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

Abstract

To provide a positive electrode active material with high energy density, high operation voltage, and high conductivity.SOLUTION: The present invention relates to a positive electrode active material for a lithium secondary battery, a manufacturing method for the same, and a lithium secondary battery including the same. More specifically, the positive electrode active material includes first particles containing a compound of Chemical Formula 1 and having a first average particle diameter, and second particles containing a compound of Chemical Formula 2 and having a second average particle diameter. Based on the total 100 wt% of the content of the first particles and the content of the second particles, the content of the first particles is 80 wt% to 97.5 wt%.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. Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a positive electrode active material having high energy density, high operating voltage, and high conductivity.

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

[0006] A positive electrode active material according to the present invention includes first particles comprising a compound of Chemical Formula 1 below and having a first average particle size, and second particles comprising a compound of Chemical Formula 2 below and having a second average particle size, wherein the content of the first particles is 80 wt % to 97.5 wt % based on a total of 100 wt % of the content of the first particles and the content of the second particles: [Chemical formula 1] Li a1 Mn z1 Fe x1 Ti y1 B b1 PO 4-c1 In Chemical Formula 1, 0.8≦a1≦1.2, 0.3≦z1≦0.7 (or 0.3≦z1<0.7), 0.3≦x1≦0.7 (or 0.3≦x1<0.7), 0.001≦y1≦0.05, 0≦b1≦0.05, 0≦c1≦0.05, and x1+y1+z1+b1=1 may be satisfied. [Chemical formula 2] Li a2 Ni z2 Mn x2 C y2 O c2 In Chemical Formula 2, 1≦a2≦1.5, 0.3≦z2≦0.7 (or 0.3≦z2<)0.7, 0.3≦x2≦0.7 (or 0.3≦x2<0.7), 0.001≦y2≦0.1 (or 0≦y2≦0.1), 2≦c2≦2.3, and z2+x2+y2=1.

[0007] Each of B in Formula 1 and C in Formula 2 may be at least one element selected from the group consisting of transition metals having an oxidation number of 3 or 4.

[0008] A method for manufacturing a positive electrode active material according to another aspect of the present invention may include preparing first particles having a first average particle size, preparing second particles having a second average particle size, and mixing the first particles so that the content of the first particles is 80% to 97.5% by weight, based on a total of 100% by weight of the first and second particles. Preparing the first particles may include mixing a manganese iron phosphate precursor, a lithium source, a carbon source, and a dopant source in a solvent 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 transition metal precursor and a lithium source to form a second mixture, drying the second mixture by spray drying, and calcining the dried second mixture.

[0009] A lithium secondary battery according to yet another aspect of the present invention may include the above-described positive electrode active material. [Effects of the Invention]

[0010] The positive electrode active material according to the present invention may include first and second particles, which are secondary particles having different compositions. This improves the electrical conductivity of the positive electrode active material layer, increases the material mix density, and reduces the binder content of the positive electrode active material layer. The lithium secondary battery according to the present invention has a relatively high operating voltage, improves low-temperature characteristics, and solves the problem of Mn leaching. [Brief explanation of the drawings]

[0011] [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 an embodiment, which can be said to have a cylindrical battery configuration. [Figure 3] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment, which can be said to have a prismatic battery shape. [Figure 4]1 is a schematic diagram showing a lithium secondary battery according to an embodiment, which can be said to have a pouch-type battery configuration. [Figure 5] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment, which can be said to have a pouch-type battery configuration. [Figure 6] 2 is an enlarged view of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. FIG. [Figure 7] 1 is a flowchart illustrating a method for manufacturing a positive electrode active material according to an embodiment of the present invention. [Figure 8a] 1 is an SEM image of the positive electrode active material of Example 3 of the present invention. [Figure 8b] 1 is an SEM image of the positive electrode active material of Example 3 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] 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.

[0013] 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.

[0014] 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.

[0015] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] The dry binder is a fiberizable polymeric material, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, ethylene oxide, or combinations thereof.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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 a combination thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0034] 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 silicon primary 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 silicon primary particles. For example, the silicon primary particles can be coated with amorphous carbon. The secondary particles can be dispersed and present in an amorphous carbon matrix.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0041] 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.

[0042] 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.

[0043] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0044] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0045] 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.

[0046] 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).

[0047] 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.

[0048] Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of nonpolar solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond, an aromatic ring, or an ether group), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane and 1,4-dioxolane, and sulfolanes.

[0049] The non-aqueous organic solvents may be used alone or in combination of two or more.

[0050] 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.

[0051] 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).

[0052] Lithium secondary battery Lithium secondary batteries may be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 2 to 5 are schematic diagrams illustrating a lithium secondary battery according to an embodiment, with FIG. 2 illustrating a cylindrical battery, FIG. 3 illustrating a prismatic battery, and FIGS. 4 and 5 illustrating pouch battery types. Referring to FIGS. 2 to 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.

