Positive electrode active material and lithium secondary battery including the same

Abstract

To provide a positive electrode active material or a lithium secondary battery having high energy density, high operation voltage, and high conductivity.SOLUTION: The present invention relates to a positive electrode active material and a lithium secondary battery including the same, which more specifically include a first particle containing a compound expressed by the following chemical formula 1 and having a first average particle diameter: [Chemical Formula 1] Lia1Mnx1Fey1Bz1 PO4-b1. In Chemical Formula 1, 0.8≤a1≤1.2, 0.45≤x1≤0.55, 0.45≤y1≤0.55, 0<z1≤0.05, 0≤b1≤0.05, and x1+y1+z1=1 are satisfied and B represents Mg and Ti.SELECTED DRAWING: Figure 6

Description

[Technical Field]

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

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

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

[0004] The problem to be solved by the present invention is to provide a positive electrode active material having high energy density, high operating voltage, high conductivity, and high conductivity.

[0005] Another problem to be solved by the present invention is to provide a lithium secondary battery having a high energy density, a high operating voltage, a high charge / discharge efficiency, and a long life. [Means for solving the problem]

[0006] A positive electrode active material according to an embodiment of the present invention may include a compound represented by Formula 1 below and may include first particles having a first average particle size. [Chemical formula 1] Li a1 Mn x1 Fe y1 Bz1 PO 4-b1 In Chemical Formula 1, 0.8 ≦ a1 ≦ 1.2, 0.45 ≦ x1 ≦ 0.55, 0.45 ≦ y1 ≦ 0.55, 0 < z1 ≦ 0.05, 0 ≦ b1 ≦ 0.05, and x1 + y1 + z1 = 1, The B can be Mg and Ti.

[0007] The positive electrode active material according to another embodiment of the present invention includes a compound of the following Chemical Formula 2 and includes first particles having a first average particle diameter, wherein the first particles are doped with Mg and Ti, and the total doping amount of Mg and Ti can be 2500 ppm to 5000 ppm: [Chemical Formula 2] Li a2 Mn x2 Fe y2 PO 4-b2 In Chemical Formula 2, 0.8 ≦ a2 ≦ 1.2, 0.45 ≦ x2 ≦ 0.55, 0.45 ≦ y2 ≦ 0.55, 0 ≦ b2 ≦ 0.05, and x2 + y2 = 1 can hold.

[0008] The lithium secondary battery according to another embodiment of the present invention includes a positive electrode including a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, 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, and in a differential capacitance (dQ / dV)-voltage charge graph, it may include a first charge peak V1 that appears at a voltage of 3.4 V to 4.0 V, a first discharge peak V2 that appears at a voltage of 3.4 V to 4.0 V, and a second charge peak V3 that appears at a voltage of 4.0 V to 4.4 V.

Advantages of the Invention

[0009] The positive electrode active material according to the present invention can improve the blend density (compression density, pellet density), capacity, and energy density. The positive electrode active material according to the present invention can smoothly adhere to the positive electrode current collector even with a relatively small amount of binder. The lithium secondary battery according to the present invention has a relatively high average voltage, charge-discharge capacity, efficiency, and energy density, and may have excellent life characteristics (capacity retention rate).

Brief Description of the Drawings

[0010] [Figure 1] 1 is a conceptual diagram illustrating a lithium secondary battery according to an embodiment of the present invention; [Figure 2] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment, which can be said to have a cylindrical battery shape. [Figure 3] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment, which can be said to have a prismatic battery shape. [Figure 4] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment, which can be said to have a pouch-type battery configuration. [Figure 5] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment, which can be said to have a pouch-type battery configuration. [Figure 6] 2 is an enlarged view of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. FIG. [Figure 7] 2 is an enlarged view of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. FIG. [Figure 8] 1 is a flowchart illustrating a method for manufacturing a positive electrode active material according to an embodiment of the present invention. [Figure 9] 1 is an SEM image of a positive electrode active material according to an example of the present invention. [Figure 10] 1 is an SEM image of a positive electrode active material according to an example of the present invention. [Figure 11] 1 is an SEM image of a positive electrode active material of a comparative example of the present invention. [Figure 12] 1 is a graph showing differential capacity for a lithium secondary battery according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] In order to fully understand the configuration and effects of the present invention, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and may be embodied in various forms and may be modified in various ways. However, the description of the present embodiment is provided to ensure complete disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0012] In this specification, when a component is referred to as being on top of another component, it means that it may be formed directly on the other component, or that a third component may be interposed between them. Also, in the drawings, the thickness of the components is exaggerated for the purpose of effectively explaining the technical content. Throughout the specification, parts designated with the same reference numerals refer to the same components.

[0013] The embodiments described herein are described with reference to cross-sectional views and / or plan views that are ideal examples of the present invention. In the drawings, the thicknesses of films and regions are exaggerated for the purpose of effectively explaining the technical content. Therefore, the regions shown in the drawings have schematic characteristics, and the shapes of the regions shown in the drawings are intended to illustrate specific forms of element regions and do not limit the scope of the invention. In various embodiments herein, terms such as "first," "second," and "third" are used to describe various components, but these components should not be limited by these terms. These terms are merely used to distinguish one component from another. The embodiments described and illustrated herein also include corresponding complementary embodiments.

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

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

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

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

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

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

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

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

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

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

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

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

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

[0027] The dry binder is a polymeric material that can be fibrous, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, ethylene oxide, or a combination thereof.

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

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

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

[0031] The material capable of reversibly inserting / extracting lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0032] The lithium metal alloy may be an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0033] As the substance capable of doping or 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 (where Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination of these. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or a combination of these.

