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

Abstract

To provide a positive electrode active material having high capacity, excellent capacity retention even after repeated charging and discharging, and the low resistance change amount, a positive electrode including the positive electrode active material, and a lithium secondary battery.SOLUTION: The present invention provides a positive electrode active material, a positive electrode including the same, and a lithium secondary battery. More specifically, the positive electrode active material includes lithium nickel composite oxide containing nickel (Ni), cobalt (Co), and aluminum (Al), a first region, and a second region that surrounds the first region and is defined to have a thickness of 1 μm in a direction from the outermost shell of the positive electrode active material to the center. The content ratio of nickel to aluminum (NNi / NAl) in the second region is 5 to 45.SELECTED DRAWING: Figure 6

Description

[Technical Field]

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

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

[0003] A lithium secondary battery is a battery that includes a cathode and an anode, each containing an active material capable of intercalating and deintercalating lithium ions, and an electrolyte. Electrical energy is produced by 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 that has a high capacity and exhibits an excellent capacity retention rate and a low resistance change even after repeated charge and discharge, a positive electrode containing the same, and a lithium secondary battery. [Means for solving the problem]

[0005] According to one embodiment of the present invention, a positive electrode active material includes a lithium-nickel-based composite oxide containing nickel (Ni), cobalt (Co), and aluminum (Al), and includes a first region and a second region surrounding the first region and having a thickness of 1 μm in a direction from the outermost shell toward the center of the positive electrode active material, and the nickel to aluminum content ratio (N Ni / N Al ) can be from 5 to 45.

[0006] A positive electrode according to an embodiment of the present invention includes a positive electrode current collector and a positive electrode active material, and the positive electrode active material may include the positive electrode active material described above.

[0007] A lithium secondary battery according to an embodiment of the present invention may include the above-described positive electrode active material. [Effects of the Invention]

[0008] The positive electrode active material according to one embodiment of the present invention, the positive electrode including the same, and the lithium secondary battery have high capacity, long life, and a low resistance change due to repeated charge and discharge. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a simplified conceptual diagram of a lithium secondary battery according to an embodiment of the present invention; [Figure 2] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 3] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 4] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 5] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 6] FIG. 2 is a cross-sectional view of a positive electrode according to an embodiment of the present invention. [Figure 7] 1 is a schematic diagram illustrating a positive electrode active material according to an embodiment of the present invention. [Figure 8] 8 is a schematic diagram for explaining a positive electrode active material according to an embodiment of the present invention, and is an enlarged view of region M in FIG. 7. FIG. [Figure 9] 1 is a schematic diagram illustrating a positive electrode active material according to an embodiment of the present invention. [Figure 10] 1 is a flowchart illustrating a method for manufacturing a positive electrode active material according to an embodiment of the present invention. [Figure 11] 3 is a flowchart illustrating step S100 of the method for producing a positive electrode active material according to the embodiment of the present invention. [Figure 12] 3 is a schematic diagram illustrating steps S300 and S500 of a method for producing a positive electrode active material according to an embodiment of the present invention. FIG. [Figure 13] FIG. 4 is a schematic diagram illustrating step S700 of the method for producing a positive electrode active material according to an embodiment of the present invention. [Figure 14] FIG. 4 is a schematic diagram illustrating step S900 of the method for producing a positive electrode active material according to an embodiment of the present invention. [Figure 15] FIG. 4 is a schematic diagram illustrating step S900 of the method for producing a positive electrode active material according to an embodiment of the present invention. [Figure 16] 1 shows a transmission electron microscope (TEM) image of a cross section of a positive electrode active material according to Example 1 and a result of mapping using energy dispersive X-ray spectroscopy (EDS). [Figure 17a] 1 shows a result of depth profiling of a cross section of the positive electrode active material according to Example 1 using a transmission electron microscope (TEM) image and energy dispersive X-ray spectroscopy (EDS). [Figure 17b] 1 shows a result of a depth analysis of a cross section of the positive electrode active material according to Example 1 using a transmission electron microscope (TEM) image and energy dispersive X-ray spectroscopy (EDS). [Figure 17c] 1 shows a result of a depth analysis of a cross section of the positive electrode active material according to Example 1 using a transmission electron microscope (TEM) image and energy dispersive X-ray spectroscopy (EDS). DETAILED DESCRIPTION OF THE INVENTION

[0010] 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 implemented in various forms and may undergo various modifications. The description of the present embodiments is provided solely to ensure complete disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0011] 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.

[0012] Unless otherwise stated herein, the singular can also include the plural. Additionally, unless otherwise stated, "A" or "B" can mean "including A, 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.

[0013] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0014] Unless otherwise defined herein, particle size refers to the average particle size. Furthermore, particle size refers to the average particle size (D50), which refers to the diameter of particles with a cumulative volume of 50% by volume in a particle size distribution. The average particle size (D50) can be measured using methods well known to those skilled in the art, such as a particle size analyzer or a transmission electron microscope (TEM) or scanning electron microscope (SEM) image. Alternatively, measurement can be performed using a measuring device that uses dynamic light scattering, and data analysis can be performed to count the number of particles in each particle size range, followed by calculation to obtain the average particle size (D50) value. Alternatively, measurement can be performed using a laser diffraction method. When measuring by the laser diffraction method, more specifically, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., MT 3000 manufactured by Microtrac), and ultrasonic waves of approximately 28 kHz are irradiated at an output of 60 W, after which the average particle size (D50) based on 50% of the particle size distribution in the measuring device can be calculated.

[0015] As used herein, the term "single particle" refers to a particle that exists independently without grain boundaries and consists of a single particle. It may refer to a single particle, a monolith structure, a single structure, or a non-aggregated particle in which particles are not aggregated with each other in the morphological phase. For example, a single particle may be a particle containing several crystals. The single particle may be in a singly separated form, or may be in a form in which less than 10 single particles are attached to each other.

[0016] 1 is a conceptual 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.

[0017] 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.

[0018] 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 migrate toward the positive electrode 10 or the negative electrode 20.

[0019] positive electrode 10 The lithium secondary battery positive electrode 10 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.

[0020] As an example, the positive electrode 10 may further include an additive that may act as a sacrificial positive electrode.

[0021] 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 and conductive material may be 0.5 wt % to 5 wt % respectively relative to 100 wt % of the positive electrode active material layer AML1.

[0022] The binder serves to firmly adhere the positive electrode active material particles to each other and to firmly adhere the positive electrode active material to the current collector COL1. Representative examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers 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, nylon, etc.

