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

Abstract

To provide a positive electrode active material or a positive electrode including the same, having high energy density, high operation voltage, and high conductivity.SOLUTION: The present invention relates to a positive electrode active material, a manufacturing method for the same, a positive electrode including the same, and a lithium secondary battery including the positive electrode, 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] LiaFexMgyTizVbPO4-c. In Chemical Formula 1, 1<z / b<5, 0.8<a≤1.2, 0.850≤x≤0.997, 0.001≤y≤0.05, 0.001≤z≤0.05, 0≤b≤0.05, 0≤c≤0.05, x+y+z+b=1 are satisfied.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode containing the same, and a lithium secondary battery containing the same. More specifically, the present invention relates to a positive electrode active material containing an olivine-based lithium compound, a positive electrode containing the same, and a lithium secondary battery containing the same.

Background Art

[0002] Recently, with the rapid replenishment of electronic devices using batteries such as mobile phones, notebook computers, and electric vehicles, the demand for secondary batteries with high energy density and high capacity is rapidly increasing. Along with this, research and development for improving the performance of lithium secondary batteries are being actively promoted.

[0003] A lithium secondary battery is a battery including a positive electrode and a negative electrode containing an active material capable of insertion (intercalation) and desorption (deintercalation) of lithium ions, and an electrolyte, and produces electrical energy by oxidation and reduction reactions when lithium ions are inserted / desorbed from the positive electrode and the negative electrode.

Summary of the Invention

Problems 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, and a positive electrode containing the same.

[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, high low-temperature characteristics, and long life.

Means for Solving the Problems

[0006] The positive electrode active material according to an embodiment of the present invention contains a compound of Chemical Formula 1 below, includes first particles having a first average particle size, and in Chemical Formula 1 below, 1 < z / b < 5 can be satisfied. [C1] Li a Fe x Mg y Ti z V b PO 4-c

[0007] In the above formula 1, 0.8 <a≦1.2、0.850≦x≦0.997、0.001≦y≦0.05、0.001≦z≦0.05、0≦b≦0.05、0≦c≦0.05であり、x+y+z+b=1である。

[0008] A positive electrode for a lithium secondary battery according to another embodiment of the present invention may include a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, wherein the positive electrode active material layer may include a positive electrode active material according to an embodiment of the present invention, a conductive material, and a binder.

[0009] 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]

[0010] The positive electrode active material according to the present invention can improve electrical conductivity, mixture density (compressed density, pellet density), capacity, and energy density. The lithium secondary battery according to the present invention can have a relatively high operating voltage and charge / discharge efficiency, and can improve low-temperature characteristics and life characteristics. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a conceptual diagram showing a lithium secondary battery according to an embodiment of the present invention; [Figure 2] 1 is a schematic diagram showing a lithium secondary battery according to one embodiment, which can be said to have a cylindrical battery configuration. [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 a SEM image of a positive electrode active material according to an embodiment of the present invention. [Figure 10] 1 is a SEM image of a positive electrode active material according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] 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.

[0013] 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.

[0014] The embodiments described herein will be described with reference to cross-sectional views and / or plan views as ideal examples of the present invention. In the drawings, the thicknesses of films and regions are exaggerated to effectively explain the technical content. Therefore, the regions shown in the drawings have schematic attributes, and the shapes of the regions shown in the drawings indicate the specific forms of the regions of the element and are not intended to limit the scope of the invention. In various embodiments of the present specification, 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 their complementary embodiments.

[0015] Unless otherwise specified herein, the singular can also include the plural. Furthermore, unless otherwise specified, "A or B" can mean "including A, including B, or including A and B." As used herein, elements referred to as "comprises" and / or "comprising" do not exclude the presence or addition of one or more other elements.

[0016] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0017] Unless otherwise defined herein, particle size refers to the average particle size. Furthermore, particle size refers to the average particle size (D50), which refers to the diameter of particles with a cumulative volume of 50% in a particle size distribution. The average particle size (D50) can be measured by methods well known to those skilled in the art, such as using a particle size analyzer or a transmission electron microscope (TEM) or scanning electron microscope (SEM) image. Alternatively, the average particle size (D50) can be measured using a measuring device that utilizes dynamic light scattering, and data analysis can be performed to count the number of particles in each particle size range, after which the average particle size (D50) can be calculated. Alternatively, the average particle size (D50) can be measured using a laser diffraction method. More specifically, in measurements using the laser diffraction method, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT3000), and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W. The average particle size (D50) based on 50% of the particle size distribution in the measuring device can then be calculated.

[0018] 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.

[0019] The positive electrode 10 and the negative electrode 20 may be separated from each other by a separator 30. The separator 30 may be disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be in contact with the electrolyte solution ELL. The positive electrode 10, the negative electrode 20, and the separator 30 may be immersed in the electrolyte solution ELL.

[0020] 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.

[0021] positive electrode 10 The positive electrode 10 for a lithium secondary battery may include a current collector COL1 and a positive electrode active material layer AML1 formed on the current collector COL1. The positive electrode active material layer AML1 includes a positive electrode active material and may further include a binder and / or a conductive material. A detailed description of the positive electrode active material layer AML1 according to an embodiment of the present invention will be provided below with reference to FIGS. 6 and 7. The current collector COL1 may be made of, but is not limited to, aluminum.

