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 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 positive electrode including the same, and a lithium secondary battery including the same. More specifically, the positive electrode 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 that is larger than the first average particle diameter. The content of the first particles is larger than that of the second particles. The ratio of the Mn content to the Co content in the positive electrode active material is 7 to 12.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode including the same, and a lithium secondary battery including the same, and more particularly to a positive electrode active material including an olivine-based lithium compound, a positive electrode including the same, and a lithium secondary battery including 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 and high-capacity secondary batteries has been increasing rapidly. Accordingly, research and development to improve the performance of lithium secondary batteries has been actively conducted.

[0003] A lithium secondary battery is a battery that includes a cathode and an anode, which contain active materials that allow the intercalation and deintercalation of lithium ions, and an electrolyte. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are inserted / deintercalated at the cathode and anode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Korean Patent No. 10-1718054 Summary of the Invention [Problem to be solved by the invention]

[0005] The problem to be solved by the present invention is to provide a positive electrode active material having high energy density, high operating voltage, and high conductivity.

[0006] 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]

[0007] A cathode active material according to the present invention may include first particles having a first average particle size, the first particles including a compound represented by Chemical Formula 1 below, and second particles having a second average particle size larger than the first average particle size, the second particles including a compound represented by Chemical Formula 2 below, the content of the first particles may be greater than the content of the second particles: [Chemical formula 1] Li a1 Fe x1 Mn y1 X z1 PO 4-b1

[0008] In the formula 1, 0.8≦a1≦1.2, 0.8≦x1≦0.9, 0.1≦y1≦0.2, 0.001≦z1≦0.05, 0≦b≦0.05, and x1+y1+z1=1, and X is at least one element selected from the group consisting of Ti, Mg, V, and Nb; [Chemical formula 2] Li a2 Ni x2 Co y2 B z2 Y c2 O 2-b2

[0009] In the formula 2, 0.8≦a2≦1.2, 0.8≦x2≦1.0, 0.05≦y2≦0.1, 0≦z2≦0.20≦c2≦0.05, 0≦b2≦0.05, and x2+y2+z2=1; B is Al, Mn, or a combination thereof; Y is at least one element selected from the group consisting of Ti, Mg, Zr, Mo, and Nb; The ratio of Mn content to Co content of the positive electrode active material may be 7 to 12.

[0010] 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.

[0011] A lithium secondary battery according to another aspect of the present invention may include the positive electrode, a negative electrode current collector, a negative electrode including 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]

[0012] The positive electrode active material according to the present invention can improve pellet density, capacity, and energy density by mixing layered second particles with an olivine-based first particle base. The positive electrode active material layer according to the present invention can be smoothly attached to a positive electrode current collector even with a relatively small amount of binder. The lithium secondary battery according to the present invention can have a relatively high average voltage. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a conceptual diagram illustrating a lithium secondary battery according to an embodiment of the present invention; [Figure 2] FIG. 2 is a schematic diagram showing a lithium secondary battery according to one embodiment, in which the battery has a cylindrical shape. [Figure 3] FIG. 3 is a schematic diagram showing a lithium secondary battery according to one embodiment, in which the battery has a prismatic shape. [Figure 4] FIG. 4 is a schematic diagram showing a lithium secondary battery according to one embodiment, in which the battery is in the form of a pouch. [Figure 5] FIG. 5 is a schematic diagram showing a lithium secondary battery according to one embodiment, in which the battery is in the form of a pouch. [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 an SEM photograph of the positive electrode active material of Production Example 1 of the present invention. [Figure 8] 1 is an SEM photograph of a positive electrode active material of Production Example 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] 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.

[0015] 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.

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

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

[0018] Unless otherwise defined herein, particle size refers to the average particle size. Furthermore, particle size refers to the average particle size (D50), which refers to the diameter of particles with a cumulative volume of 50% in a particle size distribution. The average particle size (D50) can be measured 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.

[0019] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment of the present invention. Referring to FIG. 1, the lithium secondary battery may include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte ELL.

[0020] The positive electrode 10 and the negative electrode 20 may be separated from each other by a separator 30. The separator 30 may be disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be in contact with an electrolyte solution ELL. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated in the electrolyte solution ELL.

