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

Abstract

The present invention provides a positive electrode active material that can achieve high density, high capacity, long lifespan, and high energy density, as well as a positive electrode and lithium secondary battery to which this material is applied. [Solution] The positive electrode active material according to one embodiment has an average particle size (D 50 The first positive electrode active material has a particle size of 11 μm to 20 μm and is a secondary particle form in which multiple primary particles are aggregated; average particle size (D 50 The second positive electrode active material has a particle size of 5 μm to 10 μm and is a secondary particle form in which multiple primary particles are aggregated; and the average particle size (D 50 The third positive electrode active material has a particle size of 1 μm to 7 μm and is in single-particle form; the third positive electrode active material is present in an amount of 5% to 20% by weight relative to 100% by weight of the total of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material.

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 while being easy to carry are mainly used as driving power sources for mobile information terminals such as mobile phones, notebook computers, and smart phones. 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 manganese cobalt composite oxides, lithium nickel cobalt aluminum composite oxides, lithium cobalt oxides, etc. are mainly used as positive electrode active materials. Recently, in a situation where the demand for large-sized, high-capacity, or high-energy-density lithium secondary batteries has increased rapidly, there is a need to develop a positive electrode active material that simultaneously improves stability and performance.

Summary of the Invention

Problems to be Solved by the Invention

[0004] To provide a positive electrode active material capable of realizing high density, high capacity, long life characteristics, and high energy density, a positive electrode applying the same, and a lithium secondary battery.

Means for Solving the Problems

[0005] In one embodiment, a first positive electrode active material having an average particle size (D 50 ) of 11 μm to 20 μm and in the form of secondary particles in which a plurality of primary particles are aggregated; a second positive electrode active material having an average particle size (D 50 ) of 5 μm to 10 μm and in the form of secondary particles in which a plurality of primary particles are aggregated; and an average particle size (D 50) is 1 μm to 7 μm and is a third positive electrode active material in a single particle form; and includes 5% to 20% by weight of the third positive electrode active material 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, to provide a positive electrode active material.

[0006] In another embodiment, a current collector; and a positive electrode active material layer located on the current collector; are included, and the positive electrode active material layer provides a positive electrode including the positive electrode active material.

Advantages of the Invention

[0007] The positive electrode active material according to one embodiment maximizes the capacity while minimizing the production price, ensures long-life characteristics, and improves characteristics at high voltages and high-temperature storage characteristics. The lithium secondary battery applying the positive electrode active material can exhibit high initial charge-discharge capacity and efficiency even under high-voltage driving conditions, has a high pellet density, can achieve a high energy density, and can achieve long-life characteristics.

Brief Description of the Drawings

[0008] [Figure 1] It is a diagram schematically showing a lithium secondary battery according to one embodiment. [Figure 2] It is a diagram schematically showing a lithium secondary battery according to one embodiment. [Figure 3] It is a diagram schematically showing a lithium secondary battery according to one embodiment. [Figure 4] It is a diagram schematically showing a lithium secondary battery according to one embodiment.

Modes for Carrying Out the Invention

[0009] 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.

[0010] The terms used herein are for illustrative purposes only and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0011] Here, "these combinations" refers to mixtures of components, laminates, composites, copolymers, alloys, blends, reaction products, etc.

[0012] Here, terms such as “include,” “equip,” or “possess” are intended to specify the existence of the implemented features, figures, stages, components, or combinations thereof, and should be understood not to preemptively exclude the existence or possibility of adding one or more other features, figures, stages, components, or combinations thereof.

[0013] To clearly represent various layers and regions in the drawings, thicknesses are shown enlarged, and similar parts are denoted by the same drawing reference numerals throughout the specification. When a layer, film, region, plate, or other part is said to be "on top of" or "on" another part, this includes not only when it is "directly on top of" another part, but also when there is another part in between. Conversely, when a part is said to be "directly on top of" another part, it means that there is no other part in between.

[0014] Furthermore, the term "layer" here includes not only the shapes formed on the entire surface when observed in a plan view, but also the shapes formed on a portion of the surface.

[0015] The average particle size can be measured by methods widely known to those skilled in the art, for example, by a particle size analyzer, or by transmission electron microscope images or scanning electron microscope images. Alternatively, it can be measured using dynamic light scattering, and the average particle size value can be calculated after counting the number of particles for each particle size range through data analysis. Unless otherwise defined, the average particle size is the diameter (D) of the particle whose cumulative volume in the particle size distribution is 50% by volume. 50) can mean. Also, unless otherwise defined, the average particle size is the diameter (D) of the particle whose cumulative volume in the particle size distribution is 50% by volume, obtained by measuring the size (diameter or length of the long axis) of more than 20 randomly selected particles in a scanning electron microscope image. 50 ) may be used as the average particle size.