[0023] The conductive material is used to impart conductivity to the electrode and may be any material that is electronically conductive and does not cause a chemical change in the battery. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0024] The current collector COL1 may be made of Al, but is not limited to this.

[0025] positive electrode active material The positive electrode active material in the positive electrode active material layer AML1 may be a compound capable of reversibly inserting and extracting lithium (lithiated intercalation compound). Specifically, one or more of composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0026] The composite oxide may be a lithium transition metal composite oxide, and specific examples thereof include lithium nickel-based oxide, lithium cobalt-based oxide, lithium manganese-based oxide, lithium iron phosphate-based oxide, cobalt-free nickel-manganese-based oxide, or a combination thereof.

[0027] For example, a compound represented by any one of the following chemical formulas may be used: Li a A 1-b X b O 2-c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05);Li a Mn 2-b X b O 4-c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05);Li a Ni 1-b-c Co b X c O 2-α D α (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5, 0<α<2);Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5, 0<α<2);Li a Ni b Co c L 1 d G e O2(0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0≦e≦0.1);Li a NiG b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a CoG b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn 1-b G b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn2Gb O4(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn 1-g G g PO4(0.90≦a≦1.8, 0≦g≦0.5);Li (3-f) Fe2(PO4)3(0≦f≦2);Li a FePO4(0.90≦a≦1.8).

[0028] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; and L 1 is Mn, Al, or a combination thereof.

[0029] For example, the positive electrode active material may be a high-nickel positive electrode active material in which the nickel content is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more to 99 mol% or less relative to 100 mol% of metals excluding lithium in the lithium transition metal composite oxide. The high-nickel positive electrode active material can achieve high capacity and therefore can be applied to high-capacity, high-density lithium secondary batteries.

[0030] 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.

[0031] For example, the negative electrode active material layer AML2 may contain 90 wt % to 99.5 wt % of the negative electrode active material, 0.5 wt % to 5 wt % of the binder, and 0 wt % to 5 wt % of the conductive material.

[0032] 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.

[0033] 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.

[0034] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyether resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0035] 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.

[0036] The dry binder is a fiberizable polymeric material, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, ethylene oxide, or a combination thereof.

[0037] The conductive material is used to impart conductivity to the electrode and may be any material that is electronically conductive and does not cause a chemical change in the battery. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0038] 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.

[0039] 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.

[0040] 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 crystalline carbon include graphite, such as amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite. Examples of amorphous carbon include soft or hard carbon, mesophase pitch carbide, and calcined coke.

[0041] The lithium metal alloy may be an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0042] As the 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 (where Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination of these. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or a combination of these.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] The porous substrate may be a polymer membrane made of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these polymers.

[0049] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0050] 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.

[0051] The organic material and the inorganic material may be mixed in one coating layer, or may be stacked in a coating layer containing an organic material and a coating layer containing an inorganic material.

[0052] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0053] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0054] The non-aqueous organic solvent can be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0055] Examples of the carbonate solvent 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).

[0056] 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.

[0057] 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 (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.

[0058] The non-aqueous organic solvents may be used alone or in combination of two or more.

[0059] 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.

[0060] The lithium salt is dissolved in an organic solvent and acts as a lithium ion source in the battery, enabling basic lithium secondary battery operation and promoting the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1SO2) (x and y are positive numbers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0061] 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 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 immersed in 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.

[0062] 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.

[0063] The positive electrode 10 according to an embodiment of the present invention will be described in detail below.

[0064] positive electrode 10 6 is a cross-sectional view of a positive electrode according to an embodiment of the present invention. For convenience of explanation, the following description will omit the same points as those described with reference to FIGS. 1 to 5, and will focus on the differences.

[0065] The positive electrode 10 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 CAM described below, and may further include a binder and / or a conductive material.

[0066] The content of the positive electrode active material CAM, the binder, the conductive material, and the current collector COL1 are the same as those described above.

[0067] Cathode active material CAM 7 to 9 are schematic diagrams illustrating positive electrode active materials according to embodiments of the present invention, and Fig. 8 is an enlarged view of region M in Fig. 7.

[0068] Referring to FIG. 7, the positive electrode active material CAM may be polycrystalline and may include secondary particles formed by agglomeration of at least two or more primary particles PRP.

[0069] The positive electrode active material CAM can be spherical or ellipsoidal.

[0070] The average particle size (d) of the positive electrode active material CAM may be 5 μm to 25 μm. For example, the average particle size (d) of the positive electrode active material CAM may be 7 μm to 25 μm, 10 μm to 25 μm, or 10 μm to 20 μm. For example, the average particle size (d) of the positive electrode active material CAM may be determined by measuring the particle sizes of approximately 30 secondary particles of the positive electrode active material CAM from an electron microscope photograph of the positive electrode active material CAM, and then determining the diameter of the particles that make up 50% of the cumulative volume from the particle size distribution.

[0071] The positive electrode active material CAM may include a core COR and a coating layer (CTL).

[0072] The core COR is polycrystalline and may include secondary particles formed by agglomeration of at least two or more primary particles PRP.

[0073] The core COR may include a lithium nickel-based composite oxide. The lithium nickel-based composite oxide may include lithium (Li) and a transition metal. The transition metal may include nickel (Ni). The amount of nickel (Ni) contained in the lithium nickel-based composite oxide is not limited.

[0074] For example, the lithium-nickel-based composite oxide may be a lithium-nickel-based composite oxide containing a high content of nickel (Ni). For example, the lithium-nickel-based composite oxide may be a lithium-nickel-based composite oxide in which the nickel (Ni) content of the metals excluding lithium is 60 mol% or more, 80 mol% or more, 90 mol% or more, or 95% or more, and 100 mol% or less, 99.9 mol% or less, or 99 mol% or less. In other words, the lithium-nickel-based composite oxide may be a lithium-nickel-based composite oxide in which the number of moles of nickel (Ni) relative to the total number of moles of transition metals is 60 mol% or more, 80 mol% or more, 90 mol% or more, or 95% or more, and 100 mol% or less, 99.9 mol% or less, or 99 mol% or less. If the nickel (Ni) content satisfies the above range, the positive electrode active material CAM may achieve high capacity and high performance.

