Positive electrode active material for lithium secondary battery, manufacturing method for the same, and lithium secondary battery including the same

Abstract

To provide a positive electrode active material with high energy density, high operation voltage, and high conductivity.SOLUTION: The present invention relates to a positive electrode active material for a lithium secondary battery, a manufacturing method for the same, and a lithium secondary battery including the same. More specifically, the positive electrode active material includes first particles containing a compound of Chemical Formula 1, and second particles containing a compound of Chemical Formula 2. The first particles and the second particles are included in a weight ratio of 80:20 to 60:40.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery including the same, and more particularly to a positive electrode active material including an olivine-based lithium compound, a manufacturing method thereof, and a lithium secondary battery including the same. [Background technology]

[0002] Recently, with the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, the demand for high-energy-density and high-capacity secondary batteries has been increasing rapidly. Accordingly, research and development to improve the performance of lithium secondary batteries has been actively conducted.

[0003] A lithium secondary battery is a battery that includes a cathode and an anode, which contain active materials that allow the intercalation and deintercalation of lithium ions, and an electrolyte. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are inserted / deintercalated at the cathode and anode. Summary of the Invention [Problem to be solved by the invention]

[0004] The problem to be solved by the present invention is to provide a positive electrode active material having high energy density, high operating voltage, and high conductivity.

[0005] Another object of the present invention is to provide a lithium secondary battery having high energy density, high operating voltage, and excellent low-temperature characteristics. [Means for solving the problem]

[0006] A cathode active material according to the present invention may include first particles including a compound represented by the following Formula 1, and second particles including a compound represented by the following Formula 2. The first particles and the second particles may be included in a weight ratio of 80:20 to 60:40. [Chemical formula 1] Li a1 Fe x1 B y1 PO 4-b1

[0007] In Chemical Formula 1, 0.8≦a1≦1.2, 0.9≦x1≦1.0 or 0.9≦x1<1.0, 0.001≦y1≦0.05, 0≦b1≦0.05, and x1+y1=1.

[0008] In Formula 1, B may be at least one element selected from the group consisting of Ti, Mg, V, and Nb. [Chemical formula 2] Li a2 Ni x2 Co y2 Al z2 O 2-b2

[0009] In Formula 2, 0.8≦a2≦1.2, 0.8≦x2≦0.95, 0.02≦y2≦0.1, 0.001≦z2≦0.1, 0≦b2≦0.05, and x2+y2+z2=1.

[0010] A method for preparing a positive electrode active material according to another aspect of the present invention may include preparing first particles, preparing second particles, and mixing the first particles and the second particles in a weight ratio of 80:20 to 60:40.

[0011] Producing the first particles can include mixing an iron phosphate precursor, a lithium source, a carbon source, and a dopant source to form a first mixture, drying the first mixture by spray drying, and calcining the dried first mixture.

[0012] Producing the second particles can include mixing second secondary particles with second single particles.

[0013] Preparing the second secondary particles may include mixing a nickel-based precursor and a lithium source in a solvent to form a second secondary particle mixture, drying the second secondary particle mixture by spray drying, and calcining the dried second secondary particle mixture.

[0014] Preparing the second single particle may include: adding a nickel-based precursor and a lithium source to a solvent and mixing them to form a second single particle mixture; wet-pulverizing the second single particle mixture; drying the second single particle mixture; and calcining the dried second single particle mixture.

[0015] A lithium secondary battery according to another aspect of the present invention may include the above-described positive electrode active material. [Effects of the Invention]

[0016] The cathode active material according to the present invention may have improved pellet density, capacity, and energy density by mixing layered secondary particles of several microns in size with olivine-based primary particles of several hundred nanometers in size. The cathode active material layer according to the present invention may be smoothly attached to the cathode current collector with a relatively small amount of binder. The lithium secondary battery according to the present invention may have a relatively high average voltage. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a conceptual diagram illustrating a lithium secondary battery according to an embodiment of the present invention; [Figure 2] FIG. 2 is a schematic diagram showing a lithium secondary battery according to an embodiment, in which the battery has a cylindrical shape. [Figure 3] FIG. 3 is a schematic diagram showing a lithium secondary battery according to an embodiment, in which the battery has a prismatic shape. [Figure 4] FIG. 4 is a schematic diagram showing a lithium secondary battery according to an embodiment, in which the battery is in the form of a pouch. [Figure 5]FIG. 5 is a schematic diagram showing a lithium secondary battery according to an embodiment, in which the battery is in the form of a pouch. [Figure 6] 2 is an enlarged view of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. FIG. [Figure 7A] 1 is a SEM image of a positive electrode active material according to an embodiment of the present invention. [Figure 7B] 1 is a SEM image of a positive electrode active material according to an embodiment of the present invention. [Figure 7C] 1 is a SEM image of a positive electrode active material according to an embodiment of the present invention. [Figure 8] 1 is a flowchart illustrating a method for manufacturing a positive electrode active material according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] In this specification, when a component is referred to as being on another component, it means that the component may be formed directly on the other component, or that a third component may be interposed between them. However, the present invention is not limited to the embodiments disclosed below, and may be embodied in various forms and may undergo various modifications. The description of the present embodiments is provided solely to ensure complete disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0019] In this specification, when a component is referred to as being on another component, it means that it may be formed directly on the other component, or a third component may be interposed between them. Also, in the drawings, the thickness of the components is exaggerated for the sake of efficient explanation of the technical content. Parts designated with the same reference numerals throughout the specification refer to the same components.

[0020] Unless otherwise specified herein, the singular can also include the plural. Furthermore, unless otherwise specified, "A or B" can mean "including A, including B, or including A and B." As used herein, "comprises" and / or "comprising" does not exclude the presence or addition of one or more other elements to the referenced element.

[0021] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0022] Unless otherwise defined herein, particle size refers to the average particle size. Furthermore, particle size refers to the average particle size (D50), which refers to the diameter of particles with a cumulative volume of 50% in a particle size distribution. The average particle size (D50) can be measured by methods well known to those skilled in the art, such as using a particle size analyzer or a transmission electron microscope (TEM) or scanning electron microscope (SEM) image. Alternatively, the average particle size (D50) can be measured using a measuring device that uses dynamic light scattering, and data analysis can be performed to count the number of particles in each particle size range, after which the average particle size (D50) can be calculated. Alternatively, the average particle size (D50) can be measured using a laser diffraction method. More specifically, when measuring by the laser diffraction method, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT3000), and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W. The average particle size (D50) based on 50% of the particle size distribution in the measuring device can then be calculated.

[0023] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment of the present invention. Referring to FIG. 1, the lithium secondary battery may include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte ELL.

[0024] The positive electrode 10 and the negative electrode 20 may be separated from each other by a separator 30. The separator 30 may be disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be in contact with an electrolyte solution ELL. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated in the electrolyte solution ELL.

