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

Abstract

To provide a lithium secondary battery having high energy density, high operating voltage, high charge / discharge efficiency, and excellent low-temperature characteristics.SOLUTION: The present invention relates to a positive electrode active material, a method for manufacturing the same, and a lithium secondary battery including the same. More specifically, the present invention relates to a positive electrode active material including first particles having an olivine structure and a crystal structure belonging to the Pbnm space group, and an XRD spectrum using Cu-Kα radiation has a first peak corresponding to a (200) plane of the first particles and a second peak corresponding to a (020) plane of the first particles, the full width at half maximum (FWHM) of the first peak being 0.14° to 0.25°, and the ratio of the intensity of the first peak to the intensity of the second peak being 0.55 to 0.75.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a method for producing 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 method for producing the same, and a lithium secondary battery including the same. [Background technology]

[0002] Recently, with the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, the demand for high-energy-density, high-capacity secondary batteries is rapidly increasing. As a result, 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, and high conductivity. + The object is to provide a positive electrode active material having a morphology that allows ions to diffuse quickly.

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

[0006] A cathode active material according to an embodiment of the present invention includes first particles having an olivine structure and a crystal structure belonging to the Pbnm space group. An XRD spectrum using Cu-Kα radiation may have a first peak corresponding to a (200) plane of the first particles and a second peak corresponding to a (020) plane of the first particles, the full width at half maximum (FWHM) of the first peak being 0.14° to 0.25°, and a ratio of the intensity of the first peak to the intensity of the second peak being 0.55 to 0.75.

[0007] A method for manufacturing a positive electrode active material according to another embodiment of the present invention includes: mixing an iron phosphate precursor, a lithium source, and a carbon source to form a first mixture; drying the first mixture; and calcining a second mixture obtained by mixing the dried first mixture with a dopant source. The dopant source may include at least one selected from the group consisting of a magnesium compound, a titanium compound, a vanadium compound, and an aluminum compound.

[0008] A lithium secondary battery according to another embodiment of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode may include the positive electrode active material according to an embodiment of the present invention. [Effects of the Invention]

[0009] The positive electrode active material according to the present invention can improve electrical conductivity, mixture density, capacity, and energy density. + The lithium secondary battery according to the present invention has a relatively high operating voltage and charge / discharge efficiency, and can have improved low-temperature characteristics. [Brief explanation 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] FIG. 2 is a perspective view illustrating a primary particle of a first particle according to an embodiment of the present invention. [Figure 9] 1 is a flowchart illustrating a method for manufacturing a positive electrode active material according to an embodiment 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 according to an example of the present invention. [Figure 12] 1 shows the results of XRD spectra for positive electrode active materials of examples of the present invention and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

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

[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] 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.

[0016] 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. 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.

[0017] 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 below with reference to FIGS. 6 to 8. The current collector COL1 may be made of aluminum, but is not limited to this.

[0018] negative electrode 20 The lithium secondary battery positive electrode 20 may include a current collector COL2 and a negative electrode active material layer AML2 formed on the current collector COL2. The negative electrode active material layer AML2 includes a negative electrode active material and may further include a binder and / or a conductive material.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] The water-based binder may be selected from styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyether resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0023] 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.

[0024] The dry binder is a fiberizable polymeric material, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, ethylene oxide, or combinations thereof.

[0025] The conductive material is used to impart conductivity to the electrode and may be any material that does not cause chemical changes in the constructed battery and is electronically conductive. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0026] 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.

[0027] 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.

[0028] 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 or artificial graphite. Examples of the amorphous carbon include soft or hard carbon, mesophase pitch carbide, and calcined coke.

[0029] 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.

[0030] As a substance that can be doped or undoped with lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (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 thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0031] 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) formed by combining primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon can also be located between the primary silicon particles. For example, the primary silicon particles can be coated with amorphous carbon. The secondary particles can be dispersed and present in an amorphous carbon matrix.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0038] The inorganic materials may include, but are not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0039] The organic material and the inorganic material may be mixed in one coating layer, or a coating layer containing an organic material and a coating layer containing an inorganic material may be stacked.

[0040] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0041] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0042] The non-aqueous organic solvent can be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, a non-quantum solvent, or a combination thereof.

[0043] Examples of carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl pyrrolyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0044] 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.

[0045] 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.

[0046] The non-aqueous organic solvents may be used alone or in combination of two or more.

[0047] 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.

[0048] 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 tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0049] 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 positive electrode assembly 40 to the outside.

[0050] 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.

