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, a manufacturing method for the same, and a lithium secondary battery, having 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, which more specifically include a first particle containing a compound expressed by the following chemical formula 1 and having a first average particle diameter and a second particle containing a compound expressed by the following chemical formula 2 and having a second average particle diameter that is smaller than the first average particle diameter: [Chemical Formula 1] Lia1Fex1By1 PO4-b1, and [Chemical Formula 2] Lia2Mnz2Fex2By2 PO4-b2. The content amount of the second particles is more than or equal to that of the first particles and B is at least one element selected from Ti, Mg, V, and Nb.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, laptop computers, and electric vehicles, the demand for high-energy-density, high-capacity secondary batteries has been increasing rapidly, and research and development efforts to improve the performance of lithium secondary batteries have been actively pursued.

[0003] A lithium secondary battery is a battery that includes a cathode and an anode, each containing an active material capable of intercalating and deintercalating lithium ions, and an electrolyte. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are intercalated and deintercalated from the cathode and the anode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Korean Patent Publication No. 2023-0098065 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a positive electrode active material having high energy density, high operating voltage, and high conductivity.

[0006] 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]

[0007] A cathode active material according to the present invention may include first particles having a first average particle size, the first particles comprising a compound represented by the following Chemical Formula 1, and second particles having a second average particle size smaller than the first average particle size, the second particles comprising a compound represented by the following Chemical Formula 2. The content of the second particles may be equal to or greater than the content of the first particles.

[0008] [Chemical formula 1] Li a1 Fe x1 B y1 PO 4-b1 In Chemical Formula 1, 0.8≦a1≦1.2, 0.1≦x1≦1.0, 0.001≦y1≦0.05, 0≦b1≦0.05, and x1+y1=1 may be satisfied.

[0009] [Chemical formula 2] Li a2 Mn z2 Fe x2 B y2 PO 4-b2 In Chemical Formula 2, 0.8≦a2≦1.2, 0.5≦z2≦0.9, 0.1≦x2≦0.5, 0.001≦y2≦0.05, 0≦b2≦0.05, and x2+y2+z2=1 may be satisfied.

[0010] In Formula 1 and Formula 2, B may be at least one element selected from the group consisting of Ti, Mg, V, and Nb.

[0011] According to another aspect of the present invention, a method for manufacturing a positive electrode active material may include preparing first particles having a first average particle size, preparing second particles having a second average particle size smaller than the first average particle size, and mixing the first particles with the second particles. The step of preparing the first particles may include mixing an iron phosphate precursor, a first lithium source, a first carbon source, and a first dopant source to form a first mixture, drying the first mixture by spray drying, and calcining the dried first mixture. The step of preparing the second particles may include mixing a manganese iron phosphate precursor, a second lithium source, a second carbon source, and a second dopant source to form a second mixture, wet-milling the second mixture, drying the second mixture, and calcining the dried second mixture. The second particles may be mixed so that the content of the second particles is equal to or greater than the content of the first particles.

[0012] A lithium secondary battery according to yet another aspect of the present invention may include the above-described positive electrode active material. [Effects of the Invention]

[0013] The positive electrode active material according to the present invention may include first particles, which are secondary particles, and second particles, which are single particles. This improves the electrical conductivity of the positive electrode active material layer, increases the mixture density, and reduces the binder content of the positive electrode active material layer. The lithium secondary battery according to the present invention has a relatively high operating voltage, improves low-temperature characteristics, and solves the problem of Mn leaching. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a conceptual diagram illustrating a lithium secondary battery according to an embodiment of the present invention; [Figure 2] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment, which can be said to have a cylindrical battery configuration. [Figure 3] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment, which can be said to have a prismatic battery shape. [Figure 4] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment, which can be said to have a pouch-type battery configuration. [Figure 5] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment, which can be said to have a pouch-type battery configuration. [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 7] 1 is a flowchart illustrating a method for manufacturing a positive electrode active material according to an embodiment of the present invention. [Figure 8a] 1 is an SEM image of the positive electrode active material of Example 1 of the present invention. [Figure 8b] 1 is an SEM image of the positive electrode active material of Example 3 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] In order to fully understand the configuration and effects of the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and may be realized 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.