[0025] The electrolyte ELL can be a medium for transferring lithium ions between the positive electrode 10 and the negative electrode 20. In the electrolyte ELL, the lithium ions can pass through the separator 30 and move toward the positive electrode 10 or the negative electrode 20.

[0026] positive electrode 10 The positive electrode 10 for a lithium secondary battery may include a current collector COL1 and a positive electrode active material layer AML1 formed on the current collector COL1. The positive electrode active material layer AML1 includes a positive electrode active material and may further include a binder and / or a conductive material. A detailed description of the positive electrode active material layer AML1 according to an embodiment of the present invention will be provided below with reference to FIG. 6. The current collector COL1 may be made of, but is not limited to, aluminum.

[0027] negative electrode 20 The negative electrode 20 for a lithium secondary battery includes a current collector COL2 and a negative electrode active material layer AML2 located on the current collector COL2. The negative electrode active material layer AML2 includes a negative electrode active material and may further include a binder and / or a conductive material.

[0028] For example, the negative electrode active material layer AML2 may contain 90 to 99 wt % of the negative electrode active material, 0.5 to 5 wt % of the binder, and 0 to 5 wt % of the conductive material.

[0029] The binder serves to firmly adhere the negative electrode active material particles to each other and to firmly adhere the negative electrode active material to the current collector COL 2. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0030] Examples of non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0031] The water-based binder may be selected from styrene-styrene rubber, (meth)acrylate styrene-styrene rubber, (meth)acrylonitrile-styrene 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.

[0032] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulose-based compound that can impart viscosity. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be sodium, potassium, or lithium.

[0033] The dry binder may be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0034] The conductive material is used to impart conductivity to the electrode, and any material that is electronically conductive without causing a chemical change in the battery that is constructed can be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0035] The current collector COL2 may be 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.

[0036] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and dedoped from lithium, or a transition metal oxide.

[0037] The material capable of reversibly intercalating / deintercalating lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite. Examples of amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0038] As the lithium metal alloy, 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.

[0039] As a material that can be doped and undoped with 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 (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 can be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0040] The silicon-carbon composite can be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite can be in a form in which silicon particles are coated with amorphous carbon on the surface of the silicon particles. For example, it can include secondary particles (cores) assembled from primary silicon particles and a first coating layer (shell) of amorphous carbon located on the surface of the secondary particles. Amorphous carbon can also be located between the primary silicon particles, and for example, the primary silicon particles can be coated with amorphous carbon. The secondary particles can be dispersed and present in an amorphous carbon matrix.

[0041] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite can include a core containing crystalline carbon and silicon particles and a first coating layer of amorphous carbon located on the surface of the core.

[0042] The Si-based negative electrode active material or the Sn-based negative electrode active material may be used by mixing with a carbon-based negative electrode active material.

[0043] Separator 30 Depending on the type of lithium secondary battery, a separator 30 may be present between the positive electrode 10 and the negative electrode 20. As such separator 30, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, and it goes without saying that mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0044] Separator 30 can include a porous substrate and a first coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0045] The porous substrate may be a polymer membrane formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyacetimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

[0046] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0047] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0048] The organic material and the inorganic material may be mixed in one first coating layer, or may be stacked in a form in which a first coating layer containing an organic material and a first coating layer containing an inorganic material are stacked.

[0049] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0050] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0051] The non-aqueous organic solvent can be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0052] Examples of carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0053] Examples of ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0054] Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0055] The non-aqueous organic solvents can be used alone or in combination of two or more.

[0056] In addition, when a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed and used, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0057] Lithium salts are dissolved in organic solvents and act as a source of lithium ions in the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1SO2) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethene sulfonate, lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0058] Lithium secondary battery Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 2 to 5 are schematic diagrams showing lithium secondary batteries according to embodiments, with FIG. 2 illustrating a cylindrical type, FIG. 3 illustrating a prismatic type, and FIGS. 4 and 5 illustrating pouch types. Referring to FIGS. 2 to 4, a lithium secondary battery 100 may include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the case 50, as shown in FIG. 2. Also, in FIG. 3, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 4 and 5, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting current generated in the electrode assembly 40 to the outside.

[0059] The lithium secondary battery according to an embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electrical devices, but the present invention is not limited thereto.

[0060] 6 is an enlarged view of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. Referring to FIG. 6, as described above, the positive electrode active material layer AML1 (see FIG. 1) may include first particles PTC1, second particles PTC2, a conductive material CDM, and a binder BND. The plurality of first particles PTC1 and the plurality of second particles PTC2 may constitute a positive electrode active material according to an embodiment of the present invention.

[0061] The positive electrode active material layer AML1 may further include an additive that can act as a sacrificial positive electrode.

[0062] The content of the positive electrode active materials PTC1 and PTC2 in the positive electrode active material layer AML1 may be 90 wt% to 99.5 wt% relative to 100 wt% of the positive electrode active material layer AML1, and the content of the binder BND and the conductive material CDM may be 0.5 wt% to 5 wt% each relative to 100 wt% of the positive electrode active material layer AML1.

[0063] The binder BND can bind the first particles PTC1, the second particles PTC2, and the conductive material CDM to one another. As an example, the binder BND can include, but is not limited to, at least one selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl fluoride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0064] The conductive material CDM can be used to improve the conductivity of the positive electrode active material layer AML1. Any conductive material that does not cause a chemical change in the positive electrode active material layer AML1 can be used as the conductive material CDM without limitation. For example, the conductive material CDM can include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, and the like; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0065] Hereinafter, the first particles PTC1 and the second particles PTC2 will be described in more detail.

[0066] 1st particle PTC1 6, the first particles PTC1 according to another embodiment of the present invention may have a polycrystalline form and may include secondary particles formed by agglomeration of at least two or more first primary particles NNP1. In other words, one first particle PTC1 may include a plurality of first primary particles NNP1 agglomerated together. The first particles PTC1 may have a spherical or elliptical shape.

[0067] The polycrystalline first particles PTC1 may be provided in various sizes. For example, the average particle size of the first particles PTC1 may be 3 μm to 10 μm. Specifically, the average particle size of the first particles PTC1 may be 3 μm to 7 μm, or 4 μm to 6 μm.

[0068] In one embodiment, the average particle size can be measured using a particle size analyzer. The average particle size can refer to the diameter of particles whose cumulative volume is 50% by volume (D50) in the particle size distribution.

[0069] The minimum particle size of the polycrystalline first particles PTC1, that is, the particle size of the first primary particles NNP1, may be 50 nm to 200 nm.

[0070] In one embodiment, the minimum particle size, i.e., the particle size of the first primary particles NNP1, may refer to the diameter measured by randomly selecting approximately 30 first primary particles NNP1 from an electron microscope photograph of the first particles PTC1'.

