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

Abstract

To provide a positive electrode active material for a lithium secondary battery with an excellent lifetime characteristic.SOLUTION: The present invention relates to a positive electrode active material, a manufacturing method for the same, a positive electrode including the same, and a lithium secondary battery including the positive electrode. More specifically, a lithium complex oxide and a coating layer on a surface of the lithium complex oxide are included. The positive electrode active material further includes sodium (Na) and sulfur (S). The mass fraction (S / Na) of S to Na described above is 1 to 3.SELECTED DRAWING: Figure 6

Description

[Technical Field]

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

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

[0003] A lithium secondary battery is a battery that includes a cathode and an anode, which contain active materials that allow the intercalation and deintercalation of lithium ions, and an electrolyte. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are inserted / deintercalated at the cathode and anode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Korean Patent No. 10-2327532 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a positive electrode active material for a lithium secondary battery that exhibits excellent life characteristics.

[0006] Another object of the present invention is to provide a method for producing the positive electrode active material. [Means for solving the problem]

[0007] A method for preparing a positive electrode active material according to the present invention may include the steps of preparing a lithium composite oxide represented by the following Chemical Formula 1, wet-coating the lithium composite oxide, and washing the coated lithium composite oxide with washing water, wherein the amount of washing water may be 0 wt % to 15 wt % based on the total weight of the coated lithium composite oxide. [Chemical formula 1] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1

[0008] In the formula 1, 0.9≦a1≦1.8, 0.7≦x1≦1, 0≦y1≦0.3, 0≦z1≦0.3, 0.9≦x1+y1+z1≦1.1, and 0≦b1≦0.1; M 1 and M 2 may each independently comprise 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 Z, and X may comprise one or more elements selected from the group consisting of F, P, and S.

[0009] A method for preparing a positive electrode active material according to another aspect of the present invention may include preparing a lithium composite oxide represented by Formula 1, wet-coating the lithium composite oxide, and washing the coated lithium composite oxide with washing water. The positive electrode active material may include sodium (Na) and sulfur (S), and the mass fraction of S to Na (S / Na) may be 1 to 3.

[0010] A positive electrode active material according to another aspect of the present invention may include a lithium composite oxide represented by Formula 1, and a coating layer on the surface of the lithium composite oxide. The positive electrode active material may include sodium (Na) and sulfur (S), and the mass fraction of S relative to Na (S / Na) may be 1 to 3. [Effects of the Invention]

[0011] According to an embodiment of the present invention, the amount of washing water used in the washing process after wet coating in the manufacturing process of a positive electrode active material can be limited. By limiting the amount of washing water, excessive washing can be prevented, and damage to the surface of the positive electrode active material can be minimized.

[0012] A lithium secondary battery using the positive electrode active material of the present invention can exhibit improved life characteristics. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a conceptual diagram illustrating a lithium secondary battery according to an embodiment of the present invention; [Figure 2] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment, the lithium secondary battery having a cylindrical battery shape. [Figure 3] 1 is a cross-sectional view showing a lithium secondary battery according to an embodiment. [Figure 4] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment, the battery having a prismatic shape. [Figure 5] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment, in the form of a pouch-shaped battery. [Figure 6] FIG. 2 is a schematic diagram showing the steps of coating a lithium composite oxide and washing with water. [Figure 7] FIG. 2 is a schematic diagram showing the steps of coating a lithium composite oxide and washing with water. [Figure 8] FIG. 2 is a schematic diagram showing the steps of coating a lithium composite oxide and washing with water. DETAILED DESCRIPTION OF THE INVENTION

[0014] In this specification, when a component is referred to as being on another component, it means that the component may be directly formed on the other component, or that a third component may be interposed between them. However, the present invention is not limited to the embodiments disclosed below, and may be embodied in various forms and may undergo various modifications. The description of the present embodiments is provided solely to ensure complete disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0015] In this specification, when a component is referred to as being on another component, it means that it may be formed directly on the other component, or that a third component may be interposed between them. Also, in the drawings, the thickness of the components is exaggerated for the sake of efficient explanation of the technical content. Parts designated with the same reference numerals throughout the specification refer to the same components.

[0016] Unless otherwise specified herein, the singular can also include the plural. Furthermore, unless otherwise specified, "A or B" can mean "including A, including B, or including A and B." As used herein, "comprises" and / or "comprising" does not exclude the presence or addition of one or more other elements to the referenced element.

