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

Abstract

This disclosure relates to a positive electrode active material for lithium secondary batteries, a method for producing the same, and a lithium secondary battery containing the same. A positive electrode active material for a lithium secondary battery according to one embodiment includes a single-particulate metal oxide; and a coating layer located on the surface of the metal oxide; wherein the coating layer includes a particulate compound containing a coating element, and the area of ​​the coating layer containing the particulate compound may be 35% or more of the total surface area of ​​the metal oxide.

Description

[Technical Field]

[0001] This disclosure relates to a positive electrode active material for lithium secondary batteries, a method for producing the same, and a lithium secondary battery containing the same. [Background technology]

[0002] Recently, driven by the explosive demand for electric vehicles and the need for increased driving range, the development of high-capacity, high-energy-density secondary batteries to meet these demands is being actively pursued worldwide.

[0003] To meet these requirements, a technology has been proposed that uses a high-nickel NCM cathode material with a high Ni content and configured as secondary particles.

[0004] However, increasing the nickel content reduces particle strength, leading to microcracks during charging and discharging. This increases the specific surface area of ​​the positive electrode material, leading to increased reaction with the electrolyte and increased gas generation. Additionally, the weak strength of the secondary particles causes them to break during the electrode rolling process, increasing the amount of fine powder generated and degrading the battery's lifespan.

[0005] To address this, a proposal was made to increase the strength of the particles by increasing the size of the primary particles to the maximum extent possible and manufacturing the cathode material in the form of single particles, thereby reducing the specific surface area.

[0006] However, in general, manufacturing single-particle cathode materials requires firing secondary particles at high temperatures. This often leads to over-firing, causing crystalline defects in the layered structure and resulting in a decrease in power output and lifetime characteristics. [Overview of the project] [Problems that the invention aims to solve]

[0007] This disclosure aims to provide a positive electrode active material for lithium secondary batteries with excellent output and life characteristics, a method for producing the same, and a lithium secondary battery containing the same. [Means for solving the problem]

[0008] A positive electrode active material for a lithium secondary battery according to one embodiment includes a single-particulate metal oxide; and a coating layer located on the surface of the metal oxide; wherein the coating layer includes a particulate compound containing a coating element, and the area of ​​the coating layer containing the particulate compound may be 35% or more of the total surface area of ​​the metal oxide.

[0009] A method for producing a positive electrode active material for a lithium secondary battery according to another embodiment includes the steps of: preparing a metal hydroxide containing nickel, cobalt, and manganese; mixing the metal hydroxide, lithium raw material, and doping raw material to produce a mixture; calcining the mixture to obtain a single-particulate calcined product; and mixing the calcined product and coating raw material and then heat-treating to obtain a metal oxide with a coating layer formed thereon, wherein the coating raw material may include particulate compounds having an average particle size in the range of 150 nm to 300 nm.

[0010] A positive electrode for a lithium secondary battery according to another embodiment may include the positive electrode active material according to one embodiment.

[0011] Lithium secondary batteries according to other embodiments may include the positive electrode for the lithium secondary battery according to one embodiment. [Effects of the Invention]

[0012] According to this disclosure, the occurrence of crystal defects in a layered structure can be prevented by ensuring that a coating layer containing particulate compounds occupies at least 35% of the total surface area of ​​the metal oxide on the surface of the single-particulate metal oxide.

[0013] As a result, when the positive electrode active material of one embodiment is applied, a lithium secondary battery with excellent output and high-temperature life characteristics can be realized. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a magnified SEM-EDS image of the cross-section of the positive electrode active material produced in Example 1. [Figure 2] Figure 2 shows an image (magnification 50,000x) of the positive electrode active material produced in Example 1, after mapping it to the element Co using EDS equipment, and then identifying the cobalt compounds present on the surface. [Figure 3] Figure 3 shows the line scanning results measured using EDS equipment for the positive electrode active material produced in Example 1. [Modes for carrying out the invention]

[0015] The terms first, second, third, etc., are used to describe various parts, components, regions, layers, and / or sections, but are not limited to these. These terms are used solely to distinguish one part, component, region, layer, or section from other parts, components, regions, layers, or sections. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section, to the extent that it does not fall outside the scope of the present invention.