[0016] Here, "or" is not interpreted as having an exclusive meaning; for example, "A or B" is interpreted as including A, B, A+B, etc.

[0017] The term "metal" is interpreted as encompassing general metals, transition metals, and metalloids.

[0018] positive electrode active material In one embodiment, the average particle size (D 50 The first positive electrode active material has a particle size of 11 μm to 20 μm and is a secondary particle form in which multiple primary particles are aggregated; average particle size (D 50 The second positive electrode active material has a particle size of 5 μm to 10 μm and is a secondary particle form in which multiple primary particles are aggregated; and the average particle size (D 50 The present invention provides a positive electrode active material comprising a third positive electrode active material having a particle size of 1 μm to 7 μm and being in single-particle form, wherein the third positive electrode active material is present in an amount of 5% to 20% by weight relative to 100% by weight of the total of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material.

[0019] The first positive electrode active material can be present in an amount of 60% to 90% by weight relative to 100% by weight of the total of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material, for example, 63% to 90% by weight, 67% to 90% by weight, 67% to 85% by weight, or 67% to 80% by weight, 70% to 85% by weight, or 70% to 80% by weight. In addition, the second positive electrode active material can be present in an amount of 5% to 30% by weight relative to 100% by weight of the total of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material, for example, 5% to 25% by weight, or 10% to 25% by weight. Furthermore, the mixture may contain 5% to 20% by weight of the third positive electrode active material relative to 100% by weight of the first, second, and third positive electrode active materials combined, for example, 5% to 15% by weight or 7% to 13% by weight. When mixed in these ratios, the powder resistance of the positive electrode active material is low, the powder flowability is good, and it exhibits low friction even at high rotational forces, resulting in excellent processability and a positive electrode with excellent compressibility and high density. Such a positive electrode active material can achieve high capacity while maximizing energy density.

[0020] Lithium nickel-based composite oxide In cathodes containing lithium nickel-based cathode active materials, designs have been proposed to maximize capacity and energy density and achieve long-life characteristics by mixing large particles in secondary particle form with small particles in single particle form. Cathodes are generally manufactured by coating and drying a cathode composition containing the cathode active material onto a current collector and then rolling it. In cathodes containing large particles in secondary particle form and small particles in single particle form, problems can occur in the upper layer where the rolling rolls and rolling plates come into contact during the rolling process, such as the large particles in secondary particle form breaking, cracking, or the surface being damaged. As a result, the degradation of the large particles in the upper layer is accelerated as the battery is repeatedly charged and discharged, which can lead to a decrease in lifespan characteristics. Therefore, in one embodiment, we propose a design that includes medium particles that are smaller than the large particles in secondary particle form and larger than the small particles in single particle form, and optimizes the content of large, medium, and small particles to improve powder flowability, prevent degradation of large particles, and maintain high capacity and energy density.

[0021] The first positive electrode active material, the second positive electrode active material, and the third positive electrode active material can each independently contain a lithium nickel-based composite oxide, and the lithium nickel-based composite oxide of the first positive electrode active material, the lithium nickel-based composite oxide of the second positive electrode active material, and the lithium nickel-based composite oxide of the third positive electrode active material may be the same as or different from each other, and may each independently be represented by Chemical Formula 1. [Chemical Formula 1] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 In Chemical Formula 1, 0.9 ≦ a1 ≦ 1.8, 0.3 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 0.7, 0 ≦ z1 ≦ 0.7, 0.9 ≦ x1 + y1 + z1 ≦ 1.1, and 0 ≦ b1 ≦ 0.1, and M 1 and M 2 are each independently one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and M 1 and M 2 may be different elements from each other, and X is one or more elements selected from the group consisting of F, P, and S.

[0022] In Chemical Formula 1, 0.6 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 0.4, and 0 ≦ z1 ≦ 0.4, or 0.8 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 0.2, and 0 ≦ z1 ≦ 0.2, or 0.9 ≦ x1 < 1, 0 < y1 ≦ 0.1, and 0 ≦ z1 ≦ 0.1 may also be satisfied.

[0023] In lithium nickel-based composite oxides, the nickel content may be 60 mol% or more relative to 100 mol% of the total metal excluding lithium, for example, 60 mol% to 80 mol%, 65 mol% to 80 mol%, 70 mol% to 80 mol%, 60 mol% to 79 mol%, 60 mol% to 78 mol%, or 60 mol% to 75 mol%. When the nickel content satisfies the above range, high capacity can be achieved, and structural stability can be improved even if the cobalt content is reduced.

