Positive electrode active material for lithium secondary batteries and lithium secondary batteries containing the same

Abstract

This embodiment relates to a positive electrode active material for a lithium secondary battery and a lithium secondary battery containing the same. The positive electrode active material for a lithium secondary battery according to one embodiment comprises a nickel-containing metal oxide in single-particle form; doping elements doped into the nickel-containing metal oxide; and a coating layer located on the surface of the nickel-containing metal oxide, wherein the doping elements comprise three or more types, and the coating layer may contain two or more coating elements.

Description

[Technical Field]

[0001] This embodiment relates to a positive electrode active material for a lithium secondary battery and a lithium secondary battery containing the same. [Background technology]

[0002] Recently, due to 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 requirements is being actively pursued worldwide. In particular, high-nickel NCM cathode materials with high nickel content are being used to satisfy these demands.

[0003] However, increasing the nickel content reduces particle strength, leading to microcracks during charging and discharging. Furthermore, this increases the specific surface area of ​​the cathode material, increasing the reaction with the electrolyte and thus increasing gas generation. Additionally, structural instability leads to unstable nickel. 3+ is stable Ni 2+ The phenomenon of positive ion mixing (cation mixing), which is reduced to stable NiO, increases. Therefore, there are problems with actually applying this to positive electrode active materials for lithium-ion batteries for electric vehicles and energy storage.

[0004] To solve this problem, a proposed solution involves manufacturing a cathode material in the form of single-particle form, where primary particles are aggregated into secondary particles, that is, a form where the size of the primary particles is maximized rather than a multi-particle form, and then applying this material.

[0005] However, generally, manufacturing single-particle cathode materials requires firing at higher temperatures compared to multi-particle materials. This often leads to over-firing, resulting in layered structure crystal defects and a deterioration of electrochemical properties such as capacitance and power output.

[0006] Furthermore, lowering the firing temperature to solve this problem resulted in insufficient growth of crystal grain size within a single particle, leading to a deterioration in particle strength and lifetime characteristics. [Overview of the project] [Problems that the invention aims to solve]

[0007] This embodiment aims to provide a positive electrode active material for lithium secondary batteries that has excellent electrochemical properties and improved lifespan and resistance characteristics, as well as 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 comprises a nickel-containing metal oxide in single-particle form; doping elements doped into the nickel-containing metal oxide; and a coating layer located on the surface of the nickel-containing metal oxide, wherein the doping elements comprise three or more types, and the coating layer may comprise two or more coating elements.

[0009] Lithium secondary batteries according to other embodiments may include a positive electrode containing the positive electrode active material for lithium secondary batteries according to one embodiment described above. [Effects of the Invention]

[0010] According to this embodiment, by including at least three doping elements in a single-particle nickel-containing metal oxide and a coating layer located on the surface of the nickel-containing metal oxide that includes at least two coating elements, it is possible to stabilize the crystal structure while simultaneously improving particle strength.

[0011] As a result, in this embodiment, it is possible to realize a positive electrode active material that exhibits excellent electrochemical properties, improved lifetime, and enhanced resistance characteristics even in single-particle form.

[0012] Furthermore, when applying the positive electrode active material according to this embodiment, electrodes with superior quality can be manufactured. [Modes for carrying out the invention]

[0013] The terms first, second, and third 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, without exceeding the scope of the present invention.

[0014] The technical terms used herein are for the sole purpose of referring to specific embodiments and do not 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 is to embody specific characteristics, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other characteristics, regions, integers, steps, operations, elements, and / or components.

[0015] When referring to one part being "on top of" or "on" another part, it may be directly above or on top of the other part, or there may be another part between them. In contrast, when referring to one part being "directly on top of" another part, there is no other part in between.

[0016] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as that commonly understood by a person of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted as having the meaning consistent with the relevant technical literature and the present disclosures, and are not interpreted as having an ideal or highly formal meaning unless otherwise defined.

