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

Abstract

The 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 the total transition metals is 80 mol% or more, and a cobalt-containing coating layer formed on the surface of the lithium nickel-based oxide, wherein the lithium nickel-based oxide is in the form of a single particle consisting of one single nodule or a pseudo-single particle which is a composite of 30 or fewer nodules, and the cobalt-containing coating layer is included in an amount of 2.0 mol% or more per 100 moles of the lithium nickel-based oxide, and the positive electrode active material is D 50 The particle size is 3.7 μm to 6.0 μm, 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.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0057356 filed on May 2, 2023, and all the contents disclosed in the literature of the Korean patent application are incorporated herein by reference in their entirety.

[0002] The present invention relates to a positive electrode active material, a positive electrode slurry containing the same, a method for manufacturing the same, a positive electrode containing the same, and a lithium secondary battery.

Background Art

[0003] With the development of technologies related to mobile devices and the increasing demand, the demand for secondary batteries as an energy source has been rapidly increasing. Among such secondary batteries, lithium secondary batteries having a high energy density, a high voltage, a long cycle life, and a low self-discharge rate have been commercialized and widely used. [[ID=z]]

[0004] As the positive electrode active material of a lithium secondary battery, a lithium transition metal composite oxide is used. Among them, research and development on lithium nickel-based oxides, which are easy to realize a large-capacity battery, have been more actively conducted. However, the form of secondary particles has a problem in that the generation of cracks in the positive electrode active material increases during charge and discharge.

[0005] To solve the above problems, a technique has been proposed to manufacture a positive electrode active material in the form of single particles rather than secondary particles by increasing the firing temperature during the manufacture of lithium nickel-based oxides.

[0006] However, the positive electrode active material in the form of single particles has a problem in that there are few interfaces between particles that serve as lithium ion migration paths, the lithium diffusion path inside the particles is long, the resistance is high, and the output is inferior. Therefore, conventionally, by forming the average particle size of the particles to be around 4.0 μm, it has been possible to minimize the increase in resistance and the decrease in output of the positive electrode active material in the form of single particles.

[0007] However, in order to achieve an average particle size of around 4.0 μm for the single-particle positive electrode active material, it is necessary to perform a grinding process with strong crushing force. This process generates a large amount of fine powder, which increases the viscosity of the slurry and causes a rapid decrease in phase stability.

[0008] Therefore, there is a need for technologies to improve the phase stability of the slurry and ensure stable electrode production and yield. [Overview of the project] [Problems that the invention aims to solve]

[0009] The present invention aims to solve the above-mentioned problems and to provide a positive electrode active material in which the phase stability of the slurry is improved by adjusting the particle size distribution of the positive electrode active material, the residual LiOH content, and the cobalt-containing coating layer content within a specific range, a positive electrode slurry containing the same, and a method for producing the same.

[0010] This invention relates to the D of the positive electrode active material. 50 The objective is to provide a positive electrode and lithium secondary battery with excellent electrochemical properties by adjusting them within a specific range. [Means for solving the problem]

[0011] In one aspect, the present invention relates to a positive electrode active material comprising a lithium nickel-based oxide containing nickel (Ni) and cobalt (Co), wherein the molar ratio of Ni among the total transition metals is 80 mol% or more, and a cobalt-containing coating layer formed on the surface of the lithium nickel-based oxide, wherein the lithium nickel-based oxide is in the form of a single particle consisting of one single nodule or a pseudo-single particle which is a composite of 30 or fewer nodules, the cobalt-containing coating layer is contained in an amount of 2.0 mol% or more per 100 moles of the lithium nickel-based oxide, and the positive electrode active material is D 50Provided is a positive electrode active material having a size of 3.7 μm to 6.0 μm, a residual LiOH content of 0.20% by weight or less, and a Co / Ni ratio of 0.15 to 0.40 at a depth of 45 nm from the surface.

[0012] In the lithium nickel-based oxide, the molar ratio of Ni among all transition metals can be 93 mol% or more.

[0013] The positive electrode active material can have a residual lithium content of 0.60% by weight or less.

[0014] The positive electrode active material can have a residual Li2CO3 content of 0.40% by weight or less.

[0015] The positive electrode active material is D min can be 1.0 μm or more.

[0016] The lithium nickel-based oxide can be represented by the following chemical formula 1. [Chemical formula 1] Li a Ni b Co c M 1 d M 2 e O2 In Chemical formula 1, M 1 is at least one selected from the group consisting of Mn and Al, and M 2 is at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo, and 1.0 ≦ a ≦ 1.5, 0.8 ≦ b ≦ 1.0, 0 ≦ c ≦ 0.2, 0 ≦ d ≦ 0.2, 0 ≦ e ≦ 0.1.

[0017] In another aspect, the present invention provides a positive electrode slurry containing the above positive electrode active material and a binder.

[0018] The adsorption amount of the binder with respect to the positive electrode active material can be 25.0 mg / m 2 or less.

[0019] The viscosity change rate calculated by the following formula 1 at 25°C can be 1,000% or less.

