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

Abstract

To provide a positive electrode active material with high energy density, high operation voltage, and high conductivity.SOLUTION: The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode including the same, and a lithium secondary battery including the same. More specifically, the positive electrode active material includes first particles containing a compound of Chemical Formula 1 and second particles containing a compound of Chemical Formula 2. The content of the first particles is larger than that of the second particles and the second particles are in a single particle form.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 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 No. 10-1863094 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a positive electrode active material having high energy density, high operating voltage, and high conductivity.

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

[0007] According to the concept of the present invention, the positive electrode active material can include first particles containing a compound of Chemical Formula 1 below and second particles containing a compound of Chemical Formula 2 below. The content of the first particles is greater than the content of the second particles, and the second particles can have a single-particle form. [Chemical Formula 1] Li

[0009] , , y2 , a2 , , , c2 , , , , , z2 , x2 ,

[0008] ,

[0010] , , , Mn x1 Fe y1 B z1 PO 4-c1 In Chemical Formula 1, 0.8 ≤ a1 ≤ 1.2, 0.3 ≤ x1 ≤ 0.7, 0.3 ≤ y1 ≤ 0.7, 0 ≤ z1 ≤ 0.05, 0 ≤ c1 ≤ 0.05, and x1 + y1 + z1 = 1, and B is at least one element selected from the group consisting of Ti, Mg, and V. [Chemical Formula 2] Li a2 Ni x2 Mn y2 C z2 O c2 In Chemical Formula 2, 1.1 < a2 ≤ 1.6, 0.2 ≤ x2 ≤ 0.5, 0.5 ≤ y2 ≤ 0.8, 0 ≤ z2 ≤ 0.05, 2 < c2 ≤ 2.3, and x2 + y2 + z2 = 1, and C can be at least one element selected from the group consisting of transition metals having an oxidation number of 4.

[0008] According to another concept of the present invention, the positive electrode for a lithium secondary battery 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.

[0009] According to still another concept of the present invention, a lithium secondary battery can 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.

Advantages of the Invention

[0010] The positive electrode active material according to the present invention can improve the mixture density, capacity, and energy density by mixing high-capacity second particles with an olivine-based first particle base. The lithium secondary battery according to the present invention can have a relatively high operating 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 cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 3] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 4] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 5] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 6] 2 is an enlarged view of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. FIG. [Figure 7] 2 is an enlarged view of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. FIG. [Figure 8] 1 is a flowchart illustrating a method for manufacturing a positive electrode active material according to an embodiment of the present invention. [Figure 9a] 1 is an SEM image of the positive electrode active material of Production Example 1 of the present invention. [Figure 9b] 1 is an SEM image of the positive electrode active material of Production Example 1 of the present invention. [Figure 9c] 1 is an SEM image of the positive electrode active material of Production Example 2 of the present invention. [Figure 9d] 1 is an SEM image of the positive electrode active material of Production Example 2 of the present invention. [Figure 10a] 1 is an SEM image of the positive electrode active material of Production Example 3 of the present invention. [Figure 10b] 1 is an SEM image of the positive electrode active material of Production Example 3 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] In this specification, when a component is referred to as being on another component, it means that the component may be formed directly on the other component, or that a third component may be interposed between them. However, the present invention is not limited to the embodiments disclosed below, and may be embodied in various forms and may undergo various modifications. The description of the present embodiments is provided solely to ensure complete disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art.

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

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

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

[0016] Unless otherwise defined herein, particle size refers to the average particle size. Furthermore, particle size refers to the average particle size (D50), which refers to the diameter of particles with a cumulative volume of 50% in a particle size distribution. The average particle size (D50) can be measured using methods well known to those skilled in the art, such as using a particle size analyzer or a transmission electron microscope (TEM) or scanning electron microscope (SEM) image. Alternatively, the average particle size (D50) can be measured using a measuring device that uses dynamic light scattering, and data analysis can be performed to count the number of particles in each particle size range, after which the average particle size (D50) can be calculated. Alternatively, the average particle size (D50) can be measured using a laser diffraction method. More specifically, when measuring by the laser diffraction method, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT3000), and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W. The average particle size (D50) based on 50% of the particle size distribution in the measuring device can then be calculated.

