Positive electrode active material for lithium secondary battery, manufacturing method for the same, positive electrode active material slurry including 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 positive electrode active material slurry including the same, 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, a positive electrode active material slurry including the same, and a lithium secondary battery including the same. More specifically included are: forming a mixture by mixing an iron phosphate precursor, a lithium source, a carbon source, and a dopant source; drying the mixture by spray drying; and sintering the dried mixture. The dopant source includes at least one selected from an aluminum compound, a titanium compound, a vanadium compound, and a magnesium compound.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, a positive electrode active material slurry containing the same, and a lithium secondary battery containing the same, and more particularly to a positive electrode active material containing an olivine-based lithium compound, a manufacturing method thereof, a positive electrode active material slurry containing the same, and a lithium secondary battery containing 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, high-capacity secondary batteries is rapidly increasing, and research and development efforts to improve the performance of lithium secondary batteries are being actively conducted.

[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 at the cathode and anode. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides a cathode active material having high energy density, high operating voltage, and high conductivity, a method for producing the same, and a cathode active material slurry containing the same.

[0005] Another problem to be solved by the present invention is to provide a lithium secondary battery having high energy density, high operating voltage, high charge / discharge efficiency, excellent low-temperature characteristics, and long life. [Means for solving the problem]

[0006] A method for preparing a cathode active material according to the present invention includes mixing an iron phosphate precursor, a lithium source, a carbon source, and a dopant source to form a mixture, drying the mixture by spray drying, and calcining the dried mixture, wherein the dopant source may include at least one selected from an aluminum compound, a titanium compound, a vanadium compound, and a magnesium compound.

[0007] A positive electrode active material according to another aspect of the present invention includes a compound represented by the following Chemical Formula 1, and includes first particles having a first average particle size, and the first particles may have a morphology in which second particles having a second particle size smaller than the first average particle size are aggregated together: [C1] Li a1 Fe x1 B y1 PO 4-b1

[0008] In the above Chemical Formula 1, 0.8≦a1≦1.2, 0.950≦x1≦0.999, 0.001≦y1≦0.05, 0≦b1≦0.05, and x1+y1=1, and in the above Chemical Formula 1, B is at least one element selected from the group consisting of Al, Ti, V, and Mg.

[0009] A positive electrode active material slurry according to another aspect of the present invention includes the above-described positive electrode active material, a conductive material, a binder, and a solvent, and may have a solid content of 60 to 70 wt %.

[0010] A lithium secondary battery according to yet another aspect of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes the above-described positive electrode active material, and the discharge capacity at −20° C. relative to the initial discharge capacity (discharge capacity at −20° C. / initial discharge capacity) may be 40% or more. [Effects of the Invention]

[0011] By including the cathode active material according to the present invention, the electrical conductivity of the cathode active material layer can be improved, the mix density (compressed density, pellet density) can be improved, and the solid content of the cathode active material layer can be increased. The lithium secondary battery according to the present invention has a relatively high operating voltage and charge / discharge efficiency, and can have improved low-temperature characteristics and life characteristics. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a simplified conceptual diagram of 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 one 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 one embodiment, which can be said to have a prismatic battery configuration. [Figure 4] 1 is a schematic diagram showing a lithium secondary battery according to one embodiment, which can be said to be a pouch-type battery. [Figure 5] 1 is a schematic diagram showing a lithium secondary battery according to one embodiment, which can be said to be a pouch-type battery. [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 8] FIG. 2 is an enlarged view of a positive electrode active material layer of a lithium secondary battery according to a comparative example of the present invention. [Figure 9] 1 is an SEM image of the positive electrode active material of Example 1 of the present invention. [Figure 10] 1 is an SEM image of the positive electrode active material of Comparative Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] 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 embodied in various forms and may undergo various modifications. However, the description of the present embodiments is provided to ensure complete disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0014] 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.

[0015] Unless otherwise stated herein, the singular can also include the plural. Additionally, unless otherwise stated, "A" or "B" can mean "including A but also 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.

[0016] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0017] 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% by volume 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.

[0018] 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 solution ELL.

[0019] 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.

[0020] 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.