[0075] For example, the lithium nickel-based composite oxide may be represented by the following Chemical Formula 1: [Chemical formula 1] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1

[0076] In the formula 1, 0.9≦a1≦1.8, 0.6≦x1≦1, 0≦y1≦0.2, 0≦z1≦0.2, 0.9≦x1+y1+z1≦1.1, and 0≦b1≦0.1; M 1 and M 2Each is independently one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0077] For example, in the chemical formula 1, 0.85 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 0.15, and 0 ≦ z1 ≦ 0.15, or 0.9 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 0.1, and 0 ≦ z1 ≦ 0.1 may be satisfied.

[0078] For example, x1 + y1 + z1 = 1 may be satisfied.

[0079] As an example, the lithium nickel-based composite oxide may be represented by the following chemical formula 2. The compound represented by the chemical formula 2 may be a lithium nickel cobalt-based composite oxide. [Chemical formula 2] Li a2 Ni x2 Co y2 M 3 z 2O 2-b2 X b2

[0080] In the chemical formula 2, 0.9 ≦ a2 ≦ 1.8, 0.6 ≦ x2 < 1, 0 < y2 ≦ 0.2, 0 ≦ z2 ≦ 0.2, 0.9 ≦ x2 + y2 + z2 ≦ 1.1, and 0 ≦ b2 ≦ 0.1, and M 3 Each is independently one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0081] For example, in the chemical formula 2, 0.85 ≦ x2 ≦ 0.99, 0.01 ≦ y2 ≦ 0.15, and 0.01 ≦ z2 ≦ 0.15, or 0.9 ≦ x2 ≦ 0.99, 0.01 ≦ y2 ≦ 0.1, and 0.01 ≦ z2 ≦ 0.1 may be satisfied.

[0082] For example, x2 + y2 + z2 = 1 may be satisfied.

[0083] For example, the lithium nickel-based composite oxide may be represented by the following Chemical Formula 3: The compound represented by Chemical Formula 3 may be lithium nickel cobalt aluminum oxide or lithium cobalt manganese oxide. [Chemical formula 3] Li a3 Ni x3 Co y3 M 4 z3 M 5 w3 O 2-b3 X b3

[0084] In the formula 3, 0.9≦a3≦1.8, 0.6≦x3≦0.98, 0.01≦y3≦0.19, 0.01≦z3≦0.19, 0≦w3≦0.19, 0.9≦x3+y3+z3+w3≦1.1, and 0≦b3≦0.1; M 4 is one or more elements selected from the group consisting of Al and Mn, 5 are each independently one or more elements selected from the group consisting of Al, 5B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0085] For example, in Chemical Formula 3, 0.85≦x3≦0.98, 0.01≦y3≦0.14, 0.01≦z3≦0.14, and 0≦w3≦0.14, or 0.9≦x3≦0.98, 0.01≦y3≦0.09, 0.01≦z3≦0.09, and 0≦w3≦0.09.

[0086] For example, x3+y3+z3+w3=1.

[0087] The coating layer CTL may be located on the core COR. The coating layer CTL may be located on the entire surface or at least a portion of the surface of the core COR. The coating layer CTL may include cobalt (Co) and aluminum (Al). For example, the coating layer CTL may be identified by component analysis using EDS. The inclusion of the coating layer CTL may stabilize the structure of the positive electrode active material CAM even after repeated charge and discharge, suppress side reactions on the surface of the core COR, and improve the room-temperature and high-temperature life characteristics of the positive electrode active material CAM.

[0088] For example, the cobalt (Co) in the coating layer CTL may be present in the form of a cobalt-containing compound. For example, the cobalt-containing compound may be cobalt oxide, cobalt hydroxide, cobalt carbonate, a composite thereof, or a mixture thereof. For example, the cobalt-containing compound may further contain other metal or nonmetal elements in addition to cobalt. For example, the cobalt-containing compound may further contain lithium, manganese, and / or nickel. For example, the cobalt-containing compound may be lithium cobalt oxide.

[0089] For example, aluminum (Al) in the coating layer CTL may be present in the form of an aluminum-containing compound. For example, the aluminum-containing compound may be aluminum oxide, aluminum hydroxide, aluminum carbonate, a composite thereof, or a mixture thereof. For example, the aluminum-containing compound may further contain other metal or non-metal elements in addition to aluminum. For example, the aluminum-containing compound may further contain lithium, manganese, and / or nickel. For example, the aluminum-containing compound may be lithium aluminate.

[0090] The coating layer CTL and the core COR can be distinguished by performing depth analysis of the cathode active material CAM using transmission electron microscope (TEM) images and energy dispersive X-ray spectroscopy (EDS). In this specification, in the EDS results showing the cobalt signal (Co signal) obtained by scanning the cathode active material CAM from the outermost layer toward the center of the cross section of the cathode active material CAM, the point where the cobalt signal shows the sharpest decrease after the maximum peak can be defined as the boundary between the coating layer CTL and the core COR (see Figure 17c). For example, the magnitude of the signal can be proportional to the cobalt content. For example, the cobalt content can be expressed as atomic percent (atomic percentage).

[0091] The total content of cobalt and aluminum in the coating layer (CTL) may be greater than the total content of cobalt and aluminum in the core (COR). That is, the total content of cobalt and aluminum in the coating layer (CTL) may be greater than the total content of cobalt and aluminum in the lithium nickel-based composite oxide. For example, the total content may be in atomic %.

[0092] The cobalt content in the coating layer CTL may be higher than the cobalt content in the core COR. The aluminum content in the coating layer CTL may be higher than the aluminum content in the core COR. That is, the cobalt and aluminum contents in the coating layer CTL may be higher than the cobalt and aluminum contents in the lithium nickel-based composite oxide. For example, the contents may be in atomic percent.

[0093] For example, the lithium nickel-based composite oxide may contain cobalt, but the cobalt content in the lithium nickel-based composite oxide may be less than the cobalt content in the coating layer CTL. For example, the content may be in atomic percent. On the other hand, the lithium nickel-based composite oxide may be substantially free of aluminum, and therefore the aluminum content in the lithium nickel-based composite oxide may be less than the aluminum content in the coating layer CTL. For example, being substantially free may mean containing a content of 100 ppm or less.

[0094] As another example, the lithium nickel-based composite oxide may contain both cobalt and aluminum, but the respective contents of cobalt and aluminum in the lithium nickel-based composite oxide may be less than the respective contents of cobalt and aluminum in the coating layer CTL.