[0016] In this specification, when a component is referred to as being on top of another component, it means that it may be formed directly on the other component, or that a third component may be interposed between them. Also, in the drawings, the thickness of the components is exaggerated for the purpose of effectively explaining the technical content. Throughout the specification, parts designated with the same reference numerals refer to the same components.

[0017] Unless otherwise stated herein, the singular can also include the plural. Additionally, unless otherwise stated, "A" or "B" can mean "including A, including B, or including A and B." As used herein, "comprises" and / or "comprising" do not exclude the presence or addition of one or more other elements to the referenced element.

[0018] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0019] 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 using methods well known to those skilled in the art, such as a particle size analyzer or a transmission electron microscope (TEM) or scanning electron microscope (SEM) image. Alternatively, measurement can be performed 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, followed by calculation to obtain the average particle size (D50) value. Alternatively, measurement can be performed using a laser diffraction method. When measuring by the laser diffraction method, more specifically, 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., MT 3000 manufactured by Microtrac), and ultrasonic waves of approximately 28 kHz are irradiated at an output of 60 W, after which the average particle size (D50) based on 50% of the particle size distribution in the measuring device can be calculated.

[0020] 1 is a conceptual 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 solution ELL.

[0021] 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 the electrolyte solution ELL. The positive electrode 10, the negative electrode 20, and the separator 30 may be immersed in the electrolyte solution ELL.

[0022] 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 migrate toward the positive electrode 10 or the negative electrode 20.

[0023] 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.

[0024] negative electrode 20 The lithium secondary battery positive electrode 20 may include a current collector COL2 and a negative electrode active material layer AML2 formed 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.

[0025] For example, the negative electrode active material layer AML2 may contain 90 wt % to 99 wt % of the negative electrode active material, 0.5 wt % to 5 wt % of the binder, and 0 wt % to 5 wt % of the conductive material.

[0026] The binder serves to firmly adhere the negative active material particles to each other and to firmly adhere the negative 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.

[0027] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, and combinations thereof.

[0028] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyether resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0029] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulose-based compound to 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.

[0030] The dry binder is a fiberizable polymeric material, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, ethylene oxide, or a combination thereof.

[0031] The conductive material is used to impart conductivity to the electrode and may be any material that is electronically conductive and does not cause a chemical change in the battery. 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.

[0032] 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.

[0033] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, a lithium metal alloy, a material capable of doping or dedoping lithium, or a transition metal oxide.

[0034] The material capable of reversibly inserting / extracting 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 or artificial graphite. Examples of amorphous carbon include soft or hard carbon, mesophase pitch carbide, and calcined coke.

[0035] The lithium metal alloy may be 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.

[0036] As the substance that can be doped or 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 (where 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 of these. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or a combination of these.

[0037] 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) formed by combining primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon can also be located between the primary silicon particles. For example, the primary silicon particles can be coated with amorphous carbon. The secondary particles can exist dispersed in an amorphous carbon matrix.

[0038] 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 an amorphous carbon coating layer located on the surface of the core.

[0039] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material.

[0040] 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. Such separator 30 may be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof, but 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.

[0041] Separator 30 may include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0042] The porous substrate may be a polymer membrane made 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, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these polymers.

[0043] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0044] 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.

[0045] The organic material and the inorganic material may be mixed in one coating layer, or may be stacked in a coating layer containing an organic material and a coating layer containing an inorganic material.

[0046] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0047] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0048] The non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, a non-quantum solvent, or a combination thereof.

[0049] Examples of the carbonate solvent 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).

[0050] 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.

[0051] 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 (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.

[0052] The non-aqueous organic solvents may be used alone or in combination of two or more.

[0053] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed together, and the cyclic carbonate and the chain cyclic carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0054] The lithium salt is dissolved in an organic solvent and acts as a lithium ion source in the battery, enabling basic lithium secondary battery operation and promoting the movement of lithium ions between the positive electrode and the negative electrode. 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 positive numbers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0055] 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 battery, FIG. 3 illustrating a prismatic battery, and FIGS. 4 and 5 illustrating pouch battery 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 housing 50 in which the electrode assembly 40 is housed. The positive electrode 10, the negative electrode 20, and the separator 30 may be immersed in an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the housing 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 positive electrode assembly 40 to the outside.

[0056] 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.

[0057] 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. A plurality of first particles PTC1 and a plurality of second particles PTC2 may constitute a positive electrode active material according to an embodiment of the present invention.