[0024] First positive electrode active material In one embodiment, the first positive electrode active material contains a lithium nickel-based composite oxide and is characterized by being in the form of secondary particles formed by the aggregation of a plurality of primary particles. Here, the secondary particles may be spherical, ellipsoidal, polyhedronal, or irregular in shape, and the primary particles may be spherical, ellipsoidal, plate-shaped, or a combination thereof.

[0025] Average particle size (D) of the first positive electrode active material 50 The particle size (D) of the primary particles constituting the secondary particles in the first positive electrode active material is 11 μm to 20 μm, and may be, for example, 12 μm to 19 μm or 12 μm to 18 μm. 50 The particle size may be 1 μm or less, for example, 100 nm to 1 μm, 100 nm to 900 nm, 200 nm to 800 nm, or 300 nm to 700 nm. The average particle size of the primary particles may be determined by measuring the size (diameter or length of the major axis) of more than 20 primary particles randomly using scanning electron microscope or transmission electron microscope images of the surface of the secondary particles to obtain a particle size distribution, and taking the size of the particle whose cumulative volume is 50 volume% in the particle size distribution as the average particle size. When the size of the primary particles satisfies the above range, the first positive electrode active material can achieve high initial charge / discharge capacity and efficiency, and excellent output characteristics and lifetime characteristics.

[0026] Second positive electrode active material In one embodiment, the second positive electrode active material contains a lithium nickel-based composite oxide and has a smaller average particle size (D) than the first positive electrode active material. 50The material is characterized by having a secondary particle form in which multiple primary particles are aggregated. Here, the secondary particles may be spherical, ellipsoidal, polyhedronal, or irregular in shape, and the primary particles may be spherical, ellipsoidal, plate-shaped, or a combination thereof.

[0027] Average particle size of the second positive electrode active material (D 50 The particle size (D) of the primary particles constituting the secondary particles in the second positive electrode active material is 5 μm to 10 μm, and may be, for example, 5.5 μm to 9.5 μm, or 6 μm to 9 μm. 50 The particle size may be 1 μm or less, for example, 100 nm to 1 μm, 100 nm to 900 nm, 200 nm to 800 nm, or 300 nm to 700 nm. The average particle size of the primary particles may be determined by measuring the size (diameter or length of the major axis) of more than 20 primary particles randomly using scanning electron microscope or transmission electron microscope images of the surface of the secondary particles to obtain a particle size distribution, and taking the size of the particle whose cumulative volume is 50 volume% in the particle size distribution as the average particle size. When the size of the primary particles satisfies the above range, the second positive electrode active material can achieve high initial charge / discharge capacity and efficiency, and excellent output characteristics and lifetime characteristics.

[0028] Third positive electrode active material In one embodiment, the third positive electrode active material contains a lithium nickel-based composite oxide and has a smaller average particle size (D) than the second positive electrode active material. 50 It is characterized by having a single-particle form. Here, the single particle may be spherical, ellipsoidal, plate-shaped, irregularly shaped, or a combination thereof.

[0029] A single particle is defined as a particle that exists independently without a grain boundary and consists of only one particle. It can refer to a single particle existing as an independent phase in morphology where particles are not mutually aggregated, a monolithic structure, a single-body structure, or a non-aggregated particle. For example, a single crystal may also exist. Single particles can exist alone, or they can be clustered together. For example, 2 to 10 single particles may be clustered together and in contact with each other.

[0030] Average particle size (D) of the third positive electrode active material 50 The particle size is 1 μm to 7 μm, and may be, for example, 1 μm to 5 μm, or 1 μm to 3 μm. Here, the average particle size (D 50 The particle size may be obtained by randomly measuring the size (diameter or length of the major axis) of more than 20 particles in a scanning electron microscope image of the positive electrode active material to obtain a particle size distribution, and then taking the diameter of the particle whose cumulative volume in the particle size distribution is 50% by volume as the average particle size.

[0031] A positive electrode active material according to one embodiment can achieve a high pellet density. For example, the pellet density of the positive electrode active material may be 3.3 g / cc to 4.0 g / cc, or for example, 3.4 g / cc to 3.9 g / cc, 3.5 g / cc to 3.9 g / cc, 3.5 g / cc to 3.8 g / cc, or 3.5 g / cc to 3.7 g / cc. A lithium secondary battery using such a positive electrode active material can achieve a high energy density. The pellet density is, for example, when 3 g of the sample is molded (area: 1.298 cm²). 2 Alternatively, the measurement may be taken after placing the mold bar in the mold body, then placing the mold set in a hydraulic press and pressurizing it with a pressure of 4 tons (metric tons) for 30 seconds to pelletize it.

