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

Abstract

To provide a positive electrode active material that improves the capacity characteristic, the initial charging and discharging efficiency, and the high-temperature life characteristic.SOLUTION: A positive electrode active material includes: a first positive electrode active material including layered lithium nickel manganese composite oxide, a core particle in a secondary particle mode formed by an aggregation of a plurality of primary particles, and an aluminum coating layer existing on a surface of the core particle; and a second positive electrode active material including layered lithium nickel manganese composite oxide, a core particle in a single particle mode, and an aluminum coating layer existing on a surface of the core particle, and having a smaller average particle diameter (D50) than the first positive electrode active material. In a dQ / dV graph according to the voltage, which is evaluated under conditions 1 C=200 mAh / g, 0.2 C, and an applied current of 0.5 mA to 0.7 mA after the chemical conversion, a ratio (H / V) of the peak intensity (H) to the voltage (V) in the first peak is (2.20×102) to (3.10×102).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material, 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. In recent years, 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 oxide, lithium nickel manganese cobalt composite oxide, lithium nickel cobalt aluminum composite oxide, and lithium cobalt oxide are commonly used as positive electrode active materials. Recently, demand for large-sized, high-capacity, and high-energy density lithium secondary batteries has skyrocketed, while the supply of positive electrode active materials containing the rare metal cobalt is expected to be extremely short. That is, because cobalt is expensive and its remaining reserves are limited, there is a need to develop positive electrode active materials that are free of cobalt or have a reduced cobalt content. Summary of the Invention [Problem to be solved by the invention]

[0004] As a positive electrode active material containing lithium nickel-manganese composite oxide, it increases energy density and improves performance at high temperatures and high voltages, thereby improving capacity characteristics, initial charge / discharge efficiency, and high-temperature life characteristics. [Means for solving the problem]

[0005] In one embodiment, a first positive electrode active material includes a layered lithium nickel-manganese composite oxide, a core particle in the form of a secondary particle formed by aggregating a plurality of primary particles, and an aluminum coating layer located on the surface of the core particle, and a second positive electrode active material includes a layered lithium nickel-manganese composite oxide, a core particle in the form of a single particle, and an aluminum coating layer located on the surface of the core particle, and has an average particle size (D 50 The positive electrode active material containing the second positive electrode active material having the above formula was evaluated under the conditions of 1C=200mAh / g, 0.2C, and an applied current of 0.5mA to 0.7mA after formation. In the dQ / dV graph according to the voltage, the ratio (H / V) of the peak intensity (H) to the voltage value (V) at the first peak was (2.20×10 2 )~(3.10×10 2 ) a positive electrode active material.

[0006] In another embodiment, a positive electrode is provided that 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.

[0007] In another embodiment, a lithium secondary battery is provided that includes the positive electrode, the negative electrode, and an electrolyte. [Effects of the Invention]

[0008] The positive electrode active material according to one embodiment maximizes capacity and energy density while minimizing production costs, ensuring long life characteristics and improving high voltage and high temperature characteristics. A lithium secondary battery using the positive electrode active material can exhibit high initial charge / discharge capacity and efficiency, and can achieve excellent high temperature life characteristics and high temperature storage characteristics. [Brief explanation of the drawings]

[0009] [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 graph showing dQ / dV during formation for the half cell of Example 1. [Figure 6] 1 is a graph showing dQ / dV during standard charge / discharge after formation for the half cell of Example 1. [Figure 7] 1 is a graph showing dQ / dV during formation and standard charge / discharge for the half cell of Comparative Example 1. [Figure 8] 10 is a graph showing dQ / dV during formation and standard charge / discharge for the half cell of Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0010] Although the present invention may be embodied in various different forms, it is not intended to be limited to the embodiments set forth herein.

[0011] 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.

[0012] As used herein, "combinations thereof" refers to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0013] 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 possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0014] 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 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.

[0015] Furthermore, the term "layer" as used herein includes not only shapes formed on the entire surface but also shapes formed on a portion of the surface when observed in a plan view.

[0016] 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 image or a scanning electron microscope image. Another method involves measuring using dynamic light scattering, and then performing data analysis to count the number of particles in each particle size range, and then calculating the average particle size value 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 specified, the average particle size is determined by measuring the size (diameter or length of the major axis) of 20 or more particles randomly selected in a scanning electron microscope image to obtain a particle size distribution, and then calculating the diameter (D) of the particles with a cumulative volume of 50% from the particle size distribution. 50 ) may be taken as the average particle size.

[0017] Here, "or" is not to be construed as exclusive; for example, "A or B" is to be construed as including A, B, A+B, etc.

[0018] The term "metal" is understood to include general metals, transition metals, and semimetals (metalloids).

[0019] positive electrode active material In one embodiment, a first positive electrode active material includes a layered lithium nickel-manganese composite oxide, a core particle in the form of a secondary particle formed by aggregating a plurality of primary particles, and an aluminum coating layer located on the surface of the core particle, and a second positive electrode active material includes a layered lithium nickel-manganese composite oxide, a core particle in the form of a single particle, and an aluminum coating layer located on the surface of the core particle, and has an average particle size (D 50 The present invention provides a positive electrode active material comprising a second positive electrode active material having a

[0020] The positive electrode active material was evaluated under the conditions of 1C=200mAh / g, 0.2C, and an applied current of 0.5mA to 0.7mA after formation. In the dQ / dV graph according to the voltage, the ratio (H / V) of the peak intensity (H) to the voltage value (V) at the first peak was (2.20×10 2 )~(3.10×10 2 ) is satisfied. Such a positive electrode active material has high energy density and capacity, and can achieve excellent high voltage and high temperature characteristics. The H / V ratio is, for example, 2.20 × 10 2 ~3.00×10 2 , or 2.25 × 10 2 ~2.50×10 2 The formation can be said to be the first charge / discharge process after the battery is manufactured, and the H / V value can be said to be the dQ / dV graph value in the charge / discharge cycle after the formation, that is, it can be expressed as the dQ / dV graph value during standard charge / discharge, for example, the value in the second charge / discharge cycle. The unit of the H / V ratio is mAh / gV. 2 is.