[0017] Also, unless otherwise specified, % means weight percent, and 1 ppm is 0.0001 weight percent.

[0018] As used herein, the term "these combinations" described in Markush format means one or more mixtures or combinations selected from the group consisting of the components described in the Markush format expression, and means including any one or more selected from the group consisting of the said components.

[0019] Hereinafter, embodiments of the present invention will be described in detail so that those having ordinary knowledge in the technical field to which the present invention pertains can easily implement it. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0020] Positive electrode active material for lithium secondary battery As described above, the positive electrode active material in the form of single particles has problems such as over-firing occurring, defects generating in the layered crystal structure, particle strength decreasing, and thereby high-temperature life and resistance characteristics decreasing.

[0021] However, in this embodiment, by doping a metal oxide using at least three kinds of doping elements and forming a coating layer containing two or more kinds of coating elements, such problems have been solved.

[0022] Specifically, the positive electrode active material for a lithium secondary battery according to one embodiment includes a nickel-containing metal oxide in the form of single particles; a doping element doped into the nickel-containing metal oxide; and a coating layer located on the surface of the nickel-containing metal oxide, the doping element includes three or more kinds, and the coating layer can include two or more kinds of coating elements.

[0023] In this specification, a single particle can include at least one of the structures that are distinguishable as one lump when observing the cross-section of the powder through a scanning electron microscope (SEM) in the form of a single crystal structure composed of one particle and a form in which about 2 to 20 or 2 to 10 particles are aggregated. Here, one particle means one grain or crystallite.

[0024] As in this embodiment, the single-particle active material has a smaller specific surface area, reduces gas generation due to side reactions with the electrolyte, has higher particle strength, suppresses particle cracking during rolling, and reduces crack formation due to repeated charging and discharging, compared to the conventional positive electrode active material which is formed by the aggregation of tens to hundreds of primary particles. As a result, it has the advantage of superior lifespan and safety compared to secondary particles, and enables the realization of a high energy density in the electrode.

[0025] However, as mentioned above, single-particle cathode active materials are manufactured by firing at higher temperatures compared to conventional secondary-particle cathode active materials. At this time, over-firing often occurs, which can lead to the formation of layered structure crystal defects.

[0026] In this embodiment, the nickel-containing metal oxide is doped using at least three doping elements including Al, Y, and Zr, and a coating layer is formed using at least two coating elements including Co and Al. This prevents crystal defects such as an increase in the cation mixing ratio due to high-temperature firing, and efficiently increases the crystal grain size within a single particle and the average particle size of a single particle during the firing process.

[0027] In this specification, "crystal grain" refers to a segmented region within a primary particle in which atoms form a lattice structure in a specific direction.

[0028] Here, the Co content in the positive electrode active material on which the coating layer is formed can be in the range of 0.035 moles to 0.08 moles, more specifically 0.05 moles to 0.07 moles, based on 1 mole of total transition metal contained in the nickel-containing metal oxide on which the coating layer is formed. When the Co content satisfies the above range, crystal grains can be grown to an appropriate size, production costs can be appropriately adjusted, and economic efficiency is excellent. The Al content in the positive electrode active material on which the coating layer is formed can also be in the range of 0.001 moles to 0.015 moles, more specifically 0.003 moles to 0.012 moles or 0.005 moles to 0.009 moles, based on 1 mole of total transition metal contained in the nickel-containing metal oxide on which the coating layer is formed. When the Al content satisfies the above range, degradation of the layered structure to a spinel structure can be effectively suppressed. While layered structures facilitate the desorption and insertion of lithium ions, spinel structures do not allow for smooth lithium ion movement. Therefore, by suppressing the degradation of layered structures into spinel structures, lithium ion movement can be facilitated, ultimately improving the electrochemical properties of the battery.

[0029] The content of Y can be in the range of 400 ppm to 2,000 ppm, or more specifically, in the range of 700 ppm to 1,700 ppm, based on the total weight of the nickel-containing metal oxide on which the coating layer is formed. When the content of Y satisfies the above range, grain growth can be promoted, and the crystal grain size within a single particle and the average particle size of a single particle can be efficiently increased.

