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 for a lithium secondary battery, a manufacturing method for the same, and a lithium secondary battery including the same.SOLUTION: A positive electrode active material for a lithium secondary battery includes a first particle containing a compound expressed by Chemical Formula 1 and having a first average particle diameter and a second particle containing a compound expressed by Chemical Formula 2 and having a second average particle diameter that is larger than the first average particle diameter. The mixing ratio between the first particle and the second particle is 95:5 to 99.5:0.5.SELECTED DRAWING: Figure 6a

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 replenishment of battery-powered electronic devices such as mobile phones, laptop computers, and electric vehicles, the demand for secondary batteries with high energy density and high capacity has been rapidly increasing. Accordingly, research and development to improve the performance of lithium secondary batteries has been actively carried out.

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

[0004] [Patent Document 1] Korean Patent Application Publication No. 2012-0087540 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 electrical conductivity.

[0006] Another object of the present invention is to provide a lithium secondary battery having high energy density, high operating voltage, high charge / discharge efficiency, and excellent low-temperature characteristics. [Means for solving the problem]

[0007] A cathode active material according to the present invention includes first particles having a first average particle size, the first particles comprising 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 comprising a compound represented by Chemical Formula 2 below. The mixing ratio of the first particles to the second particles may be 95:5 to 99.5:0.5. [Chemical formula 1] Li a1 Mn b1 Fe x1 B y1 PO 4-c1 In Formula 1, 0.8≦a1≦1.2, 0.5≦b1≦0.9, 0.1≦x1≦0.5, 0.001≦y1≦0.05, 0≦c1≦0.05, and b1+x1+y1=1, and B may be at least one element selected from the group consisting of Mg, Ti, V, and Al. [Chemical formula 2] Li a2 Fe b2 O c2 In the above Chemical Formula 2, 1≦a2≦5, 0.9≦b2≦1.1, and 2≦c2≦4.

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

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

[0010] The cathode active material according to the present invention may include olivine-based first particles having a size of several hundred nanometers. The cathode active material according to the present invention may include single-crystal second particles having a size of several micrometers that function as a sacrificial cathode. This may improve the composite density, capacity, and energy density of the cathode active material according to the present invention. The cathode active material layer according to the present invention may be smoothly attached to the cathode current collector even with a relatively small amount of binder. The lithium secondary battery according to the present invention may have a relatively high average voltage. [Brief explanation of the drawings]

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

[0012] In order to fully understand the configuration and effects of the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and may be embodied in various forms and may undergo various modifications. However, the description of the present embodiments is provided to ensure complete disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0013] In this specification, when a component is referred to as being on top of another component, it means that it may be formed directly on the other component, or that a third component may be interposed between them. Also, in the drawings, the thickness of the components is exaggerated for the purpose of effectively explaining the technical content. Throughout the specification, parts designated with the same reference numerals refer to the same components.

[0014] Unless otherwise stated herein, the singular can also include the plural. Additionally, unless otherwise stated, "A" or "B" can mean "including A but also including B, or including A and B." As used herein, "comprises" and / or "comprising" do not exclude the presence or addition of one or more other elements to the referenced element.

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

[0016] Unless otherwise defined herein, particle size refers to the average particle size. Furthermore, particle size refers to the average particle size (D50), which refers to the diameter of particles with a cumulative volume of 50% by volume in a particle size distribution. The average particle size (D50) can be measured using methods well known to those skilled in the art, such as a particle size analyzer or a transmission electron microscope (TEM) or scanning electron microscope (SEM) image. Alternatively, measurement can be performed using a measuring device that uses dynamic light scattering, and data analysis can be performed to count the number of particles in each particle size range, followed by calculation to obtain the average particle size (D50) value. Alternatively, measurement can be performed using a laser diffraction method. When measuring by the laser diffraction method, more specifically, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., MT 3000 manufactured by Microtrac), and ultrasonic waves of approximately 28 kHz are irradiated at an output of 60 W, after which the average particle size (D50) based on 50% of the particle size distribution in the measuring device can be calculated.

[0017] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment of the present invention. Referring to FIG. 1, the lithium secondary battery may include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte solution ELL.

[0018] The positive electrode 10 and the negative electrode 20 may be separated from each other by a separator 30. The separator 30 may be disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be in contact with an electrolyte solution ELL. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated in the electrolyte solution ELL.

[0019] The electrolyte ELL can be a medium for transferring lithium ions between the positive electrode 10 and the negative electrode 20. In the electrolyte ELL, the lithium ions can pass through the separator 30 and move toward the positive electrode 10 or the negative electrode 20.