[0021] The electrolyte ELL can be a medium for transferring lithium ions between the positive electrode 10 and the negative electrode 20. In the electrolyte ELL, the lithium ions can pass through the separator 30 and move toward the positive electrode 10 or the negative electrode 20.

[0022] positive electrode 10 The positive electrode 10 for a lithium secondary battery may include a current collector COL1 and a positive electrode active material layer AML1 formed on the current collector COL1. The positive electrode active material layer AML1 includes a positive electrode active material and may further include a binder and / or a conductive material. A detailed description of the positive electrode active material layer AML1 according to an embodiment of the present invention will be provided below with reference to FIG. 6. The current collector COL1 may be made of, but is not limited to, aluminum.

[0023] negative electrode 20 The 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.

[0024] 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.

[0025] The binder serves to firmly adhere the negative electrode active material particles to each other and to firmly adhere the negative electrode active material to the current collector COL 2. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0026] Examples of non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0027] The water-based binder may be selected from styrene-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.

[0028] 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 a mixture of one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be sodium, potassium, or lithium.

[0029] The dry binder can be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0030] 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.

[0031] As the current collector COL2, those selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrates coated with conductive metals, and combinations thereof can be used.

[0032] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes a material that can reversibly insert / desorb lithium ions, lithium metal, an alloy of lithium metal, a material that can be doped and undoped with lithium, or a transition metal oxide.

[0033] Examples of materials that can reversibly insert / desorb lithium ions include carbon-based negative electrode active materials, which can include, for example, crystalline carbon, amorphous carbon, or combinations thereof. Examples of crystalline carbon can include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon can include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0034] As the alloy of lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0035] As the material that can be 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 combinations thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or combinations thereof.

[0036] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and the surfaces of the silicon particles coated with amorphous carbon. For example, it may include secondary particles (cores) formed by assembling primary silicon particles and a first coating layer (shell) of amorphous carbon located on the surface of the secondary particles. Amorphous carbon may also be located between the primary silicon particles, for example, coating the primary silicon particles with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0037] The silicon-carbon composite may further comprise crystalline carbon. For example, the silicon-carbon composite may comprise a core comprising crystalline carbon and silicon particles and a first coating layer of amorphous carbon disposed on the core.

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

[0039] Separator 30 Depending on the type of lithium secondary battery, a separator 30 may be present between the positive electrode 10 and the negative electrode 20. 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.

[0040] Separator 30 can 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.

[0041] 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.

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

[0043] 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.

[0044] 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.

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

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

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

[0048] Examples of carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0049] Examples of ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0050] Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of 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.

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

[0052] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed together, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0053] Lithium salts are dissolved in organic solvents and act as a source of lithium ions in the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are 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).

[0054] Lithium secondary battery Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 2 through 5 are schematic diagrams illustrating 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 through 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, 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.

[0055] 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.

[0056] FIG. 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.

[0057] 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. The plurality of first particles PTC1 and the plurality of second particles PTC2 may constitute a positive electrode active material according to an embodiment of the present invention.

[0058] The positive electrode active material layer AML1 may further include an additive that can function as a sacrificial positive electrode.

[0059] 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, and the content of the binder BND and the conductive material CDM may be 0.5 wt% to 5 wt% each relative to 100 wt% of the positive electrode active material layer AML1.

[0060] 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, but is not limited to, at least one selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl fluoride, 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.

[0061] 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, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0062] Hereinafter, the first particles PTC1 and the second particles PTC2 will be described in more detail.

[0063] 1st particle PTC1 The first particle PTC1 may have a single particle shape. In this specification, a single particle may refer to a single particle without an internal grain boundary. A single particle may refer to a single particle, a monolith structure, a single structure, or a non-aggregated particle in which particles are morphologically present in an independent phase without aggregation. 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.

[0064] The first particles PTC1 may be a nano-shaped cathode active material. The first particles PTC1 may include at least one primary particle. In one embodiment, the first particles PTC1 may have a spherical or elliptical shape formed by aggregation of primary particles. In another embodiment, the first particles PTC1 may have a random shape, not a spherical shape, even if the primary particles are aggregated.

[0065] The first particles PTC1 can be provided in various sizes. For example, the average particle size of the first particles PTC1 can be 500 nm to 2.5 μm, or about 1 μm. The minimum particle size, i.e., the size of the primary particles, of the first particles PTC1 can be 100 nm to 500 nm, 100 nm to 300 nm, or 100 nm to 200 nm.

