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

Abstract

The present invention relates to a method for preparing a positive electrode active material, a positive electrode active material prepared using same, and a lithium secondary battery comprising same and, more specifically, to a method for preparing a positive electrode active material, the method comprising: forming a lithium nickel-based composite oxide; and coating the lithium nickel-based composite oxide. Forming the lithium nickel-based composite oxide comprises: forming a first aqueous solution comprising an aluminum compound and a basic 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

Method for manufacturing a cathode active material, cathode active material manufactured using the same, and lithium secondary battery including the same

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

[0002] The recent rapid proliferation of battery-powered electronic devices, such as mobile phones, laptops, and electric vehicles, has led to a rapid increase in demand for high-energy density, high-capacity secondary batteries. Accordingly, active research and development is underway to improve the performance of lithium secondary batteries.

[0003] A lithium secondary battery is a battery that includes a positive electrode and a negative electrode that contain active materials capable of intercalating and deintercalating lithium ions, and an electrolyte, and produces electrical energy through oxidation and reduction reactions when lithium ions are intercalated / deintercalated from the positive electrode and negative electrode.

[0004] The problem to be solved by the present invention is to provide a method for manufacturing a positive electrode active material having high capacity, excellent capacity retention rate and low resistance change even after repeated charge and discharge.

[0005] The problem to be solved by the present invention is to provide a positive electrode active material having excellent capacity retention and low resistance change even after repeated charge and discharge, and a lithium secondary battery including the same.

[0006] A method for manufacturing a cathode active material according to one embodiment of the present invention includes forming a lithium nickel-based composite oxide and coating the lithium nickel-based composite oxide, wherein coating the lithium nickel-based composite oxide may include: forming a first aqueous solution including an aluminum compound and a basic 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.

[0007] According to one embodiment of the present invention, a cathode active material comprises: a core comprising a lithium nickel-based composite oxide; and a coating layer positioned on the core and comprising cobalt and aluminum, wherein the coating layer comprises a first coating layer and a second coating layer on the first coating layer, and the aluminum content of the second coating layer may be greater than the aluminum content of the first coating layer.

[0008] A lithium secondary battery according to one embodiment of the present invention may include the positive electrode active material described above.

[0009] By using a method for manufacturing a positive electrode active material according to one embodiment of the present invention, it is possible to manufacture a positive electrode active material having a high capacity, a long lifespan, and a low resistance change due to repeated charge and discharge cycles, and a lithium secondary battery including the same.

[0010] FIG. 1 is a schematic diagram illustrating a lithium secondary battery according to embodiments of the present invention.

[0011] Figures 2 to 5 are cross-sectional views schematically showing a lithium secondary battery according to one embodiment.

[0012] Figure 6 is a cross-sectional view of an anode according to embodiments of the present invention.

[0013] Figures 7 to 9 are schematic diagrams illustrating positive electrode active materials according to embodiments of the present invention. Figure 8 is an enlarged view of area M of Figure 7.

[0014] Figure 10 is a flow chart for explaining a method for manufacturing a positive electrode active material according to embodiments of the present invention.

[0015] Figure 11 is a flowchart for explaining step S100 of a method for manufacturing a positive electrode active material according to embodiments of the present invention.

[0016] FIG. 12 is a schematic diagram illustrating steps S300 and S500 of a method for manufacturing a positive electrode active material according to embodiments of the present invention.

[0017] Figure 13 is a schematic diagram for explaining step S700 of a method for manufacturing a positive electrode active material according to embodiments of the present invention.

[0018] FIG. 14 and FIG. 15 are schematic diagrams for explaining step S900 of a method for manufacturing a positive electrode active material according to embodiments of the present invention.

[0019] Figures 16 and 17 are transmission electron microscopy (TEM) images and mapping results using energy dispersive spectroscopy (EDS) for a cross-section of a positive electrode active material according to Example 1.

[0020] Figure 18 shows a transmission electron microscope (TEM) image and mapping results using energy dispersive spectroscopy (EDS) for a cross-section of a positive electrode active material according to Comparative Example 2.

[0021] Figures 19a and 19b show the results of depth profiling of the cross-sections of the positive electrode active materials according to Example 1 and Comparative Example 2 using transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS).

[0022] To fully understand the structure 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, but can be implemented in various forms and subject to various modifications. However, the description of these embodiments is provided solely to ensure a complete disclosure of the present invention and to fully inform those skilled in the art of the invention of the scope of the invention.

[0023] In this specification, when a component is referred to as being on another component, it means that it can be formed directly on the other component, or a third component may be interposed between them. Furthermore, in the drawings, the thicknesses of the components are exaggerated for the sake of clarity. Parts designated by the same reference numerals throughout the specification represent the same components.

[0024] Embodiments described herein will be described with reference to cross-sectional and / or plan views, which are ideal illustrations of the present invention. In the drawings, the thicknesses of films and regions are exaggerated for the purpose of effectively explaining the technical contents. Accordingly, the regions illustrated in the drawings have a schematic nature, and the shapes of the regions illustrated in the drawings are intended to illustrate specific shapes of regions of the device and are not intended to limit the scope of the invention. Although terms such as first, second, and third are used to describe various components in various embodiments of the present specification, these components should not be limited by such terms. These terms are used only to distinguish one component from another. The embodiments described and illustrated herein also include complementary embodiments thereof.

[0025] The terminology used herein is for the purpose of describing embodiments and is not intended to limit the present invention. In this specification, the singular also includes the plural unless specifically stated otherwise. As used herein, the words "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components.

[0026]

[0027] Figure 1 is a schematic conceptual diagram illustrating a lithium secondary battery according to embodiments of the present invention. Referring to Figure 1, the lithium secondary battery may include a positive electrode (10), a negative electrode (20), a separator (30), and an electrolyte (ELL).

[0028] The positive electrode (10) and the negative electrode (20) may be spaced apart from each other with a separator (30) therebetween. The separator (30) may be placed 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 (ELL). The positive electrode (10), the negative electrode (20), and the separator (30) may be impregnated in the electrolyte (ELL).

[0029] The electrolyte (ELL) may be a medium for transferring lithium ions between the positive electrode (10) and the negative electrode (20). Within the electrolyte (ELL), the lithium ions may pass through the separator (30) and move toward the positive electrode (10) or the negative electrode (20).