[0032] positive electrode In one embodiment, the device includes a current collector and a positive electrode active material layer located on the current collector, the positive electrode active material layer providing a positive electrode containing the aforementioned positive electrode active material. The positive electrode active material layer may further contain other types of positive electrode active materials in addition to the aforementioned positive electrode active material. The positive electrode active material layer may also selectively further contain a binder, a conductive material, or a combination thereof.

[0033] According to one embodiment, the filling level of the positive electrode active material layer is 10 mg / cm². 2 ~40 mg / cm³ 2 It may be 10 mg / cm³, for example. 2 ~30 mg / cm³ 2 or 10 mg / cm³ 2 ~20 mg / cm³ 2 It is also possible that the final positive electrode is rolled, and the composite density of the positive electrode active material layer may be 3.6 g / cc to 4.0 g / cc, for example, 3.7 g / cc to 4.0 g / cc or 3.78 g / cc to 4.0 g / cc. When applying a positive electrode active material according to one embodiment, it is advantageous to achieve such a filling level and composite density, and a positive electrode satisfying the above range of filling level and composite density is suitable for realizing a high-capacity, high-energy-density lithium secondary battery.

[0034] binder The binder plays a role in ensuring that the positive electrode active material particles adhere well to each other and that the positive electrode active material adheres well to the current collector. Typical examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0035] conductive material Conductive materials are used to impart conductivity to electrodes, and any electronically conductive material that does not cause chemical changes can be used in the battery that is constructed. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0036] The content of the binder and conductive material may be 0.5% to 5% by weight, respectively, based on 100% by weight of the positive electrode active material layer.

[0037] Al can be used as the positive electrode current collector, but it is not the only option.

[0038] Lithium-ion battery In one embodiment, a lithium secondary battery is provided that includes the positive electrode, negative electrode, and electrolyte described above. As an example, the lithium secondary battery may include a positive electrode, a negative electrode, a separator membrane located between the positive and negative electrodes, and an electrolyte.

[0039] Lithium-ion batteries can be classified into cylindrical, prismatic, pouch-type, coin-type, and other types depending on their form. Figures 1 to 4 are schematic diagrams showing a lithium-ion battery according to one embodiment, where Figure 1 is cylindrical, Figure 2 is prismatic, and Figures 3 and 4 are pouch-type batteries. Referring to Figures 1 to 4, the lithium-ion 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 housed. The positive electrode 10, negative electrode 20, and separator 30 may be impregnated with an electrolyte (not shown). The lithium-ion battery 100 can include a sealing member 60 that seals the case 50, as shown in Figure 1. Also, in Figure 2, the lithium-ion battery 100 can include a positive electrode lead tab 11 and a positive electrode terminal 12, a negative electrode lead tab 21 and a negative electrode terminal 22. As shown in Figures 3 and 4, the lithium secondary battery 100 may include electrode tabs 70, namely a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical pathways for guiding the current formed in the electrode assembly 40 to the outside.

[0040] negative electrode The negative electrode may include a current collector and a negative electrode active material layer located on the current collector, the negative electrode active material layer including a negative electrode active material, and may further include a binder, a conductive material, or a combination thereof.

[0041] negative electrode active material The negative electrode active material includes a substance capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a substance that can be doped and dedoped with lithium, or a transition metal oxide.

[0042] As a substance capable of reversibly intercalating / deintercalating lithium ions, a carbon-based negative electrode active material can be used, which can include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0043] As an 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.

[0044] As a substance capable of doping and undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiOx (0 < x ≤ 2), a Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, for example, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn alloy, or a combination thereof.

[0045] The silicon-carbon composite may be a composite of silicon and amorphous carbon. The average particle size (D) of the silicon-carbon composite particles 50The particle size may be, for example, 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, it may include secondary particles (core) formed by granulating primary silicon particles, and an amorphous carbon coating layer (shell) located on the surface of these secondary particles. Amorphous carbon may also be located between the primary silicon particles, for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in the amorphous carbon matrix.

[0046] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of this core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. Examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0047] When the silicon-carbon composite contains silicon and amorphous carbon, the silicon content may be 10% to 50% by weight per 100% by weight of the silicon-carbon composite, and the amorphous carbon content may be 50% to 90% by weight. Furthermore, when the composite contains silicon, amorphous carbon, and crystalline carbon, the silicon content may be 10% to 50% by weight per 100% by weight of the silicon-carbon composite, the crystalline carbon content may be 10% to 70% by weight, and the amorphous carbon content may be 20% to 40% by weight.

[0048] Furthermore, the thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. The average particle size (D) of the silicon particles (primary particles) 50 The size may be 10 nm to 1 μm, or 10 nm to 200 nm. Silicon particles may exist as silicon alone, in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon is SiO xIt can be expressed as (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 particle with a cumulative volume of 50% by volume in the particle size distribution.

