Positive electrode active material for rechargeable lithium battery, method of manufacturing same, and rechargeable lithium battery including same

Abstract

The present application relates to a positive electrode active material for a rechargeable lithium battery, a method of manufacturing the same, and a rechargeable lithium battery including the same. The positive electrode active material includes a positive electrode active material including: a first particle having a first surface and a second surface and including a lithium composite oxide; and a first coating layer on the first surface. A surface area ratio of the first surface to the second surface ranges from about 3: 7 to about 8: 2. An amount of cobalt in the first coating layer is greater than an amount of cobalt of the first particles. An amount of cobalt in the first coating is in a range of about 30 at% to about 100 at% based on a total number of atoms in the first coating.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority from Korean Patent Application No. 10-2024-0027444 filed on February 26, 2024, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] Examples of the present invention relate to a positive electrode active material, a method of manufacturing the same, and a rechargeable lithium battery including the same. Background Art

[0004] When no alternating current (AC) power source is available to power a building, or when various electrical and electronic devices require direct current (DC) power, batteries are generally used that generate electrical energy through physical or chemical reactions to supply the generated electrical energy to the outside.

[0005] Among these batteries, primary and secondary batteries, which utilize chemical reactions, are commonly used. Primary batteries are typically consumable batteries, collectively known as dry cells. In contrast, secondary batteries are typically rechargeable lithium batteries, in which oxidation and reduction reactions are repeated at the positive and negative electrodes. A secondary battery charges when an electric current causes a reduction reaction at the positive electrode, and discharges when an oxidation reaction occurs at the positive electrode. Secondary batteries undergo repeated cycles of charge and discharge.

[0006] Lithium composite oxides containing high amounts of nickel have attracted considerable attention as positive electrode active materials for rechargeable lithium batteries. These positive electrode active materials have high energy density. Recently, the development of high-capacity rechargeable lithium batteries has led to the use of bimodal positive electrode active materials comprising a mixture of small and large particles having different average particle sizes. Summary of the Invention

[0007] Example embodiments of the present disclosure include positive electrode active materials for rechargeable lithium batteries having improved, advantageous, or desirable durability.

[0008] Example embodiments of the present disclosure include rechargeable lithium batteries having improved or superior charge and discharge efficiency, improved stability, and increased capacity retention.

[0009] According to an exemplary embodiment of the present invention, a positive electrode active material may include: a first particle having a first surface and a second surface, the first particle including a lithium composite oxide; and a first coating layer on the first surface. The surface area ratio of the first surface to the second surface may be in a range of approximately 3:7 to approximately 8:2. The amount of cobalt in the first coating layer may be greater than the amount of cobalt in the first particle. The amount of cobalt in the first coating layer may be in a range of approximately 30 at% to approximately 100 at% based on the total number of atoms in the first coating layer.

[0010] According to an exemplary embodiment of the present invention, a method for manufacturing a positive electrode active material may include synthesizing first particles including a first lithium composite oxide, synthesizing second particles including a second lithium composite oxide, and coating a precursor mixture on the mixture of the first and second particles. The precursor mixture may include a cobalt compound and an aluminum compound. The operation of coating the precursor mixture may be performed at a temperature of approximately 650° C. to approximately 900° C. The operation of coating the precursor mixture includes adding the cobalt compound and the aluminum compound such that the atomic molar ratio of cobalt to aluminum is within a range of 2:0.05 to 2:1.

[0011] According to example embodiments of the present invention, a rechargeable lithium battery may include the positive electrode active material discussed above. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 A simplified conceptual diagram illustrating a rechargeable lithium battery according to some embodiments of the present invention is illustrated.

[0013] Figure 2 and Figure 3 A diagram illustrating a positive electrode active material according to some embodiments of the present invention is illustrated.

[0014] Figure 4 A flow chart illustrating a method of manufacturing a positive electrode active material according to some embodiments of the present invention is illustrated.

[0015] Figure 5 and Figure 6 Explanation shows Figure 4 A simplified diagram of a method for manufacturing a positive electrode active material.

[0016] Figure 7 A simplified schematic diagram showing a rechargeable lithium battery according to some embodiments of the present invention is illustrated.

[0017] Figure 8A 、 Figure 8B and Figure 8C The results of SEM-EDS analysis of the first particles of the positive electrode active material of Comparative Example 1 are illustrated.

[0018] Figure 9A 、 Figure 9B and Figure 9C The results of SEM-EDS analysis of the first particles of the positive electrode active materials of Embodiment 1, Embodiment 2, and Embodiment 3 are respectively explained.

[0019] Figure 9D and Figure 9E The results of SEM-EDS analysis of the first particles of Example Embodiment 3 before and after the third calcination are respectively explained.

[0020] Figure 10A and Figure 10B The results of SEM-EDS analysis of the second particles of Example 3 before and after the third calcination are respectively explained. DETAILED DESCRIPTION

[0021] In order to fully understand the configuration and effects of the exemplary disclosure, some exemplary embodiments will be described with reference to the accompanying drawings. However, it should be noted that the present disclosure is not limited to the exemplary embodiments described below and can be implemented in various forms. On the contrary, the exemplary embodiments are provided only to disclose the present invention and to allow those skilled in the art to fully understand the scope of the present invention.

[0022] In this description, it will be understood that when an element is referred to as being "on" another element, the element may be directly on the other element or intervening elements may be present therebetween. In the drawings, the size (e.g., thickness) of some components is exaggerated for efficient explanation of technical content. Throughout the specification, the same reference numerals refer to the same elements.

[0023] Some example embodiments described in detail in this description will be discussed with reference to the cross-sectional views and / or plan views that are ideal exemplary views of the present invention. In the accompanying drawings, in order to effectively explain the technical content, the sizes (e.g., thickness) of the layers and regions are magnified. Accordingly, the regions exemplarily illustrated in the accompanying drawings have general characteristics, and the shapes of the regions exemplarily illustrated in the accompanying drawings are used to exemplarily disclose specific shapes, but are not used to limit the scope of the present invention. It will be understood that although the terms "first," "second," "third," etc. may be used to describe various elements in this article, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. The example embodiments explained and illustrated in this article include their complementary embodiments.

[0024] The terms used in this document are used only to describe specific embodiments and are not intended to limit the present invention. As used herein, singular forms are also intended to include plural forms. The terms "comprises / includes" and / or "comprising / including" used in the specification do not exclude the presence or addition of one or more other components.

[0025] The term "average particle size" or "D 50" may refer to the particle diameter when the volume cumulative percentage corresponds to 50% in the particle size distribution obtained from the volume of the particles. The average particle diameter can be measured by any suitable method widely used in the art, for example, by a particle size analyzer, a transmission electron microscopic image, or a scanning electron microscopic image. Alternatively, the average particle diameter can be obtained by performing measurement using a dynamic light scattering method, performing data analysis, counting the number of particles in each particle size range, and calculating the average particle diameter from the results. Unless otherwise specified, the average particle diameter (D 50 ) may refer to the diameter of particles accounting for 50% by volume of the cumulative volume in a particle size distribution. Alternatively, a particle size distribution may be obtained by measuring the size (diameter or major axis length) of about 12 particles randomly selected from a transmission electron microscope image, and then, unless otherwise specified, the diameter of particles accounting for 50% by volume of the cumulative volume in the particle size distribution may be referred to as the average particle diameter (D 50 ).

[0026] When the term "about" or "substantially" is used in conjunction with a numerical value in this specification, it means that the relevant numerical value includes a tolerance of 10% around the stated numerical value. When a range is specified, the range includes all values ​​therebetween, such as increments of 0.1%.