[0021] positive electrode 10 The positive electrode 10 for a lithium secondary battery is a current collector The positive electrode active material layer AML1 may include 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.

[0022] 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.

[0023] For example, the negative electrode active material layer AML2 may contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material.

[0024] 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.

[0025] 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.

[0026] The water-based 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.

[0027] 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.

[0028] The dry binder is a fiberizable polymeric material, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, ethylene oxide, or combinations thereof.

[0029] The conductive material is used to impart conductivity to the electrode and may be any material that does not cause chemical changes in the constructed battery and is electronically conductive. 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 combinations thereof.

[0030] As the current collector COL2, those selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrates coated with conductive metals, and combinations thereof can be used.

[0031] 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, an alloy of lithium metal, a material capable of doping or undoping lithium, or a transition metal oxide.

[0032] The material capable of reversibly inserting / desorbing lithium ions is a carbon-based negative electrode active material, which may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0033] As the alloy of lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0034] As the material capable of doping or undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (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.

[0035] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and the surfaces of the silicon particles coated with amorphous carbon. For example, the composite may include secondary particles (cores) formed by combining primary silicon particles, and an amorphous carbon coating layer (shell) located on the surfaces of the secondary particles. Amorphous carbon may also be located between the primary silicon particles; for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0036] The silicon-carbon composite may further comprise crystalline carbon. For example, the silicon-carbon composite may comprise a core comprising crystalline carbon and silicon particles and an amorphous carbon coating layer disposed on the core.

[0037] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0042] The inorganic materials may include, but are not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0043] The organic material and the inorganic material may be mixed in one coating layer, or a coating layer containing an organic material and a coating layer containing an inorganic material may be stacked.

[0044] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0045] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0046] The non-aqueous organic solvent can be a carbonate, ester, ether, ketone, or alcohol solvent, a non-polar solvent, or a combination thereof.

[0047] Examples of carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl pyrrolyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0048] 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.

[0049] 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 nonpolar 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.

[0050] The non-aqueous organic solvents may be used alone or in combination of two or more.

[0051] 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.

[0052] 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+1 SO2) (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).

[0053] 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 an embodiment, 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 embedded. 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 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 the current generated in the positive electrode assembly 40 to the outside.

[0054] A 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.

[0055] 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, a conductive material CDM, and a binder BND. A plurality of first particles PTC1 may constitute a positive electrode active material according to an embodiment of the present invention.

[0056] The positive electrode active material layer AML1 may further contain an additive that can serve as a sacrificial positive electrode.

[0057] The content of the positive electrode active material PTC1 in the positive electrode active material layer AML1 may be 90 wt % to 99 wt % relative to 100 wt % of the positive electrode active material layer AML1, and the contents of the binder BND and the conductive material CDM may be 0.5 wt % to 5 wt % respectively relative to 100 wt % of the positive electrode active material layer AML1.

[0058] The binder BND may bind the first particles PTC1 and the conductive material CDM to each other. For example, the binder BND may include at least one selected from the group consisting of, but not limited to, 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)acrylic styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0059] 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 a carbon-based material such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, or carbon nanotube; a metal-based material in the form of a metal powder or metal fiber containing copper, nickel, aluminum, or silver; a conductive polymer such as a polyphenylene derivative; or a combination thereof.

[0060] The first particles PTC1 will be described in more detail below.

[0061] 1st particle PTC1 The first particles PTC1 may be polycrystalline and may include secondary particles formed by agglomeration of at least two or more primary particles. In other words, one first particle PTC1 may include a plurality of second particles PTC2 agglomerated together. Each of the second particles PTC2 may be a primary particle.

[0062] The first particles PTC1 may have a first average particle size. For example, the first 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. For example, the first average particle size of the first particles PTC1 may be approximately 5 μm. In one example, the average particle size may be measured using a particle size analyzer. The average particle size may refer to the diameter of particles with a cumulative volume of 50% (D50) in the particle size distribution.

[0063] The maximum particle size (Dmax) of the first particles PTC1 may be 10 μm or more, or 15 μm or more.

