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

Abstract

To provide a positive electrode active material which has high energy density, achieves excellent life characteristics under high-voltage driving conditions, and is excellent in high-temperature storage characteristics.SOLUTION: The present embodiments relate to a positive electrode active material, a positive electrode including the same, and a lithium secondary battery. The positive electrode active material includes: a first positive electrode active material that includes a layered lithium nickel-manganese-based composite oxide and that is in a form of secondary particles each formed by agglomerating a plurality of primary particles, an average particle diameter (D50) of the secondary particles being 10-25 μm; and a second positive electrode active material that includes a layered lithium nickel-cobalt-based composite oxide and that is in a form of single particles, an average particle diameter (D50) of the single particles being 0.5-8 μm.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 Art

[0002] Lithium secondary batteries having a high energy density and being easy to carry are mainly used as driving power sources for mobile information terminals such as mobile phones, notebook computers, and smartphones. Recently, research has been actively conducted on using lithium secondary batteries having a high energy density as driving power sources or power storage power sources for hybrid vehicles and electric vehicles.

[0003] In order to realize a lithium secondary battery suitable for such applications, various positive electrode active materials have been studied. Among them, lithium nickel-based oxides, lithium nickel manganese cobalt composite oxides, lithium nickel cobalt aluminum composite oxides, lithium cobalt oxides, etc. are mainly used as positive electrode active materials. However, recently, the demand for large-sized, high-capacity, or high-energy-density lithium secondary batteries has increased rapidly, while the supply of positive electrode active materials containing rare metal cobalt is expected to be extremely insufficient. That is, since cobalt is expensive and the remaining reserves are not large, there is a need to develop positive electrode active materials excluding cobalt or reducing its content.

Summary of the Invention

Problems to be Solved by the Invention

[0004] To provide a positive electrode active material having a high energy density, excellent life characteristics under high voltage driving conditions, and excellent high temperature storage characteristics.

Means for Solving the Problems

[0005] In one embodiment, it includes a layered lithium nickel-manganese-based composite oxide, is in the form of secondary particles formed by aggregation of a plurality of primary particles, and the average particle size (D of the secondary particles 50) is a first cathode active material having an average particle size (D 50 ) of 10 μm to 25 μm, and includes a layered lithium nickel-cobalt composite oxide, and is in the form of single particles, and the average particle size of the single particles (D

[0006] ) is a second cathode active material having an average particle size of 0.5 μm to 8 μm.

[0007] In another embodiment, a lithium secondary battery including the cathode, an anode, and an electrolyte is provided.

Advantages of the Invention

[0008] The cathode active material manufactured according to one embodiment has a high capacity and energy density per unit volume, excellent initial charge / discharge efficiency and life characteristics under high voltage conditions, and excellent high temperature storage characteristics.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0010] Hereinafter, specific embodiments will be described in detail so that those skilled in the art can easily implement them. 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 present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0012] Herein, "these combinations" means a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, a reaction product, etc.

[0013] It should be understood that terms such as "comprising", "including", or "having" are intended to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0014] In the drawings, the thickness is enlarged to clearly show various layers and regions, and the same reference numerals are given to similar parts throughout the specification. When a part such as a layer, a film, a region, or a plate is "on" another part, this includes not only the case where it is directly on the other part but also the case where there are other parts in between. Conversely, when a part is "directly on" another part, it means that there are no other parts in between.

[0015] Also, herein, "layer" includes not only the shape formed on the entire surface but also the shape formed on a part of the surface when observed in a plan view.

[0016] The average particle size can be measured by methods widely known to those skilled in the art. For example, it can be measured with a particle size analyzer or by using a transmission electron microscope image or a scanning electron microscope image. In other methods, the dynamic light scattering method can be used for measurement, data analysis can be performed, the number of particles can be counted for each particle size range, and then the average particle size value can be calculated therefrom. Unless otherwise defined, the average particle size is the diameter (D) of the particles with a cumulative volume of 50% by volume in the particle size distribution. 50) can be meant. Also, unless otherwise defined, the average particle size is obtained by measuring the sizes (diameter or major axis length) of randomly over 20 particles in a scanning electron microscope image to obtain a particle size distribution, and the diameter (D 50 ) of the particles with a cumulative volume of 50% by volume in the particle size distribution is taken as the average particle size.

[0017] Here, "or" is not interpreted in an exclusive sense. For example, "A or B" is interpreted to include A, B, A + B, etc.

[0018] "Metal" is interpreted as a concept including common metals, transition metals, and metalloids.

[0019] Positive electrode active material In one embodiment, a positive electrode active material is provided that includes a layered lithium nickel-manganese composite oxide and is in the form of secondary particles formed by aggregation of a plurality of primary particles, and the average particle size (D 50 ) of the secondary particles is 10 μm to 25 μm, and a layered lithium nickel-cobalt composite oxide, and is in the form of single particles, and the average particle size (D 50 ) of the single particles is 0.5 μm to 8 μm.