[0020] positive electrode 10 The positive electrode 10 for a lithium secondary battery may include a current collector COL1 and a positive electrode active material layer AML1 formed on the current collector COL1. The positive electrode active material layer AML1 includes a positive electrode active material and may further include a binder and / or a conductive material. A detailed description of the positive electrode active material layer AML1 according to an embodiment of the present invention will be provided below with reference to FIGS. 6a and 6b. The current collector COL1 may be made of, but is not limited to, aluminum.

[0021] negative electrode 20 The lithium secondary battery positive electrode 20 may include a current collector COL2 and a negative electrode active material layer AML2 formed on the current collector COL2. The negative electrode active material layer AML2 includes a negative electrode active material and may further include a binder and / or a conductive material.

[0022] For example, the negative electrode active material layer AML2 may contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material.

[0023] The binder serves to firmly adhere the negative electrode active material particles to each other and to firmly adhere the negative electrode active material to the current collector COL 2. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0024] Non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0025] The water-based binder may be selected from styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyether resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0026] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulose-based compound to impart viscosity. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be sodium, potassium, or lithium.

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

[0028] The conductive material is used to impart conductivity to the electrode and may be any material that does not cause chemical changes in the constructed battery and is electronically conductive. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0029] As the current collector COL2, those selected from a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, and combinations thereof can be used.

[0030] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping or dedoping lithium, or a transition metal oxide.

[0031] The material capable of reversibly inserting / desorbing lithium ions is a carbon-based negative electrode active material, which may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, fired coke, and the like.

[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 material capable of doping or dedoping 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 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 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, the silicon-carbon composite may include secondary particles (cores) formed by combining primary silicon particles, and an amorphous carbon coating layer (shell) located on the surfaces of the secondary particles. Amorphous carbon may also be located between the primary silicon particles; for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0035] 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 an amorphous carbon coating layer disposed on the core.

[0036] 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.

[0037] Separator 30 Depending on the type of lithium secondary battery, a separator 30 may be present between the positive electrode 10 and the negative electrode 20. Such separator 30 may be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof, but it goes without saying that mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0038] Separator 30 may include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0039] The porous substrate may be a polymer membrane made of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

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

[0041] The inorganic materials may include, but are not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

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

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

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

[0045] The non-aqueous organic solvent can be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, a non-quantum solvent, or a combination thereof.

[0046] Examples of carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl pyrrolyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0047] Examples of ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

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

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

[0050] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed together, and the cyclic carbonate and the chain cyclic carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0051] Lithium salts are dissolved in organic solvents and act as a source of lithium ions in the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are positive numbers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0052] Lithium secondary battery Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 2 to 5 are schematic diagrams illustrating a lithium secondary battery according to an embodiment, with FIG. 2 illustrating a cylindrical battery, FIG. 3 illustrating a prismatic battery, and FIGS. 4 and 5 illustrating pouch battery types. Referring to FIGS. 2 to 5, a lithium secondary battery 100 may include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a housing 50 in which the electrode assembly 40 is embedded. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the housing 50, as shown in FIG. 2. Also, in FIG. 3, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 4 and 5, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting the current generated in the positive electrode assembly 40 to the outside.

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

[0054] 6a and 6b are enlarged views of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. As shown in FIG. 6a, 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, as described above. A plurality of first particles PTC1 and a plurality of second particles PTC2 may constitute a positive electrode active material according to an embodiment of the present invention.

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

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

[0057] A conductive material CDM can be used to improve the conductivity of the positive electrode active material layer AML1. Any conductive material that does not cause a chemical change in the positive electrode active material layer AML1 can be used as the conductive material CDM without limitation. For example, the conductive material CDM can include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, and the like; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

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

[0059] 1st particle PTC1 Referring to FIG. 6a, 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 exist in an independent phase without being aggregated with each other in terms of morphology. For example, a single particle may be a single crystal. Alternatively, a single particle may be a particle containing several crystals. A single particle may be in a singly isolated form. Alternatively, a single particle may be in a form in which 2 to 100 single particles are attached to each other.

[0060] The first particles PTC1 may be a nano-shaped cathode active material. The first particles PTC1 may include at least one primary particle NNP. As an example, the primary particles NNP may be agglomerated to have a particle shape similar to that of the second particles PTC2. The first particles PTC1 may be agglomerated primary particles NNP but may not be spherical like the second particles PTC2. That is, the first particles PTC1 may have a random shape.