[0020]

number

[0021] In other aspects, the present invention relates to a method for producing a positive electrode active material, comprising the steps of: mixing a lithium nickel-based transition metal hydroxide precursor containing nickel (Ni) and cobalt (Co) with a lithium raw material and performing primary calcination to form a lithium nickel-based oxide; and mixing the lithium nickel-based oxide with a cobalt-containing raw material and performing secondary calcination to form a positive electrode active material including a cobalt-containing coating layer, wherein the positive electrode active material comprises a lithium nickel-based oxide in which the molar ratio of Ni among the total transition metals is 80 mol% or more, and a cobalt-containing coating layer formed on the surface of the lithium nickel-based oxide, wherein the lithium nickel-based oxide is in the form of a single particle consisting of one single nodule or a pseudo-single particle which is a composite of 30 or fewer nodules, and the positive electrode active material is D 50 The present invention provides a method for producing a positive electrode active material in which the thickness is 3.7 μm to 6.0 μm, the residual LiOH content is 0.20% by weight or less, the cobalt-containing coating layer is included in an amount of 2.0 mol% or more per 100 moles of lithium nickel oxide, and the secondary calcination is performed at 600°C to 700°C.

[0022] 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.

[0023] The aforementioned primary firing can be carried out at 750°C to 880°C.

[0024] In other aspects, the present invention provides a positive electrode comprising the positive electrode active material described above.

[0025] In other respects, the present invention provides a lithium secondary battery including the positive electrode described above. [Effects of the Invention]

[0026] The cathode active material according to the present invention includes a cobalt-containing coating layer on the surface of a lithium nickel-based oxide. By adjusting the particle size, residual LiOH content, and cobalt-containing coating layer content within a specific range, the increase in slurry viscosity and the amount of adsorption with the binder are suppressed, thereby improving the phase stability of the slurry and achieving excellent processability.

[0027] The positive electrode active material according to the present invention is D 50 By adjusting these parameters within a specific range to achieve low charge transfer resistance and diffusion resistance, high initial efficiency, low initial resistance, and excellent high-temperature lifetime characteristics can be realized. [Brief explanation of the drawing]

[0028] [Figure 1] This is a Scanning Electron Microscope (SEM) image of the positive electrode active material powder produced according to Example 1 of the present invention. [Figure 2] This is a Scanning Electron Microscope (SEM) image of the positive electrode active material powder produced according to Example 2 of the present invention. [Figure 3] This is a Scanning Electron Microscope (SEM) image of the positive electrode active material powder produced according to Example 3 of the present invention. [Figure 4] This is a Scanning Electron Microscope (SEM) image of the positive electrode active material powder produced according to Comparative Example 1 of the present invention. [Figure 5] This is a Scanning Electron Microscope (SEM) image of the positive electrode active material powder produced by Comparative Example 2 of the present invention. [Figure 6]This is a Scanning Electron Microscope (SEM) image of the positive electrode active material powder produced by Comparative Example 3 of the present invention. [Figure 7] This is a Scanning Electron Microscope (SEM) image of the positive electrode active material powder produced according to Comparative Example 4 of the present invention. [Figure 8] This graph shows the XPS depth profile of the cobalt-containing coating layer contained in the positive electrode active materials produced in Examples 1-3 and Comparative Examples 1-4. [Modes for carrying out the invention]

[0029] The advantages and features of the present invention, as well as methods for achieving them, will become clearer with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and can be realized in a variety of different forms, provided that these embodiments are provided to complete the disclosure of the present invention and to fully inform a person ordinary skill in the art to which the invention pertains, and the present invention is defined by the scope of the claims. Throughout the specification, the same reference numerals refer to the same components.

[0030] Unless otherwise defined, all terms used herein (including technical and scientific terms) should be used in a way that can be commonly understood by a person of ordinary skill in the art to which this invention pertains. Furthermore, terms defined in commonly used dictionaries should not be interpreted ideally or excessively unless explicitly and specifically defined otherwise.

[0031] The terms used herein are for illustrative purposes only and do not limit the invention. In this specification, singular forms include plural forms unless otherwise specified. The terms “comprises” and / or “comprising” as used in this specification do not preclude the presence or addition of one or more other components in addition to the components mentioned.

[0032] In this specification, when a part is said to include a component, this means, unless otherwise specified to the contrary, that it may include other components rather than excluding them.

[0033] In this specification, "A and / or B" means A, or B, or A and B.

[0034] In this specification, "%" means weight percent unless otherwise explicitly indicated.

[0035] In this specification, “particle” may include one or all of the following: single particles, pseudo-single particles, primary particles, nodules, and secondary particles.

[0036] In this specification, "single particle" refers to a particle consisting of one single nodule. In this invention, "pseudo-single particle" refers to a particle that is a composite formed of 30 or fewer nodules.

[0037] In this specification, "nodule" means a particle unit body that constitutes a single particle or a pseudo-single particle, and the nodule may be a single crystal lacking crystalline grain boundaries, or a polycrystalline material in which no grain boundaries are visible when observed with a scanning electron microscope (SEM) at a field of view of 5000x to 20000x. The average grain size of the nodule can be measured by the arithmetic mean of the grain sizes of each nodule measured with a scanning electron microscope (SEM).

[0038] In this specification, "secondary particle" means a particle formed by the aggregation of several tens to hundreds of primary particles. More specifically, a secondary particle is an aggregate of 40 or more primary particles.

[0039] In this specification, "D50 " refers to the average particle size, which is the particle size at the point in the particle size distribution of the positive electrode active material where the particle volume by particle size accounts for 50%. The average particle size (D 50 The particle size distribution can be measured using a commercially available laser PSD (Particle Size Distribution) particle size analyzer. For example, after dispersing the positive electrode active material powder in a dispersion medium, the particles were introduced into a commercially available laser PSD (Particle Size Distribution) particle size analyzer (e.g., Microtrac S3500), and the particle size distribution was calculated by measuring the difference in diffraction patterns due to particle size as the particles passed through the laser beam.

