.

13. The method of claim 10, wherein: The aluminum sulfate may have an aluminum content of 0.5 mol % to 1.5 mol % based on the sum of 100 mol % of total metals excluding lithium in the core particles and aluminum of the aluminum sulfate.

14. The method of claim 10, wherein: After the core particles are added to the aqueous solvent and mixed, aluminum sulfate is added to prepare the mixed solution.

15. The method of claim 10, wherein: A coating solution is prepared by adding aluminum sulfate to the aqueous solvent and mixing, and then the core particles are added to the coating solution and mixed to prepare the mixed solution.

16. The method of claim 15, wherein: The time taken to add the core particles to the coating solution is 30 seconds / 500 g to 2 minutes / 500 g, The mixing time after adding the core particles to the coating solution is 15 minutes to 60 minutes, and The pH of the supernatant after mixing is 5.5 to 7.

5.

17. The method of claim 10, wherein: After removing the aqueous solvent from the mixed solution, drying the obtained product is performed at 40° C. to 240° C. under vacuum conditions.

18. A positive electrode comprising: a positive electrode current collector, and a positive electrode active material layer 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 9 or the positive electrode active material prepared by the method according to any one of claims 10 to 17.

19. The positive electrode of claim 18, wherein: The positive electrode active material layer has a 10 mg / cm 2 ~40mg / cm 2 The load level, The positive electrode active material layer has a density of 3.3 g / cc to 3.7 g / cc.

20. A rechargeable lithium battery comprising: The positive electrode according to claim 18 or 19, negative electrode, and Electrolytes, The charging voltage of the rechargeable lithium battery is greater than or equal to 4.45V.

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