[0016] The technical terms used herein are for reference only to specific embodiments and are not intended to limit the invention. The singular form used herein also includes the plural form unless the text explicitly indicates otherwise. The meaning of “including” as used in this specification does not embody a particular characteristic, area, integer, step, operation, element, and / or component, thereby excluding the presence or addition of other characteristics, areas, integers, steps, operations, elements, and / or components.

[0017] When referring to a part as being "above" another part, this can mean either directly above the other part or there may be other parts in between. In contrast, when referring to a part as being "directly above" another part, there are no other parts intervening between them.

[0018] Although not differently defined, all terms, including technical and scientific terms used herein, have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are additionally interpreted to have meanings consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an ideal or overly formal sense unless otherwise defined.

[0019] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0020] As used herein, the term "these combinations" described in Markush format expressions means one or more mixtures or combinations selected from the group consisting of the components described in the Markush format expressions, and means including any one or more selected from the group consisting of the said components.

[0021] Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the technical field to which the present invention pertains can easily implement them. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0022] Positive electrode active material for lithium secondary battery As described above, the single-particle positive electrode active material has a problem that over-firing occurs, defects occur in the layered crystal structure, and the characteristics of output and high-temperature life deteriorate.

[0023] However, in the present disclosure, such problems are solved by ensuring that a coating layer containing particulate compounds is located on the surface of the single-particle metal oxide over a specific area.

[0024] Specifically, the positive electrode active material for a lithium secondary battery in one physical form comprises a single-particulate metal oxide; and a coating layer located on the surface of the metal oxide; wherein the coating layer comprises a particulate compound containing a coating element, and the area of ​​the coating layer containing the particulate compound may be 35% or more of the total surface area of ​​the metal oxide.

[0025] The area of ​​the coating layer containing the particulate compound may be in the range of 35% to 50% or 36% to 45% based on the total surface area of ​​the metal oxide.

[0026] In this specification, a single particle can include at least one of the following structures: a single crystal structure consisting of one particle, and a form in which two to twenty or two to ten particles are clustered together, and which can be distinguished as a single mass when a cross-section of the powder is observed through a scanning electron microscope (SEM). Here, a single particle means a single grain (grain or crystallite).

[0027] The single-particle active material of this embodiment has a smaller specific surface area compared to conventional secondary-particle positive electrode active materials formed by the aggregation of tens to hundreds of primary particles. This reduces the amount of gas generated by side reactions with the electrolyte. Furthermore, its high particle strength suppresses particle cracking during rolling and reduces crack formation due to repeated charging and discharging. As a result, it offers advantages such as superior lifespan and safety compared to secondary particles, and enables the realization of high energy density in the electrode.

[0028] The coating layer may contain particulate compounds containing coating elements, and the average particle size of the particulate compounds may be in the range of 50 nm to 300 nm, or 100 nm to 200 nm. When the average particle size of the particulate compounds containing coating elements satisfies the above range, the coating layer can be formed uniformly.

[0029] Furthermore, the coating elements contained in the particulate compound may be diffused from the surface of the metal oxide on which the coating layer is formed toward the center to a thickness range of 75 nm or more, more specifically, 75 nm to 180 nm or 80 nm to 170 nm. When the coating elements are diffused to the aforementioned thickness range, it has the advantageous effect of enabling a positive electrode active material with excellent high-temperature lifetime characteristics.

[0030] In this embodiment, the particulate compound containing the coating element is CoO, Co2O3, CO3O4, LiCoO2, Co(OH)2, CoCl2, CoF3, CoSO4·xH2O, CoSO4·7H2O, (CH3COO)2Co·4H2O, Co(NO3)2·6H2O, (CH3CO2)2Co, CoCO3· x It may contain at least one of H2O and Co3(PO4)2.