[0058] The positive electrode active material layer AML1 may further include an additive that can act as a sacrificial positive electrode.

[0059] 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 % relative to 100 wt % of the positive electrode active material layer AML1, respectively.

[0060] The binder BND can bind the first particles PTC1, the second particles PTC2, and the conductive material CDM to one another. For example, the binder BND can include at least one selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, 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, but is not limited thereto.

[0061] 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. 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.

[0062] The first particles PTC1 and the second particles PTC2 will be described in more detail below.

[0063] 1st particle PTC1 The first particles PTC1 are polycrystalline and may include secondary particles formed by agglomeration of at least two or more primary particles NNP. In other words, one first particle PTC1 may include a plurality of primary particles NNP agglomerated together. The first particles PTC1 may have a spherical or elliptical shape.

[0064] In one embodiment, the first particles PTC1 may include a coating layer on their surfaces. The coating layer may cover the entire surface of the first particles PTC1 or a portion of the surface of the first particles PTC1. For example, the coating layer may include carbon and / or a carbon-containing compound. The coating layer may improve the structural stability and electrical conductivity of the first particles PTC1.

[0065] The 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. Metal-containing compounds such as titanium-containing compounds, magnesium-containing compounds, and vanadium-containing compounds may be, for example, metal oxides, metal hydroxides, metal carbonates, composites thereof, or mixtures thereof. The metal-containing compounds may further include other metals or non-metal elements. For example, the metal-containing compounds may further include lithium.

[0066] In one embodiment, the first particle PTC1 may further include a grain boundary coating layer on the surface of each primary particle NNP. The grain boundary coating layer may be present inside the first particle PTC1. The grain boundary coating layer may be formed by coating along the interface between primary particles NNP inside the first particle PTC1. In other words, the grain boundary coating layer may refer to a material coated on the grain boundaries inside the first particle PTC1. The grain boundary coating layer may include carbon and / or a carbon-containing compound. The 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.

[0067] 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 the region from a depth of about 10 nm from the surface of the first particle PTC1 to the entire interior, or from a depth of 10 nm to a depth of about 2 μm.

[0068] The first particles PTC1 further include a grain boundary coating portion, which may enhance structural stability and form a uniform coating layer on the surface of the first particles PTC1. In addition, the first particles PTC1 further include a grain boundary coating portion, which may further improve the electrical conductivity of the first particles PTC1.

[0069] The average particle size of the first particles PTC1 may be 2 μm to 15 μm, 3 μm to 10 μm, or 3 μm to 7 μm. The average particle size of the first particles PTC1 may be larger than the average particle size of the second particles PTC2 described below. In one embodiment, the particle size of approximately 30 first particles PTC1 is randomly selected from an electron microscope photograph of the positive electrode active material, and the average particle size is determined by measuring the diameter of particles at 50% by volume of the cumulative volume in the particle size distribution (D50). The average particle size of the primary particles NNP of the first particles PTC1 may be 10 nm to 400 nm, 20 nm to 300 nm, or 50 nm to 200 nm.

[0070] The first particles PTC1 may include an olivine-based lithium compound represented by the following Chemical Formula 1. [Chemical formula 1] Li a1 Fe x1 B y1 PO 4-b1

[0071] In Chemical Formula 1, 0.8≦a1≦1.2, 0.1≦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.

[0072] The first particles PTC1 may further contain carbon derived from the coating layer and / or the grain boundary coating layer. The carbon element content in the first particles PTC1 may be 0.5 wt% to 10 wt%, 1 wt% to 3 wt%, or 1.5 wt% to 2.5 wt%.

[0073] The first particles PTC1 may have a spherical shape formed by the aggregation of nano-sized primary particles NNP. The first particles PTC1 may exhibit the following characteristics due to the close aggregation of the primary particles NNP: The first particles PTC1 may have a spherical or elliptical shape. The average particle size (D50) of the first particles PTC1 may be 2 μm to 15 μm. The porosity of the first particles PTC1 may be about 20% to about 40%. The span value of the first particles PTC1 analyzed with a particle size analyzer may be 0.3 to 0.75.

[0074] 2nd particle PTC2 The second particles PTC2 may have a single particle form. In this specification, a single particle may refer to a single particle without an internal grain boundary. From a morphological perspective, a single particle may refer to a single particle, a monolith structure, a single structure, or a non-aggregated particle, in which particles are not cohered with each other and exist in an independent phase. 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.