[0017] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0018] Unless otherwise defined herein, particle size refers to the average particle size. Furthermore, particle size refers to the average particle size (D50), which refers to the diameter of particles with a cumulative volume of 50% in a particle size distribution. The average particle size (D50) can be measured by methods well known to those skilled in the art, such as using a particle size analyzer or a transmission electron microscope (TEM) or scanning electron microscope (SEM) image. Alternatively, the average particle size (D50) can be measured using a measuring device that uses dynamic light scattering, and data analysis can be performed to count the number of particles in each particle size range, after which the average particle size (D50) can be calculated. Alternatively, the average particle size (D50) can be measured using a laser diffraction method. More specifically, when measuring by the laser diffraction method, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT3000), and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W. The average particle size (D50) based on 50% of the particle size distribution in the measuring device can then be calculated.

[0019] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment of the present invention. Referring to FIG. 1, the lithium secondary battery may include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte ELL.

[0020] The positive electrode 10 and the negative electrode 20 may be separated from each other by a separator 30. The separator 30 may be disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be in contact with an electrolyte solution ELL. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated in the electrolyte solution ELL.

[0021] The electrolyte ELL can be a medium for transferring lithium ions between the positive electrode 10 and the negative electrode 20. In the electrolyte ELL, the lithium ions can pass through the separator 30 and move toward the positive electrode 10 or the negative electrode 20.

[0022] positive electrode 10 The positive electrode 10 for a lithium secondary battery may include a current collector COL1 and a positive electrode active material layer AML1 formed on the current collector COL1. The positive electrode active material layer AML1 includes a positive electrode active material and may further include a binder and / or a conductive material. A detailed description of the positive electrode active material layer AML1 according to an embodiment of the present invention will be provided below with reference to FIGS. 6A and 6B. The current collector COL1 may be made of, but is not limited to, aluminum.

[0023] negative electrode 20 The negative electrode 20 for a lithium secondary battery includes a current collector COL2 and a negative electrode active material layer AML2 located on the current collector COL2. The negative electrode active material layer AML2 includes a negative electrode active material and may further include a binder and / or a conductive material.

[0024] For example, the negative electrode active material layer AML2 may contain 90 to 99 wt % of the negative electrode active material, 0.5 to 5 wt % of the binder, and 0 to 5 wt % of the conductive material.

[0025] The binder serves to firmly adhere the negative electrode active material particles to each other and to firmly adhere the negative electrode active material to the current collector COL 2. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0026] Examples of non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0027] The water-based binder may be selected from styrene-styrene rubber, (meth)acrylate styrene-styrene rubber, (meth)acrylonitrile-styrene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0028] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulose-based compound that can impart viscosity. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be sodium, potassium, or lithium.

[0029] The dry binder may be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0030] The conductive material is used to impart conductivity to the electrode, and any material that is electronically conductive without causing a chemical change in the battery that is constructed can be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0031] As the current collector COL2, it is possible to use those selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0032] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

[0033] As the material capable of reversibly inserting / desorbing lithium ions, a carbon-based negative electrode active material can be included, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0034] As the alloy of lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0035] As the material capable of doping and undoping lithium, an Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiOx (0 < x < 2), an Si-Q alloy (Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 1 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or a combination thereof. <00002​The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and the surfaces of the silicon particles coated with amorphous carbon. For example, it may include secondary particles (cores) formed by assembling primary silicon particles and a first coating layer (shell) of amorphous carbon located on the surfaces of the secondary particles. Amorphous carbon may also be located between the primary silicon particles, for example, coating the primary silicon particles with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0037] 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 a first coating layer of amorphous carbon disposed on the core.

[0038] A Si-based negative electrode active material or a Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material.

[0039] Separator 30 Depending on the type of lithium secondary battery, a separator 30 may be present between the positive electrode 10 and the negative electrode 20. As such separator 30, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, and it goes without saying that mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0040] Separator 30 can include a porous substrate and a first coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0041] The porous substrate may be a polymer membrane formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

[0042] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0043] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0044] The organic material and the inorganic material may be mixed in one first coating layer, or may be stacked in a form in which a first coating layer containing an organic material and a first coating layer containing an inorganic material are stacked.

[0045] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0046] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0047] The non-aqueous organic solvent can be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0048] Examples of carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0049] Examples of ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0050] Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0051] The non-aqueous organic solvents can be used alone or in combination of two or more.

