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 having high conductivity and a high electrochemical characteristic, a manufacturing method for the positive electrode active material, and a lithium secondary battery.SOLUTION: A positive electrode active material can include a first particle containing a compound expressed by Chemical Formula 1 below and having a first average particle diameter. In a Raman spectrum of the first particle obtained by Raman spectroscopy, the ratio (ID / IG) of the peak intensity (ID) of D peak existing at a wavenumber of 1340±10 cm-1 to the peak intensity (IG) of G peak existing at a wavenumber of 1590±10 cm-1 is 0.9 to 1.3. [Chemical Formula 1] Lia1MnxFe1-xMyPO4, in which 0.8≤a1≤1.2 and 0.2<x<0.8, and 0.0001≤y≤0.05 are satisfied, and M is at least one element selected from the group consisting of Ti, Al, Mg, Zr, V, Zn, Nb, K, Y, B, and Cu.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 increase in 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 rapidly increasing. Accordingly, 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. 10-2022-0134536 Summary of the Invention [Problem to be solved by the invention]

[0005] The problem to be solved by the present invention is to provide a positive electrode active material having high conductivity and electrochemical properties.

[0006] Another object of the present invention is to provide a lithium secondary battery having high conductivity and electrochemical properties. [Means for solving the problem]

[0007] According to the concept of the present invention, the positive electrode active material can include a compound of Chemical Formula 1 below and include first particles having a first average particle size.

[0008] Among the Raman spectra obtained by Raman spectroscopy of the first particles, the ratio (I -1 / I G ) of the intensity (I -1 ) of the D peak existing at a wave number of 1340 ± 10 cm D to the intensity (I D ) of the G peak existing at a wave number of 1590 ± 10 cm G can be 0.9 to 1.3. [Chemical Formula 1] Li a1 Mn x Fe 1-x M y PO4

[0009] In Chemical Formula 1, 0.8 ≤ a1 ≤ 1.2, 0.2 < x < 0.8, 0.0001 ≤ y ≤ 0.05, and M can be at least one element selected from the group consisting of Ti, Al, Mg, Zr, V, Zn, Nb, K, Y, B, and Cu.

[0010] According to another concept of the present invention, a method for manufacturing a positive electrode active material can include mixing an iron phosphate precursor, a lithium source, a carbon source, and a dopant source to form a mixture, drying the mixture, and firing the dried mixture to produce first particles. The first particles can include a compound represented by Chemical Formula 1 below. [Chemical Formula 1] Li a1 Mn x Fe 1-x M y P O4

[0011] In the above Chemical Formula 1, 0.8 ≦ a1 ≦ 1.2, 0.2 < x < 0.8, 0.0001 ≦ y ≦ 0.05, and M can be at least one element selected from the group consisting of Ti, Al, Mg, Zr, V, Zn, Nb, K, Y, B, and Cu.

[0012] According to still another concept of the present invention, the lithium secondary battery can include the above-described positive electrode active material.

Advantages of the Invention

[0013] The positive electrode active material according to the present invention can include first particles.

[0014] The positive electrode active material according to the present invention can uniformly coat the first particles with a coating material at an optimal content by adjusting the firing temperature and the content of the doping material. The lithium secondary battery according to the present invention can improve high conductivity and electrochemical characteristics.

Brief Description of the Drawings

[0015] [Figure 1] It is a conceptual diagram schematically showing a lithium secondary battery according to an embodiment of the present invention. [Figure 2] It is a schematic diagram showing a lithium secondary battery according to an embodiment, and it can be said to be a cylindrical battery form. [Figure 3] It is a schematic diagram showing a lithium secondary battery according to an embodiment, and it can be said to be a rectangular battery form. [Figure 4] It is a schematic diagram showing a lithium secondary battery according to an embodiment, and it can be said to be a pouch-type battery form. [Figure 5] It is a schematic diagram showing a lithium secondary battery according to an embodiment, and it can be said to be a pouch-type battery form. [Figure 6] It is an enlarged view of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. [Figure 7] It is an enlarged view of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. [Figure 8]1 is a flowchart illustrating a method for manufacturing a positive electrode active material according to an embodiment of the present invention. [Figure 9a] 1 is a SEM image of a positive electrode active material according to an embodiment of the present invention. [Figure 9b] 1 is a SEM image of a positive electrode active material according to an embodiment of the present invention. [Figure 10a] 1 is a TEM image of a positive electrode active material according to an embodiment of the present invention. [Figure 10b] 1 is a TEM image of a positive electrode active material according to a comparative example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] 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 complete the disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0017] 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.