[0051] 6 and 7 are enlarged views of the positive electrode active material layer of the lithium secondary battery according to the embodiment of the present invention.

[0052] 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 the first particles PTC1 may constitute a positive electrode active material according to an embodiment of the present invention.

[0053] The positive electrode active material layer AML1 may further contain an additive that can act as a sacrificial positive electrode.

[0054] The content of the positive electrode active material 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.

[0055] The binder BND may bind the first particles PTC1 and the conductive material CDM to each other. For 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.

[0056] 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.

[0057] The first particles PTC1 will be described in more detail below.

[0058] 1st particle PTC1 The first particles PTC1 may have an olivine structure and may include an olivine-based lithium compound represented by the following Chemical Formula 1:

[0059] [Chemical formula 1] Li a Fe x Mn 1-(x+y) M 1 y PO 4-c In Chemical Formula 1, 0.8 < a ≤ 1.2, 0 ≤ x ≤ 1, 0 ≤ y ≤ 0.05, and 0 ≤ c ≤ 0.05 may hold. M 1 may be at least one element selected from the group consisting of Mg, Ti, V, and Al. M 1 may be a dopant doped into the first particle PTC1. For example, M 1 may contain Ti. For example, 0.001 ≤ y ≤ 0.05 may hold. M 1 can be controlled so that the size of the primary particles is uniform.

[0060] As an example of the present invention, referring back to FIG. 6, the first particle PTC1 may have a single-particle state. In this specification, a single particle may mean an independent particle having no grain boundary inside. A single particle is a morphological phase and may mean a single particle, a monolith structure, a single body structure, or non-aggregated particles that exist as an independent phase in which particles are not aggregated with each other. As an example, a single particle may be a single crystal. Or, a single particle may be a particle containing several crystals. A single particle may be in a form separated alone. Or, a single particle may be in a form in which two to 100 single particles are attached to each other. That is, the first particle PTC1 may be provided in various sizes. For example, the average particle size of the first particle PTC1 may be about 1 μm. The minimum particle size of the first particle PTC1, that is, the particle size of the first primary particle, may be 50 nm to 2 μm, 100 nm to 500 nm, or 200 nm to 300 nm. As an example, the minimum particle size may mean the diameter measured by arbitrarily selecting more than 30 first primary particles from an electron micrograph of the positive electrode active material.

[0061] The average particle size of the first particles PTC1 may be 500 nm to 2.5 μm. For example, the average particle size of the first particles PTC1 may be approximately 1 μm. In one embodiment, 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.

[0062] 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.

[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 described above. 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] In another embodiment of the present invention, referring again to FIG. 7, the first particles PTC1 may be polycrystalline and include secondary particles formed by agglomeration of at least two or more second primary particles. In other words, one first particle PTC1 may include a plurality of second particles PTC2 agglomerated together. For example, the second particles PTC2 may be second primary particles. The first particles PTC1 may have a spherical or ellipsoidal shape.

[0066] As an 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.

[0067] 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.

[0068] 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.

[0069] 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 %.

[0070] The average particle size (D50) of the first particles PTC1 may be 500 nm to 12 μm, 2 μm to 12 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. In one example, the average particle size may be measured using a particle size analyzer. The average particle size may refer to the diameter (D50) of particles with a cumulative volume of 50% in the particle size distribution.

[0071] The particle size of the second particles PTC2 may be 50 nm to 2 μm. For example, the particle size of the second particles PTC2 may be 200 nm or less, 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.

[0072] When the average particle diameters of the first particles and the second particles satisfy the above ranges and the size of the second particles is uniform, the charge / discharge capacity and low-temperature capacity of a lithium secondary battery including the particles can be improved.

[0073] The first particles PTC1 may have a spherical shape formed by agglomeration of the second particles PTC2. The first particles PTC1 and the second particles PTC2 may be closely agglomerated to each other, resulting in the following properties: The porosity of the first particles PTC1 may be about 20% to 40%. The Span value of the first particles PTC1 analyzed using a particle size analyzer may be 0.3 to 0.75.

[0074] The specific surface area of ​​the positive electrode active material according to the present invention is 30 m 2 For example, the specific surface area of ​​the positive electrode active material can be 10 m 2 / g~30m 2 / g, or 15m 2 / g~25m 2 / g.

[0075] The first particles PTC1 may be crystalline. A crystal may be defined as a substance having a spatially repeated pattern of atomic arrangement. The symmetry of a crystal structure is indicated by a space group. The crystal structure of the first particles PTC1 may belong to an orthorhombic crystal system and the Pbnm space group. The first particles PTC1 may include a (200) plane.