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

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

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

[0020] positive electrode 10 The positive electrode 10 for a lithium secondary battery may include a current collector COL1 and a positive electrode active material layer AML1 formed on the current collector COL1. The positive electrode active material layer AML1 includes a positive electrode active material and may further include a binder and / or a conductive material. A detailed description of the positive electrode active material layer AML1 according to an embodiment of the present invention will be provided below with reference to FIGS. 6 and 7. The current collector COL1 may be made of, but is not limited to, aluminum.

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

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

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

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

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

[0026] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulose-based compound that can impart viscosity. The cellulose-based compound may be 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 can be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0028] The conductive material is used to impart conductivity to the electrode, and any material that is electronically conductive without causing a chemical change in the battery that is constructed can be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0029] As the current collector COL2, 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, or a combination thereof can be selected and 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 and undoping lithium, or a transition metal oxide.

[0031] As the material capable of reversibly inserting / desorbing lithium ions, a carbon-based negative electrode active material can be included, 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, calcined 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 and undoping 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 a combination 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, it may include secondary particles (cores) formed by assembling primary silicon particles and a first coating layer (shell) of amorphous carbon located on the surfaces of the secondary particles. Amorphous carbon may also be located between the primary silicon particles, for example, coating the primary silicon particles with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[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 a first coating layer of amorphous carbon disposed on the core.

[0036] A Si-based negative electrode active material or a 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. As such a separator 30, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof can 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 can also be used.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0054] 6 and 7 are enlarged views of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. Referring to FIGS. 6 and 7, as described above, the positive electrode active material layer AML1 (see FIG. 1) may include first particles PTC1, second particles PTC2, a conductive material CDM, and a binder BND. 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 positive electrode active material layer AML1 may further include an additive that can function as a sacrificial positive electrode.

[0056] 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% based on 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% based on 100 wt% of the positive electrode active material layer AML1.

[0057] The binder BND can bind the first particles PTC1, the second particles PTC2, and the conductive material CDM to one another. For 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.

[0058] The conductive material CDM can be used to improve the conductivity of the positive electrode active material layer AML1. Any conductive material that does not cause a chemical change in the positive electrode active material layer AML1 can be used as the conductive material CDM 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.

[0059] The first particles PTC1 and the second particles PTC2 will be described in more detail below.

[0060] 1st particle PTC1 The first particles PTC1 may include a lithium compound having an olivine structure represented by the following Chemical Formula 1.

[0061] [Chemical formula 1] Li a1 Mn x1 Fe y1 B z1 PO 4-c1 In Chemical Formula 1, 0.8≦a1≦1.2, 0.3≦x1≦0.7, 0.3≦y1≦0.7, 0≦z1≦0.05, 0≦c1≦0.05, and x1+y1+z1=1 may be satisfied. B may be at least one element selected from the group consisting of Ti, Mg, V, and Nb, and may be a dopant doped into the first particles PTC1. The dopant B controls the size of the primary particles to be uniform, thereby improving the charge / discharge efficiency, low-temperature characteristics, and life characteristics of the lithium secondary battery.

[0062] 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.

[0063] The coating layer may further include at least one selected from the group consisting of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound. Metal-containing compounds such as titanium-containing compounds, magnesium-containing compounds, and vanadium-containing compounds may be, for example, metal oxides, metal hydroxides, metal carbonates, composites thereof, or mixtures thereof. The metal-containing compounds may further include other metals or non-metal elements. For example, the metal-containing compounds may further include lithium.

[0064] The first particles PTC1 may further contain carbon derived from the coating layer. The carbon element content in the first particles PTC1 may be 0.5 wt % to 10 wt %, 1 wt % to 3 wt %, or 1.5 wt % to 2.5 wt %.

[0065] As an example, referring again to FIG. 6, the first particle PTC1 may have a single particle shape. In this specification, a single particle may refer to a single particle having no internal grain boundary. A single particle may refer to a single particle, a monolith structure, a single structure, or a non-aggregated particle, in which particles exist in an independent phase and are not aggregated with each other in 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.

[0066] The first particles PTC1 may be a nano-shaped cathode active material. The first particles PTC1 may include at least one first primary particle. In one embodiment, the first particles PTC1 may have a spherical or elliptical shape formed by agglomeration of the first primary particles. In another embodiment, the first particles PTC1 may have a random shape, not a spherical shape, even if the first primary particles are aggregated.

[0067] 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 size of the first primary particles, may be 100 nm to 500 nm, or 100 nm to 200 nm.

[0068] 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.

