Method for preparing positive electrode active material, positive electrode active material prepared using the same, and lithium secondary battery including the same

Abstract

The present invention relates to a method for preparing a positive electrode active material, a positive electrode active material prepared using the method, and a lithium secondary battery including the positive electrode active material, and more particularly, to a method for preparing a positive electrode active material, the method including the steps of: forming a lithium nickel-based composite oxide; and coating the lithium nickel-based composite oxide. The step of coating the lithium nickel-based composite oxide includes: forming a first aqueous solution including an aluminum compound and an alkaline compound; forming a mixture including the lithium nickel-based composite oxide and the first aqueous solution; adding a second aqueous solution including a cobalt compound to the mixture; and drying and heat-treating the mixture.

Description

Technical Field

[0001] This disclosure relates to a method for preparing a positive electrode active material, the positive electrode active material prepared by the method, and a lithium secondary battery containing the positive electrode active material. Background Technology

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

[0003] A lithium secondary battery is a battery that includes a positive electrode and a negative electrode containing active materials capable of inserting and deintercalating lithium ions, as well as an electrolyte, and generates electrical energy through redox reactions when lithium ions are inserted / deintercalated at the positive and negative electrodes. Summary of the Invention

[0004] Technical issues The problem to be solved by this disclosure is to provide a method for preparing a positive electrode active material, which has high capacity and excellent capacity retention and low resistance change even during repeated charging and discharging.

[0005] Another problem this disclosure aims to solve is to provide a positive electrode active material that exhibits excellent capacity retention and low resistance change even during repeated charging and discharging, as well as a lithium secondary battery including the positive electrode active material.

[0006] Technical solution A method for preparing a positive electrode active material according to embodiments of the present disclosure includes the following steps: forming a lithium-nickel composite oxide; and coating the lithium-nickel composite oxide, wherein the step of coating the lithium-nickel composite oxide may include: forming a first aqueous solution comprising an aluminum compound and an alkaline compound; forming a mixture comprising the lithium-nickel composite oxide and the first aqueous solution; adding a second aqueous solution comprising a cobalt compound to the mixture; and drying and heat treatment.

[0007] The positive electrode active material according to embodiments of the present disclosure includes: a core comprising a lithium-nickel composite oxide; and a coating located on the core and comprising cobalt and aluminum, wherein the coating comprises a first coating and a second coating on the first coating, and the aluminum content of the second coating may be greater than the aluminum content of the first coating.

[0008] The lithium secondary battery according to embodiments of this disclosure may include the above-described positive electrode active material.

[0009] Beneficial effects By using the method for preparing a positive electrode active material according to embodiments of the present disclosure, a positive electrode active material having high capacity, long cycle life and low resistance change even during repeated charging and discharging, and a lithium secondary battery including the positive electrode active material, can be manufactured. Attached Figure Description

[0010] Figure 1 This is a schematic diagram illustrating a concept of a lithium secondary battery according to an embodiment of the present disclosure.

[0011] Figures 2 to 5 This is a schematic diagram illustrating a lithium secondary battery according to an embodiment.

[0012] Figure 6 This is a cross-sectional view of the positive electrode according to an embodiment of the present disclosure.

[0013] Figures 7 to 9 This is a schematic diagram used to explain the positive electrode active material according to embodiments of the present disclosure. Figure 8 It is magnification Figure 7 A magnified view of region M.

[0014] Figure 10 This is a flowchart for explaining a method for preparing a positive electrode active material according to embodiments of the present disclosure.

[0015] Figure 11 This is a flowchart for explaining the steps (S100) of a method for preparing a positive electrode active material according to embodiments of the present disclosure.

[0016] Figure 12 This is a schematic diagram illustrating steps (S300) and (S500) of a method for preparing a positive electrode active material according to embodiments of the present disclosure.

[0017] Figure 13 This is a schematic diagram illustrating the steps (S700) of a method for preparing a positive electrode active material according to an embodiment of the present disclosure.

[0018] Figure 14 and Figure 15 This is a schematic diagram illustrating the steps (S900) of a method for preparing a positive electrode active material according to an embodiment of the present disclosure.

[0019] Figure 16 and Figure 17 It is a transmission electron microscope (TEM) image of a cross-section of the positive electrode active material according to Example 1 and a mapping result using energy dispersive X-ray spectroscopy (EDS).

[0020] Figure 18It is a transmission electron microscope (TEM) image of a cross-section of the positive electrode active material according to Comparative Example 2 and a mapping result using energy dispersive X-ray spectroscopy (EDS).

[0021] Figure 19a and Figure 19b The results of in-depth analysis of the cross-sections of the positive electrode active materials according to Example 1 and Comparative Example 2 are shown using transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). Detailed Implementation

[0022] To fully understand the structure and effects of this disclosure, preferred embodiments of the disclosure will be described with reference to the accompanying drawings. However, this disclosure is not limited to the embodiments disclosed below, but can be implemented in various forms and can be modified in various ways. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art to which this disclosure pertains.

[0023] In this specification, when an element is referred to as being on another element, the element may be directly formed on said other element, or a third element may be placed therebetween. Furthermore, in the accompanying drawings, the thickness of the elements is exaggerated for the purpose of effectively describing the technical content. The same elements are indicated by the same reference numerals throughout the specification.

[0024] The embodiments described herein will be described with reference to sectional views and / or plan views, which serve as ideal exemplary views of this disclosure. In the drawings, the thickness of the films and regions is exaggerated for the purpose of effectively describing the technical content. Therefore, the regions shown in the drawings are schematic in nature, and the shapes of the regions shown in the drawings are intended to illustrate the specific form of the regions of the device and are not intended to limit the scope of the disclosure. In the various embodiments of this specification, terms such as first, second, third, etc., are used to describe various elements, but these elements should not be limited by these terms. These terms are used only to distinguish one element from another. The embodiments described and illustrated herein also include complementary embodiments thereof.

[0025] The terminology used in this specification is for explaining embodiments and is not intended to limit this disclosure. In this specification, the singular form includes the plural form unless explicitly stated in the context. The use of "comprising" and / or variations thereof in this specification does not exclude the presence or addition of one or more other elements besides those mentioned.

[0026] Figure 1 This is a schematic diagram illustrating a concept of a lithium secondary battery according to an embodiment of the present disclosure. (Refer to...) Figure 1 A lithium secondary battery may include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte ELL.

[0027] The positive electrode 10 and the negative electrode 20 may be spaced apart from each other, with a diaphragm 30 placed between them. The diaphragm 30 may be disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the diaphragm 30 may be in contact with the electrolyte ELL. The positive electrode 10, the negative electrode 20, and the diaphragm 30 may be immersed in the electrolyte ELL.

[0028] The electrolyte ELL can be a medium used to transfer lithium ions between the positive electrode 10 and the negative electrode 20. In the electrolyte ELL, lithium ions can pass through the separator 30 to move toward the positive electrode 10 or the negative electrode 20.

[0029] 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 also include a binder and / or a conductive material.

[0030] As an example, the positive electrode 10 may also include an additive capable of acting as a sacrificial positive electrode.