[0066] In one embodiment, the average particle size can be measured using a particle size analyzer. The average particle size can refer to the diameter of particles whose cumulative volume is 50% by volume (D50) in the particle size distribution.

[0067] In one embodiment, the minimum particle size, i.e., the size of the primary particles, may refer to the diameter measured by randomly selecting about 30 primary particles from an electron microscope photograph of the first particles PTC1.

[0068] In one embodiment, the first particles PTC1 may include a coating layer on their surfaces. The coating layer may cover the entire surface of the first particles PTC1 or 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 further include at least one selected from the group consisting of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound. The metal-containing compound, such as a titanium-containing compound, a magnesium-containing compound, or a vanadium-containing compound, 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 metal-containing compound may further include lithium. The coating layer may improve the structural stability and electrical conductivity of the first particles PTC1.

[0069] The first particles PTC1 may include an olivine-based lithium compound represented by Chemical Formula 1 below. [Chemical formula 1] Li a1 Fe x1 Mn y1 X z1 PO 4-b1

[0070] In Chemical Formula 1, 0.8≦a1≦1.2, 0.8≦x1≦0.9, 0.1≦y1≦0.2, 0.001≦z1≦0.05, 0≦b≦0.05, and x1+y1+z1=1, and X may be at least one element selected from the group consisting of Ti, Mg, V, and Nb. X may be a dopant doped into the first particle PTC1. For example, X may include Ti.

[0071] The first particles PTC1 may further contain carbon derived from the first coating layer. The carbon element content in the first particles PTC1 may be 0.5 wt% to 5 wt%, 0.5 wt% to 3 wt%, 0.5 wt% to 2.5 wt%, or 1.5 wt% to 2.5 wt%.

[0072] 2nd particle PTC2 The second particles PTC2 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 of the first particles PTC1 described above. In one embodiment, the second particles PTC2 may have a shape composed of one single particle. In another embodiment, the second particles PTC2 may have a shape in which a plurality of single particles NNP are attached to each other. The cathode active material according to the present invention includes the second particles PTC2 in a single particle shape, thereby providing a high capacity and high energy density of the secondary battery.

[0073] In one embodiment, the second particles PTC2 may include a second coating layer on their surfaces. By including the second coating layer, the second particles PTC2 can effectively prevent structural collapse due to repeated charge and discharge, thereby improving the lifespan of the secondary battery.

[0074] The second coating layer can include a boron-containing compound, an aluminum-containing compound, or a combination thereof. The metal-containing compound in the second coating layer can be, for example, a metal oxide, a metal hydroxide, a metal carbonate, a composite thereof, or a mixture thereof. The metal-containing compound can further include other metals or non-metal elements. For example, the second coating layer can further include lithium, manganese, and / or nickel, etc.

[0075] A method for measuring the metal content in the second coating layer of the second particles PTC2 may include performing scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS) on the second particles PTC2. The boron and / or aluminum content in the second coating layer may be determined through the analysis. In addition to SEM-EDS, methods for measuring the metal content in the second coating layer may also include inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0076] The average particle size of the second particles PTC2 may be 2 μm to 15 μm, 2 μm to 10 μm, or 2.5 μm to 5 μm. The average particle size of the second particles PTC2 may be larger than the average particle size of the first particles PTC1. When the second particles PTC2 include a plurality of single NNP particles, the average size of the single NNP particles of the second particles PTC2 may be larger than the average particle size of the first particles PTC1.

[0077] In one embodiment, approximately 30 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 whose cumulative volume is 50% by volume in the particle size distribution can be taken as the average particle size.

[0078] In another embodiment of the present invention, the second particles PTC2 may have the shape of secondary particles formed by aggregation of primary particles. In this case, the second particles PTC2 may have a granular or spherical shape, and the average particle size of the second particles PTC2 may be 10 μm to 30 μm, 10 μm to 20 μm, or 10 μm to 15 μm.

[0079] In another embodiment of the present invention, the second particles PTC2 may exist in a mixed form of a compound in the form of a single particle and a compound in the form of a secondary particle.

