Positive electrode active material, positive electrode slurry comprising same, method for preparing same, and positive electrode and

Abstract

A positive electrode active material according to the present invention comprises: a lithium nickel-based oxide containing nickel (Ni) and cobalt (Co), wherein the molar ratio of Ni to all transition metals is 80 mol% or more; and a cobalt-containing coating layer formed on the surface of the lithium nickel-based oxide, in which the lithium nickel-based oxide is in the form of a single particle composed of single nodules or a quasi-single particle that is a composite of 30 nodules or less, the content of the cobalt-containing coating layer is 2.0 mol% or more based on 100 mol of the lithium nickel-based oxide, and the content of the cobalt-containing coating layer is 2.0 mol% or more based on 100 mol of the lithium nickel-based oxide. And the positive electrode active material has a D50 of 3.7 [mu] m to 6.0 [mu] m, a residual LiOH content of 0.20 wt% or less, and a Co / Ni ratio of 0.15 to 0.40 at a depth of 45 nm from the surface thereof.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority from Korean Patent Application No. 10-2023-0057356, filed on May 2, 2023, the disclosure of which is incorporated herein by reference. Technical Field

[0003] The present invention relates to a positive electrode active material, a positive electrode slurry containing the same, a preparation method thereof, and a positive electrode and a lithium secondary battery containing the same. Background Art

[0004] With the development of technology and the increase in demand for mobile devices, the demand for secondary batteries as energy sources has increased significantly. Among these secondary batteries, lithium secondary batteries with high energy density, high voltage, long cycle life and low self-discharge rate have been commercialized and widely used.

[0005] Lithium transition metal composite oxides have been used as cathode active materials for lithium secondary batteries. Among these, research and development of lithium nickel oxides, which can easily achieve high-capacity batteries, is being actively pursued. However, secondary particle-based lithium nickel oxides suffer from the problem of increased crack formation in the cathode active material during charge and discharge.

[0006] In order to solve the above problems, a technology has been proposed to prepare a positive electrode active material in the form of single particles rather than secondary particles by increasing the sintering temperature during the preparation of lithium nickel-based oxides.

[0007] However, single-particle cathode active materials present a problem: The limited interparticle interfaces that serve as pathways for lithium ion migration lead to reduced output and increased resistance due to the long lithium diffusion paths within the particles. Therefore, conventionally, single-particle cathode active materials have been formed with an average particle size of approximately 4.0 μm to minimize the resistance increase and output reduction.

[0008] However, in order to reduce the average particle size of the positive electrode active material in the form of single particles to approximately 4.0 μm, a high-intensity milling process is required, in which a large amount of fine powder is generated. As a result, there is a problem that the phase stability is rapidly reduced due to the increase in slurry viscosity.

[0009] Therefore, there is a need for a technology that ensures stable electrode production and yield by improving the phase stability of the slurry. Summary of the Invention

[0010] Technical issues

[0011] One aspect of the present invention provides a positive electrode active material, a positive electrode slurry containing the same, and a preparation method thereof, which improves the phase stability of the slurry by adjusting the particle size distribution, residual LiOH content, and amount of a cobalt-containing coating layer of the positive electrode active material to specific ranges.

[0012] Another aspect of the present invention provides a method for preparing a positive electrode active material by 50 A positive electrode and a lithium secondary battery having excellent electrochemical properties adjusted to a specific range.

[0013] Technical Solution

[0014] In one aspect, the present invention provides a positive electrode active material comprising: a lithium nickel oxide containing nickel (Ni) and cobalt (Co) and having a molar ratio of Ni to all transition metals of 80 mol% or more; and a cobalt-containing coating formed on the surface of the lithium nickel oxide, wherein the lithium nickel oxide is in the form of a single particle consisting of a single nodule or a quasi-single particle as a composite of 30 or less nodules, and the content of the cobalt-containing coating is 2.0 mol% or more based on 100 mol of the lithium nickel oxide, and the D of the positive electrode active material is 2.0 mol% or more. 50 The positive electrode active material has a Co / Ni ratio of 0.15 to 0.40 at a depth of 45 nm from the surface of the positive electrode active material.

[0015] The molar ratio of Ni to all transition metals in the lithium nickel-based oxide may be 93 mol % or greater.

[0016] The residual lithium content of the positive electrode active material may be 0.60 wt % or less.

[0017] The residual Li 2 CO 3 content of the positive electrode active material may be 0.40 wt % or less.

[0018] The positive electrode active material D min It may be 1.0 μm or more.

[0019] The lithium nickel-based oxide may be represented by Chemical Formula 1.

[0020] [Chemical Formula 1]

[0021] Li a Ni b Co c M 1 d M 2 e O2

[0022] In Chemical Formula 1, M 1is at least one selected from the group consisting of manganese (Mn) and aluminum (Al), M 2 It is at least one selected from the group consisting of barium (Ba), calcium (Ca), zirconium (Zr), titanium (Ti), magnesium (Mg), tantalum (Ta), niobium (Nb) and molybdenum (Mo), 1.0≤a≤1.5, 0.8≤b≤1.0, 0≤c≤0.2, 0≤d≤0.2, and 0≤e≤0.1.

[0023] In another aspect, the present invention provides a positive electrode slurry comprising a binder and the positive electrode active material.

[0024] The amount of adsorption of the binder on the positive electrode active material can be 25.0 mg / m 2 the following.

[0025] The viscosity change rate calculated from Mathematical Formula 1 at 25° C. may be 1,000% or less.

[0026] [Mathematical formula 1]

[0027]

[0028] In another aspect, the present invention provides a method for preparing a positive electrode active material, comprising: forming a lithium nickel oxide by mixing a lithium nickel transition metal hydroxide precursor containing nickel (Ni) and cobalt (Co) with a lithium raw material and performing a primary sintering; and forming a positive electrode active material containing a cobalt-containing coating by mixing the lithium nickel oxide with a cobalt-containing raw material and performing a secondary sintering, wherein the positive electrode active material comprises a lithium nickel oxide having a molar ratio of Ni to all transition metals of 80 mol % or more, and a cobalt-containing coating formed on the surface of the lithium nickel oxide, wherein the lithium nickel oxide is in the form of a single particle composed of a single nodule or a quasi-single particle as a composite of 30 or less nodules, and the D of the positive electrode active material is 0.1% by weight. 50 The thickness is 3.7 μm to 6.0 μm, the residual LiOH content is 0.20 wt % or less, the content of the cobalt-containing coating layer is 2.0 mol % or more based on 100 mol of the lithium nickel oxide, and the secondary sintering is performed at 600° C. to 700° C.

[0029] The cobalt-containing raw material may include at least one selected from the group consisting of Co(OH)2, CoOOH, Co(OCOCH3)2.4H2O, Co(NO3)2.6H2O, CoSO4 and Co(SO4)2.7H2O.

[0030] The primary sintering may be performed at 750°C to 880°C.

[0031] In another aspect, the present invention provides a positive electrode comprising the positive electrode active material.

[0032] In another aspect, the present invention provides a lithium secondary battery comprising the positive electrode.

[0033] Beneficial effects

[0034] Since the positive electrode active material of the present invention suppresses the increase of slurry viscosity and reduces the adsorption amount of the binder by forming a cobalt-containing coating on the surface of the lithium nickel oxide and adjusting the particle size, residual LiOH content and the amount of the cobalt-containing coating to specific ranges, it can improve the phase stability of the slurry, thereby achieving excellent processability.