[0031] As mentioned above, single-particle positive electrode active materials are manufactured by firing at higher temperatures compared to conventional secondary-particle positive electrode active materials, which can lead to the occurrence of layered crystal defects. In this embodiment, by forming a coating layer containing particulate compounds that include the aforementioned coating elements on the surface of the metal oxide, it is possible to prevent crystal defects such as an increase in the cation mixing ratio due to high-temperature firing, and to efficiently increase the crystal grain size within the single particle and the average particle size of the single particle during the firing process.

[0032] The content of coating elements in the particulate compound in the coating layer may be in the range of 0.035 moles to 0.08 moles, more specifically, in the range of 0.05 moles to 0.07 moles, based on 1 mole of the total amount of transition metals contained in the metal oxide on which the coating layer is formed. In this embodiment, the coating element contained in the particulate compound may be cobalt. When the cobalt content satisfies the above range, the crystal grains can be grown to an appropriate size, and the production cost can be appropriately adjusted, resulting in excellent economic efficiency.

[0033] The coating layer may further contain additional coating elements, which may include, for example, aluminum.

[0034] On the other hand, the metal oxide of this embodiment may include nickel, cobalt, and manganese. In this case, the nickel content may be 0.8 moles or more, more specifically, in the range of 0.8 to 0.99 moles, 0.82 to 0.95 moles, or 0.82 to 0.93 moles, based on 1 mole of the total amount of nickel, cobalt, and manganese. When the nickel content satisfies the above range, a high-capacity battery can be realized.

[0035] The cobalt content may be 0.05 moles or less, more specifically, greater than 0 moles and 0.05 moles or less, based on a total of 1 mole of nickel, cobalt, and manganese.

[0036] Furthermore, the manganese content may be 0.1 moles or less, more specifically, in the range of 0.05 moles to 0.1 moles, based on a total of 1 mole of nickel, cobalt, and manganese.

[0037] The metal oxide may further contain doping elements.

[0038] Here, the doping element may include, for example, at least one of Y, Al, Zr, Nb, Mo, W, Ti, Ce, Mg, B, P, V, Sr, and B. In this embodiment, the doping element may include, for example, Y, Al, and Zr.

[0039] In this case, the content of the doping element may be in the range of 0 or more and 0.2 moles or less, based on 1 mole of the total amount of nickel, cobalt, manganese and the doping element, more specifically, in the range of 0.0005 moles to 0.1 moles, 0.0005 moles to 0.08 moles, 0.0005 moles to 0.04 moles, or 0.001 moles to 0.03 moles. Specifically, based on the total amount of nickel, cobalt, manganese and the doping element, the content of Y may be in the range of 400 ppm to 2,000 ppm, the content of Al may be in the range of 200 ppm to 1,800 ppm, and the content of Zr may be in the range of 1,200 ppm to 2,800 ppm.

[0040] In this embodiment, the doping element content refers to the amount of doping element contained in the final cathode active material.

[0041] Method for manufacturing positive electrode active material for lithium secondary batteries In other embodiments, the present invention provides a method for producing a positive electrode active material for a lithium secondary battery, comprising the steps of: preparing a metal hydroxide containing nickel, cobalt, and manganese; mixing the metal hydroxide, lithium raw material, and doping raw material to produce a mixture; calcining the mixture to obtain a single-particulate calcined product; and mixing the calcined product and coating raw material and then heat-treating to obtain a metal oxide with a coating layer formed thereon, wherein the coating raw material comprises a particulate compound having an average particle size in the range of 150 nm to 300 nm.

[0042] The step of preparing the metal hydroxides containing nickel, cobalt, and manganese can be carried out, for example, by producing an aqueous solution of a metal salt containing a nickel raw material, a cobalt raw material, a manganese raw material, and distilled water, and then supplying the aqueous solution of the metal salt to a coprecipitation reactor to produce the metal hydroxides, which can be carried out by methods for producing metal hydroxides that are generally known in the art.

[0043] In this case, the nickel raw material may be, for example, nickel-containing sulfates, acetates, nitrates, halides, sulfides, hydroxides, oxides, or oxyhydroxides. More specifically, the nickel raw material may be NiSO4, NiSO4·6H2O, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, fatty acid nickel salts, nickel halides, or combinations thereof.