[0030] The Zr content can be in the range of 1,200 ppm to 2,800 ppm, more specifically, 1,500 ppm to 2,500 ppm, based on the total weight of the nickel-containing metal oxide on which the coating layer is formed. When the Zr content meets this range, it can mitigate the contraction of lithium ion pathways during the charging and discharging processes of the battery, leading to stabilization of the layered structure. This can reduce the cation mixing ratio, and consequently improve resistance and lifespan characteristics.

[0031] On the other hand, the nickel content in the nickel-containing metal oxide of this embodiment can be 0.8 moles or more, more specifically, in the range of 0.8 moles to 0.99 moles, 0.82 to 0.95 moles, or 0.82 to 0.93 moles, based on 1 mole of total transition metals contained in the doped nickel-containing metal oxide. When the nickel content satisfies the above range, a high-capacity battery can be realized.

[0032] The nickel-containing metal oxide further contains manganese, and the manganese content can be 0.15 moles or less, more specifically in the range of 0.05 moles to 0.1 moles, based on 1 mole of total transition metals contained in the nickel-containing metal oxide on which the coating layer is formed. When the manganese content satisfies the above range, the stability of the positive electrode active material can be improved, and consequently the stability of the battery can be improved.

[0033] The nickel-containing metal oxide on which the aforementioned coating layer is formed can be represented by the following chemical formula 1.

[0034] [Chemical formula 1] Li a [Ni x Co y Mn z M1 w1 M2 w2 ]O2

[0035] In Chemical Formula 1, 0.8 ≦ a ≦ 1.2, 0.8 ≦ x ≦ 0.99, 0 < y ≦ 0.06, 0 < z ≦ 0.14, 0 < w1 ≦ 0.1, 0 ≦ w2 ≦ 0.1, x + y + z + w1 + w2 = 1, M1 is Al, Y, and Zr, and M2 contains one or more of B, Al, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, and Sr.

[0036] In Chemical Formula 1, the total content of the doping elements M1 and M2, based on 1 mole of the total of the nickel, cobalt, manganese, and doping elements, can be more than 0 and 0.2 mole or less, more specifically, in the range of 0.0005 mole to 0.1 mole, 0.0005 mole to 0.08 mole, 0.0005 mole to 0.04 mole, or 0.001 mole to 0.03 mole. The content of the doping element in the chemical formula means the doping amount of the doping element contained in the finally obtained positive electrode active material.

[0037] On the other hand, the average particle size (D50) of the positive electrode active material according to this embodiment can be 3 μm or more, more specifically, in the range of 3 μm to 6 μm. When the average particle size of the single-particle form of the positive electrode active material satisfies the above range, a lithium secondary battery excellent in electrochemical characteristics such as life characteristics and resistance increase rate can be realized. At the same time, the energy density per unit volume can also be increased, so it has a very advantageous effect.

[0038] The positive electrode active material has a temperature of 25 ± 3°C and a relative humidity of 50 ± 15%, and the moisture increase rate can be 80% or less. Also, the positive electrode active material has a temperature of 25 ± 3°C and a relative humidity of 50 ± 15%, and the residual lithium increase rate can be less than 20%. Since the positive electrode active material of this embodiment has a coating layer containing two elements on the surface of the nickel-containing metal oxide, the moisture increase rate and the residual lithium increase rate can be significantly reduced. Thereby, a positive electrode active material excellent in high-temperature life and resistance characteristics can be realized.

[0039] At the same time, the crystal size of the nickel-containing metal oxide on which the coating layer is formed can be 200 nm or larger, more specifically, in the range of 200 nm to 250 nm. When the crystal size satisfies the above range, the lifetime and electrochemical properties of the positive electrode active material of this embodiment can all be improved.