[0071] The maximum particle size (Dmax) of the polycrystalline first particles PTC1 may be 10 μm to 30 μm.

[0072] In one embodiment, the first particles PTC1 may include a first coating layer on their surfaces. The first coating layer may cover the entire surface of the first particles PTC1 or may cover only a portion of the surface of the first particles PTC1. For example, the first coating layer may include carbon and / or a carbon-containing compound. The first coating layer may further include at least one selected from the group consisting of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound. The metal-containing compound, such as a titanium-containing compound, a magnesium-containing compound, or a vanadium-containing compound, may be, for example, a metal oxide, a metal hydroxide, a metal carbonate, a composite thereof, or a mixture thereof. The metal-containing compound may further include other metals or non-metal elements. For example, the metal-containing compound may further include lithium. The first coating layer may improve the structural stability and electrical conductivity of the first particles PTC1.

[0073] In one embodiment, the first particle PTC1 may further include a first grain boundary coating layer on the surface of each of the first primary particles NNP1. The first grain boundary coating layer may be present inside the first particle PTC1. The first grain boundary coating layer may be formed by coating along the interface between the first primary particles NNP1 inside the first particle PTC1. In other words, the first grain boundary coating layer may refer to a material coated on the grain boundaries inside the first particle PTC1. The first grain boundary coating layer may include carbon and / or a carbon-containing compound. The first grain boundary coating layer may further include at least one selected from the group consisting of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound.

[0074] The interior of the first particle PTC1 described above may refer to the entire interior of the first particle PTC1 excluding the surface of the first particle PTC1. For example, the interior of the first particle PTC1 may refer to a region from a depth of about 10 nm to the entire interior of the surface of the first particle PTC1, or from a depth of 10 nm to a depth of about 2 μm.

[0075] The first particles PTC1 may further contain carbon derived from the first coating layer and / or the first grain boundary coating layer. The carbon element content in the first particles PTC1 may be 1.5 wt% to 10 wt%, 1.5 wt% to 3 wt%, or 1.5 wt% to 2.5 wt%.

[0076] The first particles PTC1 further include a grain boundary coating portion, which enhances structural stability and allows a uniform coating layer to be formed on the surface of the first particles PTC1. In addition, the first particles PTC1 further include a grain boundary coating portion, which further improves the electrical conductivity of the first particles PTC1.

[0077] The polycrystalline first particles PTC1 may exhibit the following characteristics due to the first primary particles NNP1 being closely aggregated together: The first particles PTC1 may have a spherical or elliptical shape. The porosity of the first particles PTC1 may be about 20% to about 40%. The Span value of the first particles PTC1 analyzed using a particle size analyzer may be 0.3 to 0.75.

[0078] When the first particles PTC1' are polycrystalline secondary particles, their average particle size is large, so a relatively small amount of binder BND may be required to adhere the first particles PTC1' to the current collector COL1 (see FIG. 1). For example, the content of binder BND may be 0.5 wt% to 3 wt% relative to 100 wt% of the positive electrode active material layer AML1. Reducing the binder content in the positive electrode active material layer AML1 allows for a corresponding increase in the active material content, thereby improving the capacity and energy density of the battery. Furthermore, reducing the binder content, which increases resistance, can improve the electrical conductivity of the positive electrode.

[0079] The first particles PTC1 may include an olivine-based lithium compound represented by Chemical Formula 1 below. [Chemical formula 1] Li a1 Fe x1 B y1 PO 4-b1

[0080] In Chemical Formula 1, 0.8≦a1≦1.2, 0.9≦x1≦1.0 or 0.9≦x1<1.0, 0.001≦y1≦0.05, 0≦b1≦0.05, and x1+y1=1 may be satisfied. B may be at least one element selected from the group consisting of Ti, Mg, V, and Nb. B may be a dopant doped into the first particle PTC1. For example, B may include Ti.

[0081] The doping amount of Ti may be 500 ppm to 3000 ppm. Ti doping can uniformly control the size of the first primary particles NNP1, thereby improving the charge / discharge efficiency, low-temperature characteristics, and life characteristics of the lithium secondary battery. In addition, Ti doping can stabilize the crystalline structure of the positive electrode active material, thereby improving the life characteristics of the battery.

[0082] 2nd particle PTC2 Referring again to Figure 6, the second particles PTC2 may have two particle shapes. Specifically, the second particles PTC2 may include second secondary particles PTC2_1 and second single particles PTC2_2. Again, the second particles PTC2 may have a bimodal particle size distribution.

[0083] The second secondary particles PTC2_1 may have a polycrystalline form, in which at least two or more second primary particles NNP2 are aggregated. In other words, one second secondary particle PTC2_1 may include a plurality of second primary particles NNP2 aggregated together. The second secondary particles PTC2_1 may have a spherical or elliptical shape.

[0084] The polycrystalline second secondary particles PTC2_1 may be provided in various sizes. For example, the average particle size of the second secondary particles PTC2_1 may be 10 μm to 18 μm. Specifically, the average particle size of the second secondary particles PTC2_1 may be 12 μm to 16 μm, or 13 μm to 15 μm.

[0085] In one embodiment, the average particle size can be measured using a particle size analyzer. The average particle size can refer to the diameter of particles whose cumulative volume is 50% by volume (D50) in the particle size distribution.

[0086] The minimum particle size of the polycrystalline second secondary particles PTC2_1, i.e., the particle size of the second primary particles NNP2, may be 50 nm to 200 nm.

[0087] In one embodiment, the minimum particle size, i.e., the particle size of the second primary particles NNP2, may refer to the diameter measured by randomly selecting approximately 30 second primary particles NNP2 from an electron microscope photograph of the second secondary particles PTC2_1.

[0088] In one embodiment, the second secondary particles PTC2_1 may include a second coating layer on the surface thereof. By including the second coating layer, the second secondary particles PTC2_1 may be effectively prevented from being destroyed due to repeated charge and discharge, thereby improving the lifespan of the secondary battery.

[0089] The second coating layer can include a boron-containing compound, an aluminum-containing compound, or a combination thereof. The metal-containing compound in the second coating layer can be, for example, a metal oxide, a metal hydroxide, a metal carbonate, a composite thereof, or a mixture thereof. The metal-containing compound can further include other metals or non-metal elements. For example, the second coating layer can further include lithium, manganese, and / or nickel, etc.

[0090] In one embodiment, the second secondary particles PTC2_1 may further include a second grain boundary coating layer on the surface of each of the second primary particles NNP2. The second grain boundary coating layer may be present inside the second secondary particles PTC2_1. The second grain boundary coating layer may be formed by coating along the interface between the second primary particles NNP2 inside the second secondary particles PTC2_1. Again, the second grain boundary coating layer may refer to a material coated on the grain boundaries inside the second secondary particles PTC2_1. The second grain boundary coating layer may include cobalt and / or a cobalt-containing compound.