[0021] At the first peak of the dQ / dV graph, the voltage value (V) may be located in the range of 3.60 V to 3.85 V. That is, the first peak may be located in the voltage range of 3.60 V to 3.85 V. The peak intensity (H) may be the dQ / dV value of the first peak, and may be, for example, 700 mAh / gV to 1100 mAh / gV, or 800 mAh / gV to 1000 mAh / gV.

[0022] The dQ / dV graph may be characterized by showing only one peak in the voltage range of 3.60 V to 3.85 V. Meanwhile, the dQ / dV graph according to the voltage during formation may show two peaks in the voltage range of 3.60 V to 3.85 V. That is, the positive electrode active material according to one embodiment may be characterized by showing two peaks in the voltage range during formation, and showing only one peak during standard charge-discharge cycles after formation.

[0023] Also, in the dQ / dV graph according to the voltage during formation, the voltage value of the first peak is V 1 , and the peak intensity is H 1 The voltage value of the second peak is V 2 , the peak intensity is H 2 In this case, the positive electrode active material is V 1 <V<V 2 I was able to satisfy my desires and 1 <H<H 2 The positive electrode active material satisfies m(H 1 / V 1 )<(H / V)<(H 2 / V 2 ) can be satisfied. Here, V is the voltage of the first peak in the dQ / dV graph during standard charge / discharge after the above-mentioned chemical formation, and H is the intensity of this peak. A positive electrode active material containing a layered lithium nickel-manganese composite oxide that exhibits such dQ / dV characteristics can achieve excellent characteristics at high voltages and high temperatures while exhibiting high energy density.

[0024] The positive electrode active material according to one embodiment includes a first positive electrode active material and a second positive electrode active material.

[0025] The average particle size (D 50 ) is the average particle size (D 50) is larger than the average particle size. The first positive electrode active material can be described as large grains or large particles, and the second positive electrode active material can be described as small grains or small particles. By appropriately mixing large particles in the form of secondary particles and small particles in the form of single particles, the capacity and energy density of the lithium nickel-manganese positive electrode can be maximized, and long life and high voltage characteristics can be improved. Here, the average particle size is determined by measuring the size (diameter or major axis length) of 20 or so particles randomly selected in a scanning electron microscope image of the positive electrode active material to obtain a particle size distribution, and then calculating the diameter (D) of the particles that make up 50% of the cumulative volume from the particle size distribution. 50 ) may be taken as the average particle size.

[0026] The average particle size (D 50 The average particle diameter (D ) of the single particles of the second positive electrode active material may be, for example, 10 μm to 20 μm, 10 μm to 18 μm, or 12 μm to 16 μm. 50 ) may be, for example, 1 μm to 8 μm, 1 μm to 7 μm, 1.5 μm to 6 μm, or 2 μm to 5 μm. When the average particle size of each positive electrode active material falls within the above range, a high energy density can be achieved and excellent life characteristics can be exhibited.

[0027] The first positive electrode active material is included in an amount of 60% to 95% by weight, for example, 70% to 90% by weight, based on a total of 100% by weight of the first positive electrode active material and the second positive electrode active material. The second positive electrode active material is included in an amount of 5% to 40% by weight, for example, 10% to 30% by weight, based on a total of 100% by weight of the first positive electrode active material and the second positive electrode active material. When the mixing ratio of the first positive electrode active material to the second positive electrode active material satisfies the above range, it is possible to increase the energy density while maximizing the capacity.

[0028] Lithium nickel-manganese composite oxide The layered lithium nickel-manganese composite oxide of the first positive electrode active material and the layered lithium nickel-manganese composite oxide of the second positive electrode active material may be the same as or different from each other.

[0029] The price of the rare metal cobalt has skyrocketed in recent years, spurring the development of cobalt-free or reduced-content cathode active materials. Among these, cathode active materials with olivine-based crystal structures, such as lithium iron phosphate (LFP), lithium manganese phosphate (LMP), and lithium manganese iron phosphate (LMFP), or spinel-based crystal structures, such as lithium manganese oxide (LMO), have limited lithium availability within their structures, limiting their ability to achieve high capacity. Layered lithium-nickel-manganese cathode active materials have a high lithium availability within their structures, offering excellent capacity and efficiency characteristics, making them suitable for high-capacity batteries. However, the removal of cobalt, which plays a key role in the layered structure, reduces structural stability, increases resistance, and hinders long-life performance. Furthermore, the removal of cobalt accelerates side reactions between the cathode active material and electrolyte under high-voltage and high-temperature conditions, increasing gas generation and reducing lifespan.

[0030] Therefore, in one embodiment, a positive electrode active material is proposed in which the capacity and life characteristics at high voltage of the positive electrode active material are improved by appropriately adjusting the ratio of nickel to manganese in a lithium nickel-manganese composite oxide, introducing elements other than nickel and manganese such as aluminum, or applying an appropriate coating method to introduce a uniform coating layer.

[0031] In the layered lithium nickel-manganese composite oxide, the nickel content is 60 mol% or more, relative to 100 mol% of all metals in the lithium nickel-manganese composite oxide excluding lithium, and may be, for example, 60 mol% to 80 mol%, 65 mol% to 80 mol%, 70 mol% to 80 mol%, 60 mol% to 79 mol%, 60 mol% to 78 mol%, or 60 mol% to 75 mol%, etc. When the nickel content satisfies the above range, high capacity can be achieved and structural safety can be improved even if the cobalt content is reduced.