[0061] 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 about 1 μm. The minimum particle size of the first particles PTC1, i.e., the particle size of the primary particles, may be 100 nm to 500 nm, or 100 nm to 200 nm.

[0062] As an example, 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.

[0063] As an example, the minimum particle size, i.e., the particle size of the primary particles, may refer to the diameter measured by randomly selecting about 30 primary particles in an electron microscope photograph of the first particles PTC1.

[0064] The porosity of the first particles PTC1 may be greater than 40%. The first particles PTC1 may have a Span value, as analyzed by a particle size analyzer, outside the range of 0.3 to 0.75.

[0065] In one embodiment, the first particles PTC1 may include a first coating layer on their surfaces. The first coating layer may cover the entire surface of the first particles PTC1 or a portion of the surface of the first particles PTC1. For example, the first coating layer may include carbon and / or a carbon-containing compound. The first coating layer may further include at least one selected from the group consisting of a titanium-containing compound, a magnesium-containing compound, an aluminum-containing compound, and a vanadium-containing compound. The metal-containing compound, such as a titanium-containing compound, a magnesium-containing compound, an aluminum-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 metal or non-metal elements. For example, the metal-containing compound may further include lithium. The first coating layer may improve the structural stability and electrical conductivity of the first particles PTC1.

[0066] The first particles PTC1 may include an olivine-based lithium compound represented by the following Chemical Formula 1.

[0067] [Chemical formula 1] Li a1 Mn b1 Fe x1 B y1 PO 4-c1 In chemical formula 1, 0.8≦a1≦1.2, 0.5≦b1≦0.9, 0.1≦x1≦0.5, 0.001≦y1≦0.05, 0≦c1≦0.05, and b1+x1+y1=1 B may be at least one element selected from the group consisting of Mg, Ti, V, and Al. B may be a dopant doped into the first particles PTC1. For example, B may include Ti.

[0068] 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%, or 0.5 wt% to 2 wt%.

[0069] A method for measuring the elemental content in the first coating layer of the first particles PTC1 may include performing scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS) on the first particles PTC1. The carbon and metal content in the first coating layer may be confirmed through the analysis. In addition to SEM-EDS, methods for measuring the elemental content in the first coating layer may also include inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0070] As shown in Figure 6b, the first particles PTC1 may have a secondary particle shape in which a plurality of particles are attached to each other. The secondary particles may have a shape in which 2 to 100 primary particles NNP are attached to each other. The primary particles NNP are the smallest crystalline units constituting the secondary particles and are distinguished from single particles. The first particles PTC1 may have a spherical or elliptical shape.

[0071] As an example, the first particles PTC1 may include a coating layer on their surfaces. The coating layer may cover the entire surface of the first particles PTC1 or may cover a portion of the surface of the first particles PTC1. For example, the coating layer may include carbon and / or a carbon-containing compound. The coating layer may improve the structural stability of the first particles PTC1 and thereby improve electrical conductivity.

[0072] The coating layer may further include at least one selected from the group consisting of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound. Metal-containing compounds such as titanium-containing compounds, magnesium-containing compounds, and vanadium-containing compounds may be, for example, metal oxides, metal hydroxides, metal carbonates, composites thereof, or mixtures thereof. The metal-containing compounds may further include other metals or metal elements. For example, the metal-containing compounds may further include lithium.

[0073] As an example, the first particle PTC1 may further include a grain boundary coating layer on the surface of each primary particle NNP. 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 primary particles NNP inside the first particle PTC1. In other words, the grain boundary coating layer may refer to a material coated on the grain boundaries inside the first particle PTC1. The grain boundary coating layer may include carbon and / or a carbon-containing compound. The grain boundary coating layer may further include at least one selected from the group consisting of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound.

[0074] 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.

[0075] The first particles PTC1 further include a grain boundary coating portion, which strengthens structural stability and allows a uniform coating layer to be formed on the surface of the first particles PTC1. In addition, the first particles PTC1 further include a grain boundary coating portion, which further improves the electrical conductivity of the first particles PTC1.

[0076] 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 first average particle size of the first particles PTC1 may be about 5 μm. The average particle size of the first particles PTC1 may be smaller than the average particle size of the second particles PTC2 described below. In one example, the average particle size can be measured using a particle size analyzer. The average particle size may refer to the diameter of particles whose cumulative volume is 50% by volume (D50) in the particle size distribution.