[0075] In one embodiment, the second particles PTC2 may include a coating layer on their surfaces. The coating layer may cover the entire surface of the second particles PTC2 or a portion of the surface of the second particles PTC2. For example, the coating layer may include carbon and / or a carbon-containing compound. The 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. Metal-containing compounds such as titanium-containing compounds, magnesium-containing compounds, and vanadium-containing compounds may be, for example, metal oxides, metal hydroxides, metal carbonates, composites thereof, or mixtures 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 coating layer may improve the structural stability and electrical conductivity of the second particles PTC2.

[0076] The average particle size of the second particles PTC2 may be 10 nm to 900 nm, 50 nm to 500 nm, or 80 nm to 200 nm. The average particle size of the second particles PTC2 may be the same as the average particle size of the primary particles NNP of the first particles PTC1. In one embodiment, the particle sizes of approximately 30 second particles PTC2 randomly selected from an electron microscope photograph of the positive electrode active material may be measured, and the diameter of the particles corresponding to 50% by volume of the cumulative volume in the particle size distribution (D50) may be defined as the average particle size.

[0077] The second particles PTC2 may include an olivine-based lithium compound represented by the following Chemical Formula 2. [Chemical formula 2] Li a2 Mn z2 Fe x2 B y2 PO 4-b2

[0078] In Chemical Formula 2, 0.8≦a2≦1.2, 0.5≦z2≦0.9, 0.1≦x2≦0.5, 0.001≦y2≦0.05, 0≦b2≦0.05, and x2+y2+z2=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 second particles PTC2. For example, B may include Ti.

[0079] The second particles PTC2 may further contain carbon derived from the coating layer. The carbon element content in the second particles PTC2 may be 0.5 wt% to 5 wt%, 0.5 wt% to 3 wt%, or 0.5 wt% to 2 wt%. The carbon content of the second particles PTC2 may be lower than the carbon content of the first particles PTC1. This is because the second particles PTC2 are single particles, and therefore it is difficult to smoothly form a coating layer on them compared to the first particles PTC1, which are secondary particles.

[0080] 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. The mixing ratio of the first particles PTC1 to the second particles PTC2 in the cathode active material may be 50:50 to 10:90. Alternatively, the mixing ratio may be 60:40 to 80:20. The content of the second particles PTC2 in the cathode active material may be the same as or greater than the content of the first particles PTC1.

[0081] In one embodiment, the mixing ratio of the first particles PTC1 and the second particles PTC2 may be adjusted so that the content of Mn is 20% to 55% of the total weight of metal elements excluding lithium in the positive electrode active material.

[0082] The second particles PTC2 contain Mn, which can improve the operating voltage of the secondary battery compared to the first particles PTC1. The cathode active material according to this embodiment can improve the operating voltage compared to a conventional LFP battery by adjusting the Mn content to 20% to 40% by mixing the first particles PTC1 and the second particles PTC2 in an appropriate ratio.

[0083] The compound of Formula 2 may have lower electrical conductivity than the compound of Formula 1. The present invention improves electrical conductivity and low-temperature characteristics by using second particles PTC2 as single particles. The second particles PTC2 may have structural instability, such as pseudo Jahn-Teller distortion of Mn, at high voltages, which can lead to problems with Mn elution. However, the use of structurally stable first particles PTC1 together can prevent the above-mentioned problems.

[0084] The cathode active material of the present invention may have improved mixture density, capacity, and energy density by mixing first particles PTC1, which are secondary particles, with second particles PTC2, which are single particles. In one embodiment, the cathode active material of the present invention may have a compressed density of 2.0 g / cc to 2.5 g / cc. A lithium secondary battery including the cathode active material of the present invention may have improved low-temperature characteristics.

[0085] Because the second particles PTC2, which are single particles, have a very small average particle size, a large amount of binder BND may be required to adhere the second particles PTC2 to the current collector COL1 (see FIG. 1). The cathode active material of the present invention further includes first particles PTC1, which have a large average particle size, in addition to the second particles PTC2, thereby enabling the cathode active material layer AML1 to adhere smoothly to the current collector COL1. That is, the first particles PTC1 can reduce the amount of binder BND in the cathode active material layer AML1.