[0032] The manganese content in the layered lithium nickel-manganese composite oxide is, for example, 10 mol % or more, or 15 mol % or more, relative to 100 mol % of all metals excluding lithium, and may be, for example, 10 mol % to 40 mol %, 15 mol % to 40 mol %, 15 mol % to 35 mol %, 15 mol % to 30 mol %, or 20 mol % to 30 mol %, etc. When the manganese content satisfies this range, the positive electrode active material can achieve high capacity while improving structural stability.

[0033] In each of the first and second positive electrode active materials, the lithium nickel-manganese composite oxide may be a lithium nickel-manganese-aluminum composite oxide containing aluminum in addition to nickel and manganese. The presence of aluminum in the composite oxide is advantageous for maintaining a stable layered structure even when cobalt is excluded from the structure. The aluminum content relative to 100 mol% of the lithium nickel-manganese-aluminum composite oxide may be 0.1 mol% or more, 0.5 mol% or more, or 1 mol% or more, for example, 1 mol% to 3 mol%, 1 mol% to 2.5 mol%, 1 mol% to 2 mol%, or 1 mol% to 1.9 mol%. When the aluminum content is within the above range, a stable layered structure can be maintained even when cobalt is excluded, suppressing the problem of structural collapse during charge and discharge, and achieving long-life characteristics for the positive electrode active material.

[0034] The lithium nickel-manganese composite oxide of the first positive electrode active material and the lithium nickel-manganese composite oxide of the second positive electrode active material are each independently represented by the following [Chemical Formula 1]. [Chemical formula 1] Li a1 Ni x1 Mn y1 Al z1 M 1 w1 O 2-b1 X b1

[0035] In Chemical Formula 1, 0.9 ≤ a1 ≤ 1.8, 0.6 ≤ x1 ≤ 0.8, 0.1 ≤ y1 ≤ 0.4, 0 ≤ z1 ≤ 0.03, 0 ≤ w1 ≤ 0.3, 0.9 ≤ x1 + y1 + z1 + w1 ≤ 1.1, and 0 ≤ b1 ≤ 0.1, and M 1 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from F, P, and S.

[0036] In Chemical Formula 1, 0.9 ≤ a1 ≤ 1.5 or 0.9 ≤ a1 ≤ 1.2 may also be satisfied. Further, Chemical Formula 1 may contain aluminum, and in this case, 0.6 ≤ x1 ≤ 0.8, 0.1 ≤ y1 ≤ 0.39, 0.01 ≤ z1 ≤ 0.03, and 0 ≤ w1 ≤ 0.29 can be satisfied, for example, 0.6 ≤ x1 ≤ 0.8, 0.1 ≤ y1 ≤ 0.39, 0.01 < z1 ≤ 0.03, and 0 ≤ w1 ≤ 0.29 can be satisfied.

[0037] In Chemical Formula 1, for example, 0.6 ≤ x1 ≤ 0.79, 0.6 ≤ x1 ≤ 0.78, 0.6 ≤ x1 ≤ 0.75, 0.65 ≤ x1 ≤ 0.8, or 0.7 ≤ x1 ≤ 0.79 may also be satisfied, 0.1 ≤ y1 ≤ 0.35, 0.1 ≤ y1 ≤ 0.30, 0.1 ≤ y1 ≤ 0.29, 0.15 ≤ y1 ≤ 0.39, or 0.2 ≤ y1 ≤ 0.3 may also be satisfied, 0.01 ≤ z1 ≤ 0.025, 0.01 < z1 ≤ 0.02, or 其 0.01 < z1 ≤ 0.019 may also be satisfied, 0 ≤ w1 ≤ 0.28, 0 ≤ w1 ≤ 0.27, 0 ≤ w1 ≤ 0.26, 0 ≤ w1 ≤ 0.25, 0 ≤ w1 ≤ 0.24, 0 ≤ w1 ≤ 0.23, 0 ≤ w1 ≤ 0.22, 0 ≤ w1 ≤ 0.21, 0 ≤ w1 ≤ 0.2, or 0 ≤ w1 ≤ 0.15, 0 ≤ w1 ≤ 0.1, or 0 ≤ w1 ≤ 0.09 etc. may also be satisfied. [[ID=il]]

[0038] It should be noted that there is an unclear "其" in the translation of ID=10, which needs to be further confirmed according to the specific context to ensure the accuracy of the translation.The lithium nickel-manganese composite oxide may be a cobalt-free compound that does not contain cobalt or contains only a trace amount of cobalt. That is, the lithium nickel-manganese composite oxide of the first positive electrode active material and the lithium nickel-manganese composite oxide of the second positive electrode active material may each independently contain 0 mol % to 0.01 mol % of cobalt relative to 100 mol % of all metals excluding lithium.

[0039] First positive electrode active material According to one embodiment, the aluminum concentration is uniform within the secondary particles of the first positive electrode active material, excluding the coating layer. This means that the aluminum is evenly dispersed within the particles, without an aluminum concentration gradient from the center to the surface within the particle or a higher or lower aluminum concentration at the outside than at the inside. This structure can be achieved by synthesizing a composite oxide using a nickel-manganese-aluminum hydroxide as a precursor, without additionally doping aluminum during the synthesis of the positive electrode active material. This means that the aluminum content within the primary particles is the same or similar regardless of the position of the primary particle. By selecting a primary particle at any position on the cross section of the secondary particle and measuring the aluminum content within the primary particle, rather than at the interface, the aluminum content can be expressed as the same / similar / uniform regardless of the position of the primary particle, i.e., whether the primary particle is near the center or the surface of the secondary particle. In this structure, a stable layered structure can be maintained even when cobalt is absent or present in only trace amounts, and aluminum by-products and aluminum aggregates are not generated, thereby simultaneously improving the capacity, efficiency, and life characteristics of the positive electrode active material.