[0049] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with the 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 combination, the mixing ratio may be 1:99 to 90:10 by weight ratio.

[0050] binder The binder plays a role in making the negative electrode active material particles adhere well to each other and making 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.

[0051] 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.

[0052] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluorine rubber, polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene-propylene-diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0053] When using an aqueous binder as the negative electrode binder, it may further contain a cellulosic compound that can impart viscosity. This cellulosic compound can be a mixture of one or more carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. As the alkali metal, Na, K, or Li can be used.

[0054] The dry binder is a polymer material that can be formed into fibers, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0055] conductive material Conductive materials are used to impart conductivity to electrodes, and any electronically conductive material that does not cause chemical changes can be used in the battery that is constructed. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials in the form of metal powders or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0056] The content of the negative electrode active material may be 95% to 99.5% by weight relative to 100% by weight of the negative electrode active material layer, and the content of the binder may be 0.5% to 5% by weight relative to 100% by weight of the negative electrode active material layer. For example, the negative electrode active material layer may contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0.5% to 5% by weight of the conductive material.

[0057] Current collector The negative electrode current collector may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or alloys thereof, and may be in the form of foil, sheet, or foam. The thickness of the negative electrode current collector may be, for example, 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0058] electrolyte The electrolyte for lithium secondary batteries may be, for example, an electrolyte solution, which may contain a non-aqueous organic solvent and a lithium salt.

[0059] Non-aqueous organic solvents serve as a medium through which ions involved in the electrochemical reactions of the battery can move. Non-aqueous organic solvents may be carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvents, aprotic solvents, or combinations thereof.

[0060] Examples of carbonate-based solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of ester-based solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone. As ether-based solvents, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran can be used. As ketone-based solvents, cyclohexanone can be used. As alcohol-based solvents, ethyl alcohol and isopropyl alcohol can be used, and as aprotic solvents, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, and can include double bonds, aromatic rings, or ether groups); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes can be used.

[0061] Non-aqueous organic solvents can be used alone or in combination of two or more, and the mixing ratio when using a mixture of two or more can be appropriately adjusted according to the desired battery performance; this is widely understood by those working in this field.

[0062] When using carbonate-based solvents, cyclic carbonates and linear carbonates can be mixed, and the cyclic carbonates and linear carbonates can be mixed in a volume ratio of 1:1 to 1:9.

[0063] The non-aqueous organic solvent may further contain an aromatic hydrocarbon organic solvent. For example, the carbonate solvent and the aromatic hydrocarbon organic solvent can be mixed and used in a volume ratio of 1:1 to 30:1.

[0064] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate, or ethylene carbonate compounds to improve battery life.

[0065] Typical examples of ethylene carbonate compounds include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0066] Lithium salts are substances that dissolve in organic solvents and act as a source of lithium ions in batteries, enabling the operation of basic lithium secondary batteries and facilitating the movement of lithium ions between the positive and negative electrodes. Typical examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F 2y+1 It may include one or more selected from SO2) (where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

[0067] The lithium salt concentration should ideally be within the range of 0.1 M to 2.0 M. When the lithium salt concentration falls within this range, the electrolyte has appropriate ionic conductivity and viscosity, resulting in excellent performance and effective lithium ion movement.

[0068] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators can be polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers thereof. Mixed multilayer films such as polyethylene / polypropylene two-layer separators, polyethylene / polypropylene / polyethylene three-layer separators, and polypropylene / polyethylene / polypropylene three-layer separators can also be used.

[0069] The separator may include a porous substrate and a coating layer containing organic, inorganic, or a combination thereof located on one or both sides of the porous substrate.

[0070] The porous substrate may be a polymer film formed from one polymer selected from polyethylene, polyolefins such as polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or from copolymers or mixtures of two or more of these polymers.

[0071] The porous substrate can have a thickness of approximately 1 μm to 40 μm, for example, 1 μm to 30 μm, 1 μm to 20 μm, 5 μm to 15 μm, or 10 μm to 15 μm.

[0072] The organic material may include a (meth)acrylic copolymer comprising a first structural unit derived from (meth)acrylamide, and a second structural unit comprising at least one of a structural unit derived from (meth)acrylic acid or (meth)acrylate and a structural unit derived from (meth)acrylamide sulfonic acid or a salt thereof.

[0073] The inorganic materials may include, but are not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof. The average particle size (D) of the inorganic particles. 50 The wavelength can be 1 nm to 2000 nm, for example, 100 nm to 1000 nm or 100 nm to 700 nm.