[0069] As an example, the minimum particle size, i.e., the size of the first primary particles, may refer to the diameter measured by randomly selecting about 30 primary particles from an electron microscope photograph of the first particles PTC1.

[0070] 7, the first particles PTC1 may have a polycrystalline form and include secondary particles formed by agglomeration of at least two or more first primary particles. In other words, one first particle PTC1 may include a plurality of first primary particles agglomerated together. The first particles PTC1 may have a spherical or elliptical shape.

[0071] As an example, the first particle PTC1 may further include a grain boundary coating layer on the surface of each of the first primary particles. The grain boundary coating layer may be present inside the first particle PTC1. The grain boundary coating layer may be formed by coating along the interface between the first primary particles inside the first particle PTC1. In other words, the grain boundary coating layer may refer to a material coated on the grain boundaries inside the first particle PTC1. The grain boundary coating layer may include carbon and / or a carbon-containing compound. The grain boundary coating layer may further include at least one selected from the group consisting of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound.

[0072] 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.

[0073] 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.

[0074] The first particles PTC1 may further contain carbon derived from the coating layer and / or the grain boundary coating layer. The carbon element content in the first particles PTC1 may be 0.5 wt % to 10 wt %, 1 wt % to 3 wt %, or 1.5 wt % to 2.5 wt %.

[0075] When the first particles PTC1 are secondary particles, the average particle size of the first particles PTC1 may be 2 μm to 15 μm, 3 μm to 10 μm, or 3 μm to 7 μm. For example, the average particle size of the first particles PTC1 may be approximately 5 μm. In one example, the average particle size 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.

[0076] The average size of the first primary particles may be 200 nm or less. For example, the average size of the first primary particles may be 10 nm to 200 nm, 20 nm to 200 nm, 50 nm to 200 nm, or 50 nm to 150 nm. In one embodiment, the average size of the first primary particles may refer to the diameter measured by randomly selecting approximately 30 primary particles from an electron microscope image of the positive electrode active material. The size of the first primary particles may be uniform.

[0077] When the first particles PTC1 are in a polycrystalline form, the size of the first primary particles may be smaller than when the first particles PTC1 are in a monocrystalline form. For example, when the first particles PTC1 are in a polycrystalline form, the size of the first primary particles may be about 100 nm smaller than when the first particles PTC1 are in a monocrystalline form.

[0078] When the average particle size and the average size of the first primary particles PTC1 satisfy the above-described ranges and the size of the first primary particles is uniform, the charge / discharge capacity and low-temperature capacity of a lithium secondary battery containing the same can be improved.

[0079] The first particle PTC1 can have a spherical shape formed by aggregation of nano-sized first primary particles. The first particle PTC1 can exhibit the following characteristics due to the close aggregation of the first primary particles with each other. The first particle PTC1 can have a spherical or elliptical shape. The average particle size (D50) of the first particle PTC1 can be from 2 μm to 15 μm. The porosity of the first particle PTC1 can be from about 20% to about 40%. The Span value of the first particle PTC1 analyzed by a particle size analyzer can be from 0.3 to 0.75.

[0080] 2nd particle PTC2 The second particle PTC2 can contain a lithium compound represented by the following Chemical Formula 2.

[0081] [Chemical Formula 2] Li a2 Ni x2 Mn y2 C z2 Oc2 In Chemical Formula 2, 1.1 < a2 ≤ 1.6, 0.2 ≤ x2 ≤ 0.5, 0.5 ≤ y2 ≤ 0.8, 0 ≤ z2 ≤ 0.05, 2 < c2 ≤ 2.3, and x2 + y2 + z2 = 1, and C can be at least one element selected from the group consisting of transition metals having an oxidation number of 4.

[0082] The second particle PTC2 can have a single-particle form similar to the above-described first particle PTC1. The description of the single particle can be the same as or similar to that described for the first particle PTC1 above. As an example, the second particle PTC2 can have a form composed of one single particle. As another example, the second particle PTC2 can have a form in which a plurality of single particles are attached to each other. The positive electrode active material according to the present invention can provide a high capacity and high energy density of a secondary battery by including the second particle PTC2 in a single-particle form.

[0083] As an example, the second particles PTC2 may include a second coating layer on their surfaces. By including the second coating layer, the second particles PTC2 can effectively prevent structural collapse due to repeated charge and discharge. This can improve the life characteristics of the secondary battery.

[0084] 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.