[0091] The interior of the second secondary particle PTC2_1 may refer to the entire interior of the second secondary particle PTC2_1 excluding the surface of the second secondary particle PTC2_1. For example, the interior of the second secondary particle PTC2_1 may refer to the region from a depth of about 10 nm to the entire interior of the second secondary particle PTC2_1, or from a depth of 10 nm to a depth of about 2 μm from the surface of the second secondary particle PTC2_1.

[0092] The second secondary particles PTC2_1 may further contain cobalt derived from the second coating layer and / or the second grain boundary coating layer. The cobalt element content in the second secondary particles PTC2_1 may be 1 wt% to 5 wt%, 2 wt% to 4 wt%, or 2.5 wt% to 3.5 wt%.

[0093] The second secondary particles PTC2_1 further include a grain boundary coating portion, which enhances structural stability and allows a uniform coating layer to be formed on the surface of the second secondary particles PTC2_1. Also, the second secondary particles PTC2_1 further include a grain boundary coating portion, which further improves the electrical conductivity of the second secondary particles PTC2_1.

[0094] The second single particle PTC2_2 may have a single particle shape. In this specification, a single particle may refer to a single particle without an internal grain boundary. A single particle may refer to a single particle, a monolith structure, a single structure, or a non-aggregated particle in which particles are morphologically present in an independent phase without aggregation. For example, a single particle may be a single crystal. Alternatively, a single particle may be a particle containing several crystals. A single particle may be in a singly separated form. Alternatively, a single particle may be in a form in which 2 to 100 single particles are attached to each other.

[0095] The second single particle PTC2_2 in the form of a single particle may be provided in various sizes, for example, the average particle size of the second single particle PTC2_2 may be 3 μm to 5 μm.

[0096] In one embodiment, the average particle size can be measured using a particle size analyzer. The average particle size can refer to the diameter of particles whose cumulative volume is 50% by volume (D50) in the particle size distribution.

[0097] In one embodiment, the second single particle PTC2_2 may include a second coating layer on its surface, which may be substantially the same as the second coating layer on the surface of the second secondary particle PTC2_1 described above.

[0098] The second particles PTC2 may include a lithium-nickel composite oxide as a nickel-based active material. For example, the second particles PTC2 may include a nickel-based positive electrode active material having a high nickel content. The nickel-based positive electrode active material may achieve high capacity and high performance.

[0099] Specifically, the second particles PTC2 may include a layered lithium nickel-based composite oxide represented by the following Chemical Formula 2. [Chemical formula 2] Li a2 Ni x2 Co y2 Al z2 O 2-b2

[0100] In Chemical Formula 2, 0.8≦a2≦1.2, 0.8≦x2≦0.95, 0.02≦y2≦0.1 or 0.009≦y2≦0.1, 0.001≦z2≦0.1 or 0.001≦z2≦0.03, 0≦b2≦0.05, and x2+y2+z2=1.

[0101] In one embodiment, in the case of second secondary particles PTC2_1 having a polycrystalline shape, in Chemical Formula 2, 3≦y2 / z2≦100, and based on 100 mol% of second secondary particles PTC2_1, the Al content of second secondary particles PTC2_1 may be 3 mol% or less.

[0102] As an embodiment, the second single particle PTC2_2 having a single particle shape can include a layered lithium nickel-based composite oxide represented by the following Chemical Formula 2-1. [Chemical Formula 2-1] Li a3 Ni x3 Co y3 Al z3 Mn c3 O 2-b3

[0103] In Chemical Formula 2-1, 0.9 ≦ a3 ≦ 1.1, 0.8 ≦ x3 ≦ 0.97, 0.1 ≦ y3 ≦ 0.3, 0.001 ≦ z3 ≦ 0.05, 0.01 < c3 < 0.1, 0≦ b3 ≦ 0.1, and x3 + y3 + z3 + c3 = 1 can hold.

[0104] Referring again to FIG. 6, the second particle PTC2 according to an embodiment of the present invention will be described in more detail. The second particle PTC2 of the present invention can include a second secondary particle PTC2_1 and a second single particle PTC2_2. The second secondary particle PTC2_1 and the second single particle PTC2_2 of the second particle PTC2 of the present invention can be mixed at a weight ratio of 80:20 to 60:40 based on the 100% weight ratio of the second particle. Specifically, the second particle PTC2 can be such that the second secondary particle PTC2_1 and the second single particle PTC2_2 are mixed at a weight ratio of 75:25 to 65:35.

[0105] When the mixing ratio of the second secondary particle PTC2_1 and the second single particle PTC2_2 in the second particle PTC2 is within the range, the spaces between the larger second secondary particles PTC2_1 can be filled with the smaller second single particles PTC2_2, increasing the pallet density and the capacity per unit volume (mAh / cc) of the positive electrode active material, and improving the life characteristics at high voltage and low temperature.

[0106] In one embodiment, the mixing ratio of the second secondary particles PTC2_1 and the second single particles PTC2_2 may be adjusted so that the weight of Ni contained in the second secondary particles PTC2_1 is equal to or greater than the weight of Ni contained in the second single particles PTC2_2. In this case, a positive electrode active material including these may maintain a very stable structure even after repeated charge and discharge at high voltages, thereby improving capacity, resistance, and room temperature / high temperature life characteristics. In one embodiment, the weight of Ni contained in the second secondary particles PTC2_1 may be 5 times or less the weight of Ni contained in the second single particles PTC2_2.

[0107] Referring again to FIG. 6 , a cathode active material according to an embodiment of the present invention will be described in more detail. The cathode active material of the present invention may include first particles PTC1 and second particles PTC2. In the cathode active material of the present invention, the first particles PTC1 and the second particles PTC2 may be mixed at a weight ratio of 80:20 to 60:40. Specifically, in the cathode active material, the first particles PTC1 and the second particles PTC2 may be mixed at a weight ratio of 75:25 to 65:35. When the mixing ratio of the first particles PTC1 and the second particles PTC2 in the cathode active material is within this range, the pallet density of the cathode active material can be increased, resulting in excellent life characteristics at high voltages and high temperatures and improved capacity per volume.

[0108] A lithium secondary battery including the positive electrode active material of the present invention can have improved low-temperature characteristics. Specifically, the initial discharge capacity of a lithium secondary battery including the positive electrode active material of the present invention measured at −20° C. can be 70% or more, 75% or more, or 80% or more of the initial discharge capacity measured at room temperature.

[0109] Method for producing positive electrode active material 8 is a flowchart illustrating a method for manufacturing a positive electrode active material according to an embodiment of the present invention. The method for manufacturing the first particles PTC1 according to an embodiment of the present invention will be described in more detail with reference to FIG.

