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

Abstract

To provide a positive electrode active material that can achieve high density, high capacity, and a long life characteristic, a positive electrode including the same, and a lithium secondary battery.SOLUTION: A positive electrode active material includes a first positive electrode active material containing layered lithium nickel manganese complex oxide, and a second positive electrode active material containing lithium manganese rich complex oxide in which the molar ratio of lithium to the entire metal excluding lithium is 1.1 to 3 and the manganese content per 100 mol% of the entire metal excluding lithium is 60 mol% or more. A positive electrode including this positive electrode active material and a lithium secondary battery are also provided.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-ion batteries, which offer high energy density while remaining portable, are primarily used as power sources for mobile information terminals such as mobile phones, laptops, and smartphones. Recently, research has been actively conducted on using high-energy-density lithium-ion batteries as power sources or energy storage sources for hybrid and electric vehicles.

[0003] To realize lithium secondary batteries that meet these applications, a variety of positive electrode active materials are being considered. Among them, lithium nickel oxides, lithium nickel manganese cobalt composite oxides, lithium nickel cobalt aluminum composite oxides, and lithium cobalt oxides are mainly used as positive electrode active materials. However, in recent years, while the demand for large, high-capacity, or high-energy-density lithium secondary batteries has surged, the supply of positive electrode active materials containing cobalt, a rare metal, is expected to be extremely insufficient. In other words, because cobalt is expensive and its remaining reserves are not large, there is a need to develop positive electrode active materials that either exclude cobalt or reduce its content. [Overview of the project] [Problems that the invention aims to solve]

[0004] The present invention provides a positive electrode active material that can achieve high density, high capacity, and long life characteristics, a positive electrode to which the same is applied, and a lithium secondary battery. [Means for solving the problem]

[0005] In one embodiment of the present invention, a positive electrode active material including a layered lithium nickel-manganese composite oxide, and a lithium-manganese-rich composite oxide having a molar ratio of lithium to the total metal excluding lithium of 1.1 to 3 and a manganese content of 60 mol% or more with respect to 100 mol% of the total metal excluding lithium are provided.

[0006] In another embodiment of the present invention, a positive electrode including a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, and the positive electrode active material layer includes the positive electrode active material described above.

[0007] In still another embodiment of the present invention, a lithium secondary battery including the positive electrode, a negative electrode, and an electrolyte is provided.

Advantages of the Invention

[0008] The positive electrode active material according to one embodiment of the present invention minimizes production cost and maximizes capacity, ensures long-life characteristics, and improves characteristics at high voltage and high-temperature storage characteristics. The lithium secondary battery to which the positive electrode active material is applied can exhibit high initial charge-discharge capacity and efficiency even under high-voltage driving conditions, can achieve long-life characteristics, and can effectively suppress the gas generation problem caused by high-voltage and high-temperature driving.

Brief Description of the Drawings

[0009] [Figure 1] It is a cross-sectional view schematically showing a lithium secondary battery according to one embodiment. [Figure 2] It is a cross-sectional view schematically showing a lithium secondary battery according to one embodiment. [Figure 3] It is a cross-sectional view schematically showing a lithium secondary battery according to one embodiment. [Figure 4] It is a cross-sectional view schematically showing a lithium secondary battery according to one embodiment. [Figure 5] It is a scanning electron microscope (SEM) image of large particles of the first positive electrode active material manufactured in Example 1. [Figure 6]This is a scanning electron microscope (SEM) image of the large particles of the first positive electrode active material manufactured in Example 1. [Figure 7] This is an SEM image of the small particles of the first cathode active material produced in Example 1. [Figure 8] This is an SEM image of the small particles of the first cathode active material produced in Example 1. [Figure 9] This is an SEM image of the second cathode active material produced in Example 1. [Figure 10] This is an SEM image of the second cathode active material produced in Example 1. [Figure 11] This graph compares the densities of the positive electrode mixtures produced in Example 1 and Comparative Example 1. [Modes for carrying out the invention]

[0010] The following describes specific embodiments in detail so that they can be easily implemented by those with ordinary skill in the art. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0011] The terms used herein are for illustrative purposes only and are not intended to limit the invention. Unless otherwise clearly indicated in the context, singular expressions include plural expressions.

[0012] Here, "these combinations" refers to mixtures of components, laminates, composites, copolymers, alloys, blends, reaction products, etc.

[0013] Here, terms such as “include,” “equip,” or “possess” are intended to specify the existence of a particular feature, number, stage, component, or combination thereof, and should be understood not to preemptively exclude the existence or possibility of adding one or more other features, numbers, stages, components, or combinations thereof.

[0014] To clearly represent various layers and regions in the drawings, thicknesses are shown enlarged, and similar parts are given the same drawing reference numerals throughout the specification. When a layer, film, region, plate, or other part is said to be "on top of" or "on" another part, this includes not only when it is "directly on top of" another part, but also when there is another part in between. Conversely, when a part is said to be "directly on top of" another part, it means that there is no other part in between.

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

[0016] The average particle size can be measured by methods widely known to those skilled in the art, for example, by a particle size analyzer, or by transmission electron microscopy or scanning electron microscopy. Alternatively, it can be measured using dynamic light scattering, and after performing data analysis to count the number of particles for each particle size range, the average particle size value can be calculated from this. Unless otherwise defined, the average particle size is the diameter (D) of the particle whose cumulative volume in the particle size distribution is 50% by volume. 50 ) means. Also, unless otherwise defined, the average particle size is the diameter (D) of the particle whose cumulative volume in the particle size distribution is 50% by volume, obtained by measuring the size (diameter or length of the long axis) of more than 20 randomly selected particles from a scanning electron microscope image. 50 This could be the average particle size taken from ).

[0017] Here, "or" is not interpreted in an exclusive sense; for example, "A or B" is interpreted as including A, B, A+B, etc.

[0018] The term "metal" is interpreted as a concept that includes general metals, transition metals, and metalloids (metallic semi-metals).

[0019] positive electrode active material In one embodiment, a positive electrode active material is provided that includes a first positive electrode active material containing a layered lithium nickel-manganese composite oxide, and a second positive electrode active material containing a lithium-manganese-rich composite oxide in which the molar ratio of lithium to the total metal excluding lithium is 1.1 to 3, and the manganese content is 50 mol% or more per 100 mol% of the total metal excluding lithium.