[0022] negative electrode 20 The negative electrode 20 for a lithium secondary battery includes a current collector COL2 and a negative electrode active material layer AML2 located on the current collector COL2. The negative electrode active material layer AML2 includes a negative electrode active material and may further include a binder and / or a conductive material.

[0023] For example, the negative electrode active material layer AML2 may contain 90 to 99 wt % of the negative electrode active material, 0.5 to 5 wt % of the binder, and 0 to 5 wt % of the conductive material.

[0024] 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.

[0025] 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.

[0026] The water-based binder may be selected from styrene-styrene rubber, (meth)acrylate styrene-styrene rubber, (meth)acrylonitrile-styrene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0027] When an aqueous binder is used as the negative electrode binder, a cellulose-based compound that can impart viscosity may be further included. The cellulose-based compound may be one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be sodium, potassium, or lithium.

[0028] The dry binder may be a polymeric material that can be fiberized, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0029] The conductive material is used to impart conductivity to the electrode, and any material that is electronically conductive without causing a chemical change in the battery may be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0030] As the current collector COL2, those selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrates coated with conductive metals, and combinations thereof can be used.

[0031] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

[0032] Examples of the material capable of reversibly intercalating / deintercalating the lithium ions include carbon-based negative electrode active materials, which can include, for example, crystalline carbon, amorphous carbon, or combinations thereof. Examples of the crystalline carbon can include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon can include soft carbon or hard carbon, mesophase pitch carbide, fired coke, etc.

[0033] As the alloy of the 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.

[0034] As the material capable of doping and undoping lithium, an 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), an 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 combinations thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or combinations thereof.

[0035] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and the surfaces of the silicon particles coated with amorphous carbon. For example, the silicon-carbon composite may include secondary particles (cores) formed by the accumulation of primary silicon particles and a first amorphous carbon coating layer (shell) located on the surfaces of the secondary particles. The amorphous carbon may also be located between the primary silicon particles, e.g., the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0036] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core including crystalline carbon and silicon particles and a first coating layer of amorphous carbon located on the core surface.

[0037] The Si-based or Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material.

[0038] Separator 30 Depending on the type of lithium secondary battery, a separator 30 may be present between the positive electrode 10 and the negative electrode 20. As such a separator 30, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof can be used, and it goes without saying that mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator can also be used.

[0039] Separator 30 can include a porous substrate and a first coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0040] The porous substrate may be a polymer membrane formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyacetimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these polymers.

[0041] The organic material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0042] 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.

[0043] The organic material and the inorganic material may be mixed in one first coating layer, or may be stacked in a form in which a first coating layer containing an organic material and a first coating layer containing an inorganic material are stacked.

[0044] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0045] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0046] The non-aqueous organic solvent can be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0047] Examples of the carbonate solvent that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0048] 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.

[0049] Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0050] The non-aqueous organic solvents can be used alone or in combination of two or more.

[0051] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed together, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0052] The lithium salt dissolves in an organic solvent and acts as a lithium ion source in the battery, enabling basic lithium secondary battery operation and promoting the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0053] Lithium secondary battery Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 2 to 5 are schematic diagrams showing lithium secondary batteries according to embodiments, with FIG. 2 illustrating a cylindrical type, FIG. 3 illustrating a prismatic type, and FIGS. 4 and 5 illustrating pouch 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 case 50 in which the electrode assembly 40 is housed. The positive electrode 10, the negative electrode 20, and the separator 30 may be immersed in an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the case 50, as shown in FIG. 2. Also, as shown in FIG. 3, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 4 and 5, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting current generated in the electrode assembly 40 to the outside.

[0054] 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.

[0055] 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.

[0056] The positive electrode active material layer AML1 may further include an additive that can act as a sacrificial positive electrode.

[0057] The content of the positive electrode active material 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. The contents of the binder BND and the conductive material CDM may be 0.5 wt % to 5 wt % relative to 100 wt % of the positive electrode active material layer AML1.

[0058] The binder BND can bind the first particles PTC1 and the conductive material CDM to each other. For example, the binder BND can include at least one selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon, but is not limited thereto.

[0059] The conductive material CDM can be used to improve the conductivity of the positive electrode active material layer AML1. Any conductive material that does not cause a chemical change in the positive electrode active material layer AML1 can be used as the conductive material CDM without limitation. For example, the conductive material CDM can include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, and the like; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0060] The first particles PTC1 will be described in more detail below.

[0061] 1st particle PTC1 The first particles PTC1 may include an olivine-based lithium compound represented by the following Chemical Formula 1. [Chemical Formula 1] Li a Fe x Mg y Ti<( z V b PO 4-c

[0062] In the chemical formula 1, 0.8 < a ≤ 1.2, 0.850 ≤ x ≤ 0.997, 0.001 ≤ y ≤ 0.05, 0.001 ≤ z ≤ 0.05, 0 ≤ b ≤ 0.0�, 0 ≤ c ≤ 0.05, and x + y + z + b = 1 is possible. Mg, Ti, and V can be dopants doped into the first particle PTC1. For example, y can be from 0.002 to 0.003, z can be from 0.003 🡪 0.0045, and b can be from 0.001 to 0.005, or from 0.001 to 0.003.