[0053] The lithium secondary battery according to an embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electrical devices, but the present invention is not limited thereto.

[0054] 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.

[0055] The positive electrode active material layer AML1 may further include an additive that can function as a sacrificial positive electrode.

[0056] 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.

[0057] 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.

[0058] A conductive material CDM can be used to improve the conductivity of the positive electrode active material layer AML1. Any conductive material that does not cause a chemical change in the positive electrode active material layer AML1 can be used as the conductive material CDM without limitation. For example, the conductive material CDM can include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, and the like; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0059] The first particles PTC1 and the second particles PTC2 will be described in more detail below.

[0060] 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 NNP1. In other words, one first particle PTC1 may include a plurality of first primary particles NNP1 agglomerated together. The first particles PTC1 may have a spherical or elliptical shape.

[0061] 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 may cover 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 thereby improve electrical conductivity.

[0062] The coating layer may further include at least one selected from the group consisting of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound. Metal-containing compounds such as titanium-containing compounds, magnesium-containing compounds, and vanadium-containing compounds may be, for example, metal oxides, metal hydroxides, metal carbonates, composites thereof, or mixtures thereof. The metal-containing compounds may further include other metals or metal elements. For example, the metal-containing compounds may further include lithium.

[0063] 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 NNP1. 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 NNP1 inside the first particle PTC1. In other words, the grain boundary coating layer may refer to a material coated on the grain boundaries inside the first particle PTC1. The grain boundary coating layer may include carbon and / or a carbon-containing compound. The grain boundary coating layer may further include at least one selected from the group consisting of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound.

[0064] 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.

[0065] The first particles PTC1 further include a grain boundary coating portion, which strengthens 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.

[0066] The first particles PTC1 may have a spherical shape formed by the aggregation of nano-sized first primary particles NNP1. The first particles PTC1 may exhibit the following characteristics due to the close aggregation of the first primary particles NNP1. The first particles PTC1 may have a spherical or elliptical shape. The average particle size of the first particles PTC1 may be 2 μm to 15 μm, 3 μm to 10 μm, or 3 μm to 7 μm. The average particle size of the first particles PTC1 may be larger than the average particle size of the second particles PTC2 (described below). In one example, more than 30 first particles PTC1 may be randomly selected from an electron microscope photograph of the positive electrode active material and their particle sizes measured. The diameter of the particles with a cumulative volume of 50% (D50) in the particle size distribution may be defined as the average particle size. 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.

[0067] The size (ie, average size) of the first primary particles NNP1 of the first particles PTC1 can be 10 nm to 400 nm, 20 nm to 300 nm, or 50 nm to 200 nm.

[0068] The first particles PTC1 may include an olivine-based lithium compound represented by the following Chemical Formula 1.

[0069] [Chemical formula 1] Li a1 Mn z1 Fe x1 Ti y1 B b1 PO 4-c1 In Chemical Formula 1, 0.8≦a1≦1.2, 0.3≦z1≦0.7 (or 0.3≦z1<0.7), 0.3≦x1≦0.7 (or 0.3≦x1<0.7), 0.001≦y1≦0.05, 0≦b1≦0.05, 0≦c1≦0.05, and x1+y1+z1+b1=1. B in Chemical Formula 1 is at least one element selected from the group consisting of transition metals having an oxidation state of 3 or 4, and in one embodiment, the transition metal having an oxidation state of 3 or 4 may be selected from Ti, Mn, V, Zr, Nb, Mo, Nd, or other suitable transition metals.

[0070] Mn and Ti may be dopants doped into the first particles PTC1. The amount of Ti doped may be 500 ppm to 3000 ppm. Ti doping may uniformly control the size of the first primary particles NNP1, thereby improving the charge / discharge efficiency, low-temperature characteristics, and life characteristics of the lithium secondary battery. In addition, Ti doping may stabilize the crystalline structure of the positive electrode active material, thereby improving the life characteristics of the battery.

[0071] Lithium iron phosphate-based positive electrode active materials (hereinafter referred to as LFP) with an olivine crystal structure have superior lifespan characteristics compared to other positive electrode materials, but suffer from low energy density, which causes lifespan characteristics to deteriorate under high voltage use. Lithium manganese iron phosphate-based positive electrode active materials (hereinafter referred to as LMFP), in which part of the Fe in LFP is replaced with Mn, have higher operating voltages and energy densities compared to LFP, but they can suffer from manganese leaching and excessively small grain size. If the grain size is too small, the bonding strength between the current collector and the positive electrode active material is weak, making plate processing difficult and potentially requiring a large amount of binder during plate fabrication.