[0020]

[0021] The positive electrode active material can achieve high-density characteristics, high capacity per unit volume, and high energy density, and has excellent characteristics at high voltages. Such a positive electrode active material is of low cost type and satisfies high capacity, high voltage, and high density characteristics. Therefore, when a lithium secondary battery applying this is mounted on an electric vehicle or a hybrid vehicle, long-distance driving is made possible.With respect to the total of 100% by weight of the first positive electrode active material and the second positive electrode active material, the first positive electrode active material is contained in an amount of 60% to 95% by weight, for example, 70% to 90% by weight, and the second positive electrode active material is contained in an amount of 5% to 40% by weight, for example, 10% to 30% by weight. When mixed in the above ratio, it is possible to improve the life characteristics and high-temperature storage characteristics at high voltage while maximizing the energy density.

[0022] First positive electrode active material Recently, due to the soaring price of the rare metal cobalt, there has been a demand for the development of positive electrode active materials that exclude cobalt or reduce its content. Among them, positive electrode active materials with an olivine crystal structure such as lithium iron phosphate (LFP), lithium manganese phosphate (LMP), lithium manganese iron phosphate (LMFP), or a spinel crystal structure 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-based positive electrode active materials can have a high amount of lithium within the structure, so they are excellent in capacity and efficiency characteristics and are suitable as materials for high-capacity batteries. However, when cobalt, which plays a central role in the layered structure, is removed, there are problems such as a decrease in structural stability, an increase in resistance, and difficulty in ensuring long-life characteristics. In addition, by excluding cobalt, there is a problem that the side reaction between the positive electrode active material and the electrolyte is accelerated under high voltage and high temperature conditions, resulting in an increase in gas generation and a decrease in life characteristics.

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

[0024] The first positive electrode active material contains a layered lithium nickel-manganese-based composite oxide and is in the form of secondary particles formed by aggregation of a plurality of primary particles. The average particle size (D 50) is characterized by being 10 μm to 25 μm. The first positive electrode active material is expressed as large grains or large particles.

[0025] The average particle size (D 50 ) of the secondary particles may be, for example, 10 μm to 20 μm, 10 μm to 18 μm, or 12 μm to 16 μm. Here, the average particle size (D 50 ) is obtained by measuring the sizes (diameter or major axis length) of more than 20 particles randomly in a scanning electron microscope image of the positive electrode active material to obtain a particle size distribution, and taking the diameter of the particle with a cumulative volume of 50% by volume in the particle size distribution as the average particle size.

[0026] The shape of the secondary particles may be, for example, spherical, ellipsoidal, polyhedral, amorphous (irregular shape), or a combination thereof. Here, the polyhedron refers to a three-dimensional figure having a plurality of corners such as a prism, a pyramid, or a frustum of a pyramid. The shape of the primary particles forming the secondary particles may be, for example, spherical, ellipsoidal, polyhedral, plate-like, needle-like, amorphous, or a combination thereof.

[0027] In the lithium nickel-manganese composite oxide, the nickel content may be 60 mol% or more with respect 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 satisfies the above range, high capacity can be realized, and the structural stability can be enhanced even if the cobalt content is decreased.

[0028] The manganese content may be, for example, 15 mol% or more, based on 100 mol% of the total metals excluding lithium in a lithium nickel-manganese composite oxide, and may be, for example, 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 the above range, the positive electrode active material can improve the structural stability while realizing a high capacity.

[0029] The lithium nickel-manganese composite oxide may be, as an example, a lithium nickel-manganese-aluminum composite oxide further containing aluminum in addition to nickel and manganese. When aluminum is contained in the composite oxide, it is advantageous for maintaining a stable layered structure even when the cobalt element is excluded from the structure. The aluminum content based on 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, and may be, 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 satisfies the above range, it is possible to maintain a stable layered structure even when cobalt is excluded, suppress the problem of the structure collapsing due to charge and discharge, and realize the long-life characteristics of the positive electrode active material.

[0030] According to one embodiment, the concentration of aluminum within the particles containing the lithium nickel-manganese composite oxide is 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 is not higher or lower outside than inside within the particles, and the aluminum within the particles is evenly 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 additionally doping aluminum during the synthesis process of the lithium nickel-manganese composite oxide. The particles may be in the form of secondary particles in which a plurality of primary particles are aggregated, but the aluminum content within the primary particles may be the same or similar regardless of the position of the primary particles. That is, if a primary particle is selected from an arbitrary position in the cross-section of the secondary particle and the aluminum content inside, not 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, a stable layered structure is maintained even if cobalt is absent or present in an extremely small amount, aluminum by-products and aluminum aggregates do not occur, and the capacity, efficiency, and life characteristics of the positive electrode active material can be improved simultaneously.

[0031] 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

[0032] 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.

[0033] In Chemical Formula 1, 0.9 ≦ a1 ≦ 1.5, or 0.9 ≦ a1 ≦ 1.2 may 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 are 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.

[0034] 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 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 be satisfied, 0.01 ≦ z1 ≦ 0.025, 0.01 < z1 ≦ 0.02, or 0.01 < z1 ≦ 0.019 may be satisfied, and 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 be satisfied.

