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 for a lithium secondary battery, a manufacturing method for the same, and a lithium secondary battery including the same.SOLUTION: A positive electrode active material includes a first particle containing a compound expressed by Chemical Formula 1 and having a first average particle diameter and a second particle containing a compound expressed by Chemical Formula 2 and having a second average particle diameter that is smaller than the first average particle diameter. The content amount of the first particle is more than or equal to that of the second particle. [Chemical Formula 1] Lia1Fex1B1y1 PO4-b1, in which 0.8≤a1≤1.2, 0.950≤x1≤0.999, 0.001≤y1≤0.05, 0≤b1≤0.05, and x1+y1=1 are satisfied. [Chemical Formula 2] Lia2Fex2B2y2 PO4-b2, in which 0.8≤a2≤1.2, 0.950≤x2≤0.999, 0.001≤y2≤0.05, 0≤b2≤0.05, and x2+y2=1 are satisfied. Each of B1 in Chemical Formula 1 and B2 in Chemical Formula 2 is at least one element selected from the group consisting of Ti and Mg.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 replenishment of battery-powered electronic devices such as mobile phones, laptop computers, and electric vehicles, the demand for secondary batteries with high energy density and high capacity has been rapidly increasing. Accordingly, research and development to improve the performance of lithium secondary batteries has been actively carried out.

[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] Chinese Patent No. 113942990 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 capacity, excellent low-temperature characteristics, long life, and high energy density.

[0006] Another object of the present invention is to provide a lithium secondary battery having high capacity, excellent low-temperature characteristics, long life, and high energy density. [Means for solving the problem]

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

[0008] [C1] Li a1 Fe x1 B1 y1 PO 4-b1 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;

[0009] [C2] Li a2 Fe x2 B2 y2 PO 4-b2 In the above Chemical Formula 2, 0.8≦a2≦1.2, 0.950≦x2≦0.999, 0.001≦y2≦0.05, 0≦b2≦0.05, and x2+y2=1; B1 in Chemical Formula 1 and B2 in Chemical Formula 2 each represent at least one element selected from the group consisting of Ti and Mg.

[0010] According to another aspect of the present invention, a method for preparing a positive electrode active material may include preparing first particles having a first average particle size, preparing second particles having a second average particle size smaller than the first average particle size, and mixing the first particles with the second particles. Preparing the first particles may include mixing a first iron phosphate precursor, a first lithium source, a first carbon source, and a first dopant source to form a first mixture, drying the first mixture by spray drying, and calcining the dried first mixture. Preparing the second particles may include mixing a second iron phosphate precursor, a second lithium source, a second carbon source, and a second dopant source to form a second mixture, wet-milling the second mixture, drying the second mixture, and calcining the dried second mixture. The first particles may be mixed so that the content of the first particles is equal to or greater than the content of the second particles.

[0011] According to yet another aspect of the present invention, a lithium secondary battery can include the above-described positive electrode active material. [Effects of the Invention]

[0012] The positive electrode active material according to the present invention may include first particles, which are secondary particles, and second particles, which are single particles. This improves the electrical conductivity, mix density, and binding strength with the current collector of the positive electrode active material layer, and reduces the binder content of the positive electrode active material layer. The lithium secondary battery according to the present invention may have relatively high capacity, long life, and high energy density, and may have improved low-temperature characteristics. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a conceptual diagram showing 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 have a pouch-type battery configuration. [Figure 5] 1 is a schematic diagram showing a lithium secondary battery according to one embodiment, which can be said to have a pouch-type battery configuration. [Figure 6] 2 is an enlarged view of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. FIG. [Figure 7] 1 is a flowchart illustrating a method for manufacturing a positive electrode active material according to an embodiment of the present invention. [Figure 8] 1 is a graph showing mix density values ​​according to press gaps in Examples 1 and 3-1 to 3-5 of the present invention. [Figure 9a] 1 is an SEM image of the positive electrode active material of Example 1 of the present invention. [Figure 9b] 1 is an SEM image of the positive electrode active material of Example 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] 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.

[0015] In this specification, when a component is referred to as being on another component, it means that the component may be formed directly on the other component, or that a third component may be interposed between them. However, the present invention is not limited to the embodiments disclosed below, and may be embodied in various forms and may undergo various modifications. The description of the present embodiments is provided solely to ensure complete disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0016] Unless otherwise specified herein, the singular can also include the plural. Furthermore, unless otherwise specified, "A or B" can mean "including A, including B, or including A and B." As used herein, "comprises" and / or "comprising" does not exclude the presence or addition of one or more other elements to the referenced element.