[0040] The first positive electrode active material includes an aluminum coating layer located on the surface of the secondary particles. By including the aluminum-rich layer on the surface, the first positive electrode active material effectively suppresses side reactions with the electrolyte at high voltages, improving capacity and life characteristics at high voltages. Layered lithium nickel-manganese composite oxides are susceptible to chemical attack from components in the electrolyte when the battery is operated under high voltage or high temperature conditions, resulting in frequent side reactions with the electrolyte, resulting in increased gas generation and reduced battery life and safety. However, the introduction of a coating layer according to one embodiment can alleviate these issues.

[0041] The aluminum coating layer can include, for example, aluminum oxide, lithium aluminum oxide, or a combination thereof, and can include LiAlO2 as one example.

[0042] The aluminum content of the coating layer may be 0.1 mol % to 2 mol %, for example, 0.2 mol % to 1.9 mol %, 0.3 mol % to 1.8 mol %, 0.5 mol % to 1.5 mol %, or 0.8 mol % to 1.3 mol %, relative to 100 mol % of all metals excluding lithium in the first positive electrode active material. The aluminum and other component contents in the coating layer may 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 does not increase, side reactions with the electrolyte are effectively suppressed, and the life characteristics of lithium secondary batteries at high voltages can be improved.

[0043] Layered lithium nickel-manganese composite oxides differ significantly in the residual lithium content on the particle surface compared to oxides of other compositions, such as lithium nickel-cobalt-manganese composite oxides, lithium nickel-cobalt-aluminum composite oxides, and lithium cobalt-based oxides, resulting in various surface characteristics that make it difficult to form a uniform, well-formed coating layer using conventional coating methods. Therefore, in one embodiment, a uniform coating layer can be formed on the first and / or second positive electrode active material by (i) first preparing a coating solution in which the salt is completely dissolved by adding coating materials to an aqueous solvent and mixing them together, (ii) adding core particles to this coating solution and mixing them together, and (iii) subsequently removing the solvent, drying, and heat-treating the resulting mixture. This is a salt-dissolution wet coating method, which can be considered a pre-addition method in which the salt of the coating material is first completely dissolved and then the active material particles are added. This method successfully forms a uniform, thin coating layer on the surface of the layered lithium nickel-manganese composite oxide.

[0044] This coating method can further increase the content of coating elements on the active material surface compared to conventional dry methods or post-addition wet methods. For example, the coating content on the surface of the first positive electrode active material measured by EP-EDS analysis is 5 at% to 35 at% relative to 100 at% of the total metals excluding lithium on the surface, and may be, for example, 5 at% to 30 at%, 5 at% to 25 at%, 5 at% to 25 at%, or 10 at% to 20 at%. Within this content range, the coating layer can effectively improve high-voltage characteristics without increasing the resistance of the positive electrode active material.

[0045] The coating layer of the first positive electrode active material may be in the form of a film continuously surrounding the surfaces of the secondary particles, for example, in the form of a shell surrounding the entire surfaces of the secondary particles. This is distinct from a structure in which only a portion of the surfaces of the secondary particles is partially coated. According to one embodiment, the coating layer is formed to completely surround the surfaces of the secondary particles and to a very thin and uniform thickness. As a result, the positive electrode active material exhibits improved structural stability without an increase in resistance or a decrease in capacity, effectively suppresses side reactions with the electrolyte, and reduces gas generation under high voltage and high temperature conditions, thereby achieving long-life characteristics.

[0046] The thickness of the coating layer of the first positive electrode active material may be 5 nm to 500 nm, for example, 5 nm to 450 nm, 5 nm to 400 nm, 5 nm to 350 nm, 5 nm to 300 nm, 5 nm to 250 nm, 5 nm to 200 nm, 5 nm to 150 nm, 5 nm to 100 nm, 5 nm to 80 nm, 10 nm to 50 nm, 20 nm to 500 nm, 30 nm to 500 nm, or 40 nm to 500 nm. For example, the thickness of the coating layer may be 40 nm or less. When the 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 the thickness range of the coating layer may be measured using a TEM-EDS linear profile.

[0047] The coating layer of the first positive electrode active material is characterized by its thin, uniform thickness, ranging from several tens to several hundreds of nanometers. For example, the thickness deviation of the coating layer within a single positive electrode 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 positive electrode active material particle. For example, the coating thickness deviation may be calculated by measuring the thickness at approximately 10 points on an electron microscope image of the cross section of a single positive electrode 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 coating layer of uniform thickness is well formed in the form of a film on the surface of the positive electrode active material particle, thereby improving the structural stability of the positive electrode active material, effectively suppressing side reactions with the electrolyte, and minimizing increases in resistance and capacity loss due to the coating.

[0048] The coating layer of the first positive electrode active material may further include B, Mg, Ti, V, W, Y, Zr, or a combination thereof in addition to aluminum, and in this case, structural stability may be improved, thereby improving life characteristics.

[0049] For example, the coating layer of the first positive electrode active material may further include zirconium. The zirconium content in the coating layer may be 0.05 mol % to 1 mol %, for example, 0.1 mol % to 1 mol %, 0.1 mol % to 0.9 mol %, 0.1 mol % to 0.8 mol %, or 0.1 mol % to 0.6 mol %, relative to 100 mol % of the total metals excluding lithium in the first positive electrode active material. When the zirconium content satisfies this range, the positive electrode active material does not experience a decrease in capacity or an increase in resistance, forms a good coating layer, effectively suppresses side reactions with the electrolyte, and further improves capacity characteristics and life characteristics under high-voltage driving conditions.

[0050] The coating layer of the first positive electrode active material may further contain yttrium, and in this case, the content of yttrium may be 0.1 mol % to 1 mol % relative to 100 mol % of all metals excluding lithium of the first positive electrode active material.