[0027] Figure 1 A simplified conceptual diagram illustrating a rechargeable lithium battery according to an exemplary embodiment of the present invention is illustrated. Figure 1 , a rechargeable lithium battery may include a positive electrode 100 , a negative electrode 200 , an electrolyte 300 , and a separator 400 .

[0028] The positive electrode 100 and the negative electrode 200 may be spaced apart from each other across the separator 400. The separator 400 may be disposed between the positive electrode 100 and the negative electrode 200. The positive electrode 100, the negative electrode 200, and the separator 400 may be in contact with the electrolyte 300, and the separator 400 may be immersed in the electrolyte 300.

[0029] The electrolyte 300 may be or include a medium through which lithium ions are transferred between the positive electrode 100 and the negative electrode 200. The lithium ions in the electrolyte 300 may pass through the separator 400 to move between the positive electrode 100 and the negative electrode 200.

[0030] The positive electrode 100 may include a first current collector COL1 and a positive electrode active material layer AML1 on the first current collector COL1. The first current collector COL1 may include a metal such as one or more of aluminum, copper, nickel-plated copper, stainless steel, nickel, titanium, palladium, and an aluminum-cadmium alloy. The first current collector COL1 may be shaped like a film, sheet, foil, mesh, net, porous material, foam, or non-woven fabric.

[0031] The positive electrode active material layer AML1 may include a binder, a conductive material, and a positive electrode active material. Based on the total amount of the positive electrode active material layer AML1, the amount of the positive electrode active material included may be about 80 wt % to about 99 wt %, for example, about 85 wt % to about 98 wt %. The positive electrode active material may be or include a lithium ion source. The positive electrode active material may be or include a lithium transition metal oxide, which may include not only lithium but also at least one transition metal. Figure 2 A positive electrode active material according to an example embodiment of the present invention is described in detail.

[0032] The conductive material of the positive electrode active material layer AML1 can provide electrical conductivity to the positive electrode active material layer AML1. The conductive material can include carbon materials (e.g., graphite, carbon black, acetylene black, Ketjen black, furnace black, lamp black, thermal black, and carbon fiber), metal powder, metal fiber, conductive whiskers, conductive metal oxides, conductive polymers, or any combination thereof. The conductive material can be included in an amount of approximately 1 wt% to approximately 30 wt% based on the total weight of the positive electrode active material layer AML1.

[0033] The binder of the positive electrode active material layer AML1 can enhance the adhesion between the positive electrode active material and the first current collector COL1. For example, the binder can include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer copolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or any combination thereof. The binder can be included in an amount of approximately 1 wt% to approximately 30 wt% based on the total weight of the positive electrode active material layer AML1.

[0034] The negative electrode 200 may include a second current collector COL2 and a negative electrode active material layer AML2 on the second current collector COL2. The description of the second current collector COL2 may be the same as or similar to the above description of the first current collector COL1. The second current collector COL2 may include a metal that is the same as or different from the metal of the first current collector COL1. The second current collector COL2 may have a shape that is the same as or different from the shape of the first current collector COL1.

[0035] The negative electrode active material layer AML2 may include a binder, a conductive material, and a negative electrode active material. The binder and the conductive material may be the same as the binder and the conductive material discussed above in the positive electrode active material layer AML1. Based on the total weight of the negative electrode active material layer AML2, the amount of the negative electrode active material included may be about 80 wt% to about 99 wt%, for example, about 85 wt% to about 98 wt%. The negative electrode active material may include at least one of a carbonaceous material, lithium metal, a lithium metal compound, silicon, a silicon compound, tin, and a tin compound. Metal oxides (such as TiO2) having a potential less than about 2 V may be used. x , 0<x≤2 (for example, TiO2) or SnO y , 0<y≤2 (for example, SnO2)) can also be used as a negative electrode active material. The carbonaceous material may include one or more of low crystalline carbon and high crystalline carbon.

[0036] The separator 400 may include a porous polymer film formed from or including a polyolefin polymer (such as at least one of an ethylene homopolymer, a propylene homopolymer, an ethylene-butene copolymer, an ethylene-hexene copolymer, and an ethylene-methacrylate copolymer). The separator 400 may include a porous polymer film of a single substance or a stack of multiple porous polymer films. In an exemplary embodiment of the present invention, the separator 400 may include a common porous nonwoven fabric (such as, for example, high-melting-point glass fiber or polyethylene terephthalate fiber).

[0037] The electrolyte 300 may include + B - A + may include at least one alkali metal cation (such as Li + 、Na + and K + At least one of B - may include at least one anion (such as F - 、Cl - Br - , I - 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - 、AlO4 - 、AlCl4 - PF6 - 、SbF6 - 、AsF6 - 、BF2C2O4 - BC4O8 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2- 、(CF3)5PF - 、(CF3)6P - CF3SO3 - 、C4F9SO3 - CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N - CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2 - 、SCN - and (CF3CF2SO2)2N - at least one of ).

[0038] In an exemplary embodiment of the present invention, the electrolyte 300 may include an organic solvent. The organic solvent may include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), γ-butyrolactone, or any mixture thereof.

[0039] The outer shell of the rechargeable lithium battery according to the exemplary embodiment of the present invention can be a commonly used outer shell in the art, and there is no limitation on the appearance according to the use of the battery. For example, the outer shell of the rechargeable lithium battery can have a cylindrical shape, a prismatic shape, a pouch shape, or a coin shape.

[0040] Figure 2 A diagram illustrating a positive electrode active material according to an exemplary embodiment of the present invention is illustrated. Figure 2 CAM, the positive electrode active material, can be used in the above reference Figure 1 The positive electrode active material layer AML1 discussed above is provided in the form of a powder. The positive electrode active material CAM may include a plurality of first particles PTC1, a plurality of second particles PTC2, and a plurality of aggregates ZAG.

[0041] The first particles PTC1 may have a first average particle size APD1, and the second particles PTC2 may have a second average particle size APD2. The first average particle size APD1 may be smaller than the second average particle size APD2. For example, the first average particle size APD1 may be in a range of about 1.0 μm to about 5.0 μm. The second average particle size APD2 may be in a range of about 10.0 μm to about 25.0 μm. In example embodiments, the first particles PTC1 may be referred to herein as small particles, and the second particles PTC2 may be referred to herein as large particles.

[0042] The first and second particles PTC1 and PTC2 may have a granular shape, for example, a polyhedral shape, a spherical shape, an ellipsoidal shape, a plate shape, a rod shape, or an irregular shape. For example, the first and second particles PTC1 and PTC2 may have a polyhedral shape.

[0043] In an exemplary embodiment of the present invention, the shape of the first particle PTC1 may resemble a single particle. In this description, the term "single particle" may refer to a single particle existing alone, with no grain boundaries within the particle, and a monolithic structure in which the particles are not aggregated but exist as independent phases in morphology, thus being represented as a single crystal particle. Alternatively, the single particle may be a particle comprising several crystals. The single particle may be provided in a single, isolated form, or may comprise, for example, fewer than ten individual particles bonded to one another.

[0044] The particle size distribution curve of the positive electrode active material CAM according to the exemplary embodiment of the present invention, which includes small particles (e.g., PTC1) and large particles (e.g., PTC2) having different average particle sizes, may have a bimodal shape. The small particles PTC1 may fill the pores between the large particles PTC2, so the positive electrode active material CAM may have an increased overall density. For example, the positive electrode active material CAM according to the exemplary embodiment of the present invention may have a relatively high energy density per unit volume.

[0045] In an example embodiment, the first PTC1 particles and the second PTC2 particles in the positive electrode active material CAM may have a weight ratio of about 5:95 to about 50:50. In another example embodiment, the first PTC1 particles and the second PTC2 particles in the positive electrode active material CAM may have a weight ratio of about 95:5 to about 50:50. For example, in the positive electrode active material CAM, the weight of the second PTC2 particles may be greater than the weight of the first PTC1 particles.