[0064] The second particles PTC2 may have a second particle size. The second particle size may be smaller than the first average particle size. The second particle size of the second particles PTC2 may be 200 nm or less. For example, the second particle size of the second particles PTC2 may be 10 nm to 200 nm, 20 nm to 200 nm, 50 nm to 200 nm, or 100 nm to 200 nm. In one example, the second particle size may refer to the diameter measured by randomly selecting approximately 30 second particles PTC2 from an electron microscope photograph of the positive electrode active material. The second particle size of the second particles PTC2 may be uniform.

[0065] If the particle sizes of the first particles and the second particles satisfy the above ranges and the size of the second particles is uniform, the charge / discharge capacity and low-temperature capacity of a lithium secondary battery including them can be improved.

[0066] The first particles PTC1 may include an olivine-based lithium compound represented by the following Chemical Formula 1: [C1] Li a1 Fe x1 B y1 PO 4-b1

[0067] In Chemical Formula 1, 0.8≦a1≦1.2, 0.950≦x1≦0.999, 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 Al, Ti, V, and Mg. For example, B may include Ti. B may be a dopant doped into the first particles PTC1. B may control the size of the primary particles, i.e., the second particles PTC2, to be uniform.

[0068] The doping amount of B may be 500 ppm to 3000 ppm. The doping amount of B may be defined as the weight of the doping element B relative to the total weight of metals (i.e., Fe and B) excluding lithium in the olivine-based lithium compound represented by Chemical Formula 1. If the doping amount of B satisfies the above range, the size of the second particles PTC2 can be controlled to be uniform.

[0069] For example, 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 may cover only 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.

[0070] 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.

[0071] As an example, the first particle PTC1 may further include a grain boundary coating layer on the surface of each of the second particles PTC2. 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 the second particles PTC2 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.

[0072] 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 inside, or from a depth of 10 nm to a depth of about 2 μm.

[0073] The first particles PTC1 may 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, and may further improve the electrical conductivity of the first particles PTC1.

[0074] The first particles PTC1 may further contain carbon derived from the above-mentioned coating layer and / or grain boundary coating layer. The content of carbon element 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%.

[0075] The first particles PTC1 may have a spherical shape formed by agglomeration of nano-sized second particles PTC2. The first particles PTC1 may exhibit the following characteristics due to the close agglomeration of the second particles PTC2: The first particles PTC1 may have a spherical or elliptical shape; The average particle size of the first particles PTC1 may be 2 μm to 15 μm; The porosity of the first particles PTC1 may be approximately 20% to 40%; The Span value of the first particles PTC1 analyzed using a particle size analyzer may be 0.3 to 0.75.

[0076] According to a comparative example of the present invention, the positive electrode active material layer AML1 includes a nano-type or nano-type positive electrode active material, which may include nano-sized particles NP. The particles NP may aggregate (e.g., agglomerate), and the nano-type or nano-type positive electrode active material may have a particle morphology similar to that of the first particles PTC1 shown in FIG. 6. Even if the particles NP aggregate (e.g., agglomerate), the nano-type or nano-type positive electrode active material may not have the same or similar spherical shape as the first particles PTC1, as shown in FIG. 8. In other words, the nano-type positive electrode active material may have a random morphology. The nano-type positive electrode active material may be provided in various sizes. For example, the average particle size of the nano-type positive electrode active material may be 500 nm to 2.5 μm, or 1 μm. The minimum particle size of the nano-type positive electrode active material may be 100 nm to 500 nm, or 200 nm to 300 nm. In one example, the average particle size may be measured using a particle size analyzer. The average particle size may refer to the diameter of particles with a cumulative volume of 50% (D50) in the particle size distribution. For example, the minimum particle size may refer to the diameter measured by randomly selecting approximately 30 primary particles (hereinafter referred to as first primary particles) from an electron microscope image of the nano-shaped positive electrode active material. The particle size of the first primary particles may be approximately 100 nm larger than the second particle size of the second particles PTC2. The nano-shaped positive electrode active material may have a porosity of greater than 40%. The nano-shaped positive electrode active material may have a Span value analyzed by a particle size analyzer that falls outside the range of 0.3 to 0.75.