[0072] Commonly used LMFPs have a molar ratio of Mn to Fe (Mn / Fe) of 1 or greater, for example, 1 to 4. The cathode active material according to embodiments of the present invention may have a Mn / Fe ratio of 0.1 to 0.3 or 0.15 to 0.25. Because the cathode active material according to the present invention contains a smaller amount of Mn than conventional LMFPs, the crystal grain size can be increased, thereby increasing the size of the first primary particles. When the manganese content satisfies the above range, the high-voltage life characteristics of the LFP cathode active material are improved, while the problems of manganese leaching and difficulties in electrode plate processing can be avoided.

[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 0.5 wt % to 10 wt %, 1 wt % to 3 wt %, or 1.5 wt % to 2.5 wt %.

[0074] 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 2.0 g / cc to 2.5 g / cc, or 2.3 g / cc to 2.5 g / cc.

[0075] When the first particles PTC1 are secondary particles, their large average particle size allows for a relatively small amount of binder BND required to attach the first particles to the current collector COL1 (see FIG. 1). For example, the content of binder BND may be 0.5 wt % to 3 wt % relative to 100 wt % of the positive electrode active material layer AML1. Reducing the content of binder in the positive electrode active material layer AML1 allows for a corresponding increase in the content of active material, thereby improving the capacity and energy density of the battery. Furthermore, reducing the content of binder, which increases resistance, can improve the electrical conductivity of the positive electrode.

[0076] 2nd particle PTC2 The second particles PTC2 may have a polycrystalline form and may include secondary particles formed by agglomeration of at least two or more second primary particles NNP2. In other words, one second particle PTC2 may include a plurality of second primary particles NNP2 agglomerated together. The second particles PTC2 may have a spherical or elliptical shape.

[0077] As an example, 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 may cover only a portion of the surface of the second particles PTC2. The coating layer may improve the structural stability of the second particles PTC2 and improve the electrical conductivity.

[0078] The coating layer may further include at least one selected from the group consisting of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound. Metal-containing compounds such as titanium-containing compounds, magnesium-containing compounds, and vanadium-containing compounds may be, for example, metal oxides, metal hydroxides, metal carbonates, composites thereof, or mixtures thereof. The metal-containing compounds may further include other metals or non-metal elements. For example, the metal-containing compounds may further include lithium.

[0079] As an example, the second particle PTC2 may further include a grain boundary coating layer on the surface of each of the second primary particles NNP2. The grain boundary coating layer may be present inside the second particle PTC2. The grain boundary coating layer may be formed by coating along the interface between the second primary particles NNP2 inside the second particle PTC2. In other words, the grain boundary coating layer may refer to a material coated on the grain boundaries inside the second particle PTC2. The grain boundary coating layer may include carbon and / or a carbon-containing compound. The grain boundary coating layer may further include at least one selected from the group consisting of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound.

[0080] The interior of the second particle PTC2 described above can refer to the entire interior of the second particle PTC2 excluding the surface of the second particle PTC2. For example, the interior of the second particle PTC2 can refer to the region from a depth of about 10 nm from the surface of the second particle PTC2 to the entire inside, or from a depth of 10 nm to a depth of about 2 μm.

[0081] The second particles PTC2 further include a grain boundary coating portion, which strengthens structural stability and allows a uniform coating layer to be formed on the surface of the second particles PTC2. In addition, the second particles PTC2 further include a grain boundary coating portion, which further improves the electrical conductivity of the second particles PTC1.

[0082] The second particles PTC2 may have a spherical shape formed by the aggregation of nano-sized second primary particles NNP2. The second particles PTC2 may exhibit the following characteristics due to the close aggregation of the second primary particles NNP2. The second particles PTC2 may have a spherical or elliptical shape. The average particle size of the second particles PTC2 may be 2 μm to 15 μm, 3 μm to 10 μm, or 3 μm to 7 μm. The average particle size of the second particles PTC2 may be smaller than the average particle size of the first particles PTC1. In one example, more than 30 second particles PTC2 may be randomly selected from an electron microscope photograph of the positive electrode active material, and the particle size may be measured. The diameter of the particles with a cumulative volume of 50% (D50) in the particle size distribution may be defined as the average particle size. The average particle size (D50) of the second particles PTC1 may be 2 μm to 15 μm. The porosity of the second particles PTC2 may be about 20% to about 40%. The Span value of the second particles PTC2 analyzed by a particle size analyzer may be 0.3 to 0.75.

[0083] The size of the second primary particles NNP2 of the second particles (PTC22) can be 10 nm to 400 nm, 20 nm to 300 nm, or 50 nm to 200 nm.

[0084] The second particles PTC1 may include an olivine-based lithium compound represented by the following Chemical Formula 2.

[0085] Li a2 Ni z2 Mn x2 C y2 O c2 In Chemical Formula 2, 1≦a2≦1.5, 0.3≦z2≦0.7 (or 0.3≦z2<0.7), 0.3≦x2≦0.7 (or 0.3≦x2<0.7), 0.001≦y2≦0.1 (or 0≦y2≦0.1), 2≦c2≦2.3, and z2+x2+y2=1. C in Chemical Formula 2 is at least one element selected from the group consisting of transition metals having an oxidation state of 3 or 4. In one embodiment, the transition metal having an oxidation state of 3 or 4 may be selected from Ti, Mn, V, Zr, Nb, Mo, Nd, or other suitable transition metals.

