Positive electrode active material and manufacturing method for the same, positive electrode including the same, and lithium secondary battery

Abstract

To provide a positive electrode active material including lithium cobalt complex oxide with a surface coated, in which the high capacity and a long-life characteristic are secured and the stability is improved even at high voltage, a manufacturing method for the positive electrode active material, and a positive electrode and a lithium secondary battery including the positive electrode active material.SOLUTION: A positive electrode active material includes a core particle containing lithium cobalt complex oxide, and a coating layer existing on a surface of the core particle and containing a lithium iron phosphate compound and aluminum. In an embodiment, the long-life characteristic is secured and the stability is improved even at the high voltage in the positive electrode active material. A lithium secondary battery including the positive electrode active material can exhibit the high initial charging and discharging capacity and efficiency even under the high-voltage driving conditions, and can achieve the long-life characteristic under the high-voltage high-temperature conditions.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material, a method for producing the same, a positive electrode containing the same, and a lithium secondary battery. [Background technology]

[0002] Lithium secondary batteries, which have high energy density yet are easy to carry, are widely used as power sources for mobile information terminals such as mobile phones, laptops, and smartphones. Recently, active research has been conducted into using high-energy-density lithium secondary batteries as power sources for hybrid and electric vehicles or as power storage sources.

[0003] Various positive electrode active materials have been investigated to realize lithium secondary batteries suitable for these applications. Among these, lithium nickel oxides, lithium nickel manganese cobalt composite oxides, lithium nickel cobalt aluminum composite oxides, and lithium cobalt oxides are commonly used as positive electrode active materials. However, while demand for large-sized, high-capacity, high-voltage, or high-energy-density lithium secondary batteries has rapidly increased in recent years, the reality is that lithium secondary batteries have poor stability when operated at high voltages. Therefore, there is a need to develop positive electrode active materials that have improved stability and generate less heat even when operated at high voltages. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides a cathode active material including a surface-coated lithium-cobalt composite oxide, which ensures high capacity and long life characteristics and has improved stability even at high voltages, a method for manufacturing the same, and a cathode and a lithium secondary battery including the same. [Means for solving the problem]

[0005] In one embodiment of the present invention, a positive electrode active material is provided, comprising: a core particle containing a lithium-cobalt-based composite oxide; and a coating layer located on the surface of the core particle and containing a lithium iron phosphate-based compound and aluminum.

[0006] In another embodiment of the present invention, there is provided a method for producing a cathode active material, the method including: (i) dry-mixing a lithium-cobalt-based composite oxide, a lithium iron phosphate-based compound, and an aluminum raw material to prepare a mixture; and (ii) firing the mixture in a nitrogen or inert gas atmosphere.

[0007] In yet another embodiment of the present invention, there is provided a positive electrode including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer including the positive electrode active material.

[0008] In yet another embodiment of the present invention, there is provided a lithium secondary battery comprising the above positive electrode, negative electrode, and electrolyte. [Effects of the Invention]

[0009] The cathode active material according to one embodiment of the present invention ensures long-life characteristics and improved stability even at high voltages. A lithium secondary battery using the cathode active material can exhibit high initial charge / discharge capacity and efficiency even under high-voltage driving conditions, and can achieve long-life characteristics under high-voltage and high-temperature conditions. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 2] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 3] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 4] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 5]1 is a SEM image of the positive electrode active material according to Comparative Example 1. [Figure 6] 1 is a SEM image of the positive electrode active material according to Comparative Example 1. [Figure 7] 1 is a SEM image of the positive electrode active material according to Example 1. [Figure 8] 1 is a SEM image of the positive electrode active material according to Example 1. [Figure 9] 1 is a graph showing the heat flow rate as a function of temperature of the positive electrode active materials according to Example 1 and Comparative Example 1 measured by differential scanning calorimetry. DETAILED DESCRIPTION OF THE INVENTION

[0011] Although the present invention may be embodied in many different forms, it is not limited to the embodiments set forth herein.

[0012] The terms used herein are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0013] As used herein, "combinations thereof" refers to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0014] It should be understood that the terms "comprise," "include," "comprise," or "have" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possible presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0015] In the drawings, thicknesses of various layers and regions are exaggerated for clarity, and similar parts are designated by the same reference numerals throughout the specification. When a layer, film, region, plate, or other part is said to be "on" or "above" another part, this includes not only the case where it is "directly on" another part, but also the case where there is another part between them. Conversely, when a part is said to be "directly on" another part, it means that there is no other part between them.

[0016] Here, the term "layer" includes not only a shape formed on the entire surface when observed in a plan view, but also a shape formed on a part of the surface.