[0063] In an embodiment of the present invention, when using a combination of Mg, Ti, and V as dopants of the first particle PTC1, compared with the case of using any one of Mg, Ti, and V (for example, using Ti alone) or using two of them (for example, using Ti and V), the structure of the positive electrode active material is strengthened, the size of the primary particles is controlled to be uniform, and the charge-discharge efficiency, low-temperature characteristics, and life characteristics of the lithium secondary battery can be further improved. The primary particles will be described in detail below.

[0064] The total doping amount of Mg, Ti, and V can be from 1500 ppm to 3600 ppm or from 3000 ppm to 3600 ppm. For example, the doping amount of Mg is 600 ppm, the doping amount of Ti is from 1000 ppm to 2000 ppm, and the doping amount of V can be from 500 ppm to 1000 ppm. The doping amount can be defined as the content of the doping element relative to the total weight of the metals (i.e., Fe, Mg, Ti, and V) excluding lithium in the olivine-type lithium compound represented by the chemical formula 1.

[0065] In Chemical Formula 1, z > b can be satisfied. That is, the number of moles of doped Ti may be more than the number of moles of doped V. For example, z / b > 1, 1 < z / b < 5, 2 ≤ z / b ≤ 4, or 2 ≤ z / b < 4 can be possible. As an example, b can be 0.002 or more. For example, b can be from 0.002 to 0.05.

[0066] In Chemical Formula 1, y > b can be satisfied. That is, the number of moles of doped Mg may be more than the number of moles of doped V. For example, y / b > 1, 1 < y / b < 3, 1 ≤ y / b ≤ 2.5, or 1 ≤ y / b < 2.5 can be satisfied. As an example, b may be at least 0.002. For example, b can be from 0.002 to 0.05.

[0067] In Chemical Formula 1, (y + z) > b can be satisfied. That is, the total number of moles of doped Mg and Ti may be more than the number of moles of doped V. For example, (y + z) / b > 1.5, 1.5 < (y + z) / b < 8, 2.6 ≤ (y + z) / b ≤ 6.5, or 2.6 ≤ (y + z) / b < 6.5 can be possible. As an example, b can be 0.002 or more. For example, b can be from 0.002 to 0.05.

[0068] In Chemical Formula 1, z / y > 0.5 can be satisfied. For example, in Chemical Formula 1, 1 < z / y < 5, 0.5 < z / y < 3.2, 0.5 < z / y < 2, 0.5 < z / y < 1, or 1 < z / y < 2 can be possible.

[0069] When the values of z / b, y / b, (y + z) / b, and z / y satisfy the ranges described above, the structure of the positive electrode active material is strengthened, and while controlling the size of the primary particles to be uniform, the charge-discharge efficiency, low-temperature characteristics, and life characteristics of the lithium secondary battery can be further improved.

[0070] In Chemical Formula 1, the total average oxidation number of Mg and Ti can satisfy the following Formula 1. [Formula 1] 2.5 < (y × 2 + z × 4) / (y + z) < 3.5

[0071] For example, the total average oxidation number of Mg and Ti may be 2.5<(y×2+z×4) / (y+z)<3, or 3<(y×2+z×4) / (y+z)<3.5. As an example, when the first particles PTC1 are single particles as described below, it may be 3<(y×2+z×4) / (y+z)<3.5. As an example, when the first particles are secondary particles as described below, it may be 2.5<(y×2+z×4) / (y+z)<3.5. When the value of Equation 1 satisfies the above range, the charge / discharge efficiency, low temperature characteristics, and life characteristics of the lithium secondary battery can be improved.

[0072] In one embodiment, 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 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.

[0073] 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 metal or non-metal elements. For example, the metal-containing compounds may further include lithium.

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

[0075] The cathode active material of the present invention may include the first particles PTC1, thereby improving the mixture density, capacity, and energy density. In one embodiment, the cathode active material of the present invention may have a mixture density of 2.0 g / cc to 2.5 g / cc, or 2.4 g / cc to 2.5 g / cc.

[0076] The first particles PTC1 can have a first average particle size, which can vary depending on the embodiment of FIG.

[0077] Referring again to FIG. 6, as an example, 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 single particle, a monolith structure, a single structure, or a non-aggregated particle, in which particles are morphologically present in an independent phase without cohesion. For example, a single particle may be a single crystal. Alternatively, a single particle may be a particle containing several crystals. A single particle may be in a singly isolated form. Alternatively, a single particle may be in a form in which 2 to 100 single particles are attached to each other. 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 100 nm to 500 nm, or 200 nm to 300 nm. For example, the minimum particle size may be the diameter measured by randomly selecting about 30 primary particles (hereinafter referred to as first primary particles) from an electron microscope photograph of the positive electrode active material. The average particle size of the first particles PTC1 will be described in detail below.

[0078] When the first particles PTC1 are single particles, 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 whose cumulative volume is 50% by volume (D50) in the particle size distribution.

[0079] 7, the first particles PTC1 may have a polycrystalline form and include secondary particles formed by agglomerating at least two or more primary particles. In other words, one first particle PTC1 may include a plurality of second particles PTC2 agglomerated with each other. Each of the second particles PTC2 may be a primary particle. The first particles PTC1 may have a spherical or elliptical shape.

[0080] 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.

[0081] 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 interior, or from a depth of 10 nm to a depth of about 2 μm.

[0082] The first particles PTC1 further include a grain boundary coating portion, which enhances structural stability and allows a uniform coating layer to be formed on the surface of the first particles PTC1. In addition, the first particles PTC1 further include a grain boundary coating portion, which further improves the electrical conductivity of the first particles PTC1.