[0040] In this specification, the composition and concentration of the transition metal concentration gradient within positive electrode active material particles can be determined using 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, X-ray photoelectron spectroscopy (XPS) can be used to etch positive electrode active material particles with Ar gas for 3000 seconds, measuring the atomic ratio of each metal while etching from the surface towards the center of the positive electrode active material.

[0041] The present invention will be described in more detail below.

[0042] positive electrode active material The 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 the total transition metals is 80 mol% or more, and a cobalt-containing coating layer formed on the surface of the lithium nickel-based oxide, wherein the lithium nickel-based oxide is in the form of a single particle consisting of one single nodule or a pseudo-single particle which is a composite of 30 or fewer nodules, and the cobalt-containing coating layer is included in an amount of 2.0 mol% or more per 100 moles of the lithium nickel-based oxide, and the positive electrode active material is D 50 The material is characterized by having a thickness of 3.7 μm to 6.0 μm, a residual LiOH content of 0.20% by weight or less, and a Co / Ni ratio of 0.15 to 0.40 at a depth of 45 nm from the surface.

[0043] Research and development on lithium nickel oxides are becoming more active. However, the secondary particle form has the problem of increased crack formation within the positive electrode active material during charging and discharging. To solve this problem, a technique has been proposed to increase the firing temperature during the manufacturing of lithium nickel oxides to produce positive electrode active material in single particle form instead of secondary particle form.

[0044] However, single-particle cathode active materials have the problem of having fewer interparticle interfaces that serve as pathways for lithium ions, resulting in longer lithium diffusion pathways within the particles, high resistance, and lower power output. Therefore, conventional methods have aimed to minimize the increase in resistance and decrease in power output of single-particle cathode active materials by forming them so that the average particle size is around 4.0 μm.

[0045] However, in order to achieve an average particle size of around 4.0 μm for the single-particle positive electrode active material, it is necessary to perform a grinding process with strong crushing force. This process generates a large amount of fine powder, which increases the viscosity of the slurry and causes a rapid decrease in phase stability.

[0046] The positive electrode active material according to the present invention contains nickel (Ni) and cobalt (Co), and includes a lithium nickel-based oxide in which the molar ratio of Ni to the total transition metal 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 capacitance characteristics can be achieved.

[0047] However, Ni-based positive electrode active materials containing high concentrations of Ni have high capacity because the nickel content among the transition metals constituting the positive electrode active material is higher than that of other transition metals, but the unstable Ni present on the surface of the positive electrode active material 3+ Ni 4+ A limitation exists in that the material exhibits structural instability due to ions. To overcome this structural instability, various techniques for modifying the surface of the positive electrode active material are being researched.

[0048] In connection with this, the inventors of the present invention have introduced a cobalt-containing coating layer on the surface of a Ni-based positive electrode active material containing a high concentration of Ni in order to improve surface stability, and the cobalt-containing coating layer is contained in an amount of 2.0 mol% or more per 100 moles of lithium nickel-based oxide, D 50 When a cathode active material with 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 is applied, it was found that the viscosity change rate of the slurry decreases, the amount of adsorption with the binder decreases, and the phase stability of the slurry improves.

[0049] The lithium nickel oxide is in the form of a single particle consisting of one single nodule or a pseudo-single particle, which is a composite of 30 or fewer nodules, preferably 2 to 20, and more preferably 2 to 10. Because lithium nickel oxides in the form of such single particles and / or pseudo-single particles have higher particle strength than existing lithium nickel oxides in the form of secondary particles, which consist of tens to hundreds of primary particles aggregated together, there is less particle cracking during rolling.

[0050] Furthermore, in the case of lithium nickel-based oxides in single-particle or pseudo-single-particle form according to the present invention, the number of lower-component elements (i.e., nodules) constituting the particles is small, so the volume of the primary particles changes less due to expansion and contraction during charging and discharging, and as a result, the occurrence of cracks inside the particles is also significantly reduced.

[0051] The positive electrode active material is D 50 However, it can be 3.7 μm to 6.0 μm, preferably 3.7 μm to 5.7 μm, and more preferably 3.7 μm to 5.0 μm. 50 If the particle size is less than 3.7 μm, there is a possibility that the slurry will have a high content of fine particles and the viscosity of the slurry will be excessively high. 50 If the particle size exceeds 6.0 μm, the lithium mobility in the positive electrode active material decreases, which can increase the initial resistance of lithium secondary batteries containing it.

[0052] The residual lithium in the positive electrode active material according to the present invention can be at least one selected from the group consisting of LiOH and Li2CO3.

[0053] The residual LiOH content can be 0.20% by weight or less, preferably 0.01% to 0.20% by weight, and more preferably 0.05% to 0.15% by weight. Generally, Ni-based cathode active materials containing high concentrations of Ni have the problem that, in order to obtain high capacity, the proportion of LiOH remaining on the surface of the cathode active material increases as LiOH is used as a lithium raw material in the precursor, making it difficult to suppress the increase in resistance and decrease in capacity. Therefore, it is necessary to control the residual LiOH content, but if the residual LiOH content exceeds the above numerical range, when dissolved in the solvent (NMP) during the electrode manufacturing process, it can basicize the solvent, and the basicized solvent can mix with the binder (PVdF) to gel the slurry, potentially making electrode manufacturing difficult.