[0046] Agglomerates ZAG may be included in the space between the first particles PTC1 and the second particles PTC2. Agglomerates ZAG may be derived from a coating agent (i.e., a precursor mixture) to be discussed below. Agglomerates ZAG may include at least one of cobalt (Co) and aluminum (Al). For example, agglomerates ZAG may be or include clusters formed by agglomerating portions of the coating agent that are not coated on the surfaces of the first particles PTC1 and the second particles PTC2. In example embodiments of the present invention, agglomerates ZAG may be omitted.

[0047] Figure 3 A simplified diagram showing a positive electrode active material according to an example embodiment of the present invention is illustrated.

[0048] refer to Figure 3 , the positive electrode active material CAM according to an example embodiment of the present invention may include first particles PTC1 and a first coating layer CTL1.

[0049] The first particle PTC1 may include, for example, a lithium composite oxide. The lithium composite oxide may include, for example, nickel (Ni). There is no limit on the amount of nickel (Ni) in the lithium composite oxide. The amount of nickel (Ni) in the lithium composite oxide may be defined as the molar ratio of nickel relative to the total molar number of metals other than lithium in the lithium composite oxide. The lithium composite oxide may further include at least one of cobalt (Co), aluminum (Al), manganese (Mn), sodium (Na), magnesium (Mg), calcium (Ca), yttrium (Y), titanium (Ti), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), iron (Fe), copper (Cu), silver (Ag), zinc (Zn), boron (B), gallium (Ga), carbon (C), silicon (Si), and tin (Sn). For example, the lithium composite oxide may include cobalt (Co). For example, the lithium composite oxide may include cobalt (Co) and manganese (Mn). For example, the lithium composite oxide may further include a small amount of aluminum (Al).

[0050] In an exemplary embodiment of the present invention, the first particle PTC1 may include a high-nickel lithium composite oxide. For example, the high-nickel lithium composite oxide may be or include a layered lithium composite oxide in which the amount of nickel (Ni) is equal to or greater than 60 mol%, where 60 mol% is based on the total moles of metals other than lithium in the layered lithium composite oxide.

[0051] For example, the first particle PTC1 may include a first lithium composite oxide. The first lithium composite oxide may be represented by the following Chemical Formula 1.

[0052] [Chemical Formula 1]

[0053] Li a1 Ni x1 Ma 1-x1 Ob1

[0054] In Chemical Formula 1, a1 may be approximately 0.5 to 1.5, x1 may be approximately 0.6 to 0.99, b1 may be approximately 1.8 to 2.2, 1-x1 may be approximately 0.01 to 0.4, and Ma may include at least one of Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, and Sn. In example embodiments, Ma may include at least one of Co, Al, and Mn.

[0055] In an example embodiment of the present invention, the molar ratio of x1 or Ni in Chemical Formula 1 may be greater than about 0.8 based on the total molar number of metals other than lithium in the first lithium composite oxide. When the first lithium composite oxide has a composition with a high amount of Ni (e.g., x1>0.8), the first lithium composite oxide can be calcined at a relatively low temperature. The Ni in the first lithium composite oxide may affect the power and capacity of the rechargeable lithium battery. In an example of the present disclosure, the first lithium composite oxide having a composition with a high nickel content can be used to provide a high-power rechargeable lithium battery.

[0056] In another example embodiment of the present invention, the first particle PTC1 may have a nickel (Ni) amount of less than about 60 mol %, wherein 60 mol % is based on the total moles of metals excluding lithium of the first particle PTC1.

[0057] For example, the first lithium composite oxide may be represented by the following Chemical Formula 1-1.

[0058] [Chemical Formula 1-1]

[0059] Li a1 Ni x1 Ma 1-x1 O b1

[0060] In Chemical Formula 1-1, a1 may be approximately 0.5 to 1.5, x1 may be approximately 0.01 to less than 0.6, b1 may be approximately 1.8 to 2.2, 1-x1 may be greater than approximately 0.4 to 0.99, and Ma may include at least one of Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, and Sn. In example embodiments, Ma may include at least one of Co, Al, and Mn.

[0061] According to an example embodiment of the present invention, the first PTC1 particle may be crystalline, for example, a single crystal. The first PTC1 particle may have a single crystal direction. The first PTC1 particle may be composed of or include regularly arranged atoms constituting the particle. The crystal structure may have a repeating unit cell. The unit cell may have axis vectors (a-axis, b-axis, and c-axis). The c-axis may be the direction of movement of lithium ions.

[0062] The first particle PTC1 may have a first surface S1 and a second surface S2. The first surface S1 may be a surface through which the c-axis passes. The first surface S1 may be a surface through which lithium ions enter or escape from the first particle PTC1.

[0063] The first coating layer CTL1 may be formed on the first surface S1. The first coating layer CTL1 may be formed on a portion of the surface of the first particle PTC1. The first coating layer CTL1 may have an island shape. The first coating layer CTL1 may not be detectable by electron microscope images. The first coating layer CTL1 may be detectable by a certain amount of cobalt (Co) on the surface of the first particle PTC1, as analyzed by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS).

[0064] The amount of cobalt (Co) in the first coating layer CTL1 may be greater than the amount of cobalt (Co) in the first particles PTC1. In example embodiments, the amount of cobalt (Co) in the first coating layer CTL1 may be approximately 30 at% to approximately 100 at% based on the total number of atoms in the first coating layer CTL1, and the amount of cobalt (Co) in the first particles PTC1 may be less than approximately 30 at% based on the total number of atoms in the first particles PTC1. For example, the amount of cobalt (Co) in the first coating layer CTL1 may be approximately 30 at% to approximately 99.95 at% based on the total number of atoms in the first coating layer CTL1, and the amount of cobalt (Co) in the first particles PTC1 may be approximately 2 at% to approximately 15 at% based on the total number of atoms in the first particles PTC1.

[0065] The first coating layer CTL1 may have an unevenly structured surface. The surface roughness of the first coating layer CTL1 may be greater than the surface roughness of the second surface S2. The unevenly structured surface of the first coating layer CTL1 may increase the surface area of ​​the positive electrode active material CAM. Therefore, the charge / discharge efficiency of the battery may be increased.

[0066] The amount of nickel (Ni) in the first coating layer CTL1 may be less than the amount of nickel (Ni) in the first particle PTC1. The ratio of the amount of Ni in the first coating layer CTL1 to the amount of Ni and Co in the first coating layer CTL1 may be less than the ratio of the amount of Ni in the first lithium composite oxide to the amount of Ni and Co in the first lithium composite oxide. For example, the ratio of the amount of Ni in the first coating layer CTL1 to the amount of Ni and Co in the first coating layer CTL1 may be in the range of approximately 0% to approximately 60%, or approximately 40% to approximately 60%. The ratio of the amount of Ni in the first lithium composite oxide to the amount of Ni and Co in the first lithium composite oxide may be in the range of approximately 60% to approximately 99%, or approximately 80% to approximately 98%. When the ratio of the amount of Ni in the first coating layer CTL1 and the first lithium composite oxide to the amount of Ni and Co meets the above range, desired life characteristics can be achieved.

[0067] The first coating layer CTL1 may further include aluminum (Al). According to an exemplary embodiment of the present invention, in the first coating layer CTL1, cobalt (Co) sites determined by EDS mapping analysis may overlap with aluminum (Al) sites determined by EDS mapping analysis. For example, the first coating layer CTL1 may have a uniform composition of cobalt (Co) and aluminum (Al). The aluminum (Al) in the first coating layer CTL1 may increase battery life while maintaining battery capacity.