[0051] Meanwhile, aluminum may diffuse into the secondary particles during the coating layer formation process. Therefore, the positive electrode active material according to one embodiment may further include a grain boundary coating region containing aluminum located on the surface of the primary particles within the secondary particles. The "interior of the secondary particles" may refer to the entire interior of the secondary particles excluding the surface, or may refer to the region extending from the surface of the secondary particles toward the center of the secondary particles, extending up to approximately 60% of the radius. The grain boundary coating region is a concept distinct from the coating layer on the surface of the secondary particles, and refers to a coating region formed on the surface of the primary particles located within the secondary particles. The presence of the grain boundary coating region can be confirmed by SEM-EDS analysis of a cross section of the positive electrode active material. The formation of the aluminum grain boundary coating region further stabilizes the structure of the positive electrode active material, improving its lifespan.

[0052] The aluminum content in the grain boundary coating portion is not particularly limited, and for example, the aluminum content in the grain boundary coating portion may be less than the aluminum content in the coating layer.

[0053] Meanwhile, the aluminum content of the coating layer of the first positive electrode active material may be higher than the aluminum content of the coating layer of the second positive electrode active material (described later). For example, the aluminum content of the coating layer of the first positive electrode active material and the aluminum content of the coating layer of the second positive electrode active material may be 5:1 to 2:1, or 4:1 to 2:1, in mole fraction. In this case, the aluminum in the coating layers of the first and second positive electrode active materials does not act as a resistor, improving the structural stability of each material and maximizing the capacity and life characteristics at high voltage.

[0054] Second positive electrode active material The term "single particle" of the second positive electrode active material means a particle that exists independently without a grain boundary and is composed of a single particle, and refers to a single particle, a monolith structure, a single body structure, or a non-aggregated particle in which the particles are morphologically present in an independent phase without aggregation, and may be, for example, a single crystal.

[0055] The second positive electrode active material includes an aluminum coating layer located on the surface of the single particle, which effectively suppresses side reactions with the electrolyte at high voltages and improves capacity and lifespan characteristics at high voltages.

[0056] The aluminum content in the coating layer of the second positive electrode active material is 0.1 mol% to 2 mol%, for example, 0.2 mol% to 1.9 mol%, 0.3 mol% to 1.8 mol%, 0.5 mol% to 1.5 mol%, or 0.8 mol% to 1.3 mol%, based on 100 mol% of the total metals (excluding lithium) in the second positive electrode active material. This refers to the aluminum content in the coating layer, separate from the aluminum contained within the individual 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 life characteristics of lithium secondary batteries under high-voltage and high-temperature conditions can be improved. For example, if the aluminum content of the coating layer is excessive, a uniform coating layer may not be formed or the resistance may increase, resulting in reduced charge / discharge efficiency and life characteristics. If the aluminum content of the coating layer is too low, a coating layer of appropriate thickness may not be formed, resulting in reduced effectiveness in suppressing side reactions with the electrolyte.

[0057] The coating layer of the second positive electrode active material may further include B, Mg, Ti, V, W, Y, Zr, or a combination thereof in addition to aluminum, and in this case, structural stability may be improved, thereby improving life characteristics.

[0058] For example, the coating layer of the second positive electrode active material may further include yttrium. The yttrium content in the coating layer of the second positive electrode active material is 0.1 mol % to 1 mol %, relative to 100 mol % of all metals excluding lithium in the second positive electrode active material, and may be, for example, 0.1 mol % to 0.9 mol %, 0.1 mol % to 0.8 mol %, 0.1 mol % to 0.6 mol %, 0.1 mol % to 0.4 mol %, or 0.1 mol % to 0.3 mol %. When the yttrium content satisfies this range, the positive electrode active material forms a good coating layer without a decrease in capacity or an increase in resistance, effectively suppresses side reactions with the electrolyte, and effectively reduces the amount of gas generation under high voltage and high temperature conditions.

[0059] The coating layer of the second positive electrode active material may be in the form of a film that continuously surrounds the surface of the single particle, for example, in the form of a shell that surrounds the entire surface of the single particle. This is distinct from a structure in which only a portion of the particle surface is partially coated. According to one embodiment, the coating layer may be formed to completely surround the surface of the single particle, but with a very thin and uniform thickness. As a result, the positive electrode active material does not increase in resistance or decrease in capacity, has improved structural stability, effectively suppresses side reactions with the electrolyte, and achieves long-life characteristics at high voltages.

[0060] The thickness of the coating layer of the second positive electrode active material may be 5 nm to 500 nm, for example, 5 nm to 450 nm, 5 nm to 400 nm, 5 nm to 350 nm, 5 nm to 300 nm, 5 nm to 250 nm, 5 nm to 200 nm, 5 nm to 150 nm, 5 nm to 100 nm, 5 nm to 80 nm, 10 nm to 50 nm, 20 nm to 500 nm, 30 nm to 500 nm, or 40 nm to 500 nm. For example, the thickness of the coating layer may be 40 nm or less. When the 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 can be improved, 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, and the thickness range of the coating layer may be measured by TEM-EDS line profile.

[0061] In the coating layer of the second positive electrode active material, aluminum may exist in the form of a continuous film, and yttrium may exist in the form of islands, due to the properties of each element.

[0062] In one embodiment, aluminum and yttrium may be mixed in one coating layer, and in this case, aluminum may exist in the form of a continuous film and yttrium may exist in the form of islands, but the form is not limited thereto.

[0063] In another embodiment, aluminum and yttrium may form separate layers. For example, the second positive electrode active material may include a first coating layer containing aluminum located on the surface of the single particles, and a second coating layer containing yttrium located on the first coating layer. Aluminum first adheres to or is absorbed onto the surface of the single particles to form a thin first coating layer, and yttrium is then coated on top of the first coating layer to form the second coating layer. While aluminum and yttrium may be mixed in the first and second coating layers, the first coating layer may be an aluminum-leached coating layer primarily composed of aluminum, and the second coating layer may be an yttrium-leached coating layer primarily composed of yttrium. Even in this case, yttrium may exist in the second coating layer in the form of islands, but this is not particularly limited.