[0017] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0018] Unless otherwise defined herein, particle size refers to the average particle size. Furthermore, particle size refers to the average particle size (D50), which refers to the diameter of particles with a cumulative volume of 50% in a particle size distribution. The average particle size (D50) can be measured by methods well known to those skilled in the art, such as using a particle size analyzer or a transmission electron microscope (TEM) or scanning electron microscope (SEM) image. Alternatively, the average particle size (D50) can be measured using a measuring device that uses dynamic light scattering, and data analysis can be performed to count the number of particles in each particle size range, after which the average particle size (D50) can be calculated. Alternatively, the average particle size (D50) can be measured using a laser diffraction method. More specifically, when measuring by the laser diffraction method, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT3000), and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W. The average particle size (D50) based on 50% of the particle size distribution in the measuring device can then be calculated.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] The dry binder is a fiberizable polymeric material, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, ethylene oxide, or combinations thereof.

[0030] 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 mixtures thereof.

[0031] The current collector COL2 may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0032] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, a lithium metal alloy, a material capable of doping or dedoping lithium, or a transition metal oxide.

[0033] The material capable of reversibly inserting / extracting lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite, such as amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite. Examples of amorphous carbon include soft or hard carbon, mesophase pitch carbide, and calcined coke.

[0034] 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.

[0035] As a substance that can be doped or undoped with lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (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 combinations thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or combinations thereof.

[0036] The silicon-carbon composite can be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite can be in a form in which silicon particles are coated with amorphous carbon on the surface of the silicon particles. For example, it can include secondary particles (cores) combined with primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon can also be located between the primary silicon particles, for example, the primary silicon particles can be coated with amorphous carbon. The secondary particles can be dispersed and present in an amorphous carbon matrix.

[0037] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite can include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core.

[0038] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0043] 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.

[0044] 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.

[0045] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0046] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0047] The non-aqueous organic solvent can be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, a non-quantum solvent, or a combination thereof.

[0048] 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).

[0049] 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.

[0050] 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.

[0051] The non-aqueous organic solvents may be used alone or in combination of two or more.

[0052] 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.

[0053] 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).

[0054] 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 one 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 5, 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.

[0055] 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.

[0056] 6 is an enlarged view of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. Referring to FIG. 6, as described above, the positive electrode active material layer AML1 (see FIG. 1) may include first particles PTC1, second particles PTC2, a conductive material CDM, and a binder BND. A plurality of first particles PTC1 and a plurality of second particles PTC2 may constitute a positive electrode active material according to an embodiment of the present invention.

[0057] The positive electrode active material layer AML1 may further include an additive that can function as a sacrificial positive electrode.

[0058] The content of the positive electrode active materials (PTC1 and PTC2) in the positive electrode active material layer AML1 may be 90 wt % to 99.5 wt % relative to 100 wt % of the positive electrode active material layer AML1. The content of the binder BND and the conductive material CDM may be 0.5 wt % to 5 wt % relative to 100 wt % of the positive electrode active material layer AML1.

[0059] The binder BND can bind the first particles PTC1, the second particles PTC2, and the conductive material CDM to one another. As an example, the binder BND can include at least one selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon, but is not limited thereto.

[0060] The conductive material CDM can be used to improve the conductivity of the positive electrode active material layer AML1. Any conductive material that does not cause a chemical change in the positive electrode active material layer AML1 can be used as the conductive material CDM. For example, the conductive material CDM can include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, and the like; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0061] The first particles PTC1 and the second particles PTC2 will be described in more detail below.

[0062] 1st particle PTC1 The first particles PTC1 may have a polycrystalline form and may include secondary particles formed by agglomeration of at least two or more first primary particles (NNPs). In other words, one first particle PTC1 may include a plurality of first primary particles (NNPs) agglomerated together. The first particles PTC1 may have a spherical or elliptical shape.

[0063] As an 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 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 of the first particles PTC1 and may improve electrical conductivity.

[0064] The coating layer may further include at least one selected from the group consisting of a titanium-containing compound and a magnesium-containing compound. Metal-containing compounds such as titanium-containing compounds and magnesium-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.

[0065] As an example, the first particle PTC1 may further include a grain boundary coating layer on the surface of each of the first primary particles (NNPs). 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 first primary particles (NNPs) 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 and a magnesium-containing compound.

[0066] 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.

[0067] 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.

[0068] The average particle size of the first particles PTC1 may be 2 μm to 15 μm, 3 μm to 12 μm, or 3 μm to 10 μm. The average particle size of the first particles PTC1 may be larger than the average particle size of the second particles PTC2 described below. In one embodiment, the average particle size may be measured using a particle size analyzer. The average particle size may refer to the diameter of particles whose cumulative volume is 50% by volume (D50) in the particle size distribution.