[0018] 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.

[0019] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] negative electrode 20 The negative electrode 20 for a lithium secondary battery 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.

[0026] 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.

[0027] 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.

[0028] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, and combinations thereof.

[0029] 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.

[0030] 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.

[0031] The dry binder can be a fiberizable polymeric material, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, ethylene oxide, or combinations thereof.

[0032] The conductive material is used to impart conductivity to the electrode and may be any material that is electronically conductive and does not cause chemical changes 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.

[0033] As the current collector COL2, those selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof can be used.

[0034] 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.

[0035] The material capable of reversibly inserting / desorbing the lithium ions is a carbon-based negative electrode active material, and may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0036] As the alloy of the 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.

[0037] 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 (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 thereof. The Sn-based negative electrode active material can be Sn, SnO₂, a Sn-based alloy, or a combination thereof.

[0038] 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 silicon-carbon composite may include secondary particles (cores) formed by combining primary silicon particles and amorphous carbon coating layers (shells) located on the surfaces of the secondary particles. The amorphous carbon may also be located between the primary silicon particles, e.g., the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0039] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core including crystalline carbon and silicon particles, and an amorphous carbon coating layer disposed on the surface of the core.

[0040] The Si-based or Sn-based negative electrode active material may be used in combination with a carbon-based negative electrode active material.

[0041] 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.

[0042] 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.

[0043] The porous substrate may be a polymer film 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.

[0044] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0045] 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.

[0046] 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.

[0047] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0048] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0049] 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.

[0050] Examples of the carbonate solvent 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).

[0051] 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.

[0052] 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 non-quantum solvents that can be used include nitriles such as R-CN (R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, and 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.

[0053] The non-aqueous organic solvents may be used alone or in combination of two or more.

[0054] 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.

[0055] 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+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).

[0056] 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 type, FIG. 3 illustrating a prismatic type, and FIGS. 4 and 5 illustrating pouch types. Referring to FIGS. 2 to 4, a lithium secondary battery 100 may include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a 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 current generated in the electrode assembly 40 to the outside.

[0057] 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.

[0058] 6 and 7 are enlarged views of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. Referring to FIGS. 6 and 7, 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.

[0059] The positive electrode active material layer AML1 may further include an additive that can act as a sacrificial positive electrode.

[0060] The content of the positive electrode active material PTC1 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. The contents 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.

[0061] The binder BND can bind the first particles PTC1 and the conductive material CDM to each other. As an example, the binder BND can include, but is not limited to, at least one selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl 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.

[0062] The conductive material CDM can be used to improve the conductivity of the positive electrode active material layer AML1. Any conductive material that does not cause a chemical change in the positive electrode active material layer AML1 can be used as the conductive material CDM without limitation. For example, the conductive material CDM can include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, carbon nanotube; metal-based materials containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0063] Hereinafter, the first particle PTC1 will be described in more detail.

[0064] 1st particle PTC1 The first particle PTC1 can contain an olivine-based lithium compound represented by the following chemical formula 1. [Chemical formula 1] Li a1 Mn x Fe 1-x M y PO4

[0065] In the chemical formula 1, 0.8 ≦ a1 ≦ 1.2, 0.2 < x < 0.8, 0.0001 ≦ y ≦ 0.05 can hold. M can be at least one element selected from the group consisting of Ti, Al, Mg, Zr, V, Zn, Nb, K, Y, B, and Cu. M can be a dopant doped into the first particle PTC1. For example, M can contain Ti. M can be controlled so that the size of the primary particles is uniform, and the charge-discharge efficiency, low-temperature characteristics, and life characteristics of the lithium secondary battery can be improved. The primary particles will be described in detail below.