[0030]

[0031] Bipolar (10)

[0032] A positive electrode (10) for a lithium secondary battery may include a current collector (COL1) and a positive electrode active material layer (AML1) formed on the current collector (COL1). The positive electrode active material layer (AML1) includes a positive electrode active material and may further include a binder and / or a conductive material.

[0033] For example, the anode (10) may further include an additive that can act as a sacrificial anode.

[0034] The content of the positive electrode active material in the positive electrode active material layer (AML1) may be 90 wt% to 99.5 wt% with respect to 100 wt% of the positive electrode active material layer (AML1). The contents of the binder and the conductive material may each be 0.5 wt% to 5 wt% with respect to 100 wt% of the positive electrode active material layer (AML1).

[0035] The above binder serves to adhere the positive electrode active material particles well to each other and also to adhere the positive electrode active material well to the current collector (COL1). Representative examples of the binder 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, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0036] The conductive material is used to provide conductivity to the electrode, and any material that does not cause chemical changes and is electronically conductive can be used 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 containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0037] Al can be used as the current collector (COL1), but is not limited thereto.

[0038]

[0039] positive electrode active material

[0040] As the cathode active material in the cathode active material layer (AML1), a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound) can be used. Specifically, one or more of a composite oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof can be used.

[0041] The above 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 compound, cobalt-free nickel-manganese-based oxide, or a combination thereof.

[0042] As an 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 eO2(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 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).

[0043] 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; L 1 is Mn, Al or a combination thereof.

[0044] For example, the cathode active material may be a high-nickel cathode 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 and 99 mol% or less, based on 100 mol% of metals excluding lithium in a lithium transition metal composite oxide. The high-nickel cathode active material can realize high capacity and thus can be applied to high-capacity, high-density lithium secondary batteries.

[0045]

[0046] Cathode (20)

[0047] A negative electrode (20) for a lithium secondary battery includes a current collector (COL2) and a negative electrode active material layer (AML2) positioned 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.

[0048] For example, the negative active material layer (AML2) may include 90 to 99 wt% of the negative active material, 0.5 to 5 wt% of the binder, and 0 to 5 wt% of the conductive material.

[0049] The above binder serves to adhere the negative electrode active material particles well to each other and also to adhere the negative electrode active material well to the current collector (COL2). The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0050] 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, or combinations thereof.

[0051] The above-mentioned aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluoroelastomer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0052] When using an aqueous binder as the above-mentioned negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li.

[0053] The above dry binder is a polymeric material capable of being fiberized, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0054] The conductive material is used to provide conductivity to the electrode, and any material that does not cause chemical changes and is electronically conductive can be used in the battery. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metal-based materials in the form of metal powder or metal fibers, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0055] The current collector (COL2) may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with a conductive metal, and combinations thereof.

[0056]

[0057] Negative active material

[0058] The negative active material in the negative active material layer (AML2) includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0059] The material capable of reversibly intercalating / deintercalating the lithium ions may include a carbon-based negative electrode active material, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fibrous form, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0060] As the above lithium metal alloy, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0061] As the material capable of doping and dedoping the lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material may be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x ≤ 2), a Si-Q alloy (wherein Q is selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements (excluding Si), Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0062] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, the composite may include secondary particles (cores) in which silicon primary particles are assembled and an amorphous carbon coating layer (shell) positioned on the surface of the secondary particles. The amorphous carbon may also be positioned 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 and present in an amorphous carbon matrix.

[0063] 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 layer positioned on the surface of the core.

[0064] The above Si-based negative electrode active material or Sn-based negative electrode active material can be used in a mixture with a carbon-based negative electrode active material.

[0065]

[0066] Separator (30)

[0067] Depending on the type of lithium secondary battery, a separator (30) may be present between the positive electrode (10) and the negative electrode (20). As the separator (30), a multilayer film of two or more layers of polyethylene, polypropylene, polyvinylidene fluoride, or these may be used, and of course, a mixed multilayer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may be used.

[0068] The separator (30) may include a porous substrate and a coating layer including an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0069] The above porous substrate may be a polymer film formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyarylether ketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or a copolymer or mixture of two or more thereof.

[0070] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0071] The above inorganic materials are Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, It may include inorganic particles selected from, but not limited to, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0072] The organic and inorganic substances may be mixed and present in one coating layer, or a coating layer including an organic substance and a coating layer including an inorganic substance may be present in a laminated form.

[0073]

[0074] Electrolyte (ELL)

[0075] The electrolyte (ELL) for a lithium secondary battery contains a non-aqueous organic solvent and a lithium salt.

[0076] The above non-aqueous organic solvent acts as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0077] The above non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0078] Examples of the above carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0079] 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.

[0080] Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. In addition, examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol, and examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include 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.

[0081] The above non-aqueous organic solvents can be used alone or in combination of two or more.

[0082] In addition, when using a carbonate solvent, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed in a volume ratio of 1:1 to 1:9.

[0083] The above lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions in the battery, enabling the basic operation of a lithium secondary battery and promoting the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0084]

[0085] lithium secondary battery

[0086] Lithium secondary batteries can be classified into cylindrical, square, pouch, coin, etc. types according to their shapes. FIGS. 2 to 5 are schematic diagrams illustrating lithium secondary batteries according to one embodiment, wherein FIG. 2 can be said to be a cylindrical battery, FIG. 3 a square battery, and FIGS. 4 and 5 a pouch battery. Referring to FIGS. 2 to 4, a lithium secondary battery (100) may include an electrode assembly (40) having a separator (30) interposed between a positive electrode (10) and a negative electrode (20), and a case (50) in which the electrode assembly (40) is built. The positive electrode (10), the negative electrode (20), and the separator (30) may be impregnated with an electrolyte (not shown). The lithium secondary battery (100) may include a sealing member (60) that seals the case (50) as shown in FIG. 2. In addition, in FIG. 3, the lithium secondary battery (100) may include a positive lead tab (11), a positive terminal (12), a negative lead tab (21), and a negative terminal (22). As in FIGS. 4 and 5, the lithium secondary battery (100) may include electrode tabs (70), i.e., a positive tab (71) and a negative tab (72), which serve as electrical paths for inducing current formed in the electrode assembly (40) to the outside.