[0035] As an example, the lithium nickel-manganese composite oxide may not contain cobalt or may contain a small amount, and the content of cobalt based on 100 mol% of the total metal excluding lithium may be 0 mol% to 0.01 mol%.

[0036] Coating layer The first positive electrode active material can include core particles containing a layered lithium nickel-manganese composite oxide, and a coating layer located on the surface of the core particles and containing Al, B, Mg, Ti, V, W, Y, Zn, Zr, or a combination thereof.

[0037] The lithium nickel-manganese composite oxide is liable to be chemically attacked by components in the electrolyte during battery driving under high voltage or high temperature conditions, and many side reactions with the electrolyte may occur. As a result, there are problems such as a large amount of gas generation, a decrease in battery life and safety. However, by introducing a coating layer according to an embodiment, such problems can be solved.

[0038] The coating layer may be, for example, an Al coating layer containing Al, and may further selectively contain elements such as B, Mg, Ti, V, W, Y, Zn, Zr, etc. When an Al coating layer is introduced, the high voltage performance of the first positive electrode active material can be further improved.

[0039] The layered lithium nickel-manganese composite oxide has a significantly different content of residual lithium on the particle surface from oxides of other compositions, such as lithium nickel-cobalt-manganese composite oxides, lithium nickel-cobalt-aluminum composite oxides, lithium cobalt oxides, etc. Their various surface properties are different, and it is impossible to form a coating layer with a uniform film morphology by existing coating methods. Therefore, in one embodiment, (i) a coating raw material is put into an aqueous solvent and mixed to first prepare a coating solution in which the salt is completely dissolved in a salt-dissolution method, (ii) core particles are put into this coating solution and mixed to allow the coating to proceed, and (iii) thereafter, after removing the solvent and drying, a uniform coating layer can be introduced onto the first positive electrode active material by a method of heat treatment. It can be said to be a pre-addition method in which the salt of the coating raw material is completely dissolved first and then the active material particles are added in the salt-dissolution wet coating method. By such a method, a uniform and thin film-shaped coating layer can be successfully formed on the surface of the layered lithium nickel-manganese composite oxide.

[0040] According to the coating method, compared with general dry methods and post-addition wet methods, the content of the coating element on the surface of the active material can be further increased. For example, the coating content on the surface of the first positive electrode active material measured by EP-EDS analysis may be 5 at% to 35 at% with respect to 100 at% of the total metal excluding lithium on the surface, or, for example, 5 at% to 30 at%, 5 at% to 25 at%, 5 at% to 25 at%, or 10 at% to 20 at%. In such a content range, the coating layer can effectively improve the high-voltage characteristics without increasing the resistance of the first positive electrode active material.

[0041] The coating layer may, for example, be in the form of a film that continuously surrounds the surface of the core particles, and may be, for example, in the form of a shell that surrounds the entire surface of the core particles. This is distinguished from a structure in which only a part of the surface of the core particles is partially coated. According to one embodiment, while the coating layer is formed in a form that entirely surrounds the surface of the core particles, it is formed to be very thin and have a uniform thickness. As a result, the positive electrode active material has improved structural stability without an increase in resistance or a decrease in capacitance, can effectively suppress side reactions with the electrolyte, reduces the amount of gas generation under high voltage and high temperature conditions, and can achieve long-life characteristics.

[0042] According to the method, the thickness of the coating layer of the first positive electrode active material may be 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 structural stability of the positive electrode active material can be improved without an increase in resistance or a decrease in capacitance due to the coating, and side reactions with the electrolyte can be effectively suppressed. The thickness of the coating layer is measured, for example, by SEM, TEM, TOF-SIMS, XPS, or EDS analysis, and is measured, for example, by EDS line profile analysis of the cross section of the positive electrode active material.

[0043] The coating layer according to one embodiment is characterized in that, while being as thin as several tens to several hundreds of nanometers, its thickness is uniform. For example, the deviation in the thickness of the coating layer within one positive electrode active material particle may be 20% or less, or may be 18% or less, or 15% or less. Here, the deviation in the thickness of the coating layer refers to the content of the thickness of the coating layer within one positive electrode active material particle. The deviation in the thickness of the coating layer can be obtained, for example, by measuring the thicknesses at more than 10 points in an electron microscope image of the cross-section of one positive electrode active material particle, calculating the arithmetic mean, and then dividing the absolute value of the difference between one data and the arithmetic mean value by the arithmetic mean value and multiplying by 100. The fact that the deviation or standard deviation in the thickness of the coating layer satisfies the above range means that a coating layer with a uniform thickness is formed in a good 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 the decrease in capacity due to coating.

[0044] For example, when introducing an Al coating layer, the Al content of the coating layer may be 0.1 mol% to 3.0 mol% with respect to 100 mol% of the total metal excluding lithium in the entire first positive electrode active material, or may be, for example, 0.1 mol% to 2.0 mol%, 0.5 mol% to 1.5 mol%, 0.7 mol% to 1.3 mol%.