[0034] The silicon-carbon composite can be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite can be in a form in which silicon particles are coated with amorphous carbon on the surface of the silicon particles. For example, it can include secondary particles (cores) combined with primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon is also located between the primary silicon particles, and for example, the primary silicon particles can be coated with amorphous carbon. The secondary particles can be dispersed in an amorphous carbon matrix.

[0035] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite can include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core.

[0036] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material.

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

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

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

[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 coating layer, or may be stacked in a coating layer containing an organic material and a coating layer containing an inorganic material.

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

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

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

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

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

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

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

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

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

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

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

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

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

[0056] The content of the first particles PTC1 in the positive electrode active material layer AML1 may be 90 wt % to 99.5 wt % relative to 100 wt % of the positive electrode active material layer AML1, and the contents of the binder BND and the conductive material CDM may be 0.5 wt % to 5 wt % respectively relative to 100 wt % of the positive electrode active material layer AML1.

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

[0058] The conductive material CDM can be used to improve the conductivity of the positive electrode active material layer AML1. Any conductive material that does not cause a chemical change in the positive electrode active material layer AML1 can be used as the conductive material CDM. For example, the conductive material CDM can include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, and the like; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

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

[0060] 1st particle PTC1 The first particle PTC1 may contain an olivine-based lithium compound represented by the following Chemical Formula 1.

[0061] [Chemical Formula 1] Li a1 Mn x1 Fe y1 B z1 PO 4-b1 In the Chemical Formula 1, 0.8 ≦ a1 ≦ 1.2, 0.45 ≦ x1 ≦ 0.55, 0.45 ≦ y1 ≦ 0.55, 0 < z1 ≦ 0.05, 0 ≦ b1 ≦ 0.05, and x1 + y1 + z1 = 1 may hold. Mg and Ti may be dopants doped into the first particle PTC1. For example, x1 may be 0.45 < x1 < 0.55, or 0.5. At least one of Mg and Ti controls the size of the primary particles to be uniform, and the charge-discharge efficiency, low-temperature characteristics, and life characteristics of the lithium secondary battery can be improved. The primary particles will be described in detail below.

[0062] In other words, the first particle PTC1 contains a compound of the following Chemical Formula 2, but may be doped with Mg and Ti.

[0063] [Chemical Formula 2] Li a2 Mn x2 Fe y2 PO 4-b2 In Chemical Formula 2, 0.8 ≦ a2 ≦ 1.2, 0.45 ≦ x2 ≦ 0.55, 0.45 ≦ y2 ≦ 0.55, 0 ≦ b2 ≦ 0.05, and x2 + y2 = 1 may hold. For example, x2 may be 0.45 < x2 < 0.55, or 0.5.

[0064] The doping amount of B, that is, the total doping amount of Mg and Ti, may be 2500 ppm to 5000 ppm, 4000 ppm to 5000 ppm, or 4600 ppm. The doping amount of B may be defined as the weight of the doping element with respect to the total weight of the metals (that is, Fe and Mn) excluding lithium in the olivine-based lithium compound represented by the Chemical Formula 1.

[0065] The doping amount of Mg may be 1000 ppm to 2400 ppm, or 2400 ppm. The doping amount of Mg may be defined as the weight of the doping element Mg relative to the total weight of metals (i.e., Fe, Mn, and Ti) excluding lithium in the olivine-based lithium compound represented by Chemical Formula 1.

[0066] The doping amount of Ti may be 2000 ppm, which may be defined as the weight of the doping element Ti relative to the total weight of metals (i.e., Fe, Mn, and Mg) excluding lithium in the olivine-based lithium compound represented by Chemical Formula 1.

[0067] The ratio of the Mg doping amount to the Ti doping amount (Mg doping / Ti doping amount) can be 0.3 to 1.2, 0.5 to 1.2, or 1.2.

[0068] If the doping amounts of Mg and Ti and the ratio of the doping amount of Mg to the doping amount of Ti satisfy the above-mentioned ranges, the charge / discharge efficiency, low-temperature characteristics, and life characteristics of the lithium secondary battery can be improved.

[0069] For example, the first particles PTC1 may include a coating layer on their surfaces. The coating layer may cover the entire surface of the first particles PTC1 or may cover only a portion of the surface of the first particles PTC1. For example, the coating layer may include carbon and / or a carbon-containing compound. The coating layer may improve the structural stability and electrical conductivity of the first particles PTC1.

[0070] 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.

[0071] 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 %.

[0072] The cathode active material of the present invention may include the first particles PTC1, thereby improving the composite density, capacity, and energy density. For example, the composite density of the cathode active material of the present invention may be 2.0 g / cc to 2.5 g / cc, or 2.3 g / cc to 2.4 g / cc.

[0073] The first particles PTC1 may have a first average particle size, which may vary depending on the embodiment of FIG.

[0074] As an example, referring again to FIG. 6, the first particles PTC1 may have a single particle shape. In this specification, a single particle may refer to a single particle without an internal grain boundary. A single particle may refer to a morphological phase in which particles exist as an independent phase that is not aggregated with each other, a monolith structure, a single body structure, or a non-aggregated particle. For example, a single particle may be a single crystal. Alternatively, a single particle may be a particle containing several crystals. A single particle may be in a singly separated form. Alternatively, a single particle may be in a form in which two to one hundred single particles are attached to each other. That is, the first particles PTC1 may be provided in various sizes. For example, the average particle size of the first particles PTC1 may be about 1 μm. The minimum particle size of the first particles PTC1 may be 20 nm to 500 nm, or 200 nm to 300 nm. For example, the minimum particle size may refer to the diameter measured by randomly selecting about 30 primary particles (hereinafter referred to as first primary particles) from an electron microscope image of the positive electrode active material. The average particle size of the first particles PTC1 will be described in more detail below.