[0017] The average particle size can be measured by a method well known to those skilled in the art, for example, by using a particle size analyzer or by using a transmission electron microscope or a scanning electron microscope. Alternatively, the average particle size can be calculated by measuring using a dynamic light scattering method, counting the number of particles for each particle size range through data analysis, and then calculating the average particle size. Unless otherwise defined, the average particle size is the diameter (D) of particles whose cumulative volume is 50% by volume in the particle size distribution. 50 ) and, unless otherwise defined, the average particle size is determined by measuring the size (diameter or length of the major axis) of 20 or more particles randomly selected from a scanning electron microscope image to obtain a particle size distribution, and then calculating the diameter (D 50 ) can be taken as the average particle size.

[0018] Here, "or" is not to be construed in an exclusive sense; for example, "A or B" is to be construed as including A, B, A+B, etc.

[0019] Here, the term "metal" is interpreted as a concept including general metals, transition metals, and metalloids (semimetals).

[0020] positive electrode active material In one embodiment, a positive electrode active material is provided, comprising: a core particle containing a lithium-cobalt-based composite oxide; and a coating layer located on the surface of the core particle and containing a lithium iron phosphate-based compound and aluminum.

[0021] Although lithium-cobalt-based positive electrode active materials have excellent density characteristics due to their single particle structure, they suffer from poor stability when operated at high voltages. Therefore, in order to improve the stability of lithium-cobalt-based positive electrode active materials at high voltages and reduce the amount of heat generated, one embodiment proposes a solution for improving not only high-voltage and high-temperature life characteristics but also initial charge / discharge efficiency by forming a coating layer containing a lithium iron phosphate compound and aluminum on the surface of the lithium-cobalt-based positive electrode active material.

[0022] core particle According to one embodiment, the core particle includes a lithium-cobalt-based composite oxide, and the lithium-cobalt-based composite oxide is represented by, for example, the following Chemical Formula 1: [Chemical formula 1] Li a1 Co x1 Al y1 Mg z1 M 1 w1 O 2-b1 X b1

[0023] In the above Chemical Formula 1, 0.9≦a1≦1.8, 0.8≦x1≦0.99, 0≦y1≦0.1, 0≦z1≦0.1, 0≦w1≦0.1, 0.9≦x1+y1+z1≦1.1, and 0≦b1≦0.1; M 1 is at least one element selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0024] In the formula (1), 0.9 ≦ a1 ≦ 1.5 or 0.9 ≦ a1 ≦ 1.2. Also, 0.8 < x1 ≦ 0.99, 0.82 ≦ x1 ≦ 0.99, 0.84 ≦ x1 ≦ 0.99, 0.86 ≦ x1 ≦ 0.99, 0.88 ≦ x1 ≦ 0.98, or 0.9 ≦ x1 ≦ 0.97, 0 < y1 ≦ 0.1, 0.01 ≦ y1 ≦ 0.09, 0.01 ≦ y1 ≦ 0.05, 0.01 ≦ y1 ≦ 0.03, or 0.01 ≦ y1 ≦ 0.02, 0 < z1 ≦ 0.1, 0.001 ≦ z1 ≦ 0.09, 0.001 ≦ z1 ≦ 0.05, 0.005 ≦ z1 ≦ 0.03, or 0.005 ≦ z1 ≦ 0.01, 0 < w1 ≦ 0.1, 0.001 ≦ w1 ≦ 0.075, 0.001 < w1 ≦ 0.05, or 0.001 < w1 ≦ 0.025 may be satisfied.

[0025] ​​​​​​​​​​​​​​​The average particle diameter (D) of the large particles may be small particles having a diameter of 0.5 μm to 8 μm, or may be a mixture of large particles and small particles. 50 ) is, for example, 10 μm to 20 μm, or 12 μm to 18 μm, and the average particle size of the small particles (D 50 ) may be, for example, 1 μm to 6 μm, or 2 μm to 5 μm. When the positive electrode active material contains a mixture of large particles and small particles, the large particles are contained in an amount of 60 wt% to 95 wt%, or 70 wt% to 90 wt%, and the small particles are contained in an amount of 5 wt% to 40 wt%, or 10 wt% to 30 wt%, based on a total of 100 wt% of the large particles and small particles. When the large particles and small particles are mixed in the above content ranges, the capacity and energy density can be maximized while the life characteristics can be improved. Here, the average particle size (D 50 ) may be obtained by measuring the sizes (diameter or major axis length) of 20 or more particles randomly selected from a scanning electron microscope image of the positive electrode active material to obtain a particle size distribution, and taking the diameter of particles whose cumulative volume is 50% by volume in the particle size distribution as the average particle size.

[0028] The shape of the core particle may be irregular, spherical, oval, or the like.

[0029] Coating layer According to one embodiment, the cathode active material includes a coating layer located on the surface of the core particle, the coating layer containing a lithium iron phosphate compound and aluminum. When the coating layer is formed on the cathode active material, the life or capacity characteristics at high voltage are further improved. Since the core particle has been described above, the coating layer will be omitted and only the description of the coating layer will be provided.

