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 having high energy density, high operation voltage, and high conductivity, and provide a lithium secondary battery having high energy density, high operation voltage, and a high low-temperature characteristic.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, a first particle containing a compound expressed by Chemical Formula 1 and having a first average particle diameter is included. [Chemical Formula 1] LiaFexMnyTizPO4-b, in which 0.8≤a≤1.2, 0.79≤x≤0.9, 0.1≤y≤0.2, 0.001≤z≤0.05, 0≤b≤0.05, and 0.99≤x+y+z≤1.01 are satisfied.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. [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 has been increasing rapidly, leading to active research and development efforts to improve the performance of lithium secondary batteries.

[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 Publication No. 10-2023-0125080 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 problem to be solved by 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 positive electrode active material according to an embodiment of the present invention may include a compound represented by Formula 1 below and may include first particles having a first average particle size. [Chemical formula 1] Li a Fe x Mn y Ti z PO 4-b In Chemical Formula 1, 0.8≦a≦1.2, 0.79≦x≦0.9, 0.1≦y≦0.2, 0.001≦z≦0.05, 0≦b≦0.05, and 0.99≦x+y+z≦1.01.

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

[0009] A lithium secondary battery according to another aspect of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode may include the above-described positive electrode active material. [Effects of the Invention]

[0010] The positive electrode active material according to the present invention may have improved mix density, capacity, and energy density, and the lithium secondary battery according to the present invention may have a relatively high operating voltage and improved high-voltage characteristics. [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 9] 1 is an SEM image of a positive electrode active material according to an example of the present invention. [Figure 10] 1 is an SEM image of a positive electrode active material according to an example 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 that the disclosure of the present invention is complete 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 by methods well known to those skilled in the art, such as using a particle size analyzer or a transmission electron microscope (TEM) or scanning electron microscope (SEM) image. Alternatively, the average particle size (D50) can be measured using a measuring device that utilizes 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. 6A and 6B. 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% by weight of the negative electrode active material, 0.5 to 5% by weight of the binder, and 0 to 5% by weight of the conductive material.

[0023] The binder serves to firmly adhere the negative electrode active material particles to each other and to firmly adhere the negative electrode active material to the current collector COL 2. 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 can be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations 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 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 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 (where Q is selected from an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element (excluding Si), a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0034] The silicon-carbon composite can be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite can be in a form in which silicon particles are coated with amorphous carbon on the surface of the silicon particles. For example, it can include secondary particles (cores) formed by aggregation of 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, and 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 mixing with a carbon-based negative electrode active material.

[0037] Separator 30 Depending on the type of lithium secondary battery, a separator 30 may be present between the positive electrode 10 and the negative electrode 20. As such a 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, a polypropylene / polyethylene / polypropylene three-layer separator, etc. 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 film formed from 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, polyacetimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, 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 move.

[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 the ester solvent 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, and 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, coin, and other 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 battery, FIG. 3 illustrating a prismatic battery, and FIGS. 4 and 5 illustrating pouch-shaped batteries. Referring to FIGS. 2 to 4, a lithium secondary battery 100 may include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a 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, and 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. Referring to FIGS. 6 and 7, as described above, the positive electrode active material layer AML1 (see FIG. 1) may include first particles PTC1, a conductive material CDM, and a binder BND. A plurality of first particles PTC1 may constitute a positive electrode active material according to an embodiment of the present invention.

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

[0056] The content of the positive electrode active material PTC1 in the positive electrode active material layer AML1 may be 90 wt % to 99.5 wt % relative to 100 wt % of the positive electrode active material layer AML1, and the contents 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.

[0057] The binder BND may bind the first particles PTC1, the second particles PTC2, and the conductive material CDM to one another. As an example, the binder BND may include, but is not limited to, at least one selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylic styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0058] 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.

[0059] The first particles PTC1 will be described in more detail below.

[0060] 1st particle PTC1 The first particles PTC1 may include an olivine-based lithium compound represented by the following Chemical Formula 1: [Chemical formula 1] Li a Fe x Mn y Ti z PO 4-b

[0061] In Formula 1, 0.8≦a≦1.2, 0.79≦x≦0.9, 0.1≦y≦0.2, 0.001≦z≦0.05, 0≦b≦0.05, and 0.99≦x+y+z≦1.01 may be satisfied. Mn and Ti may be dopants doped into the first particles PTC1. For example, y may be 0.12 to 0.18, and z may be 0.003 to 0.006. Ti doping may uniformly control the size of the single particles or primary particles, thereby improving the charge / discharge efficiency, low-temperature characteristics, and life characteristics of the lithium secondary battery. Ti doping may also stabilize the crystalline structure of the positive electrode active material, thereby improving the life characteristics of the battery. Primary particles will be described in detail below.