[0020] The aforementioned positive electrode active material contains little to no expensive cobalt and low-cost manganese, thereby reducing costs and increasing mass production capabilities. It also exhibits excellent high-voltage characteristics, achieves high-density properties, and further increases capacity. Because such a positive electrode active material is inexpensive and meets the requirements for high capacity, high voltage, and high-density properties, lithium secondary batteries using it can enable long-distance driving when installed in electric or hybrid vehicles.

[0021] For a total of 100% by weight of the first and second positive electrode active materials, the first positive electrode active material is included in an amount of 60% to 95% by weight, for example, 70% to 95% or 80% to 90% by weight, and the second positive electrode active material is included in an amount of 5% to 40% by weight, for example, 5% to 30% or 10% to 20% by weight. When mixed in the above ratios, it is possible to maximize energy density and achieve high capacity.

[0022] First positive electrode active material In recent years, as the price of cobalt, a rare metal, has surged, there has been a demand for the development of cathode active materials that either exclude cobalt or reduce its cobalt content. Among these, cathode active materials with olivine-based crystal structures such as lithium iron phosphate (LFP), lithium manganese phosphate (LMP), and lithium iron manganese phosphate (LMFP), or spinel crystal structures such as lithium manganese oxide (LMO), have limitations in achieving high capacity because the amount of lithium that can be utilized within the structure is small. Layered lithium nickel-manganese cathode active materials can have a high lithium content within the structure, resulting in excellent capacity and efficiency characteristics, making them suitable as materials for high-capacity batteries. However, the removal of cobalt, which plays a core role in the layered structure, leads to a decrease in structural stability, an increase in resistance, and difficulty in ensuring long lifespan characteristics. Furthermore, because cobalt is removed, side reactions between the cathode active material and electrolyte accelerate under high voltage and high temperature conditions, increasing gas generation and reducing lifespan characteristics.

[0023] Therefore, in one embodiment, we propose a method to improve the high-voltage capacity and lifetime characteristics of the first positive electrode active material by appropriately adjusting the ratio of nickel and manganese in a lithium nickel-manganese composite oxide, introducing other elements such as aluminum in addition to nickel and manganese, or introducing a uniform coating layer by applying an appropriate coating method.

[0024] Lithium nickel-manganese composite oxide In lithium nickel-manganese composite oxides, the nickel content is 60 mol% or more relative to 100 mol% of the total metal excluding lithium. For example, it may be 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%. When the nickel content meets the above range, high capacity can be achieved, and structural stability can be improved even if the cobalt content is reduced.

[0025] The manganese content is, for example, 15 mol% or more relative to 100 mol% of the total metal excluding lithium in a lithium nickel-manganese composite oxide, and can be, for example, 15 mol% to 40 mol%, 15 mol% to 35 mol%, 15 mol% to 30 mol%, or 20 mol% to 30%. When the manganese content meets the above range, the positive electrode active material can achieve high capacity and improve structural stability.

[0026] A lithium nickel-manganese composite oxide may, as an example, be a lithium nickel-manganese-aluminum composite oxide that further contains aluminum in addition to nickel and manganese. When aluminum is included in the composite oxide, it is advantageous in maintaining a stable layered structure even if the cobalt element is excluded from the structure. The aluminum content per 100 mol% of the lithium nickel-manganese-aluminum composite oxide is 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 1.5 mol% to 2.5 mol%. When the aluminum content meets the above range, a stable layered structure can be maintained even if cobalt is excluded, the problem of structural collapse due to charging and discharging can be suppressed, and the long-life characteristics of the positive electrode active material can be achieved.

[0027] According to one embodiment, the concentration of aluminum within the particles containing the lithium nickel-manganese composite oxide can be uniform. That is, it means that aluminum does not have a concentration gradient from the center to the surface within the particles, or the aluminum concentration inside the particles is not higher or lower outside than inside, and the aluminum within the particles is uniformly dispersed. This can be said to be a structure obtained by synthesizing the composite oxide using a nickel-manganese-aluminum hydroxide as a precursor by using an aluminum raw material during the production of the precursor without further doping aluminum during the synthesis process of the lithium nickel-manganese composite oxide. The particles can be in the form of secondary particles aggregated from a plurality of primary particles, and it can be said that the aluminum content inside the primary particles is the same or similar regardless of the position of the primary particles. That is, when a primary particle is selected from an arbitrary position in the cross-section of the secondary particle and the aluminum content inside rather than at the interface of the primary particle is measured, it can be expressed that the aluminum content is the same / similar / uniform regardless of the position of the primary particle, that is, whether the primary particle is close to the center or the surface of the secondary particle. In such a structure, even if cobalt is absent or present in a very small amount, a stable layered structure can be maintained, and no aluminum by-products or aluminum aggregates are generated, so that the capacity, efficiency, and life characteristics of the positive electrode active material can be improved simultaneously.

[0028] The lithium nickel-manganese composite oxide is specifically 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

[0029] 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 1is one or more elements selected from B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, and Zr, and X is one or more elements selected from F, P, and S.

[0030] In Chemical Formula 1, 0.9 ≤ a1 ≤ 1.5, or 0.9 ≤ a1 ≤ 1.2 may hold. Further, Chemical Formula 1 contains 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.

[0031] In Chemical Formula 1, for example, 0.6 ≤ x1 ≤ 0.79, 0.6 ≤ x1 ≤ 0.78, 0.6 ≤ x1 ≤ 0.75, 0.65 ≤ x1 ≤ 0.8, or 0.7 ≤ x1 ≤ 0.79, 0.1 ≤ y1 ≤ 0.35, 0.1 ≤ y1 ≤ 0.30, 0.1 ≤ y1 ≤ 0.29, 0.15 ≤ y1 ≤ 0.39, or 0.2 ≤ y1 ≤ 0.3, 0.01 ≤ z1 ≤ 0.025, 0.01 < z1 ≤ 0.02, or 0.01 < z1 ≤ 0.019, 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, 0 ≤ w1 ≤ 0.15, 0 ≤ w1 ≤ 0.1, or 0 ≤ w1 ≤ 0.09, etc. may hold.

[0032] As an example, the lithium nickel-manganese composite oxide may not contain cobalt or may contain a small amount, and the content of cobalt relative to 100 mol% of the total metal excluding lithium may be 0 mol% to 0.01 mol%.