[0030] The lithium iron phosphate-based compound may include, for example, lithium iron phosphate, lithium manganese iron phosphate, or a combination thereof. The lithium iron phosphate-based compound is specifically represented by the following Chemical Formula 2 or Chemical Formula 3. [Chemical formula 2] Li a2 Fe (1-x2) M 2 x2 PO4

[0031] In Chemical Formula 2, 0.90 ≤ a2 ≤ 1.5, 0 ≤ x2 ≤ 0.4, and M 2 is Al, Ca, Ce, Cr, Cu, La, Mg, Mn, Mo, Nb, Ni, Sn, Sr, Ti, V, W, Y, Zn, Zr, or a combination thereof.

[0032] The compound represented by Chemical Formula 2 can be a lithium iron phosphate. In Chemical Formula 2, for example, 0.90 ≤ a2 ≤ 1.2, or 0.95 ≤ a2 ≤ 1.1, and 0 ≤ x2 ≤ 0.3, 0 ≤ x2 ≤ 0.2, 0 ≤ x2 ≤ 0.1, or 0 < x2 ≤ 0.05. For example, when a2 = 1 and x2 = 0, Chemical Formula 2 is represented by LiFePO4.

[0033] [Chemical Formula 3] Li a3 Mn x3 Fe (1-x3-y3) M 3 y3 PO4

[0034] In Chemical Formula 3, 0.90 ≤ a3 ≤ 1.5, 0.1 ≤ x3 ≤ 0.9, 0 < x3 + y3 < 1, and M 3 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, Ti, V, W, Y, Zn, Zr, or a combination thereof.

[0035] [[ID=]] The compound represented by Chemical Formula 3 can be a lithium manganese iron phosphate. In Chemical Formula 3, for example, 0.90 ≤ a3 ≤ 1.2, or 0.95 ≤ a3 ≤ 1.1, and 0.2 ≤ x3 ≤ 0.8, 0.3 ≤ x3 ≤ 0.7, or 0.4 ≤ x3 ≤ 0.6. The compound represented by Chemical Formula 3 is, for example, LiMn 0.9 Fe 0.1 PO4, LiMn 0.8 Fe 0.2 PO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.5 Fe 0.5 PO4, LiMn0.4 Fe 0.6 PO4, LiMn 0.3 Fe 0.7 PO4, LiMn 0.2 Fe 0.8 PO4, or LiMn 0.1 Fe 0.9 It can be PO4, etc.

[0036] Specific examples of the lithium iron phosphate compound include LiFePO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.5 Fe 0.5 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.3 Fe 0.7 PO4, or a combination thereof.

[0037] The content of the lithium iron phosphate compound in the coating layer is 0.1 wt % to 5 wt %, for example, 0.5 wt % to 4 wt %, or 1 wt % to 3 wt %, based on 100 wt % of the total positive electrode active material. The content of the lithium iron phosphate compound in the coating layer can be measured, for example, by SEM-EDS analysis of the surface or cross section of the positive electrode active material. When the content of the lithium iron phosphate compound in the coating layer satisfies the above range, the life characteristics or stability at high voltage are further improved.

[0038] According to one embodiment, the coating layer included in the positive electrode active material includes the lithium iron phosphate-based compound and aluminum. Core particles containing lithium cobalt-based composite oxides have a low specific surface area, making it difficult to uniformly coat the surface with the lithium iron phosphate-based compound alone. However, as in one embodiment, by co-coating the lithium iron phosphate-based compound and aluminum on the core particles and applying the coating method and conditions described below, it is possible to uniformly coat the surface of the core particles with the lithium iron phosphate-based compound. The lithium iron phosphate-based compound has high phase stability, which can improve the structural stability of the lithium cobalt-based composite oxide under high-voltage and high-temperature conditions, thereby improving the battery's lifespan. Furthermore, the uniform coating of the lithium iron phosphate-based compound on the surface of the core particles reduces resistance, improving initial charge / discharge capacity and efficiency, and improving high-temperature lifespan characteristics. In addition, the aluminum in the coating layer not only improves the structural stability of the core particles and improves their lifespan characteristics, but also acts as a fluorine scavenger (F scavenger) that removes fluorine from the electrolyte, preventing HF from attacking the positive electrode surface. This in turn prevents side reactions between the positive electrode and the electrolyte, stabilizes the interface, and effectively prevents degradation of the positive electrode active material.

[0039] The aluminum content in the coating layer is 0.01 wt % to 2 wt %, for example, 0.01 wt % to 1.5 wt %, 0.05 wt % to 1 wt %, or 0.04 wt % to 0.05 wt %, based on 100 wt % of the total metals (excluding lithium) in the positive electrode active material. This refers to the aluminum content in the coating layer, separate from the aluminum contained within the core particles. The aluminum content in the coating layer can be measured, for example, by SEM-EDS analysis of the surface or cross section of the positive electrode active material. When the aluminum content in the coating layer satisfies the above range, a uniform and thin coating layer can be formed, the resistance of the positive electrode active material is not increased, side reactions with the electrolyte are effectively suppressed, and the lithium iron phosphate compound is effectively coated, thereby improving the life characteristics of lithium secondary batteries under high-voltage and high-temperature conditions.