[0062] Lithium iron phosphate-based positive electrode active materials (hereinafter referred to as LFP) with an olivine crystal structure have superior lifespan characteristics compared to other positive electrode materials, but suffer from low energy density, which causes lifespan characteristics to deteriorate when used at high voltages. Lithium manganese iron phosphate-based positive electrode active materials (hereinafter referred to as LMFP), in which some of the Fe in LFP is replaced with Mn, have higher operating voltages and energy densities compared to LFP, but manganese leaching can occur and the crystal grain size can become excessively small. If the particle size is too small, the adhesive strength between the current collector and the positive electrode active material can be weak, making plate processing difficult and requiring a large amount of binder when manufacturing the plate.

[0063] Commonly used LMFPs have a molar ratio of Mn to Fe (Mn / Fe) of 1 or greater, for example, 1 to 4. The cathode active material according to embodiments of the present invention may have a Mn / Fe ratio of 0.1 to 0.3, or 0.15 to 0.25. Because the cathode active material according to the present invention contains a smaller amount of Mn than conventional LMFPs, the crystal grain size may be larger, and therefore the primary particle size may be larger. If the manganese content satisfies the above range, the high-voltage life characteristics of the LFP cathode active material may be improved, while avoiding the problems of manganese leaching and difficulties in electrode plate processing.

[0064] 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.

[0065] 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.

[0066] 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 %.

[0067] The cathode active material of the present invention may include the first particles PTC1, thereby improving the composite density, capacity, and energy density. For example, the compressed density of the cathode active material of the present invention may be 2.0 g / cc to 2.5 g / cc, or 2.3 g / cc to 2.5 g / cc.

[0068] The first particles PTC1 may have a first average particle size, which may vary depending on the embodiment of FIG.

[0069] 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.

[0070] The first particles PTC1 may be a nano-sized positive electrode active material and may include at least one primary particle. The first particles PTC1 may exist as only one primary particle, may have a spherical morphology formed by agglomerating the primary particles, or may have a random morphology even when the primary particles are agglomerated.

[0071] In other words, 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 primary particles, may be 100 nm to 500 nm, or 200 nm to 300 nm.

[0072] 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.

[0073] As an example, the minimum particle size, that is, 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.

[0074] When the first particles PTC1 are single particles, the first average particle size is very small, so a large amount of binder BND may be required to attach the first particles to the current collector COL1 (see FIG. 1). For example, the content of binder BND may be 2 wt % to 5 wt % relative to 100 wt % of the positive electrode active material layer AML1.

[0075] 7, the first particles PTC1 may be polycrystalline and include secondary particles formed by agglomeration of at least two or more primary particles. In other words, one first particle PTC1 may include a plurality of second particles PTC2 agglomerated together. Each of the second particles PTC2 may be a primary particle. The first particles PTC1 may have a spherical or ellipsoidal shape.

[0076] As an example, the first particle PTC1 may further include a grain boundary coating layer on the surface of each of the second particles PTC2. 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 second particles PTC2 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 manganese-containing compound, and a vanadium-containing compound.

[0077] 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.

[0078] 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.

[0079] 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. The average particle size of the first particles PTC1 may be larger than the average size of the second particles PTC2 described below. In one embodiment, the average particle size may be measured using a particle size analyzer. The average particle size may refer to the diameter of particles with a cumulative volume of 50% (D50) in the particle size distribution.

[0080] The average size of the second particles PTC2 may be 200 nm or less. For example, the average size of the second particles PTC2 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 second particles PTC2 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 second particles PTC2 may be uniform.

[0081] The first particles PTC1 may have a spherical shape formed by agglomeration of nano-sized second particles PTC2. The first particles PTC1 may exhibit the following characteristics due to the close agglomeration of the second particles PTC2. 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 approximately 20% to 40%. The Span value of the first particles PTC1 analyzed using a particle size analyzer may be 0.3 to 0.75.