[0077] According to an embodiment of the present invention, the coarse-grained positive electrode active material may include the first particles PTC1 described above. Unlike the comparative example, the coarse-grained positive electrode active material may have the porosity and span value described above.

[0078] The positive electrode active material of the present invention includes the first particles PTC1, which can improve pellet density, capacity, and energy density. In one embodiment, the positive electrode active material of the present invention may have a pellet density of 2.0 g / cc to 3.0 g / cc. For example, the positive electrode active material of the present invention may have a pellet density of 2.4 g / cc to 2.6 g / cc, or 2.41 g / cc to 2.5 g / cc.

[0079] A lithium secondary battery including the positive electrode active material of the present invention may have improved low-temperature characteristics. In one embodiment, the discharge capacity at −20° C. relative to the initial discharge capacity of the lithium secondary battery (discharge capacity at −20° C. / initial discharge capacity) may be 40% or more. For example, the discharge capacity at −20° C. relative to the initial discharge capacity of the lithium secondary battery of the present invention (discharge capacity at −20° C. / initial discharge capacity) may be 45% to 70%, or 50% to 65%.

[0080] The operating voltage of a lithium secondary battery including the positive electrode active material of the present invention may be improved. In one embodiment, the operating voltage range of the lithium secondary battery of the present invention may be 3 V to 5 V. For example, the operating voltage range may be 3 V to 4.5 V, or 3.5 V to 4 V.

[0081] Lithium secondary batteries containing the positive electrode active material of the present invention may have improved life characteristics. In one embodiment, the lithium secondary battery of the present invention may have a capacity retention rate of 99% or more after 50 charge / discharge cycles at a constant current of 1.0 C at the above-mentioned voltage. For example, the capacity retention rate may be 99% to 100%, or 99.1% to 100%.

[0082] Positive electrode active material slurry The cathode active material slurry according to an embodiment of the present invention may include the above-described cathode active material PTC1, the conductive material CDM, the binder BND, and a solvent. For convenience of explanation, the following description will omit the same points as those described with reference to FIG. 6, and will focus on the differences.

[0083] In one embodiment, the viscosity of the positive electrode active material slurry may be 7000 mPa·s or less. For example, the viscosity of the positive electrode active material slurry may be 1000 mPa·s to 7000 mPa·s, 2000 mPa·s to 6000 mPa·s, or 3000 mPa·s to 4000 mPa·s. If the viscosity of the positive electrode active material slurry satisfies the above range, the positive electrode active material layer AML1 can be smoothly attached to the current collector COL1.

[0084] The cathode active material slurry of the present invention can provide a desired viscosity while containing a large amount of solids. For example, the cathode active material slurry can contain 60% to 70% solids. The solids content may refer to the weight percentage of the solid material remaining after the solvent evaporates (i.e., the dried mixture and current collector) relative to the total weight of the current collector onto which the cathode active material slurry is applied when manufacturing an electrode. The solids may include the cathode active material, a binder, and a conductive material. When the solids content satisfies the above range, the first particles PTC1 can have excellent adhesion to the current collector.

[0085] The first particles PTC1 may be attached to the current collector COL1 (see FIG. 1), and the binder BND may increase the adhesive strength between the first particles PTC1 and the current collector COL1 (see FIG. 1). For example, when fabricating a full cell, the cathode active material slurry of the present invention may contain a small amount of binder BND. That is, because the first particles PTC1 have a large first average particle size, the content of binder BND in the cathode active material layer AML1 may be reduced to ensure the desired adhesive strength between the first particles PTC1 and the current collector COL1 (see FIG. 1) when fabricating a full cell. For example, the cathode active material slurry may contain 0.5 wt % to 5 wt % of binder BND, based on the total weight of the cathode active material slurry. For example, the content of binder BND may be 0.5 wt % to 3 wt %, or 0.5 wt % to 2 wt %, based on 100 wt % of the cathode active material layer AML1. This may reduce the resistance of a lithium secondary battery including the cathode active material slurry.

[0086] Method for producing positive electrode active material FIG. 7 is a flowchart illustrating a method for manufacturing a positive electrode active material according to an embodiment of the present invention.