[0085] A method for measuring the metal content in the second coating layer of the second particles PTC2 can include performing scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) on the second particles PTC2. The analysis can confirm the content of boron and / or aluminum in the second coating layer. In addition to SEM-EDS, methods for measuring the metal content in the second coating layer can also include inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0086] In one embodiment of the present invention, the second particles PTC2 may be substantially free of cobalt (Co). For example, the cobalt (Co) content of the second particles PTC2 may be 100 ppm or less. Similarly, the first particles PTC1 may also be substantially free of cobalt (Co). By substantially omitting cobalt (Co), the cathode active material according to the present invention can provide an economical secondary battery having high capacity and operating voltage.

[0087] The average particle size of the second particles PTC2 may be 1.5 μm to 15 μm, 1.5 μm to 10 μm, or 1.5 μm to 6 μm. The average particle size of the second particles PTC2 may be larger than the average particle size of the first particles PTC1. The minimum particle size of the second particles PTC2, i.e., the size of the second primary particles, may be 0.3 μm to 1.5 μm, or 0.3 μm to 1.0 μm. The size of the second primary particles may be larger than the size of the first primary particles. For example, the size difference between the second primary particles and the first primary particles may be 200 nm or more.

[0088] 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.

[0089] As an example, the minimum particle size, i.e., the size of the second primary particles, may refer to the diameter measured by randomly selecting about 30 primary particles from an electron microscope photograph of the second particles PTC2.

[0090] In another embodiment of the present invention, the second particles PTC2 may have the form of secondary particles formed by aggregation of primary particles. In this case, the second particles PTC2 may have a granular or spherical shape, and the average particle size of the second particles PTC2 may be 10 μm to 30 μm, 10 μm to 20 μm, or 10 μm to 15 μm.

[0091] In yet another embodiment of the present invention, the second particles PTC2 may exist in a mixed form of a compound in the form of a single particle and a compound in the form of a secondary particle.

[0092] 6 and 7, a cathode active material according to an embodiment of the present invention will be described in more detail. The cathode active material according to the present invention may include first particles PTC1 and second particles PTC2. The mixing ratio of the first particles PTC1 to the second particles PTC2 in the cathode active material may be 90:10 to 70:30, or 80:20 to 70:30.

[0093] The second particles PTC2 are perlithium manganese oxides (LMR) containing an excess of lithium, and have a structure in which a layered phase (LiMO2) and a rock salt phase (Li2MnO3) are mixed. During the charge / discharge process, the rock salt phase is activated, and capacity is further enhanced through the oxygen redox reaction, providing high capacity. The cathode active material according to the present invention can improve capacity and operating voltage compared to conventional LMFP batteries by mixing the first particles PTC1 and the second particles PTC2 in an appropriate ratio.

[0094] The compound of Chemical Formula 2 (perlithium manganese-based oxide) 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.

[0095] The first particles PTC1 have the advantages of long life, high stability, and excellent low-temperature characteristics. By using the structurally stable first particles PTC1 as the main positive electrode active material, the relatively low stability and short life of the second particles PTC2 can be compensated for. Furthermore, by using the first particles PTC1 as the main active material, excellent low-temperature characteristics can be achieved.

[0096] A lithium secondary battery including the positive electrode active material of the present invention may have an excellent average voltage. In one embodiment, the average voltage of the lithium secondary battery of the present invention may be 3.5 V to 4.5 V. For example, the operating voltage range may be 3.5 V to 3.7 V, or 3.6 V to 3.65 V.

[0097] A lithium secondary battery including the positive electrode active material of the present invention may have excellent life characteristics. In one embodiment, the lithium secondary battery of the present invention may have a capacity retention rate of 95% or more after 50 charge / discharge cycles at a constant current of 0.1 C at the above-mentioned voltage. For example, the capacity retention rate may be 97% to 100%, or 98% to 100%.

[0098] The positive electrode active material of the present invention can improve the composite compaction density and energy density. In one embodiment, the compaction density of the positive electrode active material of the present invention may be 2 g / cc to 3 g / cc, 2.4 g / cc to 2.6 g / cc, or 2.6 g / cc to 2.8 g / cc.