[0066] The first particle PTC1 can have a ratio (I D / I G ) of the Raman spectrum obtained by Raman spectroscopy that can be 0.5 to 1.5. As an example, the ratio (I D / I G) can be between 0.9 and 1.3.

[0067] The Raman spectrum can be measured using a Raman spectrometer. G is 1590±10cm in the Raman spectrum -1 This means that the G peak exists at a wavenumber of I D is 1340±10cm in the Raman spectrum -1 This means that the D peak exists at a wavenumber of .

[0068] In this example, the G peak refers to a peak due to crystallized carbon, and the D peak refers to a peak due to amorphous carbon. D / I G ) allows us to grasp the degree of crystallization of carbon.

[0069] The Raman spectrum ratio (I D / I G ) has an optimum ratio range, and when the ratio is within a specific range, it can exhibit electrode slurry properties and high conductivity and electrochemical properties.

[0070] The Raman spectrum ratio (I D / I G When the value of (I) is small, the proportion of crystallized carbon increases, and the conductivity can be improved. D / I G If the value of (a) is large, the amount of amorphous carbon increases, which can deteriorate the electrode plate slurry properties and increase the surface resistance.

[0071] According to this embodiment, the Raman spectrum ratio (I D / I G If the Raman spectrum ratio (I) is less than 0.5, the electrode plate slurry characteristics will be deteriorated (a decrease in solid content and an increase in viscosity), and the resistance will increase (overvoltage due to a decrease in ionic conductivity), which will increase the amount of metal elution during the life of the electrode, resulting in a deterioration in cell performance and a decrease in electrode durability. D / I GIf the ratio exceeds 1.5, the crystallized carbon coating layer on the particle surface becomes too thick, increasing the resistance (interference with lithium ion intercalation / deintercalation), reducing the reversible capacity (specific capacity) of the positive electrode and decreasing the durability of the electrode.

[0072] 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.

[0073] 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 1.1 wt% to 2.8 wt%.

[0074] If the carbon content in the first particles PTC1 is less than 1.1 wt%, the carbon may not be uniformly distributed inside the active material particles, and if the carbon content exceeds 2.8 wt%, the carbon may be excessively added, resulting in a thick carbon coating layer on the surface of the active material particles.

[0075] The cathode active material of the present invention may have improved composite density, capacity, and energy density by including the first particles PTC1. In one embodiment, the compressed density of the cathode active material of the present invention may be 1.8 g / cc to 2.8 g / cc, or 2.0 g / cc to 2.6 g / cc.

[0076] The first particles PTC1 may have a first average particle size APD1, which may vary depending on the embodiment of FIG.

[0077] As an example, referring again to FIG. 6, the first particle PTC1 may have a single particle shape. In this specification, a single particle may refer to a single particle having no internal grain boundary. A single particle may refer to a single particle, a monolith structure, a single structure, or a non-aggregated particle, in which particles exist in an independent phase and are not aggregated with each other in morphology. 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 isolated form. Alternatively, a single particle may be in a form in which 2 to 100 single particles are attached to each other.

[0078] The first particles PTC1 may be a nano-sized positive electrode active material and may include at least one primary particle. The first particles PTC1 may consist of only one primary particle, may have a spherical shape formed by agglomeration of the primary particles, or may have a random shape formed by agglomeration of the primary particles.

[0079] In other words, when the first particles PTC1 are single particles, the first average particle size APD1 of the first particles PTC1 may be 0.2 μm to 2.5 μm. The minimum particle size of the first particles PTC1, i.e., the size of the primary particle, may be 10 nm to 200 nm.

[0080] In one embodiment, the average particle size can be measured using a particle size analyzer. The average particle size can refer to the diameter (D50) of particles whose cumulative volume is 50% by volume in a particle size distribution. In one embodiment, the minimum particle size, i.e., the size of primary particles, can refer to the diameter measured by randomly selecting about 30 primary particles from an electron microscope photograph of the first particles PTC1.