[0031] Based on a 100wt% positive electrode active material layer AML1, the content of the positive electrode active material in the AML1 layer can be from 90wt% to 99.5wt%. Based on the 100wt% positive electrode active material layer AML1, the contents of the binder and conductive material can be from 0.5wt% to 5wt%, respectively.

[0032] The binder is used to ensure good adhesion between the positive electrode active material particles and also to ensure good adhesion of 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, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylate resin, polyester resin, nylon, etc.

[0033] Conductive materials are used to impart conductivity to electrodes, and any electrically conductive material can be used in the constructed battery as long as it does not cause a chemical change. Examples of conductive materials include: carbon-based materials such as natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials in the form of metal powders or metal fibers, including copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0034] As the current collector COL1, Al can be used, but it is not limited to this.

[0035] Positive electrode active material As the positive electrode active material in the positive electrode active material layer AML1, a compound capable of reversibly inserting and deintercalating lithium (lithiation intercalation compound) can be used. Specifically, one or more of lithium and a composite oxide of metals selected from cobalt, manganese, nickel and combinations thereof can be used.

[0036] The composite oxide can be a lithium transition metal composite oxide, and specific examples include lithium nickel oxides, lithium cobalt oxides, lithium manganese oxides, lithium iron phosphate compounds, cobalt-free lithium nickel manganese oxides, or combinations thereof.

[0037] As an example, a compound represented by any of the following chemical formulas can 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 CoGb 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 Mn2G b 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).

[0038] In the chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, 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 It is Mn, Al, or a combination thereof.

[0039] As an example, the positive electrode active material can be a high-nickel positive electrode active material, in which the nickel content, based on 100 mol% of the lithium transition metal composite oxide (excluding lithium), is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more and 99 mol% or less. High-nickel positive electrode active materials can achieve high capacity and therefore can be used in high-capacity, high-density lithium secondary batteries.

[0040] 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 also include a binder and / or a conductive material. For example, the negative electrode active material layer AML2 may include 90 wt% to 99 wt% of negative electrode active material, 0.5 wt% to 5 wt% of binder, and 0 wt% to 5 wt% of conductive material.

[0041] The binder is used to ensure that the particles of the negative electrode active material adhere well to each other, and to ensure that the negative electrode active material adheres well to the current collector COL2.

[0042] As an adhesive, non-aqueous adhesives, aqueous adhesives, dry adhesives, or combinations thereof can be used. Examples of non-aqueous adhesives include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0043] Waterborne adhesives may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepoxychloropropane, 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.

[0044] When using an aqueous binder as the negative electrode binder, it may also include a cellulose-based compound capable of imparting viscosity. As a cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or their alkali metal salts may be mixed and used. As an alkali metal, Na, K, or Li may be used.

[0045] Dry binders are polymeric materials capable of being fibrous and can be, for example, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations thereof.

[0046] Conductive materials are used to impart conductivity to electrodes, and any electrically conductive material can be used in the constructed battery as long as it does not cause a chemical change. Specific examples include: carbon-based materials, such as natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials in the form of metal powders or metal fibers, including copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0047] As a current collector, COL2 can be made of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrates coated with conductive metals, and combinations thereof. Negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes materials capable of reversibly inserting / deintercalating lithium ions, lithium metal, lithium metal alloys, materials capable of doping and dedoping lithium, or transition metal oxides.

[0048] Materials capable of reversibly intercalating / deintercalating lithium ions are carbon-based negative electrode active materials, and may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite (such as natural graphite or artificial graphite in amorphous, platy, scaly, spherical or fibrous form), and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0049] As alloys of lithium metal, alloys of lithium with a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn may be used.

[0050] As materials capable of doping and dedoping lithium, Si-based negative electrode active materials or Sn-based negative electrode active materials may be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiO x (0 < x ≤ 2), Si-Q alloys (wherein Q is selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements (other than 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 may be Sn, SnO₂, Sn-based alloys, or combinations thereof.

[0051] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to an embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surfaces of the silicon particles. For example, the silicon-carbon composite may comprise secondary particles (core) formed by assembling silicon primary particles, and an amorphous carbon coating (shell) located on the surfaces of the secondary particles. Amorphous carbon is also located between the silicon primary particles, such that for example the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0052] The silicon-carbon composite may further comprise crystalline carbon. For example, the silicon-carbon composite may comprise a core comprising crystalline carbon and silicon particles, and an amorphous carbon coating located on the surface of the core.

[0053] The Si-based negative electrode active material or the Sn-based negative electrode active material may be used in mixture with the carbon-based negative electrode active material.

[0054] Diaphragm 30 Depending on the type of the lithium secondary battery, a separator 30 may be present between the positive electrode 10 and the negative electrode 20. As such a separator 30, a multilayer film of polyethylene, polypropylene, polyvinylidene fluoride, or two or more layers thereof may be used, and it is obvious that a mixed multilayer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, or the like may be used.

[0055] The diaphragm 30 may include a porous substrate and a coating on one or both surfaces of the porous substrate, comprising organic materials, inorganic materials, or combinations thereof.

[0056] The porous substrate can be a polymer membrane, which is formed from any one of polymers selected from the following, or copolymers or mixtures of two or more of them, such as polyolefins (e.g., polyethylene and polypropylene), polyesters (e.g., polyethylene terephthalate and polybutylene terephthalate), polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene ether, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene.

[0057] Organic materials may include polymers such as polyvinylidene fluoride or (meth)acrylic acid polymers.

[0058] Inorganic materials may include inorganic particles selected from, but are not limited to, Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite and combinations thereof.

[0059] Organic and inorganic materials can be mixed in a coating, or coatings containing organic materials and coatings containing inorganic materials can exist in a layered form.

[0060] Electrolyte ELL Electrolytes used in lithium secondary batteries (ELL) consist of non-aqueous organic solvents and lithium salts.

[0061] Non-aqueous organic solvents serve as the medium through which ions participating in the electrochemical reactions of a battery can move.

[0062] Non-aqueous organic solvents can be carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, or combinations thereof.

[0063] As carbonate solvents, 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), butyl carbonate (BC), etc. can be used.

[0064] As ester solvents, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonate lactone, caprolactone, etc. can be used.

[0065] As ether solvents, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc., can be used. Furthermore, as ketone solvents, cyclohexanone, etc., can be used. As alcohol solvents, ethanol, isopropanol, etc., can be used, and as aprotic solvents, the following can be used: nitriles, such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include double bonds, aromatic rings, or ether groups); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane and 1,4-dioxolane; sulfolane, etc.

[0066] Non-aqueous organic solvents can be used alone or in combination of two or more.

[0067] Furthermore, when using carbonate solvents, cyclic carbonates and chain carbonates can be mixed and used, and cyclic carbonates and chain carbonates can be mixed in a volume ratio of 1:1 to 1:9.