[0080] The second particles PTC2 may include a lithium-nickel-based composite oxide as a nickel-based active material. For example, the second particles PTC2 may include a high-nickel-based positive electrode active material containing a high content of nickel. The high-nickel-based positive electrode active material may provide high capacity and high performance.

[0081] Specifically, the second particles PTC2 may include a lithium nickel-based composite oxide having a layered structure represented by the following Chemical Formula 2. [Chemical formula 2] Li a2 Ni x2 Co y2 B z2 Y c2 O 2-b2

[0082] In Chemical Formula 2, 0.8≦a2≦1.2, 0.8≦x2≦1.0, 0.05≦y2≦0.1, 0≦z2≦0.20≦c2≦0.05, 0≦b2≦0.05, and x2+y2+z2=1, and B may be Al, Mn, or a combination thereof. Y may be at least one element selected from the group consisting of Ti, Mg, Zr, Mo, and Nb. X may be a dopant doped into the second particles PTC2.

[0083] Referring again to Figure 6, a cathode active material according to an embodiment of the present invention will be described in more detail. The cathode active material of the present invention may include first particles PTC1 and second particles PTC2. The mixing ratio of the first particles PTC1 to the second particles PTC2 in the cathode active material may be 90:10 to 70:30 by weight, or may be 85:15 to 80:20.

[0084] The Co and Mn contained in the positive electrode active material according to an embodiment of the present invention may have a certain content ratio. In other words, the ratio of the Mn content to the Co content of the positive electrode active material may have a certain range, for example, 7 to 12, 7 to 10, or 8 to 12.

[0085] As used herein, the Mn content of the positive electrode active material may refer to the number of moles of Mn relative to the total number of moles of all metals excluding lithium and a very small amount of doping material (e.g., X in Chemical Formula 1 and Y in Chemical Formula 2) in the entire positive electrode active material including the first particles PTC1 and the second particles PTC2.

[0086] As used herein, the Co content of the positive electrode active material may refer to the number of moles of Co relative to the total number of moles of all metals excluding lithium and a very small amount of doping material (e.g., X in Formula 1 and Y in Formula 2) in the entire positive electrode active material including the first particles PTC1 and the second particles PTC2.

[0087] The second particles PTC2 contain a high-nickel positive electrode active material, and therefore can provide a higher capacity than the first particles PTC1. The positive electrode active material according to this embodiment can improve the capacity and operating voltage compared to a typical LFP battery by mixing the first particles PTC1 and the second particles PTC2 in an appropriate ratio.

[0088] The compound of Chemical Formula 2 (high-nickel-based positive electrode active material) may have lower electrical conductivity than the compound of Chemical Formula 1. The present invention can improve electrical conductivity and energy density by using the second particles PTC2 as single particles.

[0089] The first particles PTC1 have the advantages of high stability and long lifespan. By using the structurally stable first particles PTC1 as the main material of the positive electrode active material, the relatively low stability and short lifespan of the second particles PTC2 can be compensated for.

[0090] When the first particles PTC1 and the second particles PTC2 have a certain mixing ratio and the ratio of the Mn content to the Co content in the positive electrode active material satisfies the above range, the capacity and density of the LFP positive electrode active material can be improved while minimizing deterioration in stability and lifespan.

[0091] The cathode active material of the present invention can improve pellet density, capacity, and energy density by mixing second particles PTC2 having a size of several microns with first particles PTC1 having a size of several hundred nanometers. In one embodiment, the compressed density of the cathode active material of the present invention can be 2.6 g / cc to 2.8 g / cc. Lithium secondary batteries including the cathode active material of the present invention can have improved low-temperature characteristics.

[0092] Because the first particles PTC1, which are single particles, have a very small average particle size, a large amount of binder BND may be required to adhere the first particles PTC1 to the current collector COL1 (see FIG. 1). The cathode active material of the present invention includes not only the first particles PTC1 but also the second particles PTC2, which have a larger average particle size, thereby enabling the cathode active material layer AML1 to be smoothly adhered to the current collector COL1. That is, the use of the second particles PTC2 allows the amount of binder BND in the cathode active material layer AML1 to be reduced.