[0069] The size of the first primary particles (NNP) of the first particles PTC1 may be 10 nm to 400 nm, 20 nm to 300 nm, or 50 nm to 200 nm. In one embodiment, the size of the first primary particles (NNP) may refer to the diameter measured by randomly selecting approximately 30 first primary particles (NNP) in an electron microscope photograph of the positive electrode active material. The size of the first primary particles (NNP) may be uniform.

[0070] The maximum particle size of the first particle PTC1 (D max ) can be between 10 μm and 30 μm.

[0071] The first particles PTC1 may include an olivine-based lithium compound represented by the following Chemical Formula 1.

[0072] [C1] Li a1 Fe x1B1 y1 PO 4-b1 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, and in Chemical Formula 1, B1 may be at least one element selected from the group consisting of Ti and Mg. B1 may be a dopant doped into the first particle PTC1.

[0073] In the first particle PTC1, B1 may be Ti and Mg. When the first particle PTC1 is doped with Ti, it can have the effect of controlling the growth of the first primary particles (NNPs) of the first particle PTC1, and as a result, the size of the first primary particles (NNPs) of the first particle PTC1 can be made more uniform and smaller. In the first particle PTC1, the atomic fraction of Ti may be greater than the atomic fraction of Mg. The first particle PTC1 may satisfy the following mathematical formula 1.

[0074]

number

[0075] The first particles PTC1 may further contain carbon derived from the coating layer and / or the grain boundary coating layer. The carbon element content in the first particles PTC1 may be 0.5 wt % to 10 wt %, 1 wt % to 3 wt %, or 1.5 wt % to 2.5 wt %.

[0076] The first particles PTC1 may have a spherical shape formed by the aggregation of nano-sized first primary particles (NNPs). The first particles PTC1 may exhibit the following characteristics due to the first primary particles (NNPs) being closely aggregated together: The first particles PTC1 may have a spherical or elliptical shape. The average particle size (D50) of the first particles PTC1 may be 2 μm to 15 μm. The porosity of the first particles PTC1 may be about 20% to about 40%. The Span value of the first particles PTC1 analyzed using a particle size analyzer may be 0.3 to 0.75.

[0077] When the first particles PTC1 are spherical and comprise nano-sized agglomerates of first primary particles (NNPs), the amount of binder BND required to attach the first particles PTC1 to the current collector COL1 (see FIG. 1) may be relatively small. For example, the amount of binder BND required to attach the first particles PTC1 to the current collector COL1 (see FIG. 1) may be less than the amount of binder BND required to attach the second particles PTC2 to the current collector COL1 (see FIG. 1). This is because the first average particle size is relatively larger than the second average particle size, thereby increasing the adhesive strength with the current collector COL1 (see FIG. 1). For example, the content of binder BND may be 0.5 wt % to 2 wt % relative to 100 wt % of the positive electrode active material layer AML1.

[0078] 2nd particle PTC2 The second particles PTC2 may have a single particle form. In this specification, a single particle may refer to a single particle 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 are morphologically present in an independent phase and are not aggregated with each other. 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.

[0079] The second particles PTC2 may be a nano-shaped cathode active material. The second particles PTC2 may include at least one second primary particle. As an example, the second primary particles may be agglomerated to have a particle shape similar to that of the first particles PTC1. The second particles PTC2 may not be spherical like the first particles PTC1, even if the second primary particles are agglomerated. That is, the second particles PTC2 may have a random shape.

[0080] The second particles PTC2 may be provided in various sizes. For example, the average particle size of the second particles PTC2 may be 0.1 μm to 2 μm, or about 1 μm. The minimum particle size of the second particles PTC2, i.e., the size of the second primary particles, may be 100 nm to 500 nm, or 200 nm to 300 nm.

[0081] In one embodiment, the minimum particle size, i.e., the size of the second primary particles, may refer to the diameter measured by randomly selecting about 30 second primary particles in an electron microscope photograph of the second particles PTC2. In one embodiment, the size of the second primary particles may be larger than the size of the first primary particles (NNP).

[0082] The porosity of the second particles PTC2 may be less than 30%. The Span value of the second particles PTC2, as analyzed by a particle size analyzer, may be outside the range of 0.3 to 0.75.