[0076] The crystallinity of the primary particles (first primary particles or second primary particles) and the first particles PTC1 will be described in detail below.

[0077] Primary particle of first particle PTC1 FIG. 8 is a perspective view illustrating a primary particle (first primary particle or second primary particle) of the first particle PTC1 according to an embodiment of the present invention.

[0078] Referring to Figure 8, the first particle PTC1 may include a primary particle having a developed (200) plane. The (200) plane of the primary particle may have a first width W1 in a first direction D1 and a second width W2 in a second direction D2. The first direction D1 and the second direction D2 may intersect with each other. The first width W1 and the second width W2 may each be within 2 µm. The shape of the (200) plane may be, but is not limited to, a polygon, a circle, an ellipse, an irregular shape, or a rectangle.

[0079] The primary particles may have a third width W3 in a third direction D3 that penetrates the (200) plane. That is, the primary particles may have a third width W3 in the third direction D3, and the third direction D3 may penetrate the (200) plane. The third width W3 may be 50 nm to 2 μm.

[0080] For example, the primary particles of the first particles PTC1 may have a plate-like shape, i.e., the primary particles of the first particles PTC1 may have a plate-like shape with a developed (200) plane. In this case, the third width W3 may be smaller than the first width W1 and the second width W2.

[0081] The primary particle of the first particle PTC1 is Li +The primary particles of the first particles PTC1 may have an olivine structure. + Ion diffusion can only proceed in one dimension. + The diffusion of ions may proceed in a direction passing through the (200) plane of the primary particles of the first particles PTC1.

[0082] The primary particles of the first particles PTC1 of the present invention have the above-mentioned morphology and therefore have the following characteristics. + If the third width W3 of the primary particle satisfies the above-mentioned range, Li + The distance that ions diffuse in the (200) direction becomes shorter, and Li + Ions can be diffused more quickly.

[0083] The crystallinity of the first particles PTC1 can be confirmed by X-ray diffraction (XRD). The XRD spectrum using Cu-Kα radiation may include multiple peaks. For example, the XRD spectrum may include a first peak P1 and a second peak P2, which may correspond to the (200) and (020) planes of the first particles PTC1, respectively. The first peak P1 may appear at a diffraction angle (2θ) ranging from 15° to 19°. The second peak P2 may appear at a diffraction angle (2θ) ranging from 29.4° to 30°. For example, the first peak P1 and the second peak P2 may appear at diffraction angles (2θ) of 17° and 29.7°, respectively.

[0084] The ratio of the intensity of the first peak to the intensity of the second peak (I P1 / I P2 ) can be 0.55 or more. For example, the ratio of the intensity of the first peak to the intensity of the second peak (I P1 / I P2 ) can be 0.55 to 0.75, or 0.57 to 0.71. The ratio of the intensity of the first peak to the intensity of the second peak (I P1 / I P2) satisfies the above-mentioned numerical range, the primary particles of the first particles PTC1 may have a shape in which the (200) plane is developed. Therefore, a large area of ​​the (200) plane can be used to absorb a large amount of Li. + The ions can be diffused.

[0085] The full width at half maximum (FWHM) of the first peak P1 may be 0.14° or more. The larger the FWHM of the first peak P1, the smaller the third width W3. The FWHM of the first peak P1 may be 0.14° or more. For example, the FWHM of the first peak P1 may be 0.14° to 0.25°. If the FWHM of the first peak P1 satisfies the above-mentioned numerical range, the first particles PTC1 have crystallinity, and the primary particles of the first particles PTC1 may have a narrow third width W3. As a result, Li + The distance that ions diffuse in the (200) direction becomes shorter, and Li + Ions can be diffused more quickly.

[0086] The low-temperature characteristics of a lithium secondary battery including the cathode active material of the present invention may be improved. That is, by using the first particle PTC1 of the present invention, a lithium secondary battery with excellent performance even at low temperatures may be provided. In one embodiment, when discharging at 0.2 C, the discharge capacity at -20°C may be 80 mAh / g to 130 mAh / g. In one embodiment, when discharging at 0.2 C, the discharge capacity at -20°C relative to the discharge capacity at 25°C (discharge capacity at -20°C / discharge capacity at 25°C) may be 50% or more. For example, when discharging at 0.2 C, the discharge capacity at -20°C relative to the discharge capacity at 25°C (discharge capacity at -20°C / discharge capacity at 25°C) may be 50% to 95%, or 55% to 85%.