[0087]

[0088] A lithium secondary battery according to one embodiment of the present invention can be applied to automobiles, mobile phones, and / or various types of electrical devices, but the present invention is not limited thereto.

[0089]

[0090] Hereinafter, the anode (10) according to embodiments of the present invention will be described in detail.

[0091]

[0092] Bipolar (10)

[0093] Figure 6 is a cross-sectional view of an anode according to embodiments of the present invention. For convenience of explanation, the same details as those described with reference to Figures 1 to 5 will be omitted below, and differences will be described in detail.

[0094] 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) to be described later, and may further include a binder and / or a conductive material.

[0095] The contents of the cathode active material (CAM), binder, conductive material, and current collector (COL1) are as described above.

[0096]

[0097] Cathode active material (CAM)

[0098] Figures 7 to 9 are cross-sectional views illustrating positive electrode active materials according to embodiments of the present invention. Figure 8 is an enlarged view of area M of Figure 7.

[0099] Referring to FIG. 7, the positive electrode active material (CAM) is in a polycrystal form and may include secondary particles in which at least two or more primary particles (PRP) are aggregated.

[0100] The cathode active material (CAM) may be spherical or oval in shape.

[0101] The average particle diameter (d) of the positive electrode active material (CAM) may be 5 μm to 25 μm. For example, the average particle diameter (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 diameter (d) of the positive electrode active material (CAM) may be obtained by randomly selecting about 30 positive electrode active materials (CAM) in the form of secondary particles from an electron microscope photograph of the positive electrode active material (CAM) and measuring the particle diameter, and taking the diameter of the particles having a cumulative volume of 50% by volume from the particle size distribution as the average particle diameter.

[0102] The cathode active material (CAM) may include a core (COR) and a coating layer (CTL).

[0103] The core (COR) is in the form of a polycrystal and may include secondary particles formed by agglomeration of at least two primary particles (PRP).

[0104] 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 content of nickel (Ni) included in the lithium nickel-based composite oxide is not limited.

[0105] For example, the lithium nickel-based composite oxide may be a lithium nickel-based composite oxide containing a high nickel (Ni) content. For example, the lithium nickel-based composite oxide may be a lithium nickel-based composite oxide in which the nickel (Ni) content among 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, the lithium nickel-based composite oxide may be a lithium nickel-based 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 satisfies the above-described range, the cathode active material (CAM) can realize high capacity and high performance.

[0106] For example, a lithium nickel-based composite oxide can be represented by the chemical formula 1 below.

[0107] [Chemical Formula 1]

[0108] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1

[0109] In the above 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, and 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.

[0110] For example, in the above 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.

[0111] For example, x1+y1+z1=1.

[0112] For example, a 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.

[0113] [Chemical Formula 2]

[0114] Li a2 Ni x2 Co y2 M 3 z2 O 2-b2 X b2

[0115] In the above 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, 및 0≤b2≤0.1이고, 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.

[0116] For example, in the above 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.

[0117] For example, x2+y2+z2=1.

[0118] For example, a lithium nickel-based composite oxide may be represented by the following chemical formula 3. The compound represented by the chemical formula 3 may be lithium nickel cobalt aluminum oxide or lithium nickel cobalt manganese oxide.

[0119] [Chemical Formula 3]

[0120] Li a3 Ni x3 Co y3 M 4 z3 M 5 w3 O 2-b3 X b3

[0121] In the above 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, and M 4 is one or more elements selected from the group consisting of Al and Mn, and M 5 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.

[0122] For example, in the above 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.

[0123] For example, x3+y3+z3+w3=1.

[0124] The coating layer (CTL) may be positioned on the core (COR). The coating layer (CTL) may be positioned 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 through component analysis using EDS. By including the coating layer (CTL), the cathode active material (CAM) may be structurally stable even when charge and discharge are repeated, side reactions on the surface of the core (COR) may be suppressed, and the room temperature and high temperature life characteristics of the cathode active material (CAM) may be improved.

[0125] For example, 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 include other metal or non-metal elements in addition to cobalt. For example, the cobalt-containing compound may further include lithium, manganese, and / or nickel. For example, the cobalt-containing compound may be lithium cobalt oxide.

[0126] For example, the 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 include other metallic or non-metallic elements in addition to aluminum. For example, the aluminum-containing compound may include lithium, manganese, and / or nickel. For example, the aluminum-containing compound may be lithium aluminate.

[0127] The coating layer (CTL) and the core (COR) can be distinguished by performing depth profiling on the cathode active material (CAM) using transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). In the present specification, in the EDS results showing the cobalt signal (Co signal) obtained by scanning the cathode active material (CAM) in the direction from the outermost edge toward the center of the cross-section of the CAM, the point where the cobalt signal (Co signal) shows the most rapid decrease after the maximum peak can be defined as the boundary of the coating layer (CTL) and the core (COR) (see Fig. 19b). For example, the size of the signal can be proportional to the content. For example, the content can be atomic%.

[0128] The total content of cobalt and aluminum within the coating layer (CTL) may be greater than the total content of cobalt and aluminum within the core (COR). That is, the total content of cobalt and aluminum within the coating layer (CTL) may be greater than the total content of cobalt and aluminum within the lithium nickel-based composite oxide. For example, the total content may be atomic%.

[0129] The cobalt content in the coating layer (CTL) may be greater than the cobalt content in the core (COR). The aluminum content in the coating layer (CTL) may be greater than the aluminum content in the core (COR). That is, the respective contents of cobalt and aluminum in the coating layer (CTL) may be greater than the respective contents of cobalt and aluminum in the lithium nickel-based composite oxide. For example, the contents may be atomic%.

[0130] For example, the lithium nickel-based composite oxide may include cobalt, but the content of cobalt in the lithium nickel-based composite oxide may be less than the content of cobalt in the coating layer (CTL). For example, the content may be atomic%. Meanwhile, the lithium nickel-based composite oxide may substantially not include aluminum, and thus the content of aluminum in the lithium nickel-based composite oxide may be less than the content of aluminum in the coating layer (CTL). For example, substantially not including may mean including a content of 100 ppm or less.