[0033] Particles containing lithium nickel-manganese composite oxides may be in the form of secondary particles formed by the aggregation of multiple primary particles, single particles, or a combination thereof. Secondary particles and single particles may be spherical, ellipsoidal, polyhedral, or irregular in shape, and the primary particles forming the secondary particles may be spherical, ellipsoidal, plate-like, or a combination thereof.

[0034] coating layer The first positive electrode active material may include core particles containing a layered lithium nickel-manganese composite oxide, and a coating layer located on the surface of the core particles containing Al, B, Mg, Ti, V, W, Y, Zr, or a combination thereof.

[0035] Lithium nickel-manganese composite oxides are susceptible to chemical attack from electrolyte components when batteries are operated under high voltage or high temperature conditions, potentially leading to numerous side reactions with the electrolyte. This can result in increased gas generation, reducing battery life and safety. However, by introducing a coating layer according to one embodiment, these problems can be resolved.

[0036] The aforementioned coating layer may, for example, be an Al coating layer containing Al, and may further selectively contain elements such as B, Mg, Ti, V, W, Y, and Zr. When an Al coating layer is introduced, the high-voltage performance of the first positive electrode active material can be further improved.

[0037] Layered lithium nickel-manganese composite oxides differ considerably from oxides of other compositions, such as lithium nickel-cobalt-manganese composite oxides, lithium nickel-cobalt-aluminum composite oxides, and lithium cobalt oxides, in terms of residual lithium content on the particle surface and many of the surface properties differ. Therefore, existing coating methods make it impossible to form a good coating layer with a uniform film morphology. In one embodiment, a coating solution is prepared by (i) adding the coating raw material to an aqueous solvent and mixing it using a salt-dissolution method until the salt is completely dissolved; (ii) adding core particles to this coating solution and mixing them to perform coating; and (iii) after removing the solvent and drying, a uniform coating layer can be introduced to the first positive electrode active material by heat treatment. This is a salt-dissolution wet coating method, and it may be a pre-addition method in which the salt, which is the coating raw material, is first completely dissolved before the active material particles are added. By this method, a uniform, thin film-morphology coating layer can be successfully formed on the surface of layered lithium nickel-manganese composite oxides.

[0038] The above coating method allows for a further increase in the content of coating elements on the active material surface compared to general dry methods and post-addition wet methods. For example, the coating content on the surface of the first positive electrode active material, as measured by EP-EDS analysis, is 5 at% to 35 at% relative to 100 at% of the total metal excluding lithium on the surface, and can 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 the high-voltage characteristics without increasing the resistance of the first positive electrode active material.

[0039] The coating layer may, for example, be in the form of a film that continuously surrounds the surface of the core particles, or it may be in the form of a shell that surrounds the entire surface of the core particles. This is distinct from a structure in which only a part of the core particle surface is partially coated. According to one embodiment, the coating layer can be formed to surround the entire surface of the core particles while being very thin and having a uniform thickness. As a result, the positive electrode active material does not experience an increase in resistance or a decrease in capacity, its structural stability is improved, side reactions with the electrolyte are effectively suppressed, gas generation under high voltage and high temperature conditions is reduced, and long-life characteristics can be achieved.

[0040] According to the above method, the thickness of the coating layer on the first positive electrode active material 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 coating layer satisfies the above thickness range, the coating can improve the structural stability of the positive electrode active material without increasing resistance or decreasing capacitance, and can effectively suppress side reactions with the electrolyte. The thickness of the coating layer can be measured by, for example, SEM, TEM, TOF-SIMS, XPS, or EDS analysis, and as an example, it can be measured by EDS line profile analysis of the cross-section of the positive electrode active material.

[0041] One embodiment is characterized by having a thin coating layer at the level of tens to hundreds of nanometers, and having a uniform thickness. 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 thickness deviation of the coating layer refers to the content of the thickness of the coating layer within a single positive electrode active material particle. The thickness deviation of the coating layer means, for example, that the thickness of more than 10 points is measured in an electron microscope image of the cross-section of a single positive electrode active material particle, the arithmetic mean is calculated, the absolute value of the difference between one data point and the arithmetic mean is divided by the arithmetic mean, and multiplied by 100. When the thickness deviation or standard deviation of the coating layer satisfies the above range, it means that a coating layer of uniform thickness is well formed in film form 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 the increase in resistance and decrease in capacity due to the coating.

[0042] In the entire first positive electrode active material, the content of the coating element relative to 100 mol% of the total metal excluding lithium varies depending on the type of coating element, but is approximately 0.01 mol% to 5 mol%, for example, it could be 0.05 mol% to 3 mol%, or 0.1 mol% to 2 mol%.

[0043] For example, when introducing an Al coating layer, the Al content of the coating layer is 0.1 mol% to 3.0 mol% relative to 100 mol% of the total metal excluding lithium in the entire first positive electrode active material, and can be, for example, 0.1 mol% to 2.0 mol%, 0.5 mol% to 1.5 mol%, or 0.7 mol% to 1.3 mol%.

[0044] When introducing an Al coating layer, the coating layer can include, for example, a layered aluminum compound, such as aluminum oxide, lithium aluminum oxide, or a combination thereof, and as an example, LiAlO2.

[0045] Large particles and small particles In one embodiment, the first positive electrode active material contains a layered lithium nickel-manganese composite oxide, and the average particle size (D 50 It contains large particles with a diameter of 10 μm to 25 μm, and layered lithium nickel-manganese composite oxide, with an average particle size (D 50 This may include small particles with a diameter of 0.5 μm to 8 μm. In this case, a high-energy-density positive electrode can be realized. Here, the average particle size (D 50 The particle size may be obtained by randomly measuring the size (diameter or length of the major axis) of more than 20 particles using scanning electron microscope images of the positive electrode active material to obtain a particle size distribution, and then taking the diameter of the particle whose cumulative volume in the particle size distribution is 50% by volume as the average particle size.

[0046] The large particles may be in the form of secondary particles formed by the aggregation of multiple primary particles. The small particles may be in the form of secondary particles or single particles.

[0047] With respect to a total of 100% by weight of the large and small particles, the large particles are present in an amount of 60% to 95% by weight, or 70% to 90% by weight, and the small particles are present in an amount of 5% to 40% by weight, or 10% to 30% by weight.

