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

Abstract

To provide a positive electrode active material being economical and having high energy density and an excellent lifetime characteristic.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 a first particle containing a compound expressed by Chemical Formula 1 and having an olivine structure, a second particle containing a compound expressed by Chemical Formula 2 and having a spinel structure, and a third particle containing a compound expressed by Chemical Formula 3. Based on 100 parts by weight of the positive electrode active material, the content amount of the third particle is 0.5 parts by weight to 1.5 parts by weight.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode containing the same, and a lithium secondary battery containing the same, and more particularly to a positive electrode active material containing an olivine-based lithium compound, a positive electrode containing the same, and a lithium secondary battery containing the same. [Background technology]

[0002] Recently, with the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, the demand for high-energy-density, high-capacity secondary batteries is rapidly increasing. As a result, research and development efforts to improve the performance of lithium secondary batteries are being actively conducted.

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

[0004] [Patent Document 1] Korean Patent No. 10-2050208 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 that is economical and has a high energy density and a high operating voltage.

[0006] Another problem to be solved by the present invention is to provide a lithium secondary battery that is economical yet has high energy density and high efficiency. [Means for solving the problem]

[0007] A cathode active material according to the present invention may include first particles having an olivine structure including a compound represented by Chemical Formula 1 below, second particles having a spinel structure including a compound represented by Chemical Formula 2 below, and third particles having a compound represented by Chemical Formula 3 below. Based on 100 parts by weight of the cathode active material, the content of the third particles may be 0.5 parts by weight to 1.5 parts by weight. [Chemical formula 1] Li a1 Fe x1 B y1 PO 4-b1 In the above Chemical Formula 1, 0.8≦a1≦1.2, 0.9≦x1≦1.1, 0.001≦y1≦0.05, and 0≦b1≦0.05; B is at least one element selected from the group consisting of Ti, Mg, V, and Nb; [Chemical formula 2] Li a2 Mn x2 C y2 O 4-b2 In the above Chemical Formula 2, 0.8≦a2≦1.2, 1.9≦x2≦2.05, 0≦y2≦0.05, and 0≦b2≦0.05; C is Mg, Al, or a combination thereof; [Chemical formula 3] Li a3 Fe x3 D y3 O 4-b3 In Chemical Formula 3, 4.9≦a3≦5.1, 0.9≦x3≦1.05, 0≦y3≦0.05, 0≦b3≦0.05, and D is Al, Mg, or a combination thereof.

[0008] A positive electrode for a lithium secondary battery according to another aspect of the present invention may include a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector. The positive electrode active material layer may include the positive electrode active material, a conductive material, and a binder.

[0009] A lithium secondary battery according to another aspect of the present invention may include the positive electrode, a negative electrode including a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector, and a separator between the positive electrode and the negative electrode. [Effects of the Invention]

[0010] The cathode active material according to the present invention may have improved composite density, capacity, and energy density by appropriately mixing the olivine-based first particles and the spinel-based second particles. Furthermore, the capacity of the cathode active material may be further improved by including a small amount of third particles that function as a sacrificial cathode. The lithium secondary battery according to the present invention may have a relatively high operating voltage and excellent lifespan. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a conceptual diagram illustrating a lithium secondary battery according to an embodiment of the present invention; [Figure 2] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 3] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 4] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 5] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [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] 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 8] 1 is a flowchart illustrating a method for manufacturing a positive electrode active material according to an embodiment of the present invention. [Figure 9a] 1 is an SEM image of the positive electrode active material of Production Example 1 of the present invention. [Figure 9b] 1 is an SEM image of the positive electrode active material of Production Example 1 of the present invention. [Figure 9c] 1 is an SEM image of the positive electrode active material of Production Example 2 of the present invention. [Figure 9d] 1 is an SEM image of the positive electrode active material of Production Example 2 of the present invention. [Figure 10a] 1 is an SEM image of the positive electrode active material of Production Example 3 of the present invention. [Figure 10b] 1 is an SEM image of the positive electrode active material of Production Example 3 of the present invention. [Figure 11] 1 is an SEM image of the positive electrode active material of Production Example 4 of the present invention. [Figure 12a] 1 is an SEM image of the positive electrode active material of Production Example 5 of the present invention. [Figure 12b] 1 is an SEM image of the positive electrode active material of Production Example 5 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] 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.

[0013] In this specification, when a component is referred to as being on 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 sake of efficient explanation of the technical content. Parts designated with the same reference numerals throughout the specification refer to the same components.

[0014] 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.

[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% 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 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.

[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 FIGS. 6 and 7. The current collector COL1 may be made of, but is not limited to, aluminum.

[0021] negative electrode 20 The negative electrode 20 for a lithium secondary battery includes a current collector COL2 and a negative electrode active material layer AML2 located 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 wt % of the negative electrode active material, 0.5 to 5 wt % of the binder, and 0 to 5 wt % 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. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof can be used.

[0024] Non-aqueous binders may 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-styrene rubber, (meth)acrylate styrene-styrene rubber, (meth)acrylonitrile-styrene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester 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 that can impart viscosity. The cellulose-based compound may be 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 may be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0028] The conductive material is used to impart conductivity to the electrode, and any material that is electronically conductive without causing a chemical change in the battery that is constructed can be used. 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 made of a material 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 / extracting lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and de-doped from 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 graphite or artificial graphite. Examples of amorphous carbon include soft carbon, 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 the substance capable of being doped and 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 and amorphous carbon are coated on the surface of the silicon particles. For example, it can include secondary particles (cores) assembled from primary silicon particles and a first coating layer (shell) of amorphous carbon 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.

[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 a first coating layer of amorphous carbon 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 being mixed 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. As such separator 30, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, and 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 first 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 formed 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 copolymer, 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 material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0042] The organic material and the inorganic material may be mixed in one first coating layer, or may be stacked in a form in which a first coating layer containing an organic material and a first coating layer containing an inorganic material are 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 migrate.