[0052] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed together, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0053] Lithium salts are dissolved in organic solvents and act as a source of lithium ions in the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethene sulfonate, lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0054] Lithium secondary battery Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 2 to 5 are schematic diagrams illustrating lithium secondary batteries according to embodiments, with FIG. 2 illustrating a cylindrical type, FIG. 3 illustrating a cross-sectional view, FIG. 4 illustrating a prismatic type, and FIG. 5 illustrating a pouch type. Referring to FIGS. 2 to 5, a lithium secondary battery 100 may include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, the negative electrode 20, and the separator 30 may be 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. Also, as shown in FIG. 3, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 4 and 5, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting current generated in the electrode assembly 40 to the outside.

[0055] The lithium secondary battery according to an embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electrical devices, but the present invention is not limited thereto.

[0056] Hereinafter, a positive electrode active material for a lithium secondary battery and a method for manufacturing the same according to an embodiment of the present invention will be described in more detail.

[0057] Lithium composite oxide preparation First, a lithium composite oxide is prepared. The lithium composite oxide according to an embodiment of the present invention may be represented by the following Chemical Formula 1: [Chemical formula 1] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1

[0058] In chemical formula 1, 0.9≦a1≦1.8, 0.7≦x1≦1, 0≦y1≦0.3, 0≦z1≦0.3, 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 Z, and X can be one or more elements selected from the group consisting of F, P, and S.

[0059] In Chemical Formula 1, 0.8≦x1≦0.99, 0.01≦y1≦0.2, and 0.01≦z1≦0.2, or 0.9≦x1≦1, 0≦y1≦0.1, and 0≦z1≦0.1.

[0060] For example, the lithium composite oxide may be a compound represented by the following Chemical Formula 2: [Chemical formula 2] Li a2 Ni x2 Co y2 M 3 z2 O 2-b2 X b2

[0061] In chemical formula 2, 0.9≦a2≦1.8, 0.7≦x2≦1, 0≦y2≦0.3, 0≦z2≦0.3, 0.9≦x2+y2+z2≦1.1, and 0≦b2≦0.1; M 3 is at least one element 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 can be one or more elements selected from the group consisting of F, P, and S.

[0062] In Chemical Formula 2, 0.8≦x1≦0.99, 0.01≦y1≦0.2, and 0.01≦z1≦0.2, or 0.9≦x2≦0.99, 0.01≦y2≦0.1, and 0.01≦z2≦0.1.

[0063] For example, the lithium composite oxide may be a compound represented by the following Chemical Formula 3. The compound of Chemical Formula 3 may be lithium nickel-cobalt-aluminum oxide or lithium nickel-cobalt-manganese oxide. [Chemical formula 3] Li a3 Ni x3 Co y3 M 4 z3 M 5 w3 O 2-b3 X b3

[0064] 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 is at least one selected from the group consisting of Al and Mn, 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 can be one or more elements selected from the group consisting of F, P, and S.

[0065] In Chemical Formula 3, 0.85≦x3≦0.98, 0.01≦y3≦0.14, 0.01≦z3≦0.14, and 0≦w3≦0.14, or 0.9≦x3≦0.98, 0.01≦y3≦0.09, 0.01≦z3≦0.09, and 0≦w3≦0.09.

[0066] The lithium composite oxide represented by Chemical Formula 1 may be prepared by mixing a transition metal precursor and a lithium-containing raw material and then calcining the mixture. The transition metal precursor contains nickel, and optionally M 1 and / or M 2 The compound may be a hydroxide, oxyhydroxide, carbonate, or organic complex of a complex transition metal containing the compound.

[0067] The transition metal precursor may be purchased as a commercially available product or may be prepared by a method for preparing a transition metal precursor well known in the art.

[0068] In one embodiment, the transition metal precursor can be obtained by a co-precipitation method. For example, the co-precipitation method can include dissolving a transition metal source material in a solvent such as distilled water, and sequentially introducing the transition metal salt solution into a reactor together with a chelating agent and a basic aqueous solution to cause precipitation. The precipitate is collected in the form of a slurry, which is then filtered and dried to obtain the transition metal precursor.

[0069] In the present invention, the transition metal source material may include a metal salt of at least one element selected from the group consisting of Ni, Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, and Sn. The metal salt may be a sulfate, nitrate, acetate, halide, hydroxide, or the like, and is not particularly limited as long as it can be dissolved in a solvent. The transition metal source material according to the present embodiment may include a nickel salt, a cobalt salt, and an aluminum salt. The transition metal source materials may be mixed in a molar ratio that is adjusted so that the positive electrode active material has high capacity characteristics. For example, x1 in Chemical Formula 1 may be determined depending on the molar ratio.