[0110] The iron phosphate precursor, lithium source, carbon source, and dopant source can be mixed in a solvent (S100). For example, the solvent can be water, ethanol, or the like. The iron phosphate precursor can be a compound containing both iron (Fe) and phosphorus (P), or a mixture of an iron (Fe)-containing compound and a phosphorus (P)-containing compound. For example, the iron phosphate precursor can include FePO4·H2O or a mixture of FeSO4 and H3PO4.

[0111] The lithium source may include at least one selected from the group consisting of lithium oxide, lithium hydroxide, lithium chloride, lithium nitrate, lithium nitrite, lithium formate, lithium acetate, lithium oxalate, lithium carbonate, lithium phosphate, lithium hydrogen phosphate, lithium dihydrogen phosphate, and lithium citrate.

[0112] The carbon source can include at least one selected from the group consisting of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol, and dopamine.

[0113] The dopant source can include an oxide containing a dopant metal and / or a chloride containing a dopant metal, for example, the dopant source can include at least one selected from the group consisting of titanium oxide, magnesium oxide, vanadium oxide, and niobium oxide.

[0114] The mixture may be subjected to wet milling (S200). A typical temperature-controllable wet mill may be used for wet milling. Specifically, at least one selected from a bead mill, a ball mill, an attrition mill, an apex mill, a super mill, and a basket mill may be used for wet milling. During the wet milling process, particles in the mixture may be milled to a fine size.

[0115] In one embodiment of the present invention, the wet-milling step (S200) may be omitted. Specifically, in order to maximize the average particle size of the first particles PTC1 that are finally produced, the wet-milling step (S200) of the precursor particles may be omitted.

[0116] A dried mixture can be formed by removing the solvent from the mixture. In one embodiment of the present invention, forming the dried mixture can include spray drying the mixture (S300). The spray drying can be performed using commonly used spray drying equipment. For example, the spray drying can be performed using at least one selected from an ultrasonic spray dryer, an air nozzle spray dryer, an ultrasonic nozzle spray dryer, a filter expansion droplet generator, and an electrostatic spray dryer.

[0117] The particles that have been refined to a primary particle size in the wet grinding process can aggregate with each other during the spray drying process to form secondary particles. Therefore, the primary particles PTC1 can be formed into secondary particles of a desired size by adjusting the flow rate and velocity of the carrier gas, temperature, residence time in the reactor, internal pressure, etc. during the spray drying process.

[0118] In one embodiment, the mixture to be spray-dried may have a total solid content of 20% to 40%. The solid content may refer to the weight of the solid material (i.e., the dried mixture) remaining after the solvent has evaporated relative to the total weight of the mixture (i.e., the spray liquid), converted into a percentage. For example, the spray liquid may have a solid content of approximately 30 wt%.

[0119] If the solid content is less than 20%, the average particle size of the first particles PTC1 becomes small, which may result in low productivity.If the solid content is more than 40%, it becomes difficult to control the average particle size of the first particles PTC1, which may result in large size deviations of the first particles PTC1.

[0120] The spray liquid according to this embodiment may have a viscosity of 1500 mPa·s to 2500 mPa·s at a solids content. For example, the spray liquid may have a viscosity of about 2000 mPa·s.

[0121] In one embodiment, spray drying can be carried out at a temperature between 100°C and 300°C. The propellant gas (e.g., air) used in spray drying can be input at a first temperature and output at a second temperature. For example, the first temperature can be between 200°C and 250°C. The second temperature can be between 80°C and 150°C.

[0122] The spray flow rate of the spraying liquid during spray drying can be 30 ml / min to 80 ml / min. If the flow rate is less than 30 ml / min, problems such as nozzle clogging and reduced productivity may occur. If the flow rate is greater than 80 ml / min, moisture condensation within the spray dryer may cause the mixture to be incompletely dried. The spraying liquid input pressure can be 0.3 MPa to 0.7 MPa. For example, the spraying liquid input pressure can be about 0.5 MPa.

[0123] The dried mixture may be calcined under an inert atmosphere (S400). The inert atmosphere may be a nitrogen atmosphere and / or an argon atmosphere. The temperature of the calcination process may be 500°C to 1000°C or 600°C to 800°C. The calcination process may be performed for 4 hours to 20 hours, or 6 hours to 12 hours. By calcining the dried mixture, first particles PTC1 containing the compound of Formula 1 described above may be formed.

[0124] In the method for producing the first particles PTC1 according to the present invention, a carbon source is introduced into an iron phosphate precursor to uniformly form a carbon coating layer on the surfaces of the primary particles. The primary particles are then closely aggregated through spray drying to form dense secondary spherical particles. As a result, the first particles PTC1 can include a stable carbon coating layer on both the exterior and interior of the first particles PTC1, thereby having a relatively high carbon content. The high carbon content of the first particles PTC1 can improve the conductivity of the positive electrode active material layer AML1.

[0125] A method for manufacturing second secondary particles PTC2_1 according to an embodiment of the present invention will now be described in detail. A high-nickel-based precursor may be prepared. The high-nickel-based precursor may contain Ni of Formula 2 above. The content of Ni relative to the total content of metals in the high-nickel-based precursor may be greater than 80 at%. In one embodiment, the high-nickel-based precursor may further contain Co and Mn.

[0126] In one embodiment, the high-nickel precursor can be obtained by a co-precipitation method. For example, the co-precipitation method can include dissolving a transition metal source material in a solvent such as distilled water, and sequentially adding the transition metal salt solution, a chelating agent, and a basic aqueous solution to a reactor to cause precipitation. The precipitate is collected in the form of a slurry, which is then filtered and dried to obtain the high-nickel precursor, which is a metal composite oxide.

[0127] In the present invention, the transition metal source material may include a metal salt of Ni. The transition metal source material may further include a metal salt of at least one of Co and Mn. The metal salt may be a sulfate, nitrate, acetate, halide, hydroxide, or the like, and is not particularly limited as long as it can be dissolved in a solvent. The transition metal source material according to this embodiment may include a nickel salt, a cobalt salt, and a manganese salt. The transition metal source materials may be mixed by adjusting the molar ratio so that the high-nickel-based precursor has a Ni content of 80 at% or more.

[0128] The high-nickel-based precursor and the lithium source can be mixed in a certain ratio to form a mixture. For example, the high-nickel-based precursor and the lithium source can be mixed in a molar ratio of about 1:1. The lithium source can include at least one selected from the group consisting of lithium oxide, lithium hydroxide, lithium chloride, lithium nitrate, lithium nitrite, lithium formate, lithium acetate, lithium oxalate, lithium carbonate, lithium phosphate, lithium hydrogen phosphate, lithium dihydrogen phosphate, and lithium citrate.