[0045] When introducing an Al coating layer, the coating layer can include, for example, a layered aluminum compound, and can include, for example, aluminum oxide, lithium-aluminum oxide, or a combination thereof, and as an example, can include LiAlO2. As an example, the first positive electrode active material can include a first coating layer containing aluminum located on the surface of the core particle and a second coating layer containing zirconium located on the first coating layer.

[0046] The content of the coating element with respect to 100 mol% of the total metal excluding lithium in the entire first positive electrode active material may vary depending on the type of the coating element, but may be about 0.01 mol% to 5 mol%, or for example, 0.05 mol% to 3 mol%, or 0.1 mol% to 2 mol%.

[0047] Second positive electrode active material The second positive electrode active material contains a layered lithium nickel-cobalt-based composite oxide, is in the form of single particles, and the average particle diameter (D 50 ) of the single particles is characterized by being 0.5 μm to 8 μm. The second positive electrode active material is expressed as small grains or small particles.

[0048] The single particle means that it exists alone without having a grain boundary within the particle and consists of one particle, and can mean a single particle, a monolith structure or a single body structure or non-aggregated particles that exist as an independent phase in which the particles do not agglomerate morphologically. As an example, it may be a single crystal.

[0049] The average particle diameter (D 50 ) of the single particles may be, for example, 0.5 μm to 6 μm, 1 μm to 5 μm, or 2 μm to 4 μm. The shape of the single particles may be, for example, spherical, ellipsoidal, polyhedral, amorphous, or a combination thereof.

[0050] In the lithium nickel-cobalt composite oxide of the second positive electrode active material, the nickel content with respect to 100 mol% of the total metal excluding lithium may be, for example, 50 mol% to 70 mol%, or may be, for example, 55 mol% to 70 mol%, or 55 mol% to 65 mol%. That is, the second positive electrode active material may be a mid-nickel positive electrode active material containing 50 to 70 mol% of nickel. When nickel in the second positive electrode active material satisfies the above content range, excellent life characteristics can be realized under high voltage driving conditions with an upper limit charging voltage of 4.45 V or more. The mid-nickel second positive electrode active material can be expressed as a material for high voltage charging of 4.45 V or more.

[0051] The nickel content with respect to 100 mol% of the total metal excluding lithium in the lithium nickel-cobalt composite oxide of the second positive electrode active material may be less than the nickel content with respect to 100 mol% of the total metal excluding lithium in the layered lithium nickel-manganese composite oxide of the first positive electrode active material, and may be, for example, less than 10 mol% to 30 mol%, or less than 15 mol% to 20 mol%.

[0052] As an example, the lithium nickel-cobalt composite oxide may be represented by Chemical Formula 2, or as a specific example, may be represented by Chemical Formula 3.

[0053] [Chemical Formula 2] Li a2 Ni x2 Co y2 M 2 z2 O 2-b2 X b2

[0054] In Chemical Formula 2, 0.9 ≦ a2 ≦ 1.2, 0.5 ≦ x2 ≦ 0.7, 0.1 ≦ y2 ≦ 0.5, 0 ≦ z2 ≦ 0.4, 0.9 ≦ x2 + y2 + z2 ≦ 1.1, and 0 ≦ b2 ≦ 0.1, and M 2is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, 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.

[0055] [Chemical Formula 3] Li a3 Ni x3 Co y3 M 3 z3 M 4 w3 O 2-b3 X b3

[0056] In the Chemical Formula 3, 0.9 ≤ a3 ≤ 1.2, 0.5 ≤ x3 ≤ 0.7, 0.1 ≤ y3 ≤ 0.4, 0.1 ≤ z3 ≤ 0.3, 0 ≤ w3 ≤ 0.1, 0.9 ≤ x3 + y3 + z3 + w3 ≤ 1.1, and 0 ≤ b3 ≤ 0.1, where M 3 is Al, Mn, or a combination thereof, and M 4 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.

[0057] As an example, the second positive electrode active material can include core particles containing a lithium nickel-cobalt-based composite oxide and a coating layer located on the surface of the core particles. The coating layer can include, for example, Al, B, Co, Mg, Si, Ti, V, W, Zn, Zr, or a combination thereof. Based on 100% by weight of the total metals excluding lithium in the second positive electrode active material, the content of the coating element may be 0.1% to 5% by weight, 0.1% to 3% by weight, 0.1% to 2% by weight, 0.1% to 1% by weight, or 0.1% to 0.9% by weight.

[0058] Positive electrode In one embodiment, a positive electrode for a lithium secondary battery containing the above-described positive electrode active material is provided. For example, the positive electrode includes 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 contains the above-described positive electrode active material and may further selectively contain a binder, a conductive material, or a combination thereof.

[0059] According to one embodiment, the loading level of the positive electrode active material layer is 10 mg / cm 2 ~40 mg / cm 2 and may be, for example, 10 mg / cm 2 ~30 mg / cm 2 or 10 mg / cm 2 ~20 mg / cm 2 Also, in the rolled final positive electrode, the density of the positive electrode active material layer may be 3.3 g / cc to 3.7 g / cc, or for example, 3.3 g / cc to 3.6 g / cc or 3.4 g / cc to 3.58 g / cc. When applying the positive electrode active material according to one embodiment, 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 within the above range is suitable for realizing a high-capacity and high-energy density lithium secondary battery.

[0060] Binder The binder serves to well adhere the positive electrode active material particles to each other and also to well adhere the positive electrode active material to the current collector. Representative examples of the binder include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc., but are not limited thereto.

[0061] Conductive material The conductive material is used to impart conductivity to the electrode, and in the battery being configured, any electron conductive material that does not cause a chemical change can be used. Examples of the conductive material include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based substances including copper, nickel, aluminum, silver, etc., in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0062] The contents of the binder and the conductive material may each be 0.5 wt% to 5 wt% based on 100 wt% of the positive electrode active material layer.

[0063] As the positive electrode current collector, Al can be used, but is not limited thereto.

[0064] Lithium secondary battery In one embodiment, a lithium secondary battery including the positive electrode, the negative electrode, and the electrolyte described above is provided. As an example, the lithium secondary battery may include a positive electrode, a negative electrode, a separator positioned between the positive electrode and the negative electrode, and an electrolytic solution.

[0065] Lithium secondary batteries are classified into cylindrical, rectangular, pouch-type, coin-type, etc. according to their form. FIGS. 1 to 4 are schematic views showing a lithium secondary battery according to an embodiment. FIG. 1 shows a circular shape, FIG. 2 shows a rectangular shape, and FIGS. 3 and 4 show a pouch-type battery form. Referring to FIGS. 1 to 4, the lithium secondary battery 100 can include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is incorporated. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolytic solution (not shown). The lithium secondary battery 100 can include a sealing member 60 for sealing the case 50 as shown in FIG. 1. Also, in FIG. 2, the lithium secondary battery 100 can include a positive electrode lead tab 11 and a positive electrode terminal 12, and a negative electrode lead tab 21 and a negative electrode terminal 22. As shown in FIGS. 3 and 4, the lithium secondary battery 100 can include electrode tabs 70, that is, a positive electrode tab 71 and a negative electrode tab 72, which serve as an electrical path for guiding the current formed by the electrode assembly 40 to the outside.

[0066] A lithium secondary battery according to an embodiment may be suitable for charging at a high voltage or for being driven at a high voltage. For example, the upper limit voltage for charging the lithium secondary battery may be 4.45 V or more, and may be 4.45 V to 4.7 V, 4.45 V to 4.6 V, or 4.45 V to 4.55 V, etc. By applying a positive electrode active material according to an embodiment, the lithium secondary battery can significantly reduce the gas generation amount even when charged at a high voltage, and can realize high capacity and long life characteristics.

[0067] Negative electrode The negative electrode can include a current collector and a negative electrode active material layer located on this current collector. The negative electrode active material layer can include a negative electrode active material and can further include a binder, a conductive material, or a combination thereof.

[0068] Negative electrode active material The negative electrode active material includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

[0069] As the material capable of reversibly inserting / desorbing the lithium ions, a carbon-based negative electrode active material can be included, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-shaped, 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.

[0070] 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.

[0071] As the material capable of doping and undoping lithium, an Si-based negative electrode active material or an 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), an Si-Q alloy (wherein Q is an element selected from an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element (excluding Si), a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and a combination 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 a combination thereof), or a combination thereof may be used. As the Sn-based negative electrode active material, Sn, SnO2, an Sn alloy, or a combination thereof may be used.

[0072] The silicon-carbon composite may be a composite of silicon and amorphous carbon. The average particle size (D 50 ) of the silicon-carbon composite particles may be, for example, 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite may be in a form in which silicon particles and amorphous carbon are coated on the surface of the silicon particles. For example, it may include secondary particles (cores) formed by granulating silicon primary particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon may also be located between the silicon primary particles, for example, the silicon primary particles are coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0073] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. Examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, and calcined coke.

[0074] When the silicon-carbon composite contains silicon and amorphous carbon, the content of silicon may be 10% by weight to 50% by weight based on 100% by weight of the silicon-carbon composite, and the content of amorphous carbon may be 50% by weight to 90% by weight. When the composite contains silicon, amorphous carbon, and crystalline carbon, the content of silicon may be 10% by weight to 50% by weight based on 100% by weight of the silicon-carbon composite, the content of crystalline carbon may be 10% by weight to 70% by weight, and the content of amorphous carbon may be 20% by weight to 40% by weight.

[0075] Also, the thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. The average particle size (D 50) may be 10 nm to 1 μm, or 10 nm to 200 nm. The silicon particles may exist alone as silicon, in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon is 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 size (D 50 ) means the diameter of the particles with a cumulative volume of 50% by volume in the particle size distribution.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated 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.

[0080] When using an aqueous binder as the negative electrode binder, a cellulose-based compound capable of imparting viscosity can be further included. As this cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof can be mixed and used. As the alkali metal, Na, K, or Li can be used.

[0081] The dry binder is a polymer substance that can be fibrillated, and for example, it may be polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0082] Conductive material The conductive material is used to impart conductivity to the electrode, and in the battery being configured, any electron conductive material that does not cause a chemical change can be used. Specific examples include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, carbon nanotube; metal-based substances containing copper, nickel, aluminum, silver, etc., in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0083] The content of the negative electrode active material may be 95% by weight to 99.5% by weight based on 100% by weight of the negative electrode active material layer, and the content of the binder may be 0.5% by weight to 5% by weight based on 100% by weight of the negative electrode active material layer. For example, the negative electrode active material layer may contain 90% by weight to 99% by weight of the negative electrode active material, 0.5% by weight to 5% by weight of the binder, and 0.5% by weight to 5% by weight of the conductive material.

[0084] 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, a sheet, or a foam. The thickness of the negative electrode current collector may be, for example, 1 μm to 20 μm, or may be 5 μm to 15 μm, or 7 μm to 10 μm.

[0085] Electrolyte The electrolyte for the lithium secondary battery may be, for example, an electrolytic solution, which may contain a non-aqueous organic solvent and a lithium salt.

[0086] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. The non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0087] As carbonate solvents, 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. can be used. As ester solvents, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. can be used. As ether solvents, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. can be used. Also, as ketone solvents, cyclohexanone, etc. can be used. As alcohol solvents, ethyl alcohol, isopropyl alcohol, etc. can be used, and as aprotic solvents, nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms and can contain a double bond, aromatic ring, or ether group), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, 1,4-dioxolane, sulfolane, etc. can be used.

[0088] The non-aqueous organic solvent can be used alone or in a mixture of two or more. When used in a mixture of two or more, the mixing ratio can be appropriately adjusted according to the intended battery performance, which can be widely understood by those skilled in the art.

[0089] When using a carbonate solvent, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed at a volume ratio of 1:1 to 1:9.

[0090] The non-aqueous organic solvent may further contain an aromatic hydrocarbon-based organic solvent. For example, the carbonate solvent and the aromatic hydrocarbon-based organic solvent can be mixed and used at a volume ratio of 1:1 to 30:1.

[0091] For improving battery life, the electrolytic solution may further contain vinyl ethyl carbonate, vinylene carbonate or an ethylene carbonate-based compound.

[0092] Typical examples of the ethylene carbonate-based compound include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate and the like.

[0093] The lithium salt is a substance that dissolves in the organic solvent, acts as a source of lithium ions in the battery to enable the operation of a basic lithium secondary battery, and plays a role in promoting the movement of lithium ions between the positive electrode and the negative electrode. Typical examples of the lithium salt include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2)(where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), lithium bis(oxalato)borate (LiBOB), and one or more selected therefrom can be included.

[0094] The concentration of the lithium salt is preferably used within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolytic solution has appropriate ion conductivity and viscosity, so that excellent performance can be exhibited and lithium ions can move effectively.

[0095] Separator Depending on the type of the lithium secondary battery, a separator may be present between the positive electrode and the negative electrode. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof can be used, and it goes without saying that mixed multilayer films such as a two-layer separator of polyethylene / polypropylene, a three-layer separator of polyethylene / polypropylene / polyethylene, and a three-layer separator of polypropylene / polyethylene / polypropylene can be used.

[0096] The separator may include a porous substrate and a coating layer containing an organic substance, an inorganic substance, or a combination thereof located on one or both surfaces of the porous substrate.

[0097] The porous substrate may be a polymer selected from any one of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyether imide, polyamide imide, polybenzimidazole, polyether sulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a polymer film formed of a copolymer or mixture of two or more of these.

[0098] The porous substrate may have a thickness of about 1 μm to 40 μm, for example, a thickness of 1 μm to 30 μm, 1 μm to 20 μm, 5 μm to 15 μm, or 10 μm to 15 μm.

[0099] The organic substance can 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.

[0100] The inorganic substance can 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 ) of the inorganic particles may be 1 nm to 2000 nm, for example, 100 nm to 1000 nm, or 100 nm to 700 nm.

[0101] The organic substance and the inorganic substance can be present as being mixed in one coating layer, or can be present in a form in which a coating layer containing the organic substance and a coating layer containing the inorganic substance are laminated.

[0102] The thickness of each of the coating layers may be 0.5 μm to 20 μm, for example, 1 μm to 10 μm, or 1 μm to 5 μm.

[0103] Hereinafter, examples and comparative examples of the present invention will be described. The following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0104] Example 1 1. Manufacture of positive electrode active material (1) Manufacture of first positive electrode active material Ni 0.75 Mn 0.23 Al 0.02(OH)2 and LiOH were mixed and mixed so that the molar ratio of Li / (Ni+Mn+Al) was 1.05, and the first heat treatment was carried out at 845 °C for 8 hours in an oxygen atmosphere, and the composition was Li 1.05 Ni 0.75 Mn 0.23 Al 0.02 O2, and secondary particle-like first lithium nickel-manganese composite oxide with an average particle size (D 50 ) of about 14 μm was produced.

[0105] Aluminum sulfate was added to the distilled water solvent and stirred at about 350 rpm for about 5 minutes to produce a coating solution. It was confirmed that the salt was completely dissolved in the coating solution and was colorless and transparent. 500 g of the produced first lithium nickel-manganese composite oxide was added to the coating solution during continuous stirring for 1.5 minutes, and stirred for about 45 minutes. At this time, the content of aluminum in aluminum sulfate was designed to be 1.0 mol% with respect to 100 mol% of the total metal excluding lithium in the final first positive electrode active material. The solvent was removed from the mixed solution using an aspirator and a filter press, and vacuum dried at 190 °C.

[0106] After adding zirconium oxide to the dried product, the second heat treatment was carried out at 825 °C for 8 hours in an oxygen atmosphere to produce the first positive electrode active material. The content of zirconium in zirconium oxide was designed to be 0.2 mol% with respect to 100 mol% of the total metal excluding lithium in the final first positive electrode active material.

[0107] (2) Manufacture of second positive electrode active material Ni 0.6 Co 0.1 Mn 0.3 (OH)2 and LiOH were mixed and mixed so that the molar ratio of Li / (Ni+Co+Mn) was 1.05, and the first heat treatment was carried out at 930 °C for 8 hours in an oxygen atmosphere. The average particle size (D 50 ) of the obtained product was ground so as to be about 3.5 μm, and single particle-like lithium nickel-cobalt composite oxide (Li 1.05 Ni 0.6 Co0.1 Mn 0.3 O2) was produced.

[0108] (3) Manufacture of mixed positive electrode active material The first positive electrode active material and the second positive electrode active material were mixed at a weight ratio of 90:10 to prepare the final positive electrode active material.

[0109] 2. Manufacture of lithium secondary battery 96% by weight of the produced positive electrode active material, 2% by weight of a polyvinylidene fluoride binder, and 2% by weight of a carbon nanotube conductive material were mixed to produce a positive electrode active material layer slurry, which was coated on an aluminum foil current collector and dried and rolled to produce a positive electrode.

[0110] A structure was produced with a polytetrafluoroethylene separator interposed between the positive electrode and the lithium metal counter electrode, and after inserting this into a battery case, an electrolytic solution in which 1M LiPF6 was dissolved in a solvent in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 3:7 was injected to produce a lithium secondary battery (half cell) by a normal method.

[0111] Example 2 A positive electrode active material and a lithium secondary battery were produced in substantially the same manner as in Example 1, except that the first positive electrode active material and the second positive electrode active material were mixed at a weight ratio of 80:20 to prepare the final positive electrode active material.

[0112] Example 3 A positive electrode active material and a lithium secondary battery were produced in substantially the same manner as in Example 1, except that the first positive electrode active material and the second positive electrode active material were mixed at a weight ratio of 70:30 to prepare the final positive electrode active material.

[0113] Example 4 A positive electrode active material and a lithium secondary battery were produced in substantially the same manner as in Example 1, except that the first positive electrode active material and the second positive electrode active material were mixed at a weight ratio of 60:40 to prepare the final positive electrode active material.

[0114] Comparative Example 1 A positive electrode active material and a lithium secondary battery were produced in substantially the same manner as in Example 1, except that only the first positive electrode active material was applied alone as the positive electrode active material.

[0115] Comparative Example 2 A positive electrode active material and a lithium secondary battery were produced in substantially the same manner as in Example 1, except that only the second positive electrode active material was applied alone as the positive electrode active material.

[0116] The pellet density of the positive electrode active materials produced in Examples 1 to 4 and Comparative Examples 1 and 2 was measured and expressed as P / D in Table 1 below. The pellet density was measured by putting 3 g of the positive electrode active material into a Mold (area: 1.298 cm 2 ), slowly inserting the Mold Bar into the Mold body, putting the Mold SET into a hydraulic press, applying a pressure of 3 ton (Metric ton) for 30 seconds, and then measuring the height.

[0117] Evaluation Example 1: Evaluation of initial charge-discharge capacity, efficiency and life characteristics The lithium secondary batteries produced in Examples 1 to 4 and Comparative Examples 1 and 2 were charged at a constant current of 0.2C to 4.45V and then at a constant voltage of 0.05C to 3.0V at 25°C, and then discharged at 0.2C to 3.0V to perform initial charge and discharge. The initial charge capacity and the initial discharge capacity are shown in Table 1 below, and the initial charge-discharge efficiency, which is the ratio of the latter to the former, is shown as efficiency in Table 1 below. Also, the initial discharge capacity was multiplied by the pellet density and expressed as the capacity per unit volume in Table 1.

[0118] Next, a cycle of charging at 1.0C and discharging at 1.0C in the voltage range of 3.0V to 4.45V was repeated 50 times at 45°C. The ratio of the discharge capacity in 50 cycles to the initial discharge capacity was calculated and shown as the life in Table 1 below.

[0119] Evaluation Example 2: Evaluation of high-temperature storage characteristics The battery in the state of being initially charged to 4.45V in Evaluation Example 1 was stored at 90°C for 24 hours, and then the amount of gas generated in the battery was measured and shown in Table 1 below.