[0070] The transition metal precursor may be mixed with a lithium source material in a certain ratio to form a mixture. For example, the transition metal precursor and the lithium source material may be mixed in a molar ratio of about 1:1. The lithium source material may be any material commonly used in the preparation of a positive electrode active material, without particular limitation. For example, the lithium source material may include lithium salts such as lithium carbonate, lithium nitrate, lithium hydroxide, or lithium sulfate.

[0071] The mixture may be placed in a furnace and subjected to a firing process. The firing temperature may be 700°C to 1,000°C. More specifically, the firing temperature may be 900°C to 1,000°C. The firing process may be performed in an oxidizing atmosphere such as air or oxygen. The heat treatment time for the firing process may be 10 to 30 hours. In another embodiment of the present invention, pre-firing may be additionally performed at 150°C to 800°C before the firing process.

[0072] A lithium composite oxide can be formed from a mixture containing a transition metal precursor and a lithium raw material through a calcination process, and the synthesized lithium composite oxide can be subjected to a pulverization process.

[0073] Wet coating of lithium composite oxide 6, a coating process can be performed on the lithium composite oxide. Specifically, lithium composite oxide particles and coating raw materials can be mixed in a solvent (e.g., distilled water). That is, in the wet coating process, the lithium composite oxide particles can be coated simultaneously with the first water wash.

[0074] The coating raw material may be, but is not limited to, an oxide, hydroxide, oxyhydroxide, carbonate, sulfate, halide, sulfide, acetate, carboxylate, or a combination thereof containing one or more elements (hereinafter referred to as "coating elements") selected from the group consisting of the elements to be coated, such as Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S, but is not limited to, the coating raw material.

[0075] Specifically, the coating source material may be, but is not limited to, cobalt hydroxide, cobalt carbonate, cobalt sulfate, cobalt oxide, cobalt nitrate, aluminum hydroxide, aluminum chloride, aluminum oxide, manganese hydroxide, manganese oxide, manganese salts, manganese chloride, or a combination thereof.

[0076] In the coating process, a precipitant, a pH adjuster, etc. may be added as needed. Specifically, a basic substance (e.g., NaOH) may be used as the precipitant or pH adjuster.

[0077] Additional cleaning of the lithium composite oxide Referring to FIGS. 6 to 8, after the coating process, a process of washing the lithium composite oxide with water may be further performed to remove lithium by-products present on the surface of the lithium composite oxide.

[0078] Lithium composite oxides containing a high concentration of nickel are structurally unstable compared to lithium composite oxides containing a low concentration of nickel, and therefore generate more lithium by-products, such as unreacted lithium hydroxide and lithium carbonate, during the manufacturing process. If a large amount of residual lithium is present in the positive electrode active material, the residual lithium reacts with the electrolyte, causing gas generation and expansion, which significantly reduces high-temperature stability. Therefore, to remove residual lithium from lithium composite oxides containing a high concentration of nickel, an additional washing process is typically performed after the coating process.

[0079] The washing step can be performed, for example, by adding the coated lithium composite oxide to ultrapure water and stirring it. Alternatively, the washing step can be performed by filtering the lithium composite oxide from the solvent used in the coating step and simultaneously adding washing water (see FIG. 7).

[0080] The amount of washing water used in the water washing process according to an embodiment of the present invention may be 0 wt % to 15 wt % of the total weight of the coated lithium composite oxide, for example, 0 wt % to 10 wt %, 3 wt % to 10 wt %, or 3 wt % to 5 wt %. Referring to Figure 8, when the amount of washing water used is 0% of the total weight of the coated lithium composite oxide, it means that no additional water washing process is performed after the coating process.

[0081] When the amount of washing water satisfies the above range, lithium by-products can be effectively removed while minimizing surface damage to the lithium composite oxide. According to one embodiment of the present invention, a significant amount of lithium by-products can be removed by using a pH adjuster in the above-described coating process. Therefore, even if washing is omitted or the washing process is performed with a small amount of washing water, lithium by-products on the lithium composite oxide can be sufficiently removed.

[0082] The washing process according to the present invention may be performed for 30 to 60 minutes, for example, 30 to 50 minutes, or 30 to 40 minutes, at a washing temperature of 25°C to 30°C.