[0054] The positive electrode active material may have a residual lithium content of 0.60% by weight or less, preferably 0.01% to 0.60% by weight, and more preferably 0.05% to 0.50% by weight. The residual Li2CO3 content may be 0.40% by weight or less, preferably 0.10% to 0.35% by weight, and more preferably 0.20% to 0.30% by weight. If the residual lithium or residual Li2CO3 content exceeds the above numerical range, it will react with the electrolyte after application to the battery, causing side effects such as swelling and gas generation, which may lead to battery swelling and ignition. Furthermore, since the residual lithium acts as a raw material for forming the coating layer in the coating layer formation process described later, if there is an excess of residual lithium on the surface of the lithium nickel oxide, the coating layer will be formed thickly, which has the problem of increasing resistance characteristics.

[0055] The cobalt-containing coating layer may be present in an amount of 2.0 mol% or more per 100 moles of lithium nickel oxide. Preferably, the cobalt-containing coating layer may be present in an amount of 2.0 mol% to 5.5 mol%, more preferably 2.0 mol% to 3.5 mol%, per 100 moles of lithium nickel oxide. If the cobalt-containing coating layer according to the present invention exceeds the above content range, the coating layer may be formed excessively thick, which may result in an increase in initial resistance. On the other hand, if the cobalt-containing coating layer is below the above content range, the unstable Ni present on the surface of the positive electrode active material may be affected. 3+ Ni 4+ There is a problem in that the limitation of structural instability due to ions is not overcome.

[0056] Furthermore, the cobalt-containing coating layer may have a Co / Ni ratio of 0.15 to 0.40, preferably 0.16 to 0.30, and more preferably 0.17 to 0.25 at a depth of 45 nm from the surface. In the present invention, the D of the positive electrode active material 50Furthermore, when the Co / Ni ratio at a depth of 45 nm, along with the residual LiOH content, satisfies the aforementioned range, it is possible to suppress the increase in slurry viscosity, reduce the amount of adsorption with the binder, and improve the phase stability of the slurry, thereby achieving excellent processability.

[0057] The positive electrode active material according to the present invention is D min However, it can be 1.0 μm or more, preferably 1.0 μm to 6.0 μm, and more preferably 1.0 μm to 5.0 μm. The minimum particle size of the positive electrode active material is D min If the above range is met, the viscosity may increase excessively during slurry preparation, potentially impairing processability.

[0058] On the other hand, the positive electrode active material according to the present invention may include a lithium nickel-based oxide, and specifically, it may include a lithium nickel-based oxide having a composition as shown in the following chemical formula 1.

[0059] [Chemical formula 1] Li a Ni b Co c M 1 d M 2 e O2

[0060] In the above chemical formula 1, M 1 is at least one selected from the group consisting of Mn and Al, preferably Mn or a combination of Mn and Al, M 2 is at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo. 2 Elements are not always present, but when present in appropriate amounts, they can promote grain growth during firing or improve the stability of the crystal structure.

[0061] The above 'a' represents the molar ratio of lithium in the lithium nickel oxide, and can be 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.

[0062] The value b represents the molar ratio of nickel to the total metals other than lithium in the lithium nickel oxide, and can be 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, excellent capacity characteristics are observed, and in particular, even better capacity characteristics can be achieved when the molar ratio of nickel is 0.90 or higher.

[0063] The aforementioned c represents the molar ratio of cobalt among the total metals other than lithium in the lithium nickel oxide, where 0 ≤ c ≤ 0.2, 0 <c<0.2、0<c≦0.18、または0<c<0.18であることができる。

[0064] The above d is M, which is the total metal other than lithium in the lithium nickel oxide. 1 The molar ratio is shown, where 0 ≤ d ≤ 0.2, 0 <d<0.2、0<d≦0.18、または0<d<0.18であることができる。

[0065] The aforementioned e is M, which is the total metal other than lithium in the lithium nickel oxide. 2 This indicates the molar ratio of elements, where 0 ≤ e ≤ 0.1, and 0 <e<0.1、または0<e≦0.08であることができる。

[0066] Method for manufacturing positive electrode active material Next, the method for producing the positive electrode active material of the present invention will be described.

[0067] When manufacturing positive electrode active materials in which the molar ratio of Ni among the total transition metals is 80 mol% or more, high firing temperatures can result in a low degree of surface structure completion and a high concentration of residual lithium. Furthermore, if the particle size of the positive electrode active material is large, there is a problem of potentially high initial resistance. Therefore, a technology is needed to improve the degree of surface structure completion by forming a coating layer on the surface of lithium nickel oxide particles, reduce the concentration of residual lithium, and lower the initial resistance by optimizing the coating conditions.

[0068] The present invention provides a method for producing a positive electrode active material, comprising the steps of: mixing a lithium nickel-based transition metal hydroxide precursor containing nickel (Ni) and cobalt (Co) with a lithium raw material and performing primary calcination to form a lithium nickel-based oxide; and mixing the lithium nickel-based oxide with a cobalt-containing raw material and performing secondary calcination to form a positive electrode active material including a cobalt-containing coating layer.