[0048] When the first positive electrode active material contains both large and small particles, the large particles are present in an amount of 40% to 90% by weight, the small particles in an amount of 5% to 40% by weight, and the second positive electrode active material in an amount of 5% to 30% by weight, relative to 100% by weight of the total of the large particles, small particles, and second positive electrode active material. By satisfying such mixing ratios, the energy density and capacity can be maximized.

[0049] As an example, the average particle size (D) of the second positive electrode active material. 50 ) is the average particle size (D) of the large particles. 50 ) is smaller than the average particle size (D 50 ) can be larger than this. In this case, the second positive electrode active material becomes a kind of medium particle, and the positive electrode can be in the form of a mixture of large, medium, and small particles, thereby effectively improving high-voltage characteristics while maximizing energy density.

[0050] In one embodiment, the large particles may include core particles in the form of secondary particles formed by the aggregation of a plurality of primary particles, and a coating layer located on the surface of the core particles containing Al, B, Mg, Ti, V, W, Y, Zr, or a combination thereof. The small particles may also include core particles in the form of single particles, and a coating layer located on the surface of the core particles containing Al, B, Mg, Ti, V, W, Y, Zr, or a combination thereof. Such a design can maximize performance at high voltages.

[0051] For example, the coating layer for the large particles may contain Al, Zr, or a combination thereof, while the coating layer for the small particles may contain Al, Y, or a combination thereof. This may represent the optimal coating composition for the large and small particles, respectively, and can further improve capacitance characteristics, lifetime characteristics, etc., at high voltages.

[0052] For example, the coating layer of the large particles contains Al, and the Al content of the coating layer relative to 100 mol% of the total metal excluding lithium in the large particles may be 0.5 mol% to 2 mol%. Similarly, the coating layer of the small particles contains Al, and the Al content of the coating layer relative to 100 mol% of the total metal excluding lithium in the small particles may be 0.1 mol% to 1 mol%.

[0053] In this case, the coating layer of the small particles may further contain Y, and the Y content of the coating layer relative to 100 mol% of the total metal excluding lithium in the small particles may be, for example, 0.01 mol% to 0.5 mol%.

[0054] On the other hand, the first positive electrode active material may contain a sulfur (S) component on its surface, which may be a property derived by applying a sulfate-based coating material such as aluminum sulfate in the coating process.

[0055] Second positive electrode active material The second cathode active material contains a lithium-manganese-rich (LMR) composite oxide. LMR materials are cathode active materials with a layered structure that contains an excess of lithium and a relatively high manganese content. In addition to capacity generation through the oxidation-reduction of existing transition metals, a new principle of oxygen oxidation-reduction is applied, resulting in high capacity generation while simultaneously attracting attention as an ultra-low-cost next-generation cathode active material due to its high proportion of low-cost manganese.

[0056] In the second positive electrode active material, the molar ratio of lithium to the total metal excluding lithium is 1.1 to 3, for example, 1.2 to 2.5, 1.3 to 2.3, or 1.5 to 2.1. In addition, the manganese content in the second positive electrode active material relative to 100 mol% of the total metal excluding lithium is 60 mol% or more, for example, 60 mol% to 90 mol%, 60 mol% to 80 mol%, 60 mol% to 75 mol%, 60 mol% to 70 mol%, or 62 mol% to 68 mol%.

[0057] The lithium-manganese-rich composite oxide of the second positive electrode active material is represented, for example, by the following chemical formula 2. [Chemical formula 2] Li 1+x2 (Ni y2 Mn z2 M 2 1-y2-z2 ) 1-x2 O 2-b2 X b2

[0058] In chemical formula 2, 0.04 ≤ x² ≤ 0.5, 0.1 ≤ y² ≤ 0.5, 0.5 ≤ z² ≤ 0.9, and 0 ≤ b² ≤ 0.1, and M 2 X is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, and Zr, and X is one or more elements selected from F, P, and S.

[0059] In the aforementioned chemical formula 2, for example, 0.05 ≤ x² ≤ 0.4 or 0.06 ≤ x² ≤ 0.3, and 0.2 ≤ y² ≤ 0.4 and 0.6 ≤ z² ≤ 0.8, or 0.3 ≤ y² ≤ 0.4 and 0.6 ≤ z² ≤ 0.7.

[0060] The second positive electrode active material is a secondary particle form consisting of aggregated primary particles, and the average particle size (D) of the second positive electrode active material is 50 The size of the saturation point is between 3 μm and 13 μm, and can be, for example, 4 μm to 12 μm, 5 μm to 10 μm, or 6 μm to 9 μm.

[0061] In the lithium-manganese-rich composite oxide of the second positive electrode active material, the cobalt content relative to 100 mol% of the total metal excluding lithium may be 0 mol% to 0.01 mol%.

[0062] The second positive electrode active material has an a-lattice constant of 2.865A or higher as determined by X-ray diffraction analysis (XRD), for example, 2.870A or higher, and can be between 2.875A and 2.885A. For example, the a-lattice constant of the positive electrode active material may be 2.875A or higher. Furthermore, the ratio of the c-lattice constant to the a-lattice constant is 4.968 or lower, for example, 4.965 or lower, 4.960 or lower, and can be between 4.955 and 4.965. When the a-lattice constant of the positive electrode active material and the ratio of the c-lattice constant to the a-lattice constant satisfy the above range, the problem of voltage drop during charging and discharging by the second positive electrode active material can be effectively improved, the energy density can be increased, and the capacity characteristics and lifetime characteristics in the high-voltage region can be improved.

[0063] The residual lithium content on the surface of the second positive electrode active material is 0.3% by weight or less, and may be, for example, 0.2% by weight or less, 0.1% by weight or less, or 0.001% to 0.1% by weight. This may be a characteristic that distinguishes it from high-nickel materials with a nickel content exceeding 70 mol%.

[0064] Pellet density The positive electrode active material according to one embodiment can achieve a high pellet density. For example, the pellet density of the positive electrode active material is 3.0 g / cc to 3.7 g / cc, and can be, for example, 3.1 g / cc to 3.6 g / cc, or 3.1 g / cc to 3.5 g / cc. A lithium secondary battery using such a positive electrode active material can achieve a high energy density.

