Positive electrode active material, producing method of the same, positive electrode including the same, and lithium secondary battery

Abstract

To provide a lithium secondary battery having achieved low resistance and improved life characteristics at high voltage and high temperature while having realized a positive electrode active material exhibiting high stability at the high voltage and a high capacity.SOLUTION: A positive electrode active material comprises: a first positive electrode active material comprising a first lithium cobalt-based oxide doped with aluminum and magnesium; and a second positive electrode active material comprising a second lithium cobalt-based oxide doped with aluminum and magnesium. An average particle diameter of the second positive electrode active material is smaller than an average particle diameter of the first positive electrode active material. The first positive electrode active material and the second positive electrode active material each include an aluminum coating layer located on each particle surface. The aluminum coating layer of the first positive electrode active material is in a shell form continuously wrapping each particle surface. A content of aluminum relative to 100 at % of a total of cobalt and aluminum measured by EP-EDS on a surface of the first positive electrode active material is 6 at% to 10 at%.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 and 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] The cathode active material used in lithium secondary batteries is mainly lithium cobalt oxide, and in recent years, research has been ongoing to achieve higher capacity. Lithium cobalt oxide has a high theoretical capacity of 274 mAh / g, but in reality, only half of this capacity can be used due to capacity reduction caused by phase transition. In particular, high-voltage charging and discharging is required to achieve high energy density, but research is currently needed to improve structural safety due to the irreversible phase transition of lithium cobalt oxide that occurs at high voltage and side reactions with the electrolyte. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides a lithium secondary battery that has low resistance and improved life characteristics at high voltages and high temperatures while realizing a positive electrode active material that exhibits high stability at high voltages and high capacity. [Means for solving the problem]

[0005] In one embodiment, a cathode active material includes a first cathode active material containing a first lithium-cobalt-based oxide doped with aluminum and magnesium; and a second cathode active material containing a second lithium-cobalt-based oxide doped with aluminum and magnesium; wherein the average particle size (D50 ) is the average particle size (D 50 ), the first positive electrode active material and the second positive electrode active material each include an aluminum coating layer located on the particle surface, the aluminum coating layer of the first positive electrode active material has a shell shape that continuously surrounds the particle surface, and the aluminum content of the first positive electrode active material is 6 at% to 10 at% relative to the total of cobalt and aluminum (100 at%) as measured on the surface of the first positive electrode active material by energy profiling energy dispersive spectroscopy (EP-EDS).

[0006] In another embodiment, the present invention provides a method for producing a cathode active material comprising the steps of: (i) preparing a first cathode active material including a first lithium-cobalt-based oxide doped with aluminum and magnesium; (ii) adding aluminum sulfate to an aqueous solvent and mixing to prepare a coating solution; (iii) adding a first cathode active material to the coating solution and mixing to prepare a mixed solution; (iv) removing the aqueous solvent from the mixed solution, drying the resultant, and heat-treating the resultant to obtain a first cathode active material including an aluminum coating layer; and (v) preparing a cathode active material including a second lithium-cobalt-based oxide doped with aluminum and magnesium, and having an average particle size (D 50 ) is the average particle size (D 50 (vi) adding aluminum oxide to the second positive electrode active material and heat-treating the resulting material to obtain a second positive electrode active material including an aluminum coating layer; and (vii) mixing the first positive electrode active material including an aluminum coating layer and the second positive electrode active material including an aluminum coating layer.

[0007] In another embodiment, a positive electrode is provided, comprising 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 comprising the positive electrode active material.

[0008] In another embodiment, a lithium secondary battery is provided, comprising: the positive electrode; a negative electrode; and an electrolyte. [Effects of the Invention]

[0009] The positive electrode active material prepared according to an embodiment has high stability at high voltage, and a lithium secondary battery including the positive electrode active material can exhibit low resistance and excellent high-temperature life while achieving high capacity and high energy density. [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 an EP-EDS image of the positive electrode active material of Example 2. [Figure 6] 10 is an EP-EDS image of the positive electrode active material of Comparative Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0011] While the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, the present invention 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] "Combinations thereof" means mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0014] It should be understood that the terms "comprise," "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] To clearly illustrate the various layers and regions in the drawings, thicknesses have been exaggerated, and similar parts have been given 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" the other part, but also the case where there are other parts between them. Conversely, when a part is said to be "directly on" another part, it means that there are no other parts between them.

[0016] When observed in a plan view, the "layer" includes not only shapes formed on the entire surface but also shapes formed on a portion of the surface.

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

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

[0019] The term "metal" is understood to include general metals, transition metals, and metalloids.

[0020] positive electrode active material In one embodiment, a cathode active material includes a first cathode active material containing a first lithium-cobalt-based oxide doped with aluminum and magnesium; and a second cathode active material containing a second lithium-cobalt-based oxide doped with aluminum and magnesium; wherein the average particle size (D 50 ) is the average particle size (D 50 ), the first positive electrode active material and the second positive electrode active material each include an aluminum coating layer located on the particle surface, the aluminum coating layer of the first positive electrode active material has a shell shape that continuously surrounds the particle surface, and the aluminum content of the first positive electrode active material is 6 at% to 10 at% relative to the total of cobalt and aluminum (100 at%) as measured on the surface of the first positive electrode active material by energy profiling energy dispersive spectroscopy (EP-EDS).

[0021] In order to prevent contraction and expansion due to charge and discharge within the positive electrode active material and to compensate for the structure that may be destroyed by rearrangement of the layer structure, a different element is doped to produce a positive electrode active material with excellent stability at high voltage. In particular, Al is used to strengthen the structural stability of the lithium cobalt-based oxide used in the positive electrode active material. 3+ and Mg 2+ Doping is possible. 3+ Co 3+ The size of the ions is similar to that of Al 3+ :0.535Å, Co 3+Since they have the same oxidation number (0.545Å) and are easy to use as a dopant, they have an Al-O bond energy (511±3kJ / mol) that is stronger than the Co-O bond energy (384.5±13.4kJ / mol). Aluminum does not participate in electrochemical reactions, but it can complement the structure of the active material when it contracts and expands during charging and discharging, and it has the advantage of being able to suppress structural changes in the positive electrode active material due to the movement of lithium ions, making it suitable for use as a dopant. In addition, Mg 2+ When doped, it is substituted at the lithium site and prevents the rearrangement of the oxygen layer from the lithium layer during charging and discharging, thereby improving the structural stability.

[0022] In one embodiment, two types of lithium-cobalt-based positive electrode active materials with different particle sizes are mixed, and the content and content ratio of aluminum and magnesium doped into the large and small particles are finely adjusted to ensure structural stability at high voltages, while at the same time providing a positive electrode active material that has successfully improved capacity, resistance, and life characteristics at high voltages.

