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

Abstract

To provide a positive electrode active material that has high energy density, high operating voltage and high conductivity.SOLUTION: The invention relates to positive electrode active materials for a rechargeable lithium battery, production methods thereof, and rechargeable lithium batteries including the same. Specifically, a positive electrode active material comprises: first particles comprising a compound of chemical formula 1 and having an olivine structure; and second particles comprising a compound of chemical formula 2 and having a spinel structure. The content of the first particles is greater than the content of the second particles.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode 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] U.S. Patent No. 10,593,946 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] A cathode active material according to the present invention may include first particles having an olivine structure, which includes a compound represented by the following Chemical Formula 1, and second particles having a spinel structure, which includes a compound represented by the following Chemical Formula 2. The content of the first particles may be greater than the content of the second particles. [Chemical formula 1] Li a1 Mn x1 Fe y1 Bz1PO 4-b1 In the above Chemical Formula 1, 0.8≦a1≦1.2, 0.5≦x1≦0.9, 0.1≦y1≦0.5, 0.001≦z1≦0.05, 0≦b1≦0.05, and 0.9≦x1+y1≦1.2; B is at least one element selected from the group consisting of Ti, Mg, V, and Nb; [Chemical formula 2] Li a2 Mn x2 C y2 O 4-b2 In Chemical Formula 2, 0.8≦a2≦1.2, 1.9≦x2≦2.05, 0≦y2≦0.05, and 0≦b2≦0.05, and C may be Mg, Al, or a combination thereof.

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

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

[0010] The cathode active material according to the present invention can improve the mixture density, capacity, and energy density by mixing the second particles having a spinel structure with the first particles having an olivine structure. The lithium secondary battery according to the present invention can have a relatively high operating voltage and an excellent lifespan. [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. [Figure 11] 1 is an X-ray diffraction analysis graph for a positive electrode active material according to Preparation 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 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, those selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof can be used.

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

[0031] Examples of the material capable of reversibly inserting / desorbing lithium ions include carbon-based negative electrode active materials, which can include, for example, crystalline carbon, amorphous carbon, or combinations thereof. Examples of crystalline carbon can include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon can include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[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 with lithium, an Si-based negative electrode active material or an 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), an Si-Q alloy (Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or combinations thereof. The Sn-based negative electrode active material can be Sn, SnO2, an Sn-based alloy, or combinations 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 copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

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

[0041] The inorganic 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 hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, and may contain a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0049] The non-aqueous organic solvents 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 % relative to 100 wt % of the positive electrode active material layer AML1. The content of the binder BND and the conductive material CDM may be 0.5 wt % to 5 wt % relative to 100 wt % of the positive electrode active material layer AML1.

[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, and the like; 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] A positive electrode active material in which the content of the first particles is greater than the content of the second particles: [Chemical formula 1] Li a1 Mn x1 Fe y1 B z1 PO 4-b1 In Chemical Formula 1, 0.8≦a1≦1.2, 0.5≦x1≦0.9, 0.1≦y1≦0.5, 0.001≦z1≦0.05, 0≦b1≦0.05, and 0.9≦x1+y1≦1.2 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 by 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 particles PTC1 may have a spherical shape formed by agglomeration of nano-sized first primary particles. The first particles PTC1 may exhibit the following characteristics due to the close agglomeration of the first primary particles: The first particles PTC1 may have a spherical or elliptical shape. The average particle size (D50) of the first particles PTC1 may be 2 μm to 15 μm. The porosity of the first particles PTC1 may be about 20% to about 40%. The Span value of the first particles PTC1 analyzed using a particle size analyzer may be 0.3 to 0.75.

[0080] When the first particles PTC1 are secondary particles, their large average particle size allows for a relatively small amount of binder BND to be used to attach the first particles PTC1 to the current collector COL1 (see FIG. 1). For example, the content of binder BND may be 0.5 wt % to 3 wt % relative to 100 wt % of the positive electrode active material layer AML1. Reducing the content of binder in the positive electrode active material layer AML1 allows for a corresponding increase in the content of active material, thereby improving the capacity and energy density of the battery. Furthermore, reducing the content of binder, which increases resistance, can improve the electrical conductivity of the positive electrode.

[0081] 2nd particle PTC2 The second particles PTC2 may include a lithium compound having a spinel structure represented by the following Chemical Formula 2.

