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

Abstract

To provide a positive electrode active material with high energy density, high operation voltage, and high conductivity.SOLUTION: The present invention relates to a positive electrode active material for a lithium secondary battery, a manufacturing method for the same, and a lithium secondary battery including the same. More specifically, the positive electrode active material includes first particles containing a compound of Chemical Formula 1 and having a first average particle diameter, and second particles containing a compound of Chemical Formula 2 and having a second average particle diameter that is larger than the first average particle diameter. The content of the first particles is greater than or equal to the content of the second particles. [Chemical Formula 1] Lia1Mnx1Fey1Bz1 PO4-b1 (in which B is at least one element selected from the group consisting of Al, Ti, V, Mg, and Nb) [Chemical Formula 2] Lia2 Nix2Coy2Mnz2Xc2O2-b2 (in which X is at least one element selected from the group consisting of Al, Ti, Mg, Zr, Mo, and Nb).SELECTED DRAWING: Figure 6

Description

[Technical Field]

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

[0002] Recently, with the rapid spread of battery-powered electronic devices such as mobile phones, notebook computers, and electric vehicles, the demand for high-energy-density, high-capacity secondary batteries has been rapidly increasing. Accordingly, research and development efforts to improve the performance of lithium secondary batteries have been actively conducted.

[0003] A lithium secondary battery is a battery that includes a cathode and an anode, each containing an active material capable of intercalating and deintercalating lithium ions, and an electrolyte. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are intercalated and deintercalated at the cathode and anode. Summary of the Invention [Problem to be solved by the invention]

[0004] 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.

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

[0006] The positive electrode active material according to the concept of the present invention can include a first particle containing a compound of Chemical Formula 1 below and having a first average particle diameter, and a second particle containing a compound of Chemical Formula 2 below and having a second average particle diameter larger than the first average particle diameter. The content of the first particle may be greater than or equal to the content of the second particle. [Chemical Formula 1] Li a1 Mn x1 Fe y1 B z1 PO 4-b1

[0007] In the above formula 1, 0.8 ≦ a1 ≦ 1.2, 0.5 ≦ x1 ≦ 0.7, 0.3 ≦ y1 ≦ 0.5, 0 < z1 ≦ 0.1, 0 ≦ b1 ≦ 0.05, and x1 + y1 + z1 = 1 can be satisfied.

[0008] B can be at least one element selected from the group consisting of Al, Ti, V, Mg, and Nb.

[0009] [Chemical Formula 2] Li a2 Ni x2 Co y2 Mn z2 X c2 O 2-b2

[0010] In the above formula 2, 0.8 ≦ a2 ≦ 1.2, 0.5 ≦ x2 ≦ 0.8, 0 ≦ y2 ≦ 0.3, 0.1 ≦ z2 ≦ 0.5 0 ≦ c2 ≦ 0.05, 0 < b2 ≦ 0.05, and x2 + y2 + z2 + c2 = 1 can be satisfied.

[0011] X can be at least one element selected from the group consisting of Al, Ti, Mg, Zr, Mo, and Nb.

[0012] The positive electrode for a lithium secondary battery according to another concept of the present invention can 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 can include the positive electrode active material, a conductive material, and a binder.

[0013] A lithium secondary battery according to another aspect of the present invention may include the positive electrode, a negative electrode current collector, a negative electrode including a negative electrode active material layer on the negative electrode current collector, and a separator between the positive electrode and the negative electrode. [Effects of the Invention]

[0014] The positive electrode active material according to the present invention can improve pellet density, capacity, and energy density by mixing layered second particles of several microns in size with olivine-based first particles of several hundred nanometers in size. The positive electrode active material layer according to the present invention can be smoothly attached to the positive electrode current collector even with a relatively small amount of binder. The lithium secondary battery according to the present invention can have a relatively high average voltage. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a conceptual diagram illustrating a lithium secondary battery according to an embodiment of the present invention; [Figure 2] FIG. 2 is a schematic diagram showing a lithium secondary battery according to an embodiment, in which the battery has a cylindrical shape. [Figure 3] FIG. 3 is a schematic diagram showing a lithium secondary battery according to an embodiment, in which the battery has a prismatic shape. [Figure 4] FIG. 4 is a schematic diagram showing a lithium secondary battery according to an embodiment, in which the battery is in the form of a pouch. [Figure 5] FIG. 5 is a schematic diagram showing a lithium secondary battery according to an embodiment, in which the battery is in the form of a pouch. [Figure 6] 2 is an enlarged view of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. FIG. [Figure 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. [Figure 8] 1 is a graph showing voltage-capacity characteristics of a lithium secondary battery according to an embodiment of the present invention. [Figure 9A]1 is a graph showing differential capacity of a lithium secondary battery according to an embodiment of the present invention. [Figure 9B] 1 is a graph showing differential capacity of a lithium secondary battery according to an embodiment of the present invention. [Figure 10] FIG. 9B is a graph showing differential capacity for the lithium secondary battery according to Example 3-3. DETAILED DESCRIPTION OF THE INVENTION

[0016] In this specification, when a component is referred to as being on another component, it means that the component may be directly formed 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 realized in various forms and may undergo various modifications. The description of the present embodiments is provided solely to ensure complete disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0017] 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 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.