[0082] When the first particles PTC1 are secondary particles, their first average particle size is large, and therefore a relatively small amount of binder BND may be required to adhere the first particles to the current collector COL1 (see FIG. 1). For example, the content of binder BND may be 0.5 wt % to 2 wt % relative to 100 wt % of the positive electrode active material layer AML1. Reducing the content of the binder in the positive electrode active material layer AML1 allows the content of the active material to be increased accordingly, thereby improving the capacity and energy density of the battery. Furthermore, reducing the content of the binder, which increases resistance, may improve the electrical conductivity of the positive electrode.

[0083] 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 at −20° C. relative to the initial capacity (capacity at −20° C. / initial capacity) of the lithium secondary battery may be 40% or more. For example, the capacity at −20° C. relative to the initial capacity (capacity at −20° C. / initial capacity) of the lithium secondary battery of the present invention may be 80% to 100%, 85% to 100%, or 90% to 99%.

[0084] The average voltage of a lithium secondary battery including the positive electrode active material of the present invention may be improved. In one embodiment, the average voltage of the lithium secondary battery of the present invention may be 3.2 V to 3.5 V. For example, the operating voltage range may be 3.25 V to 3.4 V, or 3.28 V to 3.35 V.

[0085] 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 95% or more after 50 charge / discharge cycles at a constant current of 1.0 C at the above-mentioned voltage. For example, the capacity retention rate may be 95% to 100%, or 97% to 100%.

[0086] Method for producing positive electrode active material 8 is a flow chart illustrating a method for manufacturing a positive electrode active material according to an embodiment of the present invention. The method for manufacturing the first particles PTC1 according to an embodiment of the present invention will be described in more detail with reference to FIG.

[0087] 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 iron phosphate precursor may 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 may include FePO4·H2O, or a mixture of FeSO4 and H3PO4. For example, the iron phosphate precursor may include FePO4 or a mixture of FeSO4 and H3PO4.

[0088] 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.

[0089] 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.

[0090] The dopant source may include an oxide containing a dopant metal and / or a chloride containing a dopant metal. For example, the dopant source may include at least one of Mn oxide or Mn chloride and at least one of Ti oxide or Ti chloride, as shown in Chemical Formula 1. For example, the dopant source may include at least one of Mn oxide or Mn chloride and at least one of Ti oxide or Ti chloride.

[0091] The mixture may be subjected to wet milling (S200). 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.

[0092] 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.

[0093] The solvent may be removed from the mixture to form a dried mixture S300.

[0094] 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.

[0095] 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.

[0096] The particles refined to the size of primary particles through the wet milling process can be agglomerated 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.

[0097] 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%.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] The spray pressure may be 0.3 MPa to 0.7 MPa. For example, the spray pressure may be about 0.5 MPa.

[0103] When the input amount, input pressure, and temperature of the spray drying satisfy the above-described ranges, the first particles PTC1 can have a spherical shape and a desired porosity.

[0104] 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.

[0105] The dried mixture may be calcined under an inert atmosphere (S400). The inert atmosphere may be a nitrogen atmosphere and / or an argon atmosphere. The temperature of the calcination process may be 500°C to 1000°C, or 600°C to 800°C. The 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.

[0106] The fired first particles PTC1 may be subjected to a dry grinding process (S500). The fired mixture may be ground using an air jet mill or the like.

[0107] When producing the first particles PTC1 of FIG. 6 according to one embodiment of the present invention, the sintered mixture may be pulverized at a rotation speed of 7000 rpm or more. For example, the sintered mixture may be pulverized at a rotation speed of 7000 rpm to 10000 rpm, or 7500 rpm to 9000 rpm. As a result, the first particles PTC1 may have a single particle shape as shown in FIG.

[0108] When preparing the first particles PTC1 of FIG. 7 according to another embodiment of the present invention, the sintered mixture may be pulverized at a rotation speed of 0 rpm to 7000 rpm. For example, the sintered mixture may be pulverized at a rotation speed of 4000 rpm to 7000 rpm, 4000 rpm to 6000 rpm, or 4500 rpm to 5000 rpm. Unlike when preparing the positive electrode active material of FIG. 6, the pulverization step S500 after sintering may be performed under relatively mild conditions. When preparing the positive electrode active material of FIG. 7, for example, the dry pulverization step S500 may be omitted. If the rotation speed of the pulverization step S500 satisfies the above-described range, the first particles PTC1 may maintain the shape of secondary particles. As a result, the first particles PTC1 may have the shape of secondary particles as shown in FIG. 7.