[0086] Lithium-containing manganese oxide (LMR), which contains an excess of lithium, has a crystalline structure that combines a layered phase (LiMO2) and a rock salt phase (Li2MnO3). During the charge and discharge process, the rock salt phase is activated, further increasing capacity through the oxygen redox reaction, providing high capacity.

[0087] When the second particles PTC2 are secondary particles, their large average particle size can reduce the amount of binder BND required to attach the second particles to the current collector COL1 (see FIG. 1). For example, the content of binder BND can be 0.5 wt % to 3 wt % relative to 100 wt % of the positive electrode active material layer AML1. Reducing the content of the binder in the positive electrode active material layer AML1 allows the content of the active material to be increased accordingly, thereby improving the capacity and energy density of the battery. Furthermore, reducing the content of the binder, which increases resistance, can improve the electrical conductivity of the positive electrode.

[0088] Referring again to FIG. 6 , a cathode active material according to an embodiment of the present invention will be described in more detail. The cathode active material of the present invention may include first particles PTC1 and second particles PTC2. The content of the first particles PTC1 may be 80 wt% to 97.5 wt% based on a total of 100 wt% of the content of the first particles PTC1 and the content of the second particles PTC in the cathode active material. Specifically, the content of the first particles PTC1 may be 85 wt% to 95 wt% and the content of the first particles PTC1 may be 90 wt% to 92.5 wt% based on a total of 100 wt% of the content of the first particles PTC1 and the content of the second particles PTC in the cathode active material.

[0089] In one embodiment, the mixing ratio of the first particles PTC1 and the second particles PTC2 may be adjusted so that the content of Mn is 20 at % to 50 at % of the total content of metal elements excluding lithium in the positive electrode active material.

[0090] A lithium secondary battery including the positive electrode active material of the present invention can maintain an appropriate initial charge-discharge efficiency. The initial charge-discharge efficiency of a lithium secondary battery is calculated by dividing the discharge amount measured after a single charge and discharge cycle immediately after fabrication of the lithium secondary battery by the charge amount. A high initial charge-discharge efficiency indicates a high energy density of the lithium secondary battery. However, during charging immediately after fabrication of the lithium secondary battery, the initial charge-discharge efficiency may be reduced due to the formation of an oxide film on the electrode. That is, if the initial charge-discharge efficiency is too high, an oxide film may not be sufficiently formed on the electrode, thereby reducing the lifespan of the electrolyte and electrode. In one embodiment, the initial charge-discharge efficiency of the lithium secondary battery of the present invention may be 85% to 95%, or 90% to 93%. When the initial charge-discharge efficiency of a lithium secondary battery satisfies the range, the battery may have a relatively high energy density while providing a sufficient oxide film on the electrode, thereby improving the lifespan of the electrolyte and electrode.

[0091] 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 capacity of the lithium secondary battery (capacity at −20° C. / initial capacity) may be 40% or more. For example, the capacity at −20° C. relative to the initial capacity of the lithium secondary battery of the present invention (capacity at −20° C. / initial capacity) may be 60% to 100%, 70% to 100%, or 75% to 99%.

[0092] A lithium secondary battery including the positive electrode active material of the present invention can have an improved average voltage. In one embodiment, the average voltage of the lithium secondary battery of the present invention may be 3.2 V to 4.5 V. For example, the operating voltage range may be 3.5 V to 3.7 V, or 3.6 V to 3.65 V.

[0093] A lithium secondary battery including the positive electrode active material of the present invention can have improved life characteristics. In one embodiment, the lithium secondary battery of the present invention may have a capacity retention rate of 95% or more after 50 charge / discharge cycles at a constant current of 0.1 C at the above-mentioned voltage. For example, the capacity retention rate may be 98% to 100%, or 99% to 100%.

[0094] The positive electrode active material of the present invention can improve the composite compaction density and energy density. In one embodiment, the compaction density of the positive electrode active material of the present invention may be 2 g / cc to 3 g / cc, 2.4 g / cc to 2.6 g / cc, or 2.5 g / cc to 2.6 g / cc.

[0095] A lithium secondary battery including the positive electrode active material of the present invention can have improved positive electrode utilization and energy density. The positive electrode utilization is the value obtained by dividing the capacity (mAh) of a lithium secondary battery by the mass (g) of the positive electrode active material included in the lithium secondary battery. In one embodiment, the lithium secondary battery of the present invention may have a positive electrode utilization of 135 mAh / g or more, 140 mAh / g or more, or 145 mAh / g or more. The lithium secondary battery of the present invention may have a positive electrode utilization of 200 mAh / g or less.