[0018] 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.

[0019] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0020] Unless otherwise defined herein, particle size refers to the average particle size. Furthermore, particle size refers to the average particle size (D50), which refers to the diameter of particles with a cumulative volume of 50% in a particle size distribution. The average particle size (D50) can be measured using methods well known to those skilled in the art, such as using a particle size analyzer or a transmission electron microscope (TEM) or scanning electron microscope (SEM) image. Alternatively, the average particle size (D50) can be measured using a measuring device that uses dynamic light scattering, and data analysis can be performed to count the number of particles in each particle size range, after which the average particle size (D50) can be calculated. Alternatively, the average particle size (D50) can be measured using a laser diffraction method. More specifically, when measuring by the laser diffraction method, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT3000), and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W. The average particle size (D50) based on 50% of the particle size distribution in the measuring device can then be calculated.

[0021] 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.

[0022] 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 the electrolyte solution ELL. The positive electrode 10, the negative electrode 20, and the separator 30 may be immersed in the electrolyte solution ELL.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] For example, the negative electrode active material layer AML2 may contain 90 to 99 wt % of the negative electrode active material, 0.5 to 5 wt % of the binder, and 0 to 5 wt % of the conductive material.

[0027] The binder serves to firmly adhere the negative active material particles to each other and to firmly adhere the negative 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.

[0028] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, and combinations thereof.

[0029] 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.

[0030] When an aqueous binder is used as the negative electrode binder, a cellulose-based compound that can impart viscosity may be further included. 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.

[0031] The dry binder may be a polymeric material that can be fiberized, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0032] 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 may 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.

[0033] The current collector COL2 may be made of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

[0034] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and dedoped from lithium, or a transition metal oxide.

[0035] The material capable of reversibly intercalating / deintercalating lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0036] The lithium metal alloy may be 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.

[0037] As the substance capable of being doped and undoped with lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (where Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination of these. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or a combination of these.

[0038] 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) assembled from primary silicon particles and a first coating layer (shell) of amorphous carbon located on the surface of the secondary particles. The amorphous carbon can also be located between the primary silicon particles, 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.

[0039] 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.

[0040] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by being mixed with a carbon-based negative electrode active material.

[0041] Separator 30 Depending on the type of lithium secondary battery, a separator 30 may be present between the positive electrode 10 and the negative electrode 20. As such separator 30, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, and it goes without saying that mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0042] 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.

[0043] The porous substrate may be a polymer membrane formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyacetimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these polymers.

[0044] The organic material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0045] 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.

[0046] 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.

[0047] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0048] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0049] The non-aqueous organic solvent can be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0050] Examples of the carbonate solvent 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).

[0051] 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.

[0052] 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 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.

[0053] The non-aqueous organic solvents can be used alone or in combination of two or more.

[0054] 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.

[0055] The lithium salt dissolves in an organic solvent and acts as a lithium ion source in the battery, enabling basic lithium secondary battery operation and promoting the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1SO2) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0056] 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.

[0057] 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.

[0058] 6 is an enlarged view of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. Referring to FIG. 6, as described above, the positive electrode active material layer AML1 (see FIG. 1) may include first particles PTC1, second particles PTC2, a conductive material CDM, and a binder BND. The plurality of first particles PTC1 and the plurality of second particles PTC2 may constitute a positive electrode active material according to an embodiment of the present invention.

[0059] The positive electrode active material layer AML1 may further include an additive that can act as a sacrificial positive electrode.

[0060] The content of the positive electrode active materials PTC1 and PTC2 in the positive electrode active material layer AML1 may be 90 wt% to 99.5 wt% relative to 100 wt% of the positive electrode active material layer AML1, and the content of the binder BND and the conductive material CDM may be 0.5 wt% to 5 wt% each relative to 100 wt% of the positive electrode active material layer AML1.

[0061] The binder BND can bind the first particles PTC1, the second particles PTC2, and the conductive material CDM to one another. As an example, the binder BND can include, but is not limited to, at least one selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl fluoride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0062] 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 without limitation. For example, the conductive material CDM can include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0063] Hereinafter, the first particles PTC1 and the second particles PTC2 will be described in more detail.