[0035] The positive electrode active material of the present invention is prepared by 50 Adjusted to a specific range to have low charge transfer resistance and diffusion resistance, high initial efficiency, low initial resistance and excellent high-temperature life characteristics can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a SEM (scanning electron microscope) image of the positive electrode active material powder prepared in Example 1 of the present invention.

[0037] Figure 2 This is a SEM (scanning electron microscope) image of the positive electrode active material powder prepared in Example 2 of the present invention.

[0038] Figure 3 This is a SEM (scanning electron microscope) image of the positive electrode active material powder prepared in Example 3 of the present invention.

[0039] Figure 4 This is a SEM (scanning electron microscope) image of the positive electrode active material powder prepared in Comparative Example 1 of the present invention.

[0040] Figure 5 This is a SEM (scanning electron microscope) image of the positive electrode active material powder prepared in Comparative Example 2 of the present invention.

[0041] Figure 6 This is a SEM (scanning electron microscope) image of the positive electrode active material powder prepared in Comparative Example 3 of the present invention.

[0042] Figure 7 This is a SEM (scanning electron microscope) image of the positive electrode active material powder prepared in Comparative Example 4 of the present invention.

[0043] Figure 8 Graphs showing X-ray photoelectron spectroscopy (XPS) depth profiles of the cobalt-containing coating layers included in the positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4. DETAILED DESCRIPTION

[0044] The advantages and features of the present invention and their implementation methods will be illustrated by the following embodiments described with reference to the accompanying drawings. However, the present invention can be embodied in various forms and should not be construed as limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art. Furthermore, the present invention is limited only by the scope of the claims. Like reference numerals refer to like elements throughout.

[0045] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be intended to have the meaning understood by those skilled in the art. In addition, unless there is a clear specific definition, the terms defined in the general dictionary should not be interpreted abnormally or exaggeratedly.

[0046] The terms used herein are for the purpose of describing specific exemplary embodiments only and are not intended to limit the present invention. In the specification, unless otherwise mentioned, terms in the singular may include plural forms. It will be further understood that when used in this specification, the terms "comprising" and / or "including" specify the presence of the components described, but do not exclude the presence or addition of one or more other components.

[0047] In this specification, when it is said that a part includes a certain component, unless there is specific description to the contrary, it means that it may further include other components, rather than not including other components.

[0048] The description "A and / or B" in this specification means A or B, or A and B.

[0049] In this specification, unless otherwise specifically stated, the expression "%" means % by weight.

[0050] In the present specification, the expression "particle" may include any one or all of single particles, quasi-single particles, primary particles, nodules, and secondary particles.

[0051] In this specification, the expression "single particle" refers to a particle composed of one nodule. In the present invention, the expression "quasi-single particle" refers to a composite particle composed of 30 or fewer nodules.

[0052] In this specification, the term "nodule" refers to a particle unit constituting a single particle or a quasi-single particle. The nodule may be a single crystal without grain boundaries, or may be a polycrystal with no apparent grain boundaries when observed using a scanning electron microscope (SEM) at a magnification of 5,000 to 20,000 times. The average particle size of the nodules can be measured as the arithmetic mean of the particle sizes of the nodules measured using a scanning electron microscope (SEM).

[0053] In this specification, the expression "secondary particles" refers to particles formed by the aggregation of a plurality of, for example, tens to hundreds of, primary particles. Specifically, secondary particles are aggregates of 40 or more primary particles.

[0054] In this specification, the expression "D 50 " is the average particle size, wherein it refers to the particle size when the volume of particles corresponding to the particle size in the particle size distribution of the positive electrode active material is 50%. The average particle size (D 50 ) can be measured using a commercially available laser PSD (particle size distribution) measuring instrument. For example, after dispersing the positive electrode active material powder in a dispersion medium, the dispersion medium is introduced into a commercially available laser PSD (particle size distribution) measuring instrument (e.g., Microtrac S3500), and the particle size distribution is calculated by measuring the difference in diffraction patterns caused by the particle size when the particles pass through the laser beam.

[0055] In this specification, the concentration gradient composition and concentration of transition metals in the positive electrode active material particles can be confirmed by methods such as X-ray photoelectron spectroscopy (XPS), electron probe microanalyzer (EPMA), inductively coupled plasma atomic emission spectrometer (ICP-AES) or time-of-flight secondary ion mass spectrometry (ToF-SIMS). Specifically, the positive electrode active material particles can be etched with argon (Ar) for 3000 seconds, and X-ray photoelectron spectroscopy (XPS) can be used to measure the atomic ratio of each metal while etching from the surface of the positive electrode active material to its center.

[0056] Hereinafter, the present invention will be described in more detail.

[0057] positive electrode active material

[0058] The positive electrode active material of the present invention is characterized in that it includes: a lithium nickel oxide containing nickel (Ni) and cobalt (Co) and having a molar ratio of Ni to all transition metals of 80 mol% or more; and a cobalt-containing coating formed on the surface of the lithium nickel oxide, wherein the lithium nickel oxide is in the form of a single particle composed of a single nodule or a quasi-single particle as a composite of 30 or less nodules, and the content of the cobalt-containing coating is 2.0 mol% or more based on 100 mol of the lithium nickel oxide, and the D of the positive electrode active material is 2.0 mol% or more. 50 The nanostructured particles are 3.7 to 6.0 μm in diameter, the residual LiOH content is 0.20 wt % or less, and the Co / Ni ratio at a depth of 45 nm from the surface is 0.15 to 0.40.

[0059] Research and development of lithium nickel oxides is progressing more actively. However, secondary particle-based lithium nickel oxides suffer from the problem of exacerbated crack formation in the positive electrode active material during charge and discharge. To address this issue, a technique has been proposed to produce the positive electrode active material in the form of single particles rather than secondary particles by increasing the sintering temperature during the lithium nickel oxide preparation process.

[0060] However, single-particle cathode active materials present a problem: The limited interparticle interfaces that serve as pathways for lithium ion migration lead to reduced output and increased resistance due to the long lithium diffusion paths within the particles. Therefore, conventionally, single-particle cathode active materials have been formed with an average particle size of approximately 4.0 μm to minimize the resistance increase and output reduction.

[0061] However, in order to reduce the average particle size of the positive electrode active material in the form of single particles to approximately 4.0 μm, a high-intensity milling process is required, in which a large amount of fine powder is generated. As a result, there is a problem that the phase stability is rapidly reduced due to the increase in slurry viscosity.

[0062] The positive electrode active material of the present invention comprises a lithium nickel oxide containing nickel (Ni) and cobalt (Co), wherein the molar ratio of Ni to all transition metals is 80 mol% or more, preferably 90 mol% or more, and more preferably 93 mol% or more. When the molar ratio of Ni satisfies the above range, excellent capacity characteristics can be achieved.

[0063] However, since the content of nickel in the transition metal constituting the positive electrode active material is higher than that of other transition metals, the Ni-based positive electrode active material containing a high concentration of Ni has a high capacity, but there is an unstable Ni on the surface of the positive electrode active material. 3+ and Ni 4+ ions lead to structural instability. To address this structural instability, various technologies for modifying the surface of positive electrode active materials are being studied.