[0096] A lithium secondary battery including the positive electrode active material of the present invention can have improved capacity and energy density per volume. The capacity per volume is calculated by multiplying the positive electrode utilization rate (mAh / g) of the lithium secondary battery by the density (g / cc) of the positive electrode active material included in the lithium secondary battery. In one embodiment, the lithium secondary battery of the present invention may have a capacity per volume of 300 mAh / cc or more, 350 mAh / cc or more, or 360 mAh / cc or more. The lithium secondary battery of the present invention may have a capacity per volume of 500 mAh / cc or less.

[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] A manganese iron phosphate precursor, a lithium source, a carbon source, and a dopant source may be mixed in a solvent (S100). For example, the solvent may be water, ethanol, or the like. The manganese iron phosphate precursor may be a compound containing all of manganese (Mn), iron (Fe), and phosphorus (P), or a mixture of a manganese (Mn)-containing compound and an iron (Fe)- and phosphorus (P)-containing compound. For example, the manganese iron phosphate precursor may be a compound containing Mn. x Fe 1-x PO4·H2O; a mixture of MnCO3, and FePO4·H2O; or a mixture of MnCO3, FeSO4, and H3PO4, where x can be 0.5 to 0.9.

[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 of an oxide or chloride of Mn of Chemical Formula 1 and at least one of an oxide or chloride of Ti. For example, the dopant source may include at least one of an oxide or chloride of Mn and at least one of an oxide or chloride of Ti.

[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 milled 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 (S300).

[0105] When producing the first particles PTC1 of FIG. 6 according to an embodiment of the present invention, forming the dried mixture may include subjecting the mixture to a direct evaporation method, such as electrostatic drying or spray drying.

[0106] 7, forming a dried mixture can include spray drying the mixture. 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.

[0107] 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.

[0108] 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 wt%.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] In one embodiment, spray drying can be carried out at a temperature of 100°C to 300°C. For example, spray drying can be carried out at a temperature of 200°C to 300°C, above 200°C to 300°C, or 230°C to 270°C. The propellant gas (e.g., air) used in spray drying 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.

[0113] The spray liquid may be supplied at a pressure of 0.3 MPa to 0.7 MPa. For example, the spray liquid may be supplied at a pressure of about 0.5 MPa.

[0114] When the input amount, input pressure, and temperature of the spray drying satisfy the described ranges, the first particles PTC1 can have a spherical morphology and a desired porosity.

[0115] The spray liquid flow rate for spray drying can be 30 ml / min to 80 ml / min. If the flow rate is less than 30 ml / min, problems such as nozzle clogging and reduced productivity may occur. If the flow rate is greater than 80 ml / min, moisture condensation within the spray dryer may cause the mixture to be incompletely dried. The spray liquid input pressure can be 0.3 MPa to 0.7 MPa. For example, the spray liquid input pressure can be about 0.5 MPa.

[0116] 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.

[0117] 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.

[0118] When producing the first particles PTC1 shown in FIG. 6, which is an embodiment of the present invention, the fired mixture can be pulverized at a rotation speed of 7000 rpm or more. For example, the fired mixture can be pulverized at a rotation speed of 7000 rpm to 1000 rpm, or 7500 rpm to 9000 rpm. This allows the first particles PTC1 to have a single particle morphology as shown in FIG.

[0119] When preparing the first particles PTC1 of FIG. 7, another embodiment of the present invention, the fired mixture can be pulverized at a rotation speed of 0 rpm to 7000 rpm. For example, the fired mixture can be pulverized at a rotation 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 firing can be performed under relatively mild conditions. When preparing the positive electrode active material of FIG. 7, for example, the dry pulverization step (S500) can be omitted. When the rotation 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 secondary particle shape shown in FIG. 7.

[0120] 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 an iron phosphate precursor to uniformly form a carbon coating layer on the surfaces of the primary particles. The primary particles are then closely agglomerated 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 shown in FIG. 7 can improve the conductivity of the positive electrode active material layer AML1.

[0121] A method for manufacturing the second particles PTC2 according to an embodiment of the present invention will now be described in detail. The second particles PTC2 containing lithium manganese-based oxide (hereinafter referred to as LMR) can be manufactured by mixing a transition metal precursor and a lithium source and then calcining the mixture.

[0122] The transition metal precursor may be in the form of a hydroxide, oxide, or carbonate. When a carbonate precursor is used, it is more preferable in that a positive electrode active material having a relatively high specific surface area can be produced.

[0123] The transition metal precursor can be prepared by a co-precipitation process. For example, the transition metal precursor can be prepared by dissolving each transition metal-containing raw material in a solvent to prepare a metal solution, and then mixing the metal solution, an ammonium cation complexing agent, and a basic compound, followed by a co-precipitation reaction. If necessary, an oxidizing agent or oxygen gas can be added during the co-precipitation reaction.