[0074] Organic and inorganic materials may exist mixed together in a single coating layer, or they may exist in a form where a coating layer containing organic materials and a coating layer containing inorganic materials are stacked on top of each other.

[0075] The thickness of the coating layer may be 0.5 μm to 20 μm, for example, 1 μm to 10 μm, or 1 μm to 5 μm.

[0076] Examples and comparative examples of the present invention are described below. The following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples. [Examples]

[0077] Example 1 1. Manufacturing of positive electrode active material (1) Manufacturing of the first positive electrode active material In the reactor, the aluminum precursor Al2(SO4)3(H2O) 18 An aqueous solution of aluminum precursor was prepared by mixing it with NaOH, NH4OH, and water.

[0078] Separately, nickel precursor NiSO4(H2O)6 and cobalt precursor CoSO4(H2O)7 were mixed with water to obtain aqueous solutions of the nickel precursor and cobalt precursor, respectively.

[0079] The aqueous solution of the aluminum precursor was placed in a reactor, and the aqueous solutions of the nickel precursor and cobalt precursor were added dropwise to obtain a reaction mixture. The reaction mixture was then stirred for 10 to 20 hours. The contents of the nickel precursor, cobalt precursor, and aluminum precursor in the reaction mixture were stoichiometrically controlled so that the molar ratio of nickel, cobalt, and aluminum was 91:8:1.

[0080] The pH of the reaction mixture was adjusted to 10-12 by adding an aqueous sodium hydroxide solution dropwise to the reaction mixture. The resulting precipitate was filtered, washed with water, and the resulting product was vacuum-dried at 100°C to obtain nickel-cobalt-aluminum hydroxide (Ni). 0.91 Co 0.08 Al 0.01 (OH)2 powder was produced.

[0081] The nickel-cobalt-aluminum hydroxide and lithium hydroxide (LiOH) were mixed in a mortar, and then placed in a furnace and heat-treated at 760°C for 10 hours while flowing O2 to produce the first positive electrode active material. The content of nickel-cobalt-aluminum hydroxide and lithium hydroxide was controlled so that the mixing ratio of transition metal to lithium was 1:1.05.

[0082] The first positive electrode active material produced by the above manufacturing method is Li in secondary particle form. 1.05 Ni 0.91 Co 0.08 Al 0.01 It is O2, and the average particle size of the secondary particles (D 50 The size of the secondary particles is approximately 14 μm, and the average particle size (D) of the primary particles that make up the secondary particles is approximately 14 μm. 50 A first cathode active material with a wavelength of approximately 500 nm was manufactured.

[0083] (2) Manufacturing of the second positive electrode active material Ni 0.91 Co 0.08 Al 0.01 (OH)2 and LiOH are mixed in a molar ratio of 1:1.05 and subjected to a first heat treatment at 750°C for 10 hours in an oxygen atmosphere, resulting in a composition of Li 1.05 Ni 0.91 Co 0.08 Al 0.01 O2 and the average particle size of secondary particles (D 50 The size of the secondary particles is approximately 7 μm, and the average particle size (D) of the primary particles that make up the secondary particles is approximately 7 μm. 50 A second cathode active material with a wavelength of approximately 400 nm was manufactured.

[0084] (3) Manufacturing of the third positive electrode active material Ni 0.91 Co 0.07 Mn 0.02 (OH)2 and LiOH were mixed in a molar ratio of 1:1.03 and subjected to a first heat treatment at 730°C for 10 hours in an oxygen atmosphere. Subsequently, a grinding process was carried out (jet mill with a bed weight of 300 kg, classification wheel rotation speed of 1740 rpm, blower rotation speed of 3000 rpm, pulse pressure of 0.5 bar, gap pressure of 0.4 bar, G / A of 6.3 bar (processing rate of 5 kg / min)), and the composition was Li 1.03 Ni 0.91 Co 0.07 Mn 0.02 O2 and average particle size (D 50 A third cathode active material in single-particle form with a diameter of approximately 3 μm was manufactured.

[0085] (4) Manufacturing of positive electrode active material A positive electrode active material was prepared by mixing 70% by weight of a first positive electrode active material, 20% by weight of a second positive electrode active material, and 10% by weight of a third positive electrode active material.

[0086] 2. Manufacturing of lithium-ion batteries A cathode active material layer slurry was prepared by mixing 98.5% by weight of the manufactured cathode active material, 1.0% by weight of polyvinylidene fluoride binder, and 0.5% by weight of carbon nanotube conductive material. This slurry was then coated onto an aluminum foil current collector, dried, and rolled to produce the cathode.