[0093] A lithium secondary battery including the positive electrode active material of the present invention may have improved low-temperature characteristics. In one embodiment, the capacity of the lithium secondary battery at −20° C. relative to its initial capacity (capacity at −20° C. / initial capacity) may be 40% or more. For example, the capacity of the lithium secondary battery of the present invention at −20° C. relative to its initial capacity (capacity at −20° C. / initial capacity) may be 40% to 100%, 50% to 100%, or 96% to 99%.

[0094] The 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 3V to 4V, 3.3V to 3.5V, or 3.35V to 3.5V.

[0095] 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 can 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 can be 96% to 100%, or 98% to 100%.

[0096] Method for producing positive electrode active material A method for manufacturing the first particle PTC1 according to an embodiment of the present invention will now be described in detail. An iron phosphate precursor, a lithium source, a carbon source, and a dopant source can be mixed in a solvent. For example, the solvent can be water, ethanol, or the like. The iron phosphate precursor can be a compound containing both iron (Fe) and phosphorus (P), or a mixture of an iron (Fe)-containing compound and a phosphorus (P)-containing compound. For example, the iron phosphate precursor can include FePO4·H2O or a mixture of FeSO4 and H3PO4.

[0097] 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 hydrogen phosphate, lithium dihydrogen phosphate, and lithium citrate.

[0098] The carbon source can include at least one selected from the group consisting of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol, and dopamine.

[0099] The dopant source may include an oxide containing a dopant metal and / or a chloride containing a dopant metal. The dopant source may include an oxide or chloride of Mn of Chemical Formula 1. For example, the dopant source may further include at least one selected from the group consisting of titanium oxide, vanadium oxide, and niobium oxide.

[0100] The mixture may be subjected to wet milling. A typical temperature-controllable wet mill may be used for wet milling. Specifically, at least one selected from a bead mill, a ball mill, an attrition mill, an apex mill, a super mill, and a basket mill may be used for wet milling. Through the wet milling process, particles in the mixture may be pulverized to a fine size.

[0101] The solvent may be removed from the mixture to form a dried mixture. In one embodiment, forming the dried mixture may include subjecting the mixture to direct evaporation. For example, direct evaporation may include static drying or spray drying.

[0102] The dried mixture may be calcined under an inert atmosphere. 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 described above may be formed.

[0103] The fired first particles PTC1 may be subjected to a dry grinding process, and the first particles PTC1 may have a single particle shape as shown in FIG.

[0104] A method for manufacturing second particles PTC2 according to an embodiment of the present invention will now be described in detail. A high-nickel-based precursor may be prepared. The high-nickel-based precursor may include Ni of Formula 2 above. The content of Ni relative to the total content of metals in the high-nickel-based precursor may be greater than 80 at%. In one embodiment, the high-nickel-based precursor may further include Co and Al.

[0105] In one embodiment, the high-nickel precursor can be obtained by a co-precipitation method. For example, the co-precipitation method can include dissolving a transition metal source material in a solvent such as distilled water, and sequentially introducing the transition metal salt solution, a chelating agent, and a basic aqueous solution into a reactor to cause precipitation. The precipitate is collected in the form of a slurry, which is then filtered and dried to obtain the high-nickel precursor, which is a metal composite oxide.

[0106] In the present invention, the transition metal source material may include a metal salt of Ni. The transition metal source material may further include a metal salt of at least one of Co and Al. The metal salt may be a sulfate, nitrate, acetate, halide, hydroxide, or the like, and is not particularly limited as long as it is soluble in the solvent. The transition metal source material according to the present embodiment may include a nickel salt, a cobalt salt, and a manganese salt. The transition metal source materials may be mixed by adjusting the molar ratio so that the high-nickel-based precursor has a Ni content of 80 at% or more.

[0107] The high-nickel-based precursor and the lithium source can be mixed in a certain ratio to form a mixture. For example, the high-nickel-based precursor and the lithium source can be mixed in a molar ratio of about 1:1. The lithium source can 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 hydrogen phosphate, lithium dihydrogen phosphate, and lithium citrate.

[0108] The solvent may be removed from the mixture to form a dried mixture. The dried mixture may then be calcined. The calcination temperature may be 700°C to 1,000°C or 900°C to 1,000°C. The calcination may be performed in an oxidizing atmosphere such as air or oxygen. The heat treatment time for the calcination may be 10 to 30 hours. In another embodiment of the present invention, pre-calcination may be additionally performed at 150°C to 800°C prior to the calcination.