[0124] In this case, the transition metal-containing raw material may be acetate, carbonate, nitrate, sulfate, halide, sulfide, etc. of each transition metal. Specifically, the transition metal-containing raw material may be NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, Mn2O3, MnO2, Mn3O4MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halide, cobalt oxide, cobalt nitrate, cobalt sulfate, cobalt carbonate, cobalt acetate, cobalt halide, etc.

[0125] The ammonium cation complexing agent may be at least one selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and NH4CO3.

[0126] The basic compound may be at least one selected from the group consisting of NaOH, Na2CO3, KOH, and Ca(OH)2. The form of the precursor may vary depending on the type of basic compound used. For example, when NaOH is used as the basic compound, a hydroxide-form precursor can be obtained, and when Na2CO3 is used as the basic compound, a carbonate-form precursor can be obtained. Furthermore, when a basic compound and an oxidizing agent are used together, an oxide-form precursor can be obtained.

[0127] The lithium source can be the same as or similar to the method for producing the first particles PTC1 described above.

[0128] The transition metal precursor and the lithium source may be mixed in amounts such that the total transition metal (Ni+Mn):Li molar ratio is 1:1.05 to 1:2, preferably 1:1.1 to 1:1.8, and more preferably 1:1.3 to 1:1.8.

[0129] The mixture of the transition metal precursor and the lithium source may be subjected to wet-milling (S200). The wet-milling may be the same as or similar to the method for producing the first particles PTC1 described above.

[0130] The solvent may be removed from the mixture of the transition metal precursor and the lithium source to form a dried mixture (S300). The drying may be the same as or similar to the method for producing the first particles PTC1 described above.

[0131] The dried mixture can be calcined under an inert atmosphere (S400). The calcination can be the same as or similar to the method for producing the first particles PTC1 described above.

[0132] The first particles PTC1 and second particles PTC2 prepared by the above methods can be mixed together to prepare a cathode active material according to the present invention. The content of the first particles PTC1 can be 80 wt% to 97.5 wt% based on a total of 100 wt% of the first particles PTC1 and the second particles PTC. Specifically, the content of the first particles PTC1 can be 85 wt% to 95 wt% based on a total of 100 wt% of the first particles PTC1 and the second particles PTC in the cathode active material, and the content of the first particles PTC1 can be 90 wt% to 92.5 wt% based on a total of 100 wt% of the first particles PTC1 and the second particles PTC.

[0133] 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.

[0134] 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).

[0135] The present invention will be described in more detail below through examples. However, these examples are for illustrative purposes only and the scope of the present invention is not limited to these examples.

[0136] Preparation Example 1: Preparation of primary particles (LMFP) in the form of secondary particles Iron phosphate precursor (Mn 0.6 Fe 0.4 PO4), lithium carbonate, and titanium dioxide were mixed in a molar ratio of (Mn+Fe):Li:Ti of 1:1.03:0.03. 112 wt% glucose was further added to the mixture. The mixture, which was a slurry, was spray-dried at a spray pressure of 0.5 MPa and a temperature of 230°C, followed by evaporation. The dried mixture was calcined at 750°C for 10 hours in a nitrogen atmosphere to obtain primary particles in the form of secondary particles. The average size of the primary particles within the primary particles was about 100 nm to about 200 nm.

[0137] Preparation Example 2: Preparation of secondary particles (LMR) (Ni 0.35 Mn 0.65 A transition metal precursor, )(OH)2, and a lithium source, Li2CO3, were mixed in a weight ratio of 1:1.3 to form a slurry. The slurry was spray-dried at a spray pressure of 0.5 MPa and a temperature of 230°C. The spray-dried mixture was then calcined at 600°C for 10 hours in an oxygen atmosphere to obtain secondary particles. The secondary particles had an average size of 5-10 μm, and the average size of the primary particles was about 100 nm to about 500 nm.

[0138] Preparation Example 3: Preparation of single particle first particles (LMFP) Iron phosphate precursor (Mn 0.6 Fe 0.4 PO4), lithium carbonate, and titanium dioxide were mixed in a molar ratio of (Mn+Fe):Li:Ti of 1:1.03:0.03. 112 wt% glucose was further added to the mixture. The slurry mixture was spray-dried at a spray pressure of 0.5 MPa and a temperature of 230°C, followed by evaporation. The dried mixture was calcined at 750°C for 10 hours in a nitrogen atmosphere to obtain primary particles in the form of secondary particles. The calcined product was pulverized to obtain primary particles in the form of single particles. The average size of the primary particles within the primary particles was approximately 100 nm to approximately 200 nm. In other words, in Production Example 1, Mn 0.6 Fe 0.4It describes the production of secondary particles (LMFP) by mixing PO4, lithium carbonate, and titanium dioxide with glucose, then drying and calcining the mixture to obtain primary particles of 100 to 200 nm. These primary particles aggregated to form larger secondary particles. Preparation Example 2 also describes the production of secondary particles (LMFP) by mixing a transition metal precursor (Ni 0.35 Mn 0.65 )(OH)2) with Li2CO3 and calcining the mixture to form secondary particles with primary particles of 100 to 500 nm in size and a final particle size of 5 to 10 μm. These secondary particles are larger due to agglomeration of primary particles within these secondary particles. Preparation Example 3 follows the same steps as Preparation Example 1 and involves grinding the calcined product to obtain monolithic particles with primary particles of 100 to 200 nm in size that do not agglomerate into secondary particles.