[0086] The cathode active material of the present invention may further include third particles in addition to the first particles PTC1 and second particles PTC2. The third particles may include a lithium transition metal composite oxide. Specifically, the third particles may include a lithium nickel-based oxide, a lithium cobalt-based oxide, a lithium manganese-based oxide, a cobalt-free nickel-manganese-based oxide, or a combination thereof.

[0087] For example, the third particles may include a compound represented by any one of the following chemical formulas: Li a A 1-b X b O 2-c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05);Li a Mn 2-b X b O 4-c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05);Li a Ni 1-b-c Co b X c O 2-α Dα (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5, 0<α<2);Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5, 0<α<2);Li a Ni b Co c L 1 d G e O2(0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0≦e≦0.1);Li a NiG b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a CoG b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn 1-b G b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn2G b O4(0.90≦a≦1.8, 0.001≦b≦0.1);Li (3-f) Fe2(PO4)3(0≦f≦2).

[0088] In the above formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; L 1 is Mn, Al or a combination thereof.

[0089] In one embodiment, the third particles may include a compound of Formula 3 below having a layer structure. [Chemical formula 3] Li a3 Ni x3 Ma 1-x3 O b3

[0090] In Formula 3, 0.5≦a3≦1.5, 0.6≦x3≦0.99, 1.8≦b3≦2.2, and 0.01≦1−x3≦0.4. Ma may include at least one selected from the group consisting of Co, Al, and Mn.

[0091] In one embodiment, the third particles may include a high-nickel-based positive electrode active material having a nickel content of 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more to 99 mol% or less relative to 100 mol% of metals excluding lithium in the lithium transition metal composite oxide. The high-nickel-based positive electrode active material can achieve high capacity and improve the capacity and energy density of the positive electrode active material layer AML1.

[0092] Method for producing positive electrode active material 7 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.

[0093] An iron phosphate precursor, a lithium source, a carbon source, and a dopant source may be mixed in a solvent (S100). For example, the solvent may be water, ethanol, or the like. The iron phosphate precursor may 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 may include FePO4·H2O or a mixture of FeSO4 and H3PO4.

[0094] 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 dihydrogen phosphate, lithium dihydrogen phosphate, and lithium citrate.

[0095] The carbon source may include at least one selected from the group consisting of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol, and dopamine.

[0096] The dopant source may include an oxide containing a dopant metal and / or a chloride containing a dopant metal, for example, the dopant source may include at least one selected from the group consisting of titanium oxide, magnesium oxide, vanadium oxide, and niobium oxide.

[0097] The mixture may be subjected to wet milling (S200). A typical temperature-controllable wet mill may be used for the 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 the wet milling. Through the wet milling process, particles in the mixture may be pulverized to a fine size.

[0098] 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.

[0099] The solvent may be removed from the mixture to form a dried mixture. In one embodiment of the present invention, forming the dried mixture may include spray drying the mixture (S300). The spray drying may be performed using commonly used spray drying equipment. For example, the spray drying may 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.

[0100] The particles refined to the size of primary particles through the wet milling process can aggregate together through the spray drying process to form secondary particles. Therefore, the primary particles PTC1 can be formed in the form of secondary particles of a desired size by adjusting the flow rate and velocity of the carrier gas, temperature, residence time in the reactor, and internal pressure during the spray drying process.

[0101] 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), expressed as a percentage. For example, the spray liquid may have a solid content of about 30 wt%.

[0102] If the solid content is less than 20%, the average particle size of the first particles PTC1 may become small, resulting in problems such as low productivity.If the solid content is more than 40%, it may become difficult to control the average particle size of the first particles PTC1, resulting in large size deviations of the first particles PTC1.

[0103] The spray liquid according to this embodiment may have a viscosity of 1500 mPa·s to 2500 mPa·s at the above solids content. For example, the spray liquid may have a viscosity of about 2000 mPa·s.

[0104] In one embodiment, spray drying can be performed at a temperature of 100°C to 300°C. The propellant gas (e.g., air) used in spray drying can be introduced at a first temperature and discharged at a second temperature. For example, the first temperature can be 200°C to 250°C. The second temperature can be 80°C to 150°C.

[0105] The flow rate of the spray solution for spray drying may 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, condensation of water within the spray dryer may cause the mixture to be incompletely dried. The input pressure of the spray solution may be 0.3 MPa to 0.7 MPa. For example, the input pressure of the spray solution may be about 0.5 MPa.