[0040] positive electrode In other embodiments, a current collector and a positive electrode are provided, which includes a positive electrode active material layer located on one surface of the current collector and containing the positive electrode active material according to the above-described embodiment.

[0041] 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.

[0042] 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.

[0043] On the other hand, the positive electrode active material layer may include a binder and a conductive material.

[0044] At this time, 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, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, recycled 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 can be included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0045] The conductive material is used to impart conductivity to the electrodes and can be used in the battery without any particular limitations as long as it does not induce chemical changes and has electronic conductivity. 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 can usually be included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0046] The positive electrode can be manufactured by a conventional positive electrode manufacturing method, except that the positive electrode active material is used.

[0047] 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 as described above.

[0048] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or more of these can be used individually or in mixtures of two or more. The amount of solvent used is sufficient to dissolve or disperse the cathode active material, conductive material, and binder, taking into consideration the coating thickness of the slurry and the manufacturing yield, and to provide a viscosity that allows for excellent thickness uniformity when applied for cathode manufacturing.

[0049] 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.

[0050] Lithium-ion battery Another embodiment provides a lithium secondary battery including the positive electrode.

[0051] 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, the positive electrode being as previously described. 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.

[0052] 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.

[0053] The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity. 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 usually has 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 various forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0054] The negative electrode active material layer may selectively include a binder and a conductive material together 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.

[0055] 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; metallic oxides capable of doping and dedoping with lithium, such as SiOβ (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites. One or more mixtures of these can be used. Furthermore, a metallic lithium thin film can also be used as the negative electrode active material. In addition, low-crystalline carbon and high-crystalline carbon can all be used as carbon materials. 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 micro beads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0056] The binder and conductive material may be the same as those described earlier for the positive electrode.

[0057] Next, depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators can be polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers thereof. Mixed multilayer films such as polyethylene / polypropylene two-layer separators, polyethylene / polypropylene / polyethylene three-layer separators, and polypropylene / polyethylene / polypropylene three-layer separators can also be used.

[0058] Furthermore, in the lithium secondary battery, examples of electrolytes that can be used in the manufacture of lithium secondary batteries include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes.

[0059] Specifically, the organic liquid electrolyte may contain an organic solvent and a lithium salt.

[0060] The aforementioned organic solvent can be used without special limitations as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the aforementioned organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; and dibutyl ether. A variety of solvents can be used, including 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; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group of C2-C20, which may 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 result in superior electrolyte performance.

[0061] The lithium salt can be used without special restrictions as long as it is a compound that can provide lithium ions used in lithium secondary batteries. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, 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 used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can have appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0062] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention can stably exhibit excellent discharge capacity, output characteristics, and capacity retention rate, so it is useful in portable devices such as mobile phones, notebook computers, digital cameras, and in the field of electric vehicles such as hybrid electric vehicles (HEV).

Example

[0063] Hereinafter, the embodiments of the present invention will be described in detail. However, this is only an example and the present invention is not limited thereby. The present invention is defined by the scope of the claims described below.

[0064] Example 1 (1) Production of positive electrode active material Ni 0.90 Co 0.03 Mn 0.07 After preparing a precursor of (OH)2 composition, LiOH·H2O (Samden Electrochemistry, battery grade) as a lithium raw material substance, Y2O3, ZrO2, and Al(OH)3 as doping raw material substances were uniformly mixed with the precursor to produce a mixture.

[0065] At this time, the molar ratio of lithium (Li) to the total metal (Me) excluding lithium (Li / Me) was designed to be 1.05, and doping raw materials were added to the aforementioned precursor so that the concentrations were Zr 2000 ppm, Y 1200 ppm, and Al 1000 ppm.

[0066] The mixture was placed in a firing furnace under an oxygen atmosphere and pre-fired at 680°C for 6.5 hours to obtain the pre-fired product. Subsequently, the obtained pre-fired product was placed in a firing furnace under an oxygen atmosphere and fired at 890°C for 3 hours (1 st After step (2), bake at 940°C for 1 hour. nd (step) and then bake at 780°C for 11 hours (3 rd The fired product was obtained by firing using a three-step method (step 3).