[0087] Referring to FIG. 7, 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. For example, the iron phosphate precursor may include FePO4 or a mixture of FeSO4 and H3PO4.

[0088] 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.

[0089] 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.

[0090] The dopant source may include an oxide containing a dopant metal and / or a chloride containing a dopant metal. The dopant source may include a titanium compound. For example, the dopant source may include at least one of a titanium compound or titanium chloride. For example, the dopant source may further include, in addition to the titanium compound, at least one selected from the group consisting of aluminum oxide, aluminum chloride, magnesium oxide, magnesium chloride, vanadium oxide, and vanadium chloride. The dopant source may include at least one selected from the group consisting of an aluminum compound, a titanium compound, a vanadium compound, and a magnesium compound. Or, for example, the dopant source may further include at least one selected from the group consisting of titanium oxide, titanium chloride, aluminum oxide, aluminum chloride, magnesium oxide, magnesium chloride, vanadium oxide, and vanadium chloride.

[0091] The mixture may be subjected to wet milling (S200). A typical temperature-controllable wet mill may be used for wet milling. More 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. Through the wet milling process, particles in the mixture may be pulverized to a fine size.

[0092] 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 for the precursor particles may be omitted.

[0093] 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 drying device, an air nozzle spray drying device, an ultrasonic nozzle spray drying device, a filter expansion droplet generating device, and an electrostatic spray drying device.

[0094] The particles refined to the size of primary particles through the wet-milling process can aggregate with each other to form secondary particles through the spray-drying process. 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, and internal pressure during the spray-drying process.

[0095] As an example, the mixture to be spray-dried may have a total solid content of 20% to 40% by weight. 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. As an example, the spray liquid may have a solid content of approximately 30% by weight.

[0096] If the solid content is less than 20%, the average particle size of the first particles PCT1 will be small, which may result in reduced productivity, whereas if the solid content is more than 40%, it will be difficult to control the average particle size of the first particles PCT1, which may result in increased size deviation of the first particles PCT1.

[0097] 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.

[0098] In one embodiment, the input rate of the spray dryer may be 0.1 kg / min to 0.9 kg / min. The input rate of the spray dryer may be defined as the weight of the solvent and raw material mixture input per time. In one embodiment, the input rate of the spray dryer according to the present invention may be 0.3 kg / min to 0.8 kg / min, or about 0.5 kg / min.

[0099] In one embodiment, spray drying may be carried out at a temperature of 100°C to 300°C. For example, spray drying may be carried out at a temperature of 200°C to 300°C, above 200°C to 300°C, or 230°C to 270°C. The propellant gas (e.g., air) used in spray drying may be introduced at a first temperature and discharged at a second temperature. For example, the first temperature may be 200°C to 250°C. The second temperature may be 80°C to 150°C.

[0100] The spray pressure may be 0.3 MPa to 0.7 MPa. For example, the spray pressure may be about 0.5 MPa.

[0101] When the input amount, input pressure, and temperature of the spray drying satisfy the ranges described above, the first particles PTC1 can have a spherical shape and a desired porosity.

[0102] In one embodiment, the flow rate of the spray liquid during 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 more than 80 ml / min, problems such as incomplete drying of the mixture due to condensation of water in the spray dryer may occur.

[0103] 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 time for the calcination process may be 4 hours to 20 hours, or 6 hours to 12 hours. By calcining the dried mixture, first particles PTC1 including the compound of Chemical Formula 1 described above may be formed.

[0104] After calcining the dried mixture (S400), the method may further include dry-grinding the calcined mixture (S500). The calcined mixture may be pulverized using an air jet mill or the like. The calcined mixture may be pulverized at a rotation speed of 0 rpm to 7000 rpm. For example, the calcined mixture may be pulverized at a rotation speed of 4000 rpm to 7000 rpm, 4000 rpm to 6000 rpm, or 4500 rpm to 5000 rpm. The post-calcination grinding step (S500) may be performed under relatively mild conditions. In one embodiment of the present invention, dry-grinding (S500) may be omitted. If the rotation speed in grinding step (S500) satisfies the specified range, the first particles PTC1 may maintain the shape of secondary particles. As a result, the first particles PTC1 may have the shape of secondary particles as shown in FIG. 6.