[0083] When the first particles PTC1 are secondary particles, the average particle size of the first particles PTC1 may be 2 μm to 15 μm, 3 μm to 10 μm, or 3 μm to 7 μm. For example, the average particle size of the first particles PTC1 may be approximately 5 μm. 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 embodiment, the average particle size can be measured using a particle size analyzer. The average particle size may refer to the diameter of particles whose cumulative volume is 50% by volume (D50) in the particle size distribution.

[0084] 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. In one embodiment, the particle size may refer to the diameter measured by randomly selecting approximately 30 second particles PTC2 in 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.

[0085] When the average particle diameters of the first particles and the second particles are within 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 same can be improved.

[0086] The first particles PTC1 may have a spherical shape formed by agglomeration of nano-sized second particles PTC2. The first particles PTC1 may exhibit the following characteristics due to the close agglomeration of the second particles PTC2: The first particles PTC1 may have a spherical or elliptical shape. The average particle size (D50) of the first particles PTC1 may be 2 μm to 15 μm. The porosity of the first particles PTC1 may be about 20% to about 40%. The span value of the first particles PTC1 analyzed using a particle size analyzer may be 0.3 to 0.75.

[0087] A lithium secondary battery including the positive electrode active material of the present invention may have improved low-temperature characteristics. In one embodiment, the discharge capacity at -20°C relative to the initial discharge capacity (discharge capacity at -20°C / initial discharge capacity) may be 30% or more. For example, the discharge capacity at -20°C relative to the initial discharge capacity of the lithium secondary battery of the present invention (discharge capacity at -20°C / initial discharge capacity) may be 30% to 100%, 30% to 70%, or 50% to 65%.

[0088] A lithium secondary battery including the positive electrode active material of the present invention can have an improved operating voltage. In one embodiment, the operating voltage range of the lithium secondary battery of the present invention may be 3 V to 5 V. For example, the operating voltage range may be 3 V to 4.5 V, or 3.5 V to 4 V.

[0089] A lithium secondary battery including the positive electrode active material of the present invention can have improved life characteristics. In one embodiment, the lithium secondary battery of the present invention may have a capacity retention rate of 98% or more after 50 charge / discharge cycles at a constant current of 1.0 C at the above-mentioned voltage. For example, the capacity retention rate may be 98% to 100%, or 99.8% to 100%.

[0090] Positive electrode active material slurry The cathode active material slurry according to an embodiment of the present invention may include the cathode active material PTC1, the conductive material CDM, the binder BND, and a solvent. Hereinafter, for convenience of explanation, the same matters as those described with reference to FIGS. 6 and 7 will be omitted, and only the differences will be described in detail.

[0091] 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 is within the above range, the positive electrode active material layer AML1 can be smoothly attached to the current collector COL1.

[0092] For example, when the first particles PTC1 are secondary particles, the cathode active material slurry of the present invention can achieve a desired viscosity while containing a large amount of solids. For example, the cathode active material slurry can contain 60% to 70% solids. The solid content refers to the weight of the solid material remaining after the solvent has evaporated (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, converted into a percentage. The solid content can include the cathode active material, a binder, and a conductive material. When the solid content satisfies the above range, the first particles PTC1 can have excellent binding strength to the electrode current collector.

[0093] The first particles PTC1 can adhere to the current collector COL1 (see FIG. 1), and the binder BND can increase the binding force between the first particles PTC1 and the current collector COL1 (see FIG. 1).

[0094] 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 during full cell fabrication. 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 binding strength 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 2 wt% to 5 wt%, or 3 wt% to 5 wt%, based on 100 wt% of the cathode active material layer AML1.

[0095] 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. That is, since the first particles PTC1 have a large first 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) 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%, based on 100 wt% of the cathode active material layer AML1. That is, when the first particles PTC1 are secondary particles during full cell fabrication, a smaller amount of binder BND may be required than when the first particles PTC1 are monoparticles. This may reduce the resistance of a lithium secondary battery including the first particles PTC1, which are secondary particles.

[0096] Method for producing positive electrode active material 8 is a flowchart 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.

[0097] An iron phosphate precursor, a lithium source, a carbon source, and a dopant source may be mixed in a solvent (S100). For example, the solvent may be water, ethanol, or the like. The iron phosphate precursor may be a compound containing both iron (Fe) and phosphorus (P), or a mixture of an iron (Fe)-containing compound and a phosphorus (P)-containing compound. For example, the iron phosphate precursor may include FePO4·H2O or a mixture of FeSO4 and H3PO4. For example, the iron phosphate precursor may include FePO4 or a mixture of FeSO4 and H3PO4.

[0098] The lithium source may include at least one selected from the group consisting of lithium oxide, lithium hydroxide, lithium chloride, lithium nitrate, lithium nitrite, lithium formate, lithium acetate, lithium oxalate, lithium carbonate, lithium phosphate, lithium dihydrogen phosphate, lithium dihydrogen phosphate, and lithium citrate.

[0099] The carbon source may include at least one selected from the group consisting of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol, and dopamine.