[0040] According to one embodiment, the coating layer may have an island or film form, for example, a film form continuously surrounding the surface of the core particle, for example, a shell form surrounding the entire surface of the core particle. According to one embodiment, the coating layer may be formed to a very thin and uniform thickness, which prevents an increase in resistance or a decrease in capacity of the positive electrode active material, improves structural stability, effectively suppresses side reactions with the electrolyte, reduces gas generation under high voltage and high temperature conditions, and achieves long-life characteristics.

[0041] According to one embodiment, the thickness of the coating layer is 30 nm to 500 nm, for example, 30 nm to 450 nm, 30 nm to 400 nm, 30 nm to 350 nm, 30 nm to 300 nm, 30 nm to 250 nm, 30 nm to 200 nm, 30 nm to 150 nm, 50 nm to 500 nm, 80 nm to 500 nm, or 100 nm to 500 nm. When the coating layer satisfies the above thickness range, the coating does not increase resistance or decrease capacity, but can improve the structural stability of the positive electrode active material and effectively suppress side reactions with the electrolyte. The thickness of the coating layer can be measured, for example, by TOF-SIMS, XPS, or EDS analysis, and the thickness range of the coating layer can be measured by TEM-EDS line profile analysis.

[0042] Method for producing positive electrode active material In one embodiment, a method for producing a positive electrode active material includes: (i) dry-mixing a lithium-cobalt-based composite oxide, a lithium iron phosphate-based compound, and an aluminum raw material to produce a mixture; and (ii) firing the mixture in a nitrogen or inert gas atmosphere.

[0043] The lithium cobalt composite oxide and the lithium iron phosphate compound have been described above, so a detailed description will be omitted and the aluminum raw material will be explained.

[0044] The aluminum source can include, for example, aluminum nitrate, aluminum sulfate, aluminum carbonate, aluminum hydroxide, aluminum oxide, or a combination thereof, and can specifically include aluminum hydroxide, and more specifically include Al(OH).

[0045] In step (i) of dry-mixing the lithium-cobalt composite oxide, the lithium iron phosphate compound, and the aluminum raw material, the lithium-cobalt composite oxide can be contained in an amount of 90 to 99.8% by weight, the lithium iron phosphate compound in an amount of 0.1 to 9.9% by weight, and the aluminum raw material in an amount of 0.01 to 2% by weight, based on a total of 100% by weight. Specifically, the lithium-cobalt composite oxide can be contained in an amount of 94 to 99.4% by weight, or 96 to 98% by weight, the lithium iron phosphate compound in an amount of 0.5 to 5% by weight, or 1 to 3% by weight, and the aluminum raw material in an amount of 0.01 to 1% by weight, or 0.05 to 0.1% by weight. When the content range is satisfied, a positive electrode active material can be obtained in which a coating layer containing a lithium iron phosphate compound and aluminum is uniformly and well coated on the surface of core particles containing a lithium cobalt-based composite oxide, thereby improving the initial charge / discharge capacity, efficiency, and high-temperature life characteristics of the lithium secondary battery, and improving thermal safety.

[0046] In step (i), the dry mixing speed can be 2,000 rpm or higher, for example, 2,000 rpm to 3,000 rpm, or 2,000 rpm to 2,500 rpm. The dry mixing time can be 1 minute to 60 minutes, for example, 1 minute to 30 minutes, or 1 minute to 10 minutes. If the dry mixing conditions are met, the mixture can be maintained at a temperature of 45°C or higher for 3 minutes or more upon completion of mixing, thereby allowing the lithium iron phosphate compound and aluminum to be uniformly coated on the surfaces of the core particles containing the lithium cobalt-based composite oxide.

[0047] After completing dry mixing for a certain period of time at a speed of 2,000 rpm or greater, the temperature of the mixture should be 45°C or higher, e.g., 45°C to 80°C, 45°C to 50°C, or 40°C to 45°C. This temperature can be maintained for 3 minutes or longer, e.g., 3 minutes to 10 minutes, or 3 minutes to 5 minutes. It is understood that under these conditions, the lithium iron phosphate compound can be uniformly coated on the surface of the lithium cobalt-based composite oxide-containing core particles, which have a relatively small specific surface area. According to one embodiment, the method for preparing a positive electrode active material further includes maintaining the mixture prepared in step (i) at a temperature of 45°C or higher for 3 minutes or longer.

[0048] In step (ii), the mixture is calcined. It has been confirmed that the cathode active material obtained by calcining the mixture under certain conditions has higher initial charge / discharge capacity and efficiency, and further improved high-temperature lifespan characteristics, compared to when the mixture is used as the cathode active material without calcination. The calcination is performed in a nitrogen or inert gas atmosphere. It has been confirmed that when calcined in an oxygen atmosphere or air, for example, rather than a nitrogen or inert gas atmosphere, the surface components and physical properties of the cathode active material are distorted, resulting in a significant decrease in initial charge / discharge capacity, efficiency, and high-temperature lifespan characteristics, compared to when calcined in a nitrogen or inert gas atmosphere.