[0081] When the first particles PTC1 are single particles, the first average particle diameter APD1 is very small, so a large amount of binder BND may be required to adhere the first particles to the current collector COL1 (see FIG. 1). For example, the content of binder BND may be 3 wt % to 5 wt % relative to 100 wt % of the positive electrode active material layer AML1.

[0082] 7, the first particles PTC1 may have a polycrystalline form 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.

[0083] As an example, 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.

[0084] 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.

[0085] The first particles PTC1 further include a grain boundary coating portion, which enhances structural stability and allows a uniform coating layer to be formed on the surface of the first particles PTC1. In addition, the first particles PTC1 further include a grain boundary coating portion, which further improves the electrical conductivity of the first particles PTC1.

[0086] The first particles PTC1 may have a spherical shape formed by agglomeration of nano-sized primary particles NNP. The first particles PTC1 may exhibit the following characteristics due to the primary particles NNP being closely aggregated to each other. The first particles PTC1 may have a spherical or elliptical shape.

[0087] When the first particles PTC1 are in the form of secondary particles, the first average particle size APD1 of the first particles PTC1 may be 0.2 μm to 20 μm.

[0088] In one embodiment, the average particle size can be measured using a particle size analyzer. The average particle size can refer to the diameter of particles whose cumulative volume is 50% by volume (D50) in the particle size distribution.

[0089] The first particles PTC1 may include a plurality of primary particles NNP aggregated together. The primary particles NNP may have a particle size of 10 nm to 400 nm. In one embodiment, the minimum particle size, i.e., the size of the primary particles, may refer to the diameter measured by randomly selecting about 30 primary particles from an electron microscope image of the first particles PTC1.

[0090] The porosity of the first particles PTC1 may be about 20% to about 60%. The Span value of the first particles PTC1 analyzed by a particle size analyzer may be 0.5 to 7.

[0091] Specifically, the "span" value refers to a value obtained by using D10, D50, and D90, which are indices representing particle size, and calculating the value by the formula (D90-D10) / D50.

[0092] Method for producing positive electrode active material 8 is a flowchart illustrating a method for manufacturing a positive electrode active material according to an embodiment of the present invention. The method for manufacturing the first particles PTC1 according to an embodiment of the present invention will be described in more detail with reference to FIG.

[0093] The manganese iron phosphate precursor, the lithium source, the carbon source, and the dopant source may be mixed in a solvent (S100). For example, the solvent may be water, ethanol, or the like.

[0094] 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 0.2 to 0.8.

[0095] 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.

[0096] The carbon source can include at least one selected from the group consisting of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol, and dopamine.

[0097] 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 Ti, Al, Mg, Zr, V, Zn, Nb, K, Y, B, and Cu. In one embodiment, the dopant source may include a titanium compound.

[0098] The carbon source may be mixed in an amount of 1 wt% to 10 wt% based on the total weight of the mixture. If the carbon source is added in an amount less than 1 wt%, the carbon may not be uniformly distributed inside the active material particles. If the carbon source is added in an amount greater than 10 wt%, the carbon source may be added in an excessive amount, resulting in a thick carbon coating layer being formed on the surface of the active material particles. The dopant source may be mixed in an amount of 0.01 wt% to 2 wt% based on the total weight of the mixture. If the dopant source is added in an amount less than 0.01 wt%, the conductivity effect may be negligible. If the dopant source is added in an amount greater than 1 wt%, the coating uniformity inside the active material particles may be reduced.

[0099] 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.

[0100] In one embodiment of the present invention, the wet pulverization (S200) may be omitted. Specifically, in order to maximize the average particle size of the first particles PTC1 to be finally produced, the wet pulverization (S200) of the precursor particles may be omitted.

[0101] The solvent can be removed from the mixture to form a dried mixture (S300).