[0077] The particle size of the primary particles NNP of the first particles PTC1 may be 10 to 400 nm, 20 to 300 nm, 50 to 200 nm, or 100 to 200 nm. In one embodiment, the particle size of the primary particles NNP may refer to the diameter measured by randomly selecting approximately 30 primary particles NNP in an electron microscope photograph of the positive electrode active material. The particle size of the primary particles NNP may be uniform.

[0078] The first particles PTC1 may have a spherical shape formed by the aggregation of nano-sized primary particles NNP. The first particles PTC1 may exhibit the following characteristics due to the close aggregation of the primary particles NNP: The first particles PTC1 may have a spherical or elliptical shape. The average particle size (D50) of the first particles PTC1 may be 2 μm to 15 μm. The porosity of the first particles PTC1 may be about 20% to about 40%. The Span value of the first particles PTC1 analyzed using a particle size analyzer may be 0.3 to 0.75.

[0079] 2nd particle PTC2 As shown in FIGS. 6a and 6b, 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 as or similar to that of the first particles PTC1. 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 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.

[0080] In one embodiment, the second particles PTC2 may include a second coating layer on the surface thereof. By including the second coating layer, the second particles PTC2 can effectively prevent structural collapse due to repeated charge and discharge, thereby improving the life characteristics of the secondary battery.

[0081] The second coating layer may include a boron-containing compound, an aluminum-containing compound, or a combination thereof. The metal-containing compound in the second coating layer may be, for example, a metal oxide, a metal hydroxide, a metal carbonate, a composite thereof, or a mixture thereof. The metal-containing compound may further include other metal or non-metal elements. For example, the second coating layer may further include lithium, manganese, and / or nickel.

[0082] The average particle size of the second particles PTC2 may be 2 μm to 15 μm, 2 μm to 10 μm, or 4 μm to 10 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 multiple single particles, the average size of the single particles of the second particles PTC2 may be larger than the average particle size of the first particles PTC1.

[0083] As an example, more than 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 determined as the average particle size.

[0084] The second particles PTC2 may include a lithium compound represented by the following Chemical Formula 2.

[0085] [Chemical formula 2] Li a2 Fe b2 O c2 In Chemical Formula 2, 1≦a2≦5, 0.9≦b2≦1.1, and 2≦c2≦4.

[0086] The second particles PTC2 may further include carbon derived from the coating layer. The carbon element content in the second particles PTC2 may be 0.5 wt% to 5 wt%, 0.5 wt% to 3 wt%, or 0.5 wt% to 2 wt%. The carbon content of the second particles PTC2 may be lower than the carbon content of the first particles PTC1. This is because the second particles PTC2, as single particles, are less likely to form a coating layer smoothly than the first particles PTC1, which are secondary particles.

[0087] The second particles PTC2 can participate in the formation of a solid electrolyte interface (SEI) film on the negative electrode surface during charge and discharge. The second particles PTC2 can be converted to irreversible Li, which no longer participates in charge and discharge reactions. This can cause a problem of a decrease in the capacity of the positive electrode active material layer AML1.

[0088] The second particles PTC2 according to one embodiment of the present invention may include an oxide containing Fe. The second particles PTC2 may function as a sacrificial positive electrode capable of compensating for irreversible Li. The second particles PTC2 may be decomposed during the formation process to provide Li, and may not participate in the subsequent charge / discharge process.

[0089] For example, LiFeO4 can be used as a compound constituting the second particles PTC2. It can be decomposed between 3.7V and 3.9V relative to Li to provide four Li atoms. When the second particles PTC2 containing the compound are used in the content range described below, it can sufficiently compensate for irreversible Li.

[0090] The second particles PTC2 according to one embodiment of the present invention may include Li5FeO4, LiFeO2, LiFe5O8, or a combination thereof. For example, the second particles PTC2 may include Li5FeO4. Li5FeO4 can provide many Li atoms during the formation process, thereby compensating for the irreversible Li charge more effectively. This can enhance the effect of the sacrificial positive electrode.

[0091] Referring again to Figures 6a and 6b, 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 50:50. Alternatively, the mixing ratio may be 95:5 to 99.5:0.5. The content of the first particles PTC1 in the cathode active material may be greater than the content of the second particles PTC2.

[0092] The second particles PTC2 contain a high-nickel cathode active material, and therefore can provide a higher capacity than the first particles PTC1. The cathode active material according to this embodiment can improve the capacity and operating voltage compared to a typical LMFP battery by mixing the first particles PTC1 and the second particles PTC2 in an appropriate ratio.

[0093] 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 particle PTC2 as a single particle.

[0094] The first particles PTC1 have 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.