[0064] 1st particle PTC1 The first particle PTC1 may have a single particle form. 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 morphologically exist in an independent phase without cohesion with each other. For example, a single particle may be a single crystal. Alternatively, a single particle may be a particle containing several crystals. A single particle may be in a singly separated form. Alternatively, a single particle may be in a form in which 2 to 100 single particles are attached to each other.

[0065] The first particles PTC1 may be a nano-shaped cathode active material. The first particles PTC1 may include at least one first primary particle. In one embodiment, the first primary particles may be aggregated to have a particle shape close to a sphere. The first particles PTC1 may be aggregated first primary particles, but may not be spherical. That is, the first particles PTC1 may have a random shape.

[0066] The first particles PTC1 may be provided in various sizes. For example, the average particle size of the first particles PTC1 may be 100 nm to 2.5 μm, or about 1.1 μm. The minimum particle size of the first particles PTC1, i.e., the particle size of the first primary particles, may be 100 nm to 500 nm, or 100 nm to 200 nm.

[0067] In one embodiment, the average particle size can be measured using a particle size analyzer. The average particle size can refer to the diameter of particles whose cumulative volume is 50% by volume (D50) in the particle size distribution.

[0068] In one embodiment, the minimum particle size, i.e., the particle size of the first primary particles, may refer to the diameter measured by randomly selecting about 30 first primary particles from an electron microscope photograph of the first particles PTC1.

[0069] The porosity of the first particles PTC1 may be greater than 40%. The first particles PTC1 may have a Span value out of the range of 0.3 to 0.75 as analyzed by a particle size analyzer.

[0070] 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, 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 compound may further include other metals 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.

[0071] The first particle PTC1 can contain an olivine-based lithium compound represented by Chemical Formula 1 below. [Chemical Formula 1] Li a1 Mn x1 Fe y1 B z1 PO 4-b1

[0072] In Formula 1 above, 0.8 ≤ a1 ≤ 1.2, 0.5 ≤ x1 ≤ 0.7, 0.3 ≤ y1 ≤ 0.5, 0 < z1 ≤ 0.1, 0 ≤ b1 ≤ 0.05, and x1 + y1 + z1 = 1 can hold. B can be at least one element selected from the group consisting of Al, Ti, V, Mg, and Nb. B can be a dopant doped into the first particle PTC1. For example, B can contain Ti.

[0073] The first particle PTC1 can further contain carbon derived from the first coating layer described above. The carbon element content in the first particle PTC1 can be 0.5 wt% to 5 wt%, 0.5 wt% to 3 wt%, or 0.5 wt% to 2 wt%.

[0074] 2nd particle PTC2 The second particle PTC2 can have a single particle form. As used herein, a single particle can mean an independent particle that does not have a grain boundary inside. A single particle can mean a single particle, a monolith structure, a single body structure, or a non-aggregated particle that exists as an independent phase in which particles do not agglomerate morphologically. As an example, a single particle can be a single crystal. Or, a single particle can be a particle containing several crystals. A single particle can be in a form separated alone. Or, a single particle can be in a form in which 2 to 100 single particles are attached to each other.

[0075] The second particles PTC2 may be a nano-shaped positive electrode active material. The second particles PTC2 may include at least one second primary particle NNP2. In one embodiment, the second primary particles NNP2 may be aggregated to have a particle shape close to a sphere. The second particles PTC2 may be aggregated second primary particles NNP2, but may not be spherical. That is, the second particles PTC2 may have a random shape.

[0076] The second particles PTC2 may be provided in various sizes. For example, the average particle size of the second particles PTC2 may be 2 μm to 5 μm, or about 3.5 μm. The minimum particle size of the second particles PTC2, i.e., the particle size of the second primary particles, may be 100 nm to 500 nm, or 100 nm to 200 nm.

[0077] In one embodiment, the average particle size can be measured using a particle size analyzer. The average particle size can refer to the diameter of particles whose cumulative volume is 50% by volume (D50) in the particle size distribution.

[0078] In one embodiment, the minimum particle size, i.e., the particle size of the second primary particles, may refer to the diameter measured by randomly selecting approximately 30 second primary particles from an electron microscope photograph of the second particles PTC2. In one embodiment, the particle size of the second primary particles may be larger than the particle size of the first primary particles. In another embodiment, the particle size of the second primary particles may be substantially the same as the particle size of the first primary particles. The difference between the particle size of the second primary particles and the particle size of the first primary particles may be 100 nm or less.