[0065] Pellet density can be measured by the following method: After quantifying 3g of positive electrode active material, mold (area: 1.298cm²) 2 The mold bar was placed in the mold and slowly fitted into the mold body. The mold set was then placed in a hydraulic press and pressurized with a pressure of 4 tons (metric tons) for 30 seconds. After that, the height was measured and the pellet density could be determined.

[0066] positive electrode In one embodiment, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, wherein the positive electrode active material layer provides a positive electrode containing the positive electrode active material described above. The positive electrode active material layer may further contain other types of positive electrode active materials in addition to the positive electrode active material described above. The positive electrode active material layer may also selectively further contain a binder, a conductive material, or a combination thereof.

[0067] According to one embodiment, the loading level of the positive electrode active material layer is 10 mg / cm³. 2 ~40 mg / cm³ 2 It could be 10 mg / cm³, for example. 2 ~30 mg / cm³ 2 or 10 mg / cm³ 2 ~20 mg / cm³ 2This is possible. Furthermore, the density of the positive electrode active material layer in the rolled final positive electrode can 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 or 3.5 g / cc to 3.58 g / cc. Applying a positive electrode active material according to one embodiment is advantageous in achieving such loading levels and positive electrode densities, and a positive electrode that satisfies the above range of loading levels and positive electrode densities is suitable for realizing high-capacity, high-energy-density lithium secondary batteries.

[0068] binder The binder plays a role in ensuring that the positive electrode active material particles adhere well to each other and that the positive electrode active material adheres well to the current collector. Typical examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylic styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0069] conductive material Conductive materials are used to impart conductivity to electrodes, and any electronically conductive material that does not cause chemical changes in the battery that is constructed can be used. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0070] The binder and conductive material content may be 0.5% to 5% by weight, respectively, based on 100% by weight of the positive electrode active material layer.

[0071] Al can be used as the positive electrode current collector, but it is not limited to this.

[0072] Lithium-ion rechargeable battery In one embodiment, a lithium secondary battery is provided that includes the positive electrode, negative electrode, and electrolyte described above. As an example, the lithium secondary battery may include a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte.

[0073] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch-type, coin-type, and other types depending on their form. Figures 1 to 4 are schematic diagrams showing a lithium secondary battery according to one embodiment, where Figure 1 may be circular, Figure 2 rectangular, and Figures 3 and 4 pouch-type batteries. Referring to Figures 1 to 4, the lithium secondary battery 100 may include an electrode assembly 40 with a separator 30 between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, negative electrode 20, and 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 Figure 1. Also, in Figure 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 Figures 3 and 4, the lithium secondary battery 100 may include electrode tabs 70, namely a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical pathways for inducing the current formed in the electrode assembly 40 to the outside.

[0074] A lithium secondary battery according to one embodiment may be a battery that can be charged at high voltage or is suitable for being driven at high voltage, and may have improved characteristics under high voltage conditions.

[0075] The lithium secondary battery includes a lithium-manganese-rich second positive electrode active material. To utilize the reversible positive electrode capacity of the second positive electrode active material, the initial charge must be performed at 4.60V or higher, for example, at 4.65V. Subsequent charging is performed at a lower voltage than the initial charge. Since the lithium secondary battery according to one embodiment is designed to operate in a high-voltage region, charging can be performed in a voltage range of 4.45V or higher. For example, the charge voltage after the second cycle is 4.45V or higher, and may be, for example, 4.45V to 4.6V, 4.45V to 4.55V, or 4.45V to 4.50V. By applying the positive electrode active material according to one embodiment, the lithium secondary battery can significantly reduce gas generation even when charged at high voltage, thereby achieving high capacity and long life characteristics.

[0076] 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 comprising a negative electrode active material and further comprising a binder, a conductive material, or a combination thereof.

[0077] negative electrode active material The negative electrode active material includes a substance capable of reversibly inserting / de-inserting lithium ions, lithium metal, an alloy of lithium metal, a lithium-doped and de-doped substance, or a transition metal oxide.

[0078] The material capable of reversibly inserting / deinserting lithium ions is a carbon-based anode active material, which may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, while examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, and calcined coke.

[0079] 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.

[0080] 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 can be used. As the Sn-based negative electrode active material, Sn, SnO2, a Sn alloy or a combination thereof can be used.

[0081] The silicon-carbon composite can be a composite of silicon and amorphous carbon. The average particle size (D 50 ) of the silicon-carbon composite particles can be, for example, 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite can be in a form in which silicon particles and amorphous carbon are coated on the surface of the silicon particles. For example, it can include secondary particles (cores) formed by granulating primary silicon particles, and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon can also be located between the primary silicon particles, and for example, the primary silicon particles can be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0082] The silicon-carbon composite may further contain 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.

[0083] When the silicon-carbon composite contains silicon and amorphous carbon, the content of silicon may be 10% to 50% by weight based on 100% by weight of the silicon-carbon composite, and the content of amorphous carbon may be 50% to 90% by weight. When the composite contains silicon, amorphous carbon, and crystalline carbon, based on 100% by weight of the silicon-carbon composite, the content of silicon may be 10% to 50% by weight, the content of crystalline carbon may be 10% to 70% by weight, and the content of amorphous carbon may be 20% to 40% by weight.

[0084] Also, the thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. The average particle diameter (D 50 ) of the silicon particles (primary particles) may be 10 nm to 1 μm, or 10 nm to 200 nm. The silicon particles may exist alone as silicon, or in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon may be represented by SiO x (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 diameter (D 50 ) means the diameter of the particle with a cumulative volume of 50% in the particle size distribution.

[0085] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material. When the Si-based negative electrode active material or the Sn-based negative electrode active material is mixed with the carbon-based negative electrode active material, the mixing ratio may be 1:99 to 90:10 by weight.

[0086] binder The binder plays a role in ensuring that the negative electrode active material particles adhere well to each other and that the negative electrode active material adheres 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.

[0087] Examples of non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0088] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylicated 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.

[0089] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulosic compound that can impart viscosity. This cellulosic compound can be a mixture of one or more carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. The alkali metal can be Na, K, or Li.

[0090] The dry binder is a polymeric substance that can be formed into fibers, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0091] conductive material Conductive materials are used to impart conductivity to electrodes, and any electronically conductive material that does not cause 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, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials in the form of metal powders or metal fibers, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0092] The content of the negative electrode active material is 95% to 99.5% by weight relative to 100% by weight of the negative electrode active material layer, 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.