[0064] The thicknesses of the first coating layer and the second coating layer are not particularly limited, but the thickness of the first coating layer is 5 nm to 200 nm, and may be, for example, 5 nm to 100 nm, 5 nm to 80 nm, or 10 nm to 50 nm. The thickness of the second coating layer is 5 nm to 300 nm, and may be, for example, 5 nm to 200 nm, 5 nm to 100 nm, 5 nm to 80 nm, or 10 nm to 50 nm. When each thickness falls within the above range, the coating does not increase resistance or decrease capacity, but the structural stability of the positive electrode active material is improved, side reactions with the electrolyte are effectively suppressed, and life characteristics at high voltages can be improved.

[0065] The cobalt content in the positive electrode active material according to an embodiment may be, for example, 0.01 mol % or less, 0.005 mol % or less, or 0.001 mol % or less, for example, 0 mol % to 0.01 mol %, relative to 100 mol % of all metals excluding lithium. The positive electrode active material according to an embodiment may be, for example, a cobalt-free positive electrode active material.

[0066] In addition, the positive electrode active material according to an embodiment may be characterized by being sodium-free. Although sodium ions are generally used in the manufacturing process of a positive electrode active material, the manufacturing method described below allows positive electrode active material particles with a stable structure and a coating layer with a uniform thickness to be formed without using sodium ions.

[0067] The positive electrode active material according to one embodiment may contain sulfur (S) components on the surface, which can be attributed to the aluminum coating raw material.

[0068] 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.

[0069] 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 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 high-capacity, high-energy-density lithium secondary battery.

[0070] 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)acrylate styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0071] Conductive material The conductive material is used to impart conductivity to the electrodes, and any material that is electronically conductive and does not undergo 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 containing copper, nickel, aluminum, silver, etc., in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0072] 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.

[0073] The positive electrode current collector may be made of Al, but is not limited to this.

[0074] 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.

[0075] 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 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 configurations. 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.

[0076] The lithium secondary battery according to an embodiment may be suitable for being chargeable at a high voltage or for being driven at a high voltage. For example, the charge 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 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.

[0077] 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.

[0078] 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.

[0079] 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. 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.

[0080] 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.

[0081] 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, SiO x (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.

[0082] The silicon-carbon composite may be a composite of silicon and amorphous carbon. The average particle diameter (D 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 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.

[0083] 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 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.

[0084] 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.

[0085] The thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. 50It 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 SiO x represented by (0 < x < 2). At this time, the ratio of the atomic content 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.

[0086] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used in mixture with a carbon-based negative electrode active material. When the Si-based negative electrode active material or the Sn-based negative electrode active material and the carbon-based negative electrode active material are used in mixture, the mixing ratio may be 1:99 to 90:10 by weight ratio.

[0087] Binder The binder serves to make the negative electrode active material particles adhere well to each other and also make 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] The dry binder may be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0092] Conductive material The conductive material is used to impart conductivity to the electrodes, and any material that is electronically conductive and does not undergo chemical changes 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.

[0093] 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.

[0094] 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.

[0095] electrolyte The electrolyte for a lithium secondary battery may be, for example, an electrolytic solution, which may include a non-aqueous organic solvent and a lithium salt.

[0096] 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.

[0097] 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 hydrocarbon group having a linear, branched, or cyclic structure and having 2 to 20 carbon atoms, and 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.

[0098] 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 skilled in the art.

[0099] 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 are mixed in a volume ratio of 1:1 to 1:9.

[0100] 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.

[0101] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate, or ethylene carbonate based compounds to improve battery life.

[0102] 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.

[0103] 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).

[0104] 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 has appropriate ionic conductivity and viscosity, thereby exhibiting excellent performance and allowing lithium ions to migrate effectively.

[0105] 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 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.

[0106] 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.

[0107] The porous substrate may be a polymer membrane formed from any 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] Examples of the present invention and comparative examples are described below. The following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0114] Example 1 1. Production of positive electrode active material (1) Preparation of the first positive electrode active material Ni was added so that the molar ratio of (Ni+Mn+Al):Li was 1:1.05. 0.75 Mn 0.23 Al 0.02 (OH)2 and LiOH were mixed and subjected to a first heat treatment at 845°C for 8 hours in an oxygen atmosphere to obtain a composition of Li1.05 Ni 0.75 Mn 0.23 Al 0.02 O2 and the average particle size (D 50 ) was produced as a first composite oxide in the form of secondary particles with a particle size of about 14 μm.

[0115] A coating solution was prepared by adding 600g of distilled water and aluminum sulfate to a 1L reactor and stirring at 350 rpm for 5 minutes to dissolve the salt. The coating solution was confirmed to be colorless and transparent, with the salt completely dissolved. 500g of the prepared first composite oxide was added to the continuously stirred coating solution for 1.5 minutes and stirred for 30 minutes to prepare a first mixed solution. The aluminum content in the aluminum sulfate was designed to be 1 mol% relative to 100 mol% of the total metals (excluding lithium) in the final cathode active material. The pH of the first mixed solution after stirring was confirmed to be 6.6. The solvent was then removed from the second mixed solution using an aspirator and filter press, and the solution was vacuum dried at 190°C to obtain a coated product.

[0116] The coated product was subjected to a second heat treatment at 825° C. for 8 hours in an oxygen atmosphere to prepare a first positive electrode active material.

[0117] (2) Preparation of the second positive electrode active material Ni was added so that the molar ratio of (Ni+Mn):Li:Al was 1:1.05:0.02. 0.75 Mn 0.25 (OH)2, LiOH, and Al2O3 were mixed and heat-treated in an oxygen atmosphere at 900°C for 8 hours to obtain a composition of Li 1.05 Ni 0.75 Mn 0.23 Al 0.02 O2 and the average particle size (D 50 ) was produced as a second composite oxide in the form of single particles with a particle size of about 3 μm.