[0109] In a method for manufacturing the first particles PTC1 shown in FIG. 8 according to an embodiment of the present invention, a carbon source is introduced into an iron phosphate precursor to uniformly form a carbon coating layer on the surfaces of the primary particles. The primary particles are then closely agglomerated by spray drying to form dense secondary spherical particles. As a result, the first particles PTC1 may include a stable carbon coating layer on both the exterior and interior of the first particles PTC1, thereby having a relatively high carbon content. The high carbon content of the first particles PTC1 shown in FIG. 8 may improve the conductivity of the positive electrode active material layer AML1.

[0110] Carbon element analysis according to the present invention can be performed using an Elementar Micro Cube elemental analyzer. Specific operating procedures and conditions are as follows: 1-2 mg of sample is weighed into a tin cup, placed on an automatic sampling tray, and introduced into a combustion tube via a ball valve. The sample is then burned at a combustion temperature of 1000°C. The burned gas is then reduced using reduced copper to form carbon dioxide. Carbon dioxide is detected using a TCD detector.

[0111] The carbon content was measured by quantitative analysis of the particle surface using scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS). Other methods for measuring the carbon content include inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectroscopy (ICP-OES), in addition to SEM-EDS.

[0112] The present invention will be described in more detail below with reference to examples. However, these examples are for illustrative purposes only and the scope of the present invention is not limited to these examples.

[0113] Example 1: Preparation of single particle-shaped first particles Iron phosphate precursor Fe1PO4·H2O, lithium carbonate, Mn1PO4·H2O, and titanium dioxide were mixed in a molar ratio of 0.8496:1.03:0.15:0.004. Glucose was added to the mixture at an additional 10 wt%. The mixture was subjected to a wet grinding process using a ball mill. The mixture was evaporated to dryness in a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours. The dried mixture was calcined at 650°C for 10 hours under a nitrogen atmosphere. The calcined product was pulverized at a rotation speed of 8000 rpm to obtain single-particle primary particles. The average size of the primary particles PTC1 was approximately 300 nm to 400 nm. The chemical formula of the primary particles was LiFe 0.8496 Mn 0.15 Ti 0.004 The particle shape and the doping molar amounts of Mn and Ti are shown in Table 1 below.

[0114] Example 2: Production of primary particles in the form of secondary particles Iron phosphate precursor Fe1PO4·H2O, lithium carbonate, Mn1PO4·H2O, and titanium dioxide were mixed in a molar ratio of 0.8496:1.03:0.15:0.004. Glucose was added to the mixture at 10 wt%. 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 was approximately 100 nm to 200 nm. The chemical formula of the primary particles was LiFe 0.8496 Mn 0.15 Ti 0.004 The particle shape and the doping molar amounts of Mn and Ti are shown in Table 1 below.

[0115] Example 3: Production of primary particles in the form of secondary particles The iron phosphate precursor, Fe1PO4·H2O, lithium carbonate, Mn1PO4·H2O, and titanium dioxide were mixed in a molar ratio of 0.7996:1.03:0.2:0.004. The chemical formula of the first particles was LiFe 0.7996 Mn 0.20 Ti 0.004 Except for the use of PO4, it was prepared in the same manner as in Example 2. The shape of the prepared particles and the doping molar amounts of Mn and Ti are shown in Table 1 below.

[0116] Example 4: Production of primary particles in the form of secondary particles The iron phosphate precursor, Fe1PO4·H2O, lithium carbonate, Mn1PO4·H2O, and titanium dioxide were mixed in a molar ratio of 0.8996:1.03:0.1:0.004. The chemical formula of the first particles was LiFe 0.8996 Mn 0.10 Ti 0.004 Except for the use of PO4, it was prepared in the same manner as in Example 2. The shape of the prepared particles and the doping molar amounts of Mn and Ti are shown in Table 1 below.

[0117] Comparative Example 1: Production of single particle-shaped first particles The iron phosphate precursor, FePO·H O, and lithium carbonate were mixed in a molar ratio of 1:1.03, and the chemical formula of the first particles was LiFePO, which was prepared in the same manner as in Example 1. The shape of the prepared particles and the doping molar amounts of Mn and Ti are shown in Table 1 below.