[0100] The dopant source may include an oxide containing a dopant metal and / or a chloride containing a dopant metal. For example, the dopant source may include at least one selected from the group consisting of Mg oxide, Mg chloride, Ti oxide, Ti chloride, V oxide, and V chloride of Formula 1. For example, the dopant source may include at least one of Mg oxide or Mg chloride, at least one of Ti oxide or Ti chloride, and at least one of V oxide or V chloride.

[0101] The mixture may be subjected to wet milling (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.

[0102] In one embodiment of the present invention, the wet pulverization (S200) may be omitted. Specifically, in order to maximize the average particle size of the first particles PTC1 to be finally produced, the wet pulverization (S200) of the precursor particles may be omitted.

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

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

[0105] 7, forming a dried mixture may include spray drying the mixture. A commonly used spray drying device may be used for the spray drying. For example, at least one selected from an ultrasonic spray drying device, an air nozzle spray drying device, an ultrasonic nozzle spray drying device, a filter expansion droplet generator, and an electrostatic spray drying device may be used for the spray drying.

[0106] The particles refined to the size of primary particles through the wet milling process can aggregate with each other through the spray drying process to form secondary particles. Therefore, the primary particles PTC1 can be formed in the form of secondary particles of a desired size by adjusting the flow rate and velocity of the carrier gas, temperature, residence time in the reactor, and internal pressure during the spray drying process.

[0107] In one embodiment, the mixture to be spray-dried may have a total solid content of 20% to 40%. The solid content may refer to the weight of the solid material (i.e., the dried mixture) remaining after the solvent has evaporated relative to the total weight of the mixture (i.e., the spray liquid), expressed as a percentage. For example, the spray liquid may have a solid content of approximately 30 wt%.

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

[0109] The spray liquid according to this embodiment may have a viscosity of 1500 mPa·s to 2500 mPa·s at the above solids content. For example, the spray liquid may have a viscosity of about 2000 mPa·s.

[0110] 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.

[0111] In one example, spray drying can be performed at a temperature of 100°C to 300°C. For example, spray drying can be performed at a temperature of 200°C to 300°C, greater than 200°C to 300°C, or 230°C to 270°C. The propellant gas (e.g., air) used in spray drying can be introduced at a first temperature and discharged at a second temperature. For example, the first temperature can be 200°C to 250°C. The second temperature can be 80°C to 150°C.

[0112] The spray liquid may be supplied at a pressure of 0.3 MPa to 0.7 MPa. For example, the spray liquid may be supplied at a pressure of about 0.5 MPa.

[0113] When the input amount, input pressure, and temperature of the spray drying satisfy the above-described ranges, the first particles PTC1 can have a spherical morphology and a desired porosity.

[0114] The flow rate of the spray liquid for spray drying may be 30 ml / min to 80 ml / min. If the flow rate is less than 30 ml / min, problems such as nozzle clogging and reduced productivity may occur. If the flow rate is greater than 80 ml / min, the mixture may not be completely dried due to water condensation in the spray dryer. The input pressure of the spray liquid may be 0.3 MPa to 0.7 MPa. For example, the input pressure of the spray liquid may be about 0.5 MPa.

[0115] The dried mixture may be calcined under an inert atmosphere (S400). The inert atmosphere may be a nitrogen atmosphere and / or an argon atmosphere. The temperature of the calcination process may be 500°C to 1000°C, or 600°C to 800°C. The calcination process may be performed for 4 hours to 20 hours, or 6 hours to 12 hours. By calcining the dried mixture, first particles PTC1 containing the compound of Formula 1 may be formed.

[0116] 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.

[0117] When producing the first particles PTC1 of FIG. 6 according to one embodiment of the present invention, the sintered mixture can be pulverized at a rotation speed of 7000 rpm or more. For example, the sintered mixture can be pulverized at a rotation speed of 7000 rpm to 10000 rpm, or 7500 rpm to 9000 rpm. This allows the first particles PTC1 to have a single particle morphology as shown in FIG.

[0118] When preparing the first particles PTC1 of FIG. 7, another embodiment of the present invention, the fired mixture can be pulverized at a rotation speed of 0 rpm to 7000 rpm. For example, the fired mixture can be pulverized at a rotation speed of 4000 rpm to 7000 rpm, 4000 rpm to 6000 rpm, or 4500 rpm to 5000 rpm. Unlike the preparation of the positive electrode active material of FIG. 6, the pulverization step (S500) after firing can 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. When the rotation speed of the pulverization step (S500) satisfies the above-described range, the first particles PTC1 can maintain the shape of secondary particles. As a result, the first particles PTC1 can have the secondary particle shape shown in FIG. 7.

[0119] In the 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 surface of the primary particles. The primary particles are then closely aggregated through spray drying to form dense secondary spherical particles. As a result, the first particles PTC1 can include stable carbon coating layers 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 can improve the conductivity of the positive electrode active material layer AML1.

[0120] Carbon elemental analysis according to an embodiment of the present invention can be performed using an Elementar Micro Cube elemental analyzer. Specific operating methods and conditions are as follows: 1-2 mg of sample is weighed into a tin cup, placed on an automatic sampling tray, and introduced into a combustion tube 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 produce carbon dioxide. Carbon dioxide is detected using a TCD detector.

[0121] The carbon content can be 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).

[0122] The present invention will be described in more detail with reference to the following examples. However, these examples are for illustrative purposes only and the scope of the present invention is not limited to these examples.