[0069] Lithium nickel-based transition metal oxides have a molar ratio of Ni of 80 mol% or more of the total transition metal, and are single particles consisting of one nodule or pseudo-single particles consisting of a composite of 30 or fewer nodules. Furthermore, the positive electrode active material is D 50 The thickness is 3.7 μm to 6.0 μm, the residual LiOH content is 0.20 wt% or less, the cobalt-containing coating layer is present in an amount of 2.0 mol% or more per 100 moles of lithium nickel oxide, and the secondary firing is performed at 600°C to 700°C. Since the above content applies similarly, redundant explanations are omitted.

[0070] Next, we will specifically describe each step in the method for producing the positive electrode active material.

[0071] (1) Step of forming a lithium nickel oxide First, a lithium nickel-based transition metal hydroxide precursor containing nickel (Ni) and cobalt (Co) is mixed with a lithium raw material and subjected to primary calcination to form a lithium nickel-based oxide.

[0072] Here, the lithium nickel-based transition metal hydroxide precursor, i.e., the positive electrode active material precursor, may be purchased and used from commercially available nickel-cobalt-manganese-based hydroxides, or it may be manufactured by a precursor manufacturing method well known in the art, such as the coprecipitation method.

[0073] For example, nickel (Ni), cobalt (Co), and M 1 After preparing a transition metal-containing solution containing cations, an ammonium cation-containing complex-forming agent and a basic aqueous solution can be added to the transition metal-containing solution and a coprecipitation reaction can be carried out to produce a cathode active material precursor.

[0074] The transition metal-containing solution comprises nickel-containing raw material, cobalt-containing raw material, and M 1 It may contain the raw material substance, and the M 1 The raw materials contained may be manganese-containing raw materials and / or aluminum-containing raw materials.

[0075] Nickel-containing raw materials can be, for example, nickel-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or oxyhydroxides, and specifically, they can be, but are not limited to, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, fatty acid nickel salts, nickel halides, or combinations thereof.

[0076] The cobalt-containing raw material can be cobalt-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or oxyhydroxides, and specifically can be, but are not limited to, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4, Co(SO4)2·7H2O, or combinations thereof.

[0077] Manganese-containing raw materials can be, for example, manganese-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, oxyhydroxides, or combinations thereof, and specifically, they can be, but are not limited to, manganese oxides such as Mn2O3, MnO2, Mn3O4; manganese salts such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese dicarboxylate salts, manganese citrate, manganese fatty acid salts; manganese oxyhydroxides, manganese chloride, or combinations thereof.

[0078] Aluminum-containing raw materials can be, for example, Al2O3, Al(OH)3, Al(NO3)3, Al2(SO4)3, (HO)2AlCH3CO2, HOAl(CH3CO2)2, Al(CH3CO2)3 aluminum halides, or combinations thereof.

[0079] Transition metal-containing solutions include nickel-containing raw materials, cobalt-containing raw materials, and M 1 The contained raw materials are added to a solvent, specifically water, or a mixed solvent of an organic solvent that can be homogeneously mixed with water (e.g., alcohol), to produce the product, or an aqueous solution of nickel-containing raw materials, an aqueous solution of cobalt-containing raw materials and M 1 It can be manufactured by mixing the raw materials.

[0080] The ammonium cation-containing complex-forming agent may be, for example, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or a combination thereof. On the other hand, the ammonium cation-containing complex-forming agent may also be used in the form of an aqueous solution, where the solvent may be water or a mixture of water and an organic solvent that is homogeneously miscible with water (specifically, an alcohol).

[0081] Basic compounds can be hydroxides of alkali metals or alkaline earth metals such as NaOH, KOH, or Ca(OH)2, their hydrates, or combinations thereof. Basic compounds may also be used in aqueous solution form, where the solvent can be water, or a mixture of water and an organic solvent that is homogeneously miscible with water (specifically, an alcohol).

[0082] Basic compounds are added to adjust the pH of the reaction solution, and can be added in amounts that bring the pH of the metal solution between 8 and 12.

[0083] The coprecipitation reaction can be carried out in an inert atmosphere such as nitrogen or argon, at a temperature range of 35°C to 80°C.

[0084] Through the process described above, nickel-cobalt-M 1 Hydroxide cathode active material precursor particles are generated and precipitate in the reaction solution. Nickel-containing raw material, cobalt-containing raw material and M 1 By adjusting the concentration of the raw materials, a cathode active material precursor can be produced in which the nickel (Ni) content is 60 mol% or more relative to the total metal content. The precipitated cathode active material precursor particles can be separated by conventional methods and dried to produce the cathode active material precursor.

[0085] Next, the lithium nickel-based transition metal hydroxide precursor and the lithium raw material can be mixed.

[0086] The lithium raw material can be lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides, and is not particularly limited as long as it is soluble in water. 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 one or more of these can be used as a mixture.

[0087] The positive electrode active material precursor and the lithium raw material can be mixed in molar ratios of, for example, about 1:1, about 1:1.05, about 1:1.10, about 1:1.15, or about 1:1.20, but are not limited thereto.

[0088] Next, the mixture can be subjected to primary calcination. Primary calcination can be carried out in an air or oxygen atmosphere. Primary calcination can be carried out at temperatures of 750°C to 880°C, 780°C to 880°C, 800°C to 870°C, or 820°C to 870°C. Primary calcination can be carried out for 5 to 20 hours, 6 to 12 hours, or 8 to 10 hours.

[0089] (2) A step of mixing lithium nickel oxide with a cobalt-containing raw material. Next, the lithium nickel oxide is mixed with a cobalt-containing raw material and subjected to secondary calcination to form a positive electrode active material containing a cobalt-containing coating layer.