[0075] If the first particles PTC1 are single particles, the average particle size of the first particles PTC1 may be 100 nm to 2 μm, or 500 nm to 2 μm. For example, the average particle size of the first particles PTC1 may be approximately 1 μm. In one example, the average particle size may be measured using a particle size analyzer. The average particle size may refer to the diameter of particles with a cumulative volume of 50% (D50) in the particle size distribution.

[0076] 7, the first particles PTC1 may be polycrystalline and include secondary particles formed by agglomeration of at least two or more primary particles. In other words, one first particle PTC1 may include a plurality of second particles PTC2 agglomerated together. Each of the second particles PTC2 may be a primary particle. The first particles PTC1 may have a spherical or ellipsoidal shape.

[0077] For example, the first particle PTC1 may further include a grain boundary coating layer on the surface of each of the second particles PTC2. The grain boundary coating layer may be present inside the first particle PTC1. The grain boundary coating layer may be formed by coating along the interface between the second particles PTC2 inside the first particle PTC1. In other words, the grain boundary coating layer may refer to a material coated on the grain boundaries inside the first particle PTC1. The grain boundary coating layer may include carbon and / or a carbon-containing compound. The grain boundary coating layer may further include at least one selected from the group consisting of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound.

[0078] 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.

[0079] The first particles PTC1 may further include a grain boundary coating portion, which may enhance structural stability and form a uniform coating layer on the surface of the first particles PTC1, and may further improve the electrical conductivity of the first particles PTC1.

[0080] The first particles PTC1 may further contain carbon derived from the above-mentioned coating layer and / or grain boundary coating layer. The carbon element content in the first particles PTC1 may be 0.5 wt % to 10 wt %, 1 wt % to 3 wt %, or 1.5 wt % to 2.5 wt %.

[0081] If the first particles PTC1 are secondary particles, the average particle size of the first particles PTC1 may be 2 μm to 15 μm, 3 μm to 10 μm, or 3 μm to 7 μm. For example, the average particle size of the first particles PTC1 may be approximately 5 μm. The average particle size of the first particles PTC1 may be larger than the average particle size of the second particles PTC2 described below. In one example, the average particle size may be measured using a particle size analyzer. The average particle size may refer to the diameter of particles with a cumulative volume of 50% (D50) in the particle size distribution.

[0082] The particle size of the second particles PTC2 may be 200 nm or less. For example, the particle size of the second particles PTC2 may be 10 nm to 200 nm, 20 nm to 200 nm, 50 nm to 200 nm, or 100 nm to 200 nm. As an example, the particle size may refer to the diameter measured by randomly selecting approximately 30 second particles PTC2 from an electron microscope photograph of the positive electrode active material. The particle size of the second particles PTC2 may be uniform. The particle size of the second particles PTC2 may be smaller than the particle size of the first primary particles. For example, the particle size of the second particles PTC2 may be approximately 100 nm smaller than the particle size of the first primary particles. If the average particle size of the first particles and the second particles satisfies the above range and the size of the second particles is uniform, the charge / discharge capacity and low-temperature capacity of a lithium secondary battery including them can be improved.

[0083] The first particles PTC1 may have a spherical shape formed by agglomeration of nano-sized second particles PTC2. The first particles PTC1 and the second particles PTC2 may be closely agglomerated to each other, which may result in the following characteristics: 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 approximately 20% to 40%. The Span value of the first particles PTC1 analyzed using a particle size analyzer may be 0.3 to 0.75.

[0084] A lithium secondary battery (see FIG. 1) including the positive electrode active material according to the above-described embodiment of the present invention may have an average voltage of 3.5V to 3.7V, or 3.6V when discharged at 0.1C between 2.5V and 4.25V.

[0085] Furthermore, lithium secondary batteries including the cathode active material according to embodiments of the present invention may have improved lifespan characteristics, for example, a capacity retention rate of 99% or more after 50 charge / discharge cycles at a constant current of 1.0 C at a voltage of 2.5 V to 4.25 V, or 99.7 V to 100 V.

[0086] A differential capacity (dQ / dV)-voltage charging graph for a lithium secondary battery of the present invention may include a first charging peak V1, a first discharging peak V2, and a second charging peak V3.

[0087] For example, the first charge peak V1 may occur at a voltage between 3.4 V and 4.0 V, between 3.4 V and 3.6 V, or between 3.48 V and 3.53 V. The first discharge peak V2 may occur at a voltage between 3.4 V and 4.0 V, between 3.4 V and 3.5 V, or between 3.46 V and 3.49 V. The second charge peak V3 may occur at a voltage between 4.0 V and 4.4 V, between 4.0 V and 4.2 V, or between 4.08 V and 4.10 V.

[0088] For example, the maximum peak voltage of the first charging peak V1 may occur at a voltage between 3.4 V and 3.6 V, or between 3.49 V and 3.53 V. The maximum peak voltage of the first discharging peak V2 may occur at a voltage between 3.4 V and 3.6 V, or between 3.48 V and 3.49 V. The maximum peak voltage of the second charging peak V3 may occur at a voltage between 4.0 V and 4.2 V, or between 4.099 V and 4.110 V. The maximum peak voltage may be defined as the voltage at which each peak exhibits its greatest intensity.