[0087] Positive electrode active material slurry The cathode active material slurry according to an embodiment of the present invention may include the above-described cathode active material PTC1, the conductive material CDM, the binder BND, and a solvent. For convenience of explanation, the following description will omit the same points as those described with reference to FIGS. 6 to 8, and will focus on the differences.

[0088] 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 may be smoothly attached to the current collector COL1.

[0089] In one embodiment, in the case of the first particles PTC1, which are secondary particles, the cathode active material slurry of the present invention may achieve a desired viscosity while containing a large amount of solids. For example, the cathode active material slurry may contain 60% to 70% solids. The solids 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 solids may include the cathode active material, a binder, and a conductive material. When the solids content satisfies the above range, the second particles PTC2 may have excellent adhesion to the electrode current collector.

[0090] The first particles PTC1 may be attached to the current collector COL1 (see FIG. 1), and the binder BND may increase the binding force between the first particles PTC1 and the current collector COL1 (see FIG. 1).

[0091] For example, in the case of single-particle first particles PTC1, the cathode active material slurry of the present invention may contain a large 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.

[0092] For example, in the case of the first particles PTC1, which are secondary 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 second particles PTC2 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 binding 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 0.5 wt% to 3 wt% or 0.5 wt% to 2 wt% relative to 100 wt% of the cathode active material layer AML1. That is, in the case of the first particles PTC1, which are secondary particles, a smaller amount of binder BND may be required when fabricating a full cell than the first particles PTC1, which are single particles. This may reduce the resistance of a lithium secondary battery including the first particles PTC1, which are secondary particles.

[0093] Method for producing positive electrode active material 9 is a flow chart 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 the embodiment of the present invention shown in FIGS. 6 and 7 will be described in more detail with reference to FIG.

[0094] An iron phosphate precursor (or manganese iron phosphate precursor), a lithium source, and a carbon source may be mixed in a solvent to form a first mixture S100. For example, the solvent may be water, ethanol, or the like.

[0095] The iron phosphate precursor can be a compound containing both iron (Fe) and phosphorus (P), or a mixture of iron (Fe) and phosphorus (P) containing compounds. For example, the iron phosphate precursor can include FePO4·H2O, or a mixture of FeSO4 and H3PO4. For example, the iron phosphate precursor can include FePO4 or a mixture of FeSO4 and H3PO4.

[0096] 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 between 0.2 and 0.8.

[0097] 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.

[0098] 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.

[0099] The first mixture may be wet-milled (S200). A typical temperature-controllable wet mill may be used for the 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 the wet-milling. Through the wet-milling process, particles in the mixture may be pulverized to a fine size.

[0100] 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.

[0101] The solvent may be removed from the first mixture to form a dried first mixture S300.

[0102] In producing the first particles PTC1 of FIG. 6 according to an embodiment of the present invention, forming the dried first mixture may include subjecting the mixture to a direct evaporation method, such as static drying or spray drying.

[0103] 7, forming the dried first 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.

[0104] 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.

[0105] As an example, the mixture to be spray-dried may have a total solid content of 20% to 40%. The total 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 total solid content of approximately 30 wt%.

[0106] If the total solids content is less than 20%, the average particle size of the second particles PCT2 will be small, which may result in reduced productivity, whereas if the total solids content is more than 40%, it will be difficult to control the average particle size of the second particles PCT1, which may result in a large deviation in the size of the second particles PCT2.

[0107] The spray solution according to this embodiment may have a viscosity of 1500 mPa·s to 2500 mPa·s at the total solids content described above. For example, the spray solution may have a viscosity of about 2000 mPa·s.

[0108] In one embodiment, the input rate of the spray drying may be 0.1 kg / min to 2 kg / min. For example, the input rate of the spray drying may be 0.5 kg / min to 1 kg / min. The input rate of the spray drying 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 drying according to the present invention may be approximately 0.5 kg / min.

[0109] In one embodiment, spray drying may be performed at a temperature of 100°C to 300°C. For example, spray drying may be performed 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.

[0110] The spray pressure may be 0.3 MPa to 0.7 MPa. For example, the spray pressure may be about 0.5 MPa.

[0111] If the input speed, input pressure, and temperature of the spray drying satisfy the above-mentioned ranges, the first particles PTC1 can have a spherical shape and a desired porosity.