[0049] The calcination can be carried out at a temperature ranging from 300° C. to 500° C., for example, from 350° C. to 450° C., from 370° C. to 430° C., or from 390° C. to 410° C. When the calcination temperature is within the above range, the surface of the core particles containing the lithium cobalt composite oxide is firmly coated with the lithium iron phosphate compound and aluminum, thereby ensuring high capacity and long life characteristics and improving stability even at high voltages.

[0050] positive electrode In one embodiment, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer including the positive electrode active material described above. The positive electrode active material layer may further include other positive electrode active materials in addition to the positive electrode active material described above. The positive electrode active material layer may also optionally further include a binder, a conductive material, or a combination thereof.

[0051] According to one embodiment, the loading level of the positive electrode active material layer is 10 mg / cm 2 ~40mg / cm 2 For example, 10 mg / cm 2 ~30mg / cm 2 or 10 mg / cm 2 ~20mg / cm 2 In addition, the density of the positive electrode active material layer in the final rolled 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. When using a positive electrode active material according to an embodiment, it is advantageous to achieve such a loading level and positive electrode density, and a positive electrode satisfying the above-mentioned ranges of loading level and positive electrode density is suitable for realizing a high-capacity, high-energy-density lithium secondary battery.

[0052] binder The binder serves to firmly adhere the positive electrode active material particles to each other and to firmly adhere the positive electrode active material to the current collector. Representative examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0053] Conductive material The conductive material is used to impart electrical conductivity to the electrode, and any material that is electron-conductive and does not cause chemical changes in the battery that is constructed can be used. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0054] The content of the binder and the conductive material may be 0.5% by weight to 5% by weight, respectively, relative to 100% by weight of the positive electrode active material layer.

[0055] The positive electrode current collector may be made of Al, but is not limited to this.

[0056] Lithium secondary battery In one embodiment, a lithium secondary battery is provided that includes the positive electrode, the negative electrode, and the electrolyte described above. For example, the lithium secondary battery may include a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

[0057] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 1 to 4 are schematic diagrams showing lithium secondary batteries according to an embodiment, with FIG. 1 showing a cylindrical battery, FIG. 2 showing a prismatic battery, and FIGS. 3 and 4 showing pouch-type batteries. Referring to FIGS. 1 to 4, a lithium secondary battery 100 may include an electrode assembly 40 having a positive electrode 10 and a negative electrode 20 with a separator 30 interposed therebetween, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, the negative electrode 20, and the separator 30 may be immersed in an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the case 50, as shown in FIG. 1. Also, in FIG. 2, the lithium secondary 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. As shown in FIGS. 3 and 4, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting the current generated in the electrode assembly 40 to the outside.

[0058] A lithium secondary battery according to an embodiment may be capable of being charged at a high voltage or may be suitable for being driven at a high voltage. For example, the charging voltage of the lithium secondary battery may be 4.45 V or higher, such as 4.45 V to 4.7 V, 4.45 V to 4.6 V, or 4.45 V to 4.55 V. By using a positive electrode active material according to an embodiment, the lithium secondary battery can significantly reduce gas generation even when charged at a high voltage, thereby achieving high capacity and long life characteristics.

[0059] negative electrode The negative electrode may include a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer includes a negative electrode active material and may further include a binder, a conductive material, or a combination thereof.

[0060] negative electrode active material The negative electrode active material includes a material capable of reversibly inserting / extracting lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and dedoped from lithium, or a transition metal oxide.

[0061] As the substance capable of reversibly inserting / desorbing the lithium ions, a carbon-based negative electrode active material can be used, which can include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite, or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0062] As the alloy of the lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn can be used.

[0063] As the substance capable of doping and undoping with lithium, an Si-based negative electrode active material or an Sn-based negative electrode active material can be used. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiOx (0 < x < 2), an Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, group 13 elements, group .....

[0064] The silicon-carbon composite can be a composite of silicon and amorphous carbon. The average particle size (D) of the silicon-carbon composite particles 50) may be, for example, 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles, and the surfaces of the silicon particles may be coated with amorphous carbon. For example, it may include secondary particles (cores) formed by granulating primary silicon particles, and an amorphous carbon coating layer (shell) located on the surfaces of the secondary particles. The amorphous carbon may also be located between the primary silicon particles, for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0065] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core including crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the core surface. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0066] When the silicon-carbon composite contains silicon and amorphous carbon, the silicon content may be 10 to 50% by weight and the amorphous carbon content may be 50 to 90% by weight, based on 100% by weight of the silicon-carbon composite.Alternatively, when the composite contains silicon, amorphous carbon, and crystalline carbon, the silicon content may be 10 to 50% by weight, the crystalline carbon content may be 10 to 70% by weight, and the amorphous carbon content may be 20 to 40% by weight, based on 100% by weight of the silicon-carbon composite.