[0095] The cathode active material of the present invention can improve the mixture density, capacity, and energy density by mixing the first particles PTC1, which are several hundred nanometers in size, with the second particles PTC2, which are several micrometers in size. In one embodiment, the compressed density of the cathode active material of the present invention can be 2.0 g / cc to 2.5 g / cc. A lithium secondary battery including the cathode active material of the present invention can improve low-temperature characteristics.

[0096] 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 second particles PTC2, which have a larger average particle size, allowing the cathode active material layer AML1 to adhere smoothly to the current collector COL1. In other words, the use of second particles PTC2 allows the amount of binder BND in the cathode active material layer AML1 to be reduced.

[0097] A lithium secondary battery (see FIG. 1) including the cathode active material according to the above-described embodiment of the present invention may have an average voltage of 3.2 V to 3.7 V when discharged at 0.1 C between 2.5 V and 4.4 V. In addition, a differential capacity (dQ / dV)-voltage charge graph for the lithium secondary battery of the present invention may have three to five charge peaks appearing between 3.55 V and 4.25 V. In the graph, the ratio (IB / IA) of the intensity of Peak B (IB) between 4.1 V and 4.25 V to the intensity of Peak A (IA) between 3.41 V and 3.55 V may be 0.005 to 0.008.

[0098] Method for producing positive electrode active material A method for producing first particles 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 are mixed in a solvent. 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.

[0099] The lithium source may include at least one selected from the group consisting of lithium oxide, lithium hydroxide, lithium chloride, lithium nitrate, lithium nitrite, lithium formate, lithium acetate, lithium oxalate, lithium carbonate, lithium phosphate, lithium dihydrogen phosphate, lithium dihydrogen phosphate, and lithium citrate.

[0100] The carbon source may include at least one selected from the group consisting of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol, and dopamine.

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

[0102] The mixture can be wet-milled. A typical temperature-controllable wet mill can 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 can be used for wet-milling. Through the wet-milling process, particles in the mixture can be pulverized to a fine size.

[0103] The solvent can be removed from the mixture to form a dried mixture. In one embodiment of the present invention, forming the dried mixture can include subjecting the mixture to direct evaporation. For example, direct evaporation can include static drying or spray drying.

[0104] 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 may be formed.

[0105] The fired first particles PTC1 may be subjected to a dry grinding process, so that the first particles PTC1 may have a single particle shape as shown in FIG.

[0106] A method for producing the first particles PTC1 according to an embodiment of the present invention will now be described in more detail. A manganese iron phosphate precursor, a lithium source, a carbon source, and a dopant source are mixed in a solvent. For example, the solvent may be water, ethanol, or the like.

[0107] The manganese iron phosphate precursor can be a compound containing all of manganese (Mn), iron (Fe), and phosphorus (P); a mixture of a manganese (Mn)-containing compound and a compound containing iron (Fe) and phosphorus (P); or a mixture of a manganese (Mn)-containing compound, an iron (Fe)-containing compound, and a phosphorus (P)-containing compound. For example, the manganese iron phosphate precursor can be a compound containing Mn x Fe 1-x PO4·H2O; a mixture of MnCO3 and FePO4·H2O; or a mixture of MnCO3, FeSO4 and H3PO4; where x can be 0.5 to 0.9.

[0108] The mixture can be subjected to wet milling.

[0109] The solvent can be removed from the mixture to form a dried mixture. Forming the dried mixture can include subjecting the mixture to a direct evaporation method. For example, the direct evaporation method can include static drying or spray drying. Static drying is preferably used to form the first particles PTC1 as single particles.

[0110] The dried mixture can be fired under an inert atmosphere to form first particles PTC1 containing the compound of Formula 1 described above.

[0111] The fired first particles PTC1 may be subjected to a dry grinding process, so that the first particles PTC1 may have a single particle form.

[0112] The prepared first particles PTC1 and second particles PTC2 are mixed in an appropriate ratio to form a positive electrode active material according to an embodiment of the present invention.

[0113] A method for producing the secondary particle form of the first particles PTC1 according to an embodiment of the present invention will be described in more detail. In one embodiment of the present invention, wet pulverization may be omitted. Specifically, in order to maximize the average particle size of the first particles PTC1 finally produced, wet pulverization of the precursor particles may be omitted.

[0114] A dried mixture can be formed by removing the solvent from the mixture. In one embodiment of the present invention, forming the dried mixture can include spray drying the mixture. The spray drying can be performed using commonly used spray drying equipment. For example, the spray drying can be performed using at least one selected from an ultrasonic spray dryer, an air nozzle spray dryer, an ultrasonic nozzle spray dryer, a filter expansion droplet generator, and an electrostatic spray dryer.