[0095] The molar ratio of aluminum to cobalt in the coating layer CTL (C Al / C Co ) can be 0.1 to 4. For example, the molar ratio of aluminum to cobalt in the coating layer CTL (C Al / C Co ) can be 0.1 to 3, 0.1 to 1, or 0.1 to 0.5. The cobalt content, aluminum content, and molar ratio (C Al / C Co ) satisfies the above-described range, the positive electrode active material CAM can have a long life even when repeatedly charged and discharged, and the amount of change in resistance can be reduced.

[0096] Referring to FIG. 8, the coating layer CTL may include a first coating layer CTL1 and a second coating layer CTL2.

[0097] The first coating layer CTL1 and the second coating layer CTL2 can be distinguished by performing depth analysis of the cathode active material CAM using a transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy (EDS). In this specification, in the EDS results showing the aluminum signal (Al signal) obtained by scanning the cathode active material CAM from the outermost layer toward the center of the cross section of the cathode active material CAM, the point where the aluminum signal shows the sharpest decrease after the maximum peak can be defined as the boundary between the first coating layer CTL1 and the second coating layer CTL2 (see FIG. 17b). For example, the magnitude of the signal can be proportional to the content. For example, the content can be expressed in atomic percent.

[0098] The aluminum content in the second coating layer CTL2 may be higher than the aluminum content in the first coating layer CTL1. The aluminum content in the first coating layer CTL1 may be substantially the same as the aluminum content in the core COR. "Substantially the same content" may be defined as the difference between the average aluminum signal of the first coating layer CTL1 and the average aluminum signal of the core COR within 10% in an EDS result showing an aluminum signal (Al signal) obtained by scanning the positive electrode active material CAM from the outermost layer toward the center. For example, the content may be in atomic percent.

[0099] The first coating layer CTL1 may have a first thickness TKC1. The second coating layer CTL2 may have a second thickness TKC2. The sum of the first and second thicknesses (TKC1 + TKC2) may be 25 nm to 60 nm. For example, the sum of the first and second thicknesses (TKC1 + TKC2) may be 29 nm to 55 nm, or 40 nm to 50 nm. If the sum of the first and second thicknesses (TKC1 + TKC2) satisfies the above range, the positive electrode active material CAM may have a long life and a reduced resistance change even after repeated charge and discharge.

[0100] The ratio of the second thickness to the first thickness (TKC2 / TKC1) may be between 1 and 5. For example, the ratio of the second thickness to the first thickness TK2 (TKC2 / TKC1) may be between 1.4 and 3.14, or between 2 and 3.

[0101] The ratio of the second thickness to the sum of the first and second thicknesses (TKC2 / (TKC1+TKC2)) may be 0.83 or less. For example, the ratio of the second thickness to the sum of the first and second thicknesses (TKC2 / (TKC1+TKC2)) may be 0.5 to 0.83, 0.6 to 0.80, or 0.65 to 0.8.

[0102] The ratio of the sum of the first and second thicknesses to the second thickness ((TKC1+TKC2) / TKC2) can be 1.2 or greater. For example, the ratio of the sum of the first and second thicknesses to the second thickness ((TKC1+TKC2) / TKC2) can be 1.2 to 2, 1.25 to 1.7, or 1.25 to 1.5.

[0103] If the ratio of the second thickness to the first thickness (TKC2 / TKC1), the ratio of the second thickness to the sum of the first and second thicknesses (TKC2 / (TKC1+TKC2)), and the ratio of the sum of the first and second thicknesses to the second thickness ((TKC1+TKC2) / TKC2) satisfy the above-described ranges, the positive electrode active material CAM can have a long life even after repeated charging and discharging, and the amount of change in resistance can be reduced.

[0104] The first thickness TKC1 may be the sum of the first and second thicknesses (TKC1 + TKC2) excluding the second thickness TKC2. The second thickness TKC2 may be 20 nm to 40 nm. For example, the second thickness TKC2 may be 25 nm to 40 nm, 30 nm to 40 nm, or 30 nm to 35 nm. If the first thickness TKC2 satisfies the above range, the positive electrode active material CAM may have a long life and a reduced resistance change even after repeated charge and discharge.

[0105] In addition to the coating layer CTL, the positive electrode active material CAM may further include a grain boundary coating layer on the surface of each primary particle (see PRP in FIG. 7). The grain boundary coating layer may be present inside the positive electrode active material CAM. The grain boundary coating layer may be formed by coating along the interfaces between primary particles (see PRP in FIG. 7) inside the positive electrode active material CAM. In other words, the grain boundary coating layer may refer to a coating on the grain boundaries inside the positive electrode active material CAM. The inside of the positive electrode active material CAM may refer to the entire inside of the positive electrode active material CAM excluding the surface of the positive electrode active material CAM. For example, it may refer to the region from a depth of about 10 nm from the outermost surface of the positive electrode active material CAM to the entire inside, or from a depth of 10 nm to a depth of about 2 μm.

[0106] The grain boundary coating layer may include cobalt (Co) and aluminum (Al). The cobalt (Co) and aluminum (Al) may be uniformly distributed within the grain boundary coating layer. That is, the cobalt (Co) and aluminum (Al) may be distributed in different locations within the grain boundary coating layer, or may not be concentrated in any one location. For example, mapping using energy dispersive X-ray spectroscopy (EDS) may reveal that the cobalt and aluminum within the grain boundary coating layer are located in substantially the same location.

[0107] The positive electrode active material CAM further includes a grain boundary coating layer, which enhances structural stability, induces a uniform and even coating on the surface, and appropriately controls the coating content on the surface, thereby improving the initial charge / discharge efficiency and life characteristics without increasing resistance.

[0108] Referring to FIG. 9, the positive electrode active material CAM may include a first region RG1 and a second region RG2.

[0109] The first region RG1 may be located at the center of the positive electrode active material CAM and may be defined as the region of the positive electrode active material CAM excluding the second region RG2.

[0110] The second region RG2 may be located at the outer periphery of the positive electrode active material CAM. The second region RG2 may surround the first region RG1. In this specification, the second region RG2 may be defined as a region extending from the outermost shell of the positive electrode active material CAM to a depth that can be analyzed using energy dispersive X-ray spectroscopy (EDS). The depth that can be analyzed using energy dispersive X-ray spectroscopy (EDS) may be several micrometers. For example, the depth that can be analyzed using energy dispersive X-ray spectroscopy (EDS) may be approximately 1 micrometer. As an example, the second region RG2 may be defined as a region having a thickness TKR of approximately 1 micrometer in a direction from the outermost shell toward the center of the positive electrode active material CAM.