[0045] The non-aqueous organic solvent can be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic 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 propyl 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 aprotic 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 can 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 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+1SO2) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethene sulfonate, lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0052] Lithium secondary battery Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 2 to 5 are schematic diagrams showing lithium secondary batteries according to embodiments, with FIG. 2 illustrating a cylindrical type, FIG. 3 illustrating a prismatic type, and FIGS. 4 and 5 illustrating pouch 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 case 50 in which the electrode assembly 40 is housed. 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 case 50, as shown in FIG. 2. Also, as shown in FIG. 3, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 4 and 5, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting current generated in the electrode assembly 40 to the outside.

[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 and 7 are enlarged views of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. As described above, the positive electrode active material layer AML1 (see FIG. 1) may include first particles PTC1, second particles PTC2, third particles PTC3, a conductive material CDM, and a binder BND. The plurality of first particles PTC1, the plurality of second particles PTC2, and the plurality of third particles PTC3 may constitute a positive electrode active material according to an embodiment of the present invention. The positive electrode active material layer AML1 may further include fourth particles as a positive electrode active material.

[0055] The content of the positive electrode active materials PTC1, PTC2, and PTC3 in the positive electrode active material layer AML1 may be 90 wt % to 99.5 wt % relative to 100 wt % of the positive electrode active material layer AML1, and the content of the binder BND and the conductive material CDM may be 0.5 wt % to 5 wt % respectively relative to 100 wt % of the positive electrode active material layer AML1.

[0056] The binder BND may bind the first particles PTC1, the second particles PTC2, the third particles PTC3, and the conductive material CDM to one another. As an example, the binder BND may include at least one selected from the group consisting of, but not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylic styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0057] 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.

[0058] The first particles PTC1, the second particles PTC2, and the third particles PTC3 will be described in more detail below.

[0059] 1st particle PTC1 The first particles PTC1 may include a lithium compound having an olivine structure represented by the following Chemical Formula 1:

[0060] [Chemical formula 1] Li a1 Fe x1 B y1 PO 4-b1 In Chemical Formula 1, 0.8≦a1≦1.2, 0.9≦x1≦1.1, 0.001≦y1≦0.05, and 0≦b1≦0.05 may be satisfied. B is at least one element selected from the group consisting of Ti, Mg, V, and Nb, and may be a dopant doped into the first particles PTC1. The dopant B controls the size of the primary particles to be uniform, thereby improving the charge / discharge efficiency, low-temperature characteristics, and life characteristics of the lithium secondary battery.

[0061] For example, the first particles PTC1 may include a coating layer on their surfaces. The coating layer may cover the entire surface of the first particles PTC1 or may cover only a portion of the surface of the first particles PTC1. For example, the coating layer may include carbon and / or a carbon-containing compound. The coating layer may improve the structural stability and electrical conductivity of the first particles PTC1.

[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 non-metal elements. For example, the metal-containing compounds may further include lithium.

[0063] The first particles PTC1 may further contain carbon derived from the 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 %.

[0064] As an example, referring again to FIG. 6, the first particle PTC1 may have a single particle shape. In this specification, a single particle may refer to a single particle having no internal grain boundary. A single particle may refer to a morphological phase in which particles exist as an independent phase that is not aggregated with each other, a monolith structure, a single body structure, or a non-aggregated particle. For example, a single particle may be a single crystal. Alternatively, a single particle may be a particle containing several crystals. A single particle may be in a singly separated form. Alternatively, a single particle may be in a form in which 2 to 100 single particles are attached to each other.

[0065] The first particles PTC1 may be a nano-shaped cathode active material. The first particles PTC1 may include at least one first primary particle. In one embodiment, the first particles PTC1 may have a spherical or elliptical shape formed by agglomeration of the first primary particles. In another embodiment, the first particles PTC1 may have a random shape rather than a spherical shape even when the first primary particles are agglomerated.

[0066] The first particles PTC1 may be provided in various sizes. For example, the average particle size of the first particles PTC1 may be 500 nm to 2.5 μm, or 1 μm. The minimum particle size of the first particles PTC1, i.e., the size of the first primary particles, may be 100 nm to 500 nm, or 200 nm to 300 nm.

[0067] In one example, the average particle size may be measured using a particle size analyzer. The average particle size may refer to the diameter of particles with a cumulative volume of 50% (D50) in the particle size distribution.

[0068] As an example, the minimum particle size, that is, the size of the first primary particles, may refer to the diameter measured by randomly selecting about 30 primary particles from an electron microscope photograph of the first particles PTC1.

[0069] 7, the first particles PTC1 may be polycrystalline and include secondary particles formed by agglomeration of at least two or more first primary particles. In other words, one first particle PTC1 may include a plurality of first primary particles agglomerated together. The first particles PTC1 may have a spherical or ellipsoidal shape.

[0070] For example, the first particle PTC1 may further include a grain boundary coating layer on the surface of each of the first primary particles. 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 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.

[0071] 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.

[0072] The first particles PTC1 may further include a grain boundary coating portion, which may enhance structural stability and form a uniform coating layer on the surface of the first particles PTC1, and may further improve the electrical conductivity of the first particles PTC1.

[0073] The first particles PTC1 may further contain carbon derived from the above-mentioned coating layer and / or 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] If the first particles PTC1 are secondary particles, 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. For example, the average particle size of the first particles PTC1 may be approximately 5 μm. In one example, the average particle size may be measured using a particle size analyzer. The average particle size may refer to the diameter of particles with a cumulative volume of 50% (D50) in the particle size distribution.

[0075] The average size of the first primary particles may be 200 nm or less. For example, the average size of the first primary particles may be 10 nm to 200 nm, 20 nm to 200 nm, 50 nm to 200 nm, or 100 nm to 200 nm. In one embodiment, the average size of the first primary particles may refer to the diameter measured by randomly selecting approximately 30 primary particles from an electron microscope photograph of the positive electrode active material. The size of the first primary particles may be uniform.

[0076] When the first particles PTC1 are polycrystalline, the size of the first primary particles may be smaller than when the first particles PTC1 are monoparticles. For example, when the first primary particles PTC1 are polycrystalline, the size of the first primary particles may be smaller by about 100 nm than when the first particles PTC1 are monoparticles.

[0077] If the average particle size and the average size of the first primary particles PTC1 satisfy the ranges described above and the size of the first primary particles is uniform, the charge / discharge capacity and low-temperature capacity of a lithium secondary battery containing them can be improved.