[0068] The atomic molar ratio of cobalt (Co) to aluminum (Al) in the first coating layer CTL1 may be, for example, in the range of about 2:0.05 to about 2:1 or about 2:0.1 to about 2:0.3. When the atomic molar ratio of cobalt (Co) to aluminum (Al) in the first coating layer CTL1 satisfies any of the above ranges, a battery including the positive electrode active material CAM can maintain its capacity and increase its lifespan without increasing the resistance of the battery including the positive electrode active material CAM.

[0069] The second surface S2 may be a surface of the first particle PTC1 other than the first surface S1. The first coating layer CTL1 may not be formed on the second surface S2. The amount of at least one of cobalt (Co), nickel (Ni), and aluminum (Al) in the second surface S2 may be within a range that deviates from the above-described ranges of the amount of cobalt (Co), nickel (Ni), and aluminum (Al) in the first coating layer CTL1. In another embodiment, the content of cobalt (Co), nickel (Ni), and aluminum (Al) in the second surface S2 may be substantially the same as or similar to the content of cobalt (Co), nickel (Ni), and aluminum (Al) in the first particle PTC1.

[0070] The ratio of the amount of Ni in the second surface S2 to the amount of Ni and Co in the second surface S2 may be in the range of about 60% to about 99% or about 80% to about 98%. When the ratio of the amount of Ni in the second surface S2 to the amount of Ni and Co in the second surface S2 satisfies any of the above ranges, desired life characteristics can be achieved.

[0071] The surface area ratio of the first surface S1 to the second surface S2 may be within a range of approximately 3:7 to approximately 8:2. The first coating layer CTL1 may be specified by the amount of each or at least one of cobalt (Co), nickel (Ni), and aluminum (Al) measured from the results of SEM-EDS. Thus, the region of each or at least one of the first surface S1 on which the first coating layer CTL1 is formed and the second surface S2 on which the first coating layer CTL1 is not formed may be specified. Each of the first surface S1 and the second surface S2 may refer to a region extending approximately 300 nm inward from the outermost surface of the first particle PTC1. The surface area ratio of the first surface S1 to the second surface S2 may be calculated as the ratio of the area of ​​the specified first surface S1 to the area of ​​the specified second surface S2. When the surface area ratio of the first surface S1 to the second surface S2 satisfies the above range, collapse of the positive electrode active material CAM may be reduced or prevented, and desired lifespan characteristics may be achieved.

[0072] The positive electrode active material CAM according to the example embodiment of the present invention may further include second particles PTC2 and a second coating layer CTL2.

[0073] As discussed above, the average particle size of the second particles PTC2 may be larger than the average particle size of the first particles PTC1.

[0074] The second particle PTC2 may have a shape similar to that of a secondary particle in which a plurality of primary particles are aggregated.

[0075] The second particles PTC2 may be or include polycrystalline particles. The second particles PTC2 may be or include an aggregation of a plurality of single-crystal particles.

[0076] The second particle PTC2 may include a lithium composite oxide. In example embodiments, the lithium composite oxide may include nickel (Ni). There may be no limitation on the amount of nickel (Ni) in the lithium composite oxide. The amount of nickel (Ni) in the lithium composite oxide may refer to the molar ratio of nickel in the lithium composite oxide relative to the total molar number of metals other than lithium in the lithium composite oxide. The lithium composite oxide may further include at least one of cobalt (Co), aluminum (Al), manganese (Mn), sodium (Na), magnesium (Mg), calcium (Ca), yttrium (Y), titanium (Ti), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), iron (Fe), copper (Cu), silver (Ag), zinc (Zn), boron (B), gallium (Ga), carbon (C), silicon (Si), and tin (Sn). For example, the lithium composite oxide may include cobalt (Co). For example, the lithium composite oxide may include cobalt (Co) and manganese (Mn). For example, the lithium composite oxide may further include a small amount of aluminum (Al).

[0077] In an exemplary embodiment of the present invention, the second particle PTC2 may include a high-nickel lithium composite oxide. For example, the high-nickel lithium composite oxide may be or include a layered lithium composite oxide in which the amount of nickel (Ni) is equal to or greater than 60 mol%, where 60 mol% is based on the total moles of metals other than lithium in the layered lithium composite oxide.

[0078] For example, the second particles PTC2 may include a second lithium composite oxide. The second lithium composite oxide may be represented by the following Chemical Formula 2.

[0079] [Chemical Formula 2]

[0080] Li a2 Ni x2 Mb 1-x2 O b2

[0081] In Chemical Formula 2, a2 ​​may be approximately 0.5 to 1.5, x2 may be approximately 0.6 to 0.99, b2 may be approximately 1.8 to 2.2, and 1-x2 may be approximately 0.01 to 0.4. Mb may include at least one of Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, and Sn. In example embodiments, Mb may include at least one of Co, Al, and Mn. In the present invention, transition metals and post-transition metals such as Al may be included.

[0082] In an exemplary embodiment of the present invention, the molar ratio of x2 or Ni may also be greater than about 0.8 based on the total moles of metals other than lithium in the second lithium composite oxide. However, x2 may be different from x1 discussed above.

[0083] The composition ratio of the elements included in Mb and Mb of the second lithium composite oxide may be different from the composition ratio of the elements included in Ma and Ma of the first lithium composite oxide. For example, Mb of the second lithium composite oxide may include Co and Al, while Ma of the first lithium composite oxide may include Co and Mn. For another example, each or one or more of Ma and Mb may include Co, Al, and Mn. The composition ratio of Al in Mb may be greater than the composition ratio of Al in Ma, and the composition ratio of Mn in Mb may be less than the composition ratio of Mn in Ma.

[0084] In addition to Ni, the first and second lithium composite oxides may further include Co. The first and second lithium composite oxides may also further include Al. Therefore, the rechargeable lithium battery may improve stability and capacity retention characteristics.

[0085] In another example embodiment of the present invention, the amount of nickel (Ni) of the second particle PTC2 may be less than about 60 mol %, wherein 60 mol % is based on the total moles of metals excluding lithium in the second particle PTC2.

[0086] For example, the second lithium composite oxide may be represented by the following Chemical Formula 2-1.

[0087] [Chemical Formula 2-1]

[0088] Li a2 Ni x2 Mb 1-x2 O b2

[0089] In Chemical Formula 2-1, a2 may be approximately 0.5 to 1.5, x2 may be approximately 0.01 to less than 0.6, b2 may be approximately 1.8 to 2.2, 1-x2 may be greater than approximately 0.4 to 0.99, and Mb may include at least one of Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, and Sn. In example embodiments, Mb may include Co, Al, and Mn.

[0090] The second coating layer CTL2 may be formed on the surface of the second PTC2 particle. The second coating layer CTL2 may be formed on the entire surface of the second PTC2 particle. The second coating layer CTL2 may uniformly or non-uniformly cover the surface of the second PTC2 particle. When the second coating layer CTL2 non-uniformly covers the surface of the second PTC2 particle, the second coating layer CTL2 may have an island shape. The second coating layer CTL2 may not be identified by electron microscope images. The second coating layer CTL2 may be identified by the presence of cobalt (Co) analyzed by SEM-EDS.

[0091] The amount of cobalt (Co) in the second coating layer CTL2 may be greater than the amount of cobalt (Co) in the second particles PTC2. In an exemplary embodiment, the amount of cobalt (Co) in the second coating layer CTL2 may be approximately 30 at% to approximately 100 at% based on the total number of atoms in the second coating layer CTL2, and the amount of cobalt (Co) in the second particles PTC2 may be less than approximately 30 at% based on the total number of atoms in the second particles PTC2. For example, the amount of cobalt (Co) in the second coating layer CTL2 may be approximately 30 at% to approximately 99.95 at% based on the total number of atoms in the second coating layer CTL2, and the amount of cobalt (Co) in the second particles PTC2 may be approximately 2 at% to approximately 15 at% based on the total number of atoms in the second particles PTC2. Similar to the first coating layer CTL1, the second coating layer CTL2 may have an unevenly structured surface.