[0087] A slurry of 97.5% by weight of graphite negative electrode active material, 1.5% by weight of carboxymethylcellulose, and 1% by weight of styrene-butadiene rubber was mixed in an aqueous solvent to prepare a negative electrode active material layer slurry. The slurry was coated onto a copper foil current collector, and the negative electrode was produced by drying and rolling.

[0088] A lithium secondary battery was manufactured using a conventional method with a polytetrafluoroethylene separator and an electrolyte solution prepared by dissolving 1M LiPF6 in a solvent containing a 3:7 volume ratio mixture of ethylene carbonate and dimethyl carbonate.

[0089] Examples 2 to 5 In the production of the positive electrode active material, the positive electrode active material and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the ratios of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material were mixed as shown in Table 1 below.

[0090] Comparative Examples 1 to 5 In the production of the positive electrode active material, the positive electrode active material and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the ratios of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material were mixed as shown in Table 1 below.

[0091] Evaluation Example 1: Pellet Density of Cathode Active Material The pellet density of the positive electrode active material produced by the examples and comparative examples was measured, and the results are shown in Table 1 below. After quantifying 3 g of positive electrode active material, the pellet density was measured in a mold (area: 1.298 cm²). 2 Place the mold bar into the mold body. After placing the mold set into a hydraulic press and pressurizing it with a pressure of 4 tons (metric tons) for 30 seconds, the height can be measured to determine the pellet density.

[0092] Evaluation Example 2: Composite Density of the Positive Electrode The mixture density was measured for the positive electrodes produced in the examples and comparative examples based on rolling strength, and the results are shown in Table 1 below. The mixing density of the positive electrode active material layer is the value obtained by dividing the weight of the compressed positive electrode active material layer by its volume. The mixing density of the positive electrode active material layer can be determined by measuring the cross-sectional area, thickness, and weight of the positive electrode active material layer excluding the positive electrode current collector, calculating the volume by multiplying the cross-sectional area and thickness, and then dividing the weight by that volume.

[0093] [Table 1]

[0094] Referring to Table 1, it can be confirmed that in the example containing all three positive electrode active materials, the first positive electrode active material, and the third positive electrode active material, and in which the third positive electrode active material is present in an amount of 5% to 20% by weight relative to a total of 100% by weight of the first, second, and third positive electrode active materials, the pellet density and mixture density are all superior compared to Comparative Examples 1 and 2 which do not contain the second positive electrode active material, Comparative Examples 3 and 4 which do not contain 5% to 20% by weight of the third positive electrode active material relative to a total of 100% by weight of the first, second, and third positive electrode active materials, and Comparative Example 5 which does not contain the third positive electrode active material. In particular, in Examples 1 to 4, where the third positive electrode active material is contained in an amount of 5% to 20% by weight relative 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 is contained in an amount of 70% or more by weight, it can be confirmed that the pellet density and mixture density are even better.

[0095] Evaluation Example 3: Powder Resistance The powder resistance of the positive electrode active materials produced in the examples and comparative examples was measured, and the results are shown in Table 2 below.

[0096] Powder resistance measurement involves placing 20g of positive electrode active material into a beaker with a diameter / height of 10cm / 15cm. The resistance to the powder flow is then measured while a blade with two circular stirring blades is moved clockwise from top to bottom with minimal rotational force. Initially, the powder flow pattern is read while the blade moves up and down. During this time, numerous particles interact with each other, generating resistance from the blades. The resistance to the powder flow at an initial rotational speed of 100mm / s, and then at rotational speeds reduced to 70mm / s, 40mm / s, and 10mm / s, is measured and shown in Table 2 below.

[0097] [Table 2]

[0098] Referring to Table 2, in the example containing all three positive electrode active materials, the first positive electrode active material, and the third positive electrode active material, and in which the third positive electrode active material is present in an amount of 5% to 20% by weight relative to a total of 100% by weight of the first, second, and third positive electrode active materials, it can be confirmed that less energy is required even when the speed is reduced from 100 mm / s to 10 mm / s, compared to Comparative Examples 1 and 2 which do not contain the second positive electrode active material, Comparative Examples 3 and 4 which do not contain 5% to 20% by weight of the third positive electrode active material relative to a total of 100% by weight of the first, second, and third positive electrode active materials, and Comparative Example 5 which does not contain the third positive electrode active material. This confirms that the powder has excellent flowability.

[0099] Evaluation Example 4: Initial Charge / Discharge Capacity and Efficiency The lithium secondary batteries manufactured in the examples and comparative examples were charged at 25°C with a constant current of 0.1C to an upper voltage limit of 4.3V, then with a constant voltage of 0.05C, and finally discharged at 0.1C to a cutoff voltage of 3.0V to perform initial charge and discharge. Table 3 below shows the initial charge capacity, initial discharge capacity, and the ratio of the latter to the former, calculated as efficiency.