[0083] In one embodiment, the second particles PTC2 may include a coating layer on their surfaces. The coating layer may cover the entire surface of the second particles PTC2 or a portion of the surface of the second particles PTC2. For example, the coating layer may include carbon and / or a carbon-containing compound. The coating layer may further include at least one selected from the group consisting of a titanium-containing compound and a magnesium-containing compound. Metal-containing compounds such as titanium-containing compounds and magnesium-containing compounds may be, for example, metal oxides, metal hydroxides, metal carbonates, composites thereof, or mixtures thereof. The metal-containing compound may further include other metals or non-metal elements. For example, the metal-containing compound may further include lithium. The coating layer may improve the structural stability and electrical conductivity of the second particles PTC2.

[0084] The second particles PTC2 may include an olivine-based lithium compound represented by Chemical Formula 2.

[0085] [C2] Lia2 Fe x2 B2 y2 PO 4-b2 In Chemical Formula 2, 0.8≦a2≦1.2, 0.950≦x2≦0.999, 0.001≦y2≦0.05, 0≦b2≦0.05, and x2+y2=1, and in Chemical Formula 2, B2 is at least one element selected from the group consisting of Ti and Mg.

[0086] The second particles PTC2 may further contain carbon derived from the coating layer. The carbon element content in the second particles PTC2 may be 0.5 wt % to 5 wt %, 0.5 wt % to 3 wt %, or 0.5 wt % to 2 wt %. The carbon content of the second particles PTC2 may be lower than the carbon content of the first particles PTC1. This is because the second particles PTC2 are single particles and therefore it is difficult to smoothly form a coating layer on them compared to the first particles PTC1, which are secondary particles.

[0087] When the second particles PTC2 are single particles, the amount of binder BND required to attach the second particles PTC2 to the current collector COL1 (see FIG. 1) may be relatively large. For example, the amount of binder BND required to attach the second particles PTC2 to the current collector COL1 (see FIG. 1) may be greater than the amount of binder BND required to attach the first particles PTC1 to the current collector COL1 (see FIG. 1). This is because the second average particle size is relatively smaller than the first average particle size. For example, the content of binder BND may be 2 wt % to 5 wt % relative to 100 wt % of the positive electrode active material layer AML1.

[0088] Referring again to Figure 6, a cathode active material according to an embodiment of the present invention will be described in more detail. The cathode active material of the present invention may include first particles PTC1 and second particles PTC2. The mixing weight ratio of the first particles PTC1 to the second particles PTC2 in the cathode active material may be 50:50 to 99:1, 50:50 to 90:10, or 50:50 to 70:30. The content of the first particles PTC1 in the cathode active material may be the same as or greater than the content of the second particles PTC2.

[0089] The cathode active material of the present invention can improve the mixture density, capacity, and energy density by mixing the first particles PTC1, which are secondary particles, and the second particles PTC2, which are single particles. In one embodiment, the cathode active material of the present invention can have a mixture density of 2.0 g / cc to 3.0 g / cc. A lithium secondary battery including the cathode active material of the present invention can have improved low-temperature characteristics.

[0090] Because the second particles PTC2, which are single particles, have an extremely small average particle size, a large amount of binder BND may be required to adhere the second particles PTC2 to the current collector COL1 (see FIG. 1). The cathode active material of the present invention includes not only the second particles PTC2 but also the first particles PTC1, which have a large average particle size, thereby enabling the cathode active material layer AML1 (see FIG. 1) to be smoothly adhered to the current collector COL1. That is, the first particles PTC1 can reduce the amount of binder BND in the cathode active material layer AML1.

[0091] In one embodiment, a positive electrode active material slurry including the positive electrode active material according to the present invention can be prepared. The positive electrode active material slurry can include solids and a solvent (e.g., N-methylpyrrolidone). The solids can include first particles PTC1, second particles PTC2, a conductive material CDM, and a binder BND. By further including the first particles PTC1, which are secondary particles, the positive electrode active material slurry can have a lower viscosity than a slurry including only the second particles PTC2.

[0092] In one embodiment, the viscosity of the positive electrode active material slurry according to the present invention 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. By having a viscosity within this range, the positive electrode active material slurry can be smoothly applied to the current collector (COL1 in FIG. 1).

[0093] The positive electrode active material slurry according to the present invention includes the first particles PTC1 as described above, thereby increasing the viscosity of the slurry and providing a desired slurry viscosity even with a small amount of solvent. In other words, the positive electrode active material slurry according to the present invention includes the first particles PTC1, thereby increasing the solid content of the slurry and simultaneously enabling the slurry to be smoothly applied to a current collector.

[0094] An increase in the solids content in the positive electrode active material slurry can increase the binding strength between the positive electrode active material layer (AML1, FIG. 1) and the current collector (COL1, FIG. 1). This may be because as the amount of applied positive electrode active material increases, the interaction between the positive electrode active material and the current collector (COL1, FIG. 1) also increases proportionally. In summary, the positive electrode active material slurry according to the present invention can be more smoothly applied to the current collector than a slurry containing only second particles PTC2, and at the same time, the binding strength between the positive electrode active material layer and the current collector can also be increased.