[0123] Example 1: Preparation of single particle first particles Iron phosphate precursor Fe1PO4·H2O, lithium carbonate, magnesium dioxide, and titanium dioxide were mixed to a molar ratio of Fe:Li:Mg:Ti of 1:1.03:0.0025:0.004. 10 wt% glucose was further added to the mixture. The mixture was subjected to a wet grinding process using a ball mill. The mixture was evaporated to dryness from a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours. The dried mixture was calcined at 650°C for 10 hours under a nitrogen atmosphere. The calcined product was pulverized at a rotation speed of 8000 rpm to obtain primary particles in the form of single particles. The average size of the primary particles was approximately 300 nm to approximately 400 nm. The chemical formula of the primary particles was LiFe 0.9935 Mg 0.0025 Ti 0.004 It was PO4.

[0124] Example 2: Preparation of single particle first particles The iron phosphate precursor, Fe1PO4·H2O, lithium carbonate, magnesium dioxide, titanium dioxide, and vanadium dioxide were mixed in a molar ratio of Fe:Li:Mg:Ti:V of 1:1.03:0.0025:0.004:0.002, and the chemical formula of the first particles was LiFe 0.9915 Mg 0.0025 Ti 0.004 V 0.002 It was prepared in the same manner as in Example 1, except that it was PO4.

[0125] Example 3: Preparation of primary particles in the form of secondary particles Iron phosphate precursor Fe1PO4·H2O, lithium carbonate, magnesium dioxide, and titanium dioxide were mixed to a molar ratio of Fe:Li:Mg:Ti of 1:1.03:0.0025:0.002. 10 wt% glucose was further added to the mixture. The slurry mixture was spray-dried at a spray pressure of 0.5 MPa and a temperature of 230°C to evaporate and dry. The dried mixture was calcined at 750°C for 10 hours in a nitrogen atmosphere to obtain primary particles in the form of secondary particles. The average size of the secondary particles was approximately 100 nm to 200 nm. The chemical formula of the primary particles was LiFe 0.9955 Mg 0.0025 Ti 0.002It was PO4.

[0126] Example 4: Preparation of primary particles in the form of secondary particles The iron phosphate precursor, Fe1PO4·H2O, lithium carbonate, magnesium dioxide, and titanium dioxide were mixed in a molar ratio of Fe:Li:Mg:Ti of 1:1.03:0.0025:0.004, and the chemical formula of the first particles was LiFe 0.9935 Mg 0.0025 Ti 0.004 It was prepared in the same manner as in Example 3, except that it was PO4.

[0127] Example 5: Preparation of primary particles in the form of secondary particles The iron phosphate precursor, Fe1PO4·H2O, lithium carbonate, magnesium dioxide, titanium dioxide, and vanadium dioxide were mixed in a molar ratio of Fe:Li:Mg:Ti:V of 1:1.03:0.0025:0.004:0.001, and the chemical formula of the first particles was LiFe 0.9925 Mg 0.0025 Ti 0.004 V 0.001 It was prepared in the same manner as in Example 3, except that it was PO4.

[0128] Example 6: Preparation of primary particles in the form of secondary particles The iron phosphate precursor, Fe1PO4·H2O, lithium carbonate, magnesium dioxide, titanium dioxide, and vanadium dioxide were mixed in a molar ratio of Fe:Li:Mg:Ti:V of 1:1.03:0.0025:0.004:0.002, and the chemical formula of the first particles was LiFe 0.9915 Mg 0.0025 Ti 0.004 V 0.002 It was prepared in the same manner as in Example 3, except that it was PO4.

[0129] Comparative Example 1: Preparation of single particle first particles The first particles were prepared in the same manner as in Example 1, except that iron phosphate precursor FePO·H0 and lithium carbonate were mixed in a molar ratio of Fe:Li of 1:1.03, and the chemical formula of the first particles was LiFePO.

[0130] Comparative Example 2: Preparation of single particle first particles The iron phosphate precursor, Fe1PO4·H2O, lithium carbonate, and vanadium dioxide were mixed in a molar ratio of Fe:Li:V of 1:1.03:0.02, and the chemical formula of the first particles was LiFe 0.998 Mg 0.002 It was prepared in the same manner as in Example 1, except that it was PO4.

[0131] Comparative Example 3: Preparation of single particle first particles The iron phosphate precursor, Fe1PO4·H2O, lithium carbonate, and magnesium dioxide were mixed in a molar ratio of Fe:Li:Mg of 1:1.03:0.0025, and the chemical formula of the first particles was LiFe 0.9976 Mg 0.0025 It was prepared in the same manner as in Example 1, except that it was PO4.

[0132] Comparative Example 4: Preparation of single particle first particles The iron phosphate precursor, Fe1PO4·H2O, lithium carbonate, and titanium dioxide were mixed in a molar ratio of Fe:Li:Ti of 1:1.03:0.002, and the chemical formula of the first particles was LiFe 0.998 Ti 0.002 It was prepared in the same manner as in Example 1, except that it was PO4.

[0133] Comparative Example 5: Preparation of single particle first particles The iron phosphate precursor, Fe1PO4·H2O, lithium carbonate, and titanium dioxide were mixed in a molar ratio of Fe:Li:Ti of 1:1.03:0.004, and the chemical formula of the first particles was LiFe 0.996 Ti 0.004 It was prepared in the same manner as in Example 1, except that it was PO4.