[0083] After the washing step, the lithium composite oxide may be filtered and subjected to a surface treatment. The surface treatment may include a heat treatment in an oxidizing atmosphere such as air or oxygen. The surface treatment may be performed at a temperature of 500°C to 900°C.

[0084] positive electrode active material The positive electrode active material of the present invention will be described in more detail below.

[0085] The positive electrode active material according to an embodiment of the present invention may include a lithium composite oxide represented by any of the above-described Chemical Formulas 1 to 3. In addition, as described above, the positive electrode active material according to an embodiment of the present invention may include a lithium composite oxide containing a high content of nickel.

[0086] The positive electrode active material according to an embodiment of the present invention may include sodium (Na) and sulfur (S). Na and S may be derived from a wet coating process, and in particular, S may be derived from a metal sulfate. In one embodiment, Na may be derived from a pH adjuster.

[0087] The weight ratio of Na to the total weight of the lithium composite oxide particles may be 200 ppm to 600 ppm, the mass ratio of S particles to the total weight of the lithium composite oxide particles may be 300 ppm to 800 ppm, and the mass fraction of S to sodium (S / Na) may be 1 to 5, for example, 1 to 3, or 1.5 to 3.

[0088] The "mass fraction" used in the present invention can be obtained as a result of analyzing the impurity content in the positive electrode active material using an inductively coupled plasma optical emission spectrometer (ICP), i.e., ICP-MS.

[0089] The positive electrode active material according to an embodiment of the present invention may have a residual lithium content present on the surface of 2000 ppm or less, for example, 1800 ppm or less. If the content of lithium by-products present on the surface of the positive electrode active material exceeds this range, the lithium by-products may continuously react with the lithium salt present in the electrolyte, resulting in the generation of oxygen, HF, HO, and other gases, which may adversely affect the performance of the lithium secondary battery. The residual lithium content present on the surface of the positive electrode active material can be evaluated by measuring the content of LiCO3 and LiOH remaining on the surface of the positive electrode active material using a wet method (or titration method).

[0090] The positive electrode active material according to an embodiment of the present invention may include a coating layer on the surface of lithium composite oxide particles. The coating layer may include a cobalt-containing compound, an aluminum-containing compound, or a manganese-containing compound. Specifically, the coating layer may include, but is not limited to, cobalt oxide, cobalt hydroxide, cobalt carbonate, aluminum hydroxide, aluminum chloride, manganese oxide, or a combination thereof.

[0091] The lithium secondary battery according to an embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electrical devices, but the present invention is not limited thereto.

[0092] Examples and comparative examples of the present invention will be described below. However, the examples described below are merely examples of the present invention, and the present invention is not limited to the examples described below.

[0093] (Production of positive electrode active material) Manufacturing Example 1 Lithium composite oxide preparation As metal raw materials, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O) were dissolved in distilled water as a solvent in a molar ratio of 95:4:1 to prepare a mixed solution, and ammonia water (NH4OH) and sodium hydroxide (NaOH) were prepared as a precipitant to form the complex compound.

[0094] After adding the diluted ammonia water solution to the continuous reactor, the metal raw material mixed solution is continuously added, and sodium hydroxide is added to maintain the pH inside the reactor. The reaction proceeds slowly for about 80 hours, and when the reaction stabilizes, the outflowing product is collected and washed and dried to obtain the final precursor. Therefore, the transition metal precursor (Ni 0.95 Co 0.04 Mn 0.01 (OH)2) is obtained, washed and dried.

[0095] The transition metal precursor and LiOH were mixed so that the molar ratio of lithium to the total amount of metal in the transition metal precursor was 1.04, and the mixture was subjected to a first heat treatment at about 750°C for 15 hours in an oxygen atmosphere to obtain a lithium composite oxide (LiNi 0.95 Co 0.04 Mn 0.01 O2) is obtained. The average particle size of the obtained lithium composite oxide is about 15 μm.

[0096] Lithium composite oxide coating and primary cleaning A wet coating process is carried out by adding a solvent and cobalt sulfate to distilled water, then adding and mixing the manufactured lithium composite oxide. The wet coating process is used to perform the first cleaning of the lithium composite oxide. Cobalt sulfate is added so that the cobalt content of the lithium composite oxide is 2.5 mol% relative to the total elements excluding lithium and oxygen. Sodium hydroxide is added as a pH adjuster during the coating process.