[0093] Current collector The negative electrode current collector may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or alloys thereof, and may be in the form of 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.

[0094] electrolyte The electrolyte for lithium secondary batteries can be, for example, an electrolyte solution, which may contain a non-aqueous organic solvent and a lithium salt.

[0095] Non-aqueous organic solvents act as a medium through which ions involved in the electrochemical reactions of a battery can move. Non-aqueous organic solvents can be carbonate, ester, ether, ketone, or alcoholic solvents, aprotic solvents, or combinations thereof.

[0096] Examples of carbonate-based 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), and butylene carbonate (BC). Examples of ester-based solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone. As ether-based solvents, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran can be used. As ketone-based solvents, cyclohexanone can be used. As alcohol-based solvents, ethyl alcohol and isopropyl alcohol can be used, and as aprotic solvents, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, and can include double bonds, aromatic rings, or ether groups); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes can be used.

[0097] Non-aqueous organic solvents can be used alone or in combination of two or more. When used in combination of two or more, the mixing ratio can be appropriately adjusted according to the desired battery performance, which is generally understood by those working in this field.

[0098] When using carbonate-based solvents, cyclic carbonates and linear carbonates can be mixed, and these can be mixed in a volume ratio of 1:1 to 1:9.

[0099] Non-aqueous organic solvents may further include aromatic hydrocarbon organic solvents. For example, carbonate solvents and aromatic hydrocarbon organic solvents can be mixed and used in a volume ratio of 1:1 to 30:1.

[0100] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate, or ethylene carbonate compounds to improve battery life.

[0101] Typical examples of the aforementioned ethylene carbonate compounds include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0102] Lithium salts dissolve in organic solvents and act as a source of lithium ions within batteries, enabling the operation of basic lithium secondary batteries and facilitating the movement of lithium ions between the positive and negative electrodes. Typical 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 F2y+1 It may contain one or more selected from SO2) (where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0103] The lithium salt concentration is preferably used within the range of 0.1 M to 2.0 M. When the lithium salt concentration falls within this range, the electrolyte has appropriate ionic conductivity and viscosity, resulting in excellent performance and effective lithium ion movement.

[0104] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators can be made of polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers of these materials. 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.

[0105] The separator may include a porous substrate and a coating layer containing organic, inorganic, or a combination thereof located on one or both sides of the porous substrate.

[0106] The porous substrate may be a polymer film formed from one polymer selected from polyethylene, polyolefins such as polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon®, and polytetrafluoroethylene, or from a copolymer or mixture of two or more of these polymers.

[0107] The porous substrate can have a thickness of approximately 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.

[0108] The organic substance may include a (meth)acrylic copolymer comprising a first structural unit derived from (meth)acrylamide, a second structural unit comprising at least one of a first structural unit derived from (meth)acrylic acid or (meth)acrylate, and a structural unit derived from (meth)acrylamide sulfonic acid or a salt thereof.

[0109] 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) of the inorganic particles is 50 The range is 1 nm to 2000 nm, and can be, for example, 100 nm to 1000 nm or 100 nm to 700 nm.

[0110] The organic and inorganic materials may exist mixed together in a single coating layer, or they may exist in a form in which a coating layer containing organic materials and a coating layer containing inorganic materials are stacked on top of each other.

[0111] The thickness of the coating layer is 0.5 μm to 20 μm, and can be, for example, 1 μm to 10 μm, or 1 μm to 5 μm.

[0112] The following describes examples and comparative examples of the present invention. The following examples are merely illustrative of the present invention and are not limited to the following examples.

[0113] Example 1 1. Manufacturing of positive electrode active material (1) Production of large particles of the first positive electrode active material Ni 0.75 Mn 0.23 Al 0.02 (OH)2 and LiOH are mixed in a molar ratio of 1:1.05 and subjected to a first heat treatment at 845°C for 8 hours in an oxygen atmosphere, resulting in a composition of Li 1.05 Ni 0.75 Mn 0.23 Al 0.02 It is O2 and the average particle size (D 50 A primary lithium nickel-manganese composite oxide with a secondary particle morphology of approximately 14 μm was fabricated.

[0114] Aluminum sulfate was added to distilled water as a solvent and stirred at approximately 350 rpm for about 5 minutes to prepare a coating solution. It was confirmed that the salt was completely dissolved in the coating solution and that it was colorless and transparent. 500 g of the prepared lithium nickel-manganese composite oxide was added to the coating solution while it was being continuously stirred for 1.5 minutes, and the mixture was stirred for about 45 minutes. At this time, the aluminum content in the aluminum sulfate was designed to be 1.0 mol% relative to 100 mol% of the total metal excluding lithium in the final large particles. The pH of the supernatant after stirring was 5.5. The solvent was removed from the mixed solution using an aspirator and a filter press, and the coated product was obtained by vacuum drying at 190°C.

[0115] The aforementioned coated product was subjected to a second heat treatment at 750°C for 8 hours in an oxygen atmosphere to produce large particles in the first cathode active material.

[0116] Figures 5 and 6 are SEM images of the aforementioned large particles.

[0117] (2) Production of small particles of the first positive electrode active material Ni 0.75 Mn 0.23 Al 0.02 (OH)2, LiOH, and Al2O3 are mixed in a molar ratio of 1:1:0.02 and subjected to a first heat treatment at 850°C for 8 hours in an oxygen atmosphere, resulting in a composition of LiNi 0.75 Mn 0.23 Al 0.02 It is O2 and the average particle size (D 50 A single-particle form of lithium nickel-manganese composite oxide with a particle size of approximately 3 μm was produced.

[0118] Aluminum sulfate and yttrium nitrate were added to distilled water as a solvent and mixed. Then, lithium nickel-manganese composite oxide was added and mixed for about 45 minutes. At this time, the aluminum content in the aluminum sulfate was designed to be 0.4 mol% of the total metal content excluding lithium in the final small particles, and the yttrium content in the yttrium nitrate was designed to be 0.05 mol%. After removing the solvent from the mixed solution and drying at 190°C, the mixture was heat-treated at 825°C for 8 hours in an oxygen atmosphere to produce small particles of the first cathode active material.