[0068] Lithium salts, dissolved in organic solvents, act as a source of lithium ions in batteries to enable basic operation of lithium secondary batteries and are substances used to facilitate the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include those selected from LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide, LiFSI), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F 2y+ The lithium trifluoromethane sulfonate (where x and y are integers from 1 to 20), lithium tetrafluoroethane sulfonate, lithium difluoro(oxalate)borate (LiDFOB), lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB) are one or more of these compounds.

[0069] Lithium secondary batteries Based on their shape, lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin-shaped types. Figures 2 to 5 This is a schematic diagram illustrating a lithium secondary battery according to an embodiment, wherein, Figure 2 It could be a so-called cylindrical battery. Figure 3 It could be a so-called prismatic battery, and Figure 4 and Figure 5 This could be a so-called pouch battery. (See reference...) Figures 2 to 4The lithium secondary battery 100 may include an electrode assembly 40 in which a separator 30 is disposed between a positive electrode 10 and a negative electrode 20, and a housing 50 in which the electrode assembly 40 is embedded. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 may include, for example... Figure 2 The sealing member 60 of the sealing housing 50. Furthermore, in Figure 3 In this lithium secondary battery 100, a positive electrode lead connector 11 and a positive electrode terminal 12, and a negative electrode lead connector 21 and a negative electrode terminal 22, are included. For example, in... Figure 4 and Figure 5 In the lithium secondary battery 100, electrode terminals 70 (i.e., positive electrode terminal 71 and negative electrode terminal 72) may be included, which serve as electrical paths for guiding current formed in the electrode assembly 40 to the outside.

[0070] The lithium secondary batteries according to embodiments of this disclosure can be used in automobiles, mobile phones and / or various types of electronic devices, and this disclosure is not limited thereto.

[0071] The positive electrode 10 according to embodiments of the present disclosure will be described in detail below.

[0072] Positive electrode 10 Figure 6 This is a cross-sectional view of the positive electrode according to an embodiment of the present disclosure. In the following text, references will be omitted for ease of explanation. Figures 1 to 5 The descriptions are identical to the descriptions of the items, and the differences will be described in detail.

[0073] 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 the positive electrode active material CAM, which will be described later, and may also include a binder and / or a conductive material.

[0074] The contents of the positive electrode active material CAM, binder, conductive material, and current collector COL1 are described as above.

[0075] CAM, the active material of the positive electrode Figures 7 to 9 This is a schematic diagram used to explain the positive electrode active material according to embodiments of the present disclosure. Figure 8 It is magnification Figure 7 A magnified view of region M.

[0076] Reference Figure 7 The positive electrode active material CAM is in a polycrystalline form and may include secondary particles formed by the aggregation of at least two or more primary particles PRP.

[0077] The positive electrode active material CAM can be spherical or elliptical.

[0078] The average particle size (d) of the positive electrode active material CAM can be from 5 μm to 25 μm. For example, the average particle size (d) of the positive electrode active material CAM can be from 7 μm to 25 μm, 10 μm to 25 μm, or 10 μm to 20 μm. As an example, the average particle size (d) of the positive electrode active material CAM can be obtained by arbitrarily selecting about 30 positive electrode active material CAMs in the form of secondary particles from an electron micrograph of the positive electrode active material CAM, measuring their particle size, and taking the diameter of the particles with a cumulative volume of 50 vol% in the particle size distribution as the average particle size.

[0079] The positive electrode active material CAM can include a core COR and a coating CTL.

[0080] The core COR is in a polycrystalline form and may include secondary particles formed by the aggregation of at least two or more primary particles PRP.

[0081] Nuclear COR can include lithium-nickel composite oxides. Lithium-nickel composite oxides can include lithium (Li) and transition metals. Transition metals can include nickel (Ni). The content of nickel (Ni) in lithium-nickel composite oxides is not limited.

[0082] As an example, lithium-nickel composite oxides can be lithium-nickel composite oxides that include a high content of nickel (Ni). For example, a lithium-nickel composite oxide can be a lithium-nickel composite oxide in which the content of nickel (Ni) among the metals other than lithium is 60 mol% or more, 80 mol% or more, 90 mol% or more, or 95 mol% or more and 100 mol% or less, 99.9 mol% or less, or 99 mol% or less. In other words, a lithium-nickel composite oxide can be a lithium-nickel composite oxide in which the molar number of nickel (Ni) relative to the total molar number of transition metals is 60 mol% or more, 80 mol% or more, 90 mol% or more, or 95 mol% or more and 100 mol% or less, 99.9 mol% or less, or 99 mol% or less. When the nickel (Ni) content meets the above ranges, the positive electrode active material CAM can achieve high capacity and high performance.

[0083] As an example, lithium-nickel composite oxides can be represented by the following chemical formula 1.

[0084] [Chemical Formula 1] Li a1 Ni x1 M 1 y1 M2 z1 O 2-b1 X b1 In Chemical Formula 1, 0.9≤a1≤1.8, 0.8≤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 2 are each 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.

[0085] For example, in Chemical Formula 1, 0.85≤x1≤1, 0≤y1≤0.15 and 0≤z1≤0.15 may be satisfied, or 0.9≤x1≤1, 0≤y1≤0.1 and 0≤z1≤0.1 may be satisfied.

[0086] For example, x1+y1+z1=1 may be satisfied.

[0087] By way of example, the lithium-nickel composite oxide may be represented by Chemical Formula 2 below. The compound represented by Chemical Formula 2 may be a lithium-nickel-cobalt composite oxide.

[0088] [Chemical Formula 2] Li a2 Ni x2 Co y2 M 3 z2 O 2-b2 X b2 In Chemical Formula 2, 0.9≤a2≤1.8, 0.8≤x2<1, 0<y2≤0.2, 0≤z2≤0.2, 0.9≤x2+y2+z2≤1.1, and 0≤b2≤0.1, M 3 is 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.

[0089] For example, in Chemical Formula 2, 0.85≤x2≤0.99, 0.01≤y2≤0.15 and 0.01≤z2≤0.15 may be satisfied, or 0.9≤x2≤0.99, 0.01≤y2≤0.1 and 0.01≤z2≤0.1 may be satisfied.

[0090] For example, x2+y2+z2=1 may be satisfied.

[0091] As an example, lithium-nickel composite oxides can be represented by the following chemical formula 3. Compounds represented by chemical formula 3 can be lithium-nickel-cobalt-aluminum oxides or lithium-nickel-cobalt-manganese oxides.

[0092] [Chemical Formula 3] Li a3 Ni x3 Co y3 M 4 z3 M 5 w3 O 2-b3 X b3 In chemical formula 3, 0.9 ≤ a³ ≤ 1.8, 0.8 ≤ 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 M is one or more elements selected from the group consisting of Al and Mn. 5 X is one or more elements selected from the group consisting of B, 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.

[0093] For example, in chemical formula 3, the following conditions can be met: 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.

[0094] For example, it can satisfy x³ + y³ + z³ + w³ = 1.

[0095] The coating CTL can be located on the core COR. The coating CTL can be located on the entire surface or at least a portion of the surface of the core COR. The coating CTL can include cobalt (Co) and aluminum (Al). As an example, the coating CTL can be confirmed by compositional analysis using EDS. By including the coating CTL, the positive electrode active material CAM can be structurally stable even during repeated charge and discharge, side reactions at the surface of the core COR can be suppressed, and the room temperature and high temperature cycle life characteristics of the positive electrode active material CAM can be improved.