[0064] In view of the above situation, the inventors of the present invention have found that when a cobalt-containing coating is introduced on the surface of a Ni-based positive electrode active material containing a high concentration of Ni to improve the surface stability, the content of the cobalt-containing coating is 2.0 mol% or more based on 100 mol of lithium nickel-based oxide, and D 50 In the case of a positive electrode active material having a particle size of 3.7 μm to 6.0 μm, a residual LiOH content of 0.20 wt % or less, and a Co / Ni ratio of 0.15 to 0.40 at a depth of 45 nm from the surface, the phase stability of the slurry is improved by reducing the slurry viscosity change rate and simultaneously reducing the adsorption amount of the binder.

[0065] The lithium nickel oxide is in the form of a single particle consisting of a single nodule or a quasi-single particle composed of 30 or fewer nodules, preferably 2 to 20 nodules, and more preferably 2 to 10 nodules. Because the lithium nickel oxide in the form of a single particle and / or quasi-single particle has higher particle strength than conventional lithium nickel oxide in the form of secondary particles composed of tens to hundreds of primary particles, particle cracking during the rolling process is reduced.

[0066] Moreover, for the lithium nickel oxide in the form of single particles or quasi-single particles of the present invention, since the number of sub-components (i.e., nodules) constituting the particles is small, the changes caused by the volume expansion and contraction of the primary particles during the charge and discharge process are small, thereby significantly reducing the occurrence of cracks in the particles.

[0067] The positive electrode active material D 50 It can be 3.7 μm to 6.0 μm, preferably 3.7 μm to 5.7 μm, more preferably 3.7 μm to 5.0 μm. 50 When the particle size is less than 3.7 μm, the viscosity of the slurry may increase excessively due to a large amount of fine powder during the preparation of the slurry. 50 When the thickness is greater than 6.0 μm, initial resistance of a lithium secondary battery including the positive electrode active material may increase due to reduced lithium mobility in the positive electrode active material.

[0068] The residual lithium of the positive electrode active material of the present invention may be at least one selected from the group consisting of LiOH and Li 2 CO 3 .

[0069] The residual LiOH content may be 0.20 wt % or less, preferably 0.01 wt % to 0.20 wt %, more preferably 0.05 wt % to 0.15 wt %. Typically, since Ni-based positive active materials containing high concentrations of Ni use LiOH as a lithium raw material in a precursor in order to obtain high capacity, the proportion of LiOH remaining on the surface of the positive active material increases, and thus there is a problem of being difficult to suppress an increase in resistance or a decrease in capacity. Therefore, it is necessary to control the residual LiOH content, wherein, when the residual LiOH content is greater than the above-mentioned numerical range, when the residual LiOH is dissolved in a solvent (NMP) during electrode preparation, the solvent is alkalized, and since the alkalized solvent is mixed with a binder (PVdF) to gel the slurry, it may be difficult to prepare an electrode.

[0070] The residual lithium content of the positive electrode active material can be 0.60 wt% or less, preferably 0.01 wt% to 0.60 wt%, and more preferably 0.05 wt% to 0.50 wt%. The residual Li2CO3 content can be 0.40 wt% or less, preferably 0.10 wt% to 0.35 wt%, and more preferably 0.20 wt% to 0.30 wt%. When the residual lithium or residual Li2CO3 content is greater than the above numerical range, the positive electrode active material may react with the electrolyte after being used in the battery to cause side effects such as swelling and gas generation, resulting in possible expansion and fire of the battery. In addition, since the residual lithium serves as a raw material for forming the coating in the process of forming the coating described later, when there is excessive residual lithium on the surface of the lithium nickel oxide, a thick coating is formed, resulting in an increase in resistance characteristics.

[0071] Based on 100 moles of the lithium nickel oxide, the content of the cobalt-containing coating layer may be 2.0 mole % or more. Preferably, based on 100 moles of the lithium nickel oxide, the content of the cobalt-containing coating layer may be 2.0 mole % to 5.5 mole %, more preferably 2.0 mole % to 3.5 mole %. In the case where the amount of the cobalt-containing coating layer of the present invention exceeds the above amount range, an excessively thick coating layer may be formed, which may lead to an increase in initial resistance. On the contrary, in the case where the amount of the cobalt-containing coating layer is lower than the above amount range, there is a risk of unstable Ni present on the surface of the positive electrode active material. 3+ and Ni 4+ ions lead to problems that cannot be solved due to the limitations of structural instability.

[0072] In addition, the Co / Ni ratio of the cobalt-containing coating layer at a depth of 45 nm from the surface thereof may be 0.15 to 0.40, preferably 0.16 to 0.30, and more preferably 0.17 to 0.25. 50 When the residual LiOH content satisfies the above range, excellent processability can be achieved because the phase stability of the slurry is improved by suppressing the increase in the slurry viscosity and reducing the adsorption amount of the binder.

[0073] The positive electrode active material of the present invention is D min The particle size may be 1.0 μm or larger, preferably 1.0 μm to 6.0 μm, and more preferably 1.0 μm to 5.0 μm. min When the above range is satisfied, the viscosity may excessively increase during slurry preparation to reduce workability.

[0074] The positive electrode active material of the present invention may include a lithium nickel-based oxide, and specifically may include a lithium nickel-based oxide having a composition as shown in the following Chemical Formula 1.

[0075] [Chemical Formula 1]

[0076] Li a Ni b Co c M 1 d M 2 e O2

[0077] In Chemical Formula 1, M 1 is at least one selected from the group consisting of manganese (Mn) and aluminum (Al), preferably Mn or a combination of Mn and Al, and M 2 is at least one selected from the group consisting of barium (Ba), calcium (Ca), zirconium (Zr), titanium (Ti), magnesium (Mg), tantalum (Ta), niobium (Nb), and molybdenum (Mo). The element M is not necessarily included 2 , but when it is included in an appropriate amount, it can play a role in promoting grain growth during sintering or improving the stability of the crystal structure.

[0078] a represents the molar ratio of lithium in the lithium nickel-based oxide. Among them, a can satisfy 1.0 ≤ a ≤ 1.5, 1.0 ≤ a ≤ 1.5, or 1.0 ≤ a ≤ 1.2. When the molar ratio of lithium satisfies the above range, a stable layered crystal structure can be formed.

[0079] b represents the molar ratio of nickel in all metals other than lithium in the lithium nickel-based oxide. Among them, b can satisfy 0.8 ≤ b ≤ 1.0, 0.85 ≤ b ≤ 1.0, or 0.90 ≤ b ≤ 1.0. When the molar ratio of nickel satisfies the above range, the capacity characteristics are excellent. In particular, when the molar ratio of nickel is 0.90 or more, even better capacity characteristics can be achieved.

[0080] c represents the molar ratio of cobalt in all metals other than lithium in the lithium nickel-based oxide. Among them, c can satisfy 0 ≤ c ≤ 0.2, 0 < c < 0.2, 0 < c ≤ 0.18, or 0 < c < 0.18.

[0081] d represents the molar ratio of M in all metals other than lithium in the lithium nickel-based oxide 1 , among which d can satisfy 0 ≤ d ≤ 0.2, 0 < d < 0.2, 0 < d ≤ 0.18, or 0 < d < 0.18.