[0102] When producing the first particles PTC1 of FIG. 6 according to an embodiment of the present invention, forming the dried mixture can include subjecting the mixture to a direct evaporation method, such as static drying or spray drying.

[0103] 7, forming a dried mixture can include spray drying the mixture. Spray drying can be performed using commonly used spray drying equipment. For example, spray drying can be performed using at least one selected from an ultrasonic spray dryer, an air nozzle spray dryer, an ultrasonic nozzle spray dryer, a filter expansion droplet generator, and an electrostatic spray dryer.

[0104] The particles refined to the size of primary particles through the wet milling process can be agglomerated 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.

[0105] 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%.

[0106] If the solid content is less than 20%, the average particle size of the first particles PTC1 becomes small, which can cause problems such as low productivity, whereas if the solid content is more than 40%, it becomes difficult to control the average particle size of the first particles PTC1, which can cause large size deviations of the first particles PTC1.

[0107] 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.

[0108] In one embodiment, the input rate of spray drying may be 0.1 kg / min to 0.9 kg / min. The input rate of spray drying may be defined as the weight of solids in the spray liquid input per time. For example, if 1 kg of a spray liquid with a solids content of 20% is input per minute, the input rate may be 0.2 kg / min. In one embodiment, the input rate of spray drying according to the present invention may be approximately 0.5 kg / min.

[0109] In one embodiment, spray drying may be performed at a temperature of 100°C to 300°C. For example, spray drying may be performed 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.

[0110] The spray liquid may have an input pressure of 0.2 MPa to 0.7 MPa. For example, the spray liquid may have an input pressure of about 0.5 MPa.

[0111] When the input amount, input pressure, and temperature of the spray drying satisfy the above-described ranges, the first particles PTC1 can have a spherical shape and a desired porosity.

[0112] 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, water condensation 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.

[0113] 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 calcination process may be performed in two stages, and the temperature of the first calcination may be 300°C to 600°C. The calcination time may be 1 to 10 hours, or 2 to 6 hours. The temperature of the second calcination process may be 600°C to 800°C. The calcination time may be 4 to 20 hours, or 6 to 12 hours. The dried mixture may be calcined to form first particles PTC1 containing the compound of Formula 1. If the calcination temperature is less than 600°C, the reaction temperature may be too low, resulting in the formation of other phases other than a complete olivine phase, and the carbon coated on the particle surface may not crystallize and may exist in large amounts as amorphous carbon. If the temperature of the calcination process exceeds 800°C, the surface carbon of the particles is excessively crystallized to form a thick carbon coating layer, which may hinder the desorption / insertion of lithium ions, resulting in a deterioration of electrochemical performance.In addition, the particle size increases, which may increase resistance.

[0114] The fired first particles PTC1 may be subjected to a dry grinding process (S500). The fired mixture may be ground using an air jet mill or the like.

[0115] When producing the first particles PTC1 of FIG. 6 according to one embodiment of the present invention, the sintered mixture may be pulverized at a rotation speed of 7000 rpm or more. For example, the sintered mixture may be pulverized at a rotation speed of 7000 rpm to 1000 rpm, or 7500 rpm to 9000 rpm. As a result, the first particles PTC1 may have a single particle shape, as shown in FIG.

[0116] When preparing the first particles PTC1 of FIG. 7 according to another embodiment of the present invention, the sintered mixture may be pulverized at a rotational speed of 0 rpm to 7000 rpm. For example, the sintered mixture may be pulverized at a rotational speed of 4000 rpm to 7000 rpm, 4000 rpm to 6000 rpm, or 4500 rpm to 5000 rpm. Unlike the preparation of the positive electrode active material of FIG. 6, the pulverization step (S500) after sintering may be performed under relatively mild conditions. When preparing the positive electrode active material of FIG. 7, for example, the dry pulverization step (S500) may be omitted. When the rotational speed of the pulverization step (S500) satisfies the above-described range, the first particles PTC1 can maintain the shape of secondary particles. As a result, the first particles PTC1 can have the shape of secondary particles, as shown in FIG. 7.