[0078] The first particles PTC1 may have a spherical shape formed by the aggregation of nano-sized first primary particles. The first particles PTC1 may exhibit the following characteristics due to the first primary particles being closely aggregated together: The first particles PTC1 may have a spherical or elliptical shape. The average particle size of the first particles PTC1 may be 2 μm to 15 μm. The porosity of the first particles PTC1 may be about 20% to 40%. The Span value of the first particles PTC1 analyzed using a particle size analyzer may be 0.3 to 0.75.

[0079] When the first particles PTC1 are secondary particles, their large average particle size can reduce the amount of binder BND required to attach the first particles PTC1 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 can increase the content of the active material, 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.

[0080] 2nd particle PTC2 The second particles PTC2 may include a lithium compound having a spinel structure represented by the following Chemical Formula 2:

[0081] [Chemical formula 2] Lia2 Mn x2 C y2 O 4-b2 In Chemical Formula 2, 0.8≦a2≦1.2, 1.9≦x2≦2.05, 0≦y2≦0.05, and 0≦b2≦0.05. C may be Mg, Al, or a combination thereof, and may be a dopant doped into the second particles PTC2. Mg and Al control the size of the primary particles to be uniform and stabilize the crystalline structure of the positive electrode active material, which may improve the charge / discharge efficiency, low-temperature characteristics, and life characteristics of the lithium secondary battery.

[0082] The second particles PTC2 may have a spinel structure. The spinel structure is composed of a lattice structure of tetrahedrons and octahedrons, which makes it highly stable and allows lithium ions to be inserted through various channels, resulting in excellent output. In addition, the second particles PTC2 may have excellent life characteristics.

[0083] The second particles PTC2 may be a lithium manganese oxide or a lithium cobalt oxide cathode material in which cobalt is replaced with manganese. In one embodiment of the present invention, the second particles PTC2 may be substantially free of cobalt (Co). For example, the cobalt (Co) content of the second particles PTC2 may be 100 ppm or less. In addition, the first particles PTC1 and the third particles PTC3 described below may also be substantially free of cobalt (Co). Because the cathode active material according to the present invention is substantially free of cobalt (Co), it may provide a secondary battery that is economical and has high capacity and operating voltage.

[0084] 6 and 7, the second particles PTC2 may be polycrystalline and include secondary particles formed by agglomeration of at least two or more second primary particles. In other words, one second particle PTC2 may include a plurality of second primary particles agglomerated together. The second particles PTC2 may have a spherical shape formed by agglomeration of the second primary particles, or may have a random shape even when the second primary particles are agglomerated.

[0085] The average particle size of the second particles PTC2 may be 3 μm to 20 μm, 4 μm to 15 μm, or 4 μm to 10 μm. For example, the average particle size of the first particles PTC1 may be approximately 8 μm. In one example, the average particle size may be measured using a particle size analyzer. The average particle size may refer to the diameter of particles with a cumulative volume of 50% (D50) in the particle size distribution.

[0086] The average particle size of the second primary particles constituting the second particles PTC2 may be 3 μm or less. For example, the particle size of the second primary particles may be 300 nm to 3 μm, 500 nm to 3 μm, 1 μm to 3 μm, or 2 μm to 3 μm. In one embodiment, the average particle size of the second primary particles may refer to the diameter measured by randomly selecting approximately 30 primary particles from an electron microscope image of the positive electrode active material. The size of the second primary particles may be uniform. The second primary particles may have a smaller average particle size than the first primary particles. The difference in average particle size between the second primary particles and the first primary particles may be 300 nm or more.

[0087] For example, the second particles PTC2 may include a second coating layer on the surface thereof, which can effectively prevent the second particles PTC2 from collapsing due to repeated charging and discharging.

[0088] The second coating layer may include a boron-containing compound, an aluminum-containing compound, or a combination thereof. The metal-containing compound in the second coating layer may be, for example, a metal oxide, a metal hydroxide, a metal carbonate, a composite thereof, or a mixture thereof. The metal-containing compound may further include other metals or non-metal elements. For example, the second coating layer may further include lithium, manganese, and / or nickel.

[0089] A method for measuring the metal content in the second coating layer of the second particles PTC2 may include performing scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) on the second particles PTC2. The analysis may confirm the boron and / or aluminum content in the second coating layer. In addition to SEM-EDS, methods for measuring the metal content in the second coating layer may include inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0090] Third particle PTC3 The third particles PTC3 may include a lithium compound represented by the following Chemical Formula 3:

[0091] [Chemical formula 3] Li a3 Fe x3 D y3 O 4-b3 In Chemical Formula 3, 4.9≦a3≦5.1, 0.9≦x3≦1.05, 0≦y3≦0.05, 0≦b3≦0.05, and D is Al, Mg, or a combination thereof.

[0092] The third particles PTC3 may have a single particle shape similar to the first particles PTC1 described above. The description of the single particle may be the same or similar to that described for the first particles PTC1 described above. In one embodiment, the third particles PTC3 may have a shape composed of a single particle. In another embodiment, the third particles PTC3 may have a shape composed of a plurality of single particles attached to each other. The cathode active material according to the present invention may provide high energy density by including the third particles PTC3 that function as a sacrificial cathode. The role of the third particles PTC3 will be described in more detail below.

[0093] For example, the third particles PTC3 may include a third coating layer on their surfaces. By including the third coating layer, the third particles PTC3 may be effectively prevented from collapsing due to repeated charging and discharging, thereby improving the lifespan of the secondary battery.

[0094] The third coating layer may include a magnesium-containing compound, an aluminum-containing compound, or a combination thereof. The metal-containing compound in the third coating layer may be, for example, a metal oxide, a metal hydroxide, a metal carbonate, a composite thereof, or a mixture thereof. The metal-containing compound may further include other metals or non-metal elements. For example, the third coating layer may further include lithium, manganese, and / or nickel.