[0067] The calcined material was crushed to obtain single-particle metal oxides doped with Al, Y, and Zr.

[0068] The obtained single-particle metal oxide was dry-mixed with Co(OH)2 and Al(OH)3 as coating raw materials, and then heat-treated in an oxygen atmosphere at 700°C for 5 hours to produce a positive electrode active material with a coating layer. At this time, the Co(OH)2 and Al(OH)3 were added and mixed in amounts corresponding to 2.5 mol% of Co and 1000 ppm of Al, based on the single-particle metal oxide.

[0069] (2) Manufacturing of monocells A monocell was manufactured using the positive electrode active material produced in (1) in the following manner.

[0070] Specifically, a cathode active material, a conductive material (acetylene black), and a polyvinylidene fluoride binder (product name: KF1120) were mixed in a weight ratio of 96.5:1.5:2. 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 30% by weight.

[0071] The slurry was coated onto an aluminum foil (15 μm thick), which served as the positive electrode current collector, using a doctor blade, dried, and then rolled to produce the positive electrode. The loading amount of the positive electrode was approximately 15-16 mg / cm². 2 The rolled density is approximately 3.5 g / cm³. 3 That was the case.

[0072] A monocell was manufactured using the aforementioned positive electrode, graphite negative electrode, electrolyte, and polypropylene separator in a conventional manner. Here, the electrolyte was prepared by dissolving 0.7 M LiPF6 and 0.3 M LiFSI in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (mixing ratio EC:EMC = 3:7 vol%) and then using the prepared mixed solution.

[0073] Comparative Example 1 A single-particle positive electrode active material was produced in the same manner as in Example 1, except that a coating layer was not formed.

[0074] Experimental Example 1 - Measurement of Volume Retention Rate After a formation cycle of constant current charge and discharge at 0.1C / 0.1C within a voltage of 2.5~4.25V at 45℃, a constant current charge and discharge test was performed at 0.5C / 1C. The capacity retention rate was calculated by comparing the capacity of the first cycle with the capacity measured every 50 cycles from the 50th to the 700th cycle. The results are shown in Table 1 below.

[0075] Experimental Example 2 - Measurement of Resistance Increase Rate The resistance increase rate was calculated by converting the resistance measured at 50-cycle intervals from the 50th to the 700th cycle to a percentage (%), compared to the resistance measured at high temperature (45°C) during the initial 0.5C charge / 1.0C discharge. The resistance (DC-IR (Direct current internal resistance)) was calculated by measuring the voltage value 60 seconds after applying the discharge current while charging at 4.25V, and then using the formula "(voltage before current application - voltage 60 seconds after current application) / applied current". The results are shown in Table 1 below.

[0076] [Table 1]

[0077] Referring to Table 1, it can be confirmed that the positive electrode active material according to Example 1 exhibits superior capacity retention and resistance characteristics even as the number of cycles increases, compared to the positive electrode active material according to Comparative Example 1.

[0078] Experimental Example 3 - Measurement of Change in Residual Lithium The change in residual lithium was measured for the positive electrode active material produced in Example 1 and Comparative Example 1. Specifically, 5 g of the positive electrode active material was added to 100 ml of pure water, stirred, and then filtered under reduced pressure to obtain the solution. The solution was analyzed using an Autotitrator T5 (METTLER) equipped with this system. The residual lithium value was calculated using the following formula.

[0079] LiOH=((VEQ1+VEQ2)-2*VEQ2)*C*Mw×1000 / M Li2CO3 = VEQ2 * C * Mw × 1000 / M

[0080] -VEQ1: Consumption of VEQ1 when using 0.1N_HCl (ml) -VEQ2: Consumption of 0.1N HCl from VEQ1 to VEQ2 (ml) -C: HCl concentration (N) - 0.1N -M:(Sample Weight*Soultion Weight) / DIW Weight -Mw: Molecular weight Li2CO373.89 (g / mol), LiOH 23.94 (g / mol)

[0081] TTL is a value that indicates only the amount of lithium (Li) remaining on the surface of the positive electrode active material, and was calculated using the following formula.