[0082] [Chemical formula 2] Li a2 Mn x2 C y2 PO 4-b2 In Chemical Formula 2, 0.8≦a2≦1.2, 1.9≦x2≦2.05, 0≦y2≦0.05, and 0≦b2≦0.05 may be satisfied. C may be Mg, Al, or a combination thereof, and may be a dopant doped into the first particles PTC1. Mg and Al control the size of the primary particles to be uniform and stabilize the crystalline structure of the positive electrode active material, thereby improving the charge / discharge efficiency, low-temperature characteristics, and life characteristics of the lithium secondary battery.

[0083] The second particles PTC2 may have a spinel structure. The spinel structure is composed of a lattice structure of tetrahedrons and octahedrons, which provides high stability and allows lithium ions to be inserted through various channels, resulting in excellent output. In addition, the second particles PTC2 may have excellent life characteristics.

[0084] The second particles PTC2 may be a lithium manganese oxide, a cathode material in which cobalt in lithium cobalt oxide is replaced with manganese. 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.

[0085] 6 and 7, the second particles PTC2 may have a polycrystalline form and may include secondary particles formed by agglomeration of at least two or more second primary particles. In other words, one second particle PTC2 may include a plurality of second primary particles agglomerated together. The second particles PTC2 may have a spherical form formed by agglomeration of the second primary particles, or may have a random form even when the second primary particles are agglomerated.

[0086] The average particle size of the second particles PTC2 may be 3 μm to 20 μm, 4 μm to 15 μm, or 5 μm to 10 μm. For example, the average particle size of the first particles PTC1 may be approximately 8 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.

[0087] The average size of the second primary particles constituting the second particles PTC2 may be 3 μm or less. For example, the particle size of the first primary particles may be 300 nm to 3 μm, 500 nm to 3 μm, 1 μm to 3 μm, or 2 μm to 3 μm. In one embodiment, the average size of the second 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 second primary particles may be uniform. The second primary particles may have an average size smaller than that of the first primary particles. The difference in average size between the second primary particles and the first primary particles may be 300 nm or more.

[0088] As an example, the second particles PTC2 may include a second coating layer on the surface thereof, which can effectively prevent the second particles PTC2 from collapsing due to repeated charging and discharging.

[0089] 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.

[0090] A method for measuring the metal content in the second coating layer of the second particles PTC2 may include performing scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) on the second particles PTC2. The analysis may confirm the boron and / or aluminum content in the second coating layer. In addition to SEM-EDS, other methods for measuring the metal content in the second coating layer include inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0091] 6 and 7, the cathode active material according to 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 content of the second particles PTC2 in the cathode active material may be less than the content of the first particles PTC1. The mixing ratio of the first particles PTC1 to the second particles PTC2 in the cathode active material may be 90:10 to 60:40, or 85:15 to 70:30.

[0092] In one embodiment, the mixing ratio of the first particles PTC1 and the second particles PTC2 may be adjusted so that the Mn content is 50 mol % to 60 mol % based on the total weight of metal elements excluding lithium in the positive electrode active material.

[0093] The second particles PTC2 have a high Mn content, which can improve the operating voltage of the secondary battery compared to the first particles PTC1. In addition, the second particles PTC2 have a spinel structure, which provides a stable crystal structure and superior lifespan characteristics compared to the first particles. However, the second particles PTC2, which are manganese oxide, have a problem in that they are difficult to use alone due to their low capacity and energy density.

[0094] The cathode active material according to this embodiment can have improved voltage and life characteristics compared to a typical LMFP battery by mixing the first particles PTC1 and the second particles PTC2 in an appropriate ratio, i.e., by adjusting the Mn content to 50 mol% to 60 mol%.

[0095] In one embodiment, a lithium secondary battery including the cathode active material of the present invention may have an average voltage of 3.5 V to 4.0 V or 3.6 V to 3.8 V. At the above voltages, a lithium secondary battery including the cathode active material of the present invention may have a capacity retention rate of 97% or more after 50 charge / discharge cycles at a constant current of 2.0 C. For example, the capacity retention rate may be 98% to 100%, or 99% to 100%.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] The mixture may be subjected to wet milling (S200). A typical temperature-controllable wet mill may be used for wet milling. Specifically, at least one selected from a bead mill, a ball mill, an attrition mill, an apex mill, a super mill, and a basket mill may be used for wet milling. Through the wet milling process, particles in the mixture may be pulverized to a fine size.

[0102] 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.

[0103] The solvent can be removed from the mixture to form a dried mixture (S300).

[0104] When manufacturing the first particles PTC1 of FIG. 6 according to an embodiment of the present invention, forming the dried mixture may include subjecting the mixture to a direct evaporation method, such as static drying or spray drying.

[0105] 7, forming a dried mixture can include spray drying the mixture. Spray drying can be performed using commonly used spray drying equipment. For example, 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.