[0118] Comparative Example 2: Production of single particle-shaped first particles The iron phosphate precursor, Fe1PO4·H2O, lithium carbonate, and titanium dioxide were mixed in a molar ratio of 1:1.03:0.004, and the chemical formula of the first particles was LiFe 0.996 Ti 0.004 Except for the use of PO4, it was prepared in the same manner as in Example 1. The shape of the prepared particles and the doping molar amounts of Mn and Ti are shown in Table 1 below.

[0119] Comparative Example 3: Production of single particle-shaped first particles The iron phosphate precursor, Fe1PO4·H2O, lithium carbonate, Mn1PO4·H2O, and titanium dioxide were mixed in a molar ratio of 0.9496:1.03:0.05:0.004. The first particle had the chemical formula LiFe 0.9496 Mn 0.05 Ti 0.004 Except for the use of PO4, it was prepared in the same manner as in Example 1. The shape of the prepared particles and the doping molar amounts of Mn and Ti are shown in Table 1 below.

[0120] Comparative Example 4: Production of single particle-shaped first particles The iron phosphate precursor, Fe1PO4·H2O, lithium carbonate, Mn1PO4·H2O, and titanium dioxide were mixed in a molar ratio of 0.7996:1.03:0.3:0.004. The chemical formula of the first particles was LiFe 0.6996 Mn 0.3 Ti 0.004 Except for the use of PO4, it was prepared in the same manner as in Example 1. The shape of the prepared particles and the doping molar amounts of Mn and Ti are shown in Table 1 below.

[0121] Comparative Example 5: Production of primary particles in the form of secondary particles The iron phosphate precursor, Fe1PO4·H2O, lithium carbonate, and titanium dioxide were mixed in a molar ratio of 1:1.03:0.004, and the chemical formula of the first particles was LiFe 0.996 Ti 0.004 Except for the use of PO4, it was prepared in the same manner as in Example 2. The shape of the prepared particles and the doping molar amounts of Mn and Ti are shown in Table 1 below.

[0122] Comparative Example 6: Production of primary particles in the form of secondary particles The iron phosphate precursor, Fe1PO4·H2O, lithium carbonate, Mn1PO4·H2O, and titanium dioxide were mixed in a molar ratio of 0.6996:1.03:0.3:0.004. The chemical formula of the first particles was LiFe 0.6996 Mn 0.3 Ti 0.004 Except for the use of PO4, it was prepared in the same manner as in Example 2. The shape of the prepared particles and the doping molar amounts of Mn and Ti are shown in Table 1 below.

[0123] 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.

[0124] Lithium secondary battery manufacturing A 2032-type coin half-cell was fabricated using the prepared positive electrode and a lithium metal counter electrode. A separator (approximately 16 μm thick) made of porous polyethylene (PE) film was placed between the positive electrode and the lithium metal counter electrode, and an electrolyte solution was injected to fabricate a lithium secondary battery. The electrolyte solution used was a mixture of 1.3 M LiPF6 with a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:4:3.

[0125] [Table 1]

[0126] Evaluation example 1: Analysis of the surface of the positive electrode active material FIG. 9 shows an SEM image of the first particles prepared in Example 1. FIG. 10 shows an SEM image of the first particles prepared in Example 2. Referring to FIG. 9, it can be seen that the first particles prepared in Example 1 of the present invention are in the form of fine single particles. Referring to FIG. 10, it can be seen that the first particles prepared in Example 2 of the present invention are in the form of spherical secondary particles formed by the aggregation of multiple primary particles. It can be seen that the second particles PTC2 prepared in Example 2 of the present invention are in the form of nano-sized fine primary particles. Meanwhile, referring to FIGS. 9 and 10, the primary particles of Example 2 were smaller and more uniform than the primary particles of Example 1.

[0127] Evaluation example 2: Evaluation of active materials The pellet density (PD) and carbon content of the positive electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 6 were measured. The results are shown in Table 2.

[0128] [Table 2]

[0129] Referring to Table 2, it can be seen that the positive electrode active material according to Example 1 of the present invention has a similar or higher carbon content than the positive electrode active materials according to Comparative Examples 1 to 3. It can also be seen that the positive electrode active materials according to Examples 2 to 4 have a higher composite density than Comparative Examples 1 to 6 and a similar or higher carbon content than Comparative Examples 1 to 6.

[0130] 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 4 and Comparative Examples 1 to 6 were evaluated.