[0118] The second composite oxide, Al2O3, and Y2O3 were dry mixed and heat-treated in an oxygen atmosphere at 825°C for 8 hours to produce a second positive electrode active material. At this time, the coating aluminum was mixed at 0.4 mol% and yttrium was mixed at 0.05 mol% relative to 100% by weight of the total metals excluding lithium in the final second positive electrode active material.

[0119] (3) Production of final positive electrode active material The first and second positive electrode active materials were mixed in a weight ratio of 7:3 to prepare a final positive electrode active material. The pellet density of the final positive electrode active material was confirmed to be 3.56 g / cc.

[0120] 2. Fabrication of Half-cells 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 10 mg / cm. 2 I did.

[0121] A polytetrafluoroethylene separator was placed between the positive electrode and the lithium metal counter electrode and inserted into a case. An electrolyte solution of 1M LiPF6 dissolved in a solvent made by mixing ethylene carbonate and dimethyl carbonate in a volume ratio of 3:7 was poured into the case to prepare a half-cell in the usual manner.

[0122] Comparative Example 1 A half cell was fabricated in substantially the same manner as in Example 1, except that only the first positive electrode active material was used in fabricating the positive electrode.

[0123] Comparative Example 2 A half cell was fabricated in substantially the same manner as in Example 1, except that only the second positive electrode active material was used in fabricating the positive electrode.

[0124] Comparative Example 3 A cathode active material and a half cell were prepared in substantially the same manner as in Example 1, except that in the preparation of the first cathode active material of Example 1, the first composite oxide and aluminum oxide powder were mixed in a dry state and then subjected to a second heat treatment at 825°C for 8 hours to perform an Al coating in a dry state.

[0125] Evaluation example 1: dQ / dV evaluation The half-cells produced in Example 1 and Comparative Examples 1 to 3 were charged at a constant current of 0.2 C at 25°C up to an upper voltage of 4.45 V, then at a constant voltage of 0.05 C, and then discharged at 0.2 C to a cut-off voltage of 3.0 V, to carry out a chemical formation process (first charge / discharge). Subsequently, one cycle of standard charge / discharge (second charge / discharge) was carried out under the same conditions as the chemical formation process. 1 C = 200 mAh / g, and the applied current was in the range of 0.5 mA to 0.7 mA.

[0126] A graph of dQ / dV as a function of charge / discharge voltage during formation for the battery of Example 1 is shown in FIG. 5, and a graph of dQ / dV as a function of charge / discharge voltage during standard charge / discharge is shown in FIG. 6. In FIG. 5, the voltage value at the first peak is V 1 , the dQ / dV value of the peak intensity is H 1 and the voltage value at the second peak is V 2 , the peak intensity is H 2 In Figure 6, the voltage value at the first peak is displayed as V 3 , the peak intensity is H 3 In Table 1 below, V 1 ~V 3 , and H 1 ~H 3 The value indicates H 1 / V 1 , H 2 / V 2 , and H 3 / V 3 were calculated and shown together.

[0127] [Table 1]

[0128] 5 and 6 and Table 1, in the example, the H 3 / V 3 The ratio is 2.261 x 10 2 Meet the V 1 <V 3 <V 2 , H 1 <H 3 <H 2 , and (H 1 / V 1 )<(H 3 / V 3 )<(H 2 / V 2 ) can be confirmed to be satisfied.

[0129] 7 is a graph showing dQ / dV during formation and standard charge / discharge for a half cell of Comparative Example 1, which uses only the first positive electrode active material. Referring to FIG. 7, in the case of Comparative Example 1, there are two peaks in the range of 3.65V to 3.80V during formation, but there is only one peak during standard charge / discharge thereafter. In the dQ / dV graph for Comparative Example 1 during standard charge / discharge, the H of the first peak 3 / V 3 is 2.18 x 10 2 and it is confirmed that it is outside the range according to one embodiment.

[0130] 8 is a graph showing dQ / dV during formation and standard charge / discharge for a half-cell of Comparative Example 2, which uses only the second positive electrode active material. Referring to FIG. 8, two peaks appear in the range of 3.65 V to 3.80 V during formation, and two more peaks appear during standard charge / discharge thereafter, indicating a different behavior from the dQ / dV graph according to an embodiment.

[0131] In the case of Comparative Example 3, two peaks appeared in the range of 3.65 V to 3.80 V during formation, and one peak appeared during standard charge / discharge. However, in Comparative Example 3, the voltage of the first peak (V 3 ) is 3.83V, and the peak intensity (H 3 ) is 1215, H 3 / V 3is 3.17×10 2 It was analyzed and confirmed that this is outside the range according to one embodiment.

[0132] Evaluation example 2: Characterization of battery initial charge / discharge capacity and high-temperature life The discharge capacities during standard charge and discharge in Evaluation Example 1 for the half cells of Example 1 and Comparative Examples 1 and 2 are shown as initial discharge capacities in Table 2 below. Following the standard charge and discharge, a cycle of charging at 1.0 C and discharging at 1.0 C in a voltage range of 3.0 V to 4.45 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 as high-temperature life.

[0133] [Table 2]

[0134] Referring to Table 2, Example 1 has a similar initial discharge capacity compared to Comparative Examples 1 and 2, while exhibiting improved high-temperature life characteristics.