[0112] If the input rate and temperature of the spray drying satisfy the above-mentioned ranges, the first particles PTC1 can have the desired size and shape. As a result, in the XRD spectrum, the full width at half maximum (FWHM) of the first peak P1 and the ratio of the intensity of the first peak to the intensity of the second peak (I P1 / I P2 ) each can satisfy the desired numerical range.

[0113] The flow rate of the spray liquid during 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 more than 80 ml / min, the mixture may not be completely dried due to condensation of water in the spray dryer.

[0114] The dried first mixture may be mixed with a dopant source to form a second mixture, which may be fired (S400).

[0115] 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, Ti chloride, V oxide, V chloride, Al oxide, and Al chloride. For example, the dopant source may include at least one of Ti oxide or Ti chloride.

[0116] The dosage of the dopant source may be 10,000 ppm or less. For example, the dosage of the dopant source may be 0 ppm to 10,000 ppm, 500 ppm to 10,000 ppm, or 1,000 ppm to 3,000 ppm. In one embodiment, the dosage of the dopant source may be omitted.

[0117] The calcination may be performed in an inert atmosphere. The inert atmosphere may be a nitrogen atmosphere and / or an argon atmosphere. The temperature of the calcination process may be 500°C to 1000°C, 600°C to 800°C, 650°C to 750°C, or 690°C to 750°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 containing the compound of Chemical Formula 1 described above may be formed.

[0118] If the amount of dopant source and the firing temperature are within the above-mentioned ranges, the first particles PTC1 can have the desired size and shape. As a result, in the XRD spectrum, the full width at half maximum (FWHM) of the first peak P1 and the ratio of the intensity of the first peak to the intensity of the second peak (IP1 / I P2 ) each can satisfy the desired numerical range.

[0119] 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.

[0120] 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.

[0121] 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 cathode active material of FIG. 6, the pulverization step S500 after sintering may be performed under relatively mild conditions. When preparing the cathode 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 second particles PTC2 may have the shape of secondary particles as shown in FIG. 7.

[0122] 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.

[0123] The method for manufacturing a cathode active material according to an embodiment of the present invention may include filtering and de-ironizing the dry-milled product, which may result in obtaining first particles PTC1 having a desired size.

[0124] Carbon element analysis according to an embodiment of the present invention can be performed using an Elementar Micro Cube elemental analyzer. Specific operating methods and conditions are as follows: 1-2 mg of sample is weighed into a tin cup, placed on an automatic sampling tray, and introduced into a combustion tube via a ball valve. The sample is then burned at a combustion temperature of 1000°C. The burned gas is then reduced using reduced copper to form carbon dioxide. Carbon dioxide is detected using a TCD detector.

[0125] In accordance with an embodiment of the present invention, the carbon content is measured by quantitative analysis of the particle surface using scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS). Other methods for measuring the carbon content include inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0126] 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.

[0127] Example 1: Preparation of secondary particle-like first particles PTC1 In the XRD spectrum using Cu-Kα radiation, the full width at half maximum (P1 FWHM) of the first peak was 0.1489°, and the ratio of the intensity of the first peak to the intensity of the second peak (I P1 / I P2A positive electrode active material having a ρ of 0.66 was prepared. The positive electrode active material contained first particles PTC1, which were primary particles. The positive electrode active material was manufactured as follows.

[0128] A first mixture was prepared by mixing an iron phosphate precursor (FePO4·H2O) and lithium carbonate in a molar ratio of 1:1.03 Fe:Li. 10 wt% glucose was then added to the first mixture. The first mixture, which was a slurry, was spray-dried at a rate of 0.5 kg / min, a spray pressure of 0.5 MPa, and a temperature of 230°C, followed by evaporation. Titanium dioxide was added to the dried first mixture to prepare a second mixture. The amount of titanium dioxide added was 3000 ppm. The second mixture was then calcined at 750°C for 10 hours in a nitrogen atmosphere to obtain secondary particles. The chemical formula of the first particles was LiFe. 0.994 Ti 0.006 It was PO4.

[0129] Example 2: Preparation of secondary particle-like first particles PTC1 The full width at half maximum (P1 FWHM) of the first peak is 0.1554°, and the ratio of the intensity of the first peak to the intensity of the second peak (I P1 / I P2 The cathode active material was prepared in the same manner as in Example 1, except that the calcination temperature was 730°C.