[0090] For example, the surface of the lithium nickel oxide is coated with a cobalt-containing raw material. The cobalt-containing raw material can be one or more 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 including a cobalt-containing coating layer.

[0091] In this way, by forming a cobalt-containing coating layer on the surface of the lithium nickel oxide, the larger amount of unstable Ni ions present on the surface of the positive electrode active material can be stabilized, thereby improving the stability of the positive electrode active material.

[0092] The secondary firing can be carried out at a temperature of 600°C to 700°C, preferably 630°C to 690°C, and more preferably 640°C to 690°C.

[0093] If the secondary firing temperature exceeds 700°C, cobalt may diffuse into the positive electrode active material, potentially causing a change in the crystal structure of the positive electrode active material. This can alter the residual lithium content and adversely affect the lifespan and resistance characteristics of the positive electrode active material. In other words, it may be difficult to achieve the desired residual lithium content and cobalt-containing coating layer content.

[0094] If the secondary firing temperature is below 600°C, the bonding force with the surface of the positive electrode active material is weak, and the cobalt-containing coating layer may detach from the positive electrode active material. As a result, a coating layer with a lower cobalt content is formed compared to when secondary firing is performed within the aforementioned temperature range, and the improvement in high-temperature lifetime characteristics may be minimal.

[0095] The secondary firing can be carried out for 2 to 8 hours, preferably 3 to 7 hours, and more preferably 4 to 6 hours.

[0096] By mixing lithium nickel oxide with a cobalt-containing raw material within the aforementioned firing temperature and firing time range, and performing secondary firing, a cobalt-containing coating layer with the desired content is formed on the surface of the lithium nickel oxide, thereby enabling the realization of a secondary battery with low initial resistance.

[0097] The primary and secondary firing processes do not necessarily require a separate water washing step. Conventionally, the process involved washing away residual lithium present on the surface of the positive electrode active material. This was because the presence of residual lithium caused side reactions with the electrolyte during application to batteries, leading to problems such as increased gas generation during high-temperature storage. On the other hand, in the manufacturing method according to one embodiment of the present invention, since no separate water washing step is taken, residual lithium is present on the surface of the particles. However, this residual lithium reacts with cobalt to form a LiCoO2 coating on the surface of the particles, enabling the realization of excellent high-temperature lifetime characteristics.

[0098] Positive electrode slurry Next, the positive electrode slurry according to the present invention will be described.

[0099] The positive electrode slurry according to the present invention is characterized by comprising the positive electrode active material and binder according to the present invention.

[0100] Specifically, the positive electrode slurry according to the present invention may optionally contain a conductive material. Specifically, the positive electrode slurry can be manufactured by mixing a positive electrode active material, a binder, and / or a conductive material in a solvent.

[0101] The amount of binder adsorbed onto the positive electrode active material according to the present invention is 25.0 mg / m². 2 Preferably, 10.0 mg / m² 2 ~25.0 mg / m² 2 More preferably 15.0 mg / m² 2 ~23.0 mg / m² 2 This can be the case. When the amount of binder adsorbed onto 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.

[0102] The viscosity change rate of the positive electrode slurry according to the present invention, calculated at 25°C using the following formula 1, can 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 applied to a battery, it can enable the stable production of electrodes and improved yield.

[0103]

number

[0104] 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 current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which the hydrogen atoms of these materials are substituted with Li, Na, or Ca, or various copolymers thereof. One of these materials alone or a mixture of two or more materials can be used. The binder may be present in an amount of 1% to 30% by weight, preferably 1% to 20% by weight, and more preferably 1% to 10% by weight, based on the total solid content of the positive electrode slurry.

[0105] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations in the battery it is configured in, as long as it does not cause 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 tubes such as carbon nanotubes; 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 alone or a mixture of two or more can be used. The conductive material can be present in amounts of 0.01% to 10% by weight, 0.1% to 9% by weight, or 0.1% to 5% by weight, based on the total solid content of the positive electrode slurry.

[0106] The solvent can be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), 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 should be such that it dissolves or disperses the positive electrode active material, conductive material, and binder, and has a viscosity that allows for excellent thickness uniformity when applied for the manufacture of the positive electrode, taking into consideration the coating thickness of the positive electrode slurry and the manufacturing yield.

[0107] positive electrode The positive electrode according to the present invention includes the positive electrode active material of the present invention as described above. 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 includes a positive electrode slurry containing the positive electrode active material according to the present invention. Since the positive electrode active material and the positive electrode slurry have been described above, a detailed explanation will be omitted, and only the remaining components will be described in detail below.

[0108] The positive electrode current collector is not particularly limited as long as it contains a highly conductive metal, allows the positive electrode active material layer to adhere easily, and is unreactive within the battery voltage range. The positive electrode current collector can be made of, for example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. The positive electrode current collector can also typically have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0109] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material described above. Specifically, it can be manufactured by applying the aforementioned positive electrode slurry onto a positive electrode current collector, followed by drying and rolling.

[0110] Alternatively, the positive electrode can also be manufactured by casting the positive electrode slurry onto another support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0111] Lithium-ion battery Next, the lithium secondary battery according to the present invention will be described.

[0112] The lithium secondary battery specifically includes a positive electrode, a negative electrode located opposite the positive electrode, and a separator and electrolyte interposed between the positive and negative electrodes. As the positive electrode is as described above, a detailed explanation will be omitted, and only the remaining components will be described in detail below.