[0082] TTL = LiOH result value * (Li molar mass / LiOH molar mass) + Li2CO3 result value * 2 * Li molar mass / Li2CO3 molar mass)

[0083] The results are shown in Table 2 below.

[0084] [Table 2]

[0085] Referring to Table 2, it can be confirmed that the residual lithium in Example 1, a positive electrode active material with a coating layer formed on it, was reduced by more than 55% compared to Comparative Example 1, a positive electrode active material without a coating layer. This indicates that the residual lithium remaining on the surface of the positive electrode active material reacts with the coating element, resulting in a reduction of residual lithium.

[0086] Experimental Example 4 - Measurement of the change in residual lithium over time The amount of residual lithium over time was measured for the positive electrode active materials produced in Example 1 and Comparative Example 1. Specifically, the positive electrode active material from Experimental Example 3 was stored at a temperature of 25±3°C and a relative humidity of 50±15%, and the residual lithium was analyzed at different storage times.

[0087] The results are shown in Table 3 below.

[0088] [Table 3]

[0089] Referring to Table 3, it can be seen that the positive electrode active material of Example 1 has a lower rate of residual lithium increase over time compared to the positive electrode active material of Comparative Example 1. This confirms that the surface stability of the positive electrode active material has increased through the coating.

[0090] Experimental Example 5 - Measurement of change in moisture content over time

[0091] The change in moisture content over time was measured for the positive electrode active materials produced in Example 1 and Comparative Example 1. Specifically, the positive electrode active materials were stored at a temperature of 25±3°C and a relative humidity of 50±15%, and then the moisture content was analyzed at different storage times. The moisture content of the positive electrode active materials was analyzed using an 851KF (Metrohm) instrument under the following conditions.

[0092] -Measurement temperature: 200℃ -Stirrer rate:8 -Flow rate: 60 mL / min -Blank condition: Blank Sample size 1g

[0093] The results are shown in Table 4 below.

[0094] [Table 4]

[0095] Referring to Table 4, it can be seen that the positive electrode active material of Example 1 has a significantly lower rate of moisture increase over time compared to the positive electrode active material of Comparative Example 1. This confirms that the surface stability of the positive electrode active material has increased through the coating.

[0096] Experimental Example 6 - Measurement of Crystal Grain Size The crystal grain size, c-axis, and a-axis values ​​were measured for the positive electrode active materials produced in Example 1 and Comparative Example 1 as follows. The results are shown in Table 5 below.

[0097] 1) Sample structure analysis using Rigaku's smart lab equipment

[0098] 2) Smart lab equipment configuration Goniometer radius: 300.0 mm Rotating anode x-ray tube(DPTA-II) Theta_s arm:BB Slit CBO(cross beam optics for Cutarget) Soller slit 5.0deg, 10mm Incident slit Theta_d arm:8.0mm Receiving slit Diffracted beam monochromator (DBM) unit for D / teX Ultra, D / teX Ultra Sample stage: ASC-6 (auto sample changer), Reflection knife edge

[0099] 2) Apply 45kV, 200mA (9kW) to the Cu anode to generate X-rays.

[0100] 3) Equipped optics are set to Incident slit 1 / 2 degree and Receiving slit 8.0 mm.

[0101] 4) XRD measurement with Scan 10-80°, Step 0.02°, 10° / min.

[0102] 5) Crystal grain size was calculated using Rigaku's Smart Lab Studio IIx64v4.2.82.0S / W.

[0103] 6) Calculations are performed using WPPF (Whole Powder Pattern Fitting) in software.