[0092] The amount of nickel (Ni) in the second coating layer CTL2 may be less than the amount of nickel (Ni) in the second particles PTC2. For example, the ratio of the amount of Ni in the second coating layer CTL2 to the amount of Ni and Co in the second coating layer CTL2 may be less than the ratio of the amount of Ni in the second lithium composite oxide to the amount of Ni and Co in the second lithium composite oxide. For example, the ratio of the amount of Ni in the second coating layer CTL2 to the amount of Ni and Co in the second coating layer CTL2 may be in the range of about 0% to about 60%, or about 40% to about 60%. The ratio of the amount of Ni in the second lithium composite oxide to the amount of Ni and Co in the second lithium composite oxide may be in the range of about 60% to about 99%, or about 80% to about 98%. When the ratio of the amount of Ni in the second coating layer CTL2 to the amount of Ni and Co in the second lithium composite oxide meets the above range, the desired life characteristics can be achieved.

[0093] In an exemplary embodiment of the present invention, the second coating layer CTL2 may include at least one of cobalt (Co) and aluminum (Al). The atomic molar ratio of cobalt (Co) to aluminum (Al) in the second coating layer CTL2 may be, for example, in a range of about 2:0.05 to about 2:1 or about 2:0.1 to about 2:0.3. The atomic molar ratio of cobalt (Co) to aluminum (Al) in the second coating layer CTL2 may be the same as or different from the atomic molar ratio of cobalt (Co) to aluminum (Al) in the first coating layer CTL1.

[0094] The terms "amount of cobalt (C)" and "atomic molar ratio of aluminum (Al)" used herein can be obtained by analyzing the elements on the surface of the positive electrode active material (CAM) using energy dispersive X-ray spectroscopy (EDS) or scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). Elements on the surface of the positive electrode active material (CAM) that collide with an electron beam can emit characteristic X-rays. The emitted characteristic X-rays can be analyzed by an EDX detector to determine the type and amount of the corresponding element.

[0095] Figure 4 A flowchart illustrating a method of manufacturing a positive electrode active material according to some embodiments of the present invention is illustrated. Figure 5 and Figure 6 Explanation shows Figure 4 Simplified diagram of a method for manufacturing a positive electrode active material.

[0096] refer to Figure 4 and Figure 5 , a second particle PTC2 can be synthesized (S430). The method for synthesizing the second particle PTC2 will be described in detail below. First, a second precursor PRE2 can be prepared. The second precursor PRE2 may include Ni and Mb of Chemical Formula 2 discussed above. Mb may include at least one of Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, and Sn. For example, Mb may include at least one of Co, Mn, and Al.

[0097] In example embodiments, the second precursor PRE2 can be obtained by a coprecipitation method. For example, the coprecipitation method may include dissolving a metal raw material in a solvent such as distilled water to obtain a metal salt solution, and continuously supplying the metal salt solution to a reactor along with a chelating agent and an alkaline aqueous solution to produce a precipitate. The precipitate can be collected in the form of a slurry, and the slurry solution can then be filtered and dried to obtain the metal composite oxide or the second precursor PRE2.

[0098] In an example of the present invention, the raw material of the metal may include a metal salt of at least one of Ni, Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, and Sn. The metal salt may include at least one of sulfate, nitrate, acetate, halide, and hydroxide, and there is no particular limitation as long as the metal salt is soluble in the solvent. The raw material of the metal according to the example embodiment may include at least one of nickel salt, cobalt salt, and aluminum salt. The raw materials of the metal may be mixed by adjusting the molar ratio so that the positive electrode active material has high capacity characteristics. For example, the molar ratio may determine x2 of Chemical Formula 2.

[0099] The second precursor PRE2 and the lithium raw material may be mixed in a certain ratio to form a mixture. For example, the lithium in the lithium raw material and the transition metal in the second precursor PRE2 may be mixed in a molar ratio of about 1:1. The lithium raw material may be used without particular limitation as long as it is commonly used to manufacture positive electrode active materials. For example, the lithium raw material may include at least one of a lithium salt such as lithium carbonate, lithium nitrate, lithium hydroxide, and lithium sulfate.

[0100] A mixture including a second precursor PRE2 and a lithium raw material may be added to the furnace FRC, and a second calcination process STR2 may be performed at a second temperature. The second temperature may be in the range of about 700°C to about 1,000°C. For example, the second temperature may be in the range of about 700°C to about 800°C. The second calcination process STR2 may be performed in an oxidizing atmosphere such as air or oxygen. In the second calcination process STR2, the heat treatment duration may be in the range of about 10 hours to about 30 hours. In another example embodiment of the present invention, before the second calcination process STR2, a pre-calcination process may be additionally performed at about 150°C to about 800°C.

[0101] In the second calcination process STR2, the second particles PTC2 may be formed from a mixture including the second precursor PRE2 and the lithium raw material. In another exemplary embodiment of the present invention, the synthesized second particles PTC2 may be subjected to a grinding process. The ground second particles PTC2 may have Figure 2 The second average particle size APD2 discussed in.

[0102] refer to Figure 4 and Figure 6 , a first particle PTC1 can be synthesized (S410). The method for synthesizing the first particle PTC1 will be described in detail below. First, a first precursor PRE1 can be prepared. The first precursor PRE1 may include Ni and Ma in the chemical formula 1 discussed above. Ma may include at least one of Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, and Sn. For example, Ma may include at least one of Co, Mn, and Al.

[0103] In example embodiments, the first precursor PRE1 may be obtained by a method substantially the same as or similar to that used to obtain the second precursor PRE2. However, the first precursor PRE1 may be formed to have an average particle size smaller than that of the second precursor PRE2.

[0104] The first precursor PRE1 and the lithium raw material may be mixed in a desired ratio to form a mixture. For example, the lithium in the lithium raw material and the transition metal in the first precursor PRE1 may be mixed in a molar ratio of about 1:1. The mixture including the first precursor PRE1 and the lithium raw material may be added to the furnace FRC, and a first calcination process STR1 may be performed at a first temperature. The first temperature may be in a range of about 700°C to about 1,000°C. For example, the first temperature may be in a range of about 800°C to about 950°C. The first temperature may be greater than the above-mentioned temperature. Figure 5 The second temperature discussed. In the first calcination process STR1, the heat treatment duration may be in the range of about 5 hours to about 15 hours. Other descriptions of the first calcination process STR1 may be the same as or similar to those of the second calcination process STR2.

[0105] In the first calcination process STR1, the first particles PTC1 may be formed from a mixture including the first precursor PRE1 and the lithium raw material. The synthesized first particles PTC1 may be subjected to a grinding process. The ground first particles PTC1 may have Figure 2 The first average particle size APD1 discussed in.

[0106] refer to Figure 4 , the first PTC1 particle and the second PTC2 particle may be mixed with each other (S450). In an example embodiment, the first PTC1 particle and the second PTC2 particle may be mixed at a weight ratio of about 95:5 to about 50:50. In another example embodiment, the first PTC1 particle and the second PTC2 particle may be mixed at a weight ratio of about 5:95 to about 50:50. Since the first PTC1 particle is mixed with the second PTC2 particle having an average particle size different from the average particle size of the first PTC1 particle, a positive electrode active material having a particle size distribution curve having a bimodal shape may be prepared. The first PTC1 particle and the second PTC2 particle may be cleaned and dried.