[0097] Lithium composite oxide filtration The lithium composite oxide particles are filtered from the mixed solution. No additional washing water is added. The filtering process is carried out at about 25°C for 60 minutes. The filtered lithium composite oxide particles are dried at 150°C for 12 hours and then heat-treated (i.e., surface-treated) in an oxygen atmosphere at about 850°C for 15 hours.

[0098] The ICP analysis results and the residual lithium content evaluation results for the prepared positive electrode active material particles are shown in Table 1. The residual lithium content was evaluated by measuring the Li content in LiCO3 and LiOH remaining on the surface of the positive electrode active material by a wet method (or titration method).

[0099] Manufacturing Example 2 A positive electrode active material was prepared in the same manner as in Preparation Example 1, except that the filtration process was performed for 30 minutes. The ICP analysis results and the residual lithium content evaluation results of the prepared positive electrode active material particles are shown in Table 1 below.

[0100] Manufacturing Example 3 A positive electrode active material was prepared in the same manner as in Preparation Example 1, except that additional washing was performed by adding washing water in an amount of 10 wt % based on the total weight of the lithium composite oxide particles during the filtration process. The ICP analysis results and the evaluation results of the residual lithium content of the prepared positive electrode active material particles are shown in Table 1 below.

[0101] Comparative Manufacturing Example 1 A positive electrode active material was prepared in the same manner as in Preparation Example 1, except that the pH adjuster was omitted in the coating process. The ICP analysis results and the residual lithium content evaluation results of the prepared positive electrode active material particles are shown in Table 1 below.

[0102] Comparative Manufacturing Example 2 A positive electrode active material was prepared in the same manner as in Preparation Example 1, except that additional washing was performed by adding washing water in an amount of 20 wt % based on the total weight of the lithium composite oxide particles during the filtration process. The ICP analysis results and the evaluation results of the residual lithium content of the prepared positive electrode active material particles are shown in Table 1 below.

[0103] [Table 1]

[0104] Referring to Table 1, it can be seen that the mass fraction of S to Na (S / Na) is reduced when the washing process is omitted after the coating process or when the amount of washing water is limited, as shown in Preparation Examples 1 to 3. It can also be seen that the residual lithium content is detected to be 1500 ppm or less even when the amount of washing water is limited.

[0105] (Lithium secondary battery manufacturing) Example 1 95 g of the positive electrode active material of Preparation Example 1, 3 wt % of polyvinylidene fluoride binder, and 2 wt % of carbon nanotube conductive material were mixed in N-methylpyrrolidone solvent to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to an aluminum current collector, dried, and then rolled to prepare a positive electrode.

[0106] A coin half-cell was fabricated using the prepared positive electrode and lithium metal counter electrode, with a polyethylene-polypropylene multilayer separator between them, and an electrolyte solution of 1.0 M LiPF6 lithium salt added to a solvent of ethylene carbonate and diethyl carbonate mixed in a 50:50 volume ratio.

[0107] Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material of Preparation Example 2 was used as the positive electrode active material.

[0108] Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material of Preparation Example 3 was used as the positive electrode active material.

[0109] Comparative Example 1 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material of Comparative Preparation Example 1 was used as the positive electrode active material.

[0110] Comparative Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material of Comparative Preparation Example 2 was used as the positive electrode active material.

[0111] Evaluation example 1: Charge / discharge efficiency and life characteristics Charge / discharge efficiency Each of the coin half-cells of Examples 1 and 2 and Comparative Examples 1 and 2 was charged under constant current (0.2 C) and constant voltage (4.25 V, 0.05 C cut-off) conditions to measure the charge capacity, then rested for 10 minutes, and discharged under constant current (0.2 C) conditions until the voltage reached 3.0 V to measure the discharge capacity. The ratio of the discharge capacity to the charge capacity is shown as the efficiency. The results are shown in Table 2 below.

[0112] Life characteristics After the initial charge / discharge, the battery was charged / discharged 60 times at 25°C and 1C, and the discharge capacity after 60 cycles was measured. The ratio (%) of the 60th discharge capacity to the initial discharge capacity was shown in Table 2 below as the room temperature capacity retention rate, i.e., room temperature life characteristics.