[0089] The ratio of the intensity of the first discharge peak to the intensity of the first charge peak (I V2 / I V1 ) may be 0.986 to 0.991, or 0.987 to 0.990. For example, the positive electrode active material may have a manganese (Mn) content of 52 mol% or less. That is, in Formula 1, x1 may be 0.45 to 0.52, and in Formula 2, x2 may be 0.45 to 0.52.

[0090] The ratio of the intensity of the second charging peak to the intensity of the first charging peak (I V3 / I V1 ) may be 1.17 or less, or 1.164 to 1.166. For example, the positive electrode active material may have a manganese (Mn) content of 52 mol% or less. That is, in Formula 1, x1 may be 0.45 to 0.52, and in Formula 2, x2 may be 0.45 to 0.52.

[0091] Positive electrode active material slurry A positive electrode active material slurry according to an embodiment of the present invention may include the above-described first particles PTC1, conductive material CDM, binder BND, and solvent. Hereinafter, for convenience of explanation, the same matters as those described with reference to FIGS. 6 and 7 will be omitted, and differences will be described in detail.

[0092] In one embodiment, the viscosity of the positive electrode active material slurry may be 7000 mPa·s or less. For example, the viscosity of the positive electrode active material slurry may be 1000 mPa·s to 7000 mPa·s, 2000 mPa·s to 6000 mPa·s, or 3000 mPa·s to 4000 mPa·s. When the viscosity of the positive electrode active material slurry satisfies the above range, the positive electrode active material layer AML1 can be smoothly attached to the current collector COL1.

[0093] In one embodiment, when the first particles PTC1 are secondary particles, the cathode active material slurry of the present invention may have a high solid content and still achieve a desired viscosity. For example, the cathode active material slurry may have a solid content of 60% to 70%. The solid content may refer to the weight percentage of the solid material remaining after the solvent evaporates (i.e., the dried mixture and current collector) relative to the total weight of the current collector on which the cathode active material slurry is applied during electrode fabrication. The solid content may include the cathode active material, a binder, and a conductive material. When the solid content satisfies the above range, the first particles PTC1 may have excellent adhesion to the electrode current collector.

[0094] The first particles PTC1 may be attached to the current collector COL1 (see FIG. 1), and the binder BND may increase the adhesive strength between the first particles PTC1 and the current collector COL1 (see FIG. 1).

[0095] For example, when the first particles PTC1 are single particles, the cathode active material slurry of the present invention may contain a small amount of binder BND when fabricating a full cell. That is, because the first particles PTC1 have a very small first average particle size, the content of binder BND in the cathode active material layer AML1 may be high to ensure a desired range of adhesive strength between the first particles PTC1 and the current collector COL1 (see FIG. 1) when fabricating a full cell. For example, the content of binder BND may be 2 wt % to 5 wt %, or 3 wt % to 5 wt %, based on 100 wt % of the cathode active material layer AML1.

[0096] For example, when the first particles PTC1 are secondary particles, the cathode active material slurry of the present invention may contain a small amount of binder BND during full cell fabrication. Because the first particles PTC1 have a large average particle size, the content of binder BND in the cathode active material layer AML1 may be relatively small to ensure a desired range of adhesion between the first particles PTC1 and the current collector COL1 (see FIG. 1) during full cell fabrication. For example, the content of binder BND may be 0.5 wt % to 3 wt %, or 0.5 wt % to 2 wt %, relative to 100 wt % of the cathode active material layer AML1. In other words, when the first particles PTC1 are secondary particles, a smaller amount of binder BND may be required during full cell fabrication than when the first particles PTC1 are monoparticles. This may reduce the resistance of a lithium secondary battery containing the first particles PTC1, which are secondary particles.

[0097] Method for producing positive electrode active material 8 is a flow chart illustrating a method for manufacturing a positive electrode active material according to an embodiment of the present invention. The method for manufacturing the first particles PTC1 according to an embodiment of the present invention will be described in more detail with reference to FIG.

[0098] The manganese iron phosphate precursor, the lithium source, the carbon source, and the dopant source may be placed in a solvent and mixed S100. For example, the solvent may be water, ethanol, or the like.

[0099] The manganese iron phosphate precursor can be a compound containing all of manganese (Mn), iron (Fe), and phosphorus (P), a mixture of a manganese (Mn)-containing compound and a compound containing iron (Fe) and phosphorus (P), or a mixture of a manganese (Mn)-containing compound, an iron (Fe)-containing compound, and a phosphorus (P)-containing compound. For example, the manganese iron phosphate precursor can be a compound containing Mn x Fe 1-x PO4·H2O, a mixture of MnCO3 and FePO4·H2O, or a mixture of MnCO3, FeSO4, and H3PO4, where x can be 0.2 to 0.8 (e.g., about 0.45 to about 0.55).

[0100] 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.

[0101] 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.

[0102] 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 Mg oxide, Mg chloride, Ti oxide, and Ti chloride of Chemical Formula 1. For example, the dopant source may include at least one of Mg oxide or Mg chloride and at least one of Ti oxide or Ti chloride.

[0103] 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.

[0104] In one embodiment of the present invention, the wet-milling step S200 may be omitted. Specifically, in order to maximize the average particle size of the first particles PTC1 that are finally produced, the wet-milling step S200 for the precursor particles may be omitted.

[0105] The solvent may be removed from the mixture to form a dried mixture S300.

[0106] In producing the first particles PTC1 of FIG. 6 according to an embodiment of the present invention, forming the dried mixture may include subjecting the mixture to a direct evaporation method, such as static drying or spray drying.