[0096] As an example, cobalt (Co) in the coating CTL can be present in the form of a cobalt-containing compound. For example, the cobalt-containing compound can be cobalt oxide, cobalt hydroxide, cobalt carbonate, their complexes, or mixtures thereof. As an example, the cobalt-containing compound can also include other metallic or non-metallic elements besides cobalt. For example, the cobalt-containing compound can also include lithium, manganese, and / or nickel. For example, the cobalt-containing compound can be lithium cobalt oxide, etc.

[0097] As an example, aluminum (Al) in the coating CTL can be present in the form of aluminum-containing compounds. For example, aluminum-containing compounds can be aluminum oxide, aluminum hydroxide, aluminum carbonate, their composites, or mixtures thereof. As an example, aluminum-containing compounds can also include other metallic or non-metallic elements besides aluminum. For example, aluminum-containing compounds can also include lithium, manganese, and / or nickel. For example, aluminum-containing compounds can be lithium aluminum oxide, etc.

[0098] The coating CTL and core COR can be distinguished by in-depth profiling of the positive electrode active material CAM using transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). In this specification, in the EDS results showing the Co signal obtained by scanning the positive electrode active material CAM from the outermost shell towards the center of the cross-section, the point where the Co signal shows the most abrupt decrease after the maximum peak can be defined as the boundary between the coating CTL and the core COR (see [link to documentation]). Figure 19b As an example, the signal amplitude can be proportional to the content. As an example, this content can be an atomic percentage (atomic%). The total cobalt and aluminum content in the coated CTL can be greater than the total cobalt and aluminum content in the core COR. That is, the total cobalt and aluminum content in the coated CTL can be greater than the total cobalt and aluminum content in lithium nickel composite oxides. As an example, this total content can be atomic%.

[0099] The cobalt content in the coated CTL can be greater than that in the core COR. The aluminum content in the coated CTL can also be greater than that in the core COR. In other words, the individual cobalt and aluminum contents in the coated CTL can be greater than the individual cobalt and aluminum contents in lithium-nickel composite oxides. As an example, this content can be atomic%.

[0100] As an example, lithium-nickel composite oxides include cobalt, but the cobalt content in the lithium-nickel composite oxide can be less than the cobalt content in the coating CTL. As an example, this content can be atomic%. Meanwhile, lithium-nickel composite oxides can be substantially free of aluminum, thus the aluminum content in the lithium-nickel composite oxide can be less than the aluminum content in the coating CTL. As an example, substantially free of aluminum can mean including 100 ppm or less.

[0101] As another example, lithium-nickel composite oxides include both cobalt and aluminum, but the content of cobalt and aluminum in lithium-nickel composite oxides can be less than the content of cobalt and aluminum in the coating CTL.

[0102] The molar ratio of aluminum to cobalt in the CTL coating (C Al / C Co The molar ratio (C) of aluminum to cobalt in a coating CTL can range from 0.1 to 4. Al / C Co The content of cobalt, aluminum, and molar ratio (C) in the coating CTL can be 0.1 to 3, 0.1 to 1, or 0.1 to 0.5. Al / C Co When the above range is met, the positive electrode active material CAM can have a long cycle life even during repeated charging and discharging, and can reduce resistance changes.

[0103] Reference Figure 8 The coating CTL may include a first coating CTL1 and a second coating CTL2.

[0104] The first coating CTL1 and the second coating CTL2 can be distinguished by in-depth profiling of the positive electrode active material CAM using transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). In this specification, in the EDS results showing the Al signal obtained by scanning the positive electrode active material CAM from the outermost shell towards the center of the cross-section, the point where the Al signal shows the most abrupt decrease after the maximum peak is defined as the boundary between the first coating CTL1 and the second coating CTL2 (see [link to EDS]). Figure 19a As an example, the amplitude of the signal can be proportional to the content. As an example, the content could be atomic%.

[0105] The aluminum content of the second coating CTL2 can be greater than that of the first coating CTL1. The aluminum content of the first coating CTL1 can be substantially the same as that of the core COR. A substantially similar content can be defined as the difference between the average Al signal of the second coating CTL2 and the average Al signal of the core COR being within 10% in EDS results showing Al signals obtained by scanning the positive electrode active material CAM from the outermost shell towards the center. As an example, this content can be atomic%.

[0106] The first coating CTL1 can have a first thickness (TKC1). The second coating CTL2 can have a second thickness (TKC2). The sum of the first and second thicknesses (TKC1+TKC2) can be from 25 nm to 60 nm. For example, the sum of the first and second thicknesses (TKC1+TKC2) can be from 29 nm to 55 nm or from 40 nm to 50 nm. When the sum of the first and second thicknesses (TKC1+TKC2) meets the above range, the positive electrode active material CAM can have a long cycle life even during repeated charging and discharging, and can reduce resistance changes.

[0107] The ratio of the second thickness to the first thickness (TKC2 / TKC1) can be from 1 to 5. For example, the ratio of the second thickness to the first thickness (TKC2 / TKC1) can be from 1.4 to 3.44 or from 2 to 4.

[0108] The ratio of the second thickness to the sum of the first and second thicknesses (TKC2 / (TKC1+TKC2)) can 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)) can be 0.5 to 0.83, 0.6 to 0.80, or 0.65 to 0.8.

[0109] 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.

[0110] When 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 ranges, the positive electrode active material CAM can have a long cycle life even during repeated charging and discharging, and can reduce resistance changes.

[0111] The first thickness (TKC1) can be the value obtained by subtracting the second thickness (TKC2) from the sum of the first and second thicknesses (TKC1 + TKC2). The second thickness (TKC2) can be from 20 nm to 40 nm. For example, the second thickness (TKC2) can be from 25 nm to 40 nm, 30 nm to 40 nm, or 30 nm to 35 nm. When the second thickness (TKC2) meets the above range, the positive electrode active material CAM can have a long cycle life even during repeated charging and discharging, and the resistance change can be reduced.

[0112] In addition to the coating CTL, the positive electrode active material CAM can also be included in the primary particles (see Figure 7 The grain boundary coating is applied to each surface of the PRP (Positive Electrode Active Material). The grain boundary coating can exist within the CAM (Positive Electrode Active Material). The grain boundary coating can be applied along the primary particles within the CAM (see...). Figure 7 The grain boundary coating is formed by coating the interface between the PRPs (Positive Electrode Active Material). In other words, the grain boundary coating can refer to the coating applied to the grain boundaries inside the positive electrode active material CAM. The interior of the positive electrode active material CAM can refer to the entire interior of the positive electrode active material CAM excluding its surface. For example, it can refer to the entire interior region starting from a depth of about 10 nm from the outermost surface of the positive electrode active material CAM, or the region from a depth of 10 nm to a depth of about 2 μm.