[0044] The cobalt raw material may be, for example, a cobalt-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide. More specifically, the cobalt raw material may be CoSO4. 4、 CoSO4·7H2O, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, or combinations thereof may also be used.

[0045] The manganese raw material may be, for example, manganese-containing sulfates, acetates, nitrates, halides, sulfides, hydroxides, oxides, oxyhydroxides, or combinations thereof.

[0046] More specifically, the manganese raw material may be manganese salts such as MnSO4, MnSO4·H2O, MnCO3, Mn(NO3)2, manganese acetate, manganese dicarboxylate salts, manganese citrate and manganese fatty acid salts, manganese oxides such as Mn2O3, MnO2, and Mn3O4, oxyhydroxides, manganese chloride, or a combination thereof.

[0047] Next, the metal hydroxide, lithium raw material, and doping raw material are mixed to produce a mixture.

[0048] The lithium raw material may be, for example, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides, and is not particularly limited as long as it is soluble in water. More specifically, the lithium raw material may include at least one of LiOH, Li2CO3, LiNO3, LiNO2, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or a combination thereof.

[0049] In this case, the molar ratio of lithium (Li) to the total metal (Me) excluding lithium in the mixture (Li / Me) may be in the range of 1.0 to 1.1, or 1.01 to 1.08.

[0050] The doping raw material may include, for example, at least one of the following raw materials: Al, Zr, Nb, Mo, W, Ti, Ce, Mg, B, P, V, Sr, and B. More specifically, the doping raw material may include an Al raw material, a Y raw material, and a Zr raw material.

[0051] The aforementioned Al raw material may include, but is not limited to, at least one of Al(OH)3, Al2(SO4)3, Al(NO)3, Al2O3, and AlCl3.

[0052] The aforementioned Y raw material may include, but is not limited to, at least one of Y2O3, Y(SO4)2, Y2(SO4)3, and Y(NO3)3.

[0053] The aforementioned Zr raw material may include, but is not limited to, at least one of ZrO2, Zr(SO4)2, ZrS2, and Zr(NO3)4.

[0054] Subsequently, the mixture is calcined to obtain a single-particulate calcined product.

[0055] In this embodiment, the step of obtaining the calcined product can be performed, for example, by a three-step process of calcining the mixture in the first, second, and third steps.

[0056] Specifically, the one-step firing can be carried out at a temperature of 870°C to 930°C for 2 to 6 hours, or at a temperature of 880°C to 920°C for 3 to 5 hours.

[0057] The aforementioned two-step firing can be carried out at a temperature in the range of 890°C to 960°C for 0.5 to 2 hours, or at a temperature in the range of 900°C to 940°C for 0.5 to 1.5 hours.

[0058] The aforementioned three-step firing process can be carried out at a temperature of 750°C to 870°C for 5 to 14 hours, or at a temperature of 780°C to 840°C for 7 to 12 hours.

[0059] The step of obtaining the fired product may, if necessary, be performed after pre-firing.

[0060] Next, the calcined product and the coating raw material are mixed and then heat-treated to obtain a metal oxide with a coating layer formed on it.

[0061] In this case, the heat treatment can be carried out at a temperature of 700°C to 800°C for 3 to 10 hours.

[0062] In this embodiment, the coating raw material may include particulate compounds having an average particle size in the range of 150 nm to 300 nm or 200 nm to 280 nm.

[0063] The coating raw material containing the aforementioned particulate compounds includes Co(OH)2, CoCl2, CoO, CoF3, CoSO4·xH2O, CoSO4·7H2O, (CH3COO)2Co·4H2O, Co(NO3)2·6H2O, (CH3CO2)2Co, CoCO3· x It may contain at least one of H2O, Co3(PO4)2, or a combination thereof.

[0064] The coating raw material containing the particulate compound may be added in a content range of 1.5 mol% to 3 mol% or 2.0 mol% to 2.8 mol% based on 100 g of the calcined product.

[0065] The coating raw material may further contain additional coating raw materials in addition to the particulate compound. For example, the additional coating raw material may be at least one of Al(OH)3, Al2(SO4)3, Al(NO)3, Al2O3, and AlCl3.