[0067] The thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. 50 ) can be 10 nm to 1 μm, or 10 nm to 200 nm. The silicon particles may be present as silicon alone, in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon is SiO xIt can be represented by (0 < x < 2). At this time, the atomic content ratio of Si:O indicating the degree of oxidation can be 99:1 to 33:67. In this specification, unless otherwise defined, the average particle size (D 50 ) means the diameter of the particle with a cumulative volume of 50% by volume in the particle size distribution.

[0068] The Si-based negative electrode active material or Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material. When the Si-based negative electrode active material or Sn-based negative electrode active material and the carbon-based negative electrode active material are used in combination, the mixing ratio can be 1:99 to 90:10 by weight ratio.

[0069] Binder The binder plays a role of making the negative electrode active material particles adhere well to each other and making the negative electrode active material adhere well to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder or a combination thereof can be used.

[0070] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide or a combination thereof.

[0071] The aqueous binder can be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluorine rubber, polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene-propylene-diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol and a combination thereof.

[0072] When an aqueous binder is used as the negative electrode binder, a cellulose-based compound that can impart viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be sodium, potassium, or lithium.

[0073] The dry binder can be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0074] Conductive material The conductive material is used to impart conductivity to the electrode and can be any material that is electron-conductive and does not cause chemical changes in the battery. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0075] The content of the negative electrode active material may be 95% to 99.5% by weight, and the content of the binder may be 0.5% to 5% by weight, relative to 100% by weight of the negative electrode active material layer. For example, the negative electrode active material layer may contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0.5% to 5% by weight of the conductive material.

[0076] current collector The negative electrode current collector can include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof, and can be in the form of a foil, sheet, or foam. The thickness of the negative electrode current collector can be, for example, 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0077] electrolyte The electrolyte for a lithium secondary battery can be, for example, an electrolytic solution, which can include a non-aqueous organic solvent and a lithium salt.

[0078] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reactions of the battery can migrate, and can be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0079] Examples of carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Examples of ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0080] The non-aqueous organic solvent may be used alone or in combination of two or more kinds. When a mixture of two or more kinds is used, the mixing ratio may be appropriately adjusted depending on the desired battery performance, which is widely understood by those skilled in the art.

[0081] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed in a volume ratio of 1:1 to 1:9.

[0082] The non-aqueous organic solvent may further include an aromatic hydrocarbon organic solvent. For example, a carbonate solvent and an aromatic hydrocarbon organic solvent may be mixed in a volume ratio of 1:1 to 30:1.

[0083] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate or ethylene carbonate based compounds to improve the battery life.

[0084] Representative examples of the ethylene carbonate compounds include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0085] Lithium salts are substances that dissolve in organic solvents and act as a source of lithium ions within the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are integers of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

[0086] The concentration of the lithium salt is preferably within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate ionic conductivity and viscosity, thereby exhibiting excellent performance and allowing lithium ions to migrate effectively.

[0087] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators may be made of polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more of these. Of course, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0088] The separator may include a porous substrate and a coating layer including an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0089] The porous substrate may be a polymer membrane formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these polymers.

[0090] The porous substrate can have a thickness of about 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.

[0091] The organic material may include a (meth)acrylic copolymer including 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 a (meth)acrylate and a structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof.

[0092] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof. The average particle size (D 50 ) is 1 nm to 2000 nm, and can be, for example, 100 nm to 1000 nm, or 100 nm to 700 nm.

[0093] The organic material and the inorganic material may be mixed in one coating layer, or may be stacked in a coating layer containing an organic material and a coating layer containing an inorganic material.

[0094] The thickness of each of the coating layers may be 0.5 μm to 20 μm, for example, 1 μm to 10 μm, or 1 μm to 5 μm.

[0095] Examples of the present invention and comparative examples are described below. The following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

[0096] Example 1 1. Production of positive electrode active material Co 0.985 Al 0.015 O2 and Li2CO3 were mixed in a molar ratio of 1:1.03 and heat-treated in an air atmosphere at 1050°C for 8 hours to obtain a composition of Li 1.03 Co 0.985 Al 0.015 O2 and the average particle size (D 50A lithium-cobalt-based composite oxide with a particle size of approximately 17 μm was prepared. Then, 98.95 wt% of the lithium-cobalt-based composite oxide, 1.0 wt% of LiFePO4, and 0.05 wt% of Al(OH)3 were added to a reactor with a total of 100 wt% of the lithium-cobalt-based composite oxide, LiFePO4, and Al(OH)3, and the mixture was dry-mixed by stirring at approximately 2,400 rpm for approximately 5 minutes. Upon completion of mixing, the mixture sample was confirmed to maintain a temperature of 45°C or higher for approximately 3 minutes. The resulting mixture was calcined at 400°C in a nitrogen atmosphere to prepare the final cathode active material.

[0097] 2. Lithium secondary battery manufacturing 98.5 wt % of the prepared positive electrode active material, 1.0 wt % of polyvinylidene fluoride binder, and 0.5 wt % of carbon nanotube conductive material were mixed to prepare a positive electrode active material layer slurry, which was then coated on an aluminum foil current collector, dried, and rolled to prepare a positive electrode.