[0104] [Table 5]

[0105] Referring to Table 5, it can be confirmed that the crystal grain size of the positive electrode active material produced by Example 1 is 200 nm or larger, while the crystal grain size of the positive electrode active material produced by Comparative Example 1 is less than 200 nm.

[0106] 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 invention pertains should understand that the invention can be implemented in other specific forms without altering the technical idea or essential features. Therefore, the embodiments described above should be understood to be illustrative and not limiting in all respects.

Claims

1. Nickel-containing metal oxides in single-particle form; Doped elements in the aforementioned nickel-containing metal oxide; and The coating layer located on the nickel-containing metal oxide surface is included, The aforementioned doped elements include three or more types. The coating layer comprises two or more coating elements, and is a positive electrode active material for lithium secondary batteries.

2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the coating layer comprises Co and Al.

3. The positive electrode active material for a lithium secondary battery according to claim 2, wherein the Co content in the positive electrode active material on which the coating layer is formed is in the range of 0.035 moles to 0.08 moles, based on 1 mole of total transition metals contained in the nickel-containing metal oxide on which the coating layer is formed.

4. The positive electrode active material for a lithium secondary battery according to claim 2, wherein the doped elements include Al, Y, and Zr.

5. The positive electrode active material for a lithium secondary battery according to claim 4, wherein the Al content in the positive electrode active material on which the coating layer is formed is in the range of 0.001 moles to 0.015 moles, based on 1 mole of total transition metals contained in the nickel-containing metal oxide on which the coating layer is formed.

6. The positive electrode active material for a lithium secondary battery according to claim 4, wherein the content of Y is in the range of 400 ppm to 2,000 ppm based on the total weight of the nickel-containing metal oxide on which the coating layer is formed.

7. The positive electrode active material for a lithium secondary battery according to claim 4, wherein the Zr content is in the range of 1,200 ppm to 2,800 ppm based on the total weight of the nickel-containing metal oxide on which the coating layer is formed.

8. The nickel content is 0.8 moles or more, based on 1 mole of total transition metals contained in the nickel-containing metal oxide on which the coating layer is formed, as a positive electrode active material for a lithium secondary battery according to claim 1.

9. The nickel-containing metal oxide further contains manganese, The manganese content is 0.15 moles or less, based on 1 mole of total transition metals contained in the nickel-containing metal oxide on which the coating layer is formed, as a positive electrode active material for a lithium secondary battery according to claim 8.

10. The nickel-containing metal oxide on which the coating layer is formed is the positive electrode active material for a lithium secondary battery according to claim 1, represented by the following chemical formula 1: [Chemical formula 1] Li ａ [Ni ｘ Co ｙ Mn ｚ M1 ｗ１ M2 ｗ２ ]O ２ In the above chemical formula 1, 0.8 ≤ a ≤ 1.2, 0.8 ≤ x ≤ 0.99, 0 < y ≤ 0.06, 0 < z ≤ 0.14, 0 < w1 ≤ 0.1, 0 ≤ w2 ≤ 0.1, x + y + z + w1 + w2 = 1, M1 is Al, Y and Zr, and M2 contains one or more of B, Al, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La and Sr.

11. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the positive electrode active material has a moisture content increase rate of 80% or less at a temperature of 25±3°C and a relative humidity of 50±15%.

12. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the positive electrode active material has a residual lithium increase rate of 20% or less at a temperature of 25±3°C and a relative humidity of 50±15%.

13. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the positive electrode active material on which the coating layer is formed has a residual lithium reduction rate of 55% or more with respect to the doped nickel-containing metal oxide.

14. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the average particle size (D50) of the positive electrode active material is 3 μm or more.

15. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the crystal grain size of the nickel-containing metal oxide on which the coating layer is formed is 200 nm or larger.

16. A positive electrode for a lithium secondary battery, comprising the positive electrode active material described in any one of claims 1 to 15.

17. A lithium secondary battery comprising a positive electrode for a lithium secondary battery as described in claim 16.

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