[0066] The additional coating material may be added in an amount ranging from 500 ppm to 1,500 ppm based on the total weight of the calcined product.

[0067] In this embodiment, by using a coating raw material containing particulate compounds with an average particle size of 150 nm to 300 nm, the layered crystal structure of the single-particle positive electrode active material can be stabilized, which has a very advantageous effect in that it is possible to secure a positive electrode active material with excellent high-temperature lifetime characteristics.

[0068] positive electrode In other embodiments, a current collector and a positive electrode are provided, which is located on one surface of the current collector and includes a positive electrode active material layer containing the positive electrode active material manufactured according to the above-described embodiment.

[0069] The characteristics of the positive electrode active material constituting the positive electrode active material layer are the same as those described above. Therefore, a detailed explanation of the positive electrode active material will be omitted.

[0070] The current collector can be made of, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc.

[0071] On the other hand, the positive electrode active material layer may include a binder and a conductive material.

[0072] In this case, the binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more can be used, but is not limited thereto. The binder may be included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0073] The conductive material is used to impart conductivity to the electrodes and can be used without special limitations as long as it has electronic conductivity without causing chemical changes in the battery it is configured in. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these can be used alone or a mixture of two or more, but it is not limited to these. The conductive material may usually be included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0074] The positive electrode can be manufactured by a conventional positive electrode manufacturing method, except that the positive electrode active material is used.

[0075] Specifically, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer, which includes the positive electrode active material described above and optionally a binder, conductive material, or solvent, onto a positive electrode current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode active material, binder, and conductive material are the same as described above.

[0076] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these can be used alone or a mixture of two or more. The amount of solvent used should be sufficient to dissolve or disperse the cathode active material, conductive material, and binder, taking into consideration the coating thickness and production yield of the slurry, and to have a viscosity that allows for excellent thickness uniformity when applied for cathode manufacturing.

[0077] Alternatively, the positive electrode can also be manufactured by casting the positive electrode active material layer forming composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0078] Lithium-ion rechargeable battery Another embodiment provides a lithium secondary battery including the positive electrode.

[0079] The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite the positive electrode, a separator interposed between the positive and negative electrodes, and an electrolyte, wherein the positive electrode is the same as described above. The lithium secondary battery may also selectively further include a battery container housing the electrode assembly including the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0080] In the lithium secondary battery, the negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0081] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes to the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used. The negative electrode current collector can also typically have a thickness of 3 to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in a variety of forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0082] The negative electrode active material layer may selectively include a binder and a conductive material along with the negative electrode active material. The negative electrode active material layer can also be manufactured, for example, by applying a negative electrode active material layer forming composition, which includes the negative electrode active material and selectively a binder and a conductive material, onto a negative electrode current collector and drying it, or by casting the negative electrode forming composition onto a separate support, peeling it off the support, and laminating the resulting film onto the negative electrode current collector.

[0083] As the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. β Examples include lithium-doped and dedoped metal oxides such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites. One or more of these can be used as a mixture. A metallic lithium thin film can also be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon can be used as the carbon material. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0084] The binder and conductive material may be the same as those described for the positive electrode.

[0085] Next, depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such a separator may be polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof. 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.

[0086] Furthermore, in the lithium secondary battery, the electrolyte can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte, which can be used in the manufacture of lithium secondary batteries, and is not limited to these.

[0087] Specifically, the organic liquid electrolyte may contain an organic solvent and a lithium salt.

[0088] The organic solvent can be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move, without any special limitations. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; or dibutyl ether. Other solvents that can be used include ether solvents such as ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; tolyls such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group of C2 to C20, and can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among these, carbonate-based solvents are preferred, and more preferably, a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, which can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate). In this case, mixing the cyclic carbonate and the linear carbonate in a volume ratio of about 1:1 to about 1:9 can produce an electrolyte with excellent performance.

[0089] The lithium salt can be any compound capable of providing lithium ions for use in lithium secondary batteries, without any special limitations. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within this range, the electrolyte has appropriate conductivity and viscosity, exhibiting excellent electrolyte performance, and lithium ions can move effectively.