[0117] In the method for manufacturing the first particles PTC1 shown in FIG. 7 according to an embodiment of the present invention, a carbon source is introduced into a manganese iron phosphate precursor to uniformly form a carbon coating layer on the surfaces of the primary particles. The primary particles are then closely aggregated by spray drying to form dense secondary spherical particles. As a result, the first particles PTC1 can include stable carbon coating layers on both the exterior and interior of the first particles PTC1, thereby having a relatively high carbon content. The appropriate carbon content of the first particles PTC1 shown in FIG. 7 can improve the conductivity of the positive electrode active material layer AML1.

[0118] 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. The sample is then burned at a combustion temperature of 1000°C. The burned gas is then reduced using reduced copper to form carbon dioxide. Carbon dioxide is detected using a TCD detector.

[0119] The carbon and Ti contents of the particles were measured by quantitative analysis using scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS) on the particle surface. Other methods for measuring the carbon and Ti contents include inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectroscopy (ICP-OES), in addition to SEM-EDS.

[0120] Examples of the present invention and comparative examples are described below. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0121] Example 1: Preparation of single particle positive electrode active material particles The mixture was prepared by adding Mn as an iron phosphate precursor. 0.6 Fe 0.4 The mixture was prepared by mixing PO4, lithium carbonate, and titanium dioxide. The mixture was mixed so that the molar ratio of Fe:Li:Ti was 1:1.03:0.003. The lithium carbonate was added at 10 wt% and the titanium dioxide was added at 3,000 ppm based on the total weight of the mixture. 10 wt% glucose was further added to the mixture. The mixture was wet-pulverized using a ball mill. The mixture was evaporated to dryness on a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours. The dried mixture was first baked at 450°C for 4 hours under a nitrogen atmosphere, and then secondarily baked at 700°C for 12 hours. The baked product was pulverized at a rotation speed of 8,000 rpm to obtain a single-particle cathode active material.

[0122] Example 2: Preparation of secondary particle-type positive electrode active material particles The mixture was prepared by adding Mn as an iron phosphate precursor. 0.6 Fe 0.4The cathode active material was prepared by mixing PO4, lithium carbonate, and titanium dioxide. The mixture was mixed so that the molar ratio of Fe:Li:Ti was 1:1.03:0.003. The lithium carbonate was added at 10 wt% and the titanium dioxide was added at 3,000 ppm based on the total weight of the mixture. 10 wt% glucose was also added to the mixture. The slurry mixture was spray-dried at a pressure of 0.5 MPa and a temperature of 230°C, followed by evaporation. The dried mixture was first baked at 450°C for 4 hours under a nitrogen atmosphere, and then second baked at 700°C for 12 hours to obtain a cathode active material in the form of secondary particles.

[0123] Example 3 A positive electrode active material was prepared in the same manner as in Example 1, except that titanium dioxide was added at 6,000 ppm during the preparation of the mixture.

[0124] Example 4 A positive electrode active material was prepared in the same manner as in Example 1, except that titanium dioxide was added at 500 ppm during the preparation of the mixture.

[0125] Example 5 A positive electrode active material was prepared in the same manner as in Example 1, except that the firing temperature was set to 600°C.

[0126] Example 6 A positive electrode active material was prepared in the same manner as in Example 1, except that the firing temperature was set to 800°C.

[0127] Comparative Example 1 A positive electrode active material was prepared in the same manner as in Example 1, except that the firing temperature during the secondary firing was set to 550°C.

[0128] Comparative Example 2 A positive electrode active material was prepared in the same manner as in Example 1, except that the firing temperature during the secondary firing was 850°C.

[0129] Comparative Example 3 A positive electrode active material was prepared in the same manner as in Example 1, except that the mixture was prepared without titanium dioxide.

[0130] Example 7 A positive electrode active material was prepared in the same manner as in Example 1, except that titanium dioxide was added at 10,000 ppm during the preparation of the mixture.

[0131] 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.