[0119] Figures 7 and 8 are SEM images of the fabricated small particles.

[0120] (3) Manufacturing of the second positive electrode active material Ni 0.35 Mn 0.65 (OH)2 and LiOH are mixed, and the mixture is prepared so that the molar ratio of Li / (Ni+Mn) is approximately 2.1. The mixture is then heat-treated at 950°C for 24 hours in an oxygen atmosphere to obtain a lithium-manganese-rich composite oxide (Li 1.35 (Ni 0.35 Mn0.65 ) 0.65 It contains O2, is in secondary particle form, and has an average particle size (D 50 A second positive electrode active material with a diameter of approximately 8 μm was manufactured.

[0121] Figures 9 and 10 are SEM images of the second cathode active material.

[0122] (4) Manufacturing of the final positive electrode active material The final cathode active material was prepared by mixing 70% by weight of large particles of the first cathode active material, 20% by weight of small particles of the first cathode active material, and 10% by weight of the second cathode active material. After pressurizing the final cathode active material with 4 tons of pressure for 30 seconds, the measured pellet density was approximately 3.47 g / cc.

[0123] 2. Manufacturing of lithium-ion batteries A cathode active material layer slurry was prepared by mixing 98.5% by weight of the manufactured cathode active material, 1.0% by weight of polyvinylidene fluoride binder, and 0.5% by weight of carbon nanotube conductive material. This slurry was then coated onto an aluminum foil current collector, dried, and rolled to produce the cathode.

[0124] A negative electrode active material layer slurry was prepared by mixing 97.5% by weight of graphite negative electrode active material, 1.5% by weight of carboxymethylcellulose, and 1% by weight of styrene-butadiene rubber in an aqueous solvent. The negative electrode active material layer slurry was coated onto a copper foil current collector, and the negative electrode was prepared by drying and rolling.

[0125] A lithium secondary battery was manufactured using a conventional method with a polytetrafluoroethylene separator and an electrolyte solution prepared by dissolving 1M LiPF6 in a solvent containing a 3:7 volume ratio mixture of ethylene carbonate and dimethyl carbonate.

[0126] Example 2 A positive electrode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the final positive electrode active material was produced by mixing 90% by weight of large particles of the first positive electrode active material with 10% by weight of the second positive electrode active material.

[0127] The pellet density of the final cathode active material produced in Example 2 was approximately 3.10 g / cc.

[0128] Comparative Example 1 A positive electrode active material and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the final positive electrode active material was produced by mixing 70% by weight of large particles of the first positive electrode active material with 30% by weight of small particles of the first positive electrode active material.

[0129] Comparative Example 2 The positive electrode active material and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that only large particles of the first positive electrode active material were used alone as the final positive electrode active material.

[0130] Comparative Example 3 The positive electrode active material and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that only small particles of the first positive electrode active material were used alone as the final positive electrode active material.

[0131] Evaluation Example 1: Cathode Compound Density Figure 11 shows the compound density according to the rolling strength for the positive electrode plates produced in Example 1 and Comparative Example 1. Referring to Figure 11, the rolled positive electrode density is 3.52 g / cc for Example 1 and 3.47 g / cc for Comparative Example 1, so Example 1 can achieve a higher compound density than Comparative Example 1.

[0132] Evaluation Example 2: Battery Performance Evaluation Examples 1 and 2 applied a lithium-manganese-rich material as the second positive electrode active material and employed a charging method in which the voltage was initially charged to 4.65V, and then reduced to 4.45V. Specifically, the lithium secondary batteries manufactured in Examples 1 and 2 were charged to 4.65V at 25°C with a constant current of 0.1C, the voltage was maintained until the current value reached 0.05C, and then discharged to 2.5V with a constant current of 0.1C to perform the first charge-discharge cycle. Next, the batteries were charged to 4.45V at 25°C with a constant current of 0.2C, the voltage was maintained until the current value reached 0.05C, and then discharged to 2.5V with a constant current of 0.2C to perform the second charge-discharge cycle. The second discharge capacity is shown in Table 1 below as "1st 4.65V, 2nd 4.45V capacity".

[0133] Next, the battery was charged to 1.0C and discharged to 1.0C at 45°C in a voltage range of 3.0V to 4.45V, and this cycle was repeated more than 50 times. The ratio of the discharge capacity after 50 cycles to the second discharge capacity was calculated and expressed as "4.45V Lifetime" in Table 1 below.

[0134] Separately, the lithium-lithium secondary batteries manufactured in Comparative Examples 1-3 were charged at 25°C with a constant current of 0.2C to an upper voltage limit of 4.45V, then with a constant voltage down to 0.05C, and finally discharged at 0.2C to a cutoff voltage of 3.0V to perform initial charge and discharge. The initial discharge capacity is shown in Table 1 below as "4.45V capacity".

[0135] Next, the battery was charged to 1.0C and discharged to 1.0C at a voltage range of 3.0V to 4.45V at 45℃ for more than 50 cycles. The ratio of the discharge capacity after 50 cycles to the initial discharge capacity was calculated and expressed as "4.45V Lifetime" in Table 1 below.

[0136] [Table 1]

[0137] Referring to Table 1 above, it was found that in Examples 1 and 2, the utilization rate of the positive electrode was improved compared to the comparative example, and the lifespan characteristics were enhanced.

[0138] Although preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art that utilize the basic concepts defined in the claims also fall within the scope of the present invention. [Explanation of Symbols]

[0139] 100 Lithium-ion rechargeable batteries 10 positive electrode 11 Positive lead tab 12 Positive terminal 20 negative electrode 21 Negative lead tab 22 Negative terminal 30 Separators 40 Electrode assembly 50 cases 60 Sealing member 70 electrode tabs 71 Positive Tab 72 Negative Electrode Tabs

Claims

1. A first cathode active material containing a layered lithium nickel-manganese composite oxide, and The cathode active material comprises a second cathode active material containing a lithium-manganese-rich composite oxide in which the molar ratio of lithium to the total metal excluding lithium is 1.1 to 3 and the manganese content is 50 mol% or more per 100 mol% of the total metal excluding lithium, and the first cathode active material comprises large particles having an average particle size (D 50) of 10 μm to 25 μm and small particles having an average particle size (D 50) of 0.5 μm to 8 μm.