[0113] Furthermore, the lithium secondary battery may selectively further include a battery container for housing the electrode assembly comprising the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0114] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0115] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used. The negative electrode current collector can usually have a thickness of 3 μm 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, mesh, porous material, foam, and nonwoven fabric.

[0116] The negative electrode active material layer may selectively include a binder and a conductive material together with the negative electrode active material.

[0117] 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 aforementioned metallic compounds and carbon materials, such as Si-C composites or Sn-C composites. One or more of these mixtures can be used. Furthermore, a metallic lithium thin film can also be used as the negative electrode active material. In addition, both low-crystallinity carbon and high-crystallinity carbon can be used as the carbon material. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and petroleum or coal tar pitch-derived cokes, which are high-temperature heat-treated carbons.

[0118] The negative electrode active material may be present in an amount of 80% to 99% by weight, 82% to 99% by weight, or 84% to 99% by weight, relative to the total weight of the negative electrode active material layer.

[0119] The binder is a component that helps to bond the conductive material, active material, and current collector, and is usually added in an amount of 0.1% to 10% by weight relative to the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0120] The conductive material is a component for further improving the conductivity of the negative electrode active material and can be included in an amount of 1% to 30% by weight, 1% to 20% by weight, or 1% to 10% by weight relative to the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive, and examples of such materials that can be used include 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 and metal fibers; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0121] The negative electrode active material layer can be manufactured by coating a negative electrode slurry composition, which is prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and then drying it, or by casting the negative electrode slurry composition onto another support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0122] On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Generally, any separator commonly used in lithium secondary batteries can be used without particular limitations, but those with low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity are particularly preferred. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof, can be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separators containing ceramic components or polymeric substances can be used to ensure heat resistance or mechanical strength, and can be selectively used as single-layer or multi-layer structures.

[0123] Furthermore, the electrolytes used in the present invention 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 that can be used in the manufacture of lithium secondary batteries.

[0124] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0125] The aforementioned organic solvent can be used without particular 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; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that 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) is more preferred.

[0126] The lithium salt can be used without particular limitations as long as it is a compound that can provide lithium ions for use in lithium secondary batteries. Specifically, the anion of the lithium salt is 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 - The lithium salt can be selected from 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, etc. The concentration of the lithium salt is preferably used within the range of 0.1M to 4.0M, preferably 0.5M to 3.0M, and more preferably 1.0M to 2.0M. When the concentration of the lithium salt falls within the above range, the electrolyte can exhibit excellent electrolyte performance due to having appropriate conductivity and viscosity, and lithium ions can move effectively.

[0127] In addition to the components of the electrolyte, the electrolyte may also contain one or more additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethyl alcoholamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethyl alcohol, or aluminum trichloride. Here, the additive may be present in an amount of 0.1% to 10.0% by weight relative to the total weight of the electrolyte.

[0128] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent discharge capacity, output characteristics, and capacity retention rate stably, making it useful in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0129] Accordingly, 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 same are provided.

[0130] The aforementioned battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0131] Hereinafter, embodiments of the present invention will be described in detail so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be realized in a variety of different forms and is not limited to the embodiments described herein.

[0132] Examples and Comparative Examples Example 1 - Production of positive electrode active material Positive electrode active material precursor Ni 0.93 Co 0.05 Mn 0.02 (OH)2 and lithium raw material LiOH were added to a 700L Henschel mixer so that the molar ratio of Li:transition metal (Ni+Co+Mn) was 1.05:1, and the mixture was mixed at 400 rpm in the center for 20 minutes. The mixed powder was placed in a 330mm x 330mm alumina crucible and subjected to primary calcination at 850°C for 12 hours under an oxygen atmosphere to produce LiNi 0.93 Co 0.05 Mn 0.02 O2 was produced.

[0133] Next, the primary calcined material was mixed with 12,000 ppm of Co(OH)2 so that the molar ratio of the primary calcined material to Co was 100:2. The mixture was then subjected to secondary calcination at 680°C for 5 hours to produce a positive electrode active material powder with a cobalt-containing coating layer.

[0134] Example 2 - Production of positive electrode active material The positive electrode active material powder was produced in the same manner as in Example 1, except that the primary calcined product and 18,000 ppm of Co(OH)2 were mixed so that the molar ratio of the primary calcined product to Co was 100:3, and then the mixture was secondary calcined at 680°C for 5 hours.

[0135] Example 3 - Production of positive electrode active material The positive electrode active material powder was produced in the same manner as in Example 1, except that the secondary calcination was carried out at 660°C for 5 hours.

[0136] Example 4 - Production of positive electrode active material The positive electrode active material powder was manufactured using the same method as in Example 1.

[0137] Example 5 - Production of positive electrode active material The positive electrode active material powder was manufactured using the same method as in Example 1.

[0138] Comparative Example 1 - Production of Cathode Active Material The positive electrode active material powder was produced in the same manner as in Example 1, except that the secondary calcination was carried out at 720°C for 5 hours.

[0139] Comparative Example 2 - Production of Cathode Active Material The positive electrode active material powder was produced in the same manner as in Example 1, except that the secondary calcination was carried out at 800°C for 5 hours.

[0140] Comparative Example 3 - Production of Cathode Active Material The positive electrode active material powder was produced in the same manner as in Example 1, except that the primary calcined product and 6,000 ppm Co(OH)2 were mixed so that the molar ratio of the primary calcined product to Co was 100:1, and then the mixture was secondary calcined at 680°C for 5 hours.