[0106] 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 may be formed.

[0107] In a method for manufacturing first particles PTC1 according to an embodiment of the present invention, a carbon source is introduced into an iron phosphate precursor to uniformly form a carbon coating layer on the surface of the primary particles. The primary particles are then closely agglomerated by spray drying to form dense secondary spherical particles. As a result, the first particles PTC1 may 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 may improve the conductivity of the positive electrode active material layer AML1.

[0108] A method for producing the second particle PTC2 according to an embodiment of the present invention will be described in more detail. A manganese iron phosphate precursor, a lithium source, a carbon source, and a dopant source may be mixed in a solvent. For example, the solvent may be water, ethanol, or the like. The manganese iron phosphate precursor may be a compound containing all of manganese (Mn), iron (Fe), and phosphorus (P); a mixture of a manganese (Mn)-containing compound and a compound containing iron (Fe) and phosphorus (P); or a mixture of a manganese (Mn)-containing compound, an iron (Fe)-containing compound, and a phosphorus (P)-containing compound. For example, the manganese iron phosphate precursor may be a compound containing Mn x Fe 1-x PO4·H2O; a mixture of MnCO3 and FePO4·H2O; or a mixture of MnCO3, FeSO4 and H3PO4; where x can be 0.5 to 0.9.

[0109] The lithium source, the carbon source, and the dopant source may be the same as or similar to those in the above-described method for producing the first particles PTC1.

[0110] The mixture can be subjected to wet-milling, and the wet-milling step can be the same as or similar to the method for producing the first particles PTC1 described above.

[0111] The solvent can be removed from the mixture to form a dried mixture. Forming the dried mixture can include subjecting the mixture to direct evaporation. For example, direct evaporation can include static drying or spray drying. It can be preferable to use static drying to form the second particles PTC2 into single particles.

[0112] The dried mixture may be calcined under an inert atmosphere. The conditions for the calcination process may be the same as or similar to those for the method for producing the first particles PTC1. By calcining the dried mixture, the second particles PTC2 containing the compound of Formula 2 may be formed.

[0113] The fired second particles PTC2 may be subjected to a dry-pulverization process, thereby allowing the second particles PTC2 to have a single particle form. Meanwhile, in the case of the first particles PTC1, the dry-pulverization process may be omitted.

[0114] The prepared first particles PTC1 and second particles PTC2 may be mixed in an appropriate ratio to form a positive electrode active material according to an embodiment of the present invention.

[0115] 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 via a ball valve and 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.

[0116] 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 carbon content include inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0117] Examples of the present invention and comparative examples are described below. However, the following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

[0118] Example 1: Preparation of primary particles in the form of secondary particles Iron phosphate precursor Fe1PO4, lithium carbonate, and titanium dioxide were mixed in a molar ratio of 1:1.03:0.03. 10 wt% glucose was further 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 size of the primary particles within the primary particles was approximately 100 nm to approximately 200 nm.

[0119] Example 2: Preparation of single particle first particles Iron phosphate precursor Fe1PO4, lithium carbonate, and titanium dioxide were mixed in a molar ratio of 1:1.03:0.03. 10 wt% glucose was added to the mixture. The mixture was wet-pulverized using a ball mill. The mixture was evaporated to dryness in a heating oven tray and then placed in a vacuum oven at 120°C for 4 hours. The dried mixture was calcined at 750°C for 10 hours under a nitrogen atmosphere. The calcined product was pulverized to obtain primary particles in the form of single particles. The average size of the primary particles was approximately 300nm to 400nm.

[0120] Example 3: Preparation of second particles in single particle form Mn0.6Fe 0.4 Iron phosphate precursor PO4, lithium carbonate, and titanium dioxide were mixed in a molar ratio of 1:1.03:0.03. 12 wt% glucose was added to the mixture. The mixture was subjected to a wet grinding process using a ball mill. The mixture was evaporated to dryness in a heating oven tray and then placed in a vacuum oven at 120°C for 4 hours. The dried mixture was calcined at 750°C for 10 hours under a nitrogen atmosphere. The calcined product was pulverized to obtain secondary particles in the form of single particles. The average size of the secondary particles was about 100 nm to about 300 nm.