[0115] The particles refined to the size of primary particles NNP through the wet milling process can be agglomerated together through the spray drying process to form secondary particles. Therefore, the primary particles PTC1 can be formed in the form of secondary particles of a desired size by adjusting the flow rate and velocity of the carrier gas, temperature, residence time in the reactor, and internal pressure during the spray drying process.

[0116] As an example, the mixture to be spray-dried may have a total solid content of 20% to 40%. The solid content may refer to the weight of the solid material (i.e., the dried mixture) remaining after the solvent has evaporated relative to the total weight of the mixture (i.e., the spray liquid), expressed as a percentage. As an example, the spray liquid may have a solid content of approximately 30 wt%.

[0117] If the solid content is less than 20%, the average particle size of the first particles PTC1 may become small, which may result in problems such as low productivity, whereas if the solid content is more than 40%, it may become difficult to control the average particle size of the first particles PTC1, which may result in large size deviations of the first particles PTC1.

[0118] 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.

[0119] In one embodiment, spray drying can be carried out at a temperature of 100°C to 300°C. The propellant gas (e.g., air) used in spray drying can be introduced at a first temperature and discharged at a second temperature. For example, the first temperature can be 200°C to 250°C. The second temperature can be 80°C to 150°C.

[0120] The flow rate of the spray liquid for spray drying may be 30 ml / min to 80 ml / min. If the flow rate is less than 30 ml / min, problems such as nozzle clogging and reduced productivity may occur. If the flow rate is greater than 80 ml / min, water condensation within the spray dryer may cause the mixture to be incompletely dried. The input pressure of the spray liquid may be 0.3 MPa to 0.7 MPa. For example, the input pressure of the spray liquid may be about 0.5 MPa.

[0121] 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 carried out for 4 hours to 20 hours, or 6 hours to 12 hours. By calcining the dried mixture, first particles PTC1 containing the compound of Formula 1 may be formed.

[0122] In the method for producing the secondary particle form of the first particle PTC1 according to the present invention, a carbon source is introduced into an iron phosphate precursor to uniformly form a carbon coating layer on the surface of the primary particles NNP, and then the primary particles NNP are closely aggregated through spray drying to form dense secondary spherical particles.

[0123] According to one embodiment of the present invention, the second particle PTC2 may be LFO, which can mitigate Li-ion stock loss. LFO may refer to a compound having the composition LiFeO. LFO is effective for graphite anodes and can also be used as a prelithiation source for Si anodes. LFO is a Li-rich cathode material and can have high anion redox reactivity. LFO may be introduced as an additive in the cathode, which can cause low energy density due to the presence of by-products in the cathode matrix. Additionally, the particle size of the starting material, FeO, is one of the factors that determine the reactivity of LFO.

[0124] The first particles PTC1 and the second particles PTC2 prepared by the above methods can be mixed together to prepare the cathode active material according to the present invention. The first particles PTC1 and the second particles PTC2 can be mixed in a weight ratio of 90:10 to 50:50, or 95:5 to 99.5:0.5.

[0125] Carbon elemental analysis according to an embodiment of the present invention can be performed using an Elementar Micro Cube elemental analyzer. Specific operating methods and conditions are as follows: 1-2 mg of sample is weighed into a tin cup, placed on an automatic sampling tray, and introduced into a combustion tube via a ball valve. The sample is then burned at a combustion temperature of 1000°C. The burned gas is then reduced using reduced copper to form carbon dioxide. Carbon dioxide is detected using a TCD detector.

[0126] In the present embodiment, the carbon content was measured by quantitative analysis of the particle surface using scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS). Other methods for measuring the carbon content include inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0127] Examples of the present invention and comparative examples are described below. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0128] Example 1: Production of first particles in the form of single particles and first particles in the form of secondary particles Mn 0.6 Fe 0.4 An iron phosphate precursor (FePO4), lithium carbonate, and titanium dioxide were mixed in a molar ratio of 1:1.03:0.03. 12 wt% glucose was added to the mixture. Furthermore, an iron phosphate precursor (FePO4), MnCO3, LDP (LiH2PO4), lithium carbonate, and titanium dioxide were mixed in a molar ratio of 0.4:0.6:0.6:0.43:0.03. 12 wt% glucose was added to the mixture. The mixture was wet-pulverized using a ball mill. The mixture was evaporated to dryness in a heating oven tray and then dried in a vacuum oven at 120°C for 4 hours. The dried mixture was calcined at 750°C for 10 hours under a nitrogen atmosphere. The calcined product was pulverized to obtain primary particles in the form of single particles. The average size of the primary particles was approximately 100 nm to approximately 300 nm. The mixture was spray-dried at a spray pressure of 0.5 MPa and a temperature of 230°C, followed by evaporation. The dried mixture was calcined at 750°C for 10 hours under a nitrogen atmosphere to obtain primary particles in the form of secondary particles.