[0132] Lithium secondary battery manufacturing A 2032-type coin half-cell was fabricated using the prepared positive electrode and a lithium metal 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 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.

[0133] Evaluation example 1: Measurement of carbon content of active material The dopant (Ti) content and carbon content of the positive electrode active materials of the Examples and Comparative Examples were measured, and the results are shown in Table 1.

[0134] [Table 1]

[0135] Referring to Table 1, it can be seen that the positive electrode active materials according to the embodiments of the present invention have a carbon content of 1.1 wt % to 2.8 wt % and a Ti content of 500 ppm to 10,000 ppm.

[0136] Evaluation example 2: Analysis of the surface of the positive electrode active material The surface of the positive electrode active material was observed using a scanning electron microscope (SEM). An SEM image of the positive electrode active material prepared in Example 1 is shown in Figure 9a. An SEM image of the positive electrode active material prepared in Example 2 is shown in Figure 9b. Referring to Figure 9a, it can be seen that the positive electrode active material according to Example 1 of the present invention is in the form of a single particle, and the size of the primary particle constituting the single particle is about 100 nm.

[0137] 9b, the cathode active material according to Example 2 of the present invention can be seen to have a spherical secondary particle form formed by agglomeration of a plurality of primary particles. The average particle size of the cathode active material in the form of secondary particles can be seen to be about 9 μm, and the size of the primary particles constituting the secondary particles can be seen to be about 10 nm to about 400 nm.

[0138] Evaluation Example 3: Coating uniformity of positive electrode active material To confirm the coating distribution within the positive electrode active material, a transmission electron microscope (TEM) was used for observation. The TEM image of the positive electrode active material prepared in Example 1 is shown in Figure 10a. The TEM image of the positive electrode active material prepared in Comparative Example 2 is shown in Figure 10b.

[0139] Referring to FIG. 10a, it can be seen that the carbon coating is uniformly distributed on the surface and inside of the particles of the positive electrode active material according to the embodiment of the present invention.

[0140] 10b, the positive electrode active material according to the comparative example of the present invention contains an excessive amount of carbon, resulting in the formation of a thick carbon coating layer on the particle surface. This carbon coating layer increases the specific surface area of ​​the positive electrode active material particles, which can hinder lithium migration due to increased resistance.

[0141] Evaluation example 4: Raman spectroscopy Raman spectroscopy was performed on the positive electrode active materials produced in the examples and comparative examples. The Raman spectroscopy was performed using a Raman spectrometer (LabRab HR evolution UV-VIS-NIR, manufactured by HORIBA, Ltd.) to measure the Raman spectrum of the positive electrode active material.

[0142] The results are shown in Table 2.

[0143] [Table 2]

[0144] Referring to Table 2, the Raman spectrum obtained by Raman spectroscopy shows that the G band (1594 cm -1 ) and D band (1338cm -1 ) value can be checked.

[0145] Referring to Table 2, the positive electrode active materials according to the embodiments of the present invention have a Raman spectrum ratio (I D / I G ) can be confirmed to be between 0.9 and 1.3.

[0146] Evaluation example 4: Battery characteristic evaluation The characteristics of the lithium secondary batteries manufactured using the positive electrode active materials of the Examples and Comparative Examples were evaluated.

[0147] The lithium secondary battery was initially charged at a constant current (0.2 C) and a constant voltage (4.45 V), and after a 10-minute rest, discharged to 2.5 V at a constant current (0.2 C) to perform the initial charge-discharge. Thereafter, the battery was charged and discharged once at 0.2 C / 0.2 C at -20°C. The battery characteristic evaluation results are shown in Table 3 below.

[0148] [Table 3]

[0149] Referring to Table 3, it can be seen that the secondary batteries according to the embodiments of the present invention have higher capacities than the secondary batteries according to the comparative examples. It can be seen that the secondary batteries according to the embodiments of the present invention have higher average voltages than the secondary batteries according to the comparative examples. It can also be seen that the secondary batteries according to the embodiments of the present invention exhibit better charge / discharge efficiency than the secondary batteries according to the comparative examples.