[0121] Example 4-1: Preparation of a mixture of first particles and second particles The first particles of Example 1 and the second particles of Example 3 were mixed in a mass ratio of 9:1 to prepare a positive electrode active material.

[0122] Example 4-2: Preparation of a mixture of first particles and second particles The first particles of Example 1 and the second particles of Example 3 were mixed in a mass ratio of 8:2 to prepare a positive electrode active material.

[0123] Example 4-3: Preparation of a mixture of first particles and second particles The first particles of Example 1 and the second particles of Example 3 were mixed in a mass ratio of 7:3 to prepare a positive electrode active material.

[0124] Example 4-4: Preparation of a mixture of first particles and second particles The first particles of Example 1 and the second particles of Example 3 were mixed in a mass ratio of 6:4 to prepare a positive electrode active material.

[0125] Examples 4-5: Preparation of a mixture of first particles and second particles The first particles of Example 1 and the second particles of Example 3 were mixed in a mass ratio of 5:5 to prepare a positive electrode active material.

[0126] Cathode manufacturing A positive electrode active material slurry was prepared by mixing 95 wt% of the final positive electrode active material, 3 wt% of polyvinylidene fluoride binder, and 2 wt% of carbon black conductive material in N-methylpyrrolidone solvent. The positive electrode active material slurry was applied to an aluminum current collector, dried, and then rolled to prepare a positive electrode.

[0127] Lithium secondary battery manufacturing A 2032-type coin-shaped half cell was fabricated using the prepared positive electrode and a lithium metal counter electrode. A separator (thickness: approximately 16 μm) made of porous polyethylene (PE) film was placed between the positive electrode and the lithium metal counter electrode, and an electrolyte solution was injected to fabricate a lithium secondary battery. The electrolyte used was a 1.3 M LiPF6 solution mixed with a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethylene carbonate (DMC) in a volume ratio of 3:4:3.

[0128] Evaluation example 1: Analysis of the surface of the positive electrode active material An SEM image of the cathode active material prepared in Example 1 is shown in Figure 8a. An SEM image of the cathode active material prepared in Example 3 is shown in Figure 8b. Referring to Figure 8a, it can be seen that the first particles according to the present invention are in the form of spherical secondary particles formed by agglomeration of a plurality of primary particles. Referring to Figure 8b, it can be seen that the second particles according to the present invention are in the form of fine single particles of nano-size.

[0129] Evaluation example 2: Active material evaluation The pellet density (PD) and carbon content of the positive electrode active materials of Examples 1, 2, 3, 4-1, 4-2, 4-3, and 4-5 were measured, and the results are shown in Table 1.

[0130] [Table 1]

[0131] Referring to Table 1, it can be seen that the positive electrode active materials according to Examples 4-1 to 4-5 of the present invention have superior compaction density compared to the positive electrode active material according to Example 3. It can also be seen that the positive electrode active materials according to Examples 4-1 to 4-5 of the present invention have higher carbon contents compared to the positive electrode active materials according to Examples 1 to 3.

[0132] Evaluation example 3: Battery characteristic evaluation The characteristics of lithium secondary batteries fabricated using the positive electrode active materials of Examples 1, 2, 3, 4-1, 4-2, 4-3 and 4-5 were evaluated.

[0133] The lithium secondary battery was initially charged at a constant current (0.2 C) and a constant voltage (4.25 V), and after a 10-minute rest, was discharged at a constant current (0.2 C) until the voltage reached 2.5 V. Thereafter, the battery was charged and discharged once at 0.2 C / 0.2 C at -25°C.

[0134] The results of the battery characteristic evaluation are shown in Table 2 below.

[0135] [Table 2]

[0136] Referring to Table 2, it can be seen that the secondary batteries according to Examples 4-1 to 4-5 of the present invention have higher −20° C. capacities than the secondary batteries according to Examples 1 and 2. It can be seen that the secondary batteries according to Examples 4-1 to 4-5 of the present invention have higher average voltages than the secondary batteries according to Examples 1 and 2. It can also be seen that the secondary batteries according to Examples 4-1 to 4-5 of the present invention exhibit better charge / discharge efficiency than the secondary batteries according to Examples 2 and 3.

[0137] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is natural that these also fall within the scope of the present invention.