[0095] The average particle size of the third particles PTC3 may be 2 μm to 15 μm, 2 μm to 10 μm, or 3 μm to 10 μm. The average particle size of the third particles PTC3 may be larger than the average particle size of the first particles PTC1. When the third particles PTC3 include a plurality of single particles, the average size of the single particles of the third particles PTC3 may be larger than the average particle size of the first particles PTC1.

[0096] As an example, 30 or so second particles PTC2 are randomly selected from an electron microscope photograph of the positive electrode active material, and their particle sizes are measured. The diameter (D50) of the particles with a cumulative volume of 50% in the particle size distribution can be taken as the average particle size.

[0097] The positive electrode active material may be involved in the formation of a soil electrolyte interface (SEI) film on the negative electrode surface during charge and discharge. In particular, during the initial charge and discharge reactions, Li ions present in the positive electrode may undergo irreversible chemical and physical reactions at the negative electrode, converting to irreversible Li ions that do not participate in further charge and discharge reactions. This may lead to a decrease in the capacity of the positive electrode active material.

[0098] The third particles PTC3 according to the present embodiment are an oxide containing Fe and contain abundant Li, and can act as a sacrificial positive electrode that can compensate for irreversible Li. The third particles PTC3 can be decomposed in the formation process to provide Li, and do not need to be involved in the subsequent charge / discharge process.

[0099] For example, when LiFeO is used as a compound constituting the third particle PTC3, the third particle PTC3 can be decomposed between 3.5V and 3.9V relative to Li to provide four Li ions. When the third particle PTC3 is used in the content range described below, it can sufficiently perform the role of compensating for irreversible Li.

[0100] According to an embodiment of the present invention, the third particles PTC3 may include LiFeO, LiFeO, LiFeO, or a combination thereof. For example, the third particles PTC3 may include LiFeO. LiFeO can provide many Li atoms during the formation process and compensate for the irreversible Li charge more effectively, thereby achieving a greater sacrificial positive electrode effect.

[0101] 6 and 7, the cathode active material according to the present invention will be described in more detail. The first particles PTC1 and the second particles PTC2 may constitute the main active material, and the content of the main active material may be 60 to 99.9 parts by weight based on 100 parts by weight of the cathode active material. Specifically, the content of the main active material may be 70 to 98 parts by weight, 80 to 95 parts by weight, or 85 to 90 parts by weight.

[0102] Lithium iron phosphate-based positive electrode active material (first particle, PTC1) with an olivine crystal structure is less expensive than other positive electrode materials and has excellent stability and lifespan characteristics, but is difficult to use at high voltages. Secondary particle PCT2 contains Mn, which can improve the operating voltage of secondary batteries compared to primary particle PCT1. Furthermore, secondary particle PTC2 has a spinel structure, which provides a stable crystal structure and can further improve battery lifespan characteristics.

[0103] The cathode active material according to the present invention is inexpensive and stable, and exhibits high operating voltage and excellent lifespan characteristics by using a mixture of first particles PTC1 and second particles PTC2 as the main active material. The relatively low energy density can be improved by adding third particles PTC3, which function as a sacrificial cathode.

[0104] The mixing ratio of the first particles PTC1 to the second particles PTC2 may be 4:6 to 6:4, or 4.5:5.5 to 5.5:4.5 by weight. In the main active material composed of the first particles PTC1 and the second particles PTC2, the Mn content may be 40 mol% to 70 mol%, 50 mol% to 70 mol%, or 50 mol% to 60 mol%, which is similar to the manganese content of a typical lithium manganese iron phosphate-based positive electrode active material (hereinafter referred to as LMFP).

[0105] By appropriately mixing and using the first particles PTC1 and the second particles PTC2 to have the desired manganese content, a cathode active material can be obtained that exhibits electrochemical properties similar to those of LMFP but is easier to manufacture and process than LMFP. In this specification, the Mn content in the main active material refers to the number of moles of Mn relative to the total number of moles of all metals in the entire main active material, including the first particles PTC1 and the second particles PTC2, excluding lithium and trace amounts of doping materials (e.g., B in Formula 1 and C in Formula 2).

[0106] The content of the third particles PTC3 may be 0.5 to 1.5 parts by weight based on 100 parts by weight of the positive electrode active material. If the content of the third particles PTC3, which function as a sacrificial positive electrode material, is too low, it may not be able to adequately compensate for the irreversible lithium consumed by the SEI layer. On the other hand, if the content of the third particles PTC3 is too high, the content of the positive electrode active material, which exhibits reversible charge / discharge capacity, may decrease, and residual lithium may be plated within the battery, potentially causing a short circuit or impairing stability. When the content of the third particles PTC3 satisfies this range, it may be possible to efficiently improve capacity without impairing battery stability.

[0107] The positive electrode active material of the present invention may further include fourth particles in addition to the first particles PTC1, second particles PTC2, and third particles PTC2 described above. The fourth particles may include a lithium transition metal oxide. Specifically, the fourth particles may include a lithium nickel-based oxide, a lithium cobalt-based oxide, a lithium manganese-based oxide, an iron-based oxide, a cobalt-free nickel-manganese-based oxide, or a combination thereof.

[0108] For example, the fourth particles may include a compound represented by any one of the following chemical formulas: Li a A 1-b X b O 2-c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05);Li a Mn 2-b X b O 4-c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05);Li a Ni 1-b-c Co b X c O 2-α D α (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5, 0<α<2);Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5, 0<α<2);LiNiCoL 1 d G e O2(0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0≦e≦0.1);Li a NiG b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a CoG b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn 1-b G b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li aMn2G b O4(0.90≦a≦1.8, 0.001≦b≦0.1);Li (3-f) Fe2(PO4)3(0≦f≦2).

[0109] In the chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; and L 1 is Mn, Al, or a combination thereof.

[0110] In one embodiment, the fourth particles may include a compound of the following Chemical Formula 4 having a layered structure:

[0111] [Chemical formula 4] Li a4 Ni x4 Co y4 E z4 O 2-b4 In Chemical Formula 4, 0.8≦a4≦1.2, 0.9≦x4≦1.0, 0≦y4≦0.1, 0≦z4≦0.1, 0≦b4≦0.05, and x4+y4+z4=1, and E can be Al, Mg, Mn, or a combination thereof.