[0111] The positive electrode active material CAM including the first region RG1 and the second region RG2 may include nickel (Ni), cobalt (Co), and aluminum (Al). As an example, the first region RG1 and the second region RG2 may both include nickel (Ni), cobalt (Co), and aluminum (Al). As another example, the first region RG1 may include nickel (Ni) and cobalt (Co), and the second region RG2 may include nickel (Ni), cobalt (Co), and aluminum (Al).

[0112] The contents of nickel (Ni), cobalt (Co), and aluminum (Al) in the first region RG1 and the second region RG2 can be obtained from the results of energy dispersive X-ray spectroscopy (EDS). The contents of nickel (Ni), cobalt (Co), and aluminum (Al) derived from energy dispersive X-ray spectroscopy (EDS) (N Ni , N Co , N Al ) can be expressed in atomic %. The content of nickel (Ni), cobalt (Co), and aluminum (Al) (N Ni , N Co , N Al ) may be a value calculated based on the total content (atomic %) of nickel (Ni), cobalt (Co), and aluminum (Al).

[0113] The nickel to aluminum content ratio (N Ni / NAl ) is the nickel to aluminum content ratio (N Ni / N Al ) may be larger.

[0114] As an example, the content ratio of nickel to aluminum in the first region RG1 (N Ni / N Al ) may be 45 or more. For example, the content ratio of nickel to aluminum in the first region RG1 (N Ni / N Al ) can be 46 or more, 48 or more, or 50 or more, and can be 100 or less, 99 or less, 98 or less, 95 or less, 90 or less, 85 or less, 80 or less, 75 or less, 70 or less, or 65 or less.

[0115] As an example, the content ratio of nickel to aluminum in the second region RG2 (N Ni / N Al ) can be 5 to 45. For example, the content ratio of nickel to aluminum in the second region RG2 (N Ni / N Al ) can be 8 to 45, 12 to 45, or 15 to 42.

[0116] The first region RG1 and the second region RG2 each have the same content ratio of nickel to aluminum (N Ni / N Al ), the positive electrode active material CAM can have a long life even after repeated charge and discharge, and the amount of change in resistance can be reduced.

[0117] The cobalt to aluminum content ratio (N Co / N Al ) can be 0.1 or more. For example, the content ratio of cobalt to aluminum in the second region RG2 (N Co / N Al ) may be 0.5 or more, 1 or more, or 2 or more, and may be 10 or less, 8 or less, or 6 or less. Co / N Al) satisfies the above-described range, the positive electrode active material CAM can have a long life even when repeatedly charged and discharged, and the amount of change in resistance can be reduced.

[0118] The positive electrode 10 and lithium secondary battery including the positive electrode active material CAM according to an embodiment of the present invention may have excellent life characteristics and may exhibit small resistance changes even after repeated charge and discharge. For example, the positive electrode 10 and lithium secondary battery including the positive electrode active material CAM according to an embodiment of the present invention may have a capacity retention rate of 95% or more after 50 charge and discharge cycles at 1C / 1C. Furthermore, the positive electrode 10 and lithium secondary battery including the positive electrode active material CAM according to an embodiment of the present invention may exhibit a resistance change of 60Ω or less or 35Ω or less after 50 charge and discharge cycles at 1C / 1C.

[0119] Manufacturing method of positive electrode active material CAM Fig. 10 is a flowchart illustrating a method for manufacturing a cathode active material CAM according to an embodiment of the present invention. Fig. 11 is a flowchart illustrating one embodiment of step S100 of the manufacturing method. Figs. 12 to 15 are schematic diagrams illustrating each step of the manufacturing method.

[0120] Referring to FIG. 10, a method for manufacturing a cathode active material (CAM) according to an embodiment of the present invention may include forming a lithium-nickel-based composite oxide (S100) and coating the lithium-nickel-based composite oxide.

[0121] Coating the lithium nickel-based composite oxide may include forming a first aqueous solution containing an aluminum compound and a basic compound (S300), mixing the lithium nickel-based composite oxide with the first aqueous solution to form a mixture (S500), adding a second aqueous solution containing a cobalt compound to the mixture (S700), and drying and heat treating (S900).

[0122] Referring to FIG. 11, forming a lithium nickel-based composite oxide (S1000) may include forming a nickel-based hydroxide (S120), mixing the nickel-based hydroxide with a lithium source material (S140), and heat treating (S160).

[0123] The nickel-based hydroxide may contain a transition metal. The transition metal includes nickel (Ni), and M of the above-mentioned formula 1 1 and M 2 As an example, the nickel-based hydroxide may include nickel (Ni) and cobalt (Co) as transition metals. For example, the nickel-based hydroxide may include nickel (Ni), cobalt (Co), and aluminum (Al) as transition metals. Alternatively, the nickel-based hydroxide may include nickel (Ni), cobalt (Co), and manganese (Mn) as transition metals.

[0124] The nickel-based hydroxide can be obtained by a coprecipitation method (S120). For example, the coprecipitation method can include dissolving a transition metal source material in a solvent such as distilled water, and then sequentially adding the transition metal salt solution together with a chelating agent and / or a basic aqueous solution to a reactor to cause precipitation. The precipitate is collected in a slurry form, and the slurry solution is then filtered and dried to obtain the nickel-based hydroxide, which is a metal composite oxide.

[0125] The transition metal source material may include a salt of the transition metal described above. The transition metal salt may be a sulfate, nitrate, acetate, halide, hydroxide, or the like, but is not particularly limited as long as it can be dissolved in a solvent. For example, the transition metal source material may include a nickel salt, a cobalt salt, and an aluminum salt. For another example, the transition metal source material may include a nickel salt, a cobalt salt, and a manganese salt. The transition metal source materials may be mixed in an adjusted molar ratio so that the positive electrode active material has high capacity characteristics.

[0126] The nickel-based hydroxide may be mixed with a lithium source material at a certain ratio (S140). For example, the nickel-based hydroxide and the lithium source material may be mixed at a molar ratio of approximately 1:1. The lithium source material is not particularly limited as long as it is a material commonly used in manufacturing positive electrode active materials. For example, the lithium source material may include lithium salts such as lithium carbonate, lithium nitrate, lithium hydroxide, or lithium sulfate.