[0106] 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.

[0107] 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%.

[0108] If the solid content is less than 20%, the average particle size of the first particles PTC1 may become small, which may result in problems such as low productivity, whereas if the solid content is more than 40%, it may become difficult to control the average particle size of the first particles PTC1, which may result in large size deviations of the first particles PTC1.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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 oxide (hereinafter referred to as LMO) can be manufactured by mixing a manganese source, a lithium source, and a dopant source and then sintering the mixture.

[0117] There are no particular limitations on the manganese source, and examples include MnO2, Mn3O4, and Mn2O3. However, crystallized Mn3O4, electrolytic MnO2, and Mn2O3 obtained by calcining crystallized Mn3O4 or electrolytic MnO2 are preferred, as they can further enhance the chargeability of the spinel-type lithium manganese oxide.

[0118] 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.

[0119] 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 magnesium oxide and aluminum oxide.

[0120] The manganese source and the lithium source may be mixed in amounts such that the molar ratio of Li:Mn is 1:1.6 to 1:2.4, more preferably 1:1.8 to 1:2.2.

[0121] The mixture of the manganese source 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.

[0122] The solvent may be removed from the mixture of the manganese source 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.

[0123] 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.

[0124] 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.

[0125] Examples of the present invention and comparative examples are described below. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0126] Preparation Example 1: Preparation of first particles in single particle form Mn 0.6 Fe 0.4Manganese 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.

[0127] Preparation Example 2: Preparation of primary particles in the form of secondary particles Mn 0.6 Fe 0.4 Manganese 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.

[0128] Preparation Example 3: Preparation of secondary particles After dissolving 0.170g of MnSO4·H2O and 0.228g of (NH4)2S2O8 in 100ml of distilled water, sulfuric acid was added to adjust the pH to 1, and the mixture was reacted at 130℃ for 10 hours to obtain a solid precipitate. The resulting precipitate was washed several times with distilled water and dried at 300℃ for 3 hours to obtain solid MnO2 with an average particle size of 5μm.

[0129] Li2CO3 and synthesized MnO2 were mixed so that the molar ratio of Li to Mn was 1:2, and heated at 600°C for 10 hours to synthesize LiMn2O4 particles with an average particle size of 7 μm and an average primary particle size of 0.5 μm to 2.5 μm.

[0130] 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 70:30 to prepare a positive electrode active material.

[0131] Example 2 The first particles of Preparation Example 1 and the second particles of Preparation Example 3 were mixed in a weight ratio of 83:17 to prepare a positive electrode active material.

[0132] Example 4 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.

[0133] Example 5 The first particles of Preparation Example 2 and the second particles of Preparation Example 3 were mixed in a weight ratio of 83:17 to prepare a positive electrode active material.

[0134] 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 30:70 to prepare a positive electrode active material.

[0135] 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 42:58 to prepare a positive electrode active material.

[0136] 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 56:44 to prepare a positive electrode active material.

[0137] 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.

[0138] 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 30:70 to prepare a positive electrode active material.

[0139] 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 42:58 to prepare a positive electrode active material.

[0140] Comparative Example 7 The first particles of Preparation Example 2 and the second particles of Preparation Example 3 were mixed in a weight ratio of 56:44 to prepare a positive electrode active material.

[0141] Comparative Example 8 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.

[0142] 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.

[0143] 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 prepared by mixing 1.3 M LiPF6 with a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethylene carbonate (DMC) in a volume ratio of 3:4:3.

[0144] 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.

[0145] As shown in Figures 9a and 9b, the primary particles according to Preparation Example 1 of the present invention were in the form of nano-sized, fine single particles. Referring to Figures 9c and 9d, the primary particles according to Preparation Example 2 of the present invention were in the form of spherical secondary particles formed by aggregation of primary particles. Meanwhile, the primary particles according to Preparation Example 2 were smaller and more uniform in size than the primary particles according to Preparation Example 1.

[0146] 10a and 10b, it can be seen that the second particles are in the form of secondary particles formed by agglomeration of a plurality of primary particles. While the first particles have a spherical shape, the second particles have various shapes.

[0147] Evaluation example 2: X-ray diffraction analysis The positive electrode active material of Production Example 3 was subjected to X-ray diffraction analysis, and the results are shown in FIG.

[0148] Referring to FIG. 11, it can be seen that the secondary particles prepared according to Preparation Example 3 have a spinel structure.

[0149] Evaluation Example 3: Evaluation of active materials The average pellet density (PD) of the positive electrodes of Examples 1 to 4 and Comparative Examples 1 to 8 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.