[0112] For example, the fourth particles may include a high-nickel-based positive electrode active material in which the nickel content is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more but not more than 99 mol% relative to 100 mol% of metals excluding lithium in the lithium transition metal composite oxide. The high-nickel-based positive electrode active material may provide high capacity and improve the capacity and energy density of the positive electrode active material layer AML1.

[0113] The content of the fourth particles may be 10 to 20 parts by weight based on 100 parts by weight of the positive electrode active material. When the content of the fourth particles satisfies this range, the capacity characteristics may be improved while minimizing deterioration in the life and stability of the positive electrode active material.

[0114] A lithium secondary battery including the positive electrode active material of the present invention may have improved life characteristics. In one embodiment, the lithium secondary battery of the present invention may have a capacity retention rate of 97% or more after 50 charge / discharge cycles at a voltage of 3 V to 4 V and a constant current of 1.0 C. For example, the capacity retention rate may be 98% to 100%.

[0115] A lithium secondary battery including the positive electrode active material of the present invention may have an improved energy density. In one embodiment, the energy density of the lithium secondary battery of the present invention may be 450 Wh / kg or more. For example, the energy density may be 450 Wh / kg to 550 Wh / kg, 460 Wh / kg to 500 Wh / kg, or 460 Wh / kg to 480 Wh / kg.

[0116] Method for producing positive electrode active material 8 is a flowchart illustrating a method for manufacturing a cathode 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.

[0117] The iron phosphate precursor, lithium source, carbon source, and 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 both iron (Fe) and phosphorus (P), or a mixture of iron (Fe) and phosphorus (P)-containing compounds. For example, the iron phosphate precursor may be Fe x PO4·H2O and FePO4·H2O, or a mixture of FePO4 and H3PO4, where x can be between 0.5 and 0.9.

[0118] 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.

[0119] 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.

[0120] The dopant source may include an oxide containing a dopant metal and / or a chloride containing a dopant metal. For example, the dopant source may include at least one selected from the group consisting of titanium oxide, magnesium oxide, vanadium oxide, and niobium oxide.

[0121] The mixture may be subjected to wet milling (S200). A typical temperature-controllable wet mill may be used for wet milling. More specifically, at least one selected from a bead mill, a ball mill, an attrition mill, an apex mill, a super mill, and a basket mill may be used for wet milling. Through the wet milling process, particles in the mixture may be pulverized to a fine size.

[0122] In one embodiment of the present invention, the wet-milling step S200 may be omitted. Specifically, in order to maximize the average particle size of the first particles PTC1 that are finally produced, the wet-milling step S200 for the precursor particles may be omitted.

[0123] The solvent may be removed from the mixture to form a dried mixture (S300).

[0124] In 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 static drying or spray drying.

[0125] 7, forming a dried mixture may include directly spray drying the mixture. Spray drying may be performed using commonly used spray drying equipment. For example, spray drying may be performed using at least one selected from an ultrasonic spray dryer, an air nozzle spray dryer, an ultrasonic nozzle spray dryer, a filter expansion droplet generator, and an electrostatic spray dryer.

[0126] The particles refined to the size of primary particles through the wet-milling process can aggregate with each other to form secondary particles through the spray-drying process. Therefore, the primary particles PTC1 can be formed into secondary particles of a desired size by adjusting the flow rate and velocity of the carrier gas, temperature, residence time in the reactor, and internal pressure during the spray-drying process.

[0127] 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), converted into a percentage. As an example, the spray liquid may have a solid content of approximately 30 wt%.

[0128] If the solid content is less than 20%, the average particle size of the first particles PCT1 will be small, which may result in reduced productivity, whereas if the solid content is more than 40%, it will be difficult to control the average particle size of the first particles PCT1, which may result in increased size deviation of the first particles PCT1.

[0129] 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.

[0130] As an example, 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. As an example, the input rate of spray drying according to the present invention may be approximately 0.5 kg / min.

[0131] In one embodiment, spray drying may be carried out at a temperature of 100°C to 300°C. For example, spray drying may be carried out at a temperature of 200°C to 300°C, above 200°C to 300°C, or 230°C to 270°C. The propellant gas (e.g., air) used in spray drying may be introduced at a first temperature and discharged at a second temperature. For example, the first temperature may be 200°C to 250°C. The second temperature may be 80°C to 150°C.

[0132] The spray pressure may be 0.3 MPa to 0.7 MPa. For example, the spray pressure may be about 0.5 MPa.

[0133] When the input amount, input pressure, and temperature of the spray drying satisfy the ranges described above, the first particles PTC1 can have a spherical shape and a desired porosity.

[0134] The spraying 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, problems such as incomplete drying of the mixture due to water condensation in the spray dryer may occur. The spraying liquid input pressure can be 0.3 MPa to 0.7 MPa. For example, the spraying liquid input pressure can be about 0.5 MPa.

[0135] The dried mixture is calcined under an inert atmosphere (S400). The inert atmosphere may be a nitrogen atmosphere and / or an argon atmosphere. The temperature of the calcination process may be 500°C to 1000°C, or 600°C to 800°C. The time for the calcination process may be 4 hours to 20 hours, or 6 hours to 12 hours. By calcining the dried mixture, first particles PTC1 including the compound of Chemical Formula 1 described above may be formed.

[0136] 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 oxide (hereinafter referred to as LMO) can be manufactured by mixing a manganese source, a lithium source, and a dopant source and then sintering the mixture.

[0137] The manganese source is not particularly limited, and examples thereof include MnO2, Mn3O4, and Mn2O3. However, crystallized Mn3O4, electrolytic MnO2, and Mn2O3 obtained by calcining crystallized Mn3O4 or electrolytic MnO2 are preferred, as they can further enhance the packing ability of the spinel-type lithium manganese oxide.

[0138] 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.

[0139] 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 magnesium oxide and aluminum oxide.

[0140] The manganese source and tritium source may be mixed in amounts such that the molar ratio of Li:Mn is 1:1.6 to 1:2.4, more preferably 1:1.8 to 1:2.2.

[0141] The mixture of the manganese source 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.

[0142] The solvent may be removed from the mixture of the manganese source 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.