[0095] The cathode active material of the present invention may be bimodal, including secondary particles (e.g., PTC1) and monoparticles (e.g., PTC2) having different average particle sizes. The monoparticles fill the voids between the secondary particles, thereby improving the packing density of the cathode active material layer AML1 (see FIG. 1). In other words, the cathode active material layer AML1 according to the present invention may have a relatively high energy density per unit volume.

[0096] A lithium secondary battery including the positive electrode active material of the present invention can have improved low-temperature characteristics. In one embodiment, the capacity at −20° C. relative to the initial discharge amount at 25° C. (capacity at −20° C. / initial discharge amount at 25° C.) may be 40% or more. For example, the capacity at −20° C. relative to the initial discharge amount at 25° C. (capacity at −20° C. / initial discharge amount at 25° C.) of the lithium secondary battery of the present invention may be 40% to 100%, 40% to 70%, or 40% to 60%.

[0097] Method for producing positive electrode active material 7 is a flowchart illustrating a method for manufacturing a positive electrode active material according to an embodiment of the present invention. The method for manufacturing the first particles PTC1 according to an embodiment of the present invention will be described in more detail with reference to FIG.

[0098] The iron phosphate precursor, lithium source, carbon source, and dopant source can be mixed in a solvent (S100). For example, the solvent can be water, ethanol, or the like. The iron phosphate precursor can be a compound containing both iron (Fe) and phosphorus (P), or a mixture of an iron (Fe)-containing compound and a phosphorus (P)-containing compound. For example, the iron phosphate precursor can include FePO4·H2O or a mixture of FeSO4 and H3PO4.

[0099] 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.

[0100] 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.

[0101] The dopant source may include an oxide containing a dopant metal and / or a chloride containing a dopant metal, for example, the dopant source may include at least one selected from the group consisting of titanium oxide and magnesium oxide.

[0102] The mixture may be subjected to wet milling (S200). A typical wet mill capable of controlling the temperature may be used for wet milling. Specifically, at least one selected from a bead mill, a ball mill, an attrition mill, an apex mill, a super mill, and a basket mill may be used for wet milling. Through the wet milling process, particles in the mixture may be pulverized to a fine size.

[0103] In one embodiment of the present invention, the wet-milling step (S200) may be omitted. Specifically, in order to maximize the average particle size of the first particles PTC1 that are finally produced, the wet-milling step (S200) of the precursor particles may be omitted.

[0104] The solvent can be removed from the mixture to form a dried mixture. In one embodiment of the present invention, forming the dried mixture can include spray drying the mixture (S300). The spray drying can be performed using commonly used spray drying equipment. For example, the spray drying can be performed using at least one selected from an ultrasonic spray dryer, an air nozzle spray dryer, an ultrasonic nozzle spray dryer, a filter expansion droplet generator, and an electrostatic spray dryer.

[0105] The particles refined to the size of first 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.

[0106] As an example, 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. As an example, the spray liquid may have a solid content of approximately 30% by weight.

[0107] If the solid content is less than 20%, the average particle size of the first particles PTC1 may become small, which may result in problems such as low productivity, whereas if the solid content is more than 40%, it may become difficult to control the average particle size of the first particles PTC1, which may result in large size deviations of the first particles PTC1.

[0108] 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.

[0109] In one example, spray drying can be performed at a temperature of 100°C to 300°C. The propellant gas (e.g., air) used in spray drying can be introduced at a first temperature and discharged at a second temperature. For example, the first temperature can be 200°C to 250°C. The second temperature can be 80°C to 150°C.

[0110] The flow rate of the spray liquid 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 liquid may be 0.3 MPa to 0.7 MPa. For example, the input pressure of the spray liquid may be about 0.5 MPa.

[0111] The dried mixture may be calcined under an inert atmosphere (S400). The inert atmosphere may be a nitrogen atmosphere and / or an argon atmosphere. The temperature of the calcination process may be 500°C to 1000°C, or 600°C to 800°C. The calcination process may be performed for 4 hours to 20 hours, or 6 hours to 12 hours. By calcining the dried mixture, first particles PTC1 containing the compound of Formula 1 may be formed.

[0112] A dry-pulverization process may be performed on the sintered first particles PTC1 (S500). The sintered mixture may be pulverized using an air jet mill or the like. The rotation speed of the dry-pulverization may be 0 rpm to 7000 rpm. When dry-pulverization is performed within this rotation speed range, the first particles PTC1 may have a secondary particle form. The dry-pulverization process for the first particles PTC1 may be omitted.