[0109] In one embodiment of the present invention, the sintering process can be performed after adding a flux to the mixture. The flux can be a compound containing at least one metal selected from the group consisting of Zr, La, S, and Nb. By using the flux, the second particles PTC2 can be smoothly formed into a single particle form. In addition, the average particle size of the second particles PTC2 can be increased.

[0110] Second particles PTC2 may be formed from a mixture containing a high-nickel precursor and a lithium source through a firing process, and the synthesized second particles PTC2 may be subjected to a pulverization process.

[0111] A coating process can be performed on the pulverized second particles PTC2. Specifically, the second particles PTC2 and the coating raw material can be mixed in a solvent. For example, the coating raw material can include boron and / or aluminum. After filtering and drying the second particles PTC2, a surface treatment can be performed on the second particles PTC2. The surface treatment can include a heat treatment process in an oxidizing atmosphere such as air or oxygen. The surface treatment can be performed at a temperature of 500°C to 800°C.

[0112] In another embodiment of the present invention, the coating process may include a dry coating process. For example, the second particles PTC2 and the coating raw material may be placed in a dry coating machine without a solvent and mixed by stirring. The resulting dry mixture may be subjected to a surface treatment.

[0113] The first particles PTC1 and the second particles PTC2 prepared by the above-described methods may be mixed together to prepare the cathode active material according to the present invention. The first particles PTC1 and the second particles PTC2 may be mixed in a weight ratio of 90:10 to 70:30.

[0114] 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 through 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.

[0115] According to an embodiment of the present invention, the carbon content is measured by quantitative analysis of the particle surface using scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS). Other methods for measuring the composition include inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0116] Examples and comparative examples of the present invention will be described below. However, the examples described below are merely examples of the present invention, and the present invention is not limited to the examples described below.

[0117] Production Example 1: Production of first particles Iron phosphate precursor Fe1PO4·H2O, lithium carbonate, MnPO4, and titanium phosphate dioxide were mixed in a molar ratio of 0.846:1.03:0.15:0.004. 10 wt% glucose was added to the mixture. The mixture was subjected to a wet grinding process using a ball mill. The mixture was evaporated to dryness in a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours. The dried mixture was calcined at 650°C for 10 hours under a nitrogen atmosphere. The calcined product was pulverized to obtain primary particles in the form of single particles. The chemical formula of the primary particles was LiFe 0.848 Mn 0.148 Ti 0.004The particle shape and the doping molar amounts of Mn and Ti are shown in Table 1 below.

[0118] Production Example 2: Production of second particles A high-nickel precursor was produced using the coprecipitation method. Specifically, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and aluminum sulfate (AlSO4·H2O) were dissolved in distilled water as a solvent in a molar ratio of 94:5:1 to prepare a metal raw material mixture. The metal raw material mixture, ammonia water, and sodium hydroxide were 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. 0.940 Co 0.05 Al 0.01 (OH)2) powder was obtained.

[0119] A high-nickel precursor and anhydrous lithium hydroxide (LiOH) were dry-mixed using a Henschel mixer. 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 + Al). A melting agent was added to the mixture, and heat treatment (i.e., a calcination process) was performed in an oxygen atmosphere at approximately 750°C for 15 hours to produce second particles, which are high-nickel cathode active material. The second particles were then pulverized in a jet mill at a pressure of 3 bar.

[0120] The second particles were washed by adding them to distilled water. Boron oxide and aluminum oxide were added in an amount of 3 mol% based on the total transition metal of 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) at about 700°C for 15 hours in an oxygen atmosphere.

[0121] Manufacturing Example 3 Second particles were prepared in the same manner as in Preparation Example 2, except that nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and aluminum sulfate (AlSO4·H2O) were mixed in a molar ratio of 91.5:7.5:1 as raw materials for the nickel-based metal hydroxide.

[0122] Production Example 4 Second particles were prepared in the same manner as in Preparation Example 2, except that nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and aluminum sulfate (AlSO4·H2O) were mixed in a molar ratio of 89:10:1 as raw materials for the nickel-based metal hydroxide.

[0123] Example 1: Preparation of a mixture of first particles and second particles The first particles of Preparation Example 1 and the second particles of Preparation Example 2 were mixed in a weight ratio of 80:20 to prepare a positive electrode active material.