[0082] e represents the molar ratio of element M in all metals other than lithium in the lithium nickel-based oxide 2 , among which e can satisfy 0 ≤ e ≤ 0.1, 0 < e < 0.1, or 0 < e ≤ 0.08.

[0083] Preparation method of positive electrode active material

[0084] Next, a method for preparing the positive electrode active material of the present invention will be described.

[0085] When preparing a positive electrode active material having a molar ratio of Ni to all transition metals of 80 mol% or more, due to the high sintering temperature, the surface structure integrity of the positive electrode active material may be low, and the concentration of residual lithium may be high. In addition, when the particle size of the positive electrode active material is large, there is also the problem that the initial resistance of the positive electrode active material may be high. Therefore, there is a need for a technology that can improve the integrity of the surface structure, reduce the concentration of residual lithium, and reduce the initial resistance by optimizing the coating conditions by forming a coating on the surface of lithium nickel oxide particles.

[0086] The preparation method of the positive electrode active material of the present invention includes the following steps: forming a lithium nickel oxide by mixing a lithium nickel transition metal hydroxide precursor containing nickel (Ni) and cobalt (Co) with a lithium raw material and performing a primary sintering, and forming a positive electrode active material containing a cobalt coating by mixing the lithium nickel oxide with a cobalt-containing raw material and performing a secondary sintering.

[0087] The lithium nickel transition metal oxide has a molar ratio of Ni to all transition metals of 80 mol% or more and is a single particle consisting of a single nodule or a quasi-single particle that is a composite of 30 or less nodules. 50 The thickness of the lithium nickel-based oxide is 3.7 μm to 6.0 μm, the residual LiOH content is 0.20 wt % or less, the content of the cobalt-containing coating layer is 2.0 mol % or more based on 100 mol of the lithium nickel-based oxide, and the secondary sintering is performed at 600° C. to 700° C. Since the above contents are also applicable, repeated description will be omitted.

[0088] Next, each step of the method for preparing the positive electrode active material is described in detail.

[0089] (1) Formation of lithium nickel oxide

[0090] First, a lithium nickel-based transition metal hydroxide precursor containing nickel (Ni) and cobalt (Co) is mixed with a lithium raw material and the mixture is primarily sintered to form a lithium nickel-based oxide.

[0091] In this case, commercially available precursors such as nickel cobalt manganese hydroxides can be purchased and used as lithium nickel transition metal hydroxide precursors, i.e., positive electrode active material precursors, or lithium nickel transition metal hydroxide precursors can be prepared according to precursor preparation methods known in the art, such as coprecipitation method.

[0092] For example, in the preparation of nickel (Ni), cobalt (Co) and M 1After preparing a transition metal-containing solution containing cations of ammonium, a positive electrode active material precursor can be prepared by performing a coprecipitation reaction while adding a complexing agent containing ammonium cations and an alkaline aqueous solution to the transition metal-containing solution.

[0093] The transition metal-containing solution may include a nickel-containing raw material, a cobalt-containing raw material, and a M-containing raw material. 1 Raw materials, containing M 1 The raw material may be a manganese-containing raw material and / or an aluminum-containing raw material.

[0094] The nickel-containing raw material may be, for example, a nickel-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxyl, specifically Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, fatty acid nickel salt, nickel halide or a combination thereof, but is not limited thereto.

[0095] The cobalt-containing raw material may be, for example, a cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxyl, specifically Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4, Co(SO4)2·7H2O or a combination thereof, but is not limited thereto.

[0096] The manganese-containing raw material can be, for example, manganese-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, oxyhydroxides or combinations thereof, specifically manganese oxides such as Mn2O3, MnO2 and Mn3O4; manganese salts such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese dicarboxylate, manganese citrate and fatty acid manganese salts; manganese hydroxide, manganese chloride or combinations thereof, but are not limited thereto.

[0097] The aluminum-containing raw material can be, for example, Al2O3, Al(OH)3, Al(NO3)3, Al2(SO4)3, (HO)2AlCH3CO2, HOAl(CH3CO2)2, Al(CH3CO2)3, aluminum halide, or a combination thereof.

[0098] The solution containing transition metal can be prepared by mixing nickel-containing raw material, cobalt-containing raw material and M-containing raw material. 1 The raw materials are added to a solvent (specifically water or a mixed solvent of water and an organic solvent (such as alcohol) that can be uniformly mixed with water) to prepare the solution, or the solution can be prepared by mixing an aqueous solution containing a nickel raw material, an aqueous solution containing a cobalt raw material and an aqueous solution containing M 1 The raw materials are mixed and prepared.

[0099] The complexing agent containing ammonium cations may be, for example, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or a combination thereof, but is not limited thereto. The complexing agent containing ammonium cations may also be used in the form of an aqueous solution, in which case water or a mixture of water and an organic solvent (specifically, an alcohol, etc.) that can be uniformly mixed with water may be used as the solvent.

[0100] The basic compound can be an alkali metal or alkaline earth metal hydroxide, such as NaOH, KOH or Ca(OH)2, a hydrate thereof or a combination thereof. The basic compound can also be used in the form of an aqueous solution. In this case, water or a mixture of water and an organic solvent that can be uniformly mixed with water (particularly an alcohol, etc.) can be used as the solvent.

[0101] The alkaline compound is added to adjust the pH of the reaction solution, wherein the amount of the alkaline compound added can be such that the pH of the metal solution is 8 to 12.

[0102] The coprecipitation reaction can be carried out in an inert atmosphere such as nitrogen or argon at a temperature ranging from 35°C to 80°C.

[0103] Through the above process, nickel-cobalt-M 1 The positive active material precursor particles of the hydroxide are precipitated in the reaction solution. 1 The concentration of the raw materials can prepare a positive electrode active material precursor having a nickel (Ni) content of 80 mol % or more of the total metal content. The precipitated positive electrode active material precursor particles can be separated and dried according to conventional methods to prepare a positive electrode active material precursor.

[0104] Subsequently, the lithium nickel-based transition metal hydroxide precursor may be mixed with the lithium raw material.

[0105] As the lithium raw material, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides can be used, and the lithium raw material is not particularly limited as long as it is soluble in water. Specifically, the lithium raw material can be Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, or Li3C6H5O7, and any one of them or a mixture of two or more thereof can be used.

[0106] The positive active material precursor and the lithium raw material may be mixed at a molar ratio of, for example, about 1:1, about 1:1.05, about 1:1.10, about 1:1.15, or about 1:1.20, but the present invention is not limited thereto.

[0107] Thereafter, the mixture may be subjected to a primary sintering. The primary sintering may be performed in air or an oxygen atmosphere. The primary sintering may be performed at a temperature of 750°C to 880°C, 780°C to 880°C, 800°C to 870°C, or 820°C to 870°C. The primary sintering may be performed for 5 to 20 hours, 6 to 12 hours, or 8 to 10 hours.

[0108] (2) Mixing of lithium nickel oxides and cobalt-containing raw materials

[0109] Next, a positive electrode active material including a cobalt-containing coating layer is formed by mixing the lithium nickel-based oxide with a cobalt-containing raw material and performing secondary sintering.