[0090] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent discharge capacity, output characteristics, and capacity retention rate stably, making it useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the electric vehicle field, such as hybrid electric vehicles (HEVs). [Examples]

[0091] The embodiments of the present invention will be described in detail below. However, these are presented as examples only and do not limit the present invention, which is defined only by the scope of the claims described later.

[0092] Example 1 (1) Manufacturing of positive electrode active material Ni 0.90 Co 0.03 Mn 0.07 After preparing a precursor with an (OH)2 composition, a mixture was produced by uniformly mixing the precursor with LiOH·H2O (SAMCHUN CHEMICALS, battery grade) as a lithium raw material, and Y2O3, ZrO2, and Al(OH)3 as doping raw materials.

[0093] At this time, the molar ratio of lithium (Li) to the total metal (Me) excluding lithium was designed to be 1.05, and based on the above precursor, doping raw material substances were added so that the amounts of Zr, Y, and Al were 2000 ppm, 1200 ppm, and 1000 ppm, respectively.

[0094] After the mixture was put into a firing furnace in an oxygen atmosphere, pre-firing was carried out at 680 °C for 6.5 hours to obtain a pre-fired product. Then, after the obtained pre-fired product was put into a firing furnace in an oxygen atmosphere, firing (1 st step) was carried out at 890 °C for 3 hours, and then firing (2 nd step) was carried out at 940 °C for 1 hour, and firing (3 rd step) was carried out at 780 °C for 11 hours by a three-step method to obtain a fired product.

[0095] The fired product was crushed to obtain single-particle metal oxides doped with Al, Y, and Zr.

[0096] After dry-mixing Co(OH)2 and Al(OH)3 as coating raw material substances with the obtained single-particle metal oxides, heat treatment was carried out at 700 °C for 5 hours in an oxygen atmosphere to produce a cathode active material with a coating layer formed. At this time, a raw material with an average particle size of 247 nm was used for Co(OH)2. Also, Co(OH)2 and Al(OH)3 were mixed based on the single-particle metal oxides with a content corresponding to 2.5 mol% of Co and a content corresponding to 1000 ppm of Al.

[0097] Examples 2 to 3 and Comparative Examples | 1 to 2 A cathode active material was produced in the same manner as in Example 1, except that the average particle size of the coating raw material substances and the heat treatment temperature for forming the coating layer were adjusted as shown in Table 1 below.

[0098]

Table 1

[0099] Experimental Example 1 - EDS (Energy dispersive x-ray spectroscopy) analysis

[0100] Figure 1 is a magnified SEM-EDS image of the cross-section of the positive electrode active material produced in Example 1.

[0101] Figure 2 is an image (magnification 50,000x) showing the cobalt compounds present on the surface of the positive electrode active material manufactured in Example 1, after mapping the Co element using EDS equipment.

[0102] Figure 3 shows the line scanning results measured using EDS equipment for the positive electrode active material produced in Example 1.

[0103] Referring to Figure 1, it can be confirmed that the cobalt element is present in the cross-section of the positive electrode active material manufactured in Example 1, that is, inside the surface.

[0104] Referring to Figure 2, it can be confirmed that particulate cobalt compounds are formed on the surface of the positive electrode active material manufactured in Example 1, and that they are distributed on the surface at a rate of 43% or more.

[0105] Referring to Figure 3, it can be confirmed that particulate compounds containing cobalt are present at a thickness of 120 nm from the surface of the metal oxide toward the particle center.

[0106] Next, EDS mapping was performed on the positive electrode active materials produced in Examples 1 to 3 and Comparative Examples 1 to 2. Particulate compounds containing the coating elements were identified, their size was measured, and their distribution rate, i.e., the coating layer area, was calculated. In addition, the diffusion thickness of the coating elements from the surface of the metal oxide was confirmed using EDS line scanning. The results are shown in Table 2 below.

[0107] [Table 2]

[0108] Furthermore, referring to Table 2, it can be seen that the particle size of the coating elements located on the surface of the positive electrode active material produced in Examples 1 to 3 is in the range of 50 nm to 300 nm, and the distribution rate of particulate compounds containing the coating elements is 35% or more. In addition, the diffusion thickness range of the coating elements from the surface of the metal oxide is 75 nm or more in Examples 1 to 3.