[0107] 7, forming a dried mixture may include directly spray drying the mixture. Spray drying may be performed using commonly used spray drying equipment. For example, spray drying may be performed using at least one selected from an ultrasonic spray dryer, an air nozzle spray dryer, an ultrasonic nozzle spray dryer, a filter expansion droplet generator, and an electrostatic spray dryer.

[0108] The particles refined to the size of primary particles through the wet milling process can be agglomerated to form secondary particles through the spray drying process. Therefore, the primary particles PTC1 can be formed into secondary particles of a desired size by adjusting the flow rate and velocity of the carrier gas, temperature, residence time in the reactor, and internal pressure during the spray drying process.

[0109] As an example, the mixture to be spray-dried may have a total solid content of 20% to 40%. The solid content may refer to the weight of the solid material (i.e., the dried mixture) remaining after the solvent has evaporated relative to the total weight of the mixture (i.e., the spray liquid), converted into a percentage. As an example, the spray liquid may have a solid content of approximately 30 wt%.

[0110] If the solid content is less than 20%, the average particle size of the first particles PCT1 will be small, which may result in reduced productivity, whereas if the solid content is more than 40%, it will be difficult to control the average particle size of the first particles PCT1, which may result in increased size variation of the first particles PCT1.

[0111] 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.

[0112] In one embodiment, the input rate of the spray dryer may be 0.1 kg / min to 0.9 kg / min. The input rate of the spray dryer may be defined as the weight of the solvent and raw material mixture input per time. In one embodiment, the input rate of the spray dryer according to the present invention may be about 0.5 kg / min.

[0113] In one embodiment, spray drying may be carried out at a temperature of 100°C to 300°C. For example, spray drying may be carried out at a temperature of 200°C to 300°C, above 200°C to 300°C, or 230°C to 270°C. The propellant gas (e.g., air) used in spray drying may be introduced at a first temperature and discharged at a second temperature. For example, the first temperature may be 200°C to 250°C. The second temperature may be 80°C to 150°C.

[0114] The spray pressure may be 0.3 MPa to 0.7 MPa. For example, the spray pressure may be about 0.5 MPa.

[0115] When the input amount, input pressure, and temperature of the spray drying satisfy the above-described ranges, the first particles PTC1 can have a spherical shape and a desired porosity.

[0116] The spraying liquid flow rate for spray drying can be 30 ml / min to 80 ml / min. If the flow rate is less than 30 ml / min, problems such as nozzle clogging and reduced productivity may occur. If the flow rate is greater than 80 ml / min, water condensation within the spray dryer may cause the mixture to be incompletely dried. The spraying liquid input pressure can be 0.3 MPa to 0.7 MPa. For example, the spraying liquid input pressure can be about 0.5 MPa.

[0117] The dried mixture may be calcined under an inert atmosphere (S400). The inert atmosphere may be a nitrogen atmosphere and / or an argon atmosphere. The temperature of the calcination process may be 500°C to 1000°C, or 600°C to 800°C. The time for the calcination process may be 4 hours to 20 hours, or 6 hours to 12 hours. By calcining the dried mixture, first particles PTC1 including the compound of Chemical Formula 1 described above may be formed.

[0118] The fired first particles PTC1 may be subjected to a dry grinding process (S500). The fired mixture may be ground using an air jet mill or the like.

[0119] When producing the first particles PTC1 of FIG. 6 according to one embodiment of the present invention, the sintered mixture may be pulverized at a rotation speed of 7000 rpm or more. For example, the sintered mixture may be pulverized at a rotation speed of 7000 rpm to 10000 rpm, or 7500 rpm to 9000 rpm. As a result, the first particles PTC1 may have a single particle shape as shown in FIG.

[0120] When preparing the first particles PTC1 of FIG. 7 according to another embodiment of the present invention, the sintered mixture may be pulverized at a rotation speed of 0 rpm to 7000 rpm. For example, the sintered mixture may be pulverized at a rotation speed of 4000 rpm to 7000 rpm, 4000 rpm to 6000 rpm, or 4500 rpm to 5000 rpm. Unlike when preparing the positive electrode active material of FIG. 6, the pulverization step S500 after sintering may be performed under relatively mild conditions. When preparing the positive electrode active material of FIG. 7, for example, the dry pulverization step S500 may be omitted. If the rotation speed of the pulverization step S500 satisfies the above-described range, the first particles PTC1 may maintain the shape of secondary particles. As a result, the first particles PTC1 may have the shape of secondary particles as shown in FIG. 7.

[0121] In a method for manufacturing the first particles PTC1 shown in FIG. 7 according to an embodiment of the present invention, a carbon source is introduced into an iron phosphate precursor to uniformly form a carbon coating layer on the surfaces of the primary particles. The primary particles are then closely agglomerated by spray drying to form dense secondary spherical particles. As a result, the first particles PTC1 may include a stable carbon coating layer on both the exterior and interior of the first particles PTC1, thereby having a relatively high carbon content. The high carbon content of the first particles PTC1 shown in FIG. 7 may improve the conductivity of the positive electrode active material layer AML1.

[0122] Carbon element analysis according to the present invention can be performed using an Elementar Micro Cube elemental analyzer. Specific operating procedures and conditions are as follows: 1-2 mg of sample is weighed into a tin cup, placed on an automatic sampling tray, and introduced into a combustion tube via a ball valve. The sample is then burned at a combustion temperature of 1000°C. The burned gas is then reduced using reduced copper to form carbon dioxide. Carbon dioxide is detected using a TCD detector.

[0123] To measure the carbon content of the particles according to the present invention, scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS) and quantitative analysis were performed on the particle surface. Other methods for measuring the carbon content include inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectroscopy (ICP-OES), in addition to SEM-EDS.