[0110] For example, the surface of a lithium nickel oxide is coated with a cobalt-containing raw material. The cobalt-containing raw material can be at least one of Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4, and Co(SO4)2·7H2O. Specifically, Co(OH)2 can be added to the lithium nickel oxide to form a positive electrode active material containing a cobalt-containing coating.

[0111] As described above, by forming the cobalt-containing coating layer on the surface of the lithium nickel-based oxide, a large amount of unstable Ni ions existing on the surface of the positive electrode active material can be stabilized, thereby improving the stability of the positive electrode active material.

[0112] The secondary sintering may be performed at a temperature of 600 to 700°C, preferably 630 to 690°C, more preferably 640 to 690°C.

[0113] When the secondary sintering temperature is higher than 700°C, cobalt diffuses into the positive electrode active material, causing changes in the crystal structure of the positive electrode active material and the residual lithium content, which can adversely affect the lifespan and resistance characteristics of the positive electrode active material. This makes it difficult to achieve the desired residual lithium content and cobalt coating amount.

[0114] When the secondary sintering temperature is lower than 600°C, the cobalt-containing coating may peel off from the positive electrode active material due to its weak bonding force with the surface of the positive electrode active material, and compared with the case where the secondary sintering is carried out within the above-mentioned temperature range, the effect of improving the high-temperature life characteristics may not be significant due to the formation of a coating with a lower cobalt content.

[0115] The secondary sintering may be performed for 2 to 8 hours, preferably 3 to 7 hours, and more preferably 4 to 6 hours.

[0116] As a result of mixing the lithium nickel-based oxide with the cobalt-containing raw material and performing secondary sintering within the above sintering temperature and sintering time range, a secondary battery with low initial resistance can be realized by forming a desired amount of cobalt-containing coating on the surface of the lithium nickel-based oxide.

[0117] A separate washing process may not be included between the primary sintering and the secondary sintering. Conventionally, a process of washing the residual lithium present on the surface of the positive electrode active material is performed. The reason for this is that when residual lithium is present, there are problems such as side reactions with the electrolyte when used in a battery and increased gas generation when stored at high temperatures. On the contrary, in the preparation method of an embodiment of the present invention, since a separate washing process is not performed, residual lithium exists on the surface of the particles, and the residual lithium reacts with cobalt to form a coating form of the LiCoO2 phase on the surface of the particles, thereby achieving excellent high-temperature life characteristics.

[0118] positive electrode slurry

[0119] Next, the positive electrode slurry of the present invention will be described.

[0120] The positive electrode slurry of the present invention is characterized in that it contains the binder for the positive electrode active material of the present invention.

[0121] Specifically, the positive electrode slurry of the present invention may optionally contain a conductive agent as necessary. Specifically, the positive electrode slurry may be prepared by mixing a positive electrode active material, a binder and / or a conductive agent in a solvent.

[0122] The adsorption capacity of the binder on the positive electrode active material of the present invention can be 25.0 mg / m 2 Below, preferably 10.0 mg / m 2 Up to 25.0 mg / m 2 , more preferably 15.0 mg / m 2 Up to 23.0 mg / m 2 In the case where the adsorption amount of the binder to the positive electrode active material satisfies the above range, the viscosity of the slurry can be reduced and the phase stability of the slurry can be improved.

[0123] The viscosity change rate of the positive electrode slurry of the present invention at 25°C, as calculated by the following Mathematical Formula 1, may be 1,000% or less, preferably 800% or less, and more preferably 10% to 600%. When the viscosity change rate satisfies the above range, the phase stability of the slurry can be improved, and when the slurry is used in a battery, stable electrode production and improved yield can be achieved.

[0124] [Mathematical formula 1]

[0125]

[0126] The binder improves the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the collector. Specific examples of the binder can be: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid and hydrogen are replaced by lithium (Li), sodium (Na) or calcium (Ca) polymers or their various copolymers, any one of which or a mixture of two or more can be used. Based on the total solids content of the positive electrode slurry, the content of the binder can be 1% by weight to 30% by weight, preferably 1% by weight to 20% by weight, more preferably 1% by weight to 10% by weight.

[0127] Conductive agents are used to provide conductivity to the electrodes. Any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not cause adverse chemical changes in the battery. Specific examples of conductive agents can include: graphite such as natural graphite or artificial graphite; carbon materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or fibers such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; conductive polymers such as polyphenylene derivatives, and any one of these or a mixture of two or more thereof can be used. The content of the conductive agent can be 0.01 wt% to 10 wt%, 0.1 wt% to 9 wt%, or 0.1 wt% to 5 wt%, based on the total solids content of the positive electrode slurry.

[0128] The solvent may be a solvent commonly used in the prior art, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone or water, and any one thereof or a mixture of two or more thereof may be used. Considering the coating thickness and preparation yield of the slurry, if the solvent can dissolve or disperse the positive electrode active material, the conductive agent and the binder, and can have a viscosity that can provide excellent thickness uniformity in the subsequent coating process for preparing the positive electrode, the amount of the solvent may be sufficient.

[0129] positive electrode

[0130] The positive electrode of the present invention contains the aforementioned positive electrode active material of the present invention. Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer contains a positive electrode slurry containing the positive electrode active material of the present invention. Since the positive electrode active material and positive electrode slurry have been described above, their detailed description will be omitted. Only the remaining components will be described in detail below.

[0131] The positive electrode collector may comprise a metal having high conductivity, and is not particularly limited as long as it is non-reactive within the voltage range of the battery and the positive electrode active material layer easily adheres thereto. As the positive electrode collector, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, or silver, etc., may be used. In addition, the thickness of the positive electrode collector may generally be 3 μm to 500 μm, and fine concavo-convexities may be formed on the surface of the collector to improve the adhesion of the positive electrode active material. The positive electrode collector may be used in various shapes, such as films, sheets, foils, nets, porous bodies, foams, and non-woven fabrics, for example.

[0132] In addition to using the above-mentioned positive electrode active material, the positive electrode can be prepared according to a typical method for preparing a positive electrode. Specifically, the above-mentioned positive electrode slurry is applied to a positive electrode collector, and then the coated positive electrode collector can be dried and rolled to prepare a positive electrode.

[0133] In addition, as another method, the positive electrode can be prepared by casting the positive electrode slurry on a separate support and then laminating the film separated from the support on a positive electrode collector.

[0134] lithium secondary batteries

[0135] Next, the lithium secondary battery of the present invention will be described.

[0136] The lithium secondary battery specifically includes a positive electrode, a negative electrode arranged opposite to the positive electrode, and a separator and an electrolyte inserted between the positive electrode and the negative electrode. Since the positive electrode is the same as above, its detailed description will be omitted, and only the remaining components will be described in detail below.

[0137] In addition, the lithium secondary battery may further optionally include a battery container accommodating an electrode assembly of a positive electrode, a negative electrode, and a separator, and a sealing member sealing the battery container.

[0138] In a lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector.

[0139] The negative electrode current collector is not particularly limited, as long as it has high conductivity and does not cause adverse chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or copper or stainless steel surface-treated with one of carbon, nickel, titanium, or silver, and aluminum-cadmium alloys can be used. The thickness of the negative electrode current collector can typically be 3 to 500 μm. Similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to improve the adhesion of the negative electrode active material. The negative electrode current collector can be used in various shapes, such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabrics.