[0131] As another example, the lithium nickel-based composite oxide may include 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).

[0132] The molar ratio of aluminum to cobalt in the coating layer (CTL) 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 ) may be 0.1 to 3, 0.1 to 1, or 0.1 to 0.5. The content of cobalt, the content of aluminum, and the molar ratio (C) in the coating layer (CTL) Al / C Co ) satisfies the above-described range, the positive electrode active material (CAM) can have a long lifespan and reduce the amount of change in resistance even when repeated charging and discharging are performed.

[0133] Referring to FIG. 8, the coating layer (CTL) may include a first coating layer (CTL1) and a second coating layer (CTL2).

[0134] The first coating layer (CTL1) and the second coating layer (CTL2) can be distinguished by performing depth profiling on the positive electrode active material (CAM) using transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). In the present specification, in the EDS results showing the signal of aluminum (Al signal) obtained by scanning the positive electrode active material (CAM) in the direction from the outermost edge toward the center of the cross-section of the CAM, the point where the signal of aluminum (Al signal) shows the most rapid 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. 19a). For example, the size of the signal can be proportional to the content. For example, the content can be atomic%.

[0135] The content of aluminum in the second coating layer (CTL2) may be greater than the content of aluminum in the first coating layer (CTL1). The content of aluminum in the first coating layer (CTL1) may be substantially the same as the content of aluminum in the core (COR). The substantially same content may be defined as a difference of 10% or less between the average value of the aluminum signal (Al signal) of the second coating layer (CTL2) and the average value of the aluminum signal (Al signal) of the core (COR) in the EDS result showing the aluminum signal (Al signal) obtained by scanning the positive electrode active material (CAM) in a direction from the outermost surface to the center of the positive electrode active material (CAM). For example, the content may be atomic%.

[0136] 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. When the sum of the first and second thicknesses (TKC1+TKC2) satisfies the above-described range, the positive electrode active material (CAM) may have a long lifespan even with repeated charge and discharge, and may reduce the amount of change in resistance.

[0137] The ratio of the second thickness to the first thickness (TKC2 / TKC1) may be 1 to 5. For example, the ratio of the second thickness to the first thickness (TKC2 / TKC1) may be 1.4 to 3.44, or 2 to 4.

[0138] 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.

[0139] The ratio of the sum of the first and second thicknesses to the second thickness ((TKC1+TKC2) / TKC2) may 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) may be 1.2 to 2, 1.25 to 1.7, or 1.25 to 1.5.

[0140] 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 second thickness to the sum of the first and second thicknesses ((TKC1+TKC2) / TKC2) satisfy the ranges described above, the positive electrode active material (CAM) can have a long lifespan and reduce the amount of change in resistance even when charge and discharge are repeated.

[0141] The first thickness (TKC1) may be a value obtained by subtracting the second thickness (TKC2) from the sum of the first and second thicknesses (TKC1 + 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. When the second thickness (TKC2) satisfies the above-described range, the positive electrode active material (CAM) may have a long lifespan and reduce the amount of change in resistance even when repeated charge and discharge are performed.

[0142] 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 of the primary particles (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 interface between the primary particles (see PRP in FIG. 7) inside the positive electrode active material (CAM). In other words, the grain boundary coating layer may mean that it is coated on the grain boundaries inside the positive electrode active material (CAM). The inside of the positive electrode active material (CAM) may mean the entire inside of the positive electrode active material (CAM) excluding the surface of the positive electrode active material (CAM). For example, it may mean a region from a depth of about 10 nm to the entire inside from the outermost surface of the positive electrode active material (CAM), or from a depth of 10 nm to a depth of about 2 μm.

[0143] 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 a single location. For example, mapping results using energy dispersive spectroscopy (EDS) may show that the cobalt and aluminum within the grain boundary coating layer may exist at substantially the same location.

[0144] By including an additional grain boundary coating layer in the cathode active material (CAM), structural stability is enhanced, uniform and even coating is induced on the surface, and the coating content on the surface is appropriately controlled, so that the initial charge / discharge efficiency and life characteristics can be improved without increasing resistance.

[0145] Referring to FIG. 9, the positive electrode active material (CAM) may include a first region (RG1) and a second region (RG2).

[0146] The first region (RG1) may be located at the center of the positive electrode active material (CAM). The first region (RG1) may be defined as a region in the positive electrode active material (CAM) excluding the second region (RG2).

[0147] The second region (RG2) may be located at the periphery of the positive electrode active material (CAM). The second region (RG2) may surround the first region (RG1). In the present specification, the second region (RG2) may be defined as a region from the outermost edge of the positive electrode active material (CAM) to a depth at which components can be analyzed using energy dispersive spectroscopy (EDS). The depth at which components can be analyzed using energy dispersive spectroscopy (EDS) may be several μm. For example, the depth at which components can be analyzed using energy dispersive spectroscopy (EDS) may be about 1 μm. As an example, the second region (RG2) may be defined as a region having a thickness (TKR) of about 1 μm in a direction from the outermost edge of the positive electrode active material (CAM) toward the center.

[0148] The cathode active material (CAM) including the first region (RG1) and the second region (RG2) may include nickel (Ni), cobalt (Co), and aluminum (Al). For 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).

[0149] 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 spectroscopy (EDS), respectively. The contents of nickel (Ni), cobalt (Co), and aluminum (Al) respectively derived from energy dispersive spectroscopy (EDS) (N Ni , N Co , N Al ) can be expressed in atomic%. The content of nickel (Ni), cobalt (Co) and aluminum (Al) respectively (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).

[0150] The content ratio of nickel to aluminum in the first region (RG1) (N Ni / N Al ) is the content ratio of nickel to aluminum in the second region (RG2) (N Ni / N Al ) can be greater than.

[0151] For 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) may be 46 or more, 48 or more, or 50 or more, and may 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.

[0152] For 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 ) may be 8 to 45, 12 to 45, or 15 to 42.

[0153] The first region (RG1) and the second region (RG1) each have a content ratio of nickel to aluminum (N) in the range described above. Ni / N Al ), the positive electrode active material (CAM) can have a long lifespan and reduce the amount of change in resistance even with repeated charge and discharge.