[0143] The dried mixture may be calcined under an inert atmosphere (S400). The calcination may be the same as or similar to the method for producing the first particles PTC1 described above.

[0144] The first particles PTC1 and the second particles PTC2 prepared by the above-described methods may be mixed together to prepare a cathode active material according to the present invention. The content of the first particles PTC1 may be 40 wt% to 60 wt%, based on a total of 100 wt% of the first particles PTC1 and the second particles PTC2.

[0145] A method for manufacturing the third particles PTC3 according to an embodiment of the present invention will now be described in detail. The third particles PTC3 may be manufactured by mixing an iron (Fe) source, a lithium (Li) source, and a dopant source and then sintering the mixture.

[0146] The iron source is not particularly limited, and may include at least one selected from the group consisting of Fe(III) chloride, nitrate, sulfate, phosphate, oxide, halide, and hydrates thereof.

[0147] 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.

[0148] 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 magnesium oxide and aluminum oxide.

[0149] The iron source and tritium source may be mixed in amounts to provide a Li:Fe molar ratio of 6:1 to 4:1, more preferably 5.5:1 to 4.5:1.

[0150] The mixture of the iron source 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.

[0151] The solvent may be removed from the mixture of the iron source 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. The dried mixture may be calcined under an inert atmosphere (S400). The calcination may be the same as or similar to the method for producing the first particles PTC1 described above.

[0152] The first to third particles PTC1 to PTC3 prepared by the above-described methods may be mixed together to prepare the positive electrode active material according to the present invention.

[0153] Examples and comparative examples of the present invention will be described below, but the following examples are merely examples of the present invention and are not intended to limit the scope of the present invention.

[0154] Production Example 1: Production of single particle-shaped first particles Iron phosphate precursor Fe1PO4, lithium carbonate, and titanium dioxide were mixed in a molar ratio of 1:1.03:0.004. 10 wt% glucose was added to the mixture. The mixture was wet-pulverized using a ball mill. The mixture was evaporated to dryness in a heating oven tray and then placed in a vacuum oven at 120°C for 4 hours. The dried mixture was calcined at 750°C for 10 hours under a nitrogen atmosphere. The calcined product was pulverized to obtain single-particle primary particles. The average size of the primary particles PTC1 was approximately 200nm to 300nm.

[0155] Production Example 2: Production of primary particles in the form of secondary particles Iron phosphate precursor Fe1PO4, lithium carbonate, and titanium dioxide were mixed in a molar ratio of 1:1.03:0.004. 10 wt% glucose was added to the mixture. The slurry mixture was spray-dried at a spray pressure of 0.5 MPa and a temperature of 230°C, followed by evaporation. The dried mixture was calcined at 750°C for 10 hours in a nitrogen atmosphere to obtain primary particles in the form of secondary particles. The average size of the secondary particles within the primary particles was approximately 100 nm to 200 nm.

[0156] Production Example 3: Production of secondary particles After dissolving 0.170g of MnSO4·H2O and 0.228g of (NH4)2S2O8 in 100ml of distilled water, sulfuric acid was added to adjust the pH to 1, and the mixture was reacted at 130℃ for 10 hours to obtain a solid precipitate. The obtained precipitate was washed several times with distilled water and dried at 300℃ for 3 hours to obtain solid MnO2 with an average particle size of 5μm.

[0157] Li2O3 and synthesized MnO2 were mixed so that the molar ratio of Li to Mn was 1:2, and heated at 600°C for 10 hours to form LiMn2O4 particles with an average particle size of 8 μm and an average primary particle size of 0.5 μm to 3 μm.

[0158] Production Example 4: Production of single particle-shaped third particles To prepare LiFeO4, LiOH·H2O and Fe2O3 were mixed in a ratio of Li:Fe = 5:1. The mixed powder was then milled in a Spex mill for 30 minutes and then pelletized at a pressure of 6.1 to 6.3 tons. The pellets were synthesized at 850 °C for 20 hours. An Air Jel Mill was used to grind the powder at 6000 rpm.

[0159] Production Example 5: Production of single particle-shaped fourth particles A high-nickel precursor was produced using the coprecipitation method. Specifically, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O) were dissolved in distilled water as a solvent in a molar ratio of 93:5:2 to prepare a metal raw material mixture. The metal raw material mixture, ammonia water, and sodium hydroxide were then added to a reactor and reacted. The slurry solution in the reactor was filtered and washed with high-purity distilled water. The washed material was dried in a hot air oven at 210°C for 24 hours to obtain small-particle precursors (NiSO4·6H2O) with an average particle size of approximately 4 μm. 0.93 Co 0.05 Mn 0.02 (OH)2) powder was obtained.

[0160] The high-nickel precursor and anhydrous lithium hydroxide (LiOH) were dry mixed using a Henschel mixer. The lithium and transition metals were mixed in a molar ratio of approximately 1:1. The transition metals were the sum of the transition metals contained in the high-nickel precursor (Ni + Co + Mn). A melting agent was added to the mixture, and the mixture was heat-treated (i.e., calcined) at approximately 750°C for 15 hours in an oxygen atmosphere to synthesize second particles of the high-nickel positive electrode active material. The second particles were then pulverized in a jet mill at a pressure of 3 bar.

[0161] The second particles were washed in distilled water. Boron oxide and aluminum oxide were added in an amount equivalent to 3 mol% of the total transition metals in the second particles to perform boron and aluminum coating. The second particles were dried at 150°C for 12 hours and then heat-treated (i.e., surface-treated) in an oxygen atmosphere at approximately 700°C for 15 hours.

[0162] Production Example 6: Production of main active material The first particles of Preparation Example 1 and the second particles of Preparation Example 3 were mixed in a mass ratio of 55:45 to prepare a main active material.

[0163] Manufacturing Example 7 The first particles of Preparation Example 2 and the second particles of Preparation Example 3 were mixed in a mass ratio of 55:45 to prepare a main active material.

[0164] Example 1: Preparation of final positive electrode active material The main active material of Preparation Example 6 and the third particles of Preparation Example 4 were mixed in a mass ratio of 95.5:0.5 to prepare a final positive electrode active material.