[0099] A lithium secondary battery including the positive electrode active material of the present invention can have improved positive electrode utilization and energy density. The positive electrode utilization is the value obtained by dividing the capacity (mAh) of a lithium secondary battery by the mass (g) of the positive electrode active material included in the lithium secondary battery. In one embodiment, the lithium secondary battery of the present invention may have a positive electrode utilization of 130 mAh / g or more, 140 mAh / g or more, or 150 mAh / g or more. The lithium secondary battery of the present invention may have a positive electrode utilization of 200 mAh / g or less.

[0100] A lithium secondary battery including the positive electrode active material of the present invention can have improved capacity and energy density per volume. The capacity per volume is calculated by multiplying the positive electrode utilization rate (mAh / g) of the lithium secondary battery by the density (g / cc) of the positive electrode active material. In one embodiment, the lithium secondary battery of the present invention may have a capacity per volume of 300 mAh / cc or more, 350 mAh / cc or more, or 390 mAh / cc or more. The lithium secondary battery of the present invention may have a capacity per volume of 500 mAh / cc or less.

[0101] Method for producing positive electrode active material 8 is a flowchart illustrating a method for manufacturing a cathode active material according to an embodiment of the present invention. The method for manufacturing the first particles PTC1 according to an embodiment of the present invention will be described in more detail with reference to FIG.

[0102] 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. The manganese iron phosphate precursor may be a compound containing all of manganese (Mn), iron (Fe), and phosphorus (P), or a mixture of a manganese (Mn)-containing compound and an iron (Fe)- and 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.

[0103] 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.

[0104] 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.

[0105] The dopant source may include an oxide containing a dopant metal and / or a chloride containing a dopant metal. For example, the dopant source may include at least one of an oxide or chloride of Mn of Chemical Formula 1 and at least one of an oxide or chloride of Ti. For example, the dopant source may include at least one of an oxide or chloride of Mn and at least one of an oxide or chloride of Ti.

[0106] The mixture may be subjected to wet milling (S200). A typical temperature-controllable wet mill may be used for wet milling. Specifically, at least one selected from a bead mill, a ball mill, an attrition mill, an apex mill, a super mill, and a basket mill may be used for wet milling. Through the wet milling process, particles in the mixture may be milled to a fine size.

[0107] 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.

[0108] The solvent can be removed from the mixture to form a dried mixture (S300).

[0109] When producing the first particles PTC1 of FIG. 6 according to an embodiment of the present invention, forming the dried mixture can include subjecting the mixture to a direct evaporation method, such as static drying or spray drying.

[0110] 7, forming a dried mixture can include spray drying the mixture. 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.

[0111] The particles refined to the size of primary particles 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.

[0112] In one embodiment, 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. For example, the spray liquid may have a solid content of approximately 30 wt%.

[0113] If the solid content is less than 20%, the average particle size of the first particles PTC1 becomes small, which may result in problems with low productivity, whereas if the solid content is more than 40%, it becomes difficult to control the average particle size of the first particles PTC1, which may result in large size deviations of the first particles PTC1.

[0114] 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.

[0115] In one embodiment, the input rate of spray drying may be 0.1 kg / min to 0.9 kg / min. The input rate of spray drying may be defined as the weight of solids in the spray liquid input per time. For example, if 1 kg of a spray liquid with a solids content of 20% is input per minute, the input rate may be 0.2 kg / min. In one embodiment, the input rate of spray drying according to the present invention may be approximately 0.5 kg / min.

[0116] In one embodiment, spray drying can be carried out at a temperature of 100°C to 300°C. For example, spray drying can be carried out at a temperature of 200°C to 300°C, above 200°C to 300°C, or 230°C to 270°C. The propellant gas (e.g., air) used in spray drying 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.

[0117] The spray liquid may be supplied at a pressure of 0.3 MPa to 0.7 MPa. For example, the spray liquid may be supplied at a pressure of about 0.5 MPa.

[0118] When the input amount, input pressure, and temperature of the spray drying satisfy the described ranges, the first particles PTC1 can have a spherical morphology and a desired porosity.

[0119] 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.

[0120] 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 may be formed.

[0121] A method for manufacturing the second particles PTC2 according to an embodiment of the present invention will now be described in detail. The second particles PTC2 containing lithium manganese-based oxide (hereinafter referred to as LMR) can be manufactured by mixing a transition metal precursor and a lithium source and then calcining the mixture.

[0122] The transition metal precursor may be in the form of a hydroxide, oxide, or carbonate. When a carbonate precursor is used, it is more preferable in that a positive electrode active material having a relatively high specific surface area can be prepared.