[0113] [Table 2]

[0114] Referring to Table 2, it can be seen that when the cleaning process after the coating process is omitted or the amount and time of cleaning water is limited (Examples 1 to 3), there is no significant difference in charge / discharge capacity and efficiency, but room temperature life characteristics are improved when compared to when a large amount of cleaning water is used (Comparative Example 2).In addition, when NaOH is not used (Comparative Example 1), it can be seen that the capacity is improved but the lifespan is sharply reduced because the surface is not coated.

[0115] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is natural that these also fall within the scope of the present invention. [Explanation of symbols]

[0116] 100 Lithium secondary battery 10 positive electrode 11 Positive electrode lead tab 12 Positive terminal 20 negative electrode 21 Negative electrode lead tab 22 Negative terminal 30 Separator 40 Electrode assembly 50 cases 60 Sealing member 70 Electrode tab 71 Positive electrode tab 72 Negative electrode tab

Claims

1. Preparing a lithium composite oxide represented by the following Chemical Formula 1: wet-coating the lithium composite oxide; and washing the coated lithium composite oxide with washing water, The method for preparing a positive electrode active material, wherein the amount of the washing water is 0 to 15 wt % based on the total weight of the coated lithium composite oxide. [Chemical formula 1] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 In the formula 1, 0.9≦a1≦1.8, 0.7≦x1≦1, 0≦y1≦0.3, 0≦z1≦0.3, 0.9≦x1+y1+z1≦1.1, and 0≦b1≦0.1; M 1 and M 2 each independently comprise 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 Z, and X comprises one or more elements selected from the group consisting of F, P, and S.

2. 2. The method of claim 1, wherein the washing is performed for 30 to 60 minutes.

3. 2. The method of claim 1, wherein the wet coating step comprises adding the lithium composite oxide and the coating raw material to a solvent and mixing them.

4. The method of claim 3 , wherein the wet-coating step further comprises adding a basic material.

5. 4. The method of claim 3, wherein the coating source material comprises at least one selected from the group consisting of a cobalt precursor, an aluminum precursor, and a zirconium precursor.

6. The method for preparing a positive electrode active material according to claim 1 , further comprising filtering the washed lithium composite oxide.

7. Preparing a lithium composite oxide represented by the following Chemical Formula 1: wet-coating the lithium composite oxide; and washing the coated lithium composite oxide with washing water. [Chemical formula 1] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 In the formula 1, 0.9≦a1≦1.8, 0.7≦x121, 0≦y1≦0.3, 0≦z1≦0.3, 0.9≦x1+y1+z1≦1.1, and 0≦b1≦0.1; M 1 and M 2 each independently comprise 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 Z; and X comprises one or more elements selected from the group consisting of F, P, and S; the positive electrode active material contains sodium (Na) and sulfur (S), The mass fraction of the S relative to the Na (S / Na) is 1 to 3.

8. 8. The method of claim 7, wherein the washing is performed for 30 to 60 minutes.

9. 8. The method of claim 7, wherein the wet coating step comprises adding the lithium composite oxide and the coating raw material to a solvent and mixing them.

10. The method of claim 9 , wherein the wet-coating step further comprises adding a basic material.

11. 10. The method of claim 9, wherein the coating source material comprises at least one selected from the group consisting of a cobalt precursor, an aluminum precursor, and a zirconium precursor.

12. The method for preparing a positive electrode active material according to claim 7 , further comprising filtering the washed lithium composite oxide.

13. a lithium composite oxide represented by the following chemical formula 1; a coating layer on the surface of the lithium composite oxide, further comprising sodium (Na) and sulfur (S); a mass fraction of the S relative to the Na (S / Na) of 1 to 3; [Chemical formula 1] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 In the formula 1, 0.9≦a1≦1.8, 0.7≦x1≦1, 0≦y1≦0.3, 0≦z1≦0.3, 0.9≦x1+y1+z1≦1.1, and 0≦b1≦0.1; M 1 and M 2 each independently comprise 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 Z, and X comprises one or more elements selected from the group consisting of F, P, and S.

14. The positive electrode active material according to claim 13 , wherein x is 0.8 to 0.

99.

15. The positive electrode active material according to claim 13, wherein the lithium composite oxide has a layered crystal structure.

16. The positive electrode active material of claim 13 , wherein the content of residual lithium on the surface of the positive electrode active material is 2000 ppm or less.

17. 14. The positive electrode active material of claim 13, wherein the coating layer contains at least one element selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S.

18. The positive electrode active material according to claim 13, which is produced by the method for producing a positive electrode active material according to claim 1.

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