[0154] The content ratio of cobalt to aluminum in the second region (RG2) (N Co / N Al ) may 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. The content ratio of cobalt to aluminum in the second region (RG2) (N Co / N Al ) satisfies the above-described range, the positive electrode active material (CAM) can have a long lifespan and reduce the amount of change in resistance even when repeated charging and discharging are performed.

[0155]

[0156] The positive electrode (10) and the lithium secondary battery including the positive electrode active material (CAM) according to embodiments of the present invention may have excellent life characteristics and may have small changes in resistance due to repeated charge and discharge. For example, the positive electrode (10) and the lithium secondary battery including the positive electrode active material (CAM) according to embodiments of the present invention may have a capacity retention rate of 95% or more when the charge and discharge cycle is repeated 50 times under 1C / 1C conditions. In addition, the positive electrode (10) and the lithium secondary battery including the positive electrode active material (CAM) according to embodiments of the present invention may have a resistance change amount of 60Ω or less, or 35Ω or less, even when the charge and discharge cycle is repeated 50 times under 1C / 1C conditions.

[0157]

[0158] Method for manufacturing positive electrode active material (CAM)

[0159] FIG. 10 is a flowchart illustrating a method for manufacturing a positive electrode active material (CAM) according to embodiments 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.

[0160] Referring to FIG. 10, a method for manufacturing a positive electrode active material (CAM) according to embodiments of the present invention may include forming a lithium nickel-based composite oxide (S100) and coating the lithium nickel-based composite oxide.

[0161] Coating a 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 and 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).

[0162]

[0163] Referring to FIG. 11, forming a lithium nickel-based composite oxide (S100) may include forming a nickel-based hydroxide (S120); mixing a nickel-based hydroxide and a lithium raw material (S140); and heat treating (S160).

[0164] Nickel-based hydroxides may contain transition metals. The transition metals include nickel (Ni), and M of the above-described chemical formula 1. 1 and M 2 may further include. For 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.

[0165] Nickel-based hydroxides can be obtained through a coprecipitation method (S120). For example, the coprecipitation method may involve dissolving a transition metal raw material in a solvent such as distilled water, and continuously introducing a transition metal salt solution into a reactor together with a chelating agent and / or a basic aqueous solution to cause precipitation. After collecting the precipitate in a slurry form, the slurry solution is filtered and dried to obtain nickel-based hydroxides, which are metal composite oxides.

[0166] The transition metal raw material may include a salt of the transition metal described above. Examples of the transition metal salt include sulfates, nitrates, acetates, halides, and hydroxides, and is not particularly limited as long as it can be dissolved in a solvent. For example, the transition metal raw material may include a nickel salt, a cobalt salt, and an aluminum salt. In another example, the transition metal raw material may include a nickel salt, a cobalt salt, and a manganese salt. The transition metal raw materials may be mixed in a controlled molar ratio so that the cathode active material exhibits high-capacity characteristics.

[0167] Nickel-based hydroxide can be mixed with a lithium raw material at a certain ratio (S140). For example, the nickel-based hydroxide and lithium raw material can be mixed at a molar ratio of approximately 1:1. The lithium raw material is not particularly limited as long as it is a material commonly used in the manufacture of positive electrode active materials. For example, the lithium raw material may include a lithium salt such as lithium carbonate, lithium nitrate, lithium hydroxide, or lithium sulfate.

[0168] A mixture of nickel-based hydroxide and lithium raw materials can be placed in a furnace (FRC) and heat-treated (S160). The heat treatment temperature can be 700°C to 1,000°C. For example, the heat treatment temperature can be 700°C to 800°C. The heat treatment can be performed in an oxidizing atmosphere such as air or oxygen. The heat treatment time can be 10 to 30 hours. For example, the heat treatment time can be 10 to 20 hours. For example, a preliminary firing at 150°C to 800°C can be additionally performed before the heat treatment.

[0169] For example, a grinding process can be additionally performed after heat treatment. Through the grinding process, a lithium nickel-based composite oxide having a desired average particle size can be obtained.

[0170] 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%. That is, 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.

[0171]

[0172] Referring to FIGS. 12 to 15, a lithium nickel-based composite oxide (NBO) can be coated.

[0173] Referring to Fig. 12, a first aqueous solution (AQ1) containing an aluminum compound and a basic compound can be formed (S300).

[0174] An aluminum compound may be the raw material for the aluminum coating. 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 present invention is not particularly limited to the examples described.

[0175] The aluminum compound may be added so that the molar number of aluminum is 0.05 mol% to 2 mol% relative to the total molar number of elements excluding lithium and oxygen in the lithium nickel-based composite oxide. For example, the aluminum compound may be added so that the molar number 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 number of elements excluding lithium and oxygen in the lithium nickel-based composite oxide. When the amount of the aluminum compound added satisfies the above-described range, the finally manufactured positive electrode active material can have a long lifespan and reduce the amount of change in resistance.

[0176] 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.

[0177] For example, the first aqueous solution (AQ1) may include anionic aluminum. By first producing anionic aluminum, the final manufactured positive electrode active material can have a long lifespan and reduce changes in resistance.

[0178] A mixture (MXR1) can be formed by mixing the first aqueous solution (AQ1) and a lithium nickel-based composite oxide (NBO) (S500). The mixing can be performed using a stirrer.

[0179] Mixing can be carried out for 3 to 30 minutes, but is not limited to the time stated, as long as it is sufficient time to form a homogeneous mixture (MXR1).

[0180]

[0181] Referring to FIG. 13, a second aqueous solution (AQ2) may be added to the mixture (MXR1) (S700). The second aqueous solution (AQ2) may include a cobalt compound.

[0182] The cobalt compound may be a cobalt coating raw material. For example, it may include at least one selected from the group consisting of cobalt nitrate, cobalt sulfate, cobalt oxide, cobalt hydroxide, and cobalt carbonate. However, the examples described herein are not particularly limited.