[0165] Example 2 The main active material of Preparation Example 6 and the third particles of Preparation Example 4 were mixed in a mass ratio of 99:1 to prepare a final positive electrode active material.

[0166] Example 3 The main active material of Preparation Example 6 and the third particles of Preparation Example 4 were mixed in a mass ratio of 98.5:1.5 to prepare a final positive electrode active material.

[0167] Example 4 The main active material of Preparation Example 6, the third particles of Preparation Example 4, and the fourth particles of Preparation Example 5 were mixed in a mass ratio of 84:1:15 to prepare a final positive electrode active material.

[0168] Example 5 The main active material of Preparation Example 7 and the third particles of Preparation Example 4 were mixed in a mass ratio of 99.5:0.5 to prepare a final positive electrode active material.

[0169] Example 6 The main active material of Preparation Example 7 and the third particles of Preparation Example 4 were mixed in a mass ratio of 99:1 to prepare a final positive electrode active material.

[0170] Example 7 The main active material of Preparation Example 7 and the third particles of Preparation Example 4 were mixed in a mass ratio of 98.5:1.5 to prepare a final positive electrode active material.

[0171] Example 8 The main active material of Preparation Example 7, the third particles of Preparation Example 4, and the fourth particles of Preparation Example 5 were mixed in a mass ratio of 84:1:15 to prepare a final positive electrode active material.

[0172] Comparative Example 1 The third particles of Preparation Example 4 were omitted, and the main active material of Preparation Example 6 alone was used to prepare a final positive electrode active material.

[0173] Comparative Example 2 The main active material of Preparation Example 6 and the third particles of Preparation Example 4 were mixed in a mass ratio of 99.8:0.2 to prepare a final positive electrode active material.

[0174] Comparative Example 3 The main active material of Preparation Example 6 and the third particles of Preparation Example 4 were mixed in a mass ratio of 98:2 to prepare a final positive electrode active material.

[0175] Comparative Example 4 The main active material of Preparation Example 6 and the third particles of Preparation Example 4 were mixed in a mass ratio of 95:5 to prepare a final positive electrode active material.

[0176] Comparative Example 5 The third particles of Preparation Example 4 were omitted, and the final positive electrode active material was prepared using only the main active material of Preparation Example 7.

[0177] Comparative Example 6 The main active material of Preparation Example 7 and the third particles of Preparation Example 4 were mixed in a mass ratio of 99.8:0.2 to prepare a final positive electrode active material.

[0178] Comparative Example 7 The main active material of Preparation Example 7 and the third particles of Preparation Example 4 were mixed in a mass ratio of 98:2 to prepare a final positive electrode active material.

[0179] Comparative Example 8 The main active material of Preparation Example 7 and the third particles of Preparation Example 4 were mixed in a mass ratio of 95:5 to prepare a final positive electrode active material.

[0180] Cathode manufacturing 95% by weight of the final positive electrode active material, 3% by weight of polyvinylidene fluoride binder, and 2% by weight 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.

[0181] Lithium secondary battery manufacturing A 2032-type coin half-cell was fabricated using the prepared positive electrode and a lithium metal counter electrode as the counter electrode. A separator (approximately 16 μm thick) made of porous polyethylene (PE) film was placed between the positive electrode and the lithium metal counter electrode, and an electrolyte was injected to fabricate a lithium secondary battery. The electrolyte used was a mixture of 1.3 M LiPF6 with a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethylene carbonate (DMC) in a volume ratio of 3:4:3.

[0182] Evaluation example 1: Analysis of the surface of the positive electrode active material SEM images of the first particles prepared in Preparation Examples 1 and 2 are shown in Figures 9a to 9d. SEM images of the second particles prepared in Preparation Example 3 are shown in Figures 10a and 10b. SEM images of the third particles prepared in Preparation Example 4 are shown in Figure 11. SEM images of the fourth particles prepared in Preparation Example 5 are shown in Figures 12a and 12b.

[0183] 9a and 9b, the primary particles according to Preparation Example 1 of the present invention are nano-sized fine single particles. 9c and 9d, the primary particles according to Preparation Example 2 of the present invention are agglomerated spherical secondary particles. Meanwhile, the primary particles according to Preparation Example 2 are smaller and more uniform in size than the primary particles according to Preparation Example 1.

[0184] 10a and 10b, it can be seen that the second particles have the shape of secondary particles formed by agglomeration of primary particles, and with reference to Fig. 11, it can be seen that the third particles have the shape of one single particle or a plurality of single particles attached to each other. With reference to Fig. 12a and 12b, it can be seen that the fourth particles also have the shape of single particles.

[0185] Evaluation example 2: Evaluation of active materials The average pellet density (PD) of the positive electrodes of Examples 1 to 8 and Comparative Examples 1 to 8 is shown in Table 1. The average pellet density was measured by placing 3 g of the positive electrode active material in a pellet mold and applying a force of US 4.0 tons for 30 seconds.

[0186] [Table 1]

[0187] Referring to Table 1, it can be seen that the positive electrode active materials according to Examples 1 to 8 have higher or similar average pressed densities compared to the positive electrode active materials according to Comparative Examples 1 to 8. Referring again to Table 1, it can be seen that when the first particles have a secondary particle shape, the positive electrode active materials have a higher pressed density compared to when the first particles have a single particle shape.

[0188] Evaluation example 3: Evaluation of battery characteristics The characteristics of the lithium secondary batteries manufactured using the positive electrode active materials of Examples 1 to 8 and Comparative Examples 1 to 8 were evaluated.

[0189] The lithium secondary battery was initially charged at a constant current (0.2 C) and a constant voltage (4.25 V), and then allowed to rest for 10 minutes before being discharged at a constant current (0.1 C) to 2.5 V. The initial charge-discharge cycle was then repeated 50 times at 0.1 C / 0.1 C. The battery characteristics were evaluated and shown in Table 2 below.

[0190] [Table 2]

[0191] Referring to Table 2, it can be seen that the lithium secondary batteries according to Examples 1 to 8 have similar efficiencies and average voltages as compared to the lithium secondary batteries according to Comparative Examples 1 to 8. Meanwhile, it can be seen that the lithium secondary batteries according to Examples 1 to 8 have similar or higher energy density and lifespan characteristics as compared to the lithium secondary batteries according to Comparative Examples 1 to 8. It can also be seen that when the first particles have a secondary particle shape, they have higher energy density and lifespan than when the first particles have a single particle shape.