[0129] The mixture may be mixed using a mixer at 1500 rpm for 5 minutes, and then the dried mixture may be calcined under an O2 atmosphere (S400). The temperature of the calcination process may be 500°C to 1000°C or 600°C to 800°C. The time for the calcination process may be 4 hours to 20 hours, or 6 hours to 12 hours. By calcining the mixture, second secondary particles PTC2_1 including the compound of Formula 2 described above may be formed.

[0130] In one embodiment of the present invention, the sintering process can be performed after adding a flux to the mixture. The flux can be a compound containing at least one metal selected from the group consisting of Zr, La, S, and Nb. By using the flux, the second single particles PTC2_2 can be smoothly formed into a single particle form. In addition, the average particle size of the second single particles PTC2_2 can be increased.

[0131] Through a calcination process, second secondary particles PTC2_1 can be formed from the mixture containing the high nickel-based precursor and the lithium source.

[0132] A coating process may be performed on the pulverized second secondary particles PTC2_1. Specifically, the second secondary particles PTC2_1 and a coating raw material may be mixed in a solvent. For example, the coating raw material may include cobalt and / or boron and / or aluminum. After filtering and drying the second secondary particles PTC2_1, a surface treatment may be performed on the second secondary particles PTC2_1. The surface treatment may include a heat treatment process in an oxidizing atmosphere such as air or oxygen. The surface treatment may be performed at a temperature of 500°C to 800°C.

[0133] In another embodiment of the present invention, the coating process may include a dry coating process. For example, the second secondary particles PTC2_1 and the coating raw material may be mixed in a dry coating machine without a solvent and then stirred. The resulting dry mixture may be subjected to a surface treatment.

[0134] A method for manufacturing the second single particle PTC2_2 according to an embodiment of the present invention will now be described in detail. A high-nickel-based precursor may be prepared. The high-nickel-based precursor may include Ni of the above-mentioned Chemical Formula 2. The content of Ni relative to the total content of metals in the high-nickel-based precursor may be greater than 80 at%. In one embodiment, the high-nickel-based precursor may further include Co and Mn.

[0135] In one embodiment, the high-nickel precursor can be obtained by a co-precipitation method. For example, the co-precipitation method can include dissolving a transition metal source material in a solvent such as distilled water, and sequentially adding the transition metal salt solution, a chelating agent, and a basic aqueous solution to a reactor to cause precipitation. The precipitate is collected in the form of a slurry, which is then filtered and dried to obtain the high-nickel precursor, which is a metal composite oxide.

[0136] In the present invention, the transition metal source material may include a metal salt of Ni. The transition metal source material may further include a metal salt of at least one of Co and Mn. The metal salt may be a sulfate, nitrate, acetate, halide, hydroxide, etc., and is not particularly limited as long as it can be dissolved in a solvent. The transition metal source material according to this embodiment may include a nickel salt, a cobalt salt, and a manganese salt. The transition metal source materials may be mixed by adjusting the molar ratio so that the high-nickel-based precursor has a Ni content of 80 at% or more.

[0137] The high-nickel-based precursor and the lithium source can be mixed in a certain ratio to form a mixture. For example, the high-nickel-based precursor and the lithium source can be mixed in a molar ratio of about 1:1. The lithium source can include at least one selected from the group consisting of lithium oxide, lithium hydroxide, lithium chloride, lithium nitrate, lithium nitrite, lithium formate, lithium acetate, lithium oxalate, lithium carbonate, lithium phosphate, lithium hydrogen phosphate, lithium dihydrogen phosphate, and lithium citrate.

[0138] The solvent may be removed from the mixture to form a dried mixture. The dried mixture may then be calcined. The calcination temperature may be 700°C to 1000°C or 900°C to 1000°C. The calcination may be performed in an oxidizing atmosphere such as air or oxygen. The heat treatment time for the calcination may be 10 hours to 30 hours. In another embodiment of the present invention, a pre-calcination step at 150°C to 800°C may be additionally performed prior to the calcination step.

[0139] In one embodiment of the present invention, the sintering process can be performed after adding a flux to the mixture. The flux can be a compound containing at least one metal selected from the group consisting of Zr, La, S, and Nb. The use of the flux can facilitate the formation of the second single particles PTC2_2 in a single particle form. Furthermore, the average particle size of the second single particles PTC2_2 can be increased.

[0140] The second single particles PTC2_2 can be formed from the mixture containing the high-nickel precursor and the lithium source through a calcination process, and the synthesized second single particles PTC2_2 can be subjected to a wet-pulverization process.

[0141] A coating process can be performed on the pulverized second single particles PTC2_2. Specifically, the second single particles PTC2_2 and a coating raw material can be mixed in a solvent. For example, the coating raw material can include boron and / or aluminum. After filtering and drying the second single particles PTC2_2, a surface treatment can be performed on the second single particles PTC2_2. The surface treatment can include a heat treatment process in an oxidizing atmosphere such as air or oxygen. The surface treatment can be performed at a temperature of 500°C to 800°C.

[0142] In another embodiment of the present invention, the coating process may include a dry coating process. For example, the second single particles PTC2_2 and the coating raw material may be mixed in a dry coating machine without a solvent and stirred. The resulting dry mixture may be subjected to a surface treatment.

[0143] The second secondary particles PTC2_1 and the second monolithic particles PTC2_2 prepared by the above-described methods can be mixed together to prepare the second particles PTC2 according to the present invention. The second secondary particles PTC2_1 and the second monolithic particles PTC2_2 can be mixed in a weight ratio of 80:20 to 60:40. Specifically, the second secondary particles PTC2_1 and the second monolithic particles PTC2_2 can be mixed in a weight ratio of 75:25 to 65:35. When the mixing ratio of the second secondary particles PTC2_1 and the second monolithic particles PTC2_2 is within this range, the spaces between the larger second secondary particles PTC2_1 are filled with the smaller second monolithic particles PTC2_2, thereby increasing the pallet density and capacity per volume (mAh / cc) of the positive electrode active material and improving the life characteristics at high voltage and low temperature.

[0144] The first particles PTC1 and the second particles PTC2 prepared by the above-described methods can be mixed together to prepare a positive electrode active material according to the present invention. The first particles PTC1 and the second particles PTC2 can be mixed in a weight ratio of 80:20 to 60:40. Specifically, the positive electrode active material can be mixed in a weight ratio of 75:25 to 65:35. When the mixing ratio of the first particles PTC1 and the second particles PTC2 in the positive electrode active material is within this range, the pallet density of the positive electrode active material can be increased, resulting in excellent life characteristics at high voltages and high temperatures and improved capacity per volume.

[0145] Carbon elemental analysis according to an embodiment of the present invention can be performed using an Elementar Micro Cube elemental analyzer. Specific operating methods and conditions are as follows: 1-2 mg of sample is weighed into a tin cup, placed on an automatic sampling tray, and introduced into a combustion tube through a ball valve. The sample is then burned at a combustion temperature of 1000°C. The burned gas is then reduced using reduced copper to form carbon dioxide. Carbon dioxide is detected using a TCD detector.