[0131] The lithium secondary battery was initially charged at a constant current (0.2C) and a constant voltage (4.25V), rested for 10 minutes, and then discharged to 3.0V at a constant current (0.2C) to conduct an initial charge-discharge. It was then charged and discharged 50 times at 1.0C / 1.0C at 45°C. After fabricating a new coin cell, it was charged and discharged at 0.2C / 0.2C, and the capacity was measured at -20°C. The battery characteristics were evaluated and shown in Table 3 below.

[0132] [Table 3]

[0133] Referring to Table 3, it can be seen that the secondary batteries according to Examples 1 to 4 of the present invention exhibit excellent low-temperature capacity and lifespan characteristics. Specifically, it can be seen that the secondary battery according to Example 1 of the present invention has a higher −20° C. discharge capacity and a similar or longer lifespan than the secondary batteries according to Comparative Examples 1 to 3. It can be seen that the secondary batteries according to Examples 2 to 4 of the present invention have a similar or higher −20° C. discharge capacity and a similar or longer lifespan than the secondary batteries according to Comparative Examples 5 and 6.

[0134] Meanwhile, it was confirmed that the secondary batteries according to Examples 2 to 4 had a higher charge amount than the secondary battery according to Example 1, and therefore the resistance of the secondary batteries according to Examples 2 to 4 was smaller.

[0135] 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 description of the invention, and the accompanying drawings, and it is to be understood that these modifications also fall within the scope of the present invention. [Explanation of symbols]

[0136] 100: Lithium secondary battery 10: Positive electrode 11: Positive electrode lead tab 12: Positive terminal 20: Negative electrode 21: Negative electrode lead tab 22: Negative terminal 30: Separator 40: Electrode assembly 50: Case 60: Sealing material 70: Electrode tab 71: Positive electrode tab 72: Negative electrode tab

Claims

1. A positive electrode active material comprising first particles having a first average particle size, the first particles comprising a compound represented by Chemical Formula 1: [Chemical formula 1] Li a Fe x Mn y Today z PO 4-b In Chemical Formula 1, 0.8≦a≦1.2, 0.79≦x≦0.9, 0.1≦y≦0.2, 0.001≦z≦0.05, 0≦b≦0.05, and 0.99≦x+y+z≦1.

01.

2. the y is 0.12 to 0.18; 2. The positive electrode active material according to claim 1, wherein z is 0.003 to 0.

006.

3. the first particles include a coating layer including carbon; 2. The positive electrode active material of claim 1, wherein the carbon content in the first particles is 1.5 to 2.5 wt%.

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

5. the first particles include at least one primary particle; 5. The cathode active material of claim 4, wherein the average size of the primary particles is 150 nm to 300 nm.

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

7. The positive electrode active material of claim 6 , wherein the first average particle size is 3 μm to 10 μm.

8. each of the second particles is a primary particle; The positive electrode active material of claim 6 , wherein the second particles have an average size of 100 nm to 200 nm.

9. the first particles further comprise a grain boundary coating layer on the interface between the second particles; The positive electrode active material according to claim 6 , wherein the grain boundary coating layer contains carbon.

10. The positive electrode active material of claim 6 , wherein the first particles have a porosity of 20% to 40%.

11. The positive active material of claim 6 , wherein the first particles have a Span value of 0.3 to 0.75 as analyzed by a particle size analyzer.

12. 2. The positive electrode active material according to claim 1, wherein the compressed density of the positive electrode active material is 2.0 g / cc to 2.5 g / cc.

13. 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 according to claim 1 , a conductive material, and a binder.

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

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

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

17. The positive electrode for a lithium secondary battery according to claim 13, wherein the conductive material comprises a carbon-based material, a metal-based material in the form of a metal powder or metal fiber, a conductive polymer, or a mixture thereof.

18. a positive electrode, a negative electrode, a separator, and an electrolyte solution; The positive electrode comprises the positive electrode active material according to claim 1. Lithium secondary battery.

19. 19. The lithium secondary battery according to claim 18, wherein the capacity at −20° C. relative to the initial capacity (capacity at −20° C. / initial capacity) is 85% or more.

20. 19. The lithium secondary battery according to claim 18, wherein the capacity retention rate after 50 charge / discharge cycles at a constant current of 0.1 C at a voltage of 3 V to 5 V is 95% or more.

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