[0109] Therefore, it can be seen that by appropriately controlling the particle size of the coating source, the coating elements diffuse to a deeper range from the surface of the metal oxide toward the particle center, and the coating layer formation area is also wide.

[0110] Experimental Example 2: Manufacturing of coin cells and evaluation of high-temperature life retention rate (1) Manufacturing of coin cells Using the positive electrode active materials produced in the examples and comparative examples, CR2032 coin cells were manufactured by the following method.

[0111] Specifically, a cathode active material, a conductive material (acetylene black FX35, Denka Co., Ltd.), and a polyvinylidene fluoride binder (product name: KF9709) were mixed in a weight ratio of 96.5:1.5:295:2.2:2.8. This mixture was then added to an N-methyl-2-pyrrolidone solvent to produce a cathode active material slurry, with a solid content of approximately 65-69% by weight.

[0112] The slurry was coated onto an aluminum foil (20 μm thick), which served as the positive electrode current collector, using a doctor blade. After drying, the mixture was rolled to produce the positive electrode. The loading amount of the positive electrode was approximately 15-16 mg / cm³. 2 The rolling density is approximately 3.5 g / cm³. 3 That was the case.

[0113] A 2032 coin-type half-cell was manufactured using the aforementioned positive electrode, lithium metal negative electrode (400 μm thick, NEBA), electrolyte, and polypropylene polyethylene separator by a conventional method. The electrolyte was prepared by dissolving 1 M LiPF6 in a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate (mixing ratio EC:DMC:DEC = 1:2:1 volume%) to produce a mixed solution, to which 2% by weight of vinylene carbonate (VC) was added.

[0114] (2) Measurement of volume retention rate The coin-type half-cells manufactured in (1) above were aged at room temperature (25°C) for 10 hours, and then a charge-discharge test was performed.

[0115] At 45°C, a formation cycle of constant current charge / discharge at 0.1C / 0.1C within a voltage of 2.5 to 4.25V was performed, followed by a constant current charge / discharge test at 0.5C / 1C. The capacity retention rate was calculated by comparing the capacity of the first cycle with the capacity measured at the 50th cycle. The results are shown in Table 3 below.

[0116] [Table 3]

[0117] Referring to Table 3, it can be confirmed that in Examples 1 to 3, the high-temperature capacity retention rate is significantly higher than in Comparative Examples 1 to 2. As mentioned above, by appropriately controlling the particle size of the coating source, the coating elements diffuse to a deeper range from the surface of the metal oxide toward the particle center, and a wider coating layer formation area is formed, thereby significantly improving the high-temperature lifetime characteristics of the positive electrode active material.

[0118] (3) Measurement of change in residual lithium The residual lithium content of the cathode active materials produced in Examples 1 to 3 and Comparative Examples 1 to 2 was measured using a METTLER TOLEDO T50 model. The results are shown in Table 4 below.

[0119] [Table 4]

[0120] Referring to Table 4, it can be confirmed that in Examples 1 to 3, the residual lithium is significantly lower than in Comparative Examples 1 to 2. As mentioned above, by appropriately controlling the particle size of the coating source, it can be confirmed that the residual lithium in the positive electrode active material can be significantly reduced by forming a larger coating layer area.

[0121] The present invention is not limited to the embodiments described above and can be manufactured in a variety of different forms. Those with ordinary skill in the art to which the present invention pertains will understand that the invention can be implemented in other specific forms without altering the technical idea or essential features of the invention. Therefore, the embodiments described above should be understood to be illustrative and not limiting in all respects.

Claims

1. Single-particulate metal oxides; and A coating layer located on the surface of the metal oxide; The coating layer comprises particulate compounds containing coating elements, A positive electrode active material for a lithium secondary battery, wherein the area of ​​the coating layer containing the particulate compound is 35% or more of the total surface area of ​​the metal oxide.

2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the area of ​​the coating layer containing the particulate compound is in the range of 35% to 50% based on the total surface area of ​​the metal oxide.

3. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the average particle size of the particulate compound is in the range of 50 nm to 300 nm.

4. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the coating elements contained in the particulate compound are diffused from the surface of the metal oxide on which the coating layer is formed toward the center to a thickness range of 75 nm or more.

5. The coating element contained in the particulate compound is diffused from the surface of the metal oxide on which the coating layer is formed toward the center to a thickness range of 75 nm to 180 nm, as described in claim 1.

6. The particulate compound containing the coating element is CoO, Co ２ O ３ , CO ３ O ４ , LiCoO ２ , Co(OH) ２ , CoCl ２ , CoF ３ , CoSO ４ ·xH ２ O, CoSO ４ ·7H ２ , (CH ３ COO) ２ Co·4H ２ O, Co(NO ３ ) ２ ·6H ２ , (CH ３ CO ２ ) ２ Co, CoCO ３ · ｘ H ２ O, and Co ３ (PO ４ ) ２ The positive electrode active material for a lithium secondary battery according to claim 1, comprising at least one of them.

7. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the content of coating elements contained in the particulate compound in the coating layer is in the range of 0.035 moles to 0.08 moles, based on the total amount of metal excluding lithium in the single-particulate metal oxide.

8. The positive electrode active material for a lithium secondary battery according to claim 6, wherein the coating layer may further contain additional coating elements, the additional coating elements including aluminum.

9. The aforementioned metal oxides include nickel, cobalt, and manganese. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the nickel content is 0.8 moles or more, based on a total of 1 mole of nickel, cobalt, and manganese.

10. The aforementioned metal oxide further contains a doping element, The positive electrode active material for a lithium secondary battery according to claim 9, wherein the doping element comprises at least one of Y, Al, Zr, Nb, Mo, W, Ti, Ce, Mg, B, P, V, Sr, and B.

11. Steps to prepare metal hydroxides containing nickel, cobalt, and manganese; A step of mixing the metal hydroxide, lithium raw material, and doping raw material to produce a mixture; The steps of firing the mixture to obtain a single-particulate calcined product; and The step of obtaining a metal oxide in which a coating layer is formed by heat treatment after mixing the aforementioned fired product and coating raw material material; A method for producing a positive electrode active material for a lithium secondary battery, wherein the coating raw material material includes a particulate compound having an average particle size in the range of 150 nm to 300 nm.

12. A method for producing a positive electrode active material for a lithium secondary battery according to claim 11, wherein in the step of obtaining a metal oxide on which the coating layer is formed, the heat treatment is performed at a temperature in the range of 700°C to 800°C for 3 to 10 hours.

13. The coating raw material containing the particulate compound is Co(OH) ２ CoCl ２ CoO, CoF ３ CoSO ４ ・xH ２ O, CoSO ４ 7H ２ O, (CH ３ COO) ２ Co. 4H ２ O, Co (NO ３ ) ２ 6H ２ O, (CH ３ CO ２ ) ２ Co, CoCO ３ ・ ｘ H ２ O, Co ３ (PO ４ ) ２ A method for producing a positive electrode active material for a lithium secondary battery according to claim 11, comprising at least one combination thereof.

14. The coating raw material further comprises additional coating raw material, The aforementioned additional coating raw material is Al(OH) ３ Al ２ (SO ４ ) ３ Al (NO) ３ Al ２ O ３ and AlCl ３ A method for producing a positive electrode active material for a lithium secondary battery according to claim 11, comprising at least one of the following.

15. The method for producing a positive electrode active material for a lithium secondary battery according to claim 11, wherein the step of obtaining the calcined product is a three-step process, comprising calcining in the first step, calcining in the second step, and calcining in the third step.

16. A method for producing a positive electrode active material for a lithium secondary battery according to claim 11, wherein in the step of obtaining a metal oxide on which a coating layer has been formed, the coating raw material containing the particulate compound is added in a content range of 1.5 mol% to 3 mol% based on 100 g of the calcined product.

17. A positive electrode for a lithium secondary battery, comprising the positive electrode active material described in any one of claims 1 to 10.

18. A lithium secondary battery comprising a positive electrode for a lithium secondary battery as described in claim 17.

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