[0113] Grain boundary coatings can include cobalt (Co) and aluminum (Al). Cobalt (Co) and aluminum (Al) can be uniformly distributed within the grain boundary coating. That is, cobalt (Co) and aluminum (Al) are not distributed in different locations or concentrated in any one location within the grain boundary coating. As an example, as a result of mapping using energy-dispersive X-ray spectroscopy (EDS), cobalt and aluminum in the grain boundary coating can exist in substantially the same location.

[0114] By further including a grain boundary coating, the structural stability of the positive electrode active material CAM is enhanced, a uniform and consistent coating is induced on the surface, and the coating content on the surface is appropriately adjusted, so that the initial charge and discharge efficiency and cycle life characteristics can be improved without increasing the resistance.

[0115] Reference Figure 9 The positive electrode active material CAM may include a first region RG1 and a second region RG2. The first region RG1 may be located at the central portion of the positive electrode active material CAM. The first region RG1 may be defined as the region excluding the second region RG2 from the positive electrode active material CAM.

[0116] The second region RG2 can be located at the periphery of the positive electrode active material CAM. The second region RG2 can surround the first region RG1. In this specification, the second region RG2 can be defined as the region extending from the outermost shell of the positive electrode active material CAM to a depth at which component analysis can be performed using energy-dispersive X-ray spectroscopy (EDS). The depth at which component analysis can be performed using energy-dispersive X-ray spectroscopy (EDS) can be several μm. For example, the depth at which component analysis can be performed using energy-dispersive X-ray spectroscopy (EDS) can be about 1 μm. As an example, the second region RG2 can be defined as a region extending from the outermost shell of the positive electrode active material CAM toward the center with a thickness (TKR) of about 1 μm.

[0117] 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, both the first region RG1 and the second region RG2 may 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).

[0118] The contents of nickel (Ni), cobalt (Co), and aluminum (Al) in the first region RG1 and the second region RG2 can be obtained from energy-dispersive X-ray spectroscopy (EDS) results. The contents of each of nickel (Ni), cobalt (Co), and aluminum (Al) obtained by energy-dispersive X-ray spectroscopy (EDS) are N. Ni N Co N Al It can be expressed as atomic% . The content of each of nickel (Ni), cobalt (Co), and aluminum (Al) is N. Ni N Co N Al It can be a value calculated based on the total content (atomic%) of nickel (Ni), cobalt (Co) and aluminum (Al).

[0119] The nickel-to-aluminum ratio (N) in region RG1 of the first zone Ni / N Al The content of nickel relative to aluminum in region RG2 can be greater than that in region RG2 (N). Ni / N Al ).

[0120] As an example, the nickel-to-aluminum ratio (N / A) in the first region RG1 is... Ni / N Al The content of nickel relative to aluminum in region RG1 can be 45 or greater. For example, the nickel-to-aluminum ratio (N) in region RG1 is... Ni / N Al() can be 46 or greater, 48 or greater, or 50 or greater and 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.

[0121] As an example, the nickel-to-aluminum ratio (N) in the second region RG2 is... Ni / N Al The ratio of nickel to aluminum in region RG2 can be 5 to 45. For example, the ratio of nickel to aluminum in region RG2 (N...) Ni / N Al () can be 8 to 45, 12 to 45, or 15 to 42.

[0122] When the first region RG1 and the second region RG2 respectively have a nickel to aluminum content ratio (N) within the above range, Ni / N Al When the positive electrode active material CAM is used, it can have a long cycle life even during repeated charging and discharging, and can reduce resistance changes.

[0123] The cobalt to aluminum content ratio (N) in region RG2 of the second zone Co / N Al The ratio of cobalt to aluminum (N) can be 0.1 or greater. For example, the ratio of cobalt to aluminum in region RG2 of the second region (N) can be... Co / N Al The content of cobalt relative to aluminum in the second region RG2 can be 0.5 or greater, 1 or greater, or 2 or greater and 10 or less, 8 or less, or 6 or less. Co / N Al When the above range is met, the positive electrode active material CAM can have a long cycle life even during repeated charging and discharging, and can reduce resistance changes.

[0124] The positive electrode 10 and the lithium secondary battery incorporating the positive electrode active material CAM according to embodiments of the present disclosure can exhibit excellent cycle life characteristics and small resistance changes due to repeated charging and discharging. For example, the positive electrode 10 and the lithium secondary battery incorporating the positive electrode active material CAM according to embodiments of the present disclosure can have a capacity retention rate of 95% or higher after 50 repeated charge and discharge cycles under 1C / 1C conditions. Furthermore, even after 50 repeated charge and discharge cycles under 1C / 1C conditions, the positive electrode 10 and the lithium secondary battery incorporating the positive electrode active material CAM according to embodiments of the present disclosure can have a resistance change of 60Ω or less or 35Ω or less.

[0125] Method for preparing positive electrode active material CAM Figure 10This is a flowchart for explaining a method for preparing a positive electrode active material CAM according to embodiments of the present disclosure. Figure 11 This is a flowchart of an embodiment used to explain step (S100) in the preparation method. Figures 12 to 15 This is a schematic diagram used to explain each step in the preparation method.

[0126] Reference Figure 10 The method for preparing a positive electrode active material CAM according to an embodiment of the present disclosure includes the following steps: forming a lithium nickel composite oxide (S100); and coating a lithium nickel composite oxide.

[0127] The process of coating a lithium-nickel composite oxide may include the following steps: forming a first aqueous solution AQ1 comprising an aluminum compound and an alkaline compound (S300); forming a mixture MXR1 by mixing the lithium-nickel composite oxide and the first aqueous solution (S500); adding a second aqueous solution AQ2 comprising a cobalt compound to the mixture (S700); and drying and heat treatment (S900).

[0128] Reference Figure 11 The step of forming a lithium-nickel composite oxide (S100) may include the following steps: forming a nickel hydroxide (S120); mixing the nickel hydroxide and a lithium raw material (S140); and heat treatment (S160).

[0129] Nickel hydroxides may include transition metals. Transition metals include nickel (Ni), and may also include M of formula 1 above. 1 and M 2 As an example, nickel hydroxides may include nickel (Ni) and cobalt (Co) as transition metals. Alternatively, nickel hydroxides may include nickel (Ni), cobalt (Co), and aluminum (Al) as transition metals. Alternatively, nickel hydroxides may include nickel (Ni), cobalt (Co), and manganese (Mn) as transition metals.

[0130] Nickel hydroxides (S120) can be obtained by coprecipitation. For example, coprecipitation may involve dissolving a transition metal feedstock in a solvent such as distilled water, and continuously introducing the transition metal salt solution along with a chelating agent and / or an alkaline aqueous solution into a reactor to induce precipitation. After collecting the precipitate in slurry form, the slurry solution is filtered and dried to obtain nickel hydroxides as metal complex oxides.

[0131] The transition metal raw material may include salts of the aforementioned transition metals. Sulfates, nitrates, acetates, halides, hydroxides, etc., can be used as transition metal salts, and there are no particular limitations, as long as they are soluble in a solvent. As an example, the transition metal raw material may include nickel salts, cobalt salts, and aluminum salts. As another example, the transition metal raw material may include nickel salts, cobalt salts, and manganese salts. The transition metal raw materials can be mixed by adjusting the molar ratio to give the positive electrode active material high capacity characteristics.