[0146] According to an embodiment of the present invention, the carbon content is measured by quantitative analysis of the particle surface using scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS). Other methods for measuring the composition include inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0147] The present invention will be described in more detail with reference to the following examples. However, these examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0148] Example 1 Production of first particles Iron phosphate precursor Fe1PO4, lithium carbonate, and titanium dioxide were mixed in a molar ratio of 1:1.03:0.002. 10 wt% glucose was added to the mixture. The slurry mixture was spray-dried at a spray pressure of 0.5 MPa and a temperature of 230°C, followed by evaporation. The dried mixture was calcined at 750°C for 10 hours in a nitrogen atmosphere to obtain primary particles in the form of secondary particles. The average particle size (D50) of the secondary particles was approximately 3 μm to 10 μm, the average size of the primary particles within the primary particles, i.e., the minimum particle size, was approximately 100 nm to 200 nm, and the maximum particle size of the primary particles was 10 μm or more.

[0149] Production of second particles A high-nickel precursor was manufactured using the coprecipitation method. Specifically, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and aluminum sulfate (Al2(SO4)3·18H2O) were dissolved in distilled water as a solvent in a molar ratio of 88:10:2 to prepare a metal raw material mixture. The metal raw material mixture, ammonia water, and sodium hydroxide were added to a reactor and reacted. The slurry solution in the reactor was filtered and washed with high-purity distilled water. The washed material was dried in a hot air oven at 210°C for 24 hours to obtain a large-particle precursor (NiSO4·6H2O) with an average particle size of approximately 14 μm. 0.88 Co 0.10 Al 0.02 (OH)2) powder was obtained.

[0150] A high-nickel precursor and anhydrous lithium hydroxide (LiOH) were dry-mixed using a Henschel mixer. Lithium and transition metals were mixed in a molar ratio of approximately 1:1. The transition metals were the sum of the transition metals contained in the high-nickel precursor (Ni+Co+Al). A melting agent was added to the mixture, and heat treatment (i.e., calcination process) was carried out in an oxygen atmosphere at approximately 750°C for 15 hours to synthesize third particles, which are high-nickel cathode active materials. The third particles were then pulverized in a jet mill at a pressure of 3 bar.

[0151] The third particles were washed by adding them to distilled water. Boron oxide and aluminum oxide were added in an amount of 3 mol% based on the total transition metal of the third particles to perform boron and aluminum coating. The third particles were dried at 150°C for 12 hours and then heat-treated (i.e., surface-treated) in an oxygen atmosphere at about 700°C for 15 hours.

[0152] A high-nickel precursor was manufactured using the coprecipitation method. Specifically, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and aluminum sulfate (Al2(SO4)3·18H2O) were dissolved in distilled water as a solvent in a molar ratio of 88:10:2 to prepare a metal raw material mixture. The metal raw material mixture, ammonia water, and sodium hydroxide were added to a reactor and reacted. The slurry solution in the reactor was filtered and washed with high-purity distilled water. The washed material was dried in a hot air oven at 210°C for 24 hours to obtain a small-particle precursor (NiSO4·6H2O) with an average particle size of approximately 4 μm. 0.88 Co 0.10 Al 0.01 5(OH)2) powder was obtained.

[0153] The prepared secondary particles and single particles were mixed in a weight ratio of 8:2 to prepare bimodal secondary particles.

[0154] Manufacturing of positive electrode active materials The prepared first particles and second particles are mixed in a weight ratio of 8:2 to prepare a positive electrode active material.

[0155] Cathode manufacturing 95% by weight of the positive electrode active material, 3% by weight of polyvinylidene fluoride binder, and 2% by weight of Ketjen black conductive material are mixed in N-methylpyrrolidone solvent to prepare a positive electrode active material slurry. The positive electrode active material slurry is applied to an aluminum current collector, dried, and then rolled to prepare a positive electrode.

[0156] Lithium secondary battery manufacturing A coin half-cell is fabricated using the prepared positive electrode and lithium metal counter electrode, with a polyethylene-polypropylene multilayer separator between them, and an electrolyte solution of 1.0 M LiPF6 lithium salt added to a solvent of ethylene carbonate and diethyl carbonate mixed in a 50:50 volume ratio.

[0157] Examples 2 to 9 and Comparative Examples 1 to 5 In preparing the positive electrode active material of Example 1, a positive electrode, and a battery were prepared in the same manner as in Example 1, except that the weight ratio of the first particles, the weight ratio of the second secondary particles, and the weight ratio of the second single particles were changed as shown in Table 1 below.

[0158] [Table 1]

[0159] Evaluation example 1: Analysis of the surface of the positive electrode active material FIG. 7A shows an SEM image of a first particle PTC1 of a positive active material prepared in Example 1. FIG. 7B shows an SEM image of a second secondary particle PTC2_1 of a positive active material prepared in Example 1. FIG. 7C shows an SEM image of a second single particle PTC2_2 of a positive active material prepared in Example 1. Referring to FIG. 7A, it can be seen that the first particle according to an embodiment of the present invention has a spherical secondary particle shape formed by agglomeration of a plurality of primary particles. Referring to FIG. 7B, it can be seen that the second secondary particle according to an embodiment of the present invention has a spherical secondary particle shape formed by agglomeration of a plurality of primary particles. Referring to FIG. 7C, it can be seen that the second single particle according to an embodiment of the present invention has a shape of one single particle or a shape formed by a plurality of single particles attached to each other.

[0160] Evaluation example 2: Active material evaluation The pellet density (PD) and capacity per volume (mAh / cc) of the positive electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 5 were measured, and the results are shown in Table 3.

[0161] [Table 2]

[0162] Referring to Table 2, it was confirmed that the positive electrode active materials according to Examples 1 to 9 of the present invention have superior compaction density compared to the positive electrode active materials according to Comparative Examples 1 and 4. It was also confirmed that the positive electrode active materials according to Examples 1 to 9 of the present invention have higher capacity per volume compared to the positive electrode active materials according to Comparative Examples 1 and 4.

[0163] Evaluation example 3: Room temperature initial capacity evaluation The lithium secondary batteries prepared in Examples 1 to 9 and Comparative Examples 1 to 5 were charged at a constant current of 0.2 C at 25° C. up to an upper limit voltage of 4.30 V, and then discharged at 0.2 C down to an end-of-discharge voltage of 3.0 V to measure the initial discharge capacity. The ratio of the discharge capacity to the charge capacity was calculated as efficiency, and the results are shown in Table 3 below.