[0023] In addition, we propose a method to uniformly coat the surface of the positive electrode active material with aluminum and optimize the aluminum concentration on the surface, thereby maintaining a stable structure even at high voltages, achieving high capacity, long life characteristics, and improving high-temperature storage characteristics.

[0024] When aluminum is coated to strengthen the particle surface of a positive electrode active material, aluminum has a strong tendency to diffuse into the interior of the particle, making it difficult to achieve a uniform, high-concentration aluminum shell coating on the particle surface. In one embodiment, conditions are proposed for coating the particle surface with a uniform, thin, high-concentration aluminum without increasing resistance. The aluminum concentration on the particle surface, i.e., the Al / (Co+Al) ratio, is confirmed to be 6 at% to 10 at% and a method for achieving this concentration is proposed. It has been confirmed that a lithium secondary battery employing a positive electrode active material according to one embodiment exhibits improved initial charge / discharge capacity and efficiency under high-voltage conditions, as well as improved high-temperature life and storage characteristics.

[0025] First positive electrode active material The first positive electrode active material includes a first lithium cobalt-based oxide doped with aluminum and magnesium, and the first lithium cobalt-based oxide is represented by the following Chemical Formula 1: [Chemical formula 1] Li a1 Co x1 Mg y1 Al z1 M 1 w1 O 2-b1 X b1

[0026] In Chemical Formula 1, 0.9≦a1≦1.8, 0.953≦x1≦0.965, 0.002≦y1≦0.005, 0.032≦z1≦0.04, 0≦w1≦0.002, 0.9≦x1+y1+z1+w1≦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, Zn, Y and Zr, and X is one or more elements selected from the group consisting of F, P and S.

[0027] In Chemical Formula 1, for example, 0.954≦x1≦0.965, 0.002≦y1≦0.005, 0.032≦z1≦0.039, and 0.001≦w1≦0.002, or 0.955≦x1≦0.965, 0.002≦y1≦0.005, 0.032≦z1≦0.038, and 0.001≦w1≦0.002. Furthermore, 0.9≦a1≦1.5, 0.9≦a1≦1.2, or 0.98≦a1≦1.0 may be satisfied.

[0028] The first positive electrode active material including the first lithium-cobalt-based oxide doped with aluminum and magnesium can be described as large grains or large particles. 50 ) is 7 μm to 30 μm, and may be, for example, 9 μm to 25 μm, 10 μm to 25 μm, or 12 μm to 20 μm. Here, the average particle size of the first positive electrode active material is larger than the average particle size of the second positive electrode active material described below. The positive electrode active material according to one embodiment is in a form in which large particles of the first positive electrode active material are mixed with small particles of the second positive electrode active material described below, which can improve the mixture density and achieve high capacity and high energy density.

[0029] The amount of aluminum doped relative to 100 wt% of the total first lithium cobalt-based oxide is 1.2 wt% or less (12,000 ppm or less), for example, 1.18 wt% or less, 1.16 wt% or less, 1.14 wt% or less, 1.12 wt% or less, or 1.1 wt% or less, and may be 0.8 wt% or more, 0.82 wt% or more, 0.84 wt% or more, 0.86 wt% or more, 0.88 wt% or more, or 0.9 wt% or more. When the amount of aluminum doped in the first lithium cobalt-based oxide satisfies this range, a positive electrode active material containing the first lithium cobalt-based oxide may be structurally stable at high voltages and may exhibit improved capacity, resistance, and life characteristics.

[0030] The doping amount of magnesium relative to 100 wt% of the first lithium cobalt-based oxide is 0.15 wt% or less (1500 ppm or less), for example, 0.14 wt% or less, or 0.13 wt% or less, or may be 0.01 wt% or more, 0.02 wt% or more, 0.03 wt% or more, 0.04 wt% or more, or 0.05 wt% or more. When the doping amount of magnesium in the first lithium cobalt-based oxide satisfies this range, a positive electrode active material containing the same can be structurally stable at high voltages and can exhibit improved capacity, resistance, and life characteristics.

[0031] In one embodiment, the first positive electrode active material is included in an amount of 50% to 95% by weight, for example, 60% to 90% by weight, or 70% to 90% by weight, based on 100% by weight of the total of the first and second positive electrode active materials. When the content ratio of the first positive electrode active material to the second positive electrode active material is such, the positive electrode active material including these materials can achieve high capacity, improve the mixture density, and exhibit high energy density.

[0032] In one embodiment, the first positive electrode active material includes an aluminum coating layer disposed on the particle surface, and the aluminum coating layer disposed on the particle surface of the first positive electrode active material has a shell shape that continuously surrounds the particle surface of the first positive electrode active material, for example, a shell shape that surrounds the entire particle surface of the first positive electrode active material. According to one embodiment, the aluminum coating layer can be formed to a very thin and uniform thickness while continuously surrounding the particle surface of the first positive electrode active material. As a result, the positive electrode active material has improved structural stability without increasing resistance or decreasing capacity, effectively suppresses side reactions with the electrolyte, and reduces gas generation under high voltage and high temperature conditions, thereby achieving long-life characteristics.

[0033] In one embodiment, the aluminum content on the surface of the first positive electrode active material, measured by energy profiling energy dispersive spectroscopy (EP-EDS), is 6 at% to 10 at% relative to the total of cobalt and aluminum (100 at%). The aluminum content on the surface of the first positive electrode active material, i.e., Al / (Co+Al), may be, for example, 6.2 at% to 9.8 at%, 6.4 at% to 9.6 at%, 6.6 at% to 9.4 at%, 6.8 at% to 9.2 at%, or 7 at% to 9 at%. This refers to the aluminum content in the coating layer, separate from the aluminum contained in the particles. When the aluminum content on the surface of the first positive electrode active material particles satisfies this range, a uniform and thin coating layer can be formed, the resistance of the positive electrode active material does not increase, side reactions with the electrolyte are effectively suppressed, and the life characteristics of lithium secondary batteries under high-voltage and high-temperature conditions can be improved.

[0034] In one embodiment, the thickness of the aluminum coating layer located on the surface of the first positive electrode active material particles may be 5 nm to 200 nm, e.g., 5 nm to 150 nm, 5 nm to 100 nm, 5 nm to 80 nm, 5 nm to 50 nm, or 10 nm to 50 nm. When the aluminum coating layer satisfies this thickness range, the coating does not increase resistance or decrease capacity, and the structural stability of the positive electrode active material is improved, thereby effectively suppressing side reactions with the electrolyte. The thickness of the coating layer can be measured, for example, by SEM, TEM, TOF-SIMS, XPS, or EDS analysis, for example, by EDS line profile analysis of a cross section of the positive electrode active material.