[0127] The mixture of nickel-based hydroxide and lithium raw material may be placed in a furnace (FRC) and heat-treated (S160). The heat-treatment temperature may be 700°C to 1,000°C. For example, the heat-treatment temperature may be 700°C to 800°C. The heat-treatment may be performed in an oxidizing atmosphere such as air or oxygen. The heat-treatment time may be 10 hours to 30 hours. For example, the heat-treatment time may be 10 hours to 20 hours. For example, pre-baking at 150°C to 800°C may be additionally performed before the heat-treatment.

[0128] For example, a pulverization step may be additionally carried out after the heat treatment, which allows a lithium nickel composite oxide having a desired average particle size to be obtained.

[0129] The obtained lithium nickel-based composite oxide may have substantially the same components and composition as the core COR described with reference to FIG. 7. Substantially the same composition may mean that the difference in composition is within 10%. In other words, the lithium nickel-based composite oxide may be a compound represented by Chemical Formula 1. For example, the lithium nickel-based composite oxide may be a compound represented by Chemical Formula 2 or Chemical Formula 3.

[0130] Referring to FIGS. 12 to 15, the lithium nickel-based composite oxide NBO can be coated.

[0131] Referring to FIG. 12, a first aqueous solution AQ1 including an aluminum compound and a basic compound may be formed S300.

[0132] The aluminum compound may be an aluminum coating raw material. For example, the aluminum compound may include at least one selected from the group consisting of aluminum sulfate (Al2(SO4)3) and sodium aluminate (NaAlO2). However, the aluminum compound is not limited to the examples described above.

[0133] The aluminum compound may be added so that the moles of aluminum relative to the total moles of elements excluding lithium and oxygen in the lithium nickel-based composite oxide are 0.05 mol% to 2 mol%. For example, the aluminum compound may be added so that the moles of aluminum relative to the total moles of elements excluding lithium and oxygen in the lithium nickel-based composite oxide are 0.05 mol% to 1.5 mol%, 0.05 mol% to 1 mol%, 0.1 mol% to 1 mol%, 0.2 mol% to 0.8 mol%, or 0.5 mol% to 0.8 mol%. If the amount of aluminum compound added satisfies the above range, the final cathode active material may have a long life and a reduced resistance change.

[0134] For example, the basic compound may include at least one selected from the group consisting of sodium hydroxide (NaOH), lithium hydroxide (LiOH), potassium hydroxide (KOH), and ammonia (NH). However, the basic compound may be any compound that can be used for precipitation, and is not particularly limited to the examples described above.

[0135] For example, the first aqueous solution AQ1 may contain anionic aluminum. By generating the anionic aluminum first, the final positive electrode active material may have a longer life and a reduced resistance change.

[0136] The first aqueous solution AQ1 and the lithium nickel-based composite oxide NBO may be mixed to form a mixture MXR1 (S500). The mixing may be performed using a stirrer.

[0137] The mixing can be carried out for 3 to 30 minutes, but is not limited to the times described above, as long as it is long enough to form a homogeneous mixture MXR1.

[0138] 13, a second aqueous solution AQ2 may be added to the mixture MXR1 (S700). The second aqueous solution AQ2 may include a cobalt compound.

[0139] The cobalt compound may be a cobalt coating raw material, such as at least one selected from the group consisting of cobalt nitrate, cobalt sulfate, cobalt oxide, cobalt hydroxide, and cobalt carbonate, but is not limited to the examples described above.

[0140] The cobalt compound may be added so that the moles of cobalt relative to the total moles of elements excluding lithium and oxygen in the lithium-nickel-based composite oxide are 0.25 mol% to 4 mol%. For example, the cobalt compound may be added so that the moles of cobalt relative to the total moles of elements excluding lithium and oxygen in the lithium-nickel-based composite oxide are 0.5 mol% to 4 mol%, 1 mol% to 4 mol%, 1 mol% to 3 mol%, or 1.2 mol% to 3 mol%. If the amount of cobalt compound added satisfies the above range, the final positive electrode active material may have a long life and a reduced resistance change.

[0141] The molar ratio of the amount of aluminum in the added aluminum compound to the amount of cobalt in the added cobalt compound may be 0.1 to 4. For example, the molar ratio of the amount of aluminum in the added aluminum compound to the amount of cobalt in the added cobalt compound may be 0.1 to 3, 0.1 to 1, 0.1 to 0.7, or 0.1 to 0.5. When the molar ratio of the amount of aluminum in the added aluminum compound to the amount of cobalt in the added cobalt compound satisfies the above-mentioned range, the finally produced positive electrode active material may have a long life and a reduced amount of resistance change.

[0142] For example, the second aqueous solution AQ2 may be added dropwise to the mixture MXR1, i.e., the cobalt coating source material in the second aqueous solution AQ2 may be gradually supplied to the mixture MXR1.

[0143] The addition of the second aqueous solution AQ2 can be carried out for 5 minutes to 1 hour, for example, for 10 minutes to 50 minutes, or for 20 minutes to 40 minutes.

[0144] If necessary, a precipitant, a pH adjuster, etc. may be further added to the mixture MXR1.

[0145] In this step, the deposition of aluminum and cobalt can be carried out simultaneously. Aluminum and cobalt can exist in the form of an aluminum-containing compound and a cobalt-containing compound, respectively. For example, the aluminum-containing compound can include aluminum hydroxide, and the cobalt-containing compound can include cobalt hydroxide. However, these examples are not limited to these. Aluminum and cobalt can be deposited on the surface of the lithium nickel-based composite oxide NBO. Thus, the mixture MXR2 can contain a lithium nickel-based composite oxide NBO having aluminum and cobalt deposited on its surface.

[0146] The lithium nickel-based composite oxide NBO according to the present invention may be coated by wet coating. By performing the wet coating through the above steps, cobalt and aluminum can be simultaneously and uniformly coated not only on the surface of the lithium nickel-based composite oxide NBO but also on the grain boundaries, which are the surfaces of the primary particles.

[0147] The coating of the lithium nickel-based composite oxide NBO according to an embodiment of the present invention can be performed by first adding an aluminum compound and then adding a cobalt compound, thereby forming a coating layer (CTL in FIG. 7) having the above-described structure, and the final cathode active material can have a long life and reduced resistance change.

[0148] 14 and 15, the mixture MXR2 may be dried and heat-treated to form the above-described positive electrode active material (CAM in FIG. 7) (S920 and S940).

[0149] The mixture MXR2 is filtered to remove the solvent, and then dried to obtain the dried product DPR (S920). The drying temperature can be 100°C to 300°C. The drying time can be 5 hours to 15 hours. The residual solvent can be removed by drying.