[0124] The present invention will be described in more detail below with reference to examples. However, these examples are for illustrative purposes only and the scope of the present invention is not limited to these examples.

[0125] Example 1: Preparation of single particle-shaped first particles Mn 0.5 Fe 0.5Manganese iron phosphate precursor (PO4), lithium carbonate, magnesium dioxide, and titanium dioxide were added to water in a molar ratio of (Mn+Fe):Li:Mg:Ti=1:1.03:0.01:0.004. Glucose was added to the mixture at 10 wt%. The mixture was subjected to a wet grinding process using a ball mill. The mixture was evaporated to dryness on a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours. The dried mixture was calcined at 650°C for 10 hours in a nitrogen atmosphere. The calcined product was pulverized at a rotation speed of 8000 rpm to obtain single-particle primary particles. The chemical formula of the primary particles was approximately LiMn 0.5 Fe 0.5 PO4, the doping amount of Mg was 2400 ppm, and the doping amount of Ti was 2000 ppm.

[0126] Example 2: Production of primary particles in the form of secondary particles Mn 0.5 Fe 0.5 Manganese iron phosphate precursor (PO4), lithium carbonate, magnesium dioxide, and titanium dioxide were added to water in a molar ratio of (Mn+Fe):Li:Mg:Ti=1:1.03:0.01:0.004. Glucose was added to the mixture at 10 wt%. The mixture in the form of a slurry 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 chemical formula of the primary particles was approximately LiMn 0.5 Fe 0.5 PO4, the doping amount of Mg was 2400 ppm, and the doping amount of Ti was 2000 ppm.

[0127] Comparative Example 1: Production of single particle-shaped first particles Mn 0.6 Fe 0.4 The manganese iron phosphate precursor (PO4), lithium carbonate, magnesium dioxide, and titanium dioxide were added in a molar ratio of (Mn+Fe):Li:Mg:Ti=1:1.03:0.0025:0.004, and the chemical formula of the first particles was approximately LiMn 0.6 Fe 0.5It was prepared in the same manner as in Example 1, except that the doping amount of Mg was 600 ppm in PO4.

[0128] Comparative Example 2: Production of single particle-shaped first particles Mn 0.55 Fe 0.45 The manganese iron phosphate precursor (PO4), lithium carbonate, magnesium dioxide, and titanium dioxide were added in a molar ratio of (Mn+Fe):Li:Mg:Ti=1:1.03:0.0025:0.004, and the chemical formula of the first particles was approximately LiMn 0.55 Fe 0.45 It was prepared in the same manner as in Example 1, except that the doping amount of Mg was 600 ppm in PO4.

[0129] Comparative Example 3: Production of single particle-shaped first particles Mn 0.5 Fe 0.5 The manganese iron phosphate precursor (PO4), lithium carbonate, magnesium dioxide, and titanium dioxide were added in a molar ratio of (Mn+Fe):Li:Mg:Ti=1:1.03:0.0025:0.004, and the chemical formula of the first particles was approximately LiMn 0.5 Fe 0.5 It was prepared in the same manner as in Example 1, except that the doping amount of Mg was 600 ppm in PO4.

[0130] Comparative Example 4: Production of single particle-shaped first particles Mn 0.45 Fe 0.55 The manganese iron phosphate precursor (PO4), lithium carbonate, magnesium dioxide, and titanium dioxide were added in a molar ratio of (Mn+Fe):Li:Mg:Ti=1:1.03:0.0025:0.004, and the chemical formula of the first particles was approximately LiMn 0.45 Fe 0.55 It was prepared in the same manner as in Example 1, except that the doping amount of Mg was 600 ppm in PO4.

[0131] Comparative Example 5: Production of single particle-shaped first particles Mn 0.4 Fe 0.6The manganese iron phosphate precursor (PO4), lithium carbonate, magnesium dioxide, and titanium dioxide were added in a molar ratio of (Mn+Fe):Li:Mg:Ti=1:1.03:0.0025:0.004, and the chemical formula of the first particles was approximately LiMn 0.4 Fe 0.6 It was prepared in the same manner as in Example 1, except that the doping amount of Mg was 600 ppm in PO4.

[0132] Comparative Example 6: Production of single particle-shaped first particles Mn 0.5 Fe 0.5 The manganese iron phosphate precursor (PO4) and lithium carbonate were added in a molar ratio of (Mn+Fe):Li of 1:1.03, and the chemical formula of the first particles was approximately LiMn 0.5 Fe 0.5 It was prepared in the same manner as in Example 1, except that it was PO4.

[0133] Comparative Example 7: Production of single particle-shaped first particles Mn 0.5 Fe 0.5 The manganese iron phosphate precursor (PO4), lithium carbonate, and magnesium dioxide were added in a molar ratio of (Mn+Fe):Li:Mg=1:1.03:0.0025, and the chemical formula of the first particles was approximately LiMn 0.5 Fe 0.5 It was prepared in the same manner as in Example 1, except that the doping amount of Mg was 600 ppm in PO4.

[0134] Comparative Example 8: Production of single particle-shaped first particles Mn 0.5 Fe 0.5 The manganese iron phosphate precursor (PO4), lithium carbonate, and titanium dioxide were added in a molar ratio of (Mn+Fe):Li:Ti=1:1.03:0.004, and the chemical formula of the first particles was approximately LiMn 0.5 Fe 0.5 It was prepared in the same manner as in Example 1, except that the doping amount of Ti was 2000 ppm using PO4.