[0035] In one embodiment, the aluminum coating layer is characterized by being thin and uniform, with a thickness ranging from tens to hundreds of nanometers. For example, the thickness deviation of the coating layer within a single cathode active material particle may be 20% or less, 18% or less, or 15% or less. Here, the coating thickness deviation refers to the thickness of the coating layer within a single cathode active material particle. For example, the coating thickness deviation may be calculated by measuring the thickness of 10 or more points in an electron microscope image of the cross section of a single cathode active material particle, calculating the arithmetic average, and then dividing the absolute value of the difference between one data point and the arithmetic average by the arithmetic average and multiplying the result by 100. Having the coating thickness deviation or standard deviation within the above range means that a uniformly thick coating layer is formed on the surface of the cathode active material particle in a good shape, thereby improving the structural stability of the cathode active material, effectively suppressing side reactions with the electrolyte, and minimizing resistance increase and capacity loss due to the coating.

[0036] Second positive electrode active material The second positive electrode active material includes a second lithium cobalt-based oxide doped with aluminum and magnesium, and the second lithium cobalt-based oxide is represented by the following Chemical Formula 2: [Chemical formula 2] Li a2 Co x2 Mg y2 Al z2 M 2 w2 O 2-b2 X b2

[0037] In chemical formula 2, 0.9≦a2≦1.8, 0.953≦x2≦0.965, 0.002≦y2≦0.005, 0.032≦z2≦0.04, 0≦w2≦0.002, 0.9≦x2+y2+z2+w2≦1.1, and 0≦b2≦0.1; M 2 is at least one element selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y and Zr, and X is one or more elements selected from the group consisting of F, P and S.

[0038] In Chemical Formula 2, for example, 0.954≦x2≦0.965, 0.002≦y2≦0.005, 0.032≦z2≦0.039, and 0.001≦w2≦0.002 may be satisfied, or 0.955≦x2≦0.965, 0.002≦y2≦0.005, 0.032≦z2≦0.038, and 0.001≦w2≦0.002 may be satisfied. Also, 0.9≦a2≦1.5, 0.9≦a2≦1.2, or 0.98≦a2≦1.0 may be satisfied.

[0039] The second positive electrode active material, which includes the second lithium-cobalt-based oxide doped with aluminum and magnesium, can be described as small grains or small particles. 50 ) is 1 μm to 9 μm, and may be, for example, 1 μm to 8 μm, or 2 μm to 6 μm. Here, the average particle size of the second positive electrode active material is smaller than the average particle size of the first positive electrode active material. The positive electrode active material according to one embodiment is in the form of a mixture of large particles of the first positive electrode active material and small particles of the second positive electrode active material, which can improve the mixture density and achieve high capacity and high energy density.

[0040] The amount of aluminum doped relative to 100 wt% of the total second lithium cobalt-based oxide is 1.2 wt% or less (12,000 ppm or less), for example, 1.18 wt% or less, 1.16 wt% or less, 1.14 wt% or less, 1.12 wt% or less, or 1.1 wt% or less, and may be 0.8 wt% or more, 0.82 wt% or more, 0.84 wt% or more, 0.86 wt% or more, 0.88 wt% or more, or 0.9 wt% or more. When the amount of aluminum doped in the second lithium cobalt-based oxide satisfies this range, a positive electrode active material containing the same may be structurally stable at high voltages and exhibit improved capacity, resistance, and lifespan.

[0041] The doping amount of magnesium relative to 100 wt% of the total second lithium cobalt-based oxide is 0.15 wt% or less (1500 ppm or less), for example, 0.14 wt% or less, or 0.13 wt% or less, or may be 0.01 wt% or more, 0.02 wt% or more, 0.03 wt% or more, 0.04 wt% or more, or 0.05 wt% or more. When the doping amount of magnesium in the second lithium cobalt-based oxide satisfies this range, a positive electrode active material containing the same can be structurally stable at high voltages and can exhibit improved capacity, resistance, and life characteristics.

[0042] In one embodiment, the aluminum doping amount in the second lithium cobalt-based oxide may be greater than the aluminum doping amount in the first lithium cobalt-based oxide, and the aluminum doping amount in the second lithium cobalt-based oxide may be greater than the aluminum doping amount in the first lithium cobalt-based oxide by 0.05 wt % or more, for example, 0.05 wt % to 0.50 wt %, 0.05 wt % to 0.45 wt %, 0.05 wt % to 0.40 wt %, 0.05 wt % to 0.35 wt %, or 0.05 wt % to 0.30 wt %. In this case, a positive electrode active material containing these may maintain a very stable structure even after repeated charge and discharge at high voltages, thereby improving all of the characteristics of capacity, resistance, and room temperature / high temperature life.

[0043] In one embodiment, the second positive electrode active material is included in an amount of 5% to 50% by weight, for example, 10% to 40% by weight, or 10% to 30% by weight, relative to 100% by weight of the first and second positive electrode active materials combined. When the content ratio of the first positive electrode active material to the second positive electrode active material is within this range, the positive electrode active material including these materials can achieve high capacity, improve the mixture density, and exhibit high energy density.

[0044] In one embodiment, the second positive electrode active material includes an aluminum coating layer located on the surface of the particles.

[0045] The thickness of the aluminum layer located on the surface of the second positive electrode active material particles is 5 nm to 200 nm, and may be, for example, 5 nm to 150 nm, 5 nm to 100 nm, 5 nm to 80 nm, 5 nm to 50 nm, or 10 nm to 50 nm. When the aluminum coating layer satisfies this thickness range, the coating does not increase resistance or decrease capacity, improves the structural stability of the positive electrode active material, and effectively suppresses side reactions with the electrolyte. The thickness of the coating layer can be measured, for example, by SEM, TEM, TOF-SIMS, XPS, or EDS analysis, and can be measured, for example, by EDS line profile analysis of a cross section of the positive electrode active material.

[0046] According to one embodiment, the coating layer has a uniform thickness, ranging from tens to hundreds of nanometers. For example, the thickness deviation of the coating layer within a single cathode active material particle may be 20% or less, 18% or less, or 15% or less. Here, the coating thickness deviation refers to the thickness of the coating layer within a single cathode active material particle. For example, the coating thickness deviation may be calculated by measuring the thickness of 10 or more points in an electron microscope image of the cross section of a single cathode active material particle, calculating the arithmetic mean, and then dividing the absolute value of the difference between one data point and the arithmetic mean value by the arithmetic mean value and multiplying the result by 100. Having the coating layer thickness deviation or standard deviation within the above range means that a uniformly thick coating layer is formed on the surface of the cathode active material particle in a good shape. This improves the structural stability of the cathode active material, effectively suppresses side reactions with the electrolyte, and minimizes resistance increases and capacity reductions due to the coating.