[0123] The transition metal precursor can be prepared by a coprecipitation process. For example, the transition metal precursor can be prepared by dissolving each transition metal-containing raw material in a solvent to prepare a metal solution, and then mixing the metal solution, an ammonium cation complexing agent, and a basic compound, followed by a coprecipitation reaction. If necessary, an oxidizing agent or gaseous oxygen can be further added during the coprecipitation reaction.

[0124] In this case, the transition metal-containing raw material may be acetate, carbonate, nitrate, sulfate, halide, sulfide, etc. of each transition metal. Specifically, the transition metal-containing raw material may be NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4H2O, manganese acetate, manganese halide, etc.

[0125] The ammonium cation complexing agent may be at least one selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and NH4CO3.

[0126] The basic compound may be at least one selected from the group consisting of NaOH, Na2CO3, KOH, and Ca(OH)2. The form of the precursor may vary depending on the type of basic compound used. For example, when NaOH is used as the basic compound, a hydroxide-form precursor can be obtained, and when Na2CO3 is used as the basic compound, a carbonate-form precursor can be obtained. Furthermore, when a basic compound and an oxidizing agent are used together, an oxide-form precursor can be obtained.

[0127] The lithium source may be the same as or similar to the method for producing the first particles PTC1 described above.

[0128] The transition metal precursor and the lithium source may be mixed in amounts such that the total transition metal (Ni+Mn):Li molar ratio is 1:1.05 to 1:2, preferably 1:1.1 to 1:1.8, and more preferably 1:1.3 to 1:1.8.

[0129] The mixture of the transition metal precursor and the lithium source may be subjected to wet-milling (S200). The wet-milling may be the same as or similar to the method for producing the first particles PTC1 described above.

[0130] The solvent may be removed from the mixture of the transition metal precursor and the lithium source to form a dried mixture (S300). The drying may be the same as or similar to the method for producing the first particles PTC1 described above.

[0131] The dried mixture may be calcined under an inert atmosphere (S400). The calcination may be the same as or similar to the method for producing the first particles PTC1 described above.

[0132] The first particles PTC1 and second particles PTC2 prepared by the above methods can be mixed together to prepare a cathode active material according to the present invention. The content of the first particles PTC1 can be 70 wt% to 90 wt% based on a total of 100 wt% of the first particles PTC1 and the second particles PTC2. Specifically, the content of the first particles PTC1 can be 70 wt% to 85 wt% based on a total of 100 wt% of the first particles PTC1 and the second particles PTC2 in the cathode active material, and the content of the first particles PTC1 can be 70 wt% to 80 wt% based on a total of 100 wt% of the first particles PTC1 and the second particles PTC2.

[0133] 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.

[0134] 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).

[0135] The present invention will be described in more detail below through examples. However, these examples are for illustrative purposes only and the scope of the present invention is not limited to these examples.

[0136] Preparation Example 1: Preparation of first particles in single particle form Mn 0.6 Fe 0.4 Iron phosphate precursor (PO4), lithium carbonate, and titanium dioxide were mixed in a molar ratio of 1:1.03:0.004. 10 wt% glucose was added to the mixture. The mixture was wet-pulverized using a ball mill. The mixture was evaporated to dryness in a heating oven tray and then placed in a vacuum oven at 120°C for 4 hours. The dried mixture was calcined at 750°C for 10 hours under a nitrogen atmosphere. The calcined product was pulverized to obtain primary particles in the form of single particles. The average size of the primary particles was approximately 100nm to approximately 200nm.

[0137] Preparation Example 2: Preparation of primary particles in the form of secondary particles Mn 0.6 Fe 0.4 Iron phosphate precursor PO4, lithium carbonate, and titanium dioxide were mixed in a molar ratio of 1:1.03:0.004. 10 wt% glucose was further added to the mixture. The slurry mixture was spray-dried at a spray pressure of 0.5 MPa and a temperature of 230°C, followed by evaporation. The dried mixture was calcined at 750°C for 10 hours in a nitrogen atmosphere to obtain primary particles in the form of secondary particles. The average size of the primary particles within the primary particles was approximately 50 nm to approximately 150 nm.

[0138] Preparation Example 3: Preparation of second particles in single particle form Ni 0.25 Mn 0.75 (OH)2 and LiOH were mixed so that the molar ratio of Li / (Ni+Mn) was about 1.5, and then heat-treated in an oxygen atmosphere at 950°C for 24 hours to obtain a lithium-manganese-rich composite oxide (Li 1.5 Ni 0.25 Mn 0.75 O2) and having an average particle size (D50) of about 2 μm, a second positive electrode active material in the form of single particles was prepared.