[0130] Example 3: Preparation of secondary particle-like first particles PTC1 The full width at half maximum (P1 FWHM) of the first peak is 0.1414°, and the ratio of the intensity of the first peak to the intensity of the second peak (I P1 / I P2 A positive electrode active material with a valence of 0.57 was prepared. In the manufacturing method of the positive electrode active material, Mn was used instead of the iron phosphate precursor. 0.6 Fe 0.4 The first particles were prepared in the same manner as in Example 1, except that a PO4 manganese iron phosphate precursor was used, the spray drying rate was 1.0 kg / min, the titanium dioxide amount was 1000 ppm, and the calcination temperature was 730°C. The chemical formula of the first particles was LiFe 0.4 Mn 0.598 Ti 0.002 It was PO4.

[0131] Example 4: Preparation of secondary particle-like first particles PTC1 The full width at half maximum (P1 FWHM) of the first peak is 0.1849°, and the ratio of the intensity of the first peak to the intensity of the second peak (I P1 / I P2 A positive electrode active material with a valence of 0.58 was prepared. In the manufacturing method of the positive electrode active material, Mn was used instead of the iron phosphate precursor. 0.6 Fe 0.4 The first particles were prepared in the same manner as in Example 1, except that a PO4 manganese iron phosphate precursor was used, the amount of titanium oxide added was 1000 ppm, and the firing temperature was 700°C. The chemical formula of the first particles was LiFe 0.4 Mn 0.598 Ti 0.002 It was PO4.

[0132] Example 5: Preparation of secondary particle-like first particles PTC1 The full width at half maximum (FWHM) of the first peak (P1) is 0.1657°, and the ratio of the intensity of the first peak to the intensity of the second peak (I P1 / I P2 A positive electrode active material with a valence of 0.59 was prepared. In the manufacturing method of the positive electrode active material, Mn was used instead of the iron phosphate precursor. 0.6 Fe 0.4 The first particles were prepared in the same manner as in Example 1, except that a PO4 manganese iron phosphate precursor was used, the amount of titanium oxide added was 1000 ppm, and the firing temperature was 710°C. The chemical formula of the first particles was LiFe 0.4 Mn 0.598 Ti 0.002 It was PO4.

[0133] Example 6: Preparation of secondary particle-like first particles PTC1 The full width at half maximum (P1 FWHM) of the first peak is 0.1677°, and the ratio of the intensity of the first peak to the intensity of the second peak (I P1 / I P2 ) was prepared. In the manufacturing method of the positive electrode active material, Mn was used instead of the iron phosphate precursor. 0.6 Fe 0.4The first particles were prepared in the same manner as in Example 1, except that a PO4 manganese iron phosphate precursor was used, the amount of titanium oxide added was 1500 ppm, and the firing temperature was 710°C. The chemical formula of the first particles was LiFe 0.4 Mn 0.597 Ti 0.003 It was PO4.

[0134] Example 7: Preparation of secondary particle-like first particles PTC1 The full width at half maximum (P1 FWHM) of the first peak is 0.2397°, and the ratio of the intensity of the first peak to the intensity of the second peak (I P1 / I P2 ) was prepared. In the manufacturing method of the positive electrode active material, Mn was used instead of the iron phosphate precursor. 0.6 Fe 0.4 The first particles were prepared in the same manner as in Example 1, except that a PO4 manganese iron phosphate precursor was used, the amount of titanium oxide added was 3000 ppm, and the firing temperature was 690°C. The chemical formula of the first particles was LiFe 0.4 Mn 0.594 Ti 0.006 It was PO4.

[0135] Example 8: Preparation of single particle first particle PTC1 The full width at half maximum (P1 FWHM) of the first peak is 0.1611°, and the ratio of the intensity of the first peak to the intensity of the second peak (I P1 / I P2 A positive electrode active material having a ρ of 0.65 was prepared. The positive electrode active material contained single particles, i.e., first particles PTC1. The positive electrode active material was manufactured by the following method.

[0136] The first mixture was prepared by mixing iron phosphate precursor FePO4·H2O and lithium carbonate in a molar ratio of 1:1.03 Fe:Li. 10 wt% glucose was added to the first mixture. The first mixture was subjected to a wet grinding process using a ball mill. The first mixture was evaporated to dryness in a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours. The process of adding titanium dioxide to the dried first mixture was omitted. The dried first mixture was calcined at 650°C for 10 hours in a nitrogen atmosphere. The calcined product was pulverized at a rotation speed of 800 rpm to obtain single-particle first particles. The chemical formula of the first particles was LiFePO4.