[0140] The negative electrode active material layer optionally contains a binder and a conductive agent in addition to the negative electrode active material.

[0141] Compounds that can reversibly intercalate and deintercalate lithium can be used as negative electrode active materials. Specific examples of negative electrode active materials include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metal compounds that can be alloyed with lithium, such as silicon (Si), aluminum (Al), tin (Sn), lead (Pb), zinc (Zn), bismuth (Bi), indium (In), magnesium (Mg), gallium (Ga), cadmium (Cd), Si alloys, Sn alloys, or Al alloys; metal oxides that can be doped and dedoped with lithium, such as SiO β (0<β<2), SnO2, vanadium oxide and lithium vanadium oxide; or a composite comprising a metal compound and a carbonaceous material, such as a Si-C composite or a Sn-C composite, any one of which or a mixture of two or more thereof can be used. In addition, a metallic lithium film can be used as a negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon can be used as carbon materials. Typical examples of low-crystalline carbon can be soft carbon and hard carbon, while typical examples of high-crystalline carbon can be irregular, planar, flaky, spherical or fibrous natural graphite or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-type carbon fibers, mesophase carbon microbeads, mesophase pitch and high-temperature sintered carbon, such as coke derived from petroleum or coal tar pitch.

[0142] The negative electrode active material may be contained in an amount of 80 to 99 weight %, 82 to 99 weight %, or 84 to 99 weight %, based on the total weight of the negative electrode active material layer.

[0143] The binder is a component that helps to bind the conductive agent, active material and collector, wherein the binder is usually added in an amount of 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of the binder can be polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluororubber and various copolymers thereof.

[0144] The conductive agent is a component used to further improve the conductivity of the negative electrode active material, wherein the content of the conductive agent can be 1% to 30% by weight, 1% to 20% by weight, or 1% to 10% by weight based on the total weight of the negative electrode active material layer. The conductive agent is not particularly limited as long as it has conductivity without causing adverse chemical changes in the battery. For example, conductive materials such as graphite, such as natural graphite or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers, such as carbon fibers or metal fibers; fluorocarbons; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or polyphenylene derivatives can be used.

[0145] The negative electrode active material layer can be prepared by coating a negative electrode slurry composition prepared by dissolving or dispersing an optional binder and a conductive agent and a negative electrode active material in a solvent on a negative electrode collector, and drying the coated negative electrode collector, or by casting the negative electrode slurry composition on a separate support and then laminating a film separated from the support on the negative electrode collector.

[0146] In lithium secondary batteries, the negative electrode and the positive electrode are separated by a diaphragm, and a path for the movement of lithium ions is provided, wherein any diaphragm can be used as a diaphragm without particular limitation, as long as it is commonly used in lithium secondary batteries, in particular, a diaphragm having high moisture retention for an electrolyte and low impedance to the transmission of electrolyte ions can be used. Specifically, a porous polymer film can be used, for example, a porous polymer film prepared by a polyolefin polymer (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer), or a laminated structure thereof of more than two layers can be used. In addition, a typical porous nonwoven fabric can be used, for example, a nonwoven fabric formed by high melting point glass fiber or polyethylene terephthalate fiber. In addition, a coated diaphragm comprising a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and a diaphragm with a single layer or multilayer structure can be optionally used.

[0147] In addition, the electrolyte used in the present invention may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte or a molten inorganic electrolyte that can be used in the preparation of a lithium secondary battery, but the present invention is not limited thereto.

[0148] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0149] Any organic solvent can be used as the organic solvent without particular limitation, as long as it can act as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, the following solvents can be used as the organic solvent: ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; or carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC) and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitrile such as R-CN (wherein R is a linear, branched or cyclic C2-C20 hydrocarbon group and may contain a double bond aromatic ring or an ether bond); amide such as dimethylformamide; dioxolane such as 1,3-dioxolane; or cyclopentane sulfone. Among these solvents, carbonate solvents are preferred, and more preferably a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant and a low-viscosity straight-chain carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) that can improve the charge / discharge performance of lithium-ion batteries.

[0150] Lithium salts can be used without particular limitation as long as they are compounds capable of providing lithium ions for lithium secondary batteries. Specifically, the anions of the lithium salts can be selected from the group consisting of F - 、Cl - Br - , I - 、NO3 - 、N(CN)2 - 、BF4 - CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N - CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 -、CH3CO2 - 、SCN - and (CF3CF2SO2)2N - At least one of the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI or LiB(C2O4)2 can be used as the lithium salt. The lithium salt can be used in a concentration range of 0.1M to 4.0M, preferably 0.5M to 3.0M, and more preferably 1.0M to 2.0M. If the concentration of the lithium salt is within the above range, since the electrolyte can have appropriate conductivity and viscosity, excellent performance of the electrolyte can be obtained, and lithium ions can be efficiently transferred.

[0151] In order to improve the life characteristics of the battery, suppress the reduction of the battery capacity and increase the discharge capacity of the battery, in addition to the above-mentioned electrolyte components, at least one additive may be further included in the electrolyte, such as a halogenated alkylene carbonate compound (such as difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glycol ether, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum chloride. In this case, the content of the additive may be 0.1 wt % to 10.0 wt % based on the total weight of the electrolyte.

[0152] As described above, since the lithium secondary battery including the positive electrode active material of the present invention stably exhibits excellent capacity characteristics, output characteristics and life characteristics, the lithium secondary battery is suitable for portable devices (such as mobile phones, notebook computers and digital cameras) and electric vehicles (such as hybrid electric vehicles (HEV)).

[0153] Therefore, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the battery module are provided.

[0154] The battery module or battery pack can be used as a power source for at least one of the following medium or large devices: power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or energy storage systems.

[0155] Hereinafter, examples of the present invention will be described in detail in a manner that allows those skilled in the art to which the present invention pertains to easily implement the present invention. However, the present invention can be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein.

[0156] Examples and Comparative Examples

[0157] Example 1 - Preparation of positive electrode active material

[0158] The positive electrode active material precursor Ni 0.93 Co 0.05 Mn 0.02 (OH)2 and lithium raw material LiOH were placed in a 700L Henschel mixer to make the molar ratio of Li: transition metal (Ni+Co+Mn) be 1.05:1 and mixed at a center speed of 400rpm for 20 minutes. The mixed powder was placed in an alumina crucible with a size of 330mm×330mm and sintered at 850℃ for 12 hours in an oxygen atmosphere to prepare LiNi 0.93 Co 0.05 Mn 0.02 O2.

[0159] Thereafter, the primary sintered product was mixed with 12,000 ppm of Co(OH)2 so that the molar ratio of the primary sintered product:Co was 100:2, and then secondary sintered at 680°C for 5 hours to prepare a positive electrode active material powder formed with a cobalt-containing coating layer.

[0160] Example 2 - Preparation of positive electrode active material

[0161] A positive electrode active material powder was prepared in the same manner as in Example 1, except that the primary sintered product was mixed with 18,000 ppm of Co(OH)2 so that the molar ratio of the primary sintered product:Co was 100:3, and then secondary sintering was performed at 680°C for 5 hours.

[0162] Example 3 - Preparation of positive electrode active material

[0163] A positive electrode active material powder was prepared in the same manner as in Example 1, except that the secondary sintering was performed at 660° C. for 5 hours.