[0132] Nickel hydroxides can be mixed with lithium feedstock in a certain proportion (S140). For example, nickel hydroxides and lithium feedstock can be mixed in a molar ratio of approximately 1:1. There are no particular limitations on the lithium feedstock, as long as it is a material commonly used to prepare positive electrode active materials. For example, lithium feedstock can include lithium salts (such as lithium carbonate, lithium nitrate, lithium hydroxide, or lithium sulfate).

[0133] A mixture of nickel hydroxide and lithium feedstock can be introduced into the furnace FRC and heat-treated (S160). The heat treatment temperature can be from 700°C to 1000°C. For example, the heat treatment temperature can be from 700°C to 800°C. The heat treatment can be carried out in an oxidizing atmosphere such as air or oxygen. The heat treatment time can be from 10 hours to 30 hours. For example, the heat treatment time can be from 10 hours to 20 hours. As an example, a preliminary calcination can be performed at 150°C to 800°C prior to the heat treatment.

[0134] As an example, a further pulverization process can be performed after heat treatment. This pulverization process allows for the production of lithium-nickel composite oxides with the desired average particle size.

[0135] The obtained lithium-nickel composite oxide can have the same properties as the reference. Figure 7 The described core CORs have essentially the same composition and components. Essentially the same components can mean that the difference in composition is within 10%. That is, lithium nickel composite oxides can be compounds represented by chemical formula 1. For example, lithium nickel composite oxides can be compounds represented by chemical formula 2 or chemical formula 3.

[0136] Reference Figures 12 to 15 It can be coated with lithium nickel composite oxide NBO.

[0137] Reference Figure 12 It can form a first aqueous solution AQ1 (S300) that includes aluminum compounds and basic compounds.

[0138] The aluminum compound can be an aluminum coating 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, it is not particularly limited to the examples described above.

[0139] Aluminum compounds can be added such that the molar amount of aluminum is 0.05 mol% to 2 mol% relative to the total molar amount of elements other than lithium and oxygen in the lithium-nickel composite oxide. For example, aluminum compounds can be added such that the molar amount of aluminum is 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% relative to the total molar amount of elements other than lithium and oxygen in the lithium-nickel composite oxide. When the amount of aluminum compound added meets the above ranges, the final prepared positive electrode active material can have a long cycle life and can reduce resistance changes.

[0140] 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 (NH3). However, the basic compound may be any compound that can be used for precipitation and is not particularly limited to the examples described.

[0141] As an example, the first aqueous solution AQ1 may include anionic aluminum. By first generating anionic aluminum, the final prepared positive electrode active material can have a long cycle life and reduce resistance changes.

[0142] The mixture MXR1 (S500) can be formed by mixing a first aqueous solution AQ1 with a lithium nickel composite oxide NBO. Mixing can be carried out using a stirrer.

[0143] Mixing can take anywhere from 3 to 30 minutes. However, it is not limited to the described time and can be done for any sufficient time to form a homogeneous mixture of MXR1.

[0144] Reference Figure 13 A second aqueous solution, AQ2, can be added to the mixture MXR1 (S700). The second aqueous solution AQ2 may include a cobalt compound.

[0145] The cobalt compound can be a cobalt coating material. For example, it can include at least one selected from the group consisting of cobalt nitrate, cobalt sulfate, cobalt oxide, cobalt hydroxide, and cobalt carbonate. However, it is not particularly limited to the examples described.

[0146] Cobalt compounds can be added such that the molar amount of cobalt is 0.25 mol% to 4 mol% relative to the total molar amount of elements other than lithium and oxygen in the lithium-nickel composite oxide. For example, cobalt compounds can be added such that the molar amount of cobalt is 0.5 mol% to 4 mol%, 1 mol% to 4 mol%, 1 mol% to 3 mol%, or 1.2 mol% to 3 mol% relative to the total molar amount of elements other than lithium and oxygen in the lithium-nickel composite oxide. When the amount of cobalt compound added meets the above ranges, the final prepared positive electrode active material can have a long cycle life and can reduce resistance changes.

[0147] The molar ratio of aluminum compound to cobalt compound can be from 0.1 to 4. For example, the molar ratio of aluminum compound to cobalt compound can 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 aluminum compound to cobalt compound meets the above range, the final prepared positive electrode active material can have a long cycle life and reduce resistance change.

[0148] As an example, the second aqueous solution AQ2 can be added dropwise to the mixture MXR1. That is, the cobalt coating material in the second aqueous solution AQ2 can be slowly supplied to the mixture MXR1.

[0149] Adding a second aqueous solution of AQ2 can allow the incubation period to last from 5 minutes to 1 hour. For example, adding a second aqueous solution of AQ2 can allow the incubation period to last from 10 minutes to 50 minutes or from 20 minutes to 40 minutes.

[0150] If necessary, precipitants, pH adjusters, etc., can be further introduced into the MXR1 mixture.

[0151] In this step, the precipitation of aluminum and cobalt can occur simultaneously. Aluminum and cobalt can exist, respectively, as aluminum-containing compounds and cobalt-containing compounds. As examples, aluminum-containing compounds may include aluminum hydroxide, and cobalt-containing compounds may include cobalt hydroxide, etc. However, it is not limited to the described examples. Aluminum and cobalt can precipitate on the surface of a lithium nickel composite oxide (NBO). Therefore, the mixture MXR2 may include a lithium nickel composite oxide (NBO) with aluminum and cobalt precipitated on its surface.

[0152] The coating of lithium nickel composite oxide (NBO) according to embodiments of this disclosure can be a wet coating. When wet coating is performed through the above steps, a coating CTL with a uniform thickness can be formed on the lithium nickel composite oxide (NBO). Furthermore, cobalt and aluminum can not only be simultaneously and uniformly coated on the surface of the lithium nickel composite oxide (NBO), but also simultaneously and uniformly coated on the grain boundaries of the surface, which are primary particles.

[0153] The coating of lithium nickel composite oxide (NBO) according to embodiments of this disclosure can be performed by first adding an aluminum compound and then adding a cobalt compound. Therefore, a coating having the above-described structure can be formed. Figure 7 The CTL (Cyclic Transformer of the Coefficient of Performance) ultimately produces a positive electrode active material with a long cycle life and reduced resistance variation.

[0154] Reference Figure 14 and Figure 15 The mixture MXR2 can be dried and heat-treated to form the above-mentioned positive electrode active material ( Figure 7 CAM (S920) and (S940).

[0155] The solvent is removed by filtering the MXR2 mixture, and the dried product DPR (S920) can be obtained by drying. The drying temperature can be from 100°C to 300°C. The drying time can be from 5 hours to 15 hours. Residual solvent can be removed by drying.

[0156] The dried product DPR can be introduced into the furnace FRC and heat-treated (S940). The heat treatment temperature can be from 650°C to 1000°C. For example, the heat treatment temperature can be from 650°C to 900°C or from 650°C to 800°C. The heat treatment time can be from 5 hours to 30 hours. For example, the heat treatment time can be from 10 hours to 24 hours or from 10 hours to 20 hours. When the heat treatment conditions meet the above range, the finally prepared positive electrode active material can have a long cycle life and can reduce resistance change.