[0113] In a method for manufacturing first particles PTC1 according to an embodiment of the present invention, a carbon source is introduced into an iron phosphate precursor to uniformly form a carbon coating layer on the surface of the first primary particles. The first primary particles are then closely aggregated through 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 high carbon content of the first particles PTC1 can improve the conductivity of the positive electrode active material layer AML1.

[0114] The method for producing the second particles PTC2 according to the embodiment of the present invention will be described in more detail.

[0115] The iron phosphate precursor, lithium source, carbon source, and dopant source can be mixed in a solvent. For example, the solvent can be water, ethanol, or the like. The iron phosphate precursor can be a compound containing both iron (Fe) and phosphorus (P), or a mixture of an iron (Fe)-containing compound and a phosphorus (P)-containing compound. For example, the iron phosphate precursor can include FePO4·H2O or a mixture of FeSO4 and H3PO4.

[0116] The lithium source, carbon source and dopant source may be the same as or similar to those in the method for producing the first particles PTC1 described above.

[0117] The mixture can be subjected to wet-milling, and the wet-milling process can be the same as or similar to the method for producing the first particles PTC1 described above.

[0118] The solvent can be removed from the mixture to form a dried mixture. Forming the dried mixture can include subjecting the mixture to direct evaporation. For example, direct evaporation can include static drying or spray drying. To form the second particles PTC2 as single particles, static drying is preferably used.

[0119] The dried mixture may be calcined under an inert atmosphere. The calcination conditions may be the same as or similar to those of the method for producing the first particles PTC1. By calcining the dried mixture, the second particles PTC2 containing the compound of Formula 2 may be formed.

[0120] The calcined second particles PTC2 may be subjected to a dry-milling process. The rotation speed of the dry-milling process may be 7,000 rpm to 10,000 rpm. When dry-milling is performed within this rotation speed range, the second particles PTC2 may have a single particle form. Meanwhile, in the case of the first particles PTC1 described above, the dry-milling process may be omitted.

[0121] The prepared first particles PTC1 and second particles PTC2 are mixed in an appropriate ratio to form a positive electrode active material according to an embodiment of the present invention.

[0122] 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.

[0123] In the present embodiment, 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).

[0124] 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.

[0125] Example 1: Preparation of primary particles in the form of secondary particles Iron phosphate precursor Fe1PO4·H2O, lithium carbonate, and titanium dioxide were mixed in a molar ratio of Fe:Li:T = 1:1.03:0.004. 10 wt% glucose was further added to the mixture. The slurry mixture was spray-dried at a spray pressure of 0.5 MPa and a temperature of 230°C, followed by evaporation. The dried mixture was calcined at 750°C for 10 hours under a nitrogen atmosphere to obtain primary particles in the form of secondary particles. The average particle size of the primary particles was 3 μm to 10 μm. The size of the primary particles was 50 nm to 200 nm.

[0126] Example 2: Preparation of single particle first particles Iron phosphate precursor Fe1PO4·H2O, lithium carbonate, and titanium dioxide were mixed in a molar ratio of Fe:Li:T = 1:1.03:0.004. 10% by weight of glucose was further added to the mixture. The mixture was subjected to a wet grinding process using a ball mill. The mixture was evaporated to dryness in a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours. The dried mixture was calcined at 650°C for 10 hours under a nitrogen atmosphere. The calcined product was pulverized at a rotation speed of 8000 rpm to obtain secondary particles in the form of single particles. The average particle size of the secondary particles was 0.1 μm to 2 μm. The size of the secondary primary particles of the secondary particles was 200 nm to 300 nm. Example 3-1: Preparation of a mixture of first particles and second particles The first particles of Example 1 and the second particles of Example 2 were mixed in a mass ratio of 90:10 to prepare a positive electrode active material.

[0127] Example 3-2: Preparation of a mixture of first particles and second particles The first particles of Example 1 and the second particles of Example 2 were mixed in a mass ratio of 80:20 to prepare a positive electrode active material.

[0128] Example 3-3: Preparation of a mixture of first particles and second particles The first particles of Example 1 and the second particles of Example 2 were mixed in a mass ratio of 70:30 to prepare a positive electrode active material.

[0129] Example 3-4: Preparation of a mixture of first particles and second particles The first particles of Example 1 and the second particles of Example 2 were mixed in a mass ratio of 60:40 to prepare a positive electrode active material.

[0130] Examples 3-5: Preparation of a mixture of first particles and second particles The first particles of Example 1 and the second particles of Example 2 were mixed in a mass ratio of 50:50 to prepare a positive electrode active material.