[0100] [Table 3]

[0101] Referring to Table 3, it can be confirmed that the battery efficiency is superior in the example containing all three positive electrode active materials, the first positive electrode active material, and the third positive electrode active material, with the third positive electrode active material being present in an amount of 5% to 20% by weight relative to a total of 100% by weight of the first, second, and third positive electrode active materials. This is compared to Comparative Examples 1 and 2, which do not contain the second positive electrode active material, Comparative Examples 3 and 4, which do not contain 5% to 20% by weight of the third positive electrode active material relative to a total of 100% by weight of the first, second, and third positive electrode active materials, and Comparative Example 5, which does not contain the third positive electrode active material. In particular, it can be confirmed that the battery efficiency is even better in Examples 1 to 4, which contain 5% to 20% by weight of the third positive electrode active material and 70% or more by weight of the first positive electrode active material relative to a total of 100% by weight of the first, second, and third positive electrode active materials.

[0102] Although preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concepts defined in the following claims also fall within the scope of the present invention. [Explanation of Symbols]

[0103] 100: Lithium-ion rechargeable battery 10: Positive electrode 11: Positive lead tab 12: Positive terminal 20: Negative electrode 21: Negative lead tab 22: Negative terminal 30: Separator 40: Electrode assembly 50: Case 60: Sealing member 70: Electrode Tab 71: Positive Tab 72: Negative electrode tab

Claims

1. Average particle size (D 50 The first positive electrode active material has a particle size of 11 μm to 20 μm and is a secondary particle form in which multiple primary particles are aggregated; Average particle size (D 50 The second positive electrode active material has a particle size of 5 μm to 10 μm and is a secondary particle form in which multiple primary particles are aggregated; and Average particle size (D 50 The third positive electrode active material has a particle size of 1 μm to 7 μm and is in single-particle form; A positive electrode active material comprising 5% to 20% by weight of the third positive electrode active material, relative to 100% by weight of the total of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material.

2. The positive electrode active material according to claim 1, wherein the first positive electrode active material is present in an amount of 60% to 90% by weight relative to 100% by weight of the total of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material.

3. The positive electrode active material according to claim 1, wherein the first positive electrode active material is present in an amount of 67% to 90% by weight relative to 100% by weight of the total of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material.

4. The positive electrode active material according to claim 1, wherein the first positive electrode active material is present in an amount of 67% to 80% by weight relative to 100% by weight of the total of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material.

5. The positive electrode active material according to claim 1, wherein the second positive electrode active material is present in an amount of 5% to 30% by weight relative 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.

6. The positive electrode active material according to claim 1, wherein the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material each independently contain a lithium nickel-based composite oxide.

7. The positive electrode active material according to claim 6, wherein the lithium nickel-based composite oxide has a nickel content of 60 mol% to 80 mol% relative to 100 mol% of the total metal excluding lithium.

8. The lithium nickel-based composite oxide is represented by the following chemical formula 1, and is the positive electrode active material according to claim 6: [Chemical formula 1] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 In chemical formula 1, 0.9 ≤ a1 ≤ 1.8, 0.3 ≤ x1 ≤ 1, 0 ≤ y1 ≤ 0.7, 0 ≤ z1 ≤ 0.7, 0.9 ≤ x1 + y1 + z1 ≤ 1.1, and 0 ≤ b1 ≤ 0.1, M 1 and M 2 Each of these is independently one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, M 1 and M 2 X and P are distinct elements, and X is one or more elements selected from the group consisting of F, P, and S.

9. In the first positive electrode active material, the average particle size (D) of the primary particles constituting the secondary particles 50 The positive electrode active material according to claim 1, wherein the diameter is 1 μm or less.

10. In the second positive electrode active material, the average particle size (D) of the primary particles constituting the secondary particles 50 The positive electrode active material according to claim 1, wherein the diameter is 1 μm or less.

11. The positive electrode active material according to claim 1, wherein the pellet density of the positive electrode active material is 3.5 g / cc to 3.7 g / cc.

12. Current collector; and A positive electrode active material layer located on the current collector; The positive electrode comprising the positive electrode active material layer according to any one of claims 1 to 11.

13. The positive electrode according to claim 12, wherein the composite density of the positive electrode active material layer is 3.78 g / cc to 4.0 g / cc.

14. The positive electrode according to claim 12; Negative electrode; and A lithium secondary battery containing an electrolyte.

15. The lithium secondary battery according to claim 14, wherein the negative electrode includes a carbon-based negative electrode active material, lithium metal, an alloy of lithium metal, a silicon-based negative electrode active material, or a combination thereof.

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