[0129] Preparation Example 2: Preparation of second particles in single particle form To prepare Li5FeO4, LiOH·H2O and Fe2O3 were mixed in the ratios of Li:Fe = 5:1 and 6:1, respectively. The mixed powder was then milled in a Spex mill for 30 minutes and then pelletized at a pressure of 6.1 to 6.3 tons. The pellets were calcined at 850 °C for 20 hours.

[0130] Example 1-1: Preparation of a mixture of single particle-shaped first particles and second particles Manufacturing example The first particles in the form of single particles of Preparation Example 1 and the second particles of Preparation Example 2 were mixed in a mass ratio of 99.5:0.5 to prepare a positive electrode active material.

[0131] Example 1-2: Preparation of a mixture of single particle-shaped first particles and second particles Manufacturing example The first particles in the form of single particles of Preparation Example 1 and the second particles of Preparation Example 2 were mixed in a mass ratio of 99:1 to prepare a positive electrode active material.

[0132] Examples 1-3: Preparation of a mixture of single particle-shaped first particles and second particles Manufacturing example The first particles in the form of single particles of Preparation Example 1 and the second particles of Preparation Example 2 were mixed in a mass ratio of 97.5:2.5 to prepare a positive electrode active material.

[0133] Examples 1-4: Preparation of a mixture of single particle-shaped first particles and second particles Manufacturing example The first particles in the form of single particles of Preparation Example 1 and the second particles of Preparation Example 2 were mixed in a mass ratio of 95:5 to prepare a positive electrode active material.

[0134] Example 2-1: Preparation of a mixture of primary particles and secondary particles in the form of secondary particles Manufacturing example The first particles in the form of secondary particles of Preparation Example 1 and the second particles of Preparation Example 2 were mixed in a mass ratio of 99.5:0.5 to prepare a positive electrode active material.

[0135] Example 2-2: Preparation of a mixture of primary particles and secondary particles in the form of secondary particles Manufacturing example The first particles in the form of secondary particles of Preparation Example 1 and the second particles of Preparation Example 2 were mixed in a mass ratio of 99:1 to prepare a positive electrode active material.

[0136] Example 2-3: Preparation of a mixture of primary particles and secondary particles in the form of secondary particles Manufacturing exampleThe first particles in the form of secondary particles of Preparation Example 1 and the second particles of Preparation Example 2 were mixed in a mass ratio of 97.5:2.5 to prepare a positive electrode active material.

[0137] Example 2-4: Preparation of a mixture of primary particles and secondary particles in the form of secondary particles Manufacturing example The first particles in the form of secondary particles of Preparation Example 1 and the second particles of Preparation Example 2 were mixed in a mass ratio of 95:5 to prepare a positive electrode active material.

[0138] Comparative Example 1-1: Preparation of a positive electrode active material consisting only of first particles Manufacturing example A positive electrode active material consisting of only the first particles in the form of single particles 1 was prepared.

[0139] Comparative Example 1-2: Production of a positive electrode active material consisting only of second particles A positive electrode active material consisting of only the single crystal second particles of Preparation Example 2 was prepared.

[0140] 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.

[0141] 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.

[0142] Lithium secondary battery manufacturing A coin full cell was fabricated using the prepared positive and negative electrodes. A polypropylene membrane (Celgard 3510) was used as the separator. The electrolyte was a mixture of 1.3M LiPF6 with a mixed solvent of EC (ethylene carbonate), DEC (diethyl carbonate), and FEC (fluoroethylene carbonate) (volume ratio: 2:6:2).

[0143] Evaluation example 1: Analysis of the surface of the positive electrode active material An SEM image of the first particles prepared in Example 1 is shown in Figure 7a. An SEM image of the second particles having a single crystal form is shown in Figure 7b. Referring to Figure 7a, it can be seen that the first particles according to an embodiment of the present invention have a nano-sized fine single particle form. As shown in Figure 7b, it can be seen that the second particles according to an embodiment of the present invention have a micrometer-sized single crystal form. It can be seen that the second particles have a single crystal form and are larger in particle size than the first particles when compared to Figure 7a.