[0131] Cathode manufacturing In Example 1, 97 wt% of the final positive electrode active material, 1.5 wt% of polyvinylidene fluoride binder, and 1.5 wt% of carbon black conductive material were mixed in N-methylpyrrolidone solvent to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to an aluminum current collector, dried, and then rolled to prepare a positive electrode.

[0132] In Example 2, a positive electrode was prepared in the same manner as in Example 1, except that 94 wt % of the final positive electrode active material, 3 wt % of polyvinylidene fluoride binder, and 3 wt % of carbon black conductive material were mixed in N-methylpyrrolidone solvent to prepare a positive electrode active material slurry.

[0133] In Example 3-1, a positive electrode was prepared in the same manner as in Example 1, except that 96.8 wt % of the final positive electrode active material, 1.6 wt % of polyvinylidene fluoride binder, and 1.6 wt % of carbon black conductive material were mixed in N-methylpyrrolidone solvent to prepare a positive electrode active material slurry.

[0134] In Example 3-2, a positive electrode was prepared in the same manner as in Example 1, except that 96.6 wt % of the final positive electrode active material, 1.7 wt % of polyvinylidene fluoride binder, and 1.7 wt % of carbon black conductive material were mixed in N-methylpyrrolidone solvent to prepare a positive electrode active material slurry.

[0135] In Example 3-3, a positive electrode was prepared in the same manner as in Example 1, except that 96.4 wt % of the final positive electrode active material, 1.8 wt % of polyvinylidene fluoride binder, and 1.8 wt % of carbon black conductive material were mixed in N-methylpyrrolidone solvent to prepare a positive electrode active material slurry.

[0136] In Example 3-4, a positive electrode was prepared in the same manner as in Example 1, except that 96.2 wt % of the final positive electrode active material, 1.9 wt % of polyvinylidene fluoride binder, and 1.9 wt % of carbon black conductive material were mixed in N-methylpyrrolidone solvent to prepare a positive electrode active material slurry.

[0137] In Examples 3-5, a positive electrode was prepared in the same manner as in Example 1, except that 96 wt % of the final positive electrode active material, 2 wt % of polyvinylidene fluoride binder, and 2 wt % of carbon black conductive material were mixed in N-methylpyrrolidone solvent to prepare a positive electrode active material slurry.

[0138] Lithium secondary battery manufacturing A 2032-type coin-shaped half cell was fabricated using the prepared positive electrode and a lithium metal counter electrode. A separator (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 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.

[0139] 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 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 first particles according to the present invention are in the form of spherical secondary particles formed by agglomeration of a plurality of first primary particles. Referring to Figure 9b, it can be seen that the second particles according to the present invention are in the form of fine single particles of nano-size.

[0140] Evaluation Example 2: Active Material Evaluation I The pellet density (PD) and carbon content of the positive electrode active materials of Examples 1, 2, 3-1 to 3-5 were measured. The results are shown in Table 1.

[0141] The positive electrode active materials of Examples 2, 3-1 to 3-5 were rolled in a press at press gaps of 0 μm to 50 μm, and the pellet density (PD) was measured. The results are shown in Figure 8. The press gap refers to the distance applied during compression. For example, a press gap of 10 μm means that pressure is applied until the distance between the end plate of the press and the plate on which the positive electrode active material slurry is placed becomes 10 μm.

[0142] [Table 1]

[0143] Referring to Table 1, it can be seen that the cathode active materials according to Examples 3-1 to 3-5 of the present invention have superior composite densities compared to the cathode active material of Example 2. It can also be seen that the cathode active materials according to Examples 3-1 to 3-5 of the present invention have higher carbon contents compared to the cathode active material of Example 2.

[0144] Evaluation Example 3: Active Material Evaluation II The weight ratios of the positive electrode active materials, binders, and conductive materials used in preparing the positive electrodes including the positive electrode active materials of Examples 1, 2, 3-1 to 3-5 are shown in Table 2. The binder was added in an optimal amount for each Example to ensure sufficient electrode plate binding strength for smooth preparation of the positive electrodes.

[0145] [Table 2]

[0146] Referring to Table 2, it can be seen that a smaller amount of binder is required when manufacturing a cathode including the cathode active materials according to Examples 3-1 to 3-5 of the present invention compared to Example 2. That is, it can be seen that the cathode active materials according to Examples 3-1 to 3-5 have a high binding strength between the cathode active material and the current collector, and therefore a cathode can be smoothly manufactured with a small amount of binder.

[0147] Evaluation example 4: Slurry evaluation The viscosities of the positive electrode active material slurries containing the positive electrode active materials of Examples 1, 2, 3-1 to 3-5 were measured, and the results are shown in Table 3.