[0164] Example 4 - Preparation of positive electrode active material

[0165] In the same manner as in Example 1, positive electrode active material powder was prepared.

[0166] Example 5 - Preparation of positive electrode active material

[0167] In the same manner as in Example 1, positive electrode active material powder was prepared.

[0168] Comparative Example 1—Preparation of positive electrode active material

[0169] A positive electrode active material powder was prepared in the same manner as in Example 1, except that the secondary sintering was performed at 720° C. for 5 hours.

[0170] Comparative Example 2—Preparation of positive electrode active material

[0171] A positive electrode active material powder was prepared in the same manner as in Example 1, except that the secondary sintering was performed at 800° C. for 5 hours.

[0172] Comparative Example 3—Preparation of positive electrode active material

[0173] A positive electrode active material powder was prepared in the same manner as in Example 1, except that the primary sintered product was mixed with 6,000 ppm of Co(OH)2 so that the molar ratio of the primary sintered product:Co was 100:1, and then secondary sintering was performed at 680°C for 5 hours.

[0174] Comparative Example 4—Preparation of positive electrode active material

[0175] A positive electrode active material powder was prepared in the same manner as in Example 1, except that sintering was performed once at 850° C. for 10 hours.

[0176] Comparative Example 5—Preparation of positive electrode active material

[0177] A positive electrode active material powder was prepared in the same manner as in Example 1, except that the positive electrode active material precursor and the lithium raw material LiOH were placed in a Henschel mixer, mixed at a center speed of 400 rpm for 30 minutes, and then sintered once at 950° C. for 12 hours.

[0178] Experimental Example 1—Particle Size Distribution of Positive Electrode Active Materials

[0179] After 0.05 g of each of the positive electrode active materials prepared in Examples 1 to 5 and Comparative Examples 1 to 5 was dispersed in a H2O dispersion medium, the dispersion medium was introduced into a commercially available laser PSD (particle size distribution) measuring instrument (e.g., Microtrac S3500), and the particle size distribution was calculated by measuring the difference in diffraction patterns due to particle size when the particles passed through the laser beam.

[0180] D 50 The particle size distribution of the positive electrode active material indicates the particle size at which the volume of particles corresponding to this particle size accounts for 50%. The results are shown in Tables 1 and 2 below.

[0181] Experimental Example 2—Surface Observation of Positive Electrode Active Materials

[0182] Scanning electron microscope (SEM) images of each of the positive electrode active material particles prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were obtained using a scanning electron microscope. These SEM images are shown in FIG. Figures 1 to 7 shown.

[0183] according to Figures 1 to 3 , for the positive electrode active materials prepared in Examples 1 to 3, it was confirmed that a cobalt-containing coating layer in the form of a layer or island was formed on the surface of the lithium nickel-based oxide.

[0184] On the contrary, according to Figures 4 to 7 For the positive electrode active materials prepared in Comparative Examples 1 and 2, since cobalt diffused into the particles due to the high secondary sintering temperature, almost no cobalt-containing coating was formed on the surface of the lithium nickel oxide, confirming that the surface was smooth. For the positive electrode active material prepared in Comparative Example 3, since the amount of cobalt-containing raw material was small, it was confirmed that almost no cobalt-containing coating was formed. Since the positive electrode active material prepared in Comparative Example 4 differed from Examples 1 to 3 only in that the primary sintering time was reduced, it was confirmed that a cobalt-containing coating was formed on the surface of the lithium nickel oxide.

[0185] Experimental Example 3—XPS Analysis of Positive Electrode Active Materials

[0186] While etching the cobalt-containing coatings contained in the positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 from the surface to the center by depth profile using X-ray photoelectron spectroscopy (XPS) (Thermo Fisher Scientific Inc., Nexsa2 ESCA system), the Co / Ni ratio was measured over etching time. The measurement results are shown in FIG. Figure 8 .

[0187] Specifically, the positive electrode active material particles prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were introduced into a vacuum chamber and then measured under the following conditions.

[0188] -X-ray source: monochromatic Al Kα (1486.6eV)

[0189] -X-ray spot size: 400μm

[0190] -Sputtering: Monatomic Ar (energy: 1000eV, grating width: 2mm)

[0191] - Etching rate: 0.09nm / s based on Ta205

[0192] -Operation mode: CAE (Constant Analyzer Energy) mode

[0193] -Full scan: pass energy 200eV, energy step 1eV

[0194] -Narrow scan: Scan mode, pass energy 50eV, energy step 0.1eV

[0195] - Charge compensation: neutralize electron gun 2V, 250μA

[0196] Experimental Example 4 - Measurement of Residual Lithium Content in Positive Electrode Active Materials

[0197] The residual lithium content of each of the positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 was measured. The measurement results are shown in Table 1 below.

[0198] The residual lithium content on the surface of the positive electrode active material was measured by pH titration using a Mettler Toledo T5 as a pH meter. Specifically, 10 g of each of the positive electrode active material powders prepared in Examples 1 to 3 and Comparative Examples 1 to 4 was stirred in 100 mL of distilled water for 5 minutes, and then pH titration was performed while adding 0.1 N HCl solution to the solution.

[0199] Experimental Example 5 - Measurement of Adhesive Adsorption

[0200] <Preparation of Slurry for Adsorption Measurement>

[0201] Each of the positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 was mixed with a PVdF binder (KF9700) at a weight ratio of 98.11:1.89 to prepare a slurry for measuring adsorption capacity with a solid content of 76.2% by weight. Specifically, the slurry was prepared by mixing at 45°C and 2,500 rpm for 6 hours under dry room conditions.

[0202] The adsorption slurry was centrifuged to measure the solids content of the supernatant. The adsorption of the adhesive was calculated using a TA Instruments rheometer based on the viscosity master curve for each solids content of the adhesive / slurry. The calculated results are shown in Table 1 below.

[0203] As shown in Table 1, the amount of binder adsorbed on each positive electrode active material prepared in Examples 1 to 3 is comparable to the amount of binder adsorbed on the positive electrode active material prepared in Comparative Example 3, but it can be confirmed that it is lower than the amount of binder adsorbed on the positive electrode active materials prepared in Comparative Examples 1, 2 and 4.

[0204] Experimental Example 6 - Measurement of Viscosity of Positive Electrode Slurry

[0205] <Preparation of positive electrode slurry>

[0206] The positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3, PVdF (polyvinylidene fluoride) (KF9700, Solef5130) as a binder, nitrile rubber (H-NBR) (HPD01) as a dispersant, and carbon black (B.CNT, SFG6L) and single-walled carbon nanotubes as a conductive agent were mixed in a weight ratio of 97.02:1.87:0.002:0.18:0.60:0.30:0.01 to prepare a positive electrode slurry with a solid content of 67 weight%.

[0207] Specifically, under dry room conditions, a slurry for viscosity measurement was prepared by mixing at 45° C. and 2,500 rpm for 75 minutes.

[0208] The viscosity of each positive electrode slurry was measured using a viscosity measuring device (rheometer from TA Instruments). The measurement results are shown in Table 1 below.

[0209] [Table 1]

[0210]

[0211] As shown in Table 1, it can be confirmed that the viscosity change rates of the positive electrode active materials prepared in Examples 1 to 3 are significantly lower than the viscosity change rates of the positive electrode active materials prepared in Comparative Examples 1 to 4.