[0134] Comparative Example 6: Preparation of single particle first particles The iron phosphate precursor, Fe1PO4·H2O, lithium carbonate, titanium dioxide, and vanadium dioxide were mixed in a molar ratio of Fe:Li:Ti:V of 1:1.03:0.004:0.002, and the chemical formula of the first particles was LiFe 0.996 Ti0.004 V 0.002 It was prepared in the same manner as in Example 1, except that it was PO4.

[0135] Comparative Example 7: Preparation of primary particles in the form of secondary particles The iron phosphate precursor, Fe1PO4·H2O, lithium carbonate, and titanium dioxide were mixed in a molar ratio of Fe:Li:Ti of 1:1.03:0.002, and the chemical formula of the first particles was LiFe 0.998 Ti 0.002 It was prepared in the same manner as in Example 3, except that it was PO4.

[0136] Comparative Example 8: Preparation of single particle first particles The iron phosphate precursor, Fe1PO4·H2O, lithium carbonate, magnesium dioxide, and titanium dioxide were mixed in a molar ratio of Fe:Li:Mg:Ti of 1:1.03:0.005:0.005, and the chemical formula of the first particles was LiFe 0.99 Mg 0.005 Ti 0.005 It was prepared in the same manner as in Example 1, except that it was PO4.

[0137] Comparative Example 9: Preparation of primary particles in the form of secondary particles The iron phosphate precursor, Fe1PO4·H2O, lithium carbonate, magnesium dioxide, and titanium dioxide were mixed in a molar ratio of Fe:Li:Mg:Ti of 1:1.03:0.005:0.005, and the chemical formula of the first particles was LiFe 0.99 Mg 0.005 Ti 0.005 It was prepared in the same manner as in Example 3, except that it was PO4.

[0138] Comparative Example 10: Preparation of single particle first particles The iron phosphate precursor, Fe1PO4·H2O, lithium carbonate, magnesium dioxide, titanium dioxide, and vanadium dioxide were mixed in a molar ratio of Fe:Li:Mg:Ti:V of 1:1.03:0.0025:0.005:0.001, and the chemical formula of the first particles was LiFe 0.9915 Mg 0.0025 Ti 0.005 V 0.001It was prepared in the same manner as in Example 1, except that it was PO4.

[0139] Comparative Example 11: Preparation of primary particles in the form of secondary particles The iron phosphate precursor, Fe1PO4·H2O, lithium carbonate, magnesium dioxide, titanium dioxide, and vanadium dioxide were mixed in a molar ratio of Fe:Li:Mg:Ti:V of 1:1.03:0.0015:0.005:0.001, and the chemical formula of the first particles was LiFe 0.9925 Mg 0.0015 Ti 0.005 V 0.001 It was prepared in the same manner as in Example 3, except that it was PO4.

[0140] Cathode manufacturing A positive electrode active material slurry was prepared by mixing 95 wt% of the final positive electrode active material, 3 wt% of polyvinylidene fluoride binder, and 2 wt% of carbon black conductive material in N-methylpyrrolidone solvent. The positive electrode active material slurry was applied to an aluminum current collector, dried, and then rolled to prepare a positive electrode.

[0141] Lithium secondary battery manufacturing A 2032-type coin-shaped half cell was fabricated using the prepared positive electrode and a lithium metal counter electrode. A separator (approximately 16 μm thick) made of porous polyethylene (PE) film was placed between the positive electrode and the lithium metal counter electrode, and an electrolyte solution was injected to fabricate a lithium secondary battery. The electrolyte used was a 1.3 M LiPF6 solution mixed with a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethylene carbonate (DMC) in a volume ratio of 3:4:3.

[0142] [Table 1]

[0143] Evaluation example 1: Analysis of the surface of the positive electrode active material FIG. 9 shows an SEM image of the primary particles prepared in Example 2. FIG. 10 shows an SEM image of the primary particles prepared in Example 6. Referring to FIG. 9, it can be seen that the primary particles according to Example 2 of the present invention are in the form of fine single particles. Referring to FIG. 10, it can be seen that the primary particles according to Example 6 of the present invention are in the form of spherical secondary particles formed by the aggregation of a plurality of primary particles. It can be seen that the secondary particles PTC2 according to Example 6 of the present invention are in the form of fine nano-sized single particles. Meanwhile, referring to FIGS. 9 and 10, the primary particles PTC2 according to Example 6 were smaller and more uniform than the primary particles according to Example 2.

[0144] Evaluation example 2: Active material evaluation The pellet density (PD) and carbon content of the positive electrode active materials of Examples 1 to 6 and Comparative Examples 1 to 11 were measured, and the results are shown in Table 2.

[0145] [Table 2]

[0146] Referring to Table 2, it was confirmed that the positive electrode active materials according to Examples 1 to 6 of the present invention had similar or higher pellet densities and carbon contents compared to the positive electrode active materials according to Comparative Examples 1 to 11. Specifically, it was confirmed that the positive electrode active materials according to Examples 1 and 2 of the present invention had similar or higher pellet densities and higher carbon contents compared to the positive electrode active materials according to Comparative Examples 1 to 6, 8, and 10. The positive electrode active material according to Example 2 had a higher pellet density and higher carbon content than the positive electrode active material according to Example 1. It was confirmed that the positive electrode active materials according to Examples 3 to 6 of the present invention had similar or higher pellet densities and higher carbon contents compared to the positive electrode active materials according to Comparative Examples 7, 9, and 11. The positive electrode active material according to Example 6 had a higher carbon content than the positive electrode active materials according to Examples 3 and 4. Meanwhile, it was confirmed that the positive electrode active materials according to Examples 5 and 6 had a higher carbon content compared to the positive electrode active material according to Example 2.