[0124] Example 2 The first particles of Preparation Example 1 and the second particles of Preparation Example 3 were mixed in a weight ratio of 80:20 to prepare a positive electrode active material.

[0125] Example 3 The first particles of Preparation Example 1 and the second particles of Preparation Example 3 were mixed in a weight ratio of 85:15 to prepare a positive electrode active material.

[0126] Comparative Example 1 The first particles of Preparation Example 1 and the second particles of Preparation Example 2 were mixed in a weight ratio of 90:10 to prepare a positive electrode active material.

[0127] Comparative Example 2 The first particles of Preparation Example 1 and the second particles of Preparation Example 2 were mixed in a weight ratio of 85:15 to prepare a positive electrode active material.

[0128] Comparative Example 3 The first particles of Preparation Example 1 and the second particles of Preparation Example 3 were mixed in a weight ratio of 90:10 to prepare a positive electrode active material.

[0129] Comparative Example 4 The first particles of Preparation Example 1 and the second particles of Preparation Example 4 were mixed in a weight ratio of 90:10 to prepare a positive electrode active material.

[0130] Comparative Example 5 The first particles of Preparation Example 1 and the second particles of Preparation Example 3 were mixed in a weight ratio of 75:25 to prepare a positive electrode active material.

[0131] Comparative Example 6 The first particles of Preparation Example 1 and the second particles of Preparation Example 4 were mixed in a weight ratio of 70:30 to prepare a positive electrode active material.

[0132] Comparative Example 7 The first particles of Preparation Example 1 and the second particles of Preparation Example 4 were mixed in a weight ratio of 60:40 to prepare a positive electrode active material.

[0133] 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.

[0134] Anode manufacturing Graphite, a binder, and a conductive material were mixed in N-methylpyrrolidone solvent to prepare a negative electrode active material slurry. The negative electrode active material slurry was applied to a copper current collector, dried, and then rolled to prepare a negative electrode.

[0135] Lithium secondary battery manufacturing A coin-pull cell was fabricated using the prepared positive and negative electrodes. A polypropylene membrane (Celgard 3510) was used as the separator. The electrolyte used was a 1.3M LiPF6 solution mixed with a mixed solvent of EC (ethylene carbonate), DEC (diethyl carbonate), and FEC (fluoroethylene carbonate) (volume ratio: 2:6:2).

[0136] Evaluation example 1: Analysis of the surface of the positive electrode active material FIG. 7 shows an SEM image of the first particles prepared in Preparation Example 1. FIG. 8 shows an SEM image of the second particles prepared in Preparation Example 2. Referring to FIG. 7, it can be seen that the first particles prepared in Preparation Example 1 of the present invention are in the form of fine single particles of nano size. Referring to FIG. 8, it can be seen that the second particles prepared in Preparation Example 2 of the present invention are in the form of single particles of μm size. It can be seen that the second particles are in the form of a single particle or a plurality of single particles attached to each other.

[0137] Evaluation example 2: Active material evaluation The Mn and Co contents, the ratio of the Mn content to the Co content, and the average pellet density (PD) of the positive electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 7 are 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.

[0138] [Table 1]

[0139] Referring to Table 1, it can be seen that the positive electrode active materials according to Examples 1 to 3 have similar or even higher average compressed densities than the positive electrode active materials according to Comparative Examples 1 to 7. In particular, it can be seen that the positive electrode active materials according to Examples 1 to 3 exhibit high compressed densities of 2.7 g / cc or more.

[0140] Evaluation example 3: Battery characteristic evaluation The characteristics of the lithium secondary batteries manufactured using the positive electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 7 were evaluated.

[0141] The lithium secondary battery was initially charged at a constant current (0.1C), rested for 10 minutes, and then discharged at a constant current (0.1C) until the voltage reached 3.0V. The initial charge-discharge cycle was then performed at -20°C and 0.5C / 0.5C for 50 cycles. The average voltage and capacity at -20°C were measured during the charge-discharge cycle. The battery characteristics were evaluated and are shown in Table 2 below.

[0142] [Table 2]

[0143] Referring to Table 2, it can be seen that the secondary batteries according to Examples 1 to 3 of the present invention have a higher −20° C. capacity than the secondary batteries according to Comparative Examples 1 to 4, and have similar or even higher capacity per volume.