[0105] The method for producing the first particles PTC1 according to the present invention may include introducing a carbon source into an iron phosphate precursor to uniformly form a carbon coating layer on the surfaces of the primary particles. The primary particles may then be 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.

[0106] Carbon element 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. The sample is then burned at a combustion temperature of 1000°C. The burned gas is then reduced using a reduction cavity to form carbon dioxide. Carbon dioxide is detected using a TCD detector.

[0107] In accordance with an embodiment of the present invention, the carbon content was 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), in addition to SEM-EDS.

[0108] Examples and comparative examples of the present invention will be described below, but the following examples are merely examples of the present invention and the present invention is not limited to the following examples.

[0109] Example 1: Production of primary particles in the form of secondary particles Iron phosphate precursor FePO4, lithium carbonate, and titanium dioxide were mixed in a molar ratio of Fe:Li:Ti = 1:1.03:0.002. 10% by weight of glucose was added to the mixture (S100). The mixture was then evaporated by spray drying under a spray pressure of 0.5 MPa and a temperature of 250°C (S300). The mixture was fed at a rate of 0.5 kg / min. The dried mixture was then calcined at 750°C for 10 hours in a nitrogen atmosphere to obtain primary particles in the form of secondary particles (S400). The average size of the secondary particles within the primary particles was about 100 nm to about 200 nm. The fired mixture was pulverized using an air jet mill. The rotation speed during pulverization was 5000 rpm. The doping amount of Ti was 1000 ppm, and the chemical formula of the produced primary particles was LiFe 0.998 Ti 0.002 It was PO4.

[0110] Example 2: Production of primary particles in the form of secondary particles Aluminum oxide was used instead of titanium dioxide, the doping amount of Al was 1000 ppm, and the chemical formula of the produced primary particles was LiFe 0.9965 Al 0.0035 It was prepared in the same manner as in Example 1, except that it was PO4.

[0111] Example 3: Production of primary particles in the form of secondary particles Magnesium oxide was used instead of titanium dioxide, the doping amount of Mg was 1000 ppm, and the chemical formula of the produced primary particles was LiFe 0.996 Mg 0.004 It was prepared in the same manner as in Example 1, except that it was PO4.

[0112] Example 4: Production of primary particles in the form of secondary particles Vanadium oxide was used instead of titanium dioxide, the V doping amount was 1000 ppm, and the chemical formula of the first particles produced was LiFe 0.998 V 0.002 It was prepared in the same manner as in Example 1, except that it was PO4.

[0113] Comparative Example 1: Production of single particle-shaped first particles The same method as in Example 1 was used for preparation, except that the input rate during spray drying was 1.0 kg / min.

[0114] Comparative Example 2: Production of single particle-shaped first particles The same method as in Example 1 was used for production, except that the input rate during spray drying was 1.0 kg / min, the temperature was 200° C., and the rotation speed during pulverization was 8000 rpm.

[0115] Comparative Example 3: Production of single particle-shaped first particles The same method as in Example 1 was used for production, except that the input amount during spray drying was 2.0 kg / min and the rotation speed during pulverization was 8000 rpm.

[0116] Comparative Example 4: Production of single particle-shaped first particles The same method as in Example 1 was used for production, except that the input rate during spray drying was 2.0 kg / min, the temperature was 200° C., and the rotation speed during pulverization was 8000 rpm.

[0117] Comparative Example 5: Production of single particle-shaped first particles Non-titanium-doped single-particle first particles PTC1 were prepared in the same manner as in Example 1, except that no titanium dioxide was added when preparing the mixture, the spray drying was performed at a feed rate of 2.0 kg / min at a temperature of 200°C, and the milling speed was 8000 rpm.

[0118] Comparative Example 6: Production of primary particles in the form of secondary particles The iron phosphate precursor, Fe1PO4, lithium carbonate, and titanium dioxide were mixed in a molar ratio of Fe:Li:Ti=1:1.03:0.01, and the doping amount of Ti was 5000 ppm. The chemical formula of the produced primary particles was LiFe 0.995 Ti 0.005 It was prepared in the same manner as in Example 1, except that it was PO4.