[0137] Comparative Example 1 The full width at half maximum (P1 FWHM) of the first peak is 0.1272°, and the ratio of the intensity of the first peak to the intensity of the second peak (I P1 / I P2 A positive electrode active material having a % saturation index (SSA) of 0.61 was prepared. The positive electrode active material was prepared in the same manner as in Example 1, except that the spray drying rate was 2.0 kg / min and the amount of titanium dioxide added was 0 ppm. The chemical formula of the first particles was LiFePO4.

[0138] Comparative Example 2 The full width at half maximum (P1 FWHM) of the first peak is 0.1312°, and the ratio of the intensity of the first peak to the intensity of the second peak (I P1 / I P2 A positive electrode active material having a % saturation index (SSA) of 0.64 was prepared. The positive electrode active material was prepared in the same manner as in Example 1, except that the spray drying rate was 2.0 kg, the amount of titanium dioxide added was 0 ppm, and the firing temperature was 730°C. The chemical formula of the first particles was LiFePO4.

[0139] Comparative Example 3 The full width at half maximum (P1 FWHM) of the first peak is 0.1238°, and the ratio of the intensity of the first peak to the intensity of the second peak (I P1 / I P2 A positive electrode active material with a valence of 0.68 was prepared. In the manufacturing method of the positive electrode active material, Mn was used instead of the iron phosphate precursor. 0.6Fe 0.4 The first particles were prepared in the same manner as in Example 1, except that a PO4 manganese iron phosphate precursor was used, the spray drying rate was 2.0 kg / min, and the calcination temperature was 770°C. The chemical formula of the first particles was LiFe 0.4 Mn 0.594 Ti 0.006 It was PO4.

[0140] Comparative Example 4 The full width at half maximum (P1 FWHM) of the first peak is 0.1347°, and the ratio of the intensity of the first peak to the intensity of the second peak (I P1 / I P2 A positive electrode active material having a % saturation index (SSA) of 0.66 was prepared. The positive electrode active material was prepared in the same manner as in Example 1, except that the spray drying rate was 1.0 kg / min, the amount of titanium dioxide added was 1000 ppm, and the firing temperature was 800°C. The chemical formula of the first particles was LiFe 0.998 Ti 0.002 It was PO4.

[0141] Comparative Example 5 The full width at half maximum (FWHM) of the first peak (P1) is 0.1288°, and the ratio of the intensity of the first peak to the intensity of the second peak (I P1 / I P2 ) was prepared. In the manufacturing method of the positive electrode active material, Mn was used instead of the iron phosphate precursor. 0.6 Fe 0.4 The first particles were prepared in the same manner as in Example 1, except that a PO4 manganese iron phosphate precursor was used, the spray drying rate was 2.0 kg / min, the amount of titanium dioxide added was 1000 ppm, and the calcination temperature was 730°C. The chemical formula of the first particles was LiFe 0.4 Mn 0.598 Ti 0.002 It was PO4.

[0142] Cathode manufacturing 95 wt% of the final positive electrode active material, 3 wt% of polyvinylidene fluoride binder, and 2 wt% 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.

[0143] 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 solution was injected to fabricate a lithium secondary battery. The electrolyte solution 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.

[0144] [Table 1]

[0145] Evaluation example 1: Analysis of the surface of the positive electrode active material An SEM image of the positive electrode active material prepared in Example 1 is shown in Figure 10. An SEM image of the positive electrode active material prepared in Example 8 is shown in Figure 11. The XRD spectrum results for the positive electrode active materials of the Examples and Comparative Examples are shown in Figure 12 and Table 2.

[0146] [Table 2]

[0147] Referring to Figure 10, it can be seen that the cathode active material according to Example 1 of the present invention is in the form of spherical secondary particles formed by agglomeration of a plurality of primary particles. Referring to Figure 11, it can be seen that the cathode active material according to Example 8 of the present invention is in the form of fine single particles. Referring to Figures 10 and 11, it can be seen that the particle size of the primary particles is 50 nm to 2 μm.

[0148] Referring to FIG. 12 and Table 2, the first peak P1 and the second peak P2 appeared at diffraction angles (2θ) of approximately 17° and 29.7°, respectively. Compared with the positive electrode active materials according to Comparative Examples 1 to 5, the positive electrode active materials according to Examples 1 to 8 had a larger FWHM of the first peak P1. The FWHM of the first peak P1 of the positive electrode active materials according to Examples 1 to 8 was 0.14° or more. P1 / I P2 was a minimum of 0.57.

[0149] Evaluation example 3: Evaluation of battery characteristics The characteristics of the lithium secondary batteries manufactured using the positive electrode active materials of Examples 1 to 8 and Comparative Examples 1 to 5 were evaluated.