[0150] Therefore, the carbon content of the positive electrode active material particles is in the range of 1.1 wt% to 2.8 wt%, the Ti content of the positive electrode active material particles is in the range of 500 ppm to 10,000 ppm, and the ratio of the Raman spectrum obtained by Raman spectroscopy (I D / I G ) is in the range of 0.9 to 1.3, carbon is uniformly distributed inside with an optimal content and thickness, thereby significantly improving the conductivity and electrochemical properties of the secondary battery.

[0151] 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. The present invention relates to a method for producing a granular material comprising: a first particle having a first average particle size, the first particle comprising a compound represented by Chemical Formula 1: Among the Raman spectra obtained by Raman spectroscopy, 1590 ± 10 cm -1 The intensity of the G peak (I G ) 1340±10cm -1 The intensity of the D peak (I D ) ratio (I D / I G ) is 0.9 to 1.3: [Chemical formula 1] Li a1 Mn x Fe 1-x M y PO 4 In the formula 1, 0.8≦a1≦1.2, 0.2<x<0.8, 0.0001≦y≦0.05, and M is at least one element selected from the group consisting of Ti, Al, Mg, Zr, V, Zn, Nb, K, Y, B, and Cu.

2. The doping material M in the first particles includes Ti; 2. The positive electrode active material of claim 1, wherein the content of the doping material is 500 ppm to 10,000 ppm.

3. the first particles include a coating layer containing carbon; The positive electrode active material of claim 1 , wherein the carbon content in the first particles is 1.1 wt % to 2.8 wt %.

4. The first particle is a single particle, the first average particle size is 0.2 μm to 2.5 μm; The positive electrode active material according to claim 1 .

5. the first particles include at least one primary particle; The size of the primary particles is 10 nm to 200 nm. The positive electrode active material according to claim 4 .

6. The first particles include a plurality of primary particles aggregated together, The cathode active material of claim 1 , wherein the average particle size of the primary particles is 10 nm to 400 nm.

7. the first particles are spherical secondary particles of a positive electrode active material, The positive electrode active material of claim 6 , wherein the first average particle size is 0.2 μm to 20 μm.

8. 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.

9. The positive electrode active material of claim 6 , wherein the porosity of the first particles is 20% to 60%.

10. The positive active material of claim 5 , wherein the first particles have a Span value of 0.5 to 7 as analyzed by a particle size analyzer.

11. combining an iron phosphate precursor, a lithium source, a carbon source, and a dopant source to form a mixture; drying the mixture; and calcining the dried mixture to produce first particles; The first particles include a compound represented by the following Chemical Formula 1: [Chemical formula 1] Li a1 Mn x Fe 1-x M y P O4 In the formula 1, 0.8≦a1≦1.2, 0.2<x<0.8, 0.0001≦y≦0.05, and M is at least one element selected from the group consisting of Ti, Al, Mg, Zr, V, Zn, Nb, K, Y, B, and Cu.

12. the dopant source comprises a titanium compound; The method for producing a positive electrode active material according to claim 11 .

13. The carbon source is mixed in an amount of 1 wt % to 20 wt % based on the total weight of the mixture; The dopant source is mixed in an amount of 0.01 wt % to 1 wt % based on the total weight of the mixture. The method for producing a positive electrode active material according to claim 11 .

14. Drying the mixture is carried out by spray drying. The method for producing a positive electrode active material according to claim 11 .

15. 15. The method of claim 14, wherein the mixture used as the 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.

16. The method of claim 14 , wherein the spray drying comprises agglomerating particles in the first mixture to form secondary particles.

17. The method for producing a positive electrode active material according to claim 14, wherein the spray drying is performed at a temperature of 100°C to 300°C.

18. 15. The method of claim 14, wherein the spraying pressure of the spraying solution is 0.2 MPa to 0.7 MPa, and the flow rate is 30 ml / min to 80 ml / min.

19. The method for producing a positive electrode active material according to claim 11, wherein the calcination is performed once or twice at a temperature of 300 to 800°C.

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

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