[0150] The dried product DPR may be placed in a furnace FRC for heat treatment (S940). The heat treatment temperature may be 650°C to 1000°C. For example, the heat treatment temperature may be 650°C to 900°C or 650°C to 800°C. The heat treatment time may be 5 hours to 30 hours. For example, the heat treatment time may be 10 hours to 24 hours or 10 hours to 20 hours. If the heat treatment conditions satisfy the above ranges, the final positive electrode active material may have a long life and a reduced resistance change.

[0151] Although not shown, a lithium source may be added before the heat treatment and then heat-treated. For example, the lithium source may include a lithium salt such as lithium carbonate, lithium nitrate, lithium hydroxide, or lithium sulfate. For example, the lithium source may be added so that the number of moles of lithium relative to the total number of moles of elements excluding lithium and oxygen in the lithium-nickel-based composite oxide is 0.1 mol% to 10 mol%. For example, the lithium source may be added so that the number of moles of lithium relative to the total number of moles of elements excluding lithium and oxygen in the lithium-nickel-based composite oxide is 0.1 mol% to 8 mol%, or 1 mol% to 6 mol%. Adding the lithium source in the above amounts can restore the surface of the lithium-nickel-based composite oxide damaged during the coating process. As a result, the final cathode active material may have a long life and a reduced resistance change.

[0152] 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.

[0153] Example 1 Production Example 1: Formation of lithium nickel composite oxide As raw materials for nickel hydroxide, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and aluminum sulfate (Al2(SO4)3) were dissolved in distilled water as a solvent to give a molar ratio of Ni:Co:Al of 96.5:2:1.5 to prepare a metal raw material mixture. To form a complex compound, a diluted solution of ammonia water (NH4OH) and lithium hydroxide (NaOH) were prepared as a precipitate. The metal raw material mixture, ammonia water, and sodium hydroxide were added to a reactor. The sodium hydroxide was added to maintain the pH of the mixture in the reactor. The reaction was carried out for approximately 20 hours while stirring the mixture in the reactor. The product was filtered, washed, and dried to obtain nickel hydroxide (Ni 0.965 Co 0.020 Al 0.015 (OH)2).

[0154] Nickel hydroxide and anhydrous lithium hydroxide (LiOH) were mixed in a molar ratio of 1:1.03 so that the molar ratio of lithium to the total metal amount in the nickel hydroxide was 1.03. The mixture was heat-treated in an oxygen atmosphere at a temperature of about 750°C for 15 hours to obtain a lithium-nickel composite oxide (LiNi 0.965 Co 0.020 Al 0.015 O2) was formed. The lithium nickel composite oxide was a secondary particle formed by aggregation of primary particles, and the average particle size was approximately 12 μm.

[0155] Manufacturing Example 2: Lithium nickel composite oxide coating A first aqueous solution containing aluminum sulfate (Al2(SO4)3·16H2O) and sodium hydroxide (NaOH) was prepared. Lithium-nickel composite oxide was added to the first aqueous solution. The aluminum sulfate was added so that the number of moles of aluminum relative to the total number of moles of elements excluding lithium and oxygen in the lithium-nickel composite oxide was 0.5 mol%. The mixture of the first aqueous solution and the lithium-nickel composite oxide was stirred for 5 minutes. A second aqueous solution containing cobalt sulfate (CoSO4·7H2O) was added dropwise to the mixture over 30 minutes. The cobalt sulfate was added so that the number of moles of cobalt relative to the total number of moles of elements excluding lithium and oxygen in the lithium-nickel composite oxide was 2 mol%. The ratio of the number of moles of aluminum in the aluminum sulfate added to the number of moles of cobalt in the cobalt sulfate added was 0.25. The mixture was filtered and dried at 190°C for 10 hours to obtain a dried product. 6 mol% of lithium hydroxide (LiOH) was mixed with the dried product. The mixture was heat-treated at 650° C. for 15 hours to obtain a positive electrode active material.

[0156] Example 2 The production was carried out in the same manner as in Example 1, except that cobalt sulfate and aluminum sulfate were added so that the ratio of the number of moles of aluminum in the added aluminum sulfate to the number of moles of cobalt in the added cobalt sulfate was 3.

[0157] Example 3 The production was carried out in the same manner as in Example 1, except that cobalt sulfate and aluminum sulfate were added so that the ratio of the number of moles of aluminum in the added aluminum sulfate to the number of moles of cobalt in the added cobalt sulfate was 1.

[0158] Example 4 The production was carried out in the same manner as in Example 1, except that cobalt sulfate and aluminum sulfate were added so that the ratio of the number of moles of aluminum in the added aluminum sulfate to the number of moles of cobalt in the added cobalt sulfate was 0.5.

[0159] Example 5 The production was carried out in the same manner as in Example 1, except that cobalt sulfate and aluminum sulfate were added so that the ratio of the number of moles of aluminum in the added aluminum sulfate to the number of moles of cobalt in the added cobalt sulfate was 0.17.

[0160] Comparative Example 1 A positive electrode active material coated only with cobalt was prepared.

[0161] The lithium-nickel composite oxide of Production Example 1 was added to an aqueous solution containing 6 wt% cobalt sulfate (CoSO4·7H2O) and stirred. Sodium hydroxide (NaOH) was added dropwise to the mixed solution. As a result, the ratio of the number of moles of aluminum in the added aluminum sulfate to the number of moles of cobalt in the added cobalt sulfate was 0. Next, filtration, drying, and heat treatment were performed in the same manner as in Example 1.

[0162] Cathode manufacturing 96 wt% of the positive electrode active material, 2 wt% of polyvinylidene fluoride binder, and 2 wt% of carbon nanotube 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 rolled to prepare a positive electrode.

[0163] Lithium secondary battery manufacturing A lithium metal counter electrode was used as the positive electrode and a polyethylene / polypropylene multilayer separator was placed between them. The electrolyte was a solution of 1.0M LiPF6 lithium salt added to a solvent of ethylene carbonate and diethyl carbonate mixed in a volume ratio of 50:50. A coin half-cell was fabricated by injecting the electrolyte.

[0164] [Table 1]

[0165] Experimental Example 1: Structure and Component Analysis of Positive Electrode Active Material (1) FIG. 16 shows a transmission electron microscope (TEM) image of a cross section of the positive electrode active material according to Example 1 and the results of mapping using energy dispersive X-ray spectroscopy (EDS).