[0144] Evaluation example 2: Active material evaluation The average particle size (D50) and average pellet density (PD) of the positive electrode active materials of Examples 1, 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, and 2-4 were measured, and the results are shown in Table 1.

[0145] [Table 1]

[0146] As shown in Table 1, the cathode active materials according to Examples 2-1 to 2-4 of the present invention exhibited significantly increased average particle size (D50) compared to the cathode active materials according to Examples 1-1 to 1-4. Additionally, the cathode active materials according to Examples 1-1 to 1-4 also exhibited increased average compressed density compared to the cathode active materials according to Examples 2-1 to 2-4.

[0147] Evaluation example 3: Battery characteristic evaluation The characteristics of lithium secondary batteries manufactured using the positive electrode active materials of Examples 1, 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3 and 2-4 were evaluated.

[0148] Lithium secondary batteries were prepared in the form of coin cells and powder, and initially charged at a constant current (0.1 C) and constant voltage (5 V). After a 10-minute rest, the batteries were discharged at a constant current (0.1 C) down to 3.0 V. The initial charge-discharge tests were performed. The positive electrode energy density was measured using additional powder samples. The battery characteristics were evaluated as shown in Table 2 below.

[0149] [Table 2]

[0150] As shown in Table 2, the secondary batteries according to Examples 1-1 to 2-4 of the present invention were confirmed to have excellent capacity and efficiency characteristics. Specifically, the secondary battery according to Example 1-1 of the present invention had the highest efficiency and the highest positive electrode energy density compared to the other examples. The battery according to Example 1-2 had the next highest efficiency, and it was confirmed that the optimal mixing ratios of the first particles and the second particles were 99.5:0.5 and 99:1 by weight.

[0151] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is natural that these also fall within the scope of the present invention. [Explanation of symbols]

[0152] 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. 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 mixing ratio of the first particles to the second particles is 95:5 to 99.5:0.5 of the positive electrode active material: [Chemical formula 1] Li a1 Mn b1 Fe x1 B y1 2O 4-c1 In the formula 1, 0.8≦a1≦1.2, 0.5≦b1≦0.9, 0.1≦x1≦0.5, 0.001≦y1≦0.05, 0≦c1≦0.05, and b1+x1+y1=1; B is at least one element selected from the group consisting of Mg, Ti, V, and Al; [Chemical formula 2] Li a2 Fe b2 O c2 In the above Chemical Formula 2, 1≦a2≦5, 0.9≦b2≦1.1, and 2≦c2≦4.

2. 2. The positive electrode active material of claim 1, wherein the mixing ratio is 99:1 to 99.5:0.

5.

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

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

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

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

7. The positive electrode active material of claim 1 , wherein the first average particle size is 0.4 μm to 10 μm.

8. The positive electrode active material of claim 1 , wherein the second average particle size is 4 μm to 10 μm.

9. 2. The positive electrode active material of claim 1, wherein the positive electrode active material has a compressed density of 2.0 g / cc to 2.5 g / cc.

10. 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.

11. 11. The positive electrode for a lithium secondary battery according to claim 10, 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.

12. 11. The positive electrode for a lithium secondary battery according to claim 10, 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.

13. 11. The positive electrode for a lithium secondary battery according to claim 10, 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.

14. 11. The positive electrode for a lithium secondary battery according to claim 10, wherein the conductive material comprises: a carbon-based material such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, or carbon nanotube; a metal-based material in the form of a metal powder or metal fiber containing copper, nickel, aluminum, silver, or the like; a conductive polymer such as a polyphenylene derivative; or a mixture thereof.

15. The positive electrode according to claim 10; a negative electrode including a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector; a separator between the positive electrode and the negative electrode.

16. 16. The lithium secondary battery according to claim 15, wherein the average voltage when discharged at 0.1 C between 2.5 V and 4.4 V is 3.2 V to 3.7 V.

17. 16. The lithium secondary battery according to claim 15, wherein the number of charging peaks appearing in the range of 3.55V to 4.25V in a differential capacity (dQ / dV)-voltage charging graph is 3 to 5.

18. 16. The lithium secondary battery according to claim 15, wherein in a differential capacity (dQ / dV)-voltage charging graph, the ratio (IB / IA) of the intensity of Peak B (IB) at 4.1 V to the intensity of Peak A (IA) at 3.41 V to 3.55 V is 0.005 to 0.008.

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