[0079] The porosity of the second particles PTC2 may be greater than 40%. The Span value of the second particles PTC2, as analyzed by a particle size analyzer, may be outside the range of 0.3 to 0.75.

[0080] In one embodiment, the second particles PTC2 may include a second coating layer on their surfaces. By including the second coating layer on the second particles PTC2, the collapse of the structure due to repeated charge and discharge can be effectively suppressed. Therefore, the life characteristics of the secondary battery can be improved.

[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 metals or non-metal elements. For example, the second coating layer may further include lithium, manganese, and / or nickel, etc.

[0082] A method for measuring the metal content in the second coating layer of the second particles PTC2 may include performing scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS) on the second particles PTC2. The boron and / or aluminum content in the second coating layer may be determined through this analysis. In addition to SEM-EDS, methods for measuring the metal content in the second coating layer may also include inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0083] The second particles PTC2 may include a lithium-nickel composite oxide as a nickel-based active material. For example, the second particles PTC2 may include a high-nickel-based positive electrode active material containing a high content of nickel. The high-nickel-based positive electrode active material may achieve high capacity and high performance.

[0084] Specifically, the second particles PTC2 may include a layered lithium nickel composite oxide represented by the following Chemical Formula 2. [Chemical formula 2] Li a2 Ni x2 Co y2 Mn z2 X c2 O 2-b2

[0085] In the formula 2, 0.8 ≤ a2 ≤ 1.2, 0.5 ≤ x2 ≤ 0.8, 0 ≤ y2 ≤ 0.3, 0.1 ≤ z2 ≤ 0.5, 0 ≤ c2 ≤ 0.05, 0 < b2 ≤ 0.05, and x2 + y2 + z2 + c2 = 1 may hold. X may be at least one element selected from the group consisting of Al, Ti, Mg, Zr, Mo, and Nb. X may be a dopant doped into the second particle PTC2.

[0086] Referring to FIG. 6 again, the positive electrode active material according to an embodiment of the present invention will be described in more detail. The positive electrode active material of the present invention can include a first particle PTC1 and a second particle PTC2. The mixing ratio of the first particle PTC1 and the second particle PTC2 in the positive electrode active material can be 90:10 to 50:50. Or, the mixing ratio can be 90:10 to 70:30. The content of the first particle PTC1 in the positive electrode active material may be greater than the content of the second particle PTC2.

[0087] As one embodiment, the mixing ratio of the first particle PTC1 and the second particle PTC2 may be adjusted so that the content of Mn is 20% to 55% in the total weight of the metal elements excluding lithium in the positive electrode active material.

[0088] Since the first particle PTC1 contains Mn, the operating voltage of the secondary battery can be improved compared to the second particle PTC1. The positive electrode active material according to this embodiment can improve the operating voltage compared to a general LFP battery by adjusting the content of Mn to be 20% to 45% by mixing the first particle PTC1 and the second particle PTC2 in an appropriate ratio.

[0089] As one embodiment, the mixing ratio of the first particle PTC1 and the second particle PTC2 may be adjusted so that the content of Ni is 5% to 30% in the total weight of the metal elements excluding lithium in the positive electrode active material.

[0090] The second particles PTC2 contain Ni, which can improve the energy density of the secondary battery compared to the first particles PTC1. The positive electrode active material according to this embodiment mixes the first particles PTC1 and the second particles PTC2 in an appropriate ratio and adjusts the Ni content to 10% to 20%, thereby improving the energy density compared to a typical LFP battery.

[0091] In one embodiment, the mixing ratio of the first particles PTC1 and the second particles PTC2 may be adjusted so that the weight ratio of Ni to Mn (Ni weight / Mn weight) is 0.125 to 1.5 based on the total weight of metal elements excluding lithium in the positive electrode active material. By mixing the first particles PTC1 and the second particles PTC2 in an appropriate ratio, the operating voltage and energy density can be improved compared to conventional LFP batteries.

[0092] The second particles PTC2 contain a nickel-based positive electrode active material, and thus can achieve a higher capacity than the first particles PTC1. The positive electrode active material according to this embodiment can improve the capacity and operating voltage compared to a typical LFP battery by mixing the first particles PTC1 and the second particles PTC2 in an appropriate ratio.

[0093] The compound of Chemical Formula 2 (nickel-based positive electrode active material) may have lower electrical conductivity than the compound of Chemical Formula 1. In the present invention, the second particles PTC2 are used as single particles, thereby improving electrical conductivity and energy density.

[0094] The first particles PTC1 have the advantages of high stability and long lifespan. By using the structurally stable first particles PTC1 as the main material of the positive electrode active material, the relatively low stability and short lifespan of the second particles PTC2 can be compensated for.