[0139] Example 1: Preparation of mixed positive electrode active material The first particles of Preparation Example 1 and the second particles of Preparation Example 3 were mixed in a weight ratio of 80:20 to prepare a positive electrode active material.

[0140] Example 2 The first particles of Preparation Example 1 and the second particles of Preparation Example 3 were mixed in a weight ratio of 75:25 to prepare a positive electrode active material.

[0141] Example 3 The first particles of Preparation Example 1 and the second particles of Preparation Example 3 were mixed in a weight ratio of 70:30 to prepare a positive electrode active material.

[0142] Example 4 The first particles of Preparation Example 2 and the second particles of Preparation Example 3 were mixed in a weight ratio of 80:20 to prepare a positive electrode active material.

[0143] Example 5 The first particles of Preparation Example 2 and the second particles of Preparation Example 3 were mixed in a weight ratio of 75:25 to prepare a positive electrode active material.

[0144] Example 6 The first particles of Preparation Example 2 and the second particles of Preparation Example 3 were mixed in a weight ratio of 70:30 to prepare a positive electrode active material.

[0145] Comparative Example 1 The first particles of Preparation Example 1 and the second particles of Preparation Example 3 were mixed in a weight ratio of 95:5 to prepare a positive electrode active material.

[0146] Comparative Example 2 The first particles of Preparation Example 1 and the second particles of Preparation Example 3 were mixed in a weight ratio of 85:15 to prepare a positive electrode active material.

[0147] Comparative Example 3 The first particles of Preparation Example 1 and the second particles of Preparation Example 3 were mixed in a weight ratio of 65:35 to prepare a positive electrode active material.

[0148] Comparative Example 4 The first particles of Preparation Example 2 and the second particles of Preparation Example 3 were mixed in a weight ratio of 95:5 to prepare a positive electrode active material.

[0149] Comparative Example 5 The first particles of Preparation Example 2 and the second particles of Preparation Example 3 were mixed in a weight ratio of 85:15 to prepare a positive electrode active material.

[0150] Comparative Example 6 The first particles of Preparation Example 2 and the second particles of Preparation Example 3 were mixed in a weight ratio of 65:35 to prepare a positive electrode active material.

[0151] 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.

[0152] Lithium secondary battery manufacturing A 2032-type coin half-cell was fabricated using the prepared positive electrode and a lithium metal counter electrode. A separator (approximately 16 μm thick) made of porous polyethylene (PE) film was placed between the positive electrode and the lithium metal counter electrode, and an electrolyte solution was injected to fabricate a lithium secondary battery. The electrolyte used was a solution obtained by mixing 1.3 M LiPF6 with a mixed solvent of EC (ethylene carbonate): DEC (diethyl carbonate): FEC (fluoroethylene carbonate) (2:6:2 volume ratio).

[0153] Evaluation example 1: Analysis of the surface of the positive electrode active material 9a to 9d show SEM images of the first particles prepared in Preparation Examples 1 and 2. FIGS. 10a and 10b show SEM images of the second particles prepared in Preparation Example 3.

[0154] 9a and 9b, the primary particles according to Preparation Example 1 of the present invention are in the form of nano-sized fine single particles. 9c and 9d, the primary particles according to Preparation Example 2 of the present invention are in the form of spherical secondary particles formed by aggregation of primary particles. Meanwhile, the primary particles according to Preparation Example 2 are smaller and more uniform in size than the primary particles according to Preparation Example 1.

[0155] As shown in FIGS. 10a and 10b, the second particle can be seen to be one single particle or a plurality of single particles attached to each other.

[0156] Evaluation example 2: Evaluation of active materials The average pellet density (PD) of the positive electrodes of Examples 1 to 6 and Comparative Examples 1 to 6 is shown in Table 1. The average pellet density was measured by placing 3 g of the positive electrode active material in a pellet mold and applying a force of US 4.0 tons for 30 seconds.

[0157] [Table 1]

[0158] Referring to Table 1, it can be seen that the positive electrode active materials according to Examples 1 to 6 have similar or higher compressed densities compared to the positive electrode active materials according to Comparative Examples 1 to 6. In particular, it can be seen that the positive electrode active materials according to Examples 4 to 6 have high compressed densities of 2.62 g / cc or more.