[0139] Example 1 The first particles in the form of secondary particles prepared in Preparation Example 1 and the second particles in the form of secondary particles prepared in Preparation Example 2 were mixed in a mass ratio of 97.5:2.5 to prepare a positive electrode active material.

[0140] Example 2 The first particles in the form of secondary particles prepared in Preparation Example 1 and the second particles in the form of secondary particles prepared in Preparation Example 2 were mixed in a mass ratio of 95:5 to prepare a positive electrode active material.

[0141] Example 3 The first particles in the form of secondary particles prepared in Preparation Example 1 and the second particles in the form of secondary particles prepared in Preparation Example 2 were mixed in a mass ratio of 92.5:7.5 to prepare a positive electrode active material.

[0142] Example 4 The first particles in the form of secondary particles prepared in Preparation Example 1 and the second particles in the form of secondary particles prepared in Preparation Example 2 were mixed in a mass ratio of 90:10 to prepare a positive electrode active material.

[0143] Example 5 The first particles in the form of secondary particles prepared in Preparation Example 1 and the second particles in the form of secondary particles prepared in Preparation Example 2 were mixed in a mass ratio of 85:15 to prepare a positive electrode active material.

[0144] Example 6 The first particles in the form of secondary particles prepared in Preparation Example 1 and the second particles in the form of secondary particles prepared in Preparation Example 2 were mixed in a mass ratio of 80:20 to prepare a positive electrode active material.

[0145] Comparative Example 1: Preparation of single particle first particles The single particle type primary particles produced in Production Example 3 were used as a positive electrode active material.

[0146] Comparative Example 2: Primary particles in the form of secondary particles The primary particles in the form of secondary particles produced in Production Example 1 were used as a positive electrode active material.

[0147] Comparative Example 3: Second particles in the form of secondary particles The secondary particles produced in Production Example 2 were used as a positive electrode active material.

[0148] 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.

[0149] 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 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.

[0150] Evaluation example 1: Analysis of the surface of the positive electrode active material An SEM image of the cathode active material prepared in Example 3 is shown in Figure 8a. An SEM image of the cathode active material prepared in Example 3 is shown in Figure 8b. Referring to Figure 8a, it can be seen that the first particles according to an embodiment of the present invention are in the form of spherical secondary particles formed by agglomeration of a plurality of primary particles. Referring to Figure 8b, it can be seen that the second particles according to an embodiment of the present invention are in the form of polycrystalline secondary particles formed by agglomeration of a plurality of primary particles.

[0151] Evaluation Example 2: Evaluation of active materials - Evaluation of initial charge / discharge efficiency The initial charge and discharge capacities of the positive electrode active materials of Examples 1 to 6 and Comparative Examples 1 to 3 were measured, and the initial charge and discharge efficiencies were calculated, and the results are shown in Table 1. The initial charge and discharge efficiencies were calculated by dividing the discharge capacity from the measured initial charge capacity.

[0152] [Table 1]

[0153] Referring to Table 1, it can be seen that the positive electrode active materials according to Examples 1 to 6 of the present invention have higher initial charge / discharge efficiencies and therefore higher energy densities than the positive electrode active material according to Comparative Example 3. In addition, it can be seen that the positive electrode active materials according to Examples 1 to 6 of the present invention have initial charge / discharge efficiencies of 93% or less, which indicates that an appropriate level of oxide film can be formed.

[0154] Evaluation example 3: Evaluation of active materials - Evaluation of low-temperature characteristics The initial discharge capacity at room temperature and the discharge capacity at −20° C. were measured for the positive electrode active materials of Examples 1 to 6 and Comparative Examples 1 to 3, and the low-temperature discharge efficiency was calculated. The results are shown in Table 2. The low-temperature discharge efficiency was calculated by dividing the discharge capacity measured at −20° C. by the discharge capacity measured at room temperature.

[0155] [Table 2]

[0156] Referring to Table 2, it was confirmed that the positive electrode active materials according to Examples 1 to 6 of the present invention had higher low-temperature discharge efficiencies than the positive electrode active material according to Comparative Example 3. In particular, it was confirmed that the positive electrode active materials according to Examples 1 to 4 had low-temperature discharge efficiencies of 75% or more.