[0157] Although not shown, a lithium feedstock can be introduced prior to heat treatment. For example, the lithium feedstock may include lithium salts (such as lithium carbonate, lithium nitrate, lithium hydroxide, or lithium sulfate). As an example, the lithium feedstock can be introduced such that the molar percentage of lithium is 0.1 mol% to 10 mol% relative to the total molar percentage of elements other than lithium and oxygen in the lithium-nickel composite oxide. For example, the lithium feedstock can be introduced such that the molar percentage of lithium is 0.1 mol% to 8 mol% or 1 mol% to 6 mol% relative to the total molar percentage of elements other than lithium and oxygen in the lithium-nickel composite oxide. When lithium feedstock is introduced at the above amounts, the surface of the lithium-nickel composite oxide damaged during the coating process can be repaired. Therefore, the final prepared positive electrode active material can have a long cycle life and reduced resistance variation.

[0158] The present disclosure will be described in more detail below by way of examples. However, these examples are for illustrative purposes and the scope of the disclosure is not limited to these examples.

[0159] Example 1 Preparation Example 1: Formation of Lithium Nickel Composite Oxides As raw materials for nickel hydroxide, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and aluminum sulfate (Al2(SO4)3·16H2O) were dissolved in distilled water as a solvent in a molar ratio of 96.5:2:1.5 to prepare a mixed solution of metal raw materials. Ammonia water (NH4OH) dilution solution for complex formation and sodium hydroxide (NaOH) as a precipitant were prepared. The mixed solution of metal raw materials, ammonia water, and sodium hydroxide were introduced into a reactor. Sodium hydroxide was introduced 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 (NiSO4·6H2O). 0.965 Co 0.020 Al 0.015 (OH)2).

[0160] Nickel hydroxide and anhydrous lithium hydroxide (LiOH) were mixed in a molar ratio of 1:1.03, resulting in a lithium molar ratio relative to the total metallic content of the nickel hydroxide of 1.03. The mixture was then heat-treated at approximately 750°C for 15 hours under an oxygen atmosphere to form a lithium-nickel composite oxide (LiNi). 0.965 Co 0.020 Al 0.015 O2). Lithium-nickel composite oxides are secondary particles formed by the aggregation of primary particles, with an average particle size of approximately 12 μm.

[0161] Preparation Example 2: Coating of Lithium Nickel Composite Oxides A first aqueous solution comprising aluminum sulfate (Al2(SO4)3·16H2O) and sodium hydroxide (NaOH) is formed. A lithium-nickel composite oxide is added to the first aqueous solution. At this point, aluminum sulfate is added such that the molar percentage of aluminum is 0.5 mol% relative to the total molar percentage of elements other than lithium and oxygen in the lithium-nickel composite oxide. The mixture of the first aqueous solution and the lithium-nickel composite oxide is stirred for 5 minutes. A second aqueous solution comprising cobalt sulfate (CoSO4·7H2O) is added dropwise to the mixture over 30 minutes. At this point, cobalt sulfate is added such that the molar percentage of cobalt is 2 mol% relative to the total molar percentage of elements other than lithium and oxygen in the lithium-nickel composite oxide. The ratio of the molar percentage of aluminum sulfate added to the molar percentage of cobalt sulfate added is 0.25. The mixture is filtered and dried at 190°C for 10 hours to obtain a dried product. 6 mol% lithium hydroxide (LiOH) is mixed with the dried product. The mixture is heat-treated at 650°C for 15 hours to obtain the positive electrode active material.

[0162] Example 2 The positive electrode active material was prepared in the same manner as in Example 1, except that the total number of moles of added cobalt sulfate and aluminum sulfate was 1.5 mol%.

[0163] Example 3 The positive electrode active material was prepared in the same manner as in Example 1, except that the total number of moles of added cobalt sulfate and aluminum sulfate was 3.5 mol%.

[0164] Example 4 The positive electrode active material was prepared in the same manner as in Example 1, except that the total number of moles of added cobalt sulfate and aluminum sulfate was 4.5 mol%.

[0165] Comparison Example 1 A positive electrode active material coated only with cobalt was prepared. A lithium-nickel composite oxide was added to an aqueous solution comprising 6 wt% cobalt sulfate (CoSO4·7H2O) and stirred. Sodium hydroxide (NaOH) was added dropwise to the mixture. Therefore, the molar ratio of added aluminum sulfate to added cobalt sulfate was 0. Subsequently, filtration, drying, and heat treatment were performed in the same manner as in Example 1.

[0166] Comparison Example 2 A lithium-nickel composite oxide was added to an aqueous solution comprising 6 wt% cobalt sulfate (CoSO4·7H2O) and stirred for 5 minutes. An aqueous solution comprising aluminum sulfate (Al2(SO4)3·16H2O) and sodium hydroxide (NaOH) was added dropwise to the mixture over 30 minutes. Subsequently, filtration, drying, and heat treatment were performed in the same manner as in Example 1.

[0167] Comparison Example 3 A positive electrode active material in which cobalt and aluminum are dry-coated was prepared. In the absence of solvent, a lithium-nickel composite oxide, cobalt hydroxide (Co(OH)2), and aluminum oxide (Al2O3) were placed in a dry coating machine and mixed by stirring. Subsequently, heat treatment was performed in the same manner as in Example 1.

[0168] Manufacturing of positive electrode A slurry of positive electrode active material was prepared by mixing 96 wt% of positive electrode active material, 2 wt% of polyvinylidene fluoride binder, and 2 wt% of carbon nanotube conductive material in N-methylpyrrolidone solvent. The slurry was then coated onto an aluminum current collector, dried, and rolled to fabricate the positive electrode.

[0169] Manufacturing of lithium secondary batteries A positive electrode and a lithium metal counter electrode are used, and a separator with a polyethylene-polypropylene multilayer structure is placed between the positive electrode and the lithium metal counter electrode. As the electrolyte, a solution obtained by adding 1.0 M LiPF6 lithium salt to a solvent in which ethylene carbonate and diethyl carbonate are mixed in a 50:50 volume ratio is used. A coin-shaped half-cell is fabricated by injecting the electrolyte.

[0170] [Table 1]

[0171] Experimental Example 1: Structural and Component Analysis of Positive Electrode Active Material (1) Figure 16 It is a transmission electron microscope (TEM) image of a cross-section of the positive electrode active material according to Example 1 and a mapping result using energy dispersive X-ray spectroscopy (EDS).

[0172] Reference Figure 16 According to Example 1, the positive electrode active material includes a coating on the core, and the coating comprises both cobalt and aluminum. Furthermore, according to Example 1, the positive electrode active material includes a grain boundary coating, and the grain boundary coating comprises both cobalt and aluminum. As a result of mapping the grain boundary coating, cobalt and aluminum are uniformly present in the grain boundary coating, and the cobalt and aluminum in the grain boundary coating are present in substantially the same locations.