[0135] Comparative Example 9: Production of single particle-shaped first particles Mn0.5 Fe 0.5 The manganese iron phosphate precursor (PO4), lithium carbonate, magnesium dioxide, and titanium dioxide were added in a molar ratio of (Mn+Fe):Li:Mg:Ti=1:1.03:0.02:0.004, and the chemical formula of the first particles was approximately LiMn 0.5 Fe 0.5 It was prepared in the same manner as in Example 1, except that the doping amount of Mg was 4800 ppm in PO4.

[0136] Comparative Example 10: Production of primary particles in the form of secondary particles Mn 0.5 Fe 0.5 The manganese iron phosphate precursor (PO4) and lithium carbonate were added in a molar ratio of (Mn+Fe):Li of 1:1.03, and the chemical formula of the first particles was approximately LiMn 0.5 Fe 0.5 It was prepared in the same manner as in Example 2, except that it was PO4.

[0137] Comparative Example 11: Production of primary particles in the form of secondary particles Mn 0.5 Fe 0.5 The manganese iron phosphate precursor (PO4), lithium carbonate, and magnesium dioxide were added in a molar ratio of (Mn+Fe):Li:Mg=1:1.03:0.0025, and the chemical formula of the first particles was approximately LiMn 0.5 Fe 0.5 It was prepared in the same manner as in Example 2, except that the doping amount of Mg was 600 ppm in PO4.

[0138] Comparative Example 12: Production of primary particles in the form of secondary particles Mn 0.5 Fe 0.5 The manganese iron phosphate precursor (PO4), lithium carbonate, and titanium dioxide were added in a molar ratio of (Mn+Fe):Li:Ti=1:1.03:0.004, and the chemical formula of the first particles was approximately LiMn 0.5 Fe 0.5 It was prepared in the same manner as in Example 2, except that the doping amount of Ti was 2000 ppm in PO4.

[0139] Comparative Example 13: Production of primary particles in the form of secondary particles Mn 0.4 Fe 0.6 It was prepared in the same manner as in Example 2, except that the manganese iron phosphate precursor (PO), lithium carbonate, magnesium dioxide, and titanium dioxide were mixed in a molar ratio of (Mn+Fe):Li:Mg:Ti of 1:1.03:0.01:0.004.

[0140] Comparative Example 14: Production of primary particles in the form of secondary particles Mn 0.6 Fe 0.4 It was prepared in the same manner as in Example 2, except that the manganese iron phosphate precursor (PO), lithium carbonate, magnesium dioxide, and titanium dioxide were mixed in a molar ratio of (Mn+Fe):Li:Mg:Ti of 1:1.03:0.01:0.004.

[0141] Cathode manufacturing 95% by weight of the final positive electrode active material, 3% by weight of polyvinylidene fluoride binder, and 2% by weight of carbon black conductive material were mixed in N-methylpyrrolidone solvent to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to an aluminum current collector, dried, and then rolled to prepare a positive electrode.

[0142] Lithium secondary battery manufacturing A 2032-type coin half-cell was fabricated using the prepared positive electrode and a lithium metal counter electrode as the 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 was injected to fabricate a lithium secondary battery. The electrolyte used was a mixture of 1.3 M LiPF6 with a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:4:3.

[0143] [Table 1]

[0144] Evaluation example 1: Analysis of the surface of the positive electrode active material An SEM image of the primary particles prepared in Example 1 is shown in Figure 9. An SEM image of the primary particles prepared in Example 2 is shown in Figure 10. An SEM image of the primary particles prepared in Comparative Example 1 is shown in Figure 11.

[0145] 9 and 11, it can be seen that the first particles according to Example 1 and Comparative Example 1 are in the form of fine single particles. Referring to Fig. 10, it can be seen that the first particles according to Example 2 are in the form of spherical secondary particles formed by agglomeration of a plurality of primary particles. It can also be seen that the second particles PTC2 according to Example 2 are in the form of nano-sized fine single particles. Meanwhile, referring to Figs. 9 and 10, the primary particles according to Example 2 are smaller and more uniform than the primary particles according to Example 1.

[0146] Evaluation example 2: Evaluation of active materials The pellet density (PD) of the positive electrode active materials of Examples 1 and 2 and Comparative Examples 1 to 14 was measured. The results are shown in Table 2.

[0147] [Table 2]

[0148] Evaluation example 3: Evaluation of differential capacity The differential capacity of lithium secondary batteries fabricated using the positive electrode active materials of Examples 1 and 2 and Comparative Examples 4, 5, and 13 was evaluated. The lithium secondary batteries were charged and discharged once at 0.2 C and then twice in the same manner. The evaluation results are shown in Table 3 and FIG. 12.

[0149] Table 3 shows the maximum peak voltages (V max、V1 , V max、V2 , V max、V3 ) and the ratio of the peak intensities (I V2 / I V1 , I V3 / I V1 12 is a graph showing the differential capacity (dQ / dV)-voltage charging curves measured for Example 1 and Comparative Example 1 after one charge.

[0150] [Table 3]

[0151] Referring to Table 3 and FIG. 12, Examples 1 and 2, unlike Comparative Examples 4, 5, and 13, exhibited a maximum peak voltage (V max、V1 , V max、V2 , V max、V3 ) and the ratio of peak intensities (I V2 / I V1 , I V3 / I V1 ) satisfied the above range.

[0152] Evaluation example 4: Evaluation of battery characteristics The characteristics of the lithium secondary batteries manufactured using the positive electrode active materials of Examples 1 and 2 and Comparative Examples 1 to 14 were evaluated.