[0047] Method for producing positive electrode active material In one embodiment, the present invention provides a method for producing a cathode active material comprising: (i) preparing a first cathode active material including a first lithium-cobalt-based oxide doped with aluminum and magnesium; (ii) adding aluminum sulfate to an aqueous solvent and mixing to prepare a coating solution; (iii) adding a first cathode active material to the coating solution and mixing to prepare a mixed solution; (iv) removing the aqueous solvent from the mixed solution, drying the resultant, and heat-treating the resultant to obtain a first cathode active material including an aluminum coating layer; and (v) preparing a cathode active material including a second lithium-cobalt-based oxide doped with aluminum and magnesium, the first cathode active material having an average particle size (D 50 ) is the average particle size (D 50 (vi) adding aluminum oxide to the second positive electrode active material and heat-treating the material to obtain a second positive electrode active material having an aluminum coating layer; and (vii) mixing the first positive electrode active material having an aluminum coating layer and the second positive electrode active material having an aluminum coating layer. The above-mentioned positive electrode active material can be produced by the above-mentioned production method.

[0048] The first and second positive electrode active materials can be produced by mixing a lithium raw material with a precursor of cobalt hydroxide, cobalt oxide, cobalt-based metal composite oxide, or cobalt-based metal composite hydroxide, and then heat-treating the mixture. The heat treatment is carried out at a temperature of, for example, 800°C to 1100°C, 850°C to 1050°C, or 890°C to 1010°C for 5 to 25 hours, for example, 8 to 15 hours. The precursor can be produced by a common coprecipitation method or the like.

[0049] The first cobalt-based metal composite hydroxide is represented by the following chemical formula 11, and the second cobalt-based metal composite hydroxide is represented by the following chemical formula 12.

[0050] [Chemical formula 11] Co x11 Mg y11 Alz11M 11 w11 (OH)2

[0051] In Chemical Formula 11, 0.953≦x11≦0.965, 0.002≦y11≦0.005, 0.032≦z11≦0.04, 0≦w11≦0.002, and 0.9≦x11+y11+z11+w11≦1.1; and M 11 is at least one element selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y and Zr.

[0052] In Chemical Formula 11, for example, 0.954≦x11≦0.965, 0.002≦y11≦0.005, 0.032≦z11≦0.039, and 0.001≦w11≦0.002, and may also be 0.955≦x11≦0.965, 0.002≦y11≦0.005, 0.032≦z11≦0.038, and 0.001≦w11≦0.002.

[0053] [Chemical formula 12] Co x12 Mg y12 Al z12 M 12 w12 (OH)2

[0054] In chemical formula 12, 0.953≦x12≦0.965, 0.002≦y12≦0.005, 0.032≦z12≦0.04, 0≦w12≦0.002, and 0.9≦x12+y12+z12+w12≦1.1; and M 12 is at least one element selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y and Zr.

[0055] In Chemical Formula 12, for example, 0.954≦x12≦0.965, 0.002≦y12≦0.005, 0.032≦z12≦0.039, and 0.001≦w12≦0.002, but may also be 0.955≦x12≦0.965, 0.002≦y12≦0.005, 0.032≦z12≦0.038, and 0.001≦w12≦0.002.

[0056] The first cobalt-based metal composite hydroxide may be in particulate form with an average particle size of 7 μm to 30 μm, and the second cobalt-based metal composite hydroxide may be in particulate form with an average particle size of 1 μm to 9 μm.

[0057] In a mixture containing a first positive electrode active material and a second positive electrode active material, the first positive electrode active material is contained in an amount of 50% to 95% by weight, for example, 60% to 90% by weight, or 70% to 90% by weight, based on 100% by weight of the first positive electrode active material and the second positive electrode active material. The second positive electrode active material is contained in an amount of 5% to 50% by weight, for example, 10% to 40% by weight, or 10% to 30% by weight, based on 100% by weight of the first positive electrode active material and the second positive electrode active material. When the content ratio of the first positive electrode active material to the second positive electrode active material is within this range, a positive electrode active material containing these materials can achieve high capacity, improve the mixture density, and exhibit high energy density.

[0058] The aqueous solvent may include distilled water, an alcohol-based solvent, or a combination thereof.

[0059] Aluminum sulfate is an optimal raw material for forming a coating layer according to one embodiment. The aluminum content in the aluminum sulfate is designed to be 6 at% to 10 at% relative to the total of 100 at% of cobalt and aluminum, as measured by energy profiling energy dispersive spectroscopy (EP-EDS) on the surface of the final cathode active material, for example, 6.2 at% to 9.8 at%, 6.4 at% to 9.6 at%, 6.6 at% to 9.4 at%, 6.8 at% to 9.2 at%, or 7 at% to 9 at%. Designing the aluminum coating content within this range allows for the formation of a coating layer with a thin and uniform thickness, on the order of tens to hundreds of nanometers, which reduces gas generation in lithium secondary batteries under high-voltage or high-temperature operating conditions and improves their high capacity and long-life characteristics.

[0060] In one embodiment, an aluminum precursor may be added to an aqueous solvent and mixed to prepare a coating solution, and then the first positive electrode active material may be added to the coating solution and mixed to prepare a mixed solution. This is a salt-dissolving wet coating method, which is a pre-addition method in which the salt of the coating raw material is first completely dissolved and then the first positive electrode active material is added.

[0061] In the pre-addition method, aluminum sulfate is added to the aqueous solvent and mixed for 1 to 60 minutes, for example, 3 to 30 minutes, or 5 to 10 minutes. The mixing speed may be 100 to 800 rpm, for example, 200 to 600 rpm, or 250 to 500 rpm. Under these mixing conditions, aluminum sulfate is completely dissolved in the aqueous solvent to produce a colorless, transparent coating solution. Using this coating solution, a uniform aluminum coating layer according to one embodiment can be effectively formed. The pH of the mixed coating solution may be 1.5 to 3.5, for example, 2.0 to 3.4, 2.5 to 3.3, 2.7 to 3.3, or 2.9 to 3.2.

[0062] The first positive electrode active material is added to the prepared coating solution, and the coating quality can be improved by adding the first positive electrode active material while stirring the coating solution.

[0063] The time required to add the first positive electrode active material to the coating solution is 30 seconds / 500 g to 2 minutes / 500 g, for example, 30 seconds / 500 g to 1.5 minutes / 500 g. By appropriately adjusting the addition speed, the pH of the supernatant liquid can be appropriately adjusted after the coating is completed, thereby effectively forming a uniform aluminum coating layer according to one embodiment.