[0166] 16, the positive electrode active material according to Example 1 included a coating layer on the core, which contained both cobalt and aluminum. The positive electrode active material according to Example 1 also included a grain boundary coating layer, which contained both cobalt and aluminum. Mapping of the grain boundary coating layer revealed that the cobalt and aluminum were uniformly present within the grain boundary coating layer, and that the cobalt and aluminum were present in substantially the same locations within the grain boundary coating layer.

[0167] 17a to 17c show the results of depth analysis of a cross section of the positive electrode active material according to Example 1 using a transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy (EDS). Fig. 17b and Fig. 17c show the results of depth analysis along the arrow direction in Fig. 17a.

[0168] 17a to 17c, the point where the aluminum signal shows the steepest decrease after the maximum peak is about 31 nm, and the point where the cobalt signal shows the steepest decrease after the maximum peak is about 40 nm, meaning that the thickness of the second coating layer was about 31 nm and the thickness of the first coating layer was about 9 nm.

[0169] Experimental Example 2: Structure and Component Analysis of Positive Electrode Active Material (2) The positive electrode active materials according to Examples 1 to 5 and Comparative Example 1 were subjected to component analysis using energy dispersive X-ray spectroscopy (EDS), and the results are shown in Table 2. The contents (atomic %) of nickel (Ni), cobalt (Co), and aluminum (Al) obtained by energy dispersive X-ray spectroscopy (EDS) were respectively expressed as N, Ni , N Co , N Al The ratio between the contents of nickel (Ni), cobalt (Co), and aluminum (Al) is calculated to obtain N Ni / N Al and N co / N Al The results of Examples 1 to 5 and Comparative Example 1 are the results of the second region RG2 of the positive electrode active material. Ni , N Co , N Al , N Ni / N Al , and N co / N Al The value was the same as that of the lithium nickel composite oxide of Production Example 1.

[0170] [Table 2]

[0171] Experimental Example 3: Performance evaluation of lithium secondary batteries The charge / discharge efficiency, capacity retention rate, and DC resistance of the lithium secondary batteries including the positive electrode active materials according to Examples 1 to 5 and the Comparative Example were evaluated.

[0172] The coin cells according to the examples and comparative examples were initially charged at a static current (0.2 C) and a static voltage (4.25 V, 0.05 C cut-off), and then allowed to rest for 10 minutes before discharging to 3.0 V at a static current (0.2 C). Next, they were charged and discharged 50 times at 1 C / 1 C. The capacity retention was calculated as the ratio of the discharge capacity at each cycle (25 cycles and 50 cycles) to the initial discharge capacity.

[0173] The DC resistance (DC-IR = ΔV / ΔI) was calculated from the ratio of the average voltage change (ΔV) and the average current change (ΔI) during static discharge, and the average value was shown as the result. The difference between the DC resistance at the first cycle and the DC resistance at the 50th cycle was shown as the resistance change.

[0174] The results are shown in Table 3.

[0175] [Table 3]

[0176] Referring to Table 3, it was confirmed that the lithium secondary batteries including the positive electrode active materials according to Examples 1 to 5 had excellent capacity retention rates and small changes in resistance due to repeated charge and discharge.

[0177] 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 lithium-nickel composite oxide contains nickel (Ni), cobalt (Co), and aluminum (Al), A first region; a second region that surrounds the first region and is defined as a region having a thickness of 1 μm in a direction from the outermost shell of the positive electrode active material toward the center; Including, The nickel to aluminum content ratio of the second region (N Ni / N Al ) is 5 to 45; Cathode active material.

2. The cobalt to aluminum content ratio of the second region (N Co / N Al ) is 0.1 to 10; The positive electrode active material according to claim 1 .

3. The nickel to aluminum content ratio (N Ni / N Al ) is the content ratio of nickel to aluminum in the second region RG2 (N Ni / N Al ) is greater than The positive electrode active material according to claim 1 .

4. The nickel to aluminum content ratio (N Ni / N Al ) is 46 or more, The positive electrode active material according to claim 1 .

5. The positive electrode active material includes a core containing the lithium nickel-based composite oxide; a coating layer overlying the core, the coating layer comprising cobalt and aluminum; The positive electrode active material according to claim 1 .

6. The core is a secondary particle formed by aggregation of primary particles. The positive electrode active material according to claim 5 .

7. the core comprises cobalt; The cobalt content of the core is less than the cobalt content of the coating layer; The positive electrode active material according to claim 5 .

8. In the coating layer, the molar ratio of the aluminum to the cobalt (C Al / C Co ) is 0.1 to 4; The positive electrode active material according to claim 5 .

9. the coating layers include a first coating layer on the core and a second coating layer on the first coating layer; The aluminum content of the second coating layer is greater than the aluminum content of the first coating layer. The positive electrode active material according to claim 5 .

10. a positive electrode current collector and a positive electrode active material layer, The positive electrode active material layer contains the positive electrode active material according to claim 1. Positive electrode.

11. The cobalt to aluminum content ratio of the second region (N Co / N Al ) is 0.1 to 10; The positive electrode according to claim 10.

12. The nickel to aluminum content ratio (N Ni / N Al ) is the content ratio of nickel to aluminum in the second region RG2 (N Ni / N Al ) is greater than The positive electrode according to claim 10.

13. The nickel to aluminum content ratio (N Ni / N Al ) is 46 or more, The positive electrode according to claim 10.

14. The positive electrode active material includes a core containing a lithium nickel-based composite oxide; a coating layer on the core comprising cobalt and aluminum; Including, The positive electrode according to claim 10.

15. The core is a secondary particle formed by aggregation of primary particles. The positive electrode of claim 14.

16. the core comprises cobalt; The cobalt content of the core is less than the cobalt content of the coating layer; The positive electrode of claim 14.

17. In the coating layer, the molar ratio of the aluminum to the cobalt (C Al / C Co ) is 0.1 to 4; The positive electrode of claim 14.

18. the coating layers include a first coating layer on the core and a second coating layer on the first coating layer; The aluminum content of the second coating layer is greater than the aluminum content of the first coating layer. The positive electrode of claim 14.

19. A lithium secondary battery comprising the positive electrode active material according to claim 1.

20. When the charge / discharge cycle is repeated 50 times under the condition of 1C / 1C, the capacity retention rate is 95% or more and the resistance change is 60Ω or less.

20. The lithium secondary battery according to claim 19.

Images