[0150] [Table 1]

[0151] Referring to Table 1, it can be seen that the positive electrode active materials according to Examples 1 to 4 have similar compressed densities compared to the positive electrode active materials according to Comparative Examples 1 to 8. It can also be seen that the positive electrode active materials according to Examples 1 to 4 have higher compressed densities when the first particles have a secondary particle shape than when the first particles have a single particle shape.

[0152] Evaluation example 4: Battery characteristic evaluation The characteristics of the lithium secondary batteries manufactured using the positive electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 8 were evaluated.

[0153] The lithium secondary battery was initially charged at a constant current (0.2 C) and a constant voltage (4.25 V), and after a 10-minute rest, discharged to 2.5 V at a constant current (0.2 C). Thereafter, the battery was charged and discharged 50 times at 1.0 C / 1.0 C. The battery characteristic evaluation results are shown in Table 2 below.

[0154] [Table 2]

[0155] Referring to Table 2, it can be seen that the positive electrode active materials according to Examples 1 to 4 have higher energy densities than the positive electrode active materials according to Comparative Examples 1 to 3 and Comparative Examples 5 to 7. In particular, it can be seen that the positive electrode active materials according to Examples 1 to 6 have high energy densities of 485 Wh / kg or more, which can mean that they have energy densities suitable for commercial use.

[0156] The positive electrode active materials according to Examples 1 to 6 exhibited slightly reduced initial efficiency and lifespan characteristics compared to the positive electrode active materials according to Comparative Examples 1 to 3 and 5 to 7, but were confirmed to have high initial efficiency of 94% or more and high capacity retention of 97% or more after 50 cycles.

[0157] In the case of Comparative Examples 4 and 8, compared to the positive electrode active materials of Examples 1 to 6, it was confirmed that while they had similar or slightly higher energy densities, they had low initial efficiencies of 93% or less and low capacity retention rates of 97% or less after 50 cycles.

[0158] As a result, in the cases of Examples 1 to 4, i.e., when the first particles and the second particles are mixed in an appropriate ratio, it can be confirmed that the battery has excellent properties suitable for commercial use when considering both capacity and energy density comprehensively.

[0159] 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]

[0160] 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 having an olivine structure and including a compound represented by the following Chemical Formula 1: and second particles having a spinel structure, the second particles including a compound represented by the following Chemical Formula 2: A positive electrode active material in which the content of the first particles is greater than the content of the second particles: [Chemical formula 1] Li a1 Mn x1 Fe y1 Bz 1 PO 4-b1 In the formula 1, 0.8≦a1≦1.2, 0.5≦x1≦0.9, 0.1≦y1≦0.5, 0.001≦z1≦0.05, 0≦b1≦0.05, and 0.9≦x1+y1≦1.2; B is at least one element selected from the group consisting of Ti, Mg, V, and Nb; [Chemical formula 2] Li a2 Mn x2 C y2 O 4-b2 In Chemical Formula 2, 0.8≦a2≦1.2, 1.9≦x2≦2.05, 0≦y2≦0.05, and 0≦b2≦0.05, and C is Mg, Al, or a combination thereof.

2. the first particles include at least one first primary particle; the second particles are in the form of secondary particles including a plurality of second primary particles, The positive electrode active material according to claim 1 , wherein the average size of the first primary particles is smaller than the average size of the second primary particles.

3. 2. The positive electrode active material of claim 1, wherein the content of the second particles is 15 to 30 parts by weight based on 100 parts by weight of the positive electrode active material.

4. 2. The positive electrode active material of claim 1, wherein the content of Mn is 50 mol % to 60 mol % based on the total weight of metal elements excluding lithium in the positive electrode active material.

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 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.

7. 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.

8. 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.

9. 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 8 , wherein the grain boundary coating layer contains carbon.

10. The positive electrode active material of claim 8 , wherein the porosity of the first particles is 20% to 40%.

11. The positive active material of claim 8 , wherein the first particles have a Span value of 0.3 to 0.75 as analyzed by a particle size analyzer.

12. The average size of the second primary particles of the second particles is 0.5 μm to 3 μm; The positive electrode active material of claim 1 , wherein the second average particle size of the second particles is 4 μm to 10 μm.

13. 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.

14. 2. The positive electrode active material of claim 1, wherein the positive electrode active material has a compressed density of 2.3 g / cc to 2.7 g / cc.

15. 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.

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

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

18. 16. The positive electrode for a lithium secondary battery according to claim 15, wherein the conductive material is present in an amount of 0.5 to 5 parts by weight based on 100 parts by weight of the positive electrode active material layer.

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

20. The positive electrode according to claim 15 ; 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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