[0147] Evaluation example 3: Battery characteristic evaluation The characteristics of the lithium secondary batteries manufactured using the positive electrode active materials of Examples 1 to 6 and Comparative Examples 1 to 11 were evaluated.

[0148] The lithium secondary battery was initially charged under constant current (0.1C) and constant voltage (3.8V) conditions, and after a 10-minute rest, discharged to 3.0V under constant current (0.1C) conditions to conduct the initial charge-discharge. It was then charged and discharged 50 times at 1.0C / 1.0C at -25°C. An additional coin cell was also fabricated and its capacity measured at -20°C. The battery characteristic evaluation results are shown in Table 3 below.

[0149] [Table 3]

[0150] Referring to Table 3, it was confirmed that the secondary batteries according to Examples 1 to 6 of the present invention had excellent low-temperature capacity and lifespan characteristics. Specifically, it was confirmed that the secondary batteries according to Examples 1 and 2 of the present invention had similar or higher −20°C capacities and longer lifespans compared to the secondary batteries according to Comparative Examples 1 to 6, 8, and 10. The secondary battery according to Example 2 had a higher −20°C capacity than the secondary battery according to Example 1. It was confirmed that the secondary batteries according to Examples 3 to 6 of the present invention had similar or higher −20°C capacities and longer lifespans compared to the secondary batteries according to Comparative Examples 7, 9, and 11. The secondary batteries according to Examples 5 and 6 had higher −20°C capacities and longer lifespans than the secondary batteries according to Examples 3 and 4. In addition, the secondary batteries according to Examples 5 and 6 had higher −20°C capacities and longer lifespans than the secondary batteries according to Example 2.

[0151] Meanwhile, it was confirmed that the secondary batteries according to Examples 3 to 6 had higher charge amounts than the secondary batteries according to Examples 1 and 2, and therefore the resistance of the secondary batteries according to Examples 3 to 6 was smaller.

[0152] 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 spirit 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 a first particle having a first average particle size, the first particle comprising a compound of Formula 1: In the following chemical formula 1, 1<z / b<5 is satisfied. Cathode active material: [Chemical formula 1] Li a Fe x Mg y Today z V b PO 4-c In the formula 1, 0.8<a≦1.2, 0.850≦x≦0.997, 0.001≦y≦0.05, 0.001≦z≦0.05, 0≦b≦0.05, 0≦c≦0.05, and x+y+z+b=1.

2. In the above formula 1, 1<y / b; The positive electrode active material according to claim 1 .

3. In the formula 1, 0.5<z / y<5; The total average oxidation number of the Mg and the Ti satisfies the following formula 1: The positive electrode active material according to claim 1 . [Formula 1] 2.5<(y×2+z×4) / (y+z)<3.5

4. wherein y is 0.002 to 0.003; wherein z is 0.0035 to 0.0045; The b is 0.001 to 0.

003. The positive electrode active material according to claim 1 .

5. the first particles include a coating layer containing 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 .

6. the first particle is a single particle, The first average particle size is 500 nm to 2.5 μm. The positive electrode active material according to claim 1 .

7. the first particles include a plurality of second particles aggregated together; the first average particle size is 3 μm to 10 μm; The positive electrode active material according to claim 1 .

8. each of the plurality of second particles is a primary particle; The second particles have a particle size of 200 nm or less. The positive electrode active material according to claim 7 .

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

10. The porosity of the first particles is 20% to 40%. The positive electrode active material according to claim 7 .

11. 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 7 .

12. The positive electrode active material mixture has a density of 2.0 g / cc to 2.5 g / cc. The positive electrode active material according to claim 1 .

13. a positive electrode current collector, and a positive electrode active material layer on the positive electrode current collector, The positive electrode active material layer comprises the positive electrode active material according to claim 1, a conductive material, and a binder. Positive electrode for lithium secondary batteries.

14. The content of the binder is 0.5 to 5 parts by weight based on 100 parts by weight of the positive electrode active material layer. The positive electrode for a lithium secondary battery according to claim 13.

15. the binder includes at least one selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, an epoxy resin, a (methyl)acrylic resin, a polyester resin, and nylon; The positive electrode for a lithium secondary battery according to claim 13.

16. The content of the conductive material is 0.5 parts by weight to 5 parts by weight based on 100 parts by weight of the positive electrode active material layer. The positive electrode for a lithium secondary battery according to claim 13.

17. The conductive material comprises a carbon-based material, a metal-based material in the form of a metal powder or metal fiber, a conductive polymer, or a mixture thereof; The positive electrode for a lithium secondary battery according to claim 13.

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

19. The low-temperature discharge capacity at −20° C. (discharge capacity at −20° C. / initial discharge capacity) is 30% or more of the initial discharge capacity.

19. The lithium secondary battery according to claim 18.

20. The capacity retention rate after 50 charge / discharge cycles at a constant current of 1.0 C at a voltage of 3 V to 5 V is 98% or more.

19. The lithium secondary battery according to claim 18.

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