[0095] The positive electrode active material of the present invention can improve pellet density, capacity, and energy density by mixing the first particles PTC1, which are several micrometers in size, with the second particles PTC2, which are several micrometers in size. In one embodiment, the positive electrode active material of the present invention can have a compressed density of 2.0 g / cc to 4.0 g / cc, or 2.0 g / cc to 3.0 g / cc. A lithium secondary battery including the positive electrode active material of the present invention can have improved 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 the second particles PTC2, which have a larger average particle size, thereby enabling the cathode active material layer AML1 to adhere smoothly to the current collector COL1. That is, the second particles PTC2 can reduce the amount of binder BND in the cathode active material layer AML1.

[0097] A lithium secondary battery (see FIG. 1) including the above-described positive electrode active material according to an embodiment of the present invention may have an average voltage of 3.2 V to 4.5 V when discharged at 0.1 C between 2.5 V and 4.5 V. In addition, a differential capacity (dQ / dV) vs. voltage charge graph for the lithium secondary battery of the present invention may have at least two charge peaks appearing between 3.4 V and 4.0 V. In addition, when the peak between 3.4 V and 3.6 V in the differential capacity (dQ / dV) vs. voltage charge graph for the lithium secondary battery of the present invention is defined as Peak A and the peak between 3.6 V and 4.0 V is defined as Peak B, the intensity of Peak A (IA) may be greater than the intensity of Peak B (IB).

[0098] In the graph, the ratio (IB / IA) of the intensity of Peak B (IB) between 3.6 V and 4.0 V to the intensity of Peak A (IA) between 3.4 V and 3.6 V may be 0.001 to 0.3, or 0.005 to 0.26.

[0099] Method for producing positive electrode active material 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 may be mixed in a solvent (S100). For example, the solvent may be water, ethanol, or the like.

[0100] The manganese iron phosphate precursor may 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 may be a compound containing Mn x Fe 1-x PO4·H2O; a mixture of MnCO3 and FePO4·H2O; or a mixture of MnCO3, FeSO4, and H3PO4, where x can be from 0.5 to 0.9.

[0101] The lithium source can include at least one selected from the group consisting of lithium oxide, lithium hydroxide, lithium chloride, lithium nitrate, lithium nitrite, lithium formate, lithium acetate, lithium oxalate, lithium carbonate, lithium phosphate, lithium dihydrogen phosphate, lithium dihydrogen phosphate, and lithium citrate.

[0102] The carbon source can include at least one selected from the group consisting of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol, and dopamine.

[0103] 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.

[0104] The mixture may be subjected to wet milling (S200). The wet milling may be performed using a conventional wet mill capable of controlling the temperature. Specifically, the wet milling may be performed using at least one selected from a bead mill, a ball mill, an attrition mill, an apex mill, a super mill, and a basket mill. Through the wet milling process, particles in the mixture may be milled to a fine size.

[0105] In one embodiment of the present invention, the wet-milling step (S200) may be omitted. Specifically, in order to maximize the average particle size of the first particles PTC1 that are finally produced, the wet-milling step (S200) of the precursor particles may be omitted.

[0106] 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, a direct evaporation method can include static drying or spray drying. It may be desirable to use static drying to form the first particles PTC1 as single particles.

[0107] The dried mixture may be calcined under an inert atmosphere (S400). The inert atmosphere may be a nitrogen atmosphere and / or an argon atmosphere. The temperature of the calcination process may be 500°C to 1000°C or 600°C to 800°C. The calcination process may be performed for 4 hours to 20 hours, or 6 hours to 12 hours. By calcining the dried mixture, first particles PTC1 containing the compound of Formula 1 described above may be formed.

[0108] In the method for producing the first particles PTC1 according to the present invention, a carbon coating layer can be uniformly formed on the surfaces of the primary particles by introducing a carbon source into the iron phosphate precursor.

[0109] The fired first particles PTC2 may be subjected to a dry-pulverization process. Therefore, the first particles PTC1 may have a single particle shape. Meanwhile, in the case of the first particles PTC1 described above, the dry-pulverization process may be omitted.

[0110] A method for manufacturing second particles PTC2 according to an embodiment of the present invention will now be described in detail. A nickel-based precursor may be prepared. The nickel-based precursor may include Ni of Formula 2 above. The content of Ni relative to the total content of metals in the nickel-based precursor may be greater than 50 at%. In one embodiment, the nickel-based precursor may further include Co and Mn.