[0159] Evaluation example 3: Battery characteristic evaluation The characteristics of the lithium secondary batteries manufactured using the positive electrode active materials of Examples 1 to 6 and Comparative Examples 1 to 6 were evaluated.

[0160] The lithium secondary battery was initially charged at a constant current (0.2C) and constant voltage (4.25V), and then allowed to rest for 10 minutes before discharging to 2.5V at a constant current (0.2C). It was then charged and discharged 50 times at 0.2C / 0.2C. An additional coin cell was also fabricated and its capacity measured at -20°C. The battery characteristics were evaluated and are shown in Table 2 below.

[0161] [Table 2]

[0162] Referring to Table 2, it can be seen that the positive electrode active materials according to Examples 1 to 6 have similar charge / discharge characteristics, efficiency, average voltage, and lifespan compared to the positive electrode active materials according to Comparative Examples 1 to 6.

[0163] In addition, it can be seen that the cathode active materials according to Examples 1 to 6 have excellent cathode utilization rates and capacities per volume when compared with the cathode active materials according to Comparative Examples 1 to 6. In particular, it can be seen that the cathode active materials according to Examples 5 and 6 have significantly high cathode utilization rates and capacities per volume.

[0164] In other words, it can be seen that the lithium secondary batteries prepared using the positive electrode active materials of Examples 1 to 6 have similar life spans and average voltages, and exhibit higher capacities per volume, when compared to the lithium secondary batteries prepared using the positive electrode active materials of Comparative Examples 1 to 6.

[0165] 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]

[0166] 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 including a compound represented by the following Chemical Formula 1: and second particles comprising a compound of Chemical Formula 2: The content of the first particles is greater than the content of the second particles, The second particles are a positive electrode active material having a single particle form: [Chemical formula 1] Li a1 Mn x1 Fe y1 B z1 2O 4-c1 In the formula 1, 0.8≦a1≦1.2, 0.3≦x1≦0.7, 0.3≦y1≦0.7, 0≦z1≦0.05, 0≦c1≦0.05, and x1+y1+z1=1; B is at least one element selected from the group consisting of Ti, Mg, and V; [Chemical formula 2] Li a2 Ni x2 Mn y2 C z2 O c2 In Chemical Formula 2, 1.1<a2≦1.6, 0.2≦x2≦0.5, 0.5≦y2≦0.8, 0≦z2≦0.05, 2<c2≦2.3, and x2+y2+z2=1; and C is at least one element selected from the group consisting of transition metals having an oxidation number of 4.

2. 2. The positive electrode active material of claim 1, wherein the content of the second particles is 20 to 30 parts by weight based on 100 parts by weight of the positive electrode active material.

3. The positive electrode active material according to claim 1 , wherein the B is Ti.

4. The positive electrode active material of claim 1 , wherein an average size of first primary particles of the first particles is smaller than an average size of second primary particles of the second particles.

5. the first particles include a 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 first particles have a single particle form; a first average particle size of the first particles is 0.5 μm to 2.5 μm; The positive electrode active material of claim 1 , wherein the first particles have an average primary particle size of 100 nm to 200 nm.

7. The first particles include a plurality of first primary particles that are aggregated together, a first average particle size of the first particles is 3 μm to 10 μm; The positive electrode active material of claim 1 , wherein the average size of the first primary particles is 50 nm to 150 nm.

8. the first particles further include a grain boundary coating layer on an interface between the first primary particles, The positive electrode active material according to claim 7 , wherein the grain boundary coating layer contains carbon.

9. The positive electrode active material of claim 7 , wherein the first particles have a porosity of 20% to 40%.

10. The positive active material of claim 7 , wherein the first particles have a Span value of 0.3 to 0.75 as analyzed by a particle size analyzer.

11. The average size of the second primary particles of the second particles is 0.3 μm to 1.5 μm; The positive electrode active material of claim 1 , wherein the second average particle size of the second particles is 1.5 μm to 6 μm.

12. 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.

13. 2. The positive electrode active material of claim 1, wherein the positive electrode active material has a compressed density of 2.6 g / cc to 2.9 g / cc.

14. 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.

15. 15. The positive electrode for a lithium secondary battery of claim 14, 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.

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

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

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

19. The positive electrode according to claim 14 ; a negative electrode including a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector; a separator between the positive electrode and the negative electrode.

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