[0153] The lithium secondary battery was initially charged at a constant current (0.1C) and a constant voltage (4.25V), and then allowed to rest for 10 minutes before discharging to 2.5V at a constant current (0.1C). It was then charged and discharged 50 times at 1.0C / 1.0C at -20°C. An additional coin cell was also fabricated and its capacity measured at -20°C. The battery characteristics were evaluated and are shown in Table 4 below.

[0154] [Table 4]

[0155] Referring to Table 4, it was confirmed that the secondary batteries according to Examples 1 and 2 had high average voltage and excellent lifespan characteristics. Specifically, it was confirmed that the secondary battery according to Example 1 of the present invention had a similar or higher average voltage and a longer lifespan than the secondary batteries according to Comparative Examples 1 to 9. It was confirmed that the secondary battery according to Example 2 of the present invention had a similar or higher average voltage and a longer lifespan than the secondary batteries according to Comparative Examples 10 and 14. Meanwhile, the secondary battery according to Example 2 had a longer lifespan than the secondary battery according to Example 1. In addition, the secondary battery according to Example 2 had a higher charge amount than the secondary battery according to Example 1, and therefore it was confirmed that the resistance of the secondary battery according to Example 2 was smaller. Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention may be embodied in other specific forms without changing the technical idea or essential features thereof. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and are not limiting.

Claims

1. The present invention includes first particles having a first average particle size, the first particles comprising a compound represented by the following Chemical Formula 1: Cathode active material: [Chemical formula 1] Li a1 Mn x1 Fe y1 B z1 2O 4-b1 In Chemical Formula 1, 0.8≦a1≦1.2, 0.45≦x1≦0.55, 0.45≦y1≦0.55, 0<z1≦0.05, 0≦b1≦0.05, and x1+y1+z1=1; The B is Mg and Ti.

2. The ratio of the Mg doping amount to the Ti doping amount (Mg doping / Ti doping amount) is 0.5 to 1.2; The positive electrode active material according to claim 1 .

3. the first particles include a coating layer including carbon; The carbon content in the first particles is 1.5% by weight to 2.5% by weight. The positive electrode active material according to claim 1 .

4. the first particle is a single particle, the first average particle size is 100 nm to 2 μm; The positive electrode active material according to claim 1 .

5. the first particles include a plurality of second particles aggregated together; the first average particle size is 3 μm to 10 μm; Each of the plurality of second particles is a primary particle, and the second particles have a particle size of 200 nm or less. The positive electrode active material according to claim 1 .

6. The porosity of the first particles is 20% to 40%. The positive electrode active material according to claim 5 .

7. The first particles have a Span value of 0.3 to 0.75 as analyzed by a particle size analyzer. The positive electrode active material according to claim 5 .

8. The present invention includes a first particle having a first average particle size and comprising a compound represented by the following Chemical Formula 2: the first particles are doped with Mg and Ti; The total doping amount of Mg and Ti is 2500 ppm to 5000 ppm; Cathode active material: [Chemical formula 2] Li a2 Mn x2 Fe y2 PO 4-b2 In Chemical Formula 2, 0.8≦a2≦1.2, 0.45≦x2≦0.55, 0.45≦y2≦0.55, 0≦b2≦0.05, and x2+y2=1.

9. The doping amount of Mg is 1000 ppm to 2400 ppm. The positive electrode active material according to claim 8 .

10. The doping amount of Ti is 2000 ppm; The positive electrode active material according to claim 8 .

11. The ratio of the Mg doping amount to the Ti doping amount (Mg doping / Ti doping amount) is 0.5 to 1.2; The positive electrode active material according to claim 8 .

12. the first particles include a coating layer including carbon; The carbon content in the first particles is 1.5% by weight to 2.5% by weight. The positive electrode active material according to claim 8 .

13. the first particle is a single particle, the first average particle size is 100 nm to 2 μm; The positive electrode active material according to claim 8 .

14. the first particles include a plurality of second particles aggregated together; the first average particle size is 3 μm to 10 μm; Each of the plurality of second particles is a primary particle, and the second particles have a particle size of 200 nm or less. The positive electrode active material according to claim 8 .

15. a positive electrode including a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector; 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, The differential capacity (dQ / dV)-voltage charging graph is a first charge peak V1, represented by a voltage between 3.4V and 4.0V; a first discharge peak V2 represented by a voltage between 3.4 V and 4.0 V; a second charging peak V3 represented by a voltage between 4.0 V and 4.4 V; Lithium secondary battery.

16. The ratio of the intensity of the first discharge peak to the intensity of the first charge peak (I V2 / I V1 ) is 0.986 to 0.991; The lithium secondary battery according to claim 15.

17. The ratio of the intensity of the second charging peak to the intensity of the first charging peak (I V3 / I V1 ) is 1.17 or less, The lithium secondary battery according to claim 15.

18. Between 2.5V and 4.25V, the average voltage at 0.1C discharge is 3.5V to 3.7V. The lithium secondary battery according to claim 15.

19. The capacity retention rate after 50 charge / discharge cycles at a constant current of 1.0 C at a voltage of 2.5 V to 4.25 V is 99% or more. The lithium secondary battery according to claim 15.

20. The positive electrode active material contained in the positive electrode active material layer is The present invention includes first particles having a first average particle size, the first particles comprising a compound represented by the following Chemical Formula 1: The lithium secondary battery according to claim 15: [Chemical formula 1] Li a1 Mn x1 Fe y1 B z1 2O 4-b1 In Chemical Formula 1, 0.8≦a1≦1.2, 0.45≦x1≦0.55, 0.45≦y1≦0.55, 0<z1≦0.05, 0≦b1≦0.05, and x1+y1+z1=1; The B is Mg and Ti.

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