[0107] Still refer to Figure 4 , a coating process may be performed on the first and second PTC particles ( PTC1 , PTC2 ) ( S470 ). The coating process may include coating surfaces of the first and second PTC particles ( PTC1 , PTC2 ) with cobalt (Co) and aluminum (Al).

[0108] For example, the first PTC1 particles and the second PTC2 particles may be mixed with a coating raw material (i.e., a precursor mixture). The coating raw material may be or include a mixture of a cobalt compound and an aluminum compound. For example, the cobalt compound may include at least one of cobalt nitrate, cobalt sulfate, and cobalt oxide, but the present invention is not particularly limited thereto. For example, the aluminum compound may include at least one of aluminum sulfate (Al2(SO4)3) and sodium metaaluminate (NaAlO2), but the present invention is not particularly limited thereto.

[0109] The first and second particles of PTC1, PTC2, and the coating raw material may be added and mixed in a solvent (e.g., distilled water). The first and second particles of PTC1, PTC2, and the coating raw material may be mixed uniformly or substantially uniformly in a blender. During this process, an alkali may be added for deposition. The alkali may include at least one of sodium hydroxide (NaOH), lithium hydroxide (LiOH), potassium hydroxide (KOH), and ammonia (NH3), but the present invention is not particularly limited thereto. Thereafter, the first and second particles of PTC1, PTC2 may be filtered and dried, and then the first and second particles of PTC1, PTC2 may be surface-treated. The surface treatment may include a heat treatment process in an oxidizing atmosphere (such as, for example, air or oxygen). The surface treatment may be performed at a temperature of about 500°C to about 800°C.

[0110] In another exemplary embodiment of the present invention, the coating process may include a dry coating process. For example, a mixture of the first and second PTC particles 1 and 2 and the coating raw material may be added and stirred in a dry coating apparatus without a solvent. The resulting dried mixture may be surface treated.

[0111] The heat treatment process can be performed in such a way that a mixture of the first particle PTC1 and the second particle PTC2 and the coating raw material are added to the furnace FRC, and a third calcination process is performed at a third temperature. The third temperature may be in the range of about 650°C to about 1,000°C. For example, the third temperature may be in the range of about 650°C to about 900°C or about 650°C to about 800°C. When the third temperature satisfies the above range, cobalt (Co) may be provided in the coating on the surface of the particle, and the desired battery cell capacity and charge / discharge efficiency may be achieved. The description of the third calcination process may be the same or similar to that of the first calcination process STR1.

[0112] Therefore, a reference according to an exemplary embodiment of the present invention can be manufactured. Figure 2 and Figure 3 The positive electrode active material CAM is discussed.

[0113] It can be manufactured by the common method of manufacturing positive electrodes Figure 1 The positive electrode 100 is formed by using the positive electrode active material CAM according to some exemplary embodiments of the present invention. For example, a binder, a conductive material, and the positive electrode active material CAM according to the exemplary embodiment may be dissolved or dispersed in a solvent to prepare a mixture. The binder and the conductive material may be mixed with the above-mentioned Figure 1 The binder and the conductive material discussed in the positive electrode active material layer AML1 are the same. The mixture may be coated on the first current collector COL1 and then may be dried and pressed to manufacture the positive electrode 100.

[0114] The solvent may be a material commonly used in the art, for example, dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, or a combination thereof.

[0115] In another example embodiment, the mixture may be cast on a desired support to prepare a film or positive electrode active material layer AML1. The positive electrode 100 may be manufactured by laminating the positive electrode active material layer AML1 on the first current collector COL1.

[0116] Figure 7 A simplified schematic diagram illustrating a rechargeable lithium battery according to some example embodiments of the present invention is illustrated. Figure 7 , a rechargeable lithium battery may include a positive electrode 100 , a negative electrode 200 , and a separator 400 . Figure 7 The description of the positive electrode 100, the negative electrode 200 and the separator 400 can be the same as that in the above Figure 1 The description is essentially the same as discussed in the rechargeable lithium battery of FIG.

[0117] Figure 7 The positive electrode 100, the negative electrode 200 and the separator 400 may be wound or folded to form an electrode assembly 700. The electrode assembly 700 may be housed in a battery case 500. The electrode assembly 700 may include a plurality of electrode assemblies. The separator 400 may be provided between the electrode assemblies. The battery case 500 may be provided with electrode assemblies stacked in sequence. The battery case 500 may be filled with an electrolyte (see Figure 1 300). The battery housing 500 may be sealed by a cap assembly 600. The battery housing 500 according to some example embodiments of the present invention may have a cylindrical shape, a prismatic shape, or a pouch shape. The rechargeable lithium battery according to some example embodiments of the present invention may be used in devices such as, for example, laptop computers, smartphones, or electric vehicles.

[0118] Herein, the present invention will be described in detail with reference to some exemplary embodiments.The following exemplary embodiments are provided for illustrative purposes only and are not to be construed as limiting the scope of the present invention.

[0119] Example Implementation 1

[0120] Preparation 1: Preparation of large particle precursor (ie, second precursor PRE2)

[0121] The coprecipitation method was used to prepare the large particle precursor. The steps described below were used to form nickel metal hydroxide (Ni 0.96 Co 0.02 Mn 0.02 (OH)2).

[0122] Nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O), raw materials for nickel-based metal hydroxides, were dissolved in distilled water as a solvent at a molar ratio of 96:2:2 to prepare a metal raw material mixture solution. A dilute aqueous ammonia (NH4OH) solution was prepared to form a complex compound, and sodium hydroxide (NaOH) was used as a precipitant. The metal raw material mixture solution, aqueous ammonia, and sodium hydroxide were then added to a reactor. Sodium hydroxide was added to the reactor to maintain the pH of the mixture in the reactor. While the mixture was stirred in the reactor, the reaction proceeded for approximately 20 hours.

[0123] The slurry solution in the reactor was filtered and rinsed with high-purity distilled water. The rinsed material was dried in a hot air oven at 750 ° C for 24 hours to obtain a large particle precursor (Ni 0.96 Co 0.02 Mn 0.02 (OH)2) powder.

[0124] Preparation 2: Preparation of small particle precursor (ie, first precursor PRE1)

[0125] The small particle precursor was prepared by coprecipitation method. The steps described below were used to form nickel metal hydroxide (Ni 0.96 Co 0.02 Mn 0.02 (OH)2).

[0126] Nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O), raw materials for nickel-based metal hydroxide, were dissolved in distilled water as a solvent at a molar ratio of 96:2:2 to prepare a metal raw material mixture solution. The metal raw material mixture solution, aqueous ammonia, and sodium hydroxide were added to a reactor and reacted.

[0127] The slurry solution in the reactor was filtered and rinsed with high-purity distilled water. The rinsed material was dried in a hot air oven at 210°C for 24 hours to obtain a small particle precursor (Ni 0.96 Co 0.02 Mn 0.02 (OH)2) powder.

[0128] Preparation 3: Preparation of large-particle lithium composite oxide (ie, second lithium composite oxide)

[0129] The large particle precursor of Preparation 1 and anhydrous lithium hydroxide (LiOH) were dry-mixed using a Henschel mixer. Lithium and transition metals were mixed in a molar ratio of approximately 1:1. The transition metals were the sum of the transition metals contained in the large particle precursor (Ni + Co + Mn). The mixture was heat-treated in an oxygen atmosphere at approximately 750°C for 15 hours (or a second calcination process) to synthesize second particles as a second lithium composite oxide. The second particles were ground using a jet mill at a pressure of 3 bar.