[0141] Comparative Example 4 - Production of Cathode Active Material The positive electrode active material was manufactured in the same manner as in Example 1, except that the primary firing was performed at 850°C for 10 hours.

[0142] Comparative Example 5 - Production of Cathode Active Material The cathode active material powder was produced in the same manner as in Example 1, except that the cathode active material precursor and lithium raw material LiOH were placed in a Henschel mixer, mixed at 400 rpm in the center for 30 minutes, and then subjected to primary calcination at 950°C for 12 hours under an oxygen atmosphere.

[0143] Experimental Example 1 - Particle Size Distribution of Cathode Active Material 0.05 g of each positive electrode active material prepared in Examples 1-5 and Comparative Examples 1-5 was dispersed in a dispersion medium H2O. The particles were then introduced into a commercially available laser PSD (Particle Size Distribution) particle size analyzer (e.g., Microtrac S3500), and the difference in diffraction patterns due to particle size was measured as the particles passed through the laser beam to calculate the particle size distribution.

[0144] D 50 This refers to the particle size at the point in the particle size distribution of the positive electrode active material where the particle volume by particle size accounts for 50%. The results are shown in Tables 1 and 2 below.

[0145] Experimental Example 2 - Surface Observation of the Cathode Active Material Scanning electron microscope (SEM) images were obtained for each of the cathode active material particles produced in Examples 1-3 and Comparative Examples 1-4. These SEM images are shown in Figures 1-7.

[0146] Referring to Figures 1 to 3, it can be confirmed that the positive electrode active materials produced in Examples 1 to 3 have a cobalt-containing coating layer formed in a layered or island-like manner on the surface of the lithium nickel oxide.

[0147] On the other hand, referring to Figures 4 to 7, it can be confirmed that in the positive electrode active materials produced in Comparative Examples 1 and 2, the cobalt diffused into the interior of the particles due to the high secondary firing temperature, and almost no cobalt-containing coating layer was formed on the surface of the lithium nickel oxide, resulting in a smooth surface. In the positive electrode active material produced in Comparative Example 3, the cobalt-containing raw material content was low, and it can be confirmed that almost no cobalt-containing coating layer was formed. The positive electrode active material produced in Comparative Example 4 differed from Examples 1 to 3 only in that the primary firing time was reduced, and it can be confirmed that a cobalt-containing coating layer was formed on the surface of the lithium nickel oxide.

[0148] Experimental Example 3 - XPS Analysis of Cathode Active Material Using X-ray photoelectron spectroscopy (XPS) (Thermo Fisher Scientific, Nexsa2 ESCA system), the Co / Ni ratio of the cobalt-containing coating layer in the cathode active materials prepared in Examples 1-3 and Comparative Examples 1-4 was measured over time by etching from the surface to the center. The measurement results are shown in Figure 8.

[0149] Specifically, the positive electrode active material particles produced in Examples 1-3 and Comparative Examples 1-4 were placed in a vacuum chamber, and then measured under the following conditions.

[0150] -X-ray source:Monochromated Al Kα(1486.6eV) -X-ray spot size: 400μm -Sputtering:monatomic Ar(energy:1000eV, raster width:2mm) -Etching rate: 0.09 nm / s (Ta2O5 reference) -Operation mode: CAE (Constant Analyzer Energy) mode -Survey scan: pass energy 200eV, energy step 1eV -Narrow scan: scanned mode, pass energy 50eV, energy step 0.1eV -Charge compensation: flood gun 2V, 250μA

[0151] Experimental Example 4 - Measurement of Residual Lithium Content in Cathode Active Material The residual lithium content of each positive electrode active material produced in Examples 1-3 and Comparative Examples 1-4 was measured. The measurement results are shown in Table 1 below.

[0152] The residual lithium content on the surface of the positive electrode active material was measured by pH titration, using a Mettler Toledo T5 pH meter. Specifically, 10 g of each positive electrode active material powder prepared in Examples 1-3 and Comparative Examples 1-4 was stirred in 100 ml of distilled water for 5 minutes, and then pH titration was performed while adding a 0.1 N HCl solution to the solution.

[0153] Experimental Example 5 - Measurement of Adsorption Amount with Binder <Manufacturing of slurry for measuring adsorption amount> The cathode active materials prepared in Examples 1-3 and Comparative Examples 1-4 were mixed with PVdF binder (KF9700) in a weight ratio of 98.11:1.89 to produce a slurry for adsorption measurement with a solid content of 76.2% by weight. Specifically, the slurry for adsorption measurement was prepared by mixing at 45°C and a speed of 2500 rpm for 6 hours under dry room conditions.

[0154] The slurry used for measuring adsorption was centrifuged, and the solid content of the supernatant liquid was measured. Using a rheometer manufactured by TA instruments, the amount of adsorption with the binder was calculated using viscosity master curves for each solid content of the binder / slurry. The calculation results are shown in Table 1 below.

[0155] As shown in Table 1, the adsorption amount of the positive electrode active materials produced in Examples 1-3 to the binder was at a similar level to that of the positive electrode active material produced in Comparative Example 3, but it was lower than that of the positive electrode active materials produced in Comparative Examples 1-2 and 4.

[0156] Experimental Example 6 - Viscosity Measurement of Cathode Slurry <Manufacturing of positive electrode slurry> In Examples 1-3 and Comparative Examples 1-3, the cathode active materials prