Positive electrode for lithium secondary battery, and lithium secondary battery including the same

Abstract

To provide a positive electrode for a lithium secondary battery, for realizing a prevention of deterioration and a long life of the lithium secondary battery.SOLUTION: A positive electrode active material of a lithium secondary battery, includes: a first positive electrode active material including a first lithium nickel-cobalt-based composite oxide, having in a form of second particles composed of a plurality of primary particles, and having an average particle diameter (D50) of a second particles of 10 μm to 30 μm; a second positive electrode active material including a second lithium nickel-cobalt-based composite oxide, in a form of second particles composed of the plurality of primary particles, and having an average particle diameter (D50) of the second particles is 5 μm to 9 μm; and a third positive electrode active material including a third lithium nickel-cobalt-based composite oxide, in a form of single particles, and having an average particle diameter (D50) of the single particles is 0.5 μm to 4 μm.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery including the same.

Background Art

[0002] Lithium secondary batteries having a high energy density while 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 with 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-cobalt-based composite oxides, lithium cobalt composite oxides, lithium nickel-manganese-based composite oxides, etc. are mainly used as positive electrode active materials.

[0004] Among them, lithium nickel-cobalt-based composite oxides are advantageous in realizing a high capacity while being structurally stable and realizing long-life characteristics, and can also realize a high energy density. In recent years, they have been in the spotlight as materials required for products with high capacity and high energy density.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention provides a positive electrode for a lithium secondary battery for preventing deterioration of the lithium secondary battery and realizing a long life.

Means for Solving the Problems

[0006] In one embodiment of the present invention, it includes a first lithium nickel-cobalt-based composite oxide and is in the form of secondary particles composed of a plurality of primary particles, and the average particle diameter (D of the secondary particles 50) is a first positive electrode active material having a size of 10 μm to 30 μm; a second lithium nickel-cobalt composite oxide, which is in the form of secondary particles composed of a plurality of primary particles, and the average particle size (D 50 ) of the secondary particles is 5 μm to 9 μm; and a third lithium nickel-cobalt composite oxide, which is in the form of single particles, and the average particle size (D 50 ) of the single particles is 0.5 μm to 4 μm; and a positive electrode active material for a lithium secondary battery that satisfies the following relational expression 1 is provided. [Relational Expression 1] Co 2 > Co 1 > Co 3

[0007] In the relational expression 1, Co 1 is the molar% content of cobalt with respect to 100 mol% of the metal excluding lithium in the first lithium nickel-cobalt composite oxide, and Co 2 is the molar% content of cobalt with respect to 100 mol% of the metal excluding lithium in the second lithium nickel-cobalt composite oxide, and Co 3 is the molar% content of cobalt with respect to 100 mol% of the metal excluding lithium in the third lithium nickel-cobalt composite oxide.

[0008] In one embodiment of the present invention, a positive electrode for a lithium secondary battery including 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 includes the positive electrode active material for a lithium secondary battery is provided.

[0009] In one embodiment of the present invention, a lithium secondary battery including the positive electrode for a lithium secondary battery; a negative electrode; and an electrolytic solution is provided.

[0010] In one embodiment of the present invention, a step of preparing a composition in which, with respect to a total of 100% by weight of the first cathode active material, the second cathode active material, and the third cathode active material, the content of the first cathode active material is 60 to 90% by weight, the content of the second cathode active material is 5 to 20% by weight, and the content of the third cathode active material is 5 to 20% by weight; a step of coating the composition on a current collector; and a step of rolling after drying; A method for manufacturing a positive electrode for a lithium secondary battery, wherein the first cathode active material includes a first lithium nickel-cobalt composite oxide and is in the form of secondary particles composed of a plurality of primary particles, and the average particle diameter (D 50 ) of the secondary particles is 10 μm to 30 μm, the second cathode active material includes a second lithium nickel-cobalt composite oxide and is in the form of secondary particles composed of a plurality of primary particles, and the average particle diameter (D 50 ) of the secondary particles is 5 μm to 9 μm, the third cathode active material includes a third lithium nickel-cobalt composite oxide and is in the form of single particles, and the average particle diameter (D 50 ) of the single particles is 0.5 μm to 4 μm; and provides a method for manufacturing a positive electrode for a lithium secondary battery that satisfies the following relational expression 1. [Relational Expression 1] Co 2 >Co 1 >Co 3

[0011] In the relational expression 1, Co 1 is the molar% content of cobalt with respect to 100 mol% of the metal excluding lithium in the first lithium nickel-cobalt composite oxide, Co 2 is the molar% content of cobalt with respect to 100 mol% of the metal excluding lithium in the second lithium nickel-cobalt composite oxide, and Co 3 is the molar% content of cobalt with respect to 100 mol% of the metal excluding lithium in the third lithium nickel-cobalt composite oxide. [Advantages of the Invention]

[0012] The positive electrode for a lithium secondary battery according to one embodiment of the present invention can effectively prevent deterioration during the life while realizing high capacity and energy density, and can achieve a long life.

Brief Description of the Drawings

[0013]

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Modes for Carrying Out the Invention

[0014] Hereinafter, specific embodiments will be described in detail so that those having ordinary knowledge in this technical field can easily implement them. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0015] The terms used here are used only to explain exemplary embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0016] "These combinations" means a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of components.

[0017] Terms such as "comprising", "including", or "having" are intended to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and should not be construed as precluding the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0018] To clearly represent various layers and regions in the drawings, the thickness is enlarged and shown, and the same drawing reference numerals are given to similar parts throughout the specification. When a part such as a layer, film, region, or plate is "on" or "above" another part, this includes not only the case where it is "directly above" the other part but also the case where there are other parts in between. Conversely, when a part is "directly above" another part, it means that there are no other parts in between.

[0019] "Layer" includes not only the shape formed on the entire surface but also the shape formed on a partial surface when observed in a plan view.

[0020] 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 it can also be measured from a transmission electron microscope image or a scanning electron microscope image. As another method, it can be measured using the dynamic light scattering method, and after performing data analysis to count the number of particles for each particle size range, the average particle size value can then be calculated therefrom. Unless otherwise defined, the average particle size means the diameter (D 50 ) of the particle with a cumulative volume of 50% by volume in the particle size distribution. Also, unless otherwise defined, the average particle size can be obtained by measuring the sizes (diameter or major axis length) of randomly selected more than 20 particles from a scanning electron microscope image to obtain a particle size distribution, and taking the diameter (D 50 ) of the particle with a cumulative volume of 50% by volume in the said particle size distribution as the average particle size.

[0021] "Or" is not construed in an exclusive sense. For example, "A or B" is construed to include A, B, A + B, etc.

[0022] "Metal" is interpreted as a concept including common metals, transition metals, and metalloids (semi-metals).

[0023] Cathode In one embodiment, a cathode for a lithium secondary battery includes a cathode current collector and a cathode active material layer located on the cathode current collector. The cathode active material layer includes a first lithium nickel-cobalt composite oxide and is in the form of secondary particles composed of a plurality of primary particles. The average particle diameter (D 50 ) of the secondary particles is 10 μm to 30 μm; a second lithium nickel-cobalt composite oxide is included, and it is in the form of secondary particles composed of a plurality of primary particles. The average particle diameter (D 50 ) of the secondary particles is 5 μm to 9 μm; and a third lithium nickel-cobalt composite oxide is included, and it is in the form of single particles. The average particle diameter (D 50 ) of the single particles is 0.5 μm to 4 μm. The cathode for a lithium secondary battery includes a cathode active material for a lithium secondary battery that satisfies the following relational expression 1. [Relational Expression 1] Co 2 > Co 1 > Co 3

[0024] In the relational expression 1, Co 1 is the molar percentage content of cobalt with respect to 100 mol% of the metal excluding lithium in the first lithium nickel-cobalt composite oxide, Co 2 is the molar percentage content of cobalt with respect to 100 mol% of the metal excluding lithium in the second lithium nickel-cobalt composite oxide, and Co 3 is the molar percentage content of cobalt with respect to 100 mol% of the metal excluding lithium in the third lithium nickel-cobalt composite oxide.

[0025] In a positive electrode containing a lithium nickel-cobalt-based positive electrode active material, a design has been proposed to maximize the capacity and energy density and achieve long-life characteristics by mixing large particles in the form of secondary particles and small particles in the form of single particles. However, due to the difference in kinetic behavior between the large particles in the form of secondary particles and the small particles in the form of single particles, a phenomenon occurs in which the deterioration of the large particles is accelerated while charge and discharge are repeated, resulting in a problem of deterioration of the life characteristics. Therefore, in one embodiment, by using not only large particles in the form of secondary particles and small particles in the form of single particles but also medium-sized particles in the form of secondary particles, the problem of accelerated deterioration of the large particles is effectively suppressed by achieving kinetic balance, the life characteristics are improved, and at the same time, a design that can maintain high capacity and energy density is proposed.

[0026] Positive electrode active material layer The positive electrode active material layer includes a first positive electrode active material containing a lithium nickel-cobalt-based composite oxide, a second positive electrode active material, and a third positive electrode active material. Further, the positive electrode active material layer can further include other types of positive electrode active materials, and can selectively further include a binder and / or a conductive material.

[0027] The first positive electrode active material is in the form of secondary particles composed of a plurality of primary particles, and the average particle diameter (D 50 ) of the secondary particles is 10 μm to 30 μm, and for example, it may be 11 μm to 29 μm, 12 μm to 28 μm, 13 μm to 27 μm, 14 μm to 26 μm, or 15 μm to 25 μm, and can be expressed as large grains or large particles. When the particle diameter of the secondary particles satisfies the above range, there is an advantage that high capacity and high energy density can be realized. Here, the average particle diameter (D 50 ) of the secondary particles may be obtained by measuring the sizes (diameter or major axis length) of more than 20 particles randomly in a scanning electron microscope image 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 diameter.

[0028] The second positive electrode active material is in the form of secondary particles composed of a plurality of primary particles, and the average particle diameter (D50 ) is from 5 μm to 9 μm, for example, it may be from 5.2 μm to 8.8 μm, from 5.4 μm to 8.6 μm, from 5.6 μm to 8.4 μm, from 5.8 μm to 8.2 μm, or from 6 μm to 8 μm, and can be expressed as medium-sized particles or medium grains. When the particle size of the secondary particles satisfies the above range, there are advantages that high capacity and high energy density can be realized, and at the same time, the deterioration of large particles can be alleviated. Here, the average particle size (D 50 ) may be obtained by measuring the sizes (diameter or major axis length) of more than 20 particles randomly in a scanning electron microscope image 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.

[0029] The third positive electrode active material is in the form of single particles, and the average particle size (D 50 ) is from 0.5 μm to 4 μm, for example, it may be from 0.6 μm to 3.8 μm, from 0.7 μm to 3.6 μm, from 0.8 μm to 3.4 μm, from 0.9 μm to 3.2 μm, or from 1 μm to 3 μm, and can be expressed as small-sized particles or small grains. When the particle size of the small particles satisfies the above range, there are advantages that the energy density of the positive electrode can be maximized, and at the same time, the deterioration of large particles can be alleviated. Here, the average particle size (D 50 ) may be obtained by measuring the sizes (diameter or major axis length) of more than 20 particles randomly in a scanning electron microscope image 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.

[0030] In the positive electrode active material layer, the first positive electrode active material is contained in an amount of 60 to 90% by weight, for example, 63 to 89% by weight, 66 to 88% by weight, 69 to 87% by weight, 72 to 86% by weight, or 75 to 85% by weight, based on the total 100% by weight of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material. Further, in the positive electrode active material layer, the second positive electrode active material is contained in an amount of 5 to 20% by weight, for example, 6 to 20% by weight, 7 to 20% by weight, 8 to 20% by weight, 9 to 20% by weight, or 10 to 20% by weight, based on the total 100% by weight of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material. Further, in the positive electrode active material layer, the third positive electrode active material is contained in an amount of 5 to 20% by weight, for example, 6 to 20% by weight, 7 to 20% by weight, 8 to 20% by weight, 9 to 20% by weight, or 10 to 20% by weight, based on the total 100% by weight of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material. When the contents of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material in the positive electrode active material layer satisfy the above ranges, respectively, the problem of accelerated deterioration of large particles during the charge and discharge process is suppressed, the life characteristics are improved, and high capacity and high energy density can be maintained.

[0031] The lithium nickel-cobalt-based composite oxides of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material are the same as or different from each other, and are each independently represented by the following Chemical Formula 1. [Chemical Formula 1] Li a1 Ni x1 Co y1 M 1 z1 M 2 w1 O 2-b1 X b1

[0032] In Chemical Formula 1, 0.9 ≦ a1 ≦ 1.2, 0.3 ≦ x1 ≦ 0.98, 0.01 ≦ y1 ≦ 0.69, 0.01 ≦ z1 ≦ 0.69, 0 ≦ w1 ≦ 0.69, 0.9 ≦ x1 + y1 + z1 + w1 ≦ 1.1, and 0 ≦ b1 ≦ 0.1, and M 1 is Al, Mn, or a combination thereof, and M2 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from F, P, and S.

[0033] In the chemical formula 1, 0.4 ≦ x1 ≦ 0.98, 0.01 ≦ y1 ≦ 0.59, 0.01 ≦ z1 ≦ 0.59, and 0 ≦ w1 ≦ 0.59, and it can be 0.5 ≦ x1 ≦ 0.98, 0.01 ≦ y1 ≦ 0.49, 0.01 ≦ z1 ≦ 0.49, and 0 ≦ w1 ≦ 0.49, or 0.6 ≦ x1 ≦ 0.98, 0.01 ≦ y1 ≦ 0.39, 0.01 ≦ z1 ≦ 0.39, and 0 ≦ w1 ≦ 0.39, or 0.7 ≦ x1 ≦ 0.98, 0.01 ≦ y1 ≦ 0.29, 0.01 ≦ z1 ≦ 0.29, and 0 ≦ w1 ≦ 0.29, or 0.8 ≦ x1 ≦ 0.98, 0.01 ≦ y1 ≦ 0.19, 0.01 ≦ z1 ≦ 0.19, and 0 ≦ w1 ≦ 0.19, or 0.9 ≦ x1 ≦ 0.98, 0.01 ≦ y1 ≦ 0.09, 0.01 ≦ z1 ≦ 0.09, and 0 ≦ w1 ≦ 0.

[0034] The molar percentage content of cobalt with respect to 100 mol% of the metal excluding lithium in the second lithium nickel-cobalt composite oxide is greater than the molar percentage content of cobalt with respect to 100 mol% of the metal excluding lithium in the first lithium nickel-cobalt composite oxide, for example, 1.1 to 2 times, 1.1 to 1.8 times, or 1.2 to 1.6 times greater. Also, the molar percentage content of cobalt with respect to 100 mol% of the metal excluding lithium in the first lithium nickel-cobalt composite oxide is greater than the molar percentage content of cobalt with respect to 100 mol% of the metal excluding lithium in the third lithium nickel-cobalt composite oxide, for example, 1.1 to 3 times, 1.1 to 2.5 times, or 1.2 to 2.5 times greater. The higher the cobalt content, the higher the capacity can be achieved, but there may be more side reactions with the electrolyte, or more problems such as large particles breaking or deteriorating during the life. However, according to the design of the positive electrode in one embodiment, the cobalt content of the second lithium nickel-cobalt composite oxide, which is a medium particle, is the largest, and the cobalt content of the third lithium nickel-cobalt composite oxide, which is a small particle, is the smallest. Therefore, problems such as damage to large particles during charge and discharge and accelerated deterioration of large particles are prevented, a kinetic balance of lithium ions and electrons is formed, and there is an advantage that the life characteristics of the lithium secondary battery can be improved.

[0035] The molar percentage content of cobalt with respect to 100 mol% of the metal excluding lithium in the first lithium nickel-cobalt composite oxide is 5 mol% to 20 mol%, for example, 6 mol% to 20 mol%, 7 mol% to 20 mol%, 8 mol% to 20 mol%, 9 mol% to 20 mol%, or 10 mol% to 20 mol%. Also, the molar percentage content of cobalt with respect to 100 mol% of the metal excluding lithium in the second lithium nickel-cobalt composite oxide is 10 mol% to 30 mol%, for example, 11 mol% to 29 mol%, 12 mol% to 28 mol%, 13 mol% to 27 mol%, 14 mol% to 26 mol%, or 15 mol% to 25 mol%. Further, the molar percentage content of cobalt with respect to 100 mol% of the metal excluding lithium in the third lithium nickel-cobalt composite oxide is 1 mol% to 15 mol%, for example, 2 mol% to 15 mol%, 3 mol% to 15 mol%, 4 mol% to 15 mol%, or 5 mol% to 15 mol%. When the molar percentage content of cobalt with respect to 100 mol% of the metal excluding lithium in the first, second, and third lithium nickel-cobalt composite oxides satisfies the above range, the problem of damage to large grains during the rolling process is effectively suppressed, the problem of accelerated deterioration of large particles during charge and discharge is prevented, the kinetic balance of lithium ions and electrons is formed, and there is an advantage that the life characteristics of the lithium secondary battery can be improved.

[0036] In the positive electrode active material layer, the molar percentage of cobalt with respect to 100 mol% of the metal excluding lithium in the second lithium nickel-cobalt composite oxide is 1 mol% to 10 mol% more than the molar percentage of cobalt with respect to 100 mol% of the metal excluding lithium in the first lithium nickel-cobalt composite oxide, for example, 2 mol% to 9 mol%, 3 mol% to 8 mol%, or 4 mol% to 7 mol% more. Also, the molar percentage of cobalt with respect to 100 mol% of the metal excluding lithium in the first lithium nickel-cobalt composite oxide is 1 mol% to 10 mol% more than the molar percentage of cobalt with respect to 100 mol% of the metal excluding lithium in the third lithium nickel-cobalt composite oxide, for example, 2 mol% to 9 mol%, 3 mol% to 8 mol%, or 4 mol% to 7 mol% more. When the difference in the molar percentage of cobalt with respect to 100 mol% of the metal excluding lithium in the lithium nickel-cobalt composite oxide satisfies the above range, the problem of accelerated deterioration of large particles during charge and discharge is prevented, a kinetic balance of lithium ions and electrons is formed, and there is an advantage that the life characteristics of the lithium secondary battery can be improved.

[0037] The density of the positive electrode active material layer is 3.4 g / cc to 3.9 g / cc, for example, 3.5 g / cc to 3.8 g / cc, or 3.6 g / cc to 3.7 g / cc. The density of the positive electrode active material layer means the density measured for the rolled positive electrode. When the density of the positive electrode active material layer satisfies the above range, a very high energy density and high capacity can be realized. However, in such a high-density positive electrode, there may be a problem that large particles in the particle form break or are damaged due to repeated charge and discharge. However, according to the design of the positive electrode of one embodiment, it is possible to effectively suppress damage to large particles while realizing a very high density.

[0038] For example, the number percentage of the first cathode active material in which cracks have occurred in the first cathode active material layer is 0 to 30 number %, for example, it can be 1 number % to 20 number %, or 3 number % to 10 number %. This means the number percentage of the first cathode active material in which cracks have occurred even partially with respect to 100 number % of the first cathode active material in the cathode active material layer. The presence or absence of crack generation and the crack generation ratio can be measured by SEM or TEM images of the cross-section of the cathode. When the first cathode active material in which cracks have occurred among the first cathode active materials in the cathode active material layer satisfies the above range, there is an advantage that the problem of deterioration of large particles due to repeated charge and discharge is effectively prevented, and the life characteristics of the battery are improved.

[0039] When large particles in the cathode active material layer are damaged in the rolling process, a phenomenon occurs in which nickel ions are reduced. For example, Ni 4+ ions are reduced to Ni 3+ ions. In one embodiment, while suppressing damage to large particles in the cathode active material layer, the reduction phenomenon of nickel will decrease. For example, with respect to the total 100 area % of the cross-section of the cathode active material layer, the portion occupied by Ni 3+ is approximately 1 area % to 30 area %, for example, it can be 3 area % to 20 area %, or 5 area % to 10 area %. This can be measured by TXM (Transmission X-ray Microscopy) analysis of the cross-section of the cathode after rolling or after the formation process. When the ratio of Ni 3+ in the cross-section of the cathode active material layer satisfies the above range, the problem of deterioration of large particles due to repeated charge and discharge is effectively prevented, and the life characteristics of the lithium secondary battery including the cathode can be improved.

[0040] On the one hand, the thickness of the entire positive electrode active material layer is about 10 μm to 200 μm, and for example, it can be 10 μm to 180 μm, 10 μm to 160 μm, 20 μm to 160 μm, 20 μm to 140 μm, 20 μm to 120 μm, 30 μm to 120 μm, or 30 μm to 100 μm. When the total thickness of the positive electrode active material layer satisfies the above range, while achieving high capacity, the problem of deterioration of large particles due to repeated charge and discharge is effectively prevented, and the life characteristics of the battery are improved.

[0041] Binder The binder according to one embodiment plays a role of making the positive electrode active material particles adhere well to each other and making the positive electrode active material adhere well 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.

[0042] Conductive material The conductive material according to one embodiment is used to impart conductivity to the electrode, and in the battery being configured, any material can be used as long as it is an electron conductive material that does not cause a chemical change. 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, carbon nanotube; metal-based substances in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0043] With respect to 100% by weight of the positive electrode active material layer, the content of the positive electrode active material may be 90% to 99.8% by weight, or may be 95% to 99% by weight, and the contents of the binder and the conductive material may be 0.1% to 5% by weight, or may be 0.5% to 2.5% by weight, respectively.

[0044] Current collector The positive electrode current collector according to one embodiment is not particularly limited as long as it has conductivity without inducing a chemical change in the lithium secondary battery. Specific examples include aluminum (Al), stainless steel (SUS), indium (In), magnesium (Mg), titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), germanium (Ge), lithium (Li), or combinations thereof, and as an example, it can include aluminum (Al). At this time, the form of the current collector may be a plate-shaped body or a foil-shaped body.

[0045] Method for manufacturing a positive electrode In one embodiment, a step of preparing a composition in which the content of the first positive electrode active material is 60 to 90% by weight, the content of the second positive electrode active material is 5 to 20% by weight, and the content of the third positive electrode active material is 5 to 20% by weight with respect to a total of 100% by weight of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material; a step of coating the composition on a current collector; and a step of rolling after drying; A method for manufacturing a positive electrode for a lithium secondary battery, wherein the first positive electrode active material includes a first lithium nickel-cobalt-based composite oxide and is in the form of secondary particles composed of a plurality of primary particles, and the average particle diameter (D 50 ) is 10 μm to 30 μm, the second positive electrode active material includes a second lithium nickel-cobalt-based composite oxide and is in the form of secondary particles composed of a plurality of primary particles, and the average particle diameter (D 50 ) is 5 μm to 9 μm, the third positive electrode active material includes a third lithium nickel-cobalt-based composite oxide and is a single particle, and the average particle diameter (D 50 ) is 0.5 μm to 4 μm; A method for manufacturing a positive electrode for a lithium secondary battery that satisfies the following relational expression 1 is provided. [Relational Expression 1] Co 2 >Co 1 >Co 3

[0046] In the above Relational Expression 1, Co 1 is the molar percentage content of cobalt with respect to 100 mol% of the metal excluding lithium in the first lithium nickel-cobalt composite oxide, and Co 2 is the molar percentage content of cobalt with respect to 100 mol% of the metal excluding lithium in the second lithium nickel-cobalt composite oxide, and Co 3 is the molar percentage content of cobalt with respect to 100 mol% of the metal excluding lithium in the third lithium nickel-cobalt composite oxide.

[0047] The above-described positive electrode can be manufactured by the above method. The content regarding the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material is as described above, and detailed description is omitted.

[0048] The composition includes a first positive electrode active material, a second positive electrode active material, and a third positive electrode active material, and optionally includes a binder and / or a conductive material. The composition contains the first positive electrode active material in an amount of 60% to 90% by weight, for example, 63% to 89% by weight, 66% to 88% by weight, 69% to 87% by weight, 72% to 86% by weight, or 75% to 85% by weight, based on a total of 100% by weight of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material. Further, the composition contains the second positive electrode active material in an amount of 5% to 20% by weight, for example, 6% to 20% by weight, 7% to 20% by weight, 8% to 20% by weight, 9% to 20% by weight, or 10% to 20% by weight, based on a total of 100% by weight of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material. Further, the composition contains the third positive electrode active material in an amount of 5% to 20% by weight, for example, 6% to 20% by weight, 7% to 20% by weight, 8% to 20% by weight, 9% to 20% by weight, or 10% to 20% by weight, based on a total of 100% by weight of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material. When the contents of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material in the composition satisfy the above ranges respectively, the problem of accelerated deterioration of large particles during the charge and discharge process is suppressed, the life characteristics are improved, and a high capacity and a high energy density can be maintained.

[0049] The rolling step may be to roll so that the density of the final rolled positive electrode is in the range of 3.4 g / cc to 3.9 g / cc, for example, to roll so that the density is 3.5 g / cc to 3.8 g / cc, or 3.6 g / cc to 3.7 g / cc. By rolling with such high strength, a high energy density and a high capacity can be achieved. However, in this case, there may be a problem that large particles in the form of secondary particles are broken, but according to one embodiment, by appropriately adjusting the composition, damage to the large particles can be effectively suppressed, and thereby, while realizing a high energy density, the life characteristics can be improved at the same time.

[0050] Lithium secondary battery In one embodiment, a lithium secondary battery including the positive electrode; the negative electrode; and the electrolyte is provided. Here, the electrolyte may be a liquid electrolyte or a solid electrolyte.

[0051] For example, in one embodiment, a lithium secondary battery including the above-described positive electrode, negative electrode, separator positioned between the positive electrode and the negative electrode, and electrolyte solution can be provided. As another example, an all-solid-state secondary battery including the above-described positive electrode, negative electrode, and solid electrolyte layer positioned between the positive electrode and the negative electrode can be provided.

[0052] Hereinafter, as an example, a lithium secondary battery using an electrolyte solution will be described.

[0053] Lithium secondary batteries can be 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, and it can be said that FIG. 1 is a cylindrical shape, FIG. 2 is a rectangular shape, and FIGS. 3 and 4 are pouch-type battery forms. Referring to FIGS. 1 to 4, the lithium secondary battery 100 can include an electrode assembly 40 with 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 built-in. The positive electrode 10, negative electrode 20, and separator 30 may be immersed in an electrolyte solution (not shown). The lithium secondary battery 100 can include a sealing member 60 for sealing the case 50 as shown in FIG. 1. Further, in FIG. 2, the lithium secondary battery 100 can include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 3 and 4, the lithium secondary battery 100 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.

[0054] Negative electrode The negative electrode for a lithium secondary battery includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector. The negative electrode active material layer contains a negative electrode active material and may further contain a binder and / or a conductive material.

[0055] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material dopable and dedopable with lithium, or a transition metal oxide.

[0056] Examples of the material capable of reversibly intercalating / deintercalating the lithium ions include carbon-based negative electrode active materials, which can include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0057] As the alloy of 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.

[0058] As the material dopable and dedopable with lithium, an Si-based negative electrode active material or an Sn-based negative electrode active material can be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x ≤ 2), an Si-Q alloy (wherein Q is 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), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO 2 , an Sn-based alloy, or a combination thereof.

[0059] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in a form in which silicon particles are coated with amorphous carbon on the surface of the silicon particles. For example, it may 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 is also located between the primary silicon particles. For example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0060] 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.

[0061] 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.

[0062] For example, the negative electrode active material layer can contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material.

[0063] The binder serves to well adhere the negative electrode active material particles to each other and also to well adhere the negative electrode active material to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof can be used.

[0064] 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.

[0065] 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.

[0066] When using an aqueous binder as the negative electrode binder, it may further contain a cellulose-based compound capable of imparting viscosity. 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.

[0067] The dry binder is a polymer substance capable of being fibrillated, and for example, it may be polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0068] The conductive material is used to impart conductivity to the electrode, and in the configured battery, any material can be used as long as it is an electron conductive material that does not cause a chemical change. Specific examples 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 in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0069] As the negative electrode current collector, those selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof can be used.

[0070] Electrolyte The electrolyte for a lithium secondary battery contains a non-aqueous organic solvent and a lithium salt.

[0071] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0072] 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.

[0073] As the carbonate solvent, 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 the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. can be used. As the ether solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. can be used. Further, as the ketone solvent, cyclohexanone, etc. can be used. As the alcohol solvent, ethyl alcohol, isopropyl alcohol, etc. can be used, and as the aprotic solvent, nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and can contain a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane, 1,4-dioxolane; sulfolane, etc. can be used.

[0074] The non-aqueous organic solvent can be used alone or in a mixture of two or more.

[0075] Also, 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.

[0076] The lithium salt is dissolved in an 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. Representative examples of lithium salts include LiPF 6 、LiBF 4 、LiSbF 6 、LiAsF 6 、LiClO 4 、LiAlO 2 、LiAlCl 4 、LiPO 2 F 2 、LiCl、LiI、LiN(SO 3 C 2 F 5 ) 2 、Li(FSO 2 ) 2 N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC 4 F 9 SO 3 、LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2 ) (where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP), lithium bis(oxalato)borate (LiBOB), and can include one or more selected therefrom.

[0077] Separator A separator may exist between the positive electrode and the negative electrode depending on the type of lithium secondary battery. 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 a mixed multilayer film such as a two-layer separator of polyethylene / polypropylene, a three-layer separator of polyethylene / polypropylene / polyethylene, or a three-layer separator of polypropylene / polyethylene / polypropylene can be used.

[0078] The separator may include a porous base material and a coating layer located on one or both surfaces of the porous base material and containing an organic substance, an inorganic substance, or a combination thereof.

[0079] The porous base material 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.

[0080] The organic substance may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0081] The inorganic substance is Al 2 O 3 , SiO 2 , TiO 2 , SnO 2 , CeO 2 MgO, NiO, CaO, GaO, ZnO, ZrO 2 Y 2 O 3 SrTiO 3 BaTiO 3 Mg(OH) 2 It may include, but is not limited to, inorganic particles selected from boehmite and combinations thereof.

[0082] The organic substance and the inorganic substance may be present mixed in one coating layer, or may be present in a form in which a coating layer containing the organic substance and a coating layer containing the inorganic substance are laminated.

[0083] Hereinafter, examples and comparative examples of the present invention will be described. The following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

Example

[0084] Example 1 (1) Production of positive electrode As the positive electrode active material, a first positive electrode active material in the form of secondary particles with a particle size of about 17 μm and a composition of Li 1 Ni 0.88 Co 0.1 Al 0.02 O 2 A second positive electrode active material in the form of secondary particles with a particle size of about 6 μm and a composition of Li 1 Ni 0.83 Co 0.15 Al 0.02 O 2 And a third positive electrode active material in the form of single particles with a particle size of about 3 μm and a composition of Li 1 Ni 0.93 Co 0.05 Al 0.02 O 2 A positive electrode active material obtained by mixing the three positive electrode active materials in a weight ratio of 70:10:20 was prepared.

[0085] 97.7 wt% of the prepared positive electrode active material, 1.2 wt% of the binder PVDF, and 1.1 wt% of the conductive material CNT were mixed with an NMP solvent to prepare a positive electrode composition. The prepared positive electrode composition was coated on an aluminum current collector. After drying, it was rolled so that the electrode plate density became 3.65 g / cc, and a positive electrode was manufactured in which the current collector and the positive electrode active material layer were laminated in this order. The thickness of the positive electrode active material layer in the manufactured positive electrode was about 100 μm.

[0086] (2) Production of negative electrode 97.3% by weight of graphite as the negative electrode active material, 0.5% by weight of Denka black, 0.9% by weight of carboxymethyl cellulose, and 1.3% by weight of styrene-butadiene rubber were mixed in an aqueous solvent to produce a negative electrode active material slurry. The produced negative electrode active material slurry was applied to a copper foil, dried, and then rolled to produce a negative electrode.

[0087] (3) Manufacture of Battery After manufacturing a pouch-type cell by laminating the manufactured positive electrode, a separator having a polyethylene / polypropylene multilayer structure, and the manufactured negative electrode in order, 1.0 M LiPF was added to a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 50:50. 6 An electrolytic solution containing a lithium salt was injected to fabricate a lithium secondary battery.

[0088] Example 2 The composition of the first positive electrode active material was changed to Li 1 Ni 0.78 Co 0.2 Al 0.02 O 2 and the composition of the second positive electrode active material was changed to Li 1 Ni 0.73 Co 0.25 Al 0.02 O 2 and the composition of the third positive electrode active material was changed to Li 1 Ni 0.83 Co 0.15 Al 0.02 O 2 A lithium secondary battery was manufactured in substantially the same manner as in Example 1, except that the above changes were made.

[0089] Example 3 A lithium secondary battery was manufactured in substantially the same manner as in Example 1, except that the weight ratio of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material was changed to 60:20:20 instead of 70:10:20.

[0090] Example 4 A lithium secondary battery was manufactured in substantially the same manner as in Example 1, except that the weight ratio of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material was changed to 80:5:15 instead of 70:10:20.

[0091] Comparative Example 1 The compositions of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material were all changed to Li 1 Ni 0.78 Co 0.2 Al0.02 O 2 A lithium secondary battery was manufactured in substantially the same manner as in Example 1, except that it was changed to

[0092] Comparative Example 2 The composition of the first positive electrode active material was changed to Li 1 Ni 0.78 Co 0.2 Al 0.02 O 2 and the composition of the second positive electrode active material was changed to Li 1 Ni 0.83 Co 0.15 Al 0.02 O 2 and the composition of the third positive electrode active material was changed to Li 1 Ni 0.73 Co 0.25 Al 0.02 O 2 A lithium secondary battery was manufactured in substantially the same manner as in Example 1, except for the above changes.

[0093] Comparative Example 3 A lithium secondary battery was manufactured in substantially the same manner as in Comparative Example 1, except that the weight ratio of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material was changed to 60:20:20 instead of 70:10:20.

[0094] Comparative Example 4 A lithium secondary battery was manufactured in substantially the same manner as in Comparative Example 1, except that the weight ratio of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material was changed to 80:5:15 instead of 70:10:20.

[0095] Comparative Example 5 A lithium secondary battery was manufactured in substantially the same manner as in Example 2, except that the first positive electrode active material and the third positive electrode active material of Example 2 were mixed at a weight ratio of 70:30 and the second positive electrode active material was not used.

[0096] Comparative Example 6 A lithium secondary battery was manufactured in substantially the same manner as Comparative Example 2, except that the first positive electrode active material and the third positive electrode active material of Comparative Example 2 were mixed at a weight ratio of 70:30 and the second positive electrode active material was not used.

[0097] For the purpose of assisting understanding, the design details of the positive electrode active materials of the above Examples and Comparative Examples are summarized and briefly shown in Table 1 below.

[0098]

Table 1

[0099] Evaluation Example 1: Deterioration Analysis by Rolling The lithium secondary batteries manufactured in the Examples and Comparative Examples were charged at a constant current of 0.2C to an upper limit voltage of 4.3V at 25°C, and then discharged at 0.2C to a cut-off voltage of 3.0V to perform initial charge and discharge. Next, a cycle of charging and discharging in a voltage range of 3.0V to 4.3V at a rate of 1.0C was repeated 1000 times at 45°C.

[0100] First, the positive electrodes were separated from the batteries that had undergone 1000 cycles in Example 1, Comparative Example 1, Comparative Example 5, and Comparative Example 6, and TXM (Transmission X-ray Microscopy) analysis was performed on the cross-section of the positive electrode. The results are shown in FIGS. 5 to 8 in order. FIG. 5 is an image of the cross-section of the positive electrode of Example 1, and it was found that the region reduced by large particles decreased and the phenomenon of breaking due to rolling decreased.

[0101] In contrast, FIG. 6 is an image of the cross-section of the positive electrode of Comparative Example 1, and a larger area reduced by large particles in the form of secondary particles was shown compared to Example 1. Further, FIG. 7 is an image of the cross-section of the positive electrode of Comparative Example 5, and an even larger area reduced by large particles in the form of secondary particles was shown compared to Example 1. FIG. 8 is an image of the cross-section of the positive electrode of Comparative Example 6, and it was found that reduction of nickel occurred, a very large area reduced by large particles in the form of secondary particles was shown, and a phenomenon of breaking or damage was shown.

[0102] Evaluation Example 2: Evaluation of Battery Life Characteristics The lithium secondary batteries manufactured in the examples and comparative examples as in Evaluation Example 1 were subjected to 1000 cycles, and the ratio of the discharge capacity after 1000 cycles to the initial discharge capacity was calculated and shown in Table 2 below.

[0103] [Table 2]

[0104] Referring to Table 2, it was confirmed that the life characteristics were improved in Examples 1 to 4, Comparative Example 1, and Comparative Example 4 containing medium particles as compared with Comparative Example 5 and Comparative Example 6 not containing medium particles. Further, in the case of Examples 1 to 4 in which the molar% content of cobalt in the second lithium nickel-cobalt composite oxide was larger than the molar% content of cobalt in the first lithium nickel-cobalt composite oxide, and the molar% content of cobalt in the first lithium nickel-cobalt composite oxide was larger than the molar% content of cobalt in the third lithium nickel-cobalt composite oxide, it was confirmed that the life characteristics were improved as compared with Comparative Examples 1 to 4 where this was not the case. Also, in the case of Example 1 in which the weight ratio of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material was 70:10:20, it was confirmed that the life characteristics were improved as compared with Examples 3 and 4 where this was not the case. Such a tendency could also be confirmed in the case of Comparative Example 1 from the fact that the life characteristics were improved as compared with Comparative Examples 3 and 4.

[0105] As described above in detail for the preferred embodiments, 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 claims also belong to the scope of the rights of the present invention.

Claims

1. The first lithium nickel-cobalt composite oxide is in the form of secondary particles composed of a plurality of primary particles, and the average particle size (D 50 ) is 10 μm to 30 μm; The second lithium nickel-cobalt composite oxide is in the form of secondary particles composed of a plurality of primary particles, and the average particle size of the secondary particles (D 50 ) is 5 μm to 9 μm; and The third lithium nickel-cobalt composite oxide is in the form of a single particle, and the average particle diameter (D 50 ) is 0.5 μm to 4 μm; Including, A positive electrode active material for a lithium secondary battery, which satisfies the following relational formula 1: [Relationship 1] Co 2 >Co 1 >Co 3 In the above formula 1, Co 1 is the mol% content of cobalt relative to 100 mol% of metals excluding lithium in the first lithium nickel-cobalt based composite oxide, and Co 2 is the mol% content of cobalt relative to 100 mol% of metals excluding lithium in the second lithium nickel-cobalt based composite oxide, and Co 3 is the molar percentage content of cobalt relative to 100 mol % of metals excluding lithium in the third lithium nickel-cobalt based composite oxide.

2. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the first positive electrode active material is contained in an amount of 60 to 90% by weight based on a total of 100% by weight of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material.

3. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the second positive electrode active material is contained in an amount of 5 to 20% by weight based on a total of 100% by weight of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material.

4. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the third positive electrode active material is contained in an amount of 5 to 20% by weight based on a total of 100% by weight of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material.

5. The Co 2 is Co 1 The positive electrode active material for lithium secondary batteries according to claim 1, wherein the ionic liquid is 1.1 to 2 times the ionic liquid.

6. The Co 1 is Co 3 The positive electrode active material for lithium secondary batteries according to claim 1, wherein the ionic liquid is 1.1 to 3 times the ionic liquid.

7. The Co 1 The positive electrode active material for a lithium secondary battery according to claim 1, wherein the amount of the cations is 5 mol % to 20 mol %.

8. The Co 2 The positive electrode active material for a lithium secondary battery according to claim 1, wherein the amount of the cations is 10 mol % to 30 mol %.

9. The Co 3 The positive electrode active material for lithium secondary batteries according to claim 1, wherein the amount of the cations is 1 mol % to 15 mol %.

10. The Co 2 Co 1 The positive electrode active material for a lithium secondary battery according to claim 1, wherein the amount of the positive electrode active material is 1 mol % to 10 mol % more than the amount of the positive electrode active material.

11. The Co 1 Co 3 The positive electrode active material for a lithium secondary battery according to claim 1, wherein the amount of the positive electrode active material is 1 mol % to 10 mol % more than the amount of the positive electrode active material.

12. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the density of the positive electrode active material layer is 3.4 g / cc to 3.9 g / cc.

13. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the number of first positive electrode active materials in which cracks have occurred is 0 to 10% of 100% by number of the first positive electrode active materials in the positive electrode active material layer.

14. Ni with respect to 100% of the total area of ​​the cross section of the positive electrode active material layer 3+ 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the area occupied by said metal oxide is 1 to 30 area %.

15. A positive electrode for a lithium secondary battery 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 comprises the positive electrode active material for lithium secondary batteries according to any one of claims 1 to 14.

16. preparing a composition in which the first positive electrode active material is contained in an amount of 60 to 90 wt %, the second positive electrode active material is contained in an amount of 5 to 20 wt %, and the third positive electrode active material is contained in an amount of 5 to 20 wt %, relative to 100 wt % in total of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material; coating the composition onto a current collector; and Drying and then rolling; A method for producing a positive electrode for a lithium secondary battery, comprising: The first positive electrode active material includes a first lithium nickel-cobalt based composite oxide, and is in the form of secondary particles composed of a plurality of primary particles, and the average particle diameter (D 50 The second positive electrode active material includes a second lithium nickel-cobalt based composite oxide and is in the form of secondary particles composed of a plurality of primary particles, and the average particle diameter (D 50 The third positive electrode active material includes a third lithium nickel-cobalt based composite oxide and is in the form of a single particle, and the average particle diameter (D 50 ) is 0.5 μm to 4 μm, and the following relational expression 1 is satisfied: [Relationship 1] Co 2 >Co 1 >Co 3 In the above formula 1, Co 1 is the mol% content of cobalt relative to 100 mol% of metals excluding lithium in the first lithium nickel-cobalt based composite oxide, and Co 2 is the mol% content of cobalt relative to 100 mol% of metals excluding lithium in the second lithium nickel-cobalt based composite oxide, and Co 3 is the molar percentage content of cobalt relative to 100 mol % of metals excluding lithium in the third lithium nickel-cobalt based composite oxide.

17. The positive electrode for a lithium secondary battery according to claim 15; A negative electrode; and electrolyte A lithium secondary battery comprising:

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