[0111] In one embodiment, the nickel-based precursor is obtained by a co-precipitation method. For example, the co-precipitation method may include dissolving a transition metal source material in a solvent such as distilled water, and sequentially adding the transition metal salt solution, a chelating agent, and a basic aqueous solution to a reactor to cause precipitation. The precipitate is collected in the form of a slurry, which is then filtered and dried to obtain the nickel-based precursor, which is a metal composite oxide.

[0112] In the present invention, the transition metal source material may include a metal salt of Ni. The transition metal source material may further include a metal salt of at least one of Co and Mn. The metal salt may be a sulfate, nitrate, acetate, halide, hydroxide, or the like, and is not particularly limited as long as it is soluble in a solvent. The transition metal source material according to this embodiment may include a nickel salt, a cobalt salt, and a manganese salt. The transition metal source materials may be mixed by adjusting the molar ratio so that the nickel-based precursor has a Ni content of 50 at% or more.

[0113] The nickel-based precursor and the lithium source may be mixed in a certain ratio to form a mixture. For example, the nickel-based precursor and the lithium source may be mixed in a molar ratio of about 1:1. 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.

[0114] The solvent may be removed from the mixture to form a dried mixture. The dried mixture may then be calcined. The calcination temperature may be 700°C to 1,000°C or 900°C to 1,000°C. The calcination may be performed in an oxidizing atmosphere such as air or oxygen. The heat treatment time for the calcination may be 10 to 30 hours. In another embodiment of the present invention, pre-calcination may be performed at 150°C to 800°C prior to the calcination.

[0115] In one embodiment of the present invention, the sintering process can be performed after adding a flux to the mixture. The flux can be a compound containing at least one metal selected from the group consisting of Zr, La, S, and Nb. By using the flux, the second particles PTC2 can be smoothly formed into a single particle form. In addition, the average particle size of the second particles PTC2 can be increased.

[0116] The second particles PTC2 may be formed from the mixture containing the nickel-based precursor and the lithium source through the calcination process, and the synthesized second particles PTC2 may be subjected to a pulverization process.

[0117] A coating process can be performed on the pulverized second particles PTC2. Specifically, the second particles PTC2 and a coating raw material can be mixed in a solvent. For example, the coating raw material can include boron and / or aluminum. After filtering and drying the second particles PTC2, a surface treatment can be performed on the second particles PTC2. The surface treatment can include a heat treatment process in an oxidizing atmosphere such as air or oxygen. The surface treatment can be performed at a temperature of 500°C to 800°C.

[0118] In another embodiment of the present invention, the coating process may include a dry coating process. For example, the second particles PTC2 and the coating raw material may be mixed in a dry coating machine without a solvent and then stirred. The resulting dry mixture may be subjected to the surface treatment.

[0119] The first particles PTC1 and the second particles PTC2 prepared by the above-described methods may be mixed together to prepare a cathode active material according to the present invention. The first particles PTC1 and the second particles PTC2 may be mixed in a weight ratio of 90:10 to 60:40, 90:10 to 70:30, or 80:20 to 70:30.

[0120] Carbon elemental analysis according to an embodiment of the present invention can be performed using an Elementar Micro Cube elemental analyzer. Specific operating methods and conditions are as follows: 1-2 mg of sample is weighed into a tin cup, placed on an automatic sampling tray, and introduced into a combustion tube through a ball valve. The sample is then burned at a combustion temperature of 1000°C. The burned gas is then reduced using reduced copper to form carbon dioxide. Carbon dioxide is detected using a thermal conductivity detector (TCD).

[0121] A method for measuring the carbon content according to an embodiment of the present invention is a method for quantitatively analyzing the surface of particles using scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS). Other methods for measuring the composition include inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0122] Examples and comparative examples of the present invention will be described below. However, the examples described below are merely examples of the present invention, and the present invention is not limited to these examples.

[0123] Example 1: Preparation of single particle first particles A manganese iron phosphate precursor (a mixture of MnCO3, FeSO4, and H3PO4), lithium carbonate, titanium dioxide, and glucose were added to a 7 wt% PEG and 8 wt% glucose aqueous solution in a molar ratio of 1:1.03:0.01. The mixture was wet-pulverized using a ball mill. The mixture was evaporated to dryness in a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours. The dried mixture was calcined at 650°C for 10 hours under a nitrogen atmosphere. The calcined product was pulverized to obtain primary particles in the form of single particles. The average particle size of the primary particles was approximately 100 nm to approximately 2.5 μm.