[0192] More specifically, it can be seen that the lithium secondary batteries according to Examples 1 to 4 have a higher energy density than the lithium secondary batteries according to Comparative Examples 1 to 4, and the lithium secondary batteries according to Examples 5 to 8 have a higher energy density than the lithium secondary batteries according to Comparative Examples 5 to 8. In particular, it can be seen that the lithium secondary batteries according to Examples 5 to 8 have a high energy density of 460 Wh / kg or more.

[0193] It can be seen that the lithium secondary batteries according to Examples 1 to 4 have better life characteristics than the lithium secondary batteries according to Comparative Examples 1 to 4, and the lithium secondary batteries according to Examples 5 to 8 have better life characteristics than the lithium secondary batteries according to Comparative Examples 5 to 8. In particular, it can be seen that the lithium secondary batteries according to Examples 5 to 8 have a capacity retention rate of 98.5% or more after 50 charge / discharge cycles at a constant current of 1.0 C.

[0194] Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be embodied in various modifications within the scope of the claims, the embodiments for implementing the invention, and the accompanying drawings, and it is to be understood that these also fall within the scope of the present invention. [Explanation of symbols]

[0195] 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: Cabinet 60: Sealing material 70: Electrode tab 71: Positive electrode tab 72: Negative electrode tab

Claims

1. First particles having an olivine structure and including a compound represented by the following Chemical Formula 1: Second particles having a spinel structure and including a compound represented by the following Chemical Formula 2: and third particles including a compound represented by the following Chemical Formula 3: The content of the third particles is 0.5 to 1.5 parts by weight based on 100 parts by weight of the positive electrode active material, [Chemical formula 1] Li a1 Fe x1 B y1 PO 4-b1 In the formula 1, 0.8≦a1≦1.2, 0.9≦x1≦1.1, 0.001≦y1≦0.05, and 0≦b1≦0.05; B is at least one element selected from the group consisting of Ti, Mg, V, and Nb; [Chemical formula 2] Li a2 Mn x2 C y2 O 4-b2 In Chemical Formula 2, 0.8≦a2≦1.2, 1.9≦x2≦2.05, 0≦y2≦0.05, and 0≦b2≦0.05; C is Mg, Al, or a combination thereof; [Chemical formula 3] Li a3 Fe x3 D y3 O 4-b3 In Chemical Formula 3, 4.9≦a3≦5.1, 0.9≦x3≦1.05, 0≦y3≦0.05, 0≦b3≦0.05, and D is Al, Mg, or a combination thereof.

2. 10. The cathode active material of claim 1, wherein the third particles are configured to be electrochemically inactivated after a first cycle.

3. the first particles and the second particles constitute a main active material; The positive electrode active material of claim 1 , wherein the Mn content of the main active material is 50 mol % to 60 mol %.

4. The positive electrode active material of claim 1 , wherein the mixing ratio of the first particles to the second particles is 4:6 to 6:4 by weight.

5. the first particles include at least one first primary particle; The positive electrode active material according to claim 1 , wherein the second particles have a secondary particle shape formed by agglomeration of a plurality of second primary particles.

6. The positive electrode active material according to claim 5 , wherein the average size of the first particles is smaller than the average size of the second primary particles.

7. the first particles have a single particle shape; The first particles have a first average particle size of 0.5 μm to 2.5 μm; The cathode active material of claim 5 , wherein the first primary particles have an average size of 200 nm to 300 nm.

8. The first particles include a plurality of primary particles aggregated together, The first particles have a first average particle size of 3 μm to 10 μm; The cathode active material of claim 5 , wherein the first primary particles have an average size of 100 nm to 200 nm.

9. The second particles have a second average particle size of 4 μm to 10 μm; The positive electrode active material of claim 5 , wherein the second primary particles have an average size of 0.5 μm to 3 μm.

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

11. the third particles have a single particle shape, The positive electrode active material of claim 1 , wherein the third particles have a third average particle size of 3 μm to 10 μm.

12. 10. The positive electrode active material of claim 1, further comprising fourth particles having a layered structure, the fourth particles comprising a compound represented by the following Chemical Formula 4: [Chemical formula 4] Li a4 Ni x4 Co y4 E z4 O 2-b4 In Formula 4, 0.8≦a4≦1.2, 0.9≦x4≦1.0, 0≦y4≦0.1, 0≦z4≦0.1, 0≦b4≦0.05, and x4+y4+z4=1, and E may be Al, Mg, Mn, or a combination thereof.

13. The positive electrode active material of claim 12, wherein the content of the fourth particles is 10 to 20 parts by weight based on 100 parts by weight of the positive electrode active material.

14. the fourth particle has a single particle shape, The positive electrode active material of claim 12 , wherein the fourth particles have a fourth average particle size of 2 μm to 5 μm.

15. a positive electrode current collector; a positive electrode active material layer on the positive electrode current collector, The positive electrode active material layer comprises the positive electrode active material according to any one of claims 1 to 14, a conductive material, and a binder.

16. 16. The positive electrode for a lithium secondary battery according to claim 15, wherein the content of the binder is 0.5 to 5 parts by weight based on 100 parts by weight of the positive electrode active material layer.

17. 16. The positive electrode for a lithium secondary battery according to claim 15, wherein the binder comprises 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.

18. 16. The positive electrode for a lithium secondary battery according to claim 15, wherein the conductive material is present in an amount of 0.5 to 5 parts by weight based on 100 parts by weight of the positive electrode active material layer.

19. 16. The positive electrode for a lithium secondary battery according to claim 15, wherein the conductive material comprises a carbon-based material such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, or carbon nanotube; a metal-based material in the form of a metal powder or metal fiber containing copper, nickel, aluminum, silver, or the like; a conductive polymer such as a polyphenylene derivative; or a mixture thereof.

20. The positive electrode according to claim 15 ; a negative electrode including a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector; a separator between the positive electrode and the negative electrode.

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