[0144] Furthermore, it can be seen that the lithium secondary batteries according to Examples 1 to 3 have better life characteristics than the lithium secondary batteries according to Comparative Examples 1 to 7, and exhibit a high capacity retention rate of 96.5% or more after 50 cycles.

[0145] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this and can be implemented in various modified forms within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is natural that this also falls within the scope of the present invention. [Explanation of symbols]

[0146] 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 cases 60 Sealing member 70 Electrode tab 71 Positive electrode tab 72 Negative electrode tab

Claims

1. First particles comprising a compound represented by Chemical Formula 1 below and having a first average particle size; and second particles comprising a compound of the following Chemical Formula 2 and having a second average particle size larger than the first average particle size, The content of the first particles is greater than the content of the second particles in the positive electrode active material. [Chemical formula 1] Li a1 Fe x1 Mn y1 X z1 2O 4-b1 In the formula 1, 0.8≦a1≦1.2, 0.8≦x1≦0.9, 0.1≦y1≦0.2, 0.001≦z1≦0.05, 0≦b≦0.05, and x1+y1+z1=1, and X is at least one element selected from the group consisting of Ti, Mg, V, and Nb; [Chemical formula 2] Li a2 Ni x2 Co y2 B z2 Y c2 O 2-b2 In the formula 2, 0.8≦a2≦1.2, 0.8≦x2≦1.0, 0.05≦y2≦0.1, 0≦z2≦0.20≦c2≦0.05, 0≦b2≦0.05, and x2+y2+z2=1; B is Al, Mn, or a combination thereof; and Y is at least one element selected from the group consisting of Ti, Mg, Zr, Mo, and Nb; The ratio of Mn content to Co content of the positive electrode active material is 7 to 12.

2. The positive electrode active material of claim 1 , wherein the mixing ratio of the first particles to the second particles is 90:10 to 70:30 by weight.

3. The positive electrode active material according to claim 1 , wherein each of the first particles and the second particles is a single particle.

4. The positive electrode active material of claim 1 , wherein the second particles have a shape in which a plurality of single particles are attached to each other.

5. The positive electrode active material according to claim 1 , wherein X is Ti.

6. the first particles include a first coating layer including 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 %.

7. the second particles include a second coating layer; The positive electrode active material of claim 1 , wherein the second coating layer comprises a boron-containing compound, an aluminum-containing compound, or a combination thereof.

8. The positive electrode active material of claim 1 , wherein the first average particle size is 0.5 μm to 2.5 μm.

9. The first particles include at least one primary particle; The cathode active material according to claim 1 , wherein the average particle size of the primary particles is 100 nm to 300 nm.

10. The positive electrode active material of claim 1 , wherein the second average particle size is 2.5 μm to 5 μm.

11. 2. The positive electrode active material according to claim 1, wherein the positive electrode active material has a compressed density of 2.6 g / cc to 2.8 g / cc.

12. a positive electrode current collector; a positive electrode active material layer on the positive electrode current collector, The positive electrode for a lithium secondary battery, wherein the positive electrode active material layer comprises the positive electrode active material of claim 1 , a conductive material, and a binder.

13. 13. The positive electrode for a lithium secondary battery according to claim 12, 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.

14. 13. The positive electrode for a lithium secondary battery of claim 12, 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, an epoxy resin, a (meth)acrylic resin, a polyester resin, and nylon.

15. 13. The positive electrode for a lithium secondary battery according to claim 12, wherein the content of the conductive material is 0.5 to 5 parts by weight based on 100 parts by weight of the positive electrode active material layer.

16. 13. The positive electrode for a lithium secondary battery according to claim 12, 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 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.

17. The positive electrode according to claim 12; a negative electrode including a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector; 13. The lithium secondary battery according to claim 12, further comprising a separator between the positive electrode and the negative electrode.

18. 18. The lithium secondary battery according to claim 17, wherein the average voltage is 3.3V to 3.4V when discharged at 0.1 C between 2.5V and 4.25V.

19. 18. The lithium secondary battery according to claim 17, wherein the capacity at −20° C. relative to the initial capacity (capacity at −20° C. / initial capacity) is 50% or more.

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