[0064] The time for mixing the first positive electrode active material into the coating solution after adding it is 15 to 60 minutes, and may be, for example, 20 to 50 minutes, or 30 to 45 minutes. The time from starting to add the first positive electrode active material into the coating solution to completing the mixing, i.e., the coating reaction time, can be appropriately adjusted to within about 1 hour.

[0065] In one embodiment, when the first positive electrode active material is added to the coating solution and mixing is stopped, i.e., when mixing or coating is completed, the pH of the supernatant may be in the range of 5.5 to 7.5. When the pH of the supernatant is in this range, it is advantageous in that it does not become too acidic or basic, and a uniform coating layer can be formed.

[0066] After removing the aqueous solvent from the mixed solution, the resulting product can be dried, for example, at 40°C to 240°C, 100°C to 220°C, or 150°C to 200°C, for example, under vacuum conditions, and these conditions can produce a good coated product.

[0067] After removing the aqueous solvent from the mixed solution and drying, the resulting product can be referred to as a coated product. The aluminum-containing coating layer can have a fibrous shape, such as a mesh or spider web shape. The mesh can be continuously formed across the entire particle surface. The mesh-shaped coating layer can encase the particles with a very thin and uniform thickness, thereby strengthening the surface of the positive electrode active material, improving structural stability, and improving high-temperature and high-voltage characteristics.

[0068] If the first heat treatment is performed by mixing a lithium raw material with a precursor of cobalt hydroxide or cobalt-based metal composite hydroxide and then heat treating the mixture, the heat treatment of the coated product can be referred to as the second heat treatment.

[0069] In one embodiment, the second heat treatment temperature range is set to 730°C to 1000°C. The second heat treatment temperature range may be, for example, 740°C to 1000°C, 750°C to 1000°C, 780°C to 1000°C, or 800°C to 1000°C. When the second heat treatment temperature is set within this range, aluminum tends to diffuse less into the particle interior and remains primarily on the particle surface. At the same time, the particle surface is coated with a very thin, uniformly thick shell. When controlled within this heat treatment range, the aluminum content ratio on the particle surface, i.e., Al / (Co+Al), can be controlled to 6 at% to 10 at%. The second heat treatment is performed, for example, in an oxygen atmosphere for 2 to 20 hours or 3 to 10 hours.

[0070] 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.

[0071] In 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 the final rolled positive electrode, the density of the positive electrode active material layer may be 4.1 g / cc or more, for example, 4.1 g / cc to 4.5 g / cc or 4.1 g / cc to 4.4 g / cc. When a positive electrode active material according to an embodiment is applied, it is advantageous to achieve such a loading level and positive electrode density, and a positive electrode satisfying the loading level and positive electrode density ranges is suitable for realizing a lithium secondary battery with a high capacity and a high energy density.

[0072] 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 the binder 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, nylon, etc.

[0073] Conductive material The conductive material is used to impart conductivity to the electrodes, and any material that does not undergo chemical change and is electronically conductive can be used in the battery. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0074] 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.

[0075] The positive electrode current collector may be made of Al, but is not limited to this.

[0076] Lithium secondary battery In one embodiment, a lithium secondary battery is provided that includes the positive electrode, the negative electrode, and the electrolyte. 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.

[0077] Lithium secondary batteries are classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 1 to 4 are schematic diagrams showing a lithium secondary battery according to one embodiment, with FIG. 1 illustrating a circular battery, FIG. 2 illustrating a prismatic battery, and FIGS. 3 and 4 illustrating pouch-type battery shapes. Referring to FIGS. 1 to 4, a lithium secondary battery 100 may include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 housing the electrode assembly 40. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). 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.

[0078] The lithium secondary battery according to an embodiment may be rechargeable at a high voltage or may be suitable for operation at a high voltage. For example, the charging voltage of the lithium secondary battery may be 4.5 V or higher, such as 4.5 V to 4.7 V, 4.5 V to 4.6 V, or 4.5 V to 4.55 V. By using the positive electrode active material according to an embodiment, the lithium secondary battery can significantly reduce the amount of gas generated even when charged at a high voltage, thereby achieving high capacity and long life characteristics.

[0079] 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 may further include a binder, a conductive material, or a combination thereof.

[0080] 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.

[0081] As the substance capable of reversibly inserting / desorbing the lithium ions, a carbon-based negative electrode active material can include, for example, crystalline carbon, amorphous carbon, or a combination thereof.

[0082] 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.

[0083] 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.

[0084] As the substance capable of doping and undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. As the Si-based negative electrode active material, silicon, a silicon-carbon composite, SiOx (0 < x ≤ 2), a Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, for example, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof), or a combination thereof may be used. As the Sn-based negative electrode active material, Sn, SnO2, a Sn alloy, or a combination thereof may be used.

[0085] The silicon-carbon composite may be a composite of silicon and amorphous carbon. The average particle diameter (D50 ) 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 coated with amorphous carbon. For example, it may include secondary particles (cores) formed by assembling silicon primary 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 silicon primary particles, for example, the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0086] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of the core. 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.

[0087] 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.

[0088] The thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. 50) may be 10 nm to 1 μm, or 10 nm to 200 nm. The silicon particles can exist alone as silicon, in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon is represented by SiOx (0 < x ≤ 2). At this time, the atomic content ratio of Si:O indicating the degree of oxidation may be 99:1 to 33:67. In this specification, unless otherwise defined, the average particle size (D 50 ) means the diameter of the particles with a cumulative volume of 50% in the particle size distribution.

[0089] The Si-based anode active material or Sn-based anode active material can be used in mixture with a carbon-based anode active material. When the Si-based anode active material or Sn-based anode active material and the carbon-based anode active material are used in mixture, the mixing ratio may be 1:99 to 90:10 by weight ratio.

[0090] Binder The binder serves to well adhere the anode active material particles to each other and also to well adhere the anode active material to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof can be used.

[0091] 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.

[0092] The water-based binder may be selected from styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0093] 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.

[0094] The dry binder may be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0095] Conductive material The conductive material is used to impart conductivity to the electrodes, and any material that does not undergo chemical change and is electronically conductive in the battery that is constructed can be used. 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.

[0096] 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 agent.

[0097] current collector The negative electrode current collector may contain, 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 may be in the form of a foil, sheet, or foam. The thickness of the negative electrode current collector may be, for example, 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0098] electrolyte An example of an electrolyte for a lithium secondary battery is an electrolytic solution, which can include a non-aqueous organic solvent and a lithium salt.

[0099] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reactions of the battery can migrate, and may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0100] Examples of carbonate solvents 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 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.

[0101] The non-aqueous organic solvents can be used alone or in combination of two or more kinds. When two or more kinds are used in combination, the mixing ratio can be appropriately adjusted depending on the desired battery performance, which is widely understood by those working in the field.