[0098] Anode active material layer slurry was prepared by mixing 97.5 wt% graphite anode active material, 1.5 wt% carboxymethyl cellulose, and 1 wt% styrene butadiene rubber in an aqueous solvent. The anode active material layer slurry was coated onto a copper foil current collector, dried, and rolled to prepare anodes.

[0099] A lithium secondary battery was fabricated in a conventional manner using a polytetrafluoroethylene separator and an electrolyte solution prepared by dissolving 1M LiPF6 in a solvent containing a mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 3:7.

[0100] Example 2 A positive electrode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that 97.95 wt % of lithium-cobalt-based composite oxide, 2.0 wt % of LiFePO4, and 0.05 wt % of Al(OH)3 were added in the preparation of the positive electrode active material.

[0101] Example 3 A positive electrode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that 96.95 wt % of lithium-cobalt-based composite oxide, 3.0 wt % of LiFePO4, and 0.05 wt % of Al(OH)3 were added in the preparation of the positive electrode active material.

[0102] Comparative Example 1 A lithium secondary battery was manufactured in substantially the same manner as in Example 1, except that in the preparation of the positive electrode active material, a lithium-cobalt-based composite oxide was used as the final positive electrode active material.

[0103] Comparative Example 2 In preparing the positive electrode active material, 99.0 wt % of a lithium-cobalt-based composite oxide and 1.0 wt % of LiFePO4 were added, i.e., Al(OH)3 was not added, and the mixture was dry-mixed by stirring at 1,200 rpm for about 5 minutes. A positive electrode active material and a lithium secondary battery were prepared in substantially the same manner as in Example 1, except that a calcination process was not performed.

[0104] Comparative Example 3 A positive electrode active material and a lithium secondary battery were manufactured in substantially the same manner as in Comparative Example 2, except that the positive electrode active material was prepared by stirring at 2,400 rpm for about 5 minutes.

[0105] Comparative Example 4 In preparing the positive electrode active material, 99.95 wt % of lithium-cobalt-based composite oxide and 0.05 wt % of Al(OH) were added, i.e., LiFePO was not added, and a mixture was prepared. A positive electrode active material and a lithium secondary battery were prepared in substantially the same manner as in Example 1, except that the calcination process was not performed.

[0106] Comparative Example 5 A positive electrode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the process of calcining the mixture was not performed in the preparation of the positive electrode active material.

[0107] Comparative Example 6 A positive electrode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the calcination process was performed in an air atmosphere instead of a nitrogen atmosphere in the preparation of the positive electrode active material.

[0108] The manufacturing methods of Examples 1 to 3 and Comparative Examples 1 to 6 are summarized in Table 1 below.

[0109] [Table 1]

[0110] Evaluation example 1: Surface analysis of positive electrode active material The positive electrode active materials prepared in Example 1 and Comparative Example 1 were photographed using a scanning electron microscope and compared. Figures 5 and 6 are SEM images of the particle surfaces of the positive electrode active material of Comparative Example 1, and Figures 7 and 8 are SEM images of the particle surfaces of the positive electrode active material of Example 1, which contains LiFePO4 and aluminum on the surface of the positive electrode active material. Referring to Figures 5 to 8, it can be seen that the positive electrode active material of Example 1 has a more uniform coating of LiFePO4 and aluminum particles on the particle surfaces of the positive electrode active material than Comparative Example 1.

[0111] Evaluation example 2: Initial charge / discharge capacity and efficiency evaluation The lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 6 were initially charged and discharged at 25° C. at a constant current of 0.2 C to an upper limit voltage of 4.55 V, at a constant voltage of 0.05 C, and then discharged at 0.2 C to an end voltage of 3.0 V. Table 2 below shows the initial charge capacity, initial discharge capacity, and the ratio of the latter to the former calculated as efficiency.

[0112] Evaluation example 3: High temperature life characteristics Following the initial charge and discharge of Evaluation Example 2, a cycle of charging at 1.0 C and discharging at 1.0 C in a voltage range of 3.0 V to 4.55 V at 45°C was repeated 50 times or more, and the ratio of the 50-cycle discharge capacity to the initial discharge capacity was calculated and shown in Table 2 below.

[0113] [Table 2]

[0114] Referring to Table 2 above, it can be seen that in Examples 1 to 3, in which LiFePO4 and aluminum hydroxide are added and stirred and fired under specific conditions to form LiFePO4 and aluminum on the surface of the positive electrode active material, the charge capacity, discharge capacity, and high-temperature life characteristics are excellent.