[0124] Example 2: Preparation of second particles in single particle form A nickel-based precursor was manufactured using the coprecipitation method. Specifically, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O) were dissolved in distilled water as a solvent in a molar ratio of 60:10:30 to prepare a metal raw material mixture. The metal raw material mixture, ammonia water, and sodium hydroxide were added to a reactor and reacted. The slurry solution in the reactor was filtered and washed with high-purity distilled water. The washed material was dried in a hot air oven at 210°C for 24 hours to obtain a small-particle precursor (NiSO4·6H2O) with an average particle size of approximately 4 μm. 0.60 Co 0.1 Mn 0.3 (OH)2) powder was obtained.

[0125] A nickel-based precursor and anhydrous lithium hydroxide (LiOH) were dry-mixed using a Henschel mixer. The lithium and transition metals were mixed in a molar ratio of approximately 1.04:1. The transition metals were the total amount of transition metals (Ni, Co, Mn) contained in the nickel-based precursor. A melting agent was added to the mixture, and the mixture was heat-treated (i.e., calcined) in an oxygen atmosphere at approximately 750°C for 15 hours to synthesize second particles, which are nickel-based positive electrode active materials. The second particles were pulverized in a jet mill at a pressure of 3 bar.

[0126] The second particles were washed by adding them to distilled water. Boron oxide and aluminum oxide were added in an amount equivalent to 3 mol% of the total amount of transition metals in the second particles to perform boron and aluminum coating. The second particles were dried at 150°C for 12 hours and then heat-treated (i.e., surface-treated) at approximately 700°C for 15 hours in an oxygen atmosphere.

[0127] Example 3-1: Preparation of a mixture of first particles and second particles The first particles of Example 1 and the second particles of Example 2 were mixed in a mass ratio of 9:1 to prepare a positive electrode active material.

[0128] Example 3-2: Preparation of a mixture of first particles and second particles The first particles of Example 1 and the second particles of Example 2 were mixed in a mass ratio of 8:2 to prepare a positive electrode active material.

[0129] Example 3-3: Preparation of a mixture of first particles and second particles The first particles of Example 1 and the second particles of Example 2 were mixed in a mass ratio of 7:3 to prepare a positive electrode active material.

[0130] Example 3-4: Preparation of a mixture of first particles and second particles The first particles of Example 1 and the second particles of Example 2 were mixed in a mass ratio of 6:4 to prepare a positive electrode active material.

[0131] Examples 3-5: Preparation of a mixture of first particles and second particles The first particles of Example 1 and the second particles of Example 2 were mixed in a mass ratio of 5:5 to prepare a positive electrode active material.

[0132] 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.

[0133] Anode manufacturing Graphite, a binder, and a conductive material were mixed in N-methylpyrrolidone solvent to prepare a negative electrode active material slurry, which was then coated on a copper current collector, dried, and rolled to prepare a negative electrode.

[0134] Lithium secondary battery manufacturing A coin-pull cell was fabricated using the prepared positive and negative electrodes. A polypropylene membrane (Celgard 3510) was used as the separator. The electrolyte was a mixture of 1.3M LiPF6 and a mixed solvent of EC (ethylene carbonate), DEC (diethyl carbonate), and FEC (fluoroethylene carbonate) (2:6:2 volume ratio).

[0135] Evaluation example 1: Analysis of the surface of the positive electrode active material FIG. 7A shows an SEM image of the first particles prepared in Example 1. FIG. 7B shows an SEM image of the second particles prepared in Example 2. Referring to FIG. 7A, it can be seen that the first particles according to an embodiment of the present invention are in the form of fine single particles of μm size. Referring to FIG. 7B, it can be seen that the second particles according to an embodiment of the present invention are in the form of single particles of μm size. It can be seen that the first particles and the second particles are in the form of a single particle or a plurality of single particles attached to each other.

[0136] 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, 2, 3-1, 3-2, 3-3, 3-4, and 3-5 were measured, and the results are shown in Table 1.

[0137] [Table 1]

[0138] Referring to Table 1, it can be seen that the cathode active materials according to Examples 3-1 to 3-5 of the present invention have a higher average particle size (D50) than the cathode active material of Example 1. It can also be seen that the cathode active materials according to Examples 3-1 to 3-5 have a higher average compressed density than the cathode active material of Example 1.

[0139] Evaluation example 3: Battery characteristic evaluation The characteristics of lithium secondary batteries manufactured using the positive electrode active materials of Examples 1, 2, 3-1, 3-2, 3-3, 3-4, and 3-5 were evaluated.

[0140] The lithium secondary battery was initially charged at a constant current (1C), rested for 10 minutes, and then discharged to 2.5V at a constant current (1C) to perform initial charge-discharge. It was then charged and discharged 50 times at 4.5V-2.5V 1C / 1C at 45°C. The average voltage and capacity at 45°C were measured during the charge-discharge cycle. The battery characteristics evaluation results are shown in Table 2 below.