[0183] The cobalt compound may be added so that the mole number of cobalt is 0.25 mol% to 4 mol% relative to the total mole number of elements excluding lithium and oxygen in the lithium nickel-based composite oxide. For example, the cobalt compound may be added so that the mole number 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 mole number of elements excluding lithium and oxygen in the lithium nickel-based composite oxide. When the amount of the cobalt compound added satisfies the above-described range, the finally manufactured positive electrode active material can have a long lifespan and reduce the amount of change in resistance.

[0184] The molar ratio of the amount of the aluminum compound added to the cobalt compound may be 0.1 to 4. For example, the molar ratio of the amount of the aluminum compound added to the 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 the aluminum compound added to the cobalt compound satisfies the above-described range, the finally manufactured positive electrode active material may have a long lifespan and reduce the amount of change in resistance.

[0185] For example, the second aqueous solution (AQ2) can be dropped into the mixture (MXR1). That is, the cobalt coating raw material in the second aqueous solution (AQ2) can be slowly supplied to the mixture (MXR1).

[0186] The addition of the second aqueous solution (AQ2) can be performed for 5 minutes to 1 hour. For example, the addition of the second aqueous solution (AQ2) can be performed for 10 minutes to 50 minutes, or for 20 minutes to 40 minutes.

[0187] If necessary, precipitant, pH adjuster, etc. can be added to the mixture (MXR1).

[0188] In this step, the precipitation of aluminum and cobalt may occur simultaneously. Aluminum and cobalt may exist in the form of an aluminum-containing compound and a cobalt-containing compound, respectively. For example, the aluminum-containing compound may include aluminum hydroxide, and the cobalt-containing compound may include cobalt hydroxide, and the like. However, the present invention is not limited to the examples described. Aluminum and cobalt may be precipitated on the surface of the lithium nickel-based composite oxide (NBO). Thus, the mixture (MXR2) may include a lithium nickel-based composite oxide (NBO) on which aluminum and cobalt are precipitated on the surface.

[0189] The coating of the lithium nickel-based composite oxide (NBO) according to embodiments of the present invention may be wet coating. By performing wet coating through the steps described above, a coating layer (CTL) having a uniform thickness can be formed on the lithium nickel-based composite oxide (NBO). In addition, 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.

[0190] Coating of a lithium nickel-based composite oxide (NBO) according to embodiments of the present invention can be performed by first adding an aluminum compound and then adding a cobalt compound. Thus, a coating layer having the structure described above (CTL in FIG. 7) can be formed, and the resulting positive electrode active material can have a long lifespan and reduce resistance variation.

[0191]

[0192] Referring to FIGS. 14 and 15, the mixture (MXR2) can be dried and heat-treated to form the above-described positive electrode active material (CAM of FIG. 7) (S920 and S940).

[0193] The mixture (MXR2) can be filtered to remove the solvent, and dried to obtain a dried product (DPR) (S920). The drying temperature can be between 100°C and 300°C. The drying time can be between 5 and 15 hours. The residual solvent can be removed through drying.

[0194] The dried product (DPR) can be heat-treated by placing it in a furnace (FRC) (S940). The heat-treatment temperature can be 650°C to 1000°C. For example, the heat-treatment temperature can be 650°C to 900°C, or 650°C to 800°C. The heat-treatment time can be 5 hours to 30 hours. For example, the heat-treatment time can be 10 hours to 24 hours, or 10 hours to 20 hours. When the heat-treatment conditions satisfy the above-described range, the finally manufactured positive electrode active material can have a long lifespan and reduce the amount of resistance change.

[0195] Although not shown, a lithium raw material may be additionally added before the heat treatment and heat treatment may be performed. For example, the lithium raw material may include a lithium salt such as lithium carbonate, lithium nitrate, lithium hydroxide, or lithium sulfate. For example, the lithium raw material may be added so that the molar number of lithium is 0.1 mol% to 10 mol% based on the total molar number of elements excluding lithium and oxygen in the lithium nickel-based composite oxide. For example, the lithium raw material may be added so that the molar number of lithium is 0.1 mol% to 8 mol%, or 1 mol% to 6 mol% based on the total molar number of elements excluding lithium and oxygen in the lithium nickel-based composite oxide. When the lithium raw material is added in the amount described above, the surface of the lithium nickel-based composite oxide damaged during the coating process can be repaired. As a result, the final manufactured positive electrode active material can have a long lifespan and the amount of change in resistance can be reduced.

[0196]

[0197] Hereinafter, the present invention will be described in more detail through examples. However, these examples are intended to exemplify the present invention and the scope of the present invention is not limited to these examples.

[0198]

[0199] Example 1

[0200] Manufacturing Example 1: Formation of lithium nickel-based composite oxide

[0201] As raw materials for nickel-based hydroxides, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and aluminum sulfate (Al₂(SO₄)₃·16H2O) were dissolved in distilled water as a solvent at a molar ratio of 96.5:2:1.5 to prepare a mixture of metal raw materials. To form a complex, a diluted ammonia aqueous solution (NH4OH) and sodium hydroxide (NaOH) were prepared as a precipitant. The mixture of metal raw materials, ammonia aqueous solution, 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 about 20 hours while stirring the mixture in the reactor. The product was filtered, washed, and dried to obtain nickel-based hydroxides (Ni 0.965 Co 0.020 Al 0.015 (OH)2) was obtained.

[0202] 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 of nickel hydroxide was 1.03. The mixture was heat-treated at a temperature of about 750°C for 15 hours under an oxygen atmosphere to obtain a lithium nickel composite oxide (LiNi 0.965 Co 0.020 Al 0.015 O2) was formed. The lithium nickel-based composite oxide was a secondary particle formed by agglomeration of primary particles, and the average particle diameter was approximately 12 μm.

[0203]

[0204] Manufacturing Example 2: Coating of lithium nickel-based composite oxide

[0205] A first aqueous solution containing aluminum sulfate (Al₂(SO₄)₃·16H2O) and sodium hydroxide (NaOH) was formed. A lithium nickel-based composite oxide was added to the first aqueous solution. At this time, aluminum sulfate was added so that the molar number of aluminum was 0.5 mol% with respect to the total molar number of elements excluding lithium and oxygen in the lithium nickel-based composite oxide. The mixture of the first aqueous solution and the lithium nickel-based 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. At this time, cobalt sulfate was added so that the molar number of cobalt was 2 mol% with respect to the total molar number of elements excluding lithium and oxygen in the lithium nickel-based composite oxide. The ratio of the molar number of the added aluminum sulfate to the molar number of the added cobalt sulfate was 0.25. The above mixture was filtered and dried at 190°C for 10 hours to obtain a dry product. 6 mol% 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.