[0120]

Table 1

[0121] Referring to Table 1, it can be seen that the cathode active materials of Examples 1 to 4 all had a high pellet density of 3.29 g / cc or more, and the lithium secondary batteries of Examples 1 to 4 had an improved capacity per unit volume compared to the comparative examples, and the life characteristics were also maintained at an excellent level. Also, in the high-temperature storage evaluation, the gas generation amount was evaluated to be in a low range.

[0122] Comparative Example 1 was the case where only the first cathode active material was applied. Although the initial discharge capacity per unit weight increased, the pellet density of the cathode active material decreased, and ultimately, the capacity per unit volume decreased. As a result, it was confirmed that it was disadvantageous in terms of energy density compared to the examples. In the case of Comparative Example 1, the life characteristics were also slightly lower compared to the examples, and the gas generation amount during high-temperature storage was also measured to be higher.

[0123] Comparative Example 2 was the case where only the second cathode active material was applied. Although the initial discharge capacity per unit weight increased, the pellet density of the cathode active material significantly decreased, and ultimately, the capacity per unit volume decreased significantly. As a result, it was confirmed that it was disadvantageous in terms of energy density compared to the examples.

[0124] Comparative Example 3 was the case where a single-particle high-nickel-based cathode active material was applied as the second cathode active material. In this case, it was revealed that the life in the high-voltage region dropped sharply. It was confirmed that the high-nickel-based cathode active material was difficult to drive in the high-voltage region where the upper charge limit voltage was increased to 4.45 V. The cathode active material according to one embodiment can be said to be a material optimized for the high-voltage driving conditions with an upper charge limit voltage of 4.45 V or more.

[0125] Although the preferred embodiments have been described in detail above, the scope of the rights of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concepts defined in the following claims also belong to the scope of the rights of the present invention.

Explanation of Signs

[0126] 100: Lithium secondary battery, 10: Positive electrode 11: Positive electrode lead tab, 12: Positive electrode terminal 20: Negative electrode, 21: Negative electrode lead tab 22: Negative electrode terminal, 30: Separator 40: Electrode assembly, 50: Case 60: Sealing member, 70: Electrode tab 71: Positive electrode tab, 72: Negative electrode tab

Claims

1. It contains a layered lithium nickel-manganese composite oxide and is in the form of secondary particles formed by aggregation of a plurality of primary particles. The average particle size (D 50 ) of the secondary particles is 10 μm to 25 μm, and a first positive electrode active material, A positive electrode active material including a layered lithium nickel-cobalt-based composite oxide, being in a single particle form, and having an average particle size (D 50 ) of 0.5 μm to 8 μm for the single particle.

2. The positive electrode active material according to claim 1, wherein the first positive electrode active material is contained in an amount of 60% by weight to 95% by weight and the second positive electrode active material is contained in an amount of 5% by weight to 40% by weight with respect to a total 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 with respect to 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 aluminum content is 1 mol% to 3 mol% with respect to 100 mol% of the total metal excluding lithium.

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

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

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

9. The positive electrode active material according to claim 8, wherein the coating layer contains Al and is in a shell form 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 content of nickel with respect to 100 mol% of the total metals excluding lithium in the lithium nickel-cobalt composite oxide of the second positive electrode active material is 50 mol% to 70 mol%.

13. The positive electrode active material according to claim 12, wherein the second positive electrode active material is for high voltage charging of 4.45 V or more.

14. The positive electrode active material according to claim 1, wherein the content of nickel with respect to 100 mol% of the total metals excluding lithium in the lithium nickel-cobalt composite oxide of the second positive electrode active material is less than the content of nickel with respect to 100 mol% of the total metals excluding lithium in the layered lithium nickel-manganese composite oxide of the first positive electrode active material.

15. The positive electrode active material according to claim 1, wherein the lithium nickel-cobalt composite oxide of the second positive electrode active material is represented by Chemical Formula 2: [Chemical Formula 2] Li a2 Ni x2 Co y2 M 2 z2 O 2-b2 X b2 In the chemical formula 2, 0.9 ≤ a2 ≤ 1.2, 0.5 ≤ x2 ≤ 0.7, 0.1 ≤ y2 ≤ 0.5, 0 ≤ z2 ≤ 0.4, 0.9 ≤ x2 + y2 + z2 ≤ 1.1, and 0 ≤ b2 ≤ 0.1, and M 2 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, 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.

16. Comprising a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, The positive electrode active material layer is a positive electrode containing the positive electrode active material according to any one of claims 1 to 15.

17. The loading level of the positive electrode active material layer is 10 mg / cm 2 to 40 mg / cm 2 The positive electrode according to claim 16, wherein the positive electrode is such.

18. The positive electrode according to claim 16, wherein the density of the positive electrode active material layer is 3.3 g / cc to 3.7 g / cc.

19. A lithium secondary battery comprising the positive electrode according to claim 16, a negative electrode, and an electrolyte.

20. The lithium secondary battery according to claim 19, wherein the upper limit charging voltage is 4.45 V or more.

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