[0115] In contrast, Comparative Examples 1 to 4, which did not contain LiFePO4 and / or aluminum hydroxide, showed poorer high-temperature lifespan characteristics than the Examples. In particular, Comparative Examples 1 to 3, which did not contain aluminum hydroxide, showed even poorer high-temperature lifespan characteristics than the other Comparative Examples. Furthermore, Comparative Example 5, which coated LiFePO4 and aluminum hydroxide but did not undergo a calcination process, and Comparative Example 6, which performed the calcination process in an air atmosphere, also showed poorer high-temperature lifespan characteristics than the Examples. In other words, the positive electrode active materials according to the Examples, which were obtained by dry-mixing core particles containing a lithium-cobalt-based composite oxide, a lithium iron phosphate-based compound, and aluminum under certain conditions and then calcining them under certain conditions, showed improved initial charge / discharge capacity and efficiency, as well as improved high-temperature lifespan characteristics.

[0116] Evaluation example 4: DSC The thermal stability of the positive electrode active materials prepared in Example 1 and Comparative Example 1 was measured by differential scanning calorimetry (DSC) to measure the heat flow rate as a function of temperature. The results are shown in Figure 9. The measurements were performed using a differential scanning calorimeter (SENSYS Evo, manufactured by SETARAM). Specifically, the thermal stability of the positive electrode active materials prepared in Example 1 and Comparative Example 1 was measured by differential scanning calorimetry (DSC) to measure the heat flow rate as a function of temperature. The results are shown in Figure 9. + 15 mg of the electrode charged with ) was taken, 20 μL of electrolyte was added, and measurements were performed up to 400°C at a heating rate of 10°C per minute.

[0117] Referring to FIG. 9, it can be seen that in the case of Example 1, in which LiFePO4 and aluminum are included on the surface of the cathode active material, the onset is delayed and the peak temperature appears at a higher temperature than in the cathode active material of Comparative Example 1. As a result, it can be seen that the amount of heat generated during DSC measurement is reduced and thermal stability is improved.

[0118] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited to these, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the claims also fall within the scope of the present invention. [Explanation of symbols]

[0119] 100: Lithium secondary battery 10: Positive electrode 11: Positive electrode lead tab 12: Positive terminal 20: Negative electrode 21: Negative electrode lead tab 22: Negative terminal 30: Separator 40: Electrode assembly 50: Case 60: Sealing material 70: Electrode tab 71: Positive electrode tab 72: Negative electrode tab

Claims

1. Core particles containing a lithium-cobalt composite oxide; and a coating layer located on the surface of the core particle and containing a lithium iron phosphate compound and aluminum; A positive electrode active material comprising:

2. The positive electrode active material according to claim 1 , wherein the lithium-cobalt-based composite oxide is represented by the following chemical formula 1: [Chemical formula 1] Li a1 Co x1 Al y1 MM z1 M 1 w1 O 2-b1 X b1 In the formula 1, 0.9≦a1≦1.8, 0.8≦x1≦0.99, 0≦y1≦0.1, 0≦z1≦0.1, 0≦w1≦0.1, 0.9≦x1+y1+z1≦1.1, and 0≦b1≦0.1; M 1 is at least one element selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

3. The average particle diameter (D 50 2. The positive electrode active material according to claim 1, wherein the particle size is 9 μm to 25 μm.

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

5. The lithium iron phosphate compound is LiFePO 4 , LiMn 0.7 Fe 0.3 P.O. 4 , LiMn 0.6 Fe 0.4 P.O. 4 , LiMn 0.5 Fe 0.5 P.O. 4 , LiMn 0.4 Fe 0.6 P.O. 4 , LiMn 0.3 Fe 0.7 P.O. 4 or a combination thereof.

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

7. 2. The cathode active material of claim 1, wherein the aluminum content in the coating layer is 0.01 wt % to 2 wt % based on 100 wt % of the total metals excluding lithium in the cathode active material.

8. The cathode active material of claim 1 , wherein the coating layer has a thickness of 30 nm to 500 nm.

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

10. The method of claim 9 , wherein the dry mixing in step (i) is performed at 2,000 rpm or more.

11. 10. The method for producing a positive electrode active material according to claim 9, wherein the aluminum source comprises aluminum nitrate, aluminum sulfate, aluminum carbonate, aluminum hydroxide, aluminum oxide, or a combination thereof.

12. 10. The method for producing a positive electrode active material according to claim 9, wherein the lithium cobalt composite oxide is mixed in an amount of 90% by weight to 99.8% by weight, the lithium iron phosphate compound is mixed in an amount of 0.1% by weight to 9.9% by weight, and the aluminum raw material is mixed in an amount of 0.01% by weight to 2% by weight, relative to a total of 100% by weight of the lithium cobalt composite oxide, the lithium iron phosphate compound, and the aluminum raw material.

13. The method of claim 9, further comprising maintaining the mixture prepared in step (i) at a temperature of 45° C. or higher for 3 minutes or more.

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

15. a positive electrode current collector, and a positive electrode active material layer located on the positive electrode current collector Including, The positive electrode active material layer comprises the positive electrode active material according to any one of claims 1 to 8.

16. The positive electrode according to claim 15; a negative electrode; and Electrolyte; A lithium secondary battery comprising:

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