[0141] [Table 2]

[0142] Referring to Table 2, it can be seen that the secondary batteries according to Examples 3-1 to 3-4 of the present invention have a much greater capacity increase than the secondary battery according to Example 1. It can also be seen that the secondary batteries according to Examples 3-1 to 3-5 have a much better capacity retention rate at 45°C than the secondary battery according to Example 2.

[0143] The voltage-capacity characteristics of the lithium secondary batteries prepared using the positive electrode active materials of Examples 1, 3-1, and 3-3 were measured and are shown in Figure 8. Referring to Figure 8, it can be seen that the secondary batteries prepared in Examples 3-1 and 3-3 have increased capacities compared to the secondary battery prepared in Example 1.

[0144] The differential capacity of the lithium secondary batteries manufactured using the positive electrode active materials of Examples 1, 2, and 3-3 was evaluated.

[0145] The lithium secondary battery was charged and discharged once at 1 C, and then twice in the same manner. Figure 9A shows the measured differential capacity (dQ / dV) vs. voltage charge curve, Figure 9B is an enlarged graph of Figure 9A in the voltage range of 3.2 to 4.5 V, and Figure 10 shows only the graph of Example 3-3 in Figure 9B.

[0146] 10, it can be seen that the secondary battery according to Example 3-3 has two or more charging peaks appearing at voltages between 3.4 V and 4.0 V. In contrast, the secondary battery according to Example 1 has only one peak in the voltage range.

[0147] Referring to FIG. 10, it can be seen that the ratio (IB / IA) of the intensity of Peak B (IB) between 3.6 V and 4.0 V to the intensity of Peak A (IA) between 3.4 V and 3.6 V of the secondary battery according to Example 3-3 is about 0.26.

[0148] 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]

[0149] 100 Lithium secondary battery 10 positive electrode 11 Positive electrode lead tab 12 Positive terminal 20 negative electrode 21 Negative electrode lead tab 22 Negative terminal 30 Separator 40 Electrode assembly 50 cases 60 Sealing member 70 Electrode tab 71 Positive electrode tab 72 Negative electrode tab PTC1 1st particle PTC2 2nd particle NNP1 1st primary particle NNP2 2nd primary particle CDM conductive material BND Binder

Claims

1. First particles comprising a compound represented by Chemical Formula 1 below and having a first average particle size; and second particles comprising a compound of the following Chemical Formula 2 and having a second average particle size larger than the first average particle size, The content of the first particles in the positive electrode active material is greater than or equal to the content of the second particles. [Chemical formula 1] Li a1 Mn x1 Fe y1 B z1 2O 4-b1 (In the above formula 1, 0.8≦a1≦1.2, 0.5≦x1≦0.7, 0.3≦y1≦0.5, 0<z1≦0.1, 0≦b1≦0.05, and x1+y1+z1=1, B is at least one element selected from the group consisting of Al, Ti, V, Mg, and Nb. [Chemical formula 2] Li a2 Ni x2 Co y2 Mn z2 X c2 O 2-b2 (In the above formula 2, 0.8≦a2≦1.2, 0.5≦x2≦0.8, 0≦y2≦0.3, 0.1≦z2≦0.50≦c2≦0.05, 0<b2≦0.05, and x2+y2+z2+c2=1, X is at least one element selected from the group consisting of Al, Ti, Mg, Zr, Mo, and Nb.

2. The positive electrode active material of claim 1 , wherein a mixing ratio of the first particles to the second particles is in the range of 90:10 to 50:

50.

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

4. the second particles have a shape in which a plurality of single particles are adhered to each other, The positive electrode active material according to claim 1 , wherein the first particles have an average particle size smaller than the average particle size of the second particles.

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 of 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 particles have an average particle size of 100 nm to 2.5 μm.

8. The positive electrode active material of claim 1 , wherein the second average particle size is 2 μm to 5 μm.

9. 2. The positive electrode active material according to claim 1, wherein the positive electrode active material has a compressed density of 2.0 g / cc to 4.0 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 of 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, an epoxy resin, a (meth)acrylic resin, a 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 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 at least two charging peaks appear at voltages between 3.4V and 4.0V in a differential capacity (dQ / dV)-voltage charging graph.

17. In the differential capacity (dQ / dV)-voltage charging graph, having a peak A at 3.4V to 3.6V; Peak B at 3.6V to 4.0V; 16. The lithium secondary battery according to claim 15, wherein the intensity of the peak A (IA) is greater than the intensity of the peak B (IB).

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) between 3.6 V and 4.0 V to the intensity of Peak A (IA) between 3.4 V and 3.6 V is 0.005 to 0.26.

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