[0206]

[0207] Example 2

[0208] It was manufactured in the same manner as Example 1, except that the total mole number of added cobalt sulfate and the mole number of added aluminum sulfate was added to be 1.5 mol%.

[0209]

[0210] Example 3

[0211] It was manufactured in the same manner as Example 1, except that the total mole number of added cobalt sulfate and the mole number of added aluminum sulfate was added to be 3.5 mol%.

[0212]

[0213] Example 4

[0214] It was manufactured in the same manner as Example 1, except that the total mole number of added cobalt sulfate and the mole number of added aluminum sulfate was added to be 4.5 mol%.

[0215]

[0216] Comparative Example 1

[0217] A positive electrode active material coated only with cobalt was prepared.

[0218] A lithium nickel composite oxide was added to an aqueous solution containing 6 wt% cobalt sulfate (CoSO4·7H2O) and stirred. Sodium hydroxide (NaOH) was added dropwise to the mixture. As a result, the ratio of the moles of added aluminum sulfate to the moles of added cobalt sulfate was 0. Subsequent filtration, drying, and heat treatment were performed in the same manner as in Example 1.

[0219]

[0220] Comparative Example 2

[0221] A lithium nickel composite oxide was added to an aqueous solution containing 6 wt% cobalt sulfate (CoSO4·7H2O) and stirred for 5 minutes. An aqueous solution containing aluminum sulfate (Al₂(SO₄)₃·16H2O) and sodium hydroxide (NaOH) was added dropwise to the mixture over 30 minutes. Subsequent filtration, drying, and heat treatment were performed in the same manner as in Example 1.

[0222]

[0223] Comparative Example 3

[0224] A cathode active material dry-coated with cobalt and aluminum was prepared.

[0225] Lithium nickel-based composite oxide, cobalt hydroxide (Co(OH)2), and aluminum oxide (Al2O3) were placed in a dry coating machine without a solvent and mixed by stirring. The heat treatment was then performed in the same manner as in Example 1.

[0226]

[0227] Manufacturing of anodes

[0228] 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 an N-methylpyrrolidone solvent. The positive electrode active material slurry was applied to an aluminum current collector, dried, and rolled to prepare a positive electrode.

[0229]

[0230] Manufacturing of lithium secondary batteries

[0231] A lithium metal counter electrode was used as the positive electrode and counter electrode, and a polyethylene polypropylene multilayer separator was interposed between them. The electrolyte was a solution containing 1.0 M LiPF6 lithium salt added to a solvent containing ethylene carbonate and diethyl carbonate in a volume ratio of 50:50. A coin half-cell was manufactured by injecting the electrolyte.

[0232]

[0233] Addition amount of cobalt (mol%) Addition amount of aluminum (mol%) Total coating amount (mol%) Molar ratio of addition amount (Co / Al) Example 1 20.5 2.54 Example 21.2 0.3 1.54 Example 32.8 0.7 3.54 Example 43.6 0.9 4.54 Comparative Example 1 20.2 4 Comparative Example 220.5 2.54 Comparative Example 320.5 2.54

[0234]

[0235] Experimental Example 1: Structural and Component Analysis of Positive Electrode Active Materials (1)

[0236] Figure 16 shows a transmission electron microscope (TEM) image and mapping results using energy dispersive spectroscopy (EDS) for a cross-section of a positive electrode active material according to Example 1.

[0237] Referring to FIG. 16, the positive electrode active material according to Example 1 included a coating layer on the core, and the coating layer included both cobalt and aluminum. In addition, the positive electrode active material according to Example 1 included a grain boundary coating layer, and the grain boundary coating layer included both cobalt and aluminum. As a result of mapping the grain boundary coating layer, cobalt and aluminum were uniformly present within the grain boundary coating layer, and the cobalt and aluminum within the grain boundary coating layer were present at substantially the same location.

[0238]

[0239] Experimental Example 2: Structural and Component Analysis of Positive Electrode Active Materials (2)

[0240] Figures 17 and 18 are transmission electron microscopy (TEM) images and mapping results using energy dispersive spectroscopy (EDS) for the cross-sections of the positive electrode active materials according to Example 1 and Comparative Example 2, respectively. Figures 19a and 19b are depth profiling results for the cross-sections of the positive electrode active materials according to Example 1 and Comparative Example 2, respectively, using transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). Figures 19a and 19b are depth profiling results along the arrow directions of Figures 17 and 18.

[0241] Referring to FIGS. 17 to 19, the point where the aluminum signal (Al signal) shows the most rapid decrease after the maximum peak was calculated as the thickness of the second coating layer (TKC2), and the point where the cobalt signal (Co signal) shows the most rapid decrease after the maximum peak was calculated as the total thickness of the first and second coating layers (TKC1+TKC2), and these values ​​are shown in Table 2. The same analysis was conducted for Examples 2 to 4 and Comparative Example 1.

[0242] In the case of the positive electrode active material according to Comparative Example 3, it was confirmed in the transmission electron microscope (TEM) image of the cross-section that the coating layer (CTL) was formed relatively unevenly. As a result of mapping using the transmission electron microscope (TEM) image and energy dispersive spectroscopy (EDS) of the cross-section of the positive electrode active material according to Comparative Example 3, the thickness of the coating layer (CTL) varied from about 2 nm to 60 nm, and the distribution of aluminum and cobalt within the coating layer (CTL) was uneven, making it impossible to specify the first coating layer (CTL1) and the second coating layer (CTL2). In addition, cobalt and aluminum were mainly distributed on the side relatively close to the surface of the positive electrode active material among the grain boundary coating layers, and as shown in FIG. 16, cobalt and aluminum were not observed at substantially the same locations, but rather, locations where cobalt was mainly distributed locally and locations where aluminum was mainly distributed locally were each observed at different locations.