[0130] Preparation 4: Preparation of small-particle lithium composite oxide (ie, first lithium composite oxide)

[0131] The small particle precursor of Preparation 2 and anhydrous lithium hydroxide (LiOH) were dry-mixed using a Henschel mixer. Lithium and transition metal were mixed in a molar ratio of approximately 1:1. The transition metal was the sum of the transition metals included in the small particle precursor (Ni + Co + Mn). The mixture was heat-treated in an oxygen atmosphere at approximately 910° C. for 15 hours (or a first calcination process) to synthesize first particles as a first lithium composite oxide. The first particles were ground using a jet mill at a pressure of 3 bar.

[0132] Preparation 5: Preparation of bimodal particles

[0133] The second particles (Preparation 3) having an average particle size of 18 μm and the first particles (Preparation 4) having an average particle size of 3 μm were mixed in a weight ratio of 70:30 to prepare bimodal particles. The bimodal particles were added and rinsed with distilled water. A precursor mixture was mixed with the bimodal particles to perform a cobalt and aluminum coating process. The precursor mixture was formed by a solution comprising a cobalt compound and a sodium hydroxide solution comprising an aluminum compound. The precursor mixture included cobalt sulfate (CoSO4·7H2O) and aluminum sulfate (Al2(SO4)3) such that the molar amount of cobalt was 2 mol% and the molar amount of aluminum was 0.1 mol% relative to the total amount of transition metals of the bimodal particles. Table 1 below lists the amount of cobalt atoms and the amount of aluminum atoms. Thereafter, the solution was filtered and dried, and then 5 mol% lithium hydroxide (LiOH) was mixed with the solution. About 2 mol% lithium hydroxide was added for cobalt (Co) coating. The mixture was heat-treated in an oxygen atmosphere at about 700° C. for 15 hours (or a third calcination process) to perform coating of cobalt (Co) and aluminum (Al). Thus, the positive electrode active material according to the present embodiment was obtained.

[0134] Preparation 6: Fabrication of Rechargeable Lithium Batteries

[0135] 96 g of the positive electrode active material of Preparation 5, 2 g of polyvinylidene fluoride, 47 g of N-methylpyrrolidone as a solvent, and 2 g of carbon black as a conductive material were mixed to prepare a positive electrode active material slurry.

[0136] A positive electrode active material slurry was applied to aluminum foil using a doctor blade to form a thin electrode plate. The thin electrode plate was dried at 135°C for 3 hours or longer, then pressed and vacuum-dried to produce a positive electrode.

[0137] A 2032-inch coin cell was fabricated using a positive electrode and a lithium metal counter electrode. A separator (approximately 16 μm thick) formed of a porous polyethylene (PE) film was inserted between the positive electrode and the lithium metal counter electrode. An electrolyte was introduced to fabricate the 2032-inch coin cell. The electrolyte was a solution of 1.1 M LiPF₆ dissolved in a solvent comprising ethylene carbonate (EC) and ethyl methyl carbonate (EMC) mixed in a volume ratio of 3:5.

[0138] Example Implementation 2

[0139] A rechargeable lithium battery was manufactured by substantially the same method as Example Embodiment 1, except that aluminum sulfate (Al2(SO4)3) was added in Preparation 5 so that the molar amount of aluminum was 0.5 mol% relative to the total amount of transition metals of the bimodal particles.

[0140] Example Implementation 3

[0141] A rechargeable lithium battery was manufactured by substantially the same method as Example Embodiment 1, except that aluminum sulfate (Al2(SO4)3) was added in Preparation 5 so that the molar amount of aluminum was 1.0 mol% relative to the total amount of transition metals of the bimodal particles.

[0142] Comparative Example 1

[0143] A rechargeable lithium battery was manufactured by substantially the same method as that of Example Embodiment 1, except that aluminum sulfate (Al 2 (SO 4 ) 3 ) was not added in Preparation 5.

[0144] Comparative Example 2

[0145] A rechargeable lithium battery was manufactured by substantially the same method as in Example Implementation 1, except that in Preparation 5, instead of adding cobalt sulfate, about 3 mol % of lithium hydroxide was added and aluminum sulfate (Al2(SO4)3) was added so that the molar amount of aluminum was 0.5 mol % relative to the total amount of transition metals of the bimodal particles.

[0146] Comparative Example 3

[0147] A rechargeable lithium battery was manufactured by substantially the same method as Example Embodiment 1, except that in Preparation 5, neither cobalt sulfate nor aluminum sulfate was added, and about 3 mol % of lithium hydroxide was added.

[0148] Comparative Example 4

[0149] A rechargeable lithium battery was manufactured by substantially the same method as Example Embodiment 1, except that aluminum sulfate (Al2(SO4)3) was additionally added in Preparation 5 so that the molar amount of aluminum was 2 mol% relative to the total amount of transition metals of the bimodal particles.

[0150] [Table 1]

[0151] category Amount of Co (mol%) Amount of Al (mol%) Example Implementation 1 2 0.1 Example Implementation 2 2 0.5 Example Implementation 3 2 1.0 Comparative Example 1 2 0 Comparative Example 2 0 0.5 Comparative Example 3 0 0 Comparative Example 4 2 2

[0152] Experimental Example 1: Structure and Elemental Analysis (SEM-EDS) of Positive Electrode Active Material

[0153] The positive electrode active material produced in Example 1 was photographed using a scanning electron microscope (SEM) for energy dispersive X-ray spectroscopy (EDS). The elements on the surface of the first particle PTC1 (small particle) were analyzed, and the elements on the surface of the second particle PTC2 (large particle) were analyzed. Herein, Example 1, Example 2, and Example 3 may be referred to as Example 1, Example 2, and Example 3, respectively. The positive electrode active materials produced in Examples 2 and 3, as well as Comparative Example 1, were analyzed using SEM-EDS under the same conditions.

[0154] The results are Figures 8A to 8C 、 Figures 9A to 9E and Figures 10A and 10B Shown in. Figures 8A to 8C The SEM-EDS results of the first particle PTC1 in Comparative Example 1 are shown. Figure 9A 、 Figure 9B and Figure 9C SEM-EDS results of the first particles PTC1 in Embodiment 1, Embodiment 2, and Embodiment 3 are shown respectively. Figure 9D and Figure 9E SEM-EDS results of the first particles PTC1 in Example 3 before and after the third calcination are respectively shown. Figure 10A and Figure 10B SEM-EDS results of the second particles PTC2 in Example 3 before and after the third calcination are respectively shown.

[0155] refer to Figure 8A 、 Figure 8B and Figure 8C , it was determined that the first coating layer CTL1 was formed on a portion of the surface of the first particle PTC1 of Comparative Example 1, or on the first surface S1 of the first particle PTC1. It was found that the first coating layer CTL1 of Comparative Example 1 included cobalt (Co), and the amount of cobalt in the first coating layer CTL1 was greater than the amount of cobalt in the first particle PTC1.

[0156] refer to Figure 9A 、 Figure 9B and Figure 9C , it can be determined that the first coating layer CTL1 is formed on a portion of the surface of the first particle PTC1 of Embodiments 1 to 3, or is formed on the first surface S1 of the first particle PTC1. Figure 9D and Figure 9E The first coating layer CTL1 includes cobalt (Co) and aluminum (Al). In Embodiments 1, 2, and 3, the atomic molar ratios of cobalt (Co) and aluminum (Al) are 2:0.1, 2:0.5, and 2:1.0, respectively. Cobalt (Co) and aluminum (Al) are present in the same location. After the third calcination, the first coating layer CTL1 includes an unevenly structured portion. Cobalt (Co) and aluminum (Al) are distributed in the unevenly structured portion.