[0173] Experimental Example 2: Structural and Component Analysis of Positive Electrode Active Material (2) Figure 17 and Figure 18 The images are transmission electron microscopy (TEM) images of cross-sections of the positive electrode active materials according to Example 1 and Comparative Example 2, and mapping results using energy-dispersive X-ray spectroscopy (EDS). Figure 19a and Figure 19b The results of in-depth analysis of the cross-sections of the positive electrode active materials according to Example 1 and Comparative Example 2 are shown using transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). Figure 19a and Figure 19b It shows along Figure 17 and Figure 18 The results of in-depth analysis based on the arrow direction.

[0174] Reference Figures 17 to 1 9. As shown in Table 2, the point where the Al signal drops most sharply after its maximum peak is calculated as the second thickness of the second coating (TKC2), and the point where the Co signal drops most sharply after its maximum peak is calculated as the total thickness of the first and second coatings (TKC1+TKC2). Examples 2 through 4 and Comparative Example 1 are analyzed in the same manner.

[0175] In the case of the positive electrode active material according to Comparative Example 3, it was confirmed from the transmission electron microscopy (TEM) image of the cross-section that the coating CTL was relatively non-uniformly formed. As a result of the TEM image of the cross-section of the positive electrode active material according to Comparative Example 3 and the mapping results using energy-dispersive X-ray spectroscopy (EDS), the thickness of the coating CTL varied from approximately 2 nm to 60 nm, and the distribution of aluminum and cobalt in the coating CTL was non-uniform, making it impossible to designate a first coating CTL1 and a second coating CTL2. Furthermore, in the grain boundary coating, cobalt and aluminum were mainly distributed on the side relatively close to the surface of the positive electrode active material, in contrast to... Figure 16 Cobalt and aluminum were not observed at essentially the same locations, but at different locations, cobalt was found to be locally predominantly distributed and aluminum was found to be locally predominantly distributed.

[0176] [Table 2]

[0177] Experimental Example 3: Performance Evaluation of Lithium Secondary Batteries The evaluation includes the charging and discharging efficiency, capacity retention, and DC resistance of lithium secondary batteries based on the positive electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 3.

[0178] The coin-type batteries, according to the example and comparative examples, were initially charged under constant current (0.2C) and constant voltage (4.25V, 0.05C cutoff) conditions, allowed to rest for 10 minutes, and then discharged to 3.0V under constant current (0.2C) conditions for initial charge and discharge. Thereafter, 50 charge and discharge cycles were repeated at 1C / 1C. Capacity retention was calculated as the ratio of the discharge capacity to the initial discharge capacity per cycle (25 cycles and 50 cycles).

[0179] During constant current discharge, the DC resistance (DC-IR = ΔV / ΔI) is calculated as the ratio of the average voltage change (ΔV) to the average current change (ΔI), and the average value is shown as the result. The difference between the DC resistance in the 1st cycle and the DC resistance in the 50th cycle is shown as the ratio of the DC resistance in the 1st cycle to the DC resistance in the 1st cycle, as the DC resistance change. The results are shown in Table 3.

[0180] [Table 3]

[0181] Referring to Table 3, it is confirmed that the lithium secondary battery including the positive electrode active material according to Examples 1 to 4 has excellent capacity retention and small resistance variation with repeated charging and discharging.

[0182] Although embodiments of the present disclosure have been described with reference to the accompanying drawings, the present disclosure may be implemented in other specific forms without altering its technical concept or essential characteristics. Therefore, it should be understood that the above embodiments are illustrative in all respects and not restrictive.

Claims

1. A method for preparing a positive electrode active material, the method comprising the following steps: Formation of lithium-nickel composite oxides; as well as Coating the lithium-nickel composite oxide, The step of coating the lithium-nickel composite oxide includes: forming a first aqueous solution comprising an aluminum compound and an alkaline compound; forming a mixture comprising the lithium-nickel composite oxide and the first aqueous solution; adding a second aqueous solution comprising a cobalt compound to the mixture; and drying and heat treatment.

2. The method according to claim 1, wherein, The aluminum compound includes at least one selected from the group consisting of aluminum sulfate and sodium aluminate.

3. The method according to claim 1, wherein, The alkaline compound includes at least one selected from the group consisting of sodium hydroxide, lithium hydroxide, potassium hydroxide, and ammonia.

4. The method according to claim 1, wherein, The process of forming the mixture takes 3 to 30 minutes.

5. The method according to claim 1, wherein, The cobalt compound includes at least one selected from the group consisting of cobalt nitrate, cobalt sulfate, cobalt oxide, cobalt hydroxide, and cobalt carbonate.

6. The method according to claim 1, wherein, The step of adding the second aqueous solution, which includes the cobalt compound, to the mixture is carried out for 5 minutes to 1 hour.

7. The method according to claim 1, wherein, The heat treatment is carried out at a temperature of 650°C to 900°C.

8. The method according to claim 1, wherein, The aluminum compound is added such that the molar percentage of aluminum is 0.05 mol% to 2 mol% relative to the total molar percentage of elements other than lithium and oxygen in the lithium-nickel composite oxide, and The cobalt compound is added such that the molar amount of cobalt is 0.25 mol% to 4 mol% relative to the total molar amount of elements other than lithium and oxygen in the lithium-nickel composite oxide.

9. A positive electrode active material, said positive electrode active material comprising: Cores, including lithium-nickel composite oxides; as well as A coating, located on the core, comprises cobalt and aluminum. The coating comprises a first coating and a second coating on top of the first coating, and The aluminum content of the second coating is greater than that of the first coating.

10. The positive electrode active material according to claim 9, wherein, The core is a secondary particle formed by the aggregation of primary particles.

11. The positive electrode active material according to claim 9, wherein, The lithium-nickel composite oxide has a nickel content of 60 mol% or more among metals other than lithium.

12. The positive electrode active material according to claim 9, wherein, The lithium-nickel composite oxide includes cobalt, and The cobalt content of the lithium-nickel composite oxide is less than that of the coating.

13. The positive electrode active material according to claim 9, wherein, The lithium-nickel composite oxide includes aluminum, and The aluminum content of the lithium-nickel composite oxide is less than the aluminum content of the coating.

14. The positive electrode active material according to claim 9, wherein, In the coating, the molar ratio of aluminum to cobalt (C) Al / C Co The value ranges from 0.1 to 4.

15. The positive electrode active material according to claim 9, wherein, The total thickness of the first coating and the second coating is 25 nm to 60 nm.

16. The positive electrode active material according to claim 9, wherein, The ratio of the thickness of the second coating to the thickness of the first coating is 1 to 5.

17. The positive electrode active material according to claim 9, wherein, The ratio of the total thickness of the first coating and the second coating to the thickness of the second coating is 1.2 to 2.

18. The positive electrode active material according to claim 9, wherein, The thickness of the second coating is 20 nm to 40 nm.

19. The positive electrode active material according to claim 9, wherein, The average particle size of the positive electrode active material is 5 μm to 25 μm.

20. A lithium secondary battery, the lithium secondary battery comprising the positive electrode active material according to claim 9.

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