[0102] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed and used, and the cyclic carbonate and the chain carbonate are mixed in a volume ratio of 1:1 to 1:9.

[0103] The non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent. For example, a carbonate-based solvent and an aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of 1:1 to 30:1.

[0104] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate, or ethylene carbonate based compounds to improve battery life.

[0105] 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.

[0106] 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(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB).

[0107] The lithium salt concentration is preferably within the range of 0.1 M to 2.0 M. When the lithium salt concentration is within this range, the electrolyte solution has appropriate ion conductivity and viscosity, thereby exhibiting excellent performance and allowing lithium ions to migrate effectively.

[0108] 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 materials. Of course, mixed multilayer films such as polyethylene / polypropylene two-layer separators, polyethylene / polypropylene / polyethylene three-layer separators, and polypropylene / polyethylene / polypropylene three-layer separators can also be used.

[0109] 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.

[0110] The porous substrate may be a polymer film 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, polyether imide, polyamide imide, polybenzimidazole, polyether sulfone, 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.

[0111] 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.

[0112] 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 (meth)acrylate, and a structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof.

[0113] 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 may be, for example, 100 nm to 1000 nm, or 100 nm to 700 nm.

[0114] 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.

[0115] The thickness of each of the coating layers is 0.5 μm to 20 μm, and may be, for example, 1 μm to 10 μm, or 1 μm to 5 μm.

[0116] Examples and comparative examples of the present invention will be described below. The following examples are illustrative of the present invention, and the present invention is not limited to the following examples.

[0117] Example 1 Manufacturing of positive electrode active materials The first cobalt transition metal composite oxide (Co) had an Al content of 11000 ppm (1.1 wt%) and an Mg content of 1250 ppm (0.125 wt%). 0.955 Mg 0.005 Al 0.04O2) and Li2CO3 were mixed in a molar ratio of 1:1.04 between the total metal of the first cobalt transition metal composite oxide and the lithium of Li2CO3, and then heat-treated in an air atmosphere at approximately 1000°C for 10 hours to obtain an average particle size (D 50 ) is about 20 μm of the first lithium cobalt oxide (Li 1.04 Co 0.955 Mg 0.005 Al 0.04 O2) was produced.

[0118] 600g of distilled water and aluminum sulfate were added to a 1L reactor and stirred at 500 rpm for 5 minutes to dissolve the salt, producing a coating solution. The salt was confirmed to have completely dissolved in the coating solution, making it colorless and transparent. 500g of the first lithium cobalt-based oxide prepared above was added to the continuously stirred coating solution for 1.5 minutes and stirred for 30 minutes. The aluminum content in the aluminum sulfate was designed to be 0.05wt% based on 100wt% of the total metals (excluding lithium) in the final positive electrode active material.

[0119] The solvent was removed from the mixed solution using an aspirator and a filter press, and the mixture was dried in vacuum at 190°C to obtain a coated product.

[0120] The coated product was subjected to a second heat treatment at 750° C. for 8 hours in an air atmosphere to prepare a first positive electrode active material.

[0121] Next, a second cobalt transition metal composite oxide (Co) containing 10,000 ppm (1.0 wt%) of Al and 1,250 ppm (0.125 wt%) of Mg was prepared. 0.958 Al 0.037 Mg 0.005 O2) and Li2CO3 were mixed in a molar ratio of 1:0.51 between the total metal of the cobalt-transition metal composite oxide and the lithium of Li2CO3, and then heat-treated in an air atmosphere at approximately 900°C for 10 hours to obtain a mean particle size (D 50 ) is about 4 μm of the second lithium cobalt oxide (Li 1.02 Co 0.958 Al 0.037 Mg0.005 O2) was produced.

[0122] Aluminum oxide was added to the second lithium cobalt-based oxide, and then heat-treated at 600° C. for 5 hours to prepare a second positive electrode active material.

[0123] The first and second positive electrode active materials were mixed in a weight ratio of 8:2 to prepare a final positive electrode active material.

[0124] Cathode 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. At this time, the loading level of the positive electrode active material layer was 20 mg / cm. 2 and the density of the final rolled cathode is about 4.1 g / cc.

[0125] Lithium secondary battery manufacturing 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.

[0126] 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.

[0127] Example 2 The first positive electrode active material was prepared in substantially the same manner as in Example 1, except that the aluminum content in the aluminum sulfate was designed to be 0.1 wt % based on 100 wt % of the total metals excluding lithium in the final positive electrode active material.

[0128] Example 3 The first positive electrode active material was prepared in substantially the same manner as in Example 1, except that the aluminum content in the aluminum sulfate was designed to be 0.2 wt % based on 100 wt % of the total metals excluding lithium in the final positive electrode active material.

[0129] Example 4 The first positive electrode active material was prepared in substantially the same manner as in Example 1, except that the aluminum content in the aluminum sulfate was designed to be 0.27 wt % based on 100 wt % of the total metals excluding lithium in the final positive electrode active material.

[0130] Example 5 In the preparation of the first positive electrode active material, a first cobalt-transition metal composite oxide (LiCo) having an Al content of 9000 ppm (0.9 wt %) and an Mg content of 1000 ppm (0.1 wt %) was used. 0.963 Mg 0.004 Al 0.033 O2) was used to prepare the second positive electrode active material, and a second cobalt transition metal composite oxide (LiCo 0.956 Mg 0.004 Al 0.04 The preparation was carried out in substantially the same manner as in Example 1, except that O2) was used.

[0131] Example 6 The first positive electrode active material was prepared in substantially the same manner as in Example 5, except that the aluminum content in the aluminum sulfate was designed to be 0.1 wt % based on 100 wt % of the total metals excluding lithium in the final positive electrode active material.

[0132] Example 7 The first positive electrode active material was prepared in substantially the same manner as in Example 5, except that the aluminum content in the aluminum sulfate was designed to be 0.2 wt % based on 100 wt % of the total metals excluding lithium in the final positive electrode active material.

[0133] Example 8 The first positive electrode active material was prepared in substantially the same manner as in Example 5, except that the aluminum content in the aluminum sulfate was designed to be 0.27 wt % based on 100 wt % of the total metals excluding lithium in the final positive electrode active material.

[0134] Example 9 In the preparation of the first positive electrode active material, a first cobalt-transition metal composite oxide (LiCo) having an Al content of 10,000 ppm (1.0 wt %) and an Mg content of 1,000 ppm (0.1 wt %) was used. 0.959 Mg 0.004 Al 0.037 O2) was used to prepare the second positive electrode active material, and a second cobalt transition metal composite oxide (LiCo 0.956 Mg 0.004 Al 0.04 The preparation was carried out in substantially the same manner as in Example 2, except that O2 was used.