[0148] [Table 3]

[0149] Referring to Table 3, it can be seen that the viscosity of the positive electrode active material slurries according to Examples 3-1 to 3-5 of the present invention is lower than that of Example 2. That is, when preparing a positive electrode active material slurry having a desired viscosity, it can be prepared so that the positive electrode active material slurries according to Examples 3-1 to 3-5 contain a smaller amount of solvent and therefore a larger amount of solids. Therefore, it can be seen that when an electrode is prepared using the positive electrode active material slurries according to Examples 3-1 to 3-5, it is possible to facilitate coating of the slurry on a current collector and also increase the bonding strength between the positive electrode active material layer and the current collector.

[0150] Evaluation example 5: Battery characteristic evaluation The characteristics of the lithium secondary batteries prepared using the positive electrode active materials of Examples 1, 2, 3-1 to 3-5 were evaluated, and the results are shown in Table 4.

[0151] The lithium secondary battery was initially charged under constant current (0.2C) and constant voltage (3.8V) conditions, and after a 10-minute rest, discharged to 2.5V under constant current (0.2C) conditions to conduct the initial charge-discharge. It was then charged and discharged 50 times at 1.0C / 1.0C at 25°C. An additional coin cell was also fabricated and the 0.2C capacity was measured at -20°C.

[0152] [Table 4]

[0153] Referring to Table 4, it can be seen that the secondary batteries according to Examples 3-1 to 3-5 of the present invention have higher −20° C. capacities than the secondary battery according to Example 2. It can also be seen that the secondary batteries according to Examples 3-1 to 3-5 of the present invention have longer lifespans than the secondary battery according to Example 2. It can also be seen that the secondary batteries according to Examples 3-1 to 3-5 of the present invention exhibit better charge / discharge efficiency than the secondary battery according to Example 2.

[0154] 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. [Explanation of symbols]

[0155] 100: Lithium secondary battery 10: Positive electrode 11: Positive electrode lead tab 12: Positive electrode terminal 20: Negative electrode 21: Negative electrode lead tab 22: Negative terminal 30: Separator 40: Electrode assembly 50: Case 60: Sealing member 70: Electrode tab 71: Positive electrode tab 72: Negative electrode tab

Claims

1. First particles comprising a compound represented by Chemical Formula 1 below and having a first average particle size; and second particles comprising a compound of the following Chemical Formula 2 and having a second average particle size smaller than the first average particle size, A positive electrode active material in which the content of the first particles is equal to or greater than the content of the second particles: [Chemical formula 1] Li a1 Fe x1 B1 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; [Chemical 2] Li a2 Fe x2 B2 y2 PO 4-b2 In Chemical Formula 2, 0.8≦a2≦1.2, 0.950≦x2≦0.999, 0.001≦y2≦0.05, 0≦b2≦0.05, and x2+y2=1; B1 in Formula 1 and B2 in Formula 2 each represent at least one element selected from the group consisting of Ti and Mg.

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

3. 2. The positive electrode active material of claim 1, wherein the first particles and the second particles are mixed in a weight ratio of 50:50 to 70:

30.

4. the first particles include a plurality of first primary particles aggregated together, the second particles include at least one second primary particle; The positive electrode active material according to claim 1 , wherein the size of the plurality of first primary particles is smaller than the size of the second primary particles.

5. The positive electrode active material of claim 1 , wherein the first average particle size is 3 μm to 10 μm.

6. The maximum particle size (D max 2. The positive electrode active material according to claim 1, wherein the thickness of the first and second electrodes is 10 μm to 30 μm.

7. The positive electrode active material of claim 1 , wherein the second average particle size is 0.1 μm to 2 μm.

8. the first particles include a plurality of first primary particles aggregated together, The positive electrode active material of claim 1 , wherein the first primary particles have an average particle size of 50 nm to 200 nm.

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

10. the second particles include a second coating layer containing carbon; The positive electrode active material of claim 9 , wherein the carbon content in the first particles is greater than the carbon content in the second particles.

11. In the first particles, B1 is Ti and Mg, the atomic fraction of Ti is greater than the atomic fraction of Mg in the first particles; 2. The positive electrode active material of claim 1, wherein the first particles satisfy the following formula 1: [Equation 1]

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

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

14. 2. The positive electrode active material according to claim 1, wherein the positive electrode active material has a mixture density of 2.0 g / cc to 3.0 g / cc.

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

16. 6. The method of claim 5, wherein the mixing weight ratio of the first particles to the second particles is 50:50 to 70:

30.

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

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

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

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

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