[0135] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, 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]

[0136] 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 tap 71: Positive electrode tab 72: Negative electrode tab

Claims

1. a first positive electrode active material including: a core particle in the form of a secondary particle formed by aggregating a plurality of primary particles, the core particle including a layered lithium nickel-manganese composite oxide; and an aluminum coating layer located on a surface of the core particle; The present invention relates to a layered lithium nickel-manganese composite oxide, which includes a core particle in the form of a single particle and an aluminum coating layer located on the surface of the core particle, and has an average particle size (D 50 a positive electrode active material including a second positive electrode active material having In the dQ / dV graph according to the voltage evaluated under the conditions of 1C = 200 mAh / g, 0.2C, and applied current of 0.5 mA to 0.7 mA after formation, the ratio (H / V) of peak intensity (H) to voltage (V) at the first peak was (2.20 × 10 2 ) ~ (3.10 x 10 2 ) is a positive electrode active material.

2. 2. The positive electrode active material according to claim 1, wherein the first peak of the dQ / dV graph is located in a voltage (V) range of 3.60 V to 3.85 V and has a peak intensity (H) in a range of 800 mAh / gV to 1000 mAh / gV.

3. 2. The positive electrode active material of claim 1, wherein the dQ / dV graph includes only one peak in a voltage range of 3.60V to 3.85V.

4. 4. The positive electrode active material according to claim 3, wherein a dQ / dV graph as a function of voltage during formation shows two peaks in a voltage range of 3.60V to 3.85V.

5. The graph of dQ / dV according to the voltage during formation shows the first voltage value (V 1 ) and the second voltage value (V 2 ) shows a peak, and V 1 <V<V 2 The positive electrode active material according to claim 4 , which satisfies the above formula:

6. In the graph of dQ / dV according to the voltage during anodization, the first voltage value (V 1 ) the peak intensity at H 1 and the second voltage value (V 2 ) the peak intensity at H 2 When H 1 <H<H 2 The positive electrode active material according to claim 5 , which satisfies the above formula:

7. (H 1 / V 1 )<(H / V)<(H 2 / V 2 7. The positive electrode active material according to claim 6, wherein

8. 2. The cathode active material according to claim 1, wherein the first cathode active material is contained in an amount of 60% by weight to 95% by weight, and the second cathode active material is contained in an amount of 5% by weight to 40% by weight, relative to a total of 100% by weight of the first cathode active material and the second cathode active material.

9. The average particle size (D 50 ) is 10 μm to 20 μm, 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 8 μm.

10. 2. The positive electrode active material according to claim 1, wherein the layered lithium nickel-manganese composite oxide of the first positive electrode active material and the layered lithium nickel-manganese composite oxide of the second positive electrode active material are the same or different, and each independently has a nickel content of 60 mol % to 80 mol % and a manganese content of 10 mol % or more, relative to 100 mol % of all metals excluding lithium.

11. the layered lithium nickel-manganese composite oxide of the first positive electrode active material and the layered lithium nickel-manganese composite oxide of the second positive electrode active material are each independently a layered lithium nickel-manganese-aluminum composite oxide further containing aluminum in addition to nickel and manganese, 2. The positive electrode active material according to claim 1, wherein the layered lithium nickel-manganese-aluminum composite oxide has an aluminum content of 1 mol % to 3 mol % relative to 100 mol % of all metals excluding lithium.

12. 2. The positive electrode active material according to claim 1, wherein the layered lithium nickel-manganese composite oxide of the first positive electrode active material and the layered lithium nickel-manganese composite oxide of the second positive electrode active material each independently contain 0 mol % to 0.01 mol % of cobalt relative to 100 mol % of all metals excluding lithium.

13. The layered lithium nickel-manganese composite oxide of the first positive electrode active material and the layered lithium nickel-manganese composite oxide of the second positive electrode active material are each independently represented by the following chemical formula 1: [Chemical formula 1] Li a1 Ni x1 Mn y1 Al z1 M 1 w1 O 2-b1 X b1 In Chemical Formula 1, 0.9≦a1≦1.8, 0.6≦x1≦0.8, 0.1≦y1≦0.4, 0≦z1≦0.03, 0≦w1≦0.3, 0.9≦x1+y1+z1+w1≦1.1, and 0≦b1≦0.1; M 1 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from F, P, and S.

14. the aluminum content of the coating layer is 0.1 mol % to 2 mol % relative to 100 mol % of all metals excluding lithium in the first positive electrode active material; the aluminum content of the coating layer is 0.1 mol % to 2 mol % relative to 100 mol % of all metals excluding lithium in the second positive electrode active material; 2. The positive electrode active material according to claim 1, wherein the aluminum content of the coating layer of the first positive electrode active material and the aluminum content of the coating layer of the second positive electrode active material are in a molar ratio of 5:1 to 2:

1.

15. 2. The cathode active material of claim 1, wherein the aluminum coating layer of the first cathode active material and the aluminum coating layer of the second cathode active material are in the form of a shell continuously surrounding the particle surface, and the coating layer has a thickness of 5 nm to 500 nm.

16. The positive electrode active material of claim 1 , wherein the first positive electrode active material further comprises a grain boundary coating portion located on a surface of the primary particle inside the secondary particle and containing aluminum.

17. 2. The positive electrode active material of claim 1, wherein the aluminum coating layer of the first positive electrode active material and / or the aluminum coating layer of the second positive electrode active material further comprises B, Mg, Ti, V, W, Y, Zr, or a combination thereof.

18. the aluminum coating layer of the second positive electrode active material further contains yttrium; 2. The cathode active material according to claim 1, wherein the content of yttrium in the coating layer is 0.1 mol % to 1 mol % relative to 100 mol % of all metals excluding lithium in the second cathode active material.

19. a positive electrode current collector, and a positive electrode including a positive electrode active material layer located on the positive electrode current collector, The positive electrode active material layer contains the positive electrode active material according to any one of claims 1 to 18, The loading level of the positive electrode active material layer is 10 mg / cm 2 ~40 mg / cm 2 and The density of the positive electrode active material layer is 3.3 g / cc to 3.7 g / cc.

20. The positive electrode according to claim 19 . a negative electrode, and Contains electrolytes, A lithium secondary battery having an upper limit charging voltage of 4.45V or higher.

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