[0135] Example 10 The first positive electrode active material was prepared in substantially the same manner as in Example 9, except that the aluminum content in the aluminum sulfate was designed to be 0.27 wt % based on 100 wt % of the total metals excluding lithium in the final positive electrode active material.

[0136] Comparative Example 1 The first positive electrode active material was prepared in substantially the same manner as in Example 1, except that the aluminum coating was not performed.

[0137] Comparative Example 2 The first positive electrode active material was prepared in substantially the same manner as in Example 1, except that instead of a wet coating process in which a coating solution containing distilled water and aluminum sulfate was prepared, and the prepared first lithium cobalt-based oxide was added to the coating solution, dried, and heat-treated, a dry coating process in which aluminum oxide was added to the prepared first lithium cobalt-based oxide and then heat-treated at 600°C for 5 hours was performed.

[0138] Comparative Example 3 The first positive electrode active material was prepared in substantially the same manner as in Comparative Example 2, except that the aluminum content in the aluminum sulfate was designed to be 0.1 wt % relative to 100 wt % of the total metals excluding lithium in the final positive electrode active material.

[0139] Comparative Example 4 The first positive electrode active material was prepared in substantially the same manner as in Comparative Example 2, except that the aluminum content in the aluminum sulfate was designed to be 0.27 wt % relative to 100 wt % of the total metals excluding lithium in the final positive electrode active material.

[0140] Comparative Example 5 The first positive electrode active material was prepared in substantially the same manner as in Example 5, except that instead of a wet coating process in which a coating solution containing distilled water and aluminum sulfate was prepared, and the prepared first lithium cobalt-based oxide was added to the coating solution, dried, and heat-treated, a dry coating process in which aluminum oxide was added to the prepared first lithium cobalt-based oxide and then heat-treated at 600°C for 5 hours was performed.

[0141] Comparative Example 6 The first positive electrode active material was prepared in substantially the same manner as in Comparative Example 5, except that the aluminum content in the aluminum sulfate was designed to be 0.1 wt % relative to 100 wt % of the total metals excluding lithium in the final positive electrode active material.

[0142] Comparative Example 7 The first positive electrode active material was prepared in substantially the same manner as in Comparative Example 5, except that the aluminum content in the aluminum sulfate was designed to be 0.2 wt % based on 100 wt % of the total metals excluding lithium in the final positive electrode active material.

[0143] Comparative Example 8 The first positive electrode active material was prepared in substantially the same manner as in Comparative Example 5, except that the aluminum content in the aluminum sulfate was designed to be 0.27 wt % relative to 100 wt % of the total metals excluding lithium in the final positive electrode active material.

[0144] The positive electrode active materials produced in Examples 1 to 10 and Comparative Examples 1 to 8 are briefly summarized in Table 1 below.

[0145] [Table 1]

[0146] Evaluation example 1: Aluminum content on the surface of the active material EP-EDS analysis was performed on the positive electrode active materials of Example 2, Comparative Example 3, and Comparative Example 4, and the ratio of the Al content (at%) to the total amount of Co and Al (100 at%) on the particle surface (Al / (Co+Al)) was calculated and shown in Table 2. The EP-EDS analysis was performed using a Thermo Fisher Helios G4 HX under conditions of 3 kV and 0.8 nA.

[0147] [Table 2]

[0148] Referring to Table 2, Example 2 and Comparative Example 3 used the same first lithium-cobalt-based oxide and second lithium-cobalt-based oxide, but the aluminum coating layer of the first positive electrode active material was wet-coated in Example 2, while the aluminum coating layer of the first positive electrode active material was dry-coated in Comparative Example 3. It can be seen that the aluminum content on the surface of the positive electrode active material in Example 2 was higher than that in Comparative Example 3.

[0149] Furthermore, in order to achieve an aluminum content on the surface of a cathode active material similar to that of Example 2 through dry coating, the aluminum content in aluminum sulfate should be designed to be 0.27 wt % relative to 100 wt % of the total metals excluding lithium in the final cathode active material, as in Comparative Example 4. However, in this case, it has been confirmed that the capacity and life characteristics are reduced, as described below.

[0150] Next, the first cathode active materials prepared in Example 2 and Comparative Example 3 were photographed using EP-EDS, and the results are shown in FIGS. 5 and 6. EP-EDS analysis was performed using a Thermo Fisher Helios G4 HX at 5 kV and 3.2 nA. Referring to FIG. 5, it can be seen that Al was coated on the particle surface in the form of a thin film. Meanwhile, referring to FIG. 6, it can be seen that Al was not uniformly distributed on the particle surface, but was distributed in the form of particles or locally aggregated. This confirms that the Al content on the surface increased during the wet coating process in Example 2 compared to the dry coating process in Comparative Example 3, enabling a more uniform coating.

[0151] Evaluation example 2: Initial capacity evaluation The lithium secondary batteries prepared in Examples 1 to 10 and Comparative Examples 1 to 8 were charged at a constant current of 0.2 C at 25° C. up to an upper limit voltage of 4.59 V, and then discharged at 0.2 C down to an end-of-discharge voltage of 3.0 V to measure the initial discharge capacity. The initial charge capacity, initial discharge capacity, and the ratio of the discharge capacity to the charge capacity were calculated as efficiency, and the results are shown in Table 3 below.

[0152] Evaluation example 3: High temperature life evaluation Following the initial charge and discharge of Evaluation Example 2, the cycle of charging and discharging at 1.0 C in the voltage range of 3.0 V to 4.59 V at 45°C was repeated 30 times or more, and the ratio of the 30-cycle discharge capacity to the initial discharge capacity was calculated and shown in Table 3 below as the high-temperature life.

[0153] [Table 3]

[0154] Referring to Table 3, Comparative Examples 1 to 8 were analyzed to have significantly low 4.59V high temperature lifespans of less than 70%. On the other hand, Examples 1 to 4 were analyzed to have higher 4.59V high temperature lifespans than Comparative Examples 1 to 4, and Examples 5 to 8 were analyzed to have higher 4.59V high temperature lifespans than not only Comparative Examples 5 to 8 but also Examples 1 to 4.

[0155] For example, comparing Example 6 and Comparative Example 6, the Al content of the first positive electrode active material was 0.9 wt % and the Al content of the second positive electrode active material was 1.0 wt %, respectively, but the difference was the Al coating method of the first positive electrode active material (wet vs. dry). In this case, it was confirmed that Example 6 had a superior 4.59 V high-temperature life compared to Comparative Example 6. Also, comparing Example 2 and Comparative Example 3, the Al content of the first positive electrode active material was 1.1 wt % and the Al content of the second positive electrode active material was 1.0 wt %, respectively, but the difference was the Al coating method of the first positive electrode active material (wet vs. dry). In this case, it was confirmed that Example 2 had a superior 4.59 V high-temperature life compared to Comparative Example 2.