[0119] [Table 1]

[0120] Cathode manufacturing A positive electrode active material slurry was prepared by mixing 96 wt% of the final positive electrode active material, 2 wt% of polyvinylidene fluoride binder, and 2 wt% of carbon black conductive material in N-methylpyrrolidone solvent. In Examples 1 to 4 and Comparative Example 6, 3 mL of N-methylpyrrolidone solvent was added, and in Comparative Examples 1 to 5, 6 mL of N-methylpyrrolidone solvent was added.

[0121] The positive electrode active material slurry was applied to an aluminum current collector, dried, and then rolled to prepare a positive electrode.

[0122] Lithium secondary battery manufacturing A 2032-type coin half-cell was fabricated using the prepared positive electrode and a lithium metal counter electrode as the counter electrode. A separator (approximately 16 μm thick) made of porous polyethylene (PE) film was placed between the positive electrode and the lithium metal counter electrode, and an electrolyte was injected to fabricate a lithium secondary battery. The electrolyte used was a mixture of 1.3 M LiPF6 with a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethylene carbonate (DMC) in a volume ratio of 3:4:3.

[0123] Evaluation example 1: Analysis of the surface of the positive electrode active material An SEM image of the positive electrode active material prepared in Example 1 is shown in FIG. 9. An SEM image of the positive electrode active material prepared in Comparative Example 1 is shown in FIG. 10. The size of the primary particles was measured, and the results are shown in Table 2.

[0124] [Table 2]

[0125] Referring to Figure 9, it can be seen that the first particles according to an embodiment of the present invention are spherical secondary particles formed by agglomeration of a plurality of primary particles. Referring to Figure 10, it can be seen that the first particles are fine single particles. Referring to Figures 9, 10, and Table 2, it can be seen that the size of the primary particles PTC2 according to the embodiment is smaller and more uniform than that of the primary particles according to the comparative example.

[0126] Evaluation example 2: Evaluation of active materials The composite density (PD) and carbon content of the positive electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 6 were measured, and the results are shown in Table 3.

[0127] [Table 3]

[0128] Referring to Table 3, it can be seen that the cathode active materials according to Examples 1 to 4 of the present invention have superior composite densities compared to the cathode active materials according to Comparative Examples 1 to 5. It can also be seen that the cathode active materials according to Examples 1 to 4 of the present invention have higher carbon contents compared to Comparative Examples 1 to 5.

[0129] On the other hand, the positive electrode active material according to Example 1 had a higher mixture density and a higher carbon content than the positive electrode active material according to Comparative Example 5.

[0130] Evaluation example 3: Evaluation of battery characteristics The viscosity of the positive electrode active material slurries containing the positive electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 6 was measured, and the results are shown in Table 4.

[0131] [Table 4]

[0132] Referring to Table 4, it was confirmed that the viscosities of the positive electrode active material slurries according to Examples 1 to 4 of the present invention were 1.5 to 3 times lower than those of Comparative Examples 1 to 5. That is, when preparing positive electrode active material slurries having a desired viscosity, it was confirmed that Examples 1 to 4 could be prepared to contain a higher solid content than Comparative Examples 1 to 5. As a result, when an electrode is prepared using the positive electrode active material slurries according to the present invention, a positive electrode active material with excellent adhesive strength can be provided.

[0133] Evaluation example 4: Evaluation of battery characteristics The characteristics of the lithium secondary batteries manufactured using the positive electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 6 were evaluated.

[0134] The lithium secondary battery was initially charged at a constant current (0.1C) and a constant voltage (3.8V), and then allowed to rest for 10 minutes before discharging to 3.0V at a constant current (0.1C). It was then charged and discharged 50 times at 1.0C / 1.0C at -20°C. An additional coin cell was also fabricated and its capacity measured at -20°C. The battery characteristics were evaluated and are shown in Table 5 below.