2. The positive electrode active material according to claim 1, wherein the first positive electrode active material is present in an amount of 60% to 95% by weight and the second positive electrode active material is present in an amount of 5% to 40% by weight, based on a total weight of 100% by weight of the first positive electrode active material and the second positive electrode active material.

3. The positive electrode active material according to claim 1, wherein the layered lithium nickel-manganese composite oxide of the first positive electrode active material has a nickel content of 60 mol% to 80 mol% and a manganese content of 10 mol% or more, based on 100 mol% of the total metal excluding lithium.

4. The positive electrode active material according to claim 1, wherein the layered lithium nickel-manganese composite oxide of the first positive electrode active material further contains aluminum, and the content of aluminum is 1 mol% to 3 mol% relative to 100 mol% of the total metal excluding lithium.

5. The positive electrode active material according to claim 4, wherein the concentration of aluminum is uniform within the layered lithium nickel-manganese composite oxide of the first positive electrode active material.

6. The positive electrode active material according to claim 1, wherein in the layered lithium nickel-manganese composite oxide of the first positive electrode active material, the cobalt content is 0 mol% to 0.01 mol% relative to 100 mol% of the total metal excluding lithium.

7. The first positive electrode active material is the layered lithium nickel-manganese composite oxide represented by chemical formula 1, as described in claim 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, and M 1 is one or more elements selected from B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, and Zr, and X is one or more elements selected from F, P, and S.

8. The first positive electrode active material consists of core particles containing a layered lithium nickel-manganese composite oxide, and The positive electrode active material according to claim 1, comprising a coating layer located on the surface of the core particles and containing Al, B, Mg, Ti, V, W, Y, Zr, or a combination thereof.

9. The positive electrode active material according to claim 8, wherein the coating layer contains Al and has a shell shape that continuously surrounds the surface of the core particles.

10. The positive electrode active material according to claim 8, wherein the thickness of the coating layer is 5 nm to 200 nm.

11. The positive electrode active material according to claim 8, wherein the content of the coating layer component is 0.01 mol% to 5 mol% with respect to 100 mol% of the total metal excluding lithium in the first positive electrode active material.

12. The positive electrode active material according to claim 1, wherein the large particles and the small particles contain a layered lithium nickel-manganese composite oxide.

13. The aforementioned large particle is a secondary particle form formed by the aggregation of multiple primary particles. The positive electrode active material according to claim 1, wherein the small particles are in the form of single particles.

14. The positive electrode active material according to claim 1, wherein, with respect to a total of 100% by weight of the large particles and the small particles, the large particles are present in an amount of 60% to 95% by weight and the small particles are present in an amount of 5% to 40% by weight.

15. With respect to 100% by weight of the large particles, the small particles, and the second positive electrode active material, The aforementioned large particles are present in an amount of 40% to 90% by weight. The aforementioned small particles are present in an amount of 5% to 40% by weight. The positive electrode active material according to claim 1, wherein the second positive electrode active material is contained in an amount of 5% to 30% by weight.

16. Average particle size of the second positive electrode active material (D 50 ) is the average particle size (D) of the large particles. 50 ) is smaller than the average particle size (D 50 The positive electrode active material according to claim 1, which is larger than ).

17. The aforementioned large particles include core particles in the form of secondary particles formed by the aggregation of a plurality of primary particles, and a coating layer located on the surface of the core particles that contains Al, B, Mg, Ti, V, W, Y, Zr, or a combination thereof. The positive electrode active material according to claim 1, wherein the small particles comprise core particles in single-particle form and a coating layer located on the surface of the core particles containing Al, B, Mg, Ti, V, W, Y, Zr, or a combination thereof.

18. The aforementioned large particle coating layer comprises Al, Zr, or a combination thereof. The positive electrode active material according to claim 17, wherein the coating layer of the small particles comprises Al, Y, or a combination thereof.

19. The coating layer of the large particles contains Al, and the Al content of the coating layer relative to 100 mol% of the total metal excluding lithium in the large particles is 0.5 mol% to 2 mol%. The positive electrode active material according to claim 17, wherein the coating layer of the small particles contains Al, and the Al content of the coating layer relative to 100 mol% of the total metal excluding lithium in the small particles is 0.1 mol% to 1 mol%.

20. The positive electrode active material according to claim 19, wherein the coating layer of the small particles further contains Y, and the Y content of the coating layer in the small particles is 0.01 mol% to 0.5 mol% relative to 100 mol% of the total metal excluding lithium.

21. The lithium-manganese-rich composite oxide of the second positive electrode active material is represented by chemical formula 2, as described in claim 1: [Chemical formula 2] Li 1+x2 (N y2 Mn z2 M 2 1-y2-z2 ) 1-x2 O 2-b2 X b2 In chemical formula 2, 0.04 ≤ x² ≤ 0.5, 0.1 ≤ y² ≤ 0.5, 0.5 ≤ z² ≤ 0.9, and 0 ≤ b² ≤ 0.1, M 2 X is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, and Zr, and X is one or more elements selected from F, P, and S.

22. The positive electrode active material according to claim 1, wherein the second positive electrode active material is in the form of secondary particles formed by the aggregation of a plurality of primary particles.

23. Average particle size of the second positive electrode active material (D 50 The positive electrode active material according to claim 1, wherein the diameter is 3 μm to 13 μm.

24. The positive electrode active material according to claim 1, wherein in the lithium-manganese-rich composite oxide of the second positive electrode active material, the cobalt content is 0 mol% to 0.01 mol% relative to 100 mol% of the total metal excluding lithium.

25. The positive electrode active material according to claim 1, wherein the pellet density of the positive electrode active material is 3.0 g / cc to 3.7 g / cc.

26. Positive electrode current collector, and The positive electrode active material layer located on the positive electrode current collector is included, The positive electrode comprises the positive electrode active material layer according to any one of claims 1 to 25.

27. The positive electrode according to claim 26, wherein the density of the positive electrode active material layer is 3.3 g / cc to 3.7 g / cc.

28. The positive electrode according to claim 26, Negative electrode, and A lithium-ion secondary battery containing an electrolyte.

29. The initial charging voltage is 4.60V or higher. The lithium secondary battery according to claim 28, wherein the subsequent charging voltage is lower than the initial charging voltage and is 4.45V or higher.

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