[0243]

[0244] ClassificationTKC1+TKC2(nm)TKC2(nm)TKC1(nm)(TKC1+TKC2) / TKC2TKC2 / (TKC1+TKC2)TKC2 / TKC1Example 1403191.290.783.44Example 2292271.320.763.14Example 34833151.450.692.2Example 45532231.720.581.4Comparative Example 114.2014.2-00Comparative Example 217.5152.51.160.866

[0245]

[0246] Experimental Example 3: Performance Evaluation of Lithium Secondary Battery

[0247] The charge / discharge efficiency, capacity retention rate, and DC resistance of lithium secondary batteries including the positive electrode active materials according to Examples 1 to 4 and Comparative Examples 1 to 3 were evaluated.

[0248] Coin cells according to the examples and comparative examples were initially charged under constant current (0.2 C) and constant voltage (4.25 V, 0.05 C cut-off) conditions, rested for 10 minutes, and then discharged under constant current (0.2 C) conditions until the voltage reached 3.0 V to perform initial charge-discharge. Afterwards, charge-discharge was repeated 50 times at 1C / 1C. The capacity retention rate was calculated as the ratio of the discharge capacity at each cycle (25 cycles and 50 cycles) to the initial discharge capacity.

[0249] The DC resistance (DC-IR=△V / △I) was calculated from the ratio of the average voltage change (△V) and average current change (△I) during constant current discharge, and their average value was expressed as the result. The difference between the DC resistance in the first cycle and the DC resistance in the 50th cycle was expressed as the resistance change.

[0250] The results are shown in Table 3.

[0251]

[0252] ClassificationCharge capacity (mAh / g)Discharge capacity (mAh / g)Efficiency (%)Capacity retention rate (%, 50cyc)DC-IR (Ω, 1cyc)DC-IR (Ω, 50cyc)DC-IR change (%)Example 1250.1222.789.095.87.510.134.9Example 2249.1219.688.195.27.411.251.4Example 3247.2224.290.796.37.710.232.5Example 4242.3211.587.395.17.810.230.8Comparative example 1247.8219.788.695.67.011.361.6Comparative example 2249.1220.388.495.67.211.152.8 Comparative example 3249.0216.887.194.57.510.134.9

[0253]

[0254] Referring to Table 3, it was confirmed that the lithium secondary batteries including the positive electrode active materials according to Examples 1 to 4 had excellent capacity retention and small resistance changes due to repeated charge and discharge.

[0255]

[0256] While embodiments of the present invention have been described with reference to the attached drawings, the present invention may be implemented in other specific forms without altering the technical spirit or essential features thereof. Therefore, it should be understood that the embodiments described above are exemplary in all respects and are not limiting.

Claims

1. Comprising forming a lithium nickel-based composite oxide and coating the lithium nickel-based composite oxide, Coating the above lithium nickel-based composite oxide: Forming a first aqueous solution comprising an aluminum compound and a basic compound; Forming a mixture comprising the lithium nickel-based composite oxide and the first aqueous solution; Adding a second aqueous solution containing a cobalt compound to the above mixture; and Including drying and heat treatment, Method for manufacturing positive electrode active material.

2. In paragraph 1, The above aluminum compound comprises at least one selected from the group consisting of aluminum sulfate and sodium aluminate. Method for manufacturing positive electrode active material.

3. In paragraph 1, The basic compound comprises at least one selected from the group consisting of sodium hydroxide, lithium hydroxide, potassium hydroxide and ammonia. Method for manufacturing positive electrode active material.

4. In paragraph 1, Forming the above mixture is performed for 3 to 30 minutes, Method for manufacturing positive electrode active material.

5. In paragraph 1, The cobalt compound comprises at least one selected from the group consisting of cobalt nitrate, cobalt sulfate, cobalt oxide, cobalt hydroxide and cobalt carbonate. Method for manufacturing positive electrode active material.

6. In paragraph 1, Adding a second aqueous solution containing a cobalt compound to the above mixture is performed for 5 minutes to 1 hour. Method for manufacturing positive electrode active material.

7. In paragraph 1, The above heat treatment is performed at a temperature of 650°C to 900°C. Method for manufacturing positive electrode active material.

8. In paragraph 1, The above aluminum compound is added so that the molar number of aluminum is 0.05 mol% to 2 mol% relative to the total molar number of elements excluding lithium and oxygen in the lithium nickel-based composite oxide, The above cobalt compound is added so that the mole number of cobalt is 0.25 mol% to 4 mol% relative to the total mole number of elements excluding lithium and oxygen in the lithium nickel-based composite oxide. Method for manufacturing positive electrode active material.

9. A core comprising a lithium nickel-based composite oxide; and A coating layer positioned on the core and containing cobalt and aluminum, The coating layer includes a first coating layer 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. Positive active material.

10. In paragraph 9, The above core is a secondary particle formed by agglomeration of primary particles. Positive active material.

11. In paragraph 9, The above lithium nickel composite oxide has a nickel content of 60 mol% or more among metals other than lithium. Positive active material.

12. In paragraph 9, The above lithium nickel-based composite oxide contains cobalt, The cobalt content of the above lithium nickel composite oxide is less than the cobalt content of the above coating layer. Positive active material.

13. In paragraph 9, The above lithium nickel-based composite oxide contains aluminum, The aluminum content of the lithium nickel-based composite oxide is less than the aluminum content of the coating layer. Positive active material.

14. In paragraph 9, In the above coating layer, the molar ratio of the aluminum to the cobalt (C Al / C Co ) is 0.1 to 4, Positive active material.

15. In paragraph 9, The total thickness of the first coating layer and the second coating layer is 25 nm to 60 nm, Positive active material.

16. In paragraph 9, The ratio of the thickness of the second coating layer to the thickness of the first coating layer is 1 to 5, Positive active material.

17. In paragraph 9, The ratio of the total thickness of the first and second coating layers to the thickness of the second coating layer is 1.2 to 2, Positive active material.

18. In paragraph 9, The thickness of the second coating layer is 20 nm to 40 nm, Positive active material.

19. In paragraph 9, The average particle diameter of the above positive electrode active material is 5㎛ to 25㎛, Positive active material.

20. A lithium secondary battery comprising the positive electrode active material described in Article 9.

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