Claims

1. First particles comprising a compound represented by Chemical Formula 1 below and having a first average particle size; second particles comprising a compound of the following Chemical Formula 2 and having a second average particle size smaller than the first average particle size; Including, The content of the second particles is equal to or greater than the content of the first particles in the positive electrode active material. [Chemical formula 1] Li a1 Fe x1 B y1 PO 4-b1 (In the above Chemical Formula 1, 0.8≦a1≦1.2, 0.1≦x1≦1.0, 0.001≦y1≦0.05, 0≦b1≦0.05, and x1+y1=1, and B is at least one element selected from the group consisting of Ti, Mg, V, and Nb.) [Chemical formula 2] Li a2 Mn z2 Fe x2 B y2 2O 4-b2 (In the above Chemical Formula 2, 0.8≦a2≦1.2, 0.5≦z2≦0.9, 0.1≦x2≦0.5, 0.001≦y2≦0.05, 0≦b2≦0.05, and x2+y2+z2=1, and B is at least one element selected from the group consisting of Ti, Mg, V, and Nb.)

2. the first particles are spherical secondary particles, The positive electrode active material according to claim 1 , wherein the second particles are single particles.

3. The positive electrode active material of claim 1 , wherein the mixing ratio of the first particles to the second particles is in the range of 50:50 to 10:

90.

4. 2. The positive electrode active material of claim 1, wherein the content of Mn is 20% to 55% of the total weight of metal elements excluding lithium in the positive electrode active material.

5. 2. The positive electrode active material of claim 1, wherein the positive electrode active material has a compressed density of 2.0 g / cc to 2.5 g / cc.

6. 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 2.5 wt %.

7. the first particles further include a grain boundary coating layer on an interface between the primary particles, The positive electrode active material according to claim 6 , wherein the grain boundary coating layer contains carbon.

8. The positive electrode active material of claim 1 , wherein the first particles have a porosity of 20% to 40%.

9. The positive active material of claim 1 , wherein the first particles have a span value of 0.3 to 0.75 as determined by a particle size analyzer.

10. The positive electrode active material of claim 1 , further comprising third particles comprising a compound of Formula 3: [Chemical formula 3] Li a3 Ni x3 Ma 1-x 3O b3 (In the above Chemical Formula 3, 0.5≦a3≦1.5, 0.6≦x3≦0.99, 1.8≦b3≦2.2, and 0.01≦1−x3≦0.4, Ma is at least one selected from the group consisting of Co, Al, and Mn.

11. the second particles include a second coating layer containing carbon; The positive electrode active material of claim 1 , wherein the carbon content in the second particles is 1.5 wt % to 2.5 wt %.

12. The positive electrode active material of claim 1 , wherein the first average particle size is 3 μm to 7 μm.

13. The positive electrode active material of claim 1 , wherein the second average particle size is 50 nm to 500 nm.

14. The first particles include a plurality of primary particles that are aggregated together, The positive electrode active material according to claim 1 , wherein the average particle size of the primary particles is smaller than the second average particle size.

15. producing first particles having a first average particle size; producing second particles having a second average particle size smaller than the first average particle size; mixing the first particles and the second particles; Including, The step of producing the first particles includes: combining an iron phosphate precursor, a first lithium source, a first carbon source, and a first dopant source to form a first mixture; drying the first mixture by spray drying; calcining the dried first mixture; Including, The step of producing the second particles includes: combining a manganese iron phosphate precursor, a second lithium source, a second carbon source, and a second dopant source to form a second mixture; wet-milling the second mixture; drying the second mixture; calcining the dried second mixture; and Including, The method for manufacturing a positive electrode active material, wherein the second particles are mixed so that the content of the first particles is equal to or greater than the content of the second particles.

16. 16. The method of claim 15, wherein the mixing ratio of the first particles to the second particles is 50:50 to 10:

90.

17. 16. The method of claim 15, wherein the first mixture used as a spray liquid for the spray drying has a solid content of 20% to 40% and a viscosity of 1500 mPa·s to 2500 mPa·s.

18. The method of claim 15 , wherein the spray drying comprises agglomerating particles in the first mixture to form secondary particles.

19. The spray drying is carried out at a temperature of 100°C to 300°C, 16. The method of claim 15, wherein the spraying pressure of the spraying solution is 0.3 MPa to 0.7 MPa, and the flow rate is 30 ml / min to 80 ml / min.

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

Images