[0156] Meanwhile, comparing Example 2 and Example 6, the Al coating of the first positive electrode active material was wet coated in the same amount of 0.1 wt %, but the Al content of the first positive electrode active material was higher than that of the second positive electrode active material in Example 2, while the Al content of the second positive electrode active material was higher than that of the first positive electrode active material in Example 6. In this case, it was confirmed that Example 6 had a superior 4.59 V high-temperature life compared to Example 2.

[0157] 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 following claims also fall within the scope of the present invention. [Explanation of symbols]

[0158] 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 tap 72: Negative tap

Claims

1. a first positive electrode active material containing a first lithium-cobalt-based oxide doped with aluminum and magnesium; and a second positive electrode active material containing a second lithium-cobalt-based oxide doped with aluminum and magnesium; The average particle size (D 50 ) is the average particle size (D 50 ) smaller than the first positive electrode active material and the second positive electrode active material each include an aluminum coating layer located on a particle surface; The aluminum coating layer of the first positive electrode active material has a shell shape that continuously surrounds the particle surface, The positive electrode active material has an aluminum content of 6 at % to 10 at % relative to 100 at % of the total of cobalt and aluminum as measured by energy profiling energy dispersive spectroscopy (EP-EDS) on the surface of the first positive electrode active material.

2. 2. The positive electrode active material of claim 1, wherein the first lithium cobalt-based oxide doped with aluminum and magnesium is represented by the following Chemical Formula 1: [Chemical formula 1] Li a1 Co x1 MM y1 Al z1 M 1 w1 O 2-b1 X b1 In Chemical Formula 1, 0.9≦a1≦1.8, 0.953≦x1≦0.965, 0.002≦y1≦0.005, 0.032≦z1≦0.04, 0≦w1≦0.002, 0.9≦x1+y1+z1+w1≦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, Zn, Y and Zr, and X is one or more elements selected from the group consisting of F, P and S.

3. The average particle size (D 50 2. The positive electrode active material according to claim 1, wherein the thickness of the first electrode layer is 7 μm to 30 μm.

4. 2. The positive electrode active material of claim 1, wherein the second lithium cobalt-based oxide doped with aluminum and magnesium is represented by the following Chemical Formula 2: [Chemical formula 2] Li a2 Co x2 MM y2 Al z2 M 2 w2 O 2-b2 X b2 In Chemical Formula 2, 0.9≦a2≦1.8, 0.953≦x2≦0.965, 0.002≦y2≦0.005, 0.032≦z2≦0.04, 0≦w2≦0.002, 0.9≦x2+y2+z2+w2≦1.1, and 0≦b2≦0.1; M 2 is at least one element selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y and Zr, and X is one or more elements selected from the group consisting of F, P and S.

5. The average particle size (D 50 2. The positive electrode active material according to claim 1, wherein the thickness of the first and second electrodes is 1 μm to 9 μm.

6. The doping amount of aluminum relative to the total weight of the first lithium-cobalt-based oxide is 0.9 weight % to 1.1 weight %; The doping amount of aluminum relative to the total weight of the second lithium cobalt-based oxide is 0.9 weight % to 1.1 weight %. The positive electrode active material according to claim 1 .

7. 2. The positive electrode active material according to claim 1, wherein the amount of aluminum doped in the second lithium-cobalt-based oxide is greater than the amount of aluminum doped in the first lithium-cobalt-based oxide.

8. 8. The positive electrode active material according to claim 7, wherein the amount of aluminum doped in the second lithium-cobalt-based oxide is 0.05% by weight to 0.5% by weight greater than the amount of aluminum doped in the first lithium-cobalt-based oxide.

9. The doping amount of magnesium relative to the total weight of the first lithium-cobalt-based oxide is 0.05 weight % to 0.15 weight %; The doping amount of magnesium relative to the total weight of the second lithium cobalt-based oxide is 0.05 weight % to 0.15 weight %. The positive electrode active material according to claim 1 .

10. 2. The cathode active material according to claim 1, wherein the first cathode active material is included in an amount of 50 wt% to 95 wt% and the second cathode active material is included in an amount of 5 wt% to 50 wt% relative to 100 wt% of the total of the first cathode active material and the second cathode active material.

11. The cathode active material of claim 1, wherein the aluminum coating layer has a thickness of 5 nm to 200 nm.

12. The positive electrode active material of claim 1 , wherein the thickness of the coating layer within one positive electrode active material particle has a deviation of 20% or less.

13. (i) providing a first positive electrode active material including a first lithium-cobalt-based oxide doped with aluminum and magnesium; (ii) adding aluminum sulfate to an aqueous solvent and mixing to prepare a coating solution; (iii) adding a first positive electrode active material to the coating solution and mixing them to prepare a mixed solution; (iv) removing the aqueous solvent from the mixed solution, drying the resultant, and then heat-treating the resultant to obtain a first positive electrode active material including an aluminum coating layer; (v) a second lithium cobalt-based oxide doped with aluminum and magnesium, having an average particle size (D 50 ) is the average particle size (D 50 providing a second positive electrode active material having a size smaller than the first positive electrode active material; (vi) adding aluminum oxide to the second positive electrode active material and heat treating the second positive electrode active material to obtain a second positive electrode active material including an aluminum coating layer; and (vii) mixing the first positive electrode active material including the aluminum coating layer and the second positive electrode active material including the aluminum coating layer; A method for producing a positive electrode active material, comprising:

14. In the step (iii), the time required to add the first positive electrode active material to the coating solution is 30 seconds / 500 g to 2 minutes / 500 g; The time for mixing the first positive electrode active material into the coating solution is 15 to 60 minutes. After mixing, the pH of the supernatant is 5.5 to 7.

5. The method for producing a positive electrode active material according to claim 13 .

15. In the step (iv), the coated product obtained by drying the obtained product comprises an aluminum coating layer on the particle surface, and the aluminum coating layer has a mesh or spider web shape; The heat treatment is carried out at a temperature range of 730°C to 1000°C. The method for producing a positive electrode active material according to claim 13 .

16. 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 12.

17. The loading level of the positive electrode active material layer is 10 mg / cm 2 ~30 mg / cm 2 17. The positive electrode of claim 16, wherein

18. 17. The positive electrode according to claim 16, wherein the density of the positive electrode active material layer is 4.1 g / cc to 4.5 g / cc.

19. The positive electrode of claim 16 ; a negative electrode; and Electrolyte; A lithium secondary battery comprising:

20. 20. The lithium secondary battery according to claim 19, wherein the charging voltage of the lithium secondary battery is 4.5 V or higher.

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