[0212] Experimental Example 6: Analysis of the Electrochemical Characteristics of Lithium Secondary Batteries

[0213] The initial efficiency, initial resistance, and high-temperature life characteristics of lithium secondary battery half cells prepared using the positive electrode active materials prepared in Examples 4 and 5 and Comparative Example 5 were analyzed. The analysis results are shown in Table 2 below.

[0214] <Preparation of Lithium Secondary Battery>

[0215] Each positive electrode active material prepared in Examples 4 and 5 and Comparative Example 5, a conductive agent (carbon black, Denka), and a PVdF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. One surface of an aluminum current collector was coated with the positive electrode slurry, dried at 500°C, and then rolled to prepare a positive electrode.

[0216] A lithium metal electrode was used as the negative electrode.

[0217] An electrode assembly was prepared by placing a separator between the positive and negative electrodes prepared above, the electrode assembly was placed in a battery case, and then an electrolyte was injected into the battery case to prepare a battery cell. The electrolyte was prepared by dissolving 0.6M LiPF6 in a mixed organic solvent obtained by mixing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:2:1, and adding 2% by weight of vinylene carbonate (VC).

[0218] <Analysis of Initial Efficiency, Initial Resistance, and High-Temperature Life Characteristics>

[0219] The lithium secondary battery prepared as described above was charged and discharged.

[0220] Specifically, for the initial efficiency, each lithium secondary battery was charged to 4.25 V at 0.2 C and then discharged to 2.5 V at 0.2 C in a constant current-constant voltage (CC-CV) mode at 25° C. for one charge-discharge cycle. The initial efficiency was calculated as follows.

[0221] Initial efficiency (%) = (discharge capacity in one charge-discharge cycle / charge capacity in one charge-discharge cycle) × 100

[0222] Specifically, the initial resistance was calculated based on the discharge capacity in one charge-discharge cycle measured at 0.2 C. The initial resistance was calculated using the voltage change rate when a current of 1.0 C was applied for 10 seconds after the state of charge (SOC) was set to 95% at 0.2 C over two charge-discharge cycles. Furthermore, the initial resistance was calculated using the voltage change rate after the SOC was set to 50% over two charge-discharge cycles and the voltage change rate after the SOC was set to 10% over two charge-discharge cycles.

[0223] Specifically, each lithium secondary battery was charged at 0.5C to 4.25V and discharged at 1.0C to 2.5V in CC-CV mode at 45°C for 50 charge-discharge cycles. The capacity retention rate was then measured to evaluate high-temperature life characteristics. The capacity retention rate was calculated as follows.

[0224] Capacity retention (%) = (discharge capacity after n charge-discharge cycles / discharge capacity after one charge-discharge cycle) × 100

[0225] [Table 2]

[0226]

[0227] As shown in Table 2, it can be confirmed that the 50 The lithium secondary battery of the positive electrode active material of Comparative Example 5 with a diameter greater than 6.0 μm and the lithium secondary battery containing D 50Compared with the lithium secondary battery of the positive electrode active materials of Examples 4 and 5 with a diameter of 3.7 μm to 6.0 μm, the initial efficiency is lower, the initial resistance is higher, and the capacity retention rate is lower. 50 Positive electrode active materials with a particle size greater than 6.0 μm are thought to have an increased initial resistance in lithium secondary batteries containing such materials, as lithium mobility decreases as the diffusion distance of lithium ions within the particles increases. Furthermore, increased charge transfer resistance and diffusion resistance are thought to reduce initial efficiency and capacity retention.

Claims

1. A positive electrode active material comprising: A lithium nickel oxide containing nickel (Ni) and cobalt (Co) in which the molar ratio of Ni to all transition metals is 80 mol % or more; and a cobalt-containing coating formed on the surface of the lithium nickel oxide, The lithium nickel oxide is in the form of a single particle consisting of a single nodule or a quasi-single particle as a composite of 30 or less nodules. The content of the cobalt-containing coating layer is 2.0 mol% or more based on 100 mol of the lithium nickel-based oxide, and The positive electrode active material D 50 The positive electrode active material has a Co / Ni ratio of 0.15 to 0.40 at a depth of 45 nm from the surface of the positive electrode active material.

2. The positive electrode active material according to claim 1, wherein The molar ratio of Ni to all transition metals in the lithium nickel oxide is 93 mol % or more.

3. The positive electrode active material according to claim 1, wherein The positive electrode active material has a residual lithium content of 0.60 wt % or less.

4. The positive electrode active material according to claim 1, wherein The residual Li2CO3 content of the positive electrode active material is 0.40 wt% or less.

5. The positive electrode active material according to claim 1, wherein The positive electrode active material D min 1.0 μm or more.

6. The positive electrode active material according to claim 1, wherein The lithium nickel oxide is represented by Chemical Formula 1: [Chemical Formula 1] Li a Ni b Co c M 1 d M 2 e O2 Wherein, in Chemical Formula 1, M 1 is at least one selected from the group consisting of manganese (Mn) and aluminum (Al), M 2 It is at least one selected from the group consisting of barium (Ba), calcium (Ca), zirconium (Zr), titanium (Ti), magnesium (Mg), tantalum (Ta), niobium (Nb) and molybdenum (Mo), 1.0≤a≤1.5, 0.8≤b≤1.0, 0≤c≤0.2, 0≤d≤0.2, and 0≤e≤0.

1. 7 . A positive electrode slurry comprising a binder and the positive electrode active material according to claim 1 .

8. The positive electrode slurry according to claim 7, wherein: The adsorption amount of the binder on the positive electrode active material is 25.0 mg / m 2 the following.

9. The positive electrode slurry according to claim 7, wherein: The viscosity change rate calculated by Mathematical Formula 1 at 25°C is 1,000% or less: [Mathematical formula 1] 10. A method for preparing a positive electrode active material, the method comprising: forming a lithium nickel-based oxide by mixing a lithium nickel-based transition metal hydroxide precursor containing nickel (Ni) and cobalt (Co) with a lithium raw material and performing a primary sintering; and The positive electrode active material containing the cobalt coating is formed by mixing the lithium nickel oxide with a cobalt-containing raw material and performing secondary sintering. The positive electrode active material comprises a lithium nickel oxide having a molar ratio of Ni to all transition metals of 80 mol % or more, and a cobalt-containing coating formed on the surface of the lithium nickel oxide. The lithium nickel oxide is in the form of a single particle consisting of a single nodule or a quasi-single particle as a composite of 30 or less nodules, and the D of the positive electrode active material is 50 The thickness of the lithium nickel oxide is 3.7 μm to 6.0 μm, the residual LiOH content is 0.20 wt % or less, and the content of the cobalt-containing coating layer is 2.0 mol % or more based on 100 mol of the lithium nickel oxide. The secondary sintering is performed at 600°C to 700°C.

11. The method according to claim 10, wherein: The cobalt-containing raw material includes at least one selected from the group consisting of Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4 and Co(SO4)2·7H2O.

12. The method of claim 10, wherein: The primary sintering is performed at 750°C to 880°C. 13 . A positive electrode comprising the positive electrode active material according to claim 1 . A lithium secondary battery comprising the positive electrode according to claim 13 .

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