[0157] refer to Figure 10A and Figure 10B It can be determined that in Example 3, the second coating layer CTL2 is formed to cover the surface of the second particles PTC2. Cobalt (Co) and aluminum (Al) are included in the second coating layer CTL2. In Example 1, Example 2, and Example 3, the atomic molar ratios of cobalt (Co) and aluminum (Al) are 2:0.1, 2:0.5, and 2:1.0, respectively. Cobalt (Co) and aluminum (Al) are present in the same position. After the third calcination, the second coating layer CTL2 includes an unevenly structured portion. Cobalt (Co) and aluminum (Al) are distributed in the unevenly structured portion.

[0158] Experimental Example 2: Battery Cell Performance and Lifespan Characteristics of Rechargeable Lithium Batteries

[0159] The charge / discharge efficiency and capacity retention rate of the coin cells of Example Embodiments 1 to 3 and Comparative Examples 1 to 4 were evaluated using a charge / discharge test system (manufacturer: TOYO, model: TOYO-3100).

[0160] At 45°C, each of the coin cell batteries was charged at a constant current of 0.2C until the voltage reached 4.3V, and then charged at a constant voltage until the current reached 0.05C to measure the charge capacity; after a pause of about 10 minutes, the fully charged battery cell was discharged at a constant current of 0.2C until the voltage reached 3V to measure the discharge capacity; and this cycle was repeated 50 times.

[0161] Table 2 lists the charge / discharge efficiency and capacity retention of the coin cell batteries in Embodiments 1 to 3 and Comparative Examples 1 to 4. The charge / discharge efficiency is calculated as follows: "Charge / discharge efficiency = discharge capacity after the first cycle / charge capacity after the first cycle." The capacity retention after the 50th cycle is calculated as follows: "Capacity retention after the 50th cycle = discharge capacity after the 50th cycle / discharge capacity after the first cycle."

[0162] [Table 2]

[0163]

[0164]

[0165] Referring to Table 1, the coin cells of Example Embodiments 1 to 3 exhibited improved, favorable, or desirable charge / discharge efficiency and capacity retention. The charge and discharge capacities of the coin cells of Example Embodiments 1 to 3 were greater than those of the coin cells of Comparative Examples 1 to 4. It was confirmed that the charge capacity of the coin cell of Comparative Example 4 was less than that of the coin cells of Example Embodiments 1 to 3. Therefore, it can be understood that when the amount of Al deviates from the above range, the resistance of the positive electrode active material becomes higher.

[0166] It was also confirmed that the capacity retention rate of the coin cell cells of Example Embodiments 1 to 3 was greater than the capacity retention rate of the coin cell cells of Comparative Examples 1 to 4. Therefore, it is estimated that the positive electrode active materials of Examples 1 to 3 have improved, favorable, or desired durability, and the coin cell cells of Example Embodiments 1 to 3 exhibit more excellent stability.

[0167] In the positive electrode active material for a rechargeable lithium battery according to an example embodiment, the first particle, which is a small particle, may include cobalt (Co) and aluminum (Al) on a portion of its surface. Therefore, the positive electrode active material of the present invention can exhibit improved, favorable, or desired durability. A rechargeable lithium battery using the positive electrode active material of the example embodiment can improve discharge efficiency / discharge efficiency and capacity retention.

[0168] Although some exemplary embodiments of the present invention have been discussed with reference to the accompanying drawings, it will be understood that various changes in form and detail may be made thereto without departing from the spirit and scope of the exemplary embodiments. Therefore, it will be understood that the above exemplary embodiments are only illustrative and not restrictive in all aspects.

Claims

1. A positive electrode active material comprising: a first particle having a first surface and a second surface, the first particle comprising a lithium composite oxide; as well as a first coating, on said first surface, wherein the surface area ratio of the first surface to the second surface is in the range of 3:7 to 8:2, wherein the amount of cobalt in the first coating is greater than the amount of cobalt in the first particle, wherein the amount of cobalt in the first coating layer is in the range of 30 at % to 100 at % based on the total number of atoms in the first coating layer, and The positive electrode active material is used in a rechargeable lithium battery. 2 . The positive electrode active material of claim 1 , wherein the first coating layer further comprises aluminum. 3 . The positive electrode active material according to claim 2 , wherein the atomic molar ratio of cobalt to aluminum in the first coating layer is in the range of 2:0.05 to 2:

1. The positive electrode active material according to claim 1 , wherein the first particles are single crystals. 5 . The positive electrode active material according to claim 1 , wherein the average particle size of the first particles is in the range of 1 μm to 5 μm.

6. The positive electrode active material of claim 1, wherein the first particle comprises a first lithium composite oxide represented by Chemical Formula 1, Chemical formula 1 Li a1 Ni x1 Ma 1-x1 O b1 Wherein in Chemical Formula 1: a1 is 0.5~1.5, x1 is 0.6 to 0.99, b1 is 1.8 to 2.2, and Ma includes Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, At least one of W, Fe, Cu, Ag, Zn, B, Ga, C, Si and Sn.

7. The positive electrode active material according to claim 1, further comprising: Second particle; and a second coating on the surface of the second particle, The average particle size of the second particles is greater than the average particle size of the first particles. 8 . The positive electrode active material according to claim 7 , wherein the average particle size of the second particles is in the range of 10 μm to 25 μm. 9 . The positive electrode active material according to claim 7 , wherein the second particle is a secondary particle in which a plurality of primary particles are aggregated. 10 . The positive electrode active material according to claim 7 , wherein the second particles are polycrystalline.

11. The positive electrode active material of claim 7, wherein the amount of cobalt in the second coating layer is greater than the amount of cobalt in the second particles, Wherein the amount of cobalt in the second coating layer is in a range of 30 at % to 100 at % based on the total number of atoms in the second coating layer.

12. The positive electrode active material of claim 7, wherein the second coating layer comprises at least one of cobalt and aluminum, The atomic molar ratio of cobalt to aluminum in the second coating layer is in the range of 2:0.05 to 2:

1. 13 . The positive electrode active material of claim 7 , wherein the second coating layer is formed on the entire surface of the second particle.

14. The positive electrode active material of claim 7, wherein the second particle comprises a second lithium composite oxide represented by Chemical Formula 2, Chemical formula 2 Yes a2 In x2 Yes 1-x2 SHE b2 In Chemical Formula 2, a2 is 0.5 to 1.5, x2 is 0.6~0.99, b2 is 1.8 to 2.2, and Mb includes Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, At least one of W, Fe, Cu, Ag, Zn, B, Ga, C, Si and Sn.

15. A method for producing a positive electrode active material, the method comprising: synthesizing first particles including a first lithium composite oxide; synthesizing second particles including a second lithium composite oxide; as well as coating a precursor mixture on the mixture of the first particles and the second particles, wherein the precursor mixture comprises a cobalt compound and an aluminum compound, and The coating of the precursor mixture is carried out at a temperature of 650° C. to 900° C.

16. The method of claim 15, wherein: In coating the precursor mixture, The cobalt compound includes at least one of cobalt nitrate, cobalt sulfate and cobalt oxide, and The aluminum compound includes at least one of aluminum sulfate and sodium metaaluminate.

17. The method of claim 15, wherein: Applying the precursor mixture includes adding the cobalt compound and the aluminum compound such that an atomic molar ratio of cobalt to aluminum is in a range of 2:0.05 to 2:

1.

18. The method of claim 15, wherein applying the precursor mixture comprises depositing using a base, The alkali comprises at least one of sodium hydroxide, lithium hydroxide, potassium hydroxide and ammonia.

19. The method of claim 15, wherein applying the precursor mixture comprises performing a wet coating process. 20 . A rechargeable lithium battery comprising the positive electrode active material according to claim 1 or a positive electrode active material produced by the method according to claim 15 .

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