[0164] Evaluation example 4: Low temperature initial capacity evaluation The battery that underwent initial charge and discharge in Evaluation Example 3 was subjected to a charge and discharge experiment at -20°C to measure the discharge capacity, and the ratio of the discharge capacity at -20°C to the initial discharge capacity was evaluated as low-temperature life characteristics, and the results are shown in Table 3 below.

[0165] Evaluation example 5: Life characteristics evaluation The lithium secondary batteries prepared in Examples 1 to 9 and Comparative Examples 1 to 5 were charged and discharged 50 times in the same manner as in Evaluation Example 3, and the discharge capacity after 50 cycles was measured. The ratio of the 50th discharge capacity to the initial discharge capacity was evaluated, and the results are shown in Table 3 below.

[0166] [Table 3]

[0167] Referring to Table 2, it can be seen that Examples 1 to 8 have higher compressed densities and capacities per volume than Comparative Examples 1 and 4, which do not contain secondary particles or contain relatively less secondary particles than the Examples.

[0168] Referring to Table 3, it can be seen that Examples 1 to 8 have excellent effects in low-temperature initial capacity evaluation and life characteristics compared to Comparative Examples 2 and 3 in which the first particles are not mixed.

[0169] Referring to Table 2, it can be seen that Example 2 has a higher compression density and volumetric capacity than Examples 1 and 3. It can be seen that Example 5 has a higher compression density and volumetric capacity than Examples 4 and 6. It can be seen that Example 8 has a higher compression density and volumetric capacity than Examples 7 and 9.

[0170] Referring to Table 3, it can be seen that Example 2 has better life characteristics than Examples 1 and 3. It can be seen that Example 5 has better life characteristics than Examples 4 and 6. It can be seen that Example 8 has better life characteristics than Examples 7 and 9.

[0171] Although the present invention has been described above with reference to the accompanying drawings, it should be understood that the present invention may be embodied in other specific forms without changing the technical spirit or essential features thereof. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and are not limiting. [Explanation of symbols]

[0172] 100 Lithium secondary battery 10 positive electrode 11 Positive electrode lead tab 12 Positive terminal 20 negative electrode 21 Negative electrode lead tab 22 Negative terminal 30 Separator 40 Electrode assembly 50 cases 60 Sealing member 70 Electrode tab 71 Positive electrode tab 72 Negative electrode tab PTC1 1st particle PTC2 2nd particle NNP1 1st primary particle NNP2 2nd primary particle CDM conductive material BND Binder

Claims

1. First particles including a compound represented by the following Chemical Formula 1: and second particles comprising a compound of Chemical Formula 2: The positive electrode active material includes the first particles and the second particles in a weight ratio of 80:20 to 60:

40. [Chemical formula 1] Li a1 Fe x1 B y1 PO 4-b1 In the formula 1, 0.8≦a1≦1.2, 0.9≦x1≦1.0, 0.001≦y1≦0.05, 0≦b1≦0.05, and x1+y1=1; B is at least one element selected from the group consisting of Ti, Mg, V, and Nb; [Chemical formula 2] Li a2 Ni x2 Co y2 Al z2 O 2-b2 In Chemical Formula 2, 0.8≦a2≦1.2, 0.8≦x2≦0.95, 0.02≦y2≦0.1, 0.001≦z2≦0.1, 0≦b2≦0.05, and x2+y2+z2=1.

2. The positive electrode active material of claim 1 , wherein the first particles have a polycrystalline shape.

3. The positive electrode active material according to claim 2 , comprising a plurality of first primary particles agglomerated together.

4. The positive electrode active material of claim 3 , wherein the first particles have an average particle size of 3 μm to 10 μm.

5. The positive electrode active material of claim 3 , wherein the first particles have a minimum particle size of 50 nm to 200 nm.

6. B is a dopant doped into the first particles, The B is Ti, The positive electrode active material of claim 1 , wherein the Ti doping amount of the first particles is 500 ppm to 3,000 ppm.

7. the first particles include a first coating layer containing carbon; The positive electrode active material of claim 1 , wherein the carbon content in the first particles is 1.5 wt % to 10 wt %.

8. The positive electrode active material of claim 1 , wherein the first particles have a Span value of 0.3 to 0.75 as analyzed by a particle size analyzer.

9. The positive electrode active material of claim 1 , wherein the first particles have a porosity of 20% to 30%.

10. The positive electrode active material of claim 1 , wherein the second particles include second secondary particles in the form of polycrystalline secondary particles and second single particles in the form of single particles.

11. The positive electrode active material of claim 10 , wherein the second secondary particles and the second single particles are contained in a weight ratio of 80:20 to 60:40 based on 100 weight ratio of the second particles.

12. The positive electrode active material according to claim 10 , wherein the second secondary particles have an average particle size of 10 μm to 18 μm.

13. The positive electrode active material of claim 10 , wherein the second secondary particles have a minimum particle size of 50 nm to 200 nm.

14. The cathode active material according to claim 10 , wherein the second particles have an average particle size of 3 μm to 5 μm.

15. The second secondary particles are 11. The positive electrode active material of claim 10, comprising a compound in which, in Chemical Formula 2, 3<y2 / z2<100, and an Al content of the second secondary particles PTC2_1 is 3 mol% or less, based on 100 mol% of the second secondary particles PTC2_1.

16. The second single particle is The positive electrode active material according to claim 10, comprising a compound represented by the following Chemical Formula 2-1: [Chemical formula 2-1] Li a3 Ni x3 Co y3 Al z3 Mn c3 O 2-b3 In Chemical Formula 2-1, 0.9≦a3≦1.1, 0.8≦x3≦0.97, 0.1≦y3≦0.3, 0.001≦z3≦0.05, 0.01<c3<0.1, 0≦b3≦0.1, and x3+y3+z3+c3=1.

17. The positive electrode active material of claim 10 , wherein the weight of Ni contained in the second secondary particles is equal to or greater than the weight of Ni contained in the second single particles.

18. Producing first particles; Producing second particles; mixing the first particles and the second particles in a weight ratio of 80:20 to 60:40; Producing the first particles comprises: combining an iron phosphate precursor, a lithium source, a carbon source, and a dopant source to form a first mixture; drying the first mixture by spray drying; and calcining the dried first mixture; Producing the second particles comprises: mixing the second secondary particles with the second single particles; Producing the second secondary particles includes: Adding and mixing a nickel-based precursor and a lithium source into a solvent to form a second secondary particle mixture; drying the second secondary particle mixture by spray drying; and calcining the dried second secondary particle mixture; Producing the second single particles includes: Adding a nickel-based precursor and a lithium source to a solvent and mixing them to form a second single particle mixture; wet-milling the second single particle mixture; drying the second single particle mixture; and calcining the dried second single particle mixture.

19. The method of claim 18 , further comprising mixing the second secondary particles and the second single particles in a weight ratio of 80:20 to 60:

40.

20. A lithium secondary battery comprising the positive electrode active material according to claim 1.

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