[0150] The lithium secondary batteries were initially charged at a constant current (0.2C) and constant voltage (3.8V for LFP, 4.25V for LMFP), and after a 10-minute rest, discharged to 2.5V at a constant current (0.2C) to conduct the initial charge-discharge. Additionally, coin cells were fabricated and the discharge capacity was measured at -20°C. The battery characteristics evaluation results are shown in Table 3 below.

[0151] [Table 3]

[0152] Referring to Table 3, it was confirmed that the secondary batteries according to Examples 1 to 8 of the present invention had excellent low-temperature capacity. Specifically, the secondary batteries according to Examples 1 to 8 of the present invention had higher discharge capacities at -20°C than the secondary batteries according to Comparative Examples 1 to 5. Furthermore, unlike Comparative Examples 1 to 5, the secondary batteries according to Examples 1 to 8 had discharge capacities at -20°C of the discharge capacities at 25°C (discharge capacities at -20°C / discharge capacities at 25°C) of 50% or more when discharged at 0.2C. Thereby, the FWHM and I P1 / I P2 If each of these satisfies the above range, it can be confirmed that the low-temperature characteristics of the lithium secondary battery are significantly improved. 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 first particle has an olivine structure and a crystal structure belonging to the Pbnm space group; an XRD spectrum using Cu-Kα radiation has a first peak corresponding to a (200) plane of the first particles and a second peak corresponding to a (020) plane of the first particles; the full width at half maximum (FWHM) of the first peak is between 0.14° and 0.25°; the ratio of the intensity of the first peak to the intensity of the second peak is 0.55 to 0.75; Cathode active material.

2. The first peak is represented by a diffraction angle (2θ) in the range of 15° to 19°. The positive electrode active material according to claim 1 .

3. The second peak is represented by a diffraction angle (2θ) in the range of 29.4° to 30°. The positive electrode active material according to claim 1 .

4. The first particles include primary particles having a developed (200) plane. The positive electrode active material according to claim 1 .

5. The (200) plane is a first width in a first direction; a second width in a second direction intersecting the first direction, each of the first width and the second width is within 2 μm; The positive electrode active material according to claim 4 .

6. The primary particle has a third width in a third direction penetrating the (200) plane, the third width is between 50 nm and 2 μm; The positive electrode active material according to claim 4 .

7. The morphology of the primary particles includes a plate-like morphology. The positive electrode active material according to claim 4 .

8. Li + Ion diffusion proceeds in a direction passing through the (200) plane of the primary particle. The positive electrode active material according to claim 4 .

9. The first particles are represented by the following formula 1: [Chemical formula 1] Li a Fe x Mn 1-(x+y) M １ y PO 4-c (In Chemical Formula 1, 0.8<a≦1.2, 0≦x≦1, 0≦y≦0.05, and 0≦c≦0.05; and in Chemical Formula 1, M １ is at least one element selected from the group consisting of Mg, Ti, V, and Al) The positive electrode active material of claim 1 , comprising a compound of the formula:

10. the first particle is a single particle; The positive electrode active material according to claim 1 .

11. the first particles are primary particles, A plurality of primary particles are aggregated together to form secondary particles. The positive electrode active material according to claim 1 .

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

13. The specific surface area is 30m 2 / g or less, The positive electrode active material according to claim 1 .

14. combining an iron phosphate precursor, a lithium source, and a carbon source to form a first mixture; drying the first mixture; and firing the second mixture obtained by mixing the dried first mixture with a dopant source; the dopant source includes at least one selected from the group consisting of a magnesium compound, a titanium compound, a vanadium compound, and an aluminum compound; A method for producing a positive electrode active material.

15. the drying comprises spray drying; The input rate of the spray drying is 0.5 kg / min to 1 kg / min; The method for producing a positive electrode active material according to claim 14.

16. The drying temperature is 100°C to 300°C. The method for producing a positive electrode active material according to claim 14.

17. The amount of the dopant source added is 10,000 ppm or less; The method for producing a positive electrode active material according to claim 14.

18. The firing temperature is 500°C to 1000°C. The method for producing a positive electrode active material according to claim 14.

19. a positive electrode, a negative electrode, a separator, and an electrolyte solution; The positive electrode comprises the positive electrode active material according to claim 1. Lithium secondary battery.

20. When discharging at 0.2C, the discharge amount at -20°C is 50% or more compared to the discharge amount at 25°C (discharge amount at -20°C / discharge amount at 25°C).

20. The lithium secondary battery according to claim 19.

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