[0135] [Table 5]

[0136] Referring to Table 5, it can be seen that the secondary batteries according to Examples 1 to 4 of the present invention have higher −20° C. discharge capacities than the secondary batteries according to Comparative Examples 1 to 6. It can also be seen that the secondary batteries according to Examples 1 to 4 of the present invention exhibit superior charge / discharge efficiency and lifespan than the secondary batteries according to Comparative Examples 1 to 6.

[0137] Meanwhile, the secondary batteries according to Examples 1 to 4 have a higher charge capacity than the secondary batteries according to Comparative Examples 1 to 6, and therefore it was confirmed that the resistance of the secondary batteries according to Examples 1 to 4 is smaller.

[0138] Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be embodied in various modifications within the scope of the claims, the embodiments for implementing the invention, and the accompanying drawings, and it is to be understood that these also fall within the scope of the present invention. [Explanation of symbols]

[0139] 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 cabinets 60 Sealing member 70 Electrode tab 71 Positive electrode tab 72 Negative electrode tab

Claims

1. combining an iron phosphate precursor, a lithium source, a carbon source, and a dopant source to form a mixture; drying the mixture by spray drying; and calcining the dried mixture; the dopant source includes at least one selected from an aluminum compound, a titanium compound, a vanadium compound, and a magnesium compound; A method for producing a positive electrode active material.

2. the dopant source includes at least one selected from titanium oxide and titanium chloride; The method for producing the positive electrode active material according to claim 1 .

3. The input rate of the spray drying is 0.1 kg / min to 0.9 kg / min; The method for producing the positive electrode active material according to claim 1 .

4. The spray pressure of the spray drying is 0.3 MPa to 0.7 MPa; The method for producing the positive electrode active material according to claim 1 .

5. The spray drying temperature is 200°C to 300°C. The method for producing the positive electrode active material according to claim 1 .

6. drying the mixture includes agglomerating particles in the mixture to form secondary particles. The method for producing the positive electrode active material according to claim 1 .

7. subsequent to calcining the dried mixture, further comprising dry-grinding the calcined mixture; The grinding is carried out at a rotation speed of 4000 rpm to 7000 rpm. The method for producing the positive electrode active material according to claim 1 .

8. The present invention includes a first particle comprising the compound of Formula 1 and having a first average particle size, The first particles have a form in which second particles having a second particle diameter smaller than the first average particle diameter are aggregated together. Cathode active material: [Chemical formula 1] Li a1 Fe x1 B y1 PO 4-b1 In the formula 1, 0.8≦a1≦1.2, 0.950≦x1≦0.999, 0.001≦y1≦0.05, 0≦b1≦0.05, and x1+y1=1; In Formula 1, B is at least one element selected from the group consisting of Al, Ti, V, and Mg.

9. In the above formula 1, B is Ti. The positive electrode active material according to claim 8 .

10. the first average particle size is 2 μm to 15 μm; The positive electrode active material according to claim 8 .

11. The second particle size is 200 nm or less. The positive electrode active material according to claim 8 .

12. the first particles include a coating layer including carbon; The carbon content in the first particles is 1.5% by weight to 2.5% by weight. The positive electrode active material according to claim 8 .

13. the first particles further comprise a grain boundary coating layer on the interface between the second particles; The grain boundary coating layer contains carbon. The positive electrode active material according to claim 8 .

14. The porosity of the first particles is 20% to 40%. The positive electrode active material according to claim 8 .

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

16. The positive electrode active material has a mixture density of 2.0 g / cc to 3.0 g / cc. The positive electrode active material according to claim 8 .

17. The positive electrode active material according to claim 8, a conductive material, a binder, and a solvent are included, having a solids content of 60% to 70% by weight; Positive electrode active material slurry.

18. The content of the binder is 0.5 wt % to 5 wt % based on the total weight of the positive electrode active material slurry. The positive electrode active material slurry according to claim 17 .

19. The viscosity is 7000 mPa s or less. The positive electrode active material slurry according to claim 17 .

20. It includes a positive electrode, a negative electrode, a separator, and an electrolyte solution. The positive electrode comprises the positive electrode active material according to claim 8, The discharge capacity at −20° C. relative to the initial discharge capacity (discharge capacity at −20° C. / initial discharge capacity) is 40% or more. Lithium secondary battery.

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