[0157] Evaluation Example 4: Evaluation of active materials The average voltage (V), capacity retention rate (%, @50 cy), pellet density (PD), and energy density (positive electrode utilization rate and capacity per volume) of the positive electrode active materials of Examples 1 to 6 and Comparative Examples 1 to 3 were measured, and the results are shown in Table 3.

[0158] [Table 3]

[0159] Referring to Table 3, it can be seen that the positive electrode active materials according to Examples 1 to 6 of the present invention have higher energy densities than the positive electrode active materials according to Comparative Examples 1 and 2.

[0160] Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention may be embodied in other specific forms without changing the technical spirit or essential features thereof. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and are not limiting. [Explanation of symbols]

[0161] 100: Lithium secondary battery 10: Positive electrode 11: Positive electrode lead tab 12: Positive terminal 20: Negative electrode 21: Negative electrode lead tab 22: Negative terminal 30: Separator 40: Electrode assembly 50: Case 60: Sealing material 70: Electrode tab 71: Positive electrode tab 72: Negative electrode tab PTC1: 1st particle PTC2: 2nd particle NNP1: 1st primary particle NNP2: 2nd primary particle CDM: Conductive material BND: Binder

Claims

1. First particles comprising a compound represented by Chemical Formula 1 below and having a first average particle size; and second particles having a second average particle size, the second particles comprising a compound of Chemical Formula 2: A positive electrode active material in which the content of the first particles is 80 wt % to 97.5 wt % based on a total of 100 wt % of the content of the first particles and the content of the second particles: [Chemical formula 1] Li a1 Mn z1 Fe x1 Today y1 B b1 PO 4-c1 In Chemical Formula 1, 0.8≦a1≦1.2, 0.3≦z1≦0.7 (or 0.3≦z1<0.7), 0.3≦x1≦0.7 (or 0.3≦x1<0.7), 0.001≦y1≦0.05, 0≦b1≦0.05, 0≦c1≦0.05, and x1+y1+z1+b1=1; [Chemical formula 2] Li a2 Ni z2 Mn x2 C y2 O c2 In Chemical Formula 2, 1≦a2≦1.5, 0.3≦z2≦0.7 (or 0.3≦z2<0.7), 0.3≦x2≦0.7 (or 0.3≦x2<0.7), 0.001≦y2≦0.1 (or 0≦y2≦0.1), 2≦c2≦2.3, and z2+x2+y2=1; Each of B in Formula 1 and C in Formula 2 is at least one element selected from the group consisting of transition metals having an oxidation number of 3 or 4.

2. 2. The positive electrode active material of claim 1, wherein the content of the first particles is 90 to 95 wt% based on 100 wt% of the total content of the first particles and the second particles.

3. The first particles include a plurality of first primary particles that are aggregated together, The positive electrode active material of claim 1 , wherein the second particles include a plurality of second primary particles that are aggregated together.

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

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

6. The positive electrode active material of claim 1 , wherein the second particles have a polycrystalline morphology.

7. The mixing ratio of the first particles and the second particles is such that the Mn content is 20 at % to 50 at % of the total content of metal elements excluding lithium in the positive electrode active material. The positive electrode active material according to claim 1 .

8. The positive electrode active material of claim 1 , wherein the first particles are doped with Ti in an amount of 1,000 ppm to 3,000 ppm.

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

10. the first particles and the second particles include a first coating layer containing carbon; The positive electrode active material of claim 1 , wherein the carbon content in the first particles and the second particles is 1.0 to 1.8 wt %.

11. 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.

12. 2. The positive electrode active material of claim 1, wherein the second 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 30%.

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

15. Producing first particles having a first average particle size; producing second particles having a second average particle size; and mixing the first particles so that the content of the first particles is 80 wt % to 97.5 wt % based on a total of 100 wt % of the content of the first particles and the content of the second particles, Producing the first particles comprises: mixing a manganese iron phosphate precursor, a lithium source, a carbon source, and a dopant source in a solvent to form a first mixture; drying the first mixture by spray drying; and calcining the dried first mixture; Producing the second particles comprises: combining a transition metal precursor and a lithium source to form a second mixture; drying the second mixture by spray drying; and calcining the dried second mixture.

16. 16. The method of claim 15, comprising mixing the first particles so that the content of the first particles is 90 wt% to 95 wt% based on a total of 100 wt% of the first particles and the second particles.

17. 16. The method of claim 15, wherein the mixing ratio of the first particles and the second particles is such that a Mn content is 20 at % to 50 at % of the total content of metal elements excluding lithium in the positive electrode active material.

18. The spray drying agglomerating particles in the first mixture to form secondary particles; agglomerating particles in the second mixture to form secondary particles. The method for producing a positive electrode active material according to claim 15.

19. The first mixture and the second mixture used as the spray liquid for the spray drying are having a solids content of 20% to 40% by weight, The method for producing a positive electrode active material according to claim 15, wherein the positive electrode active material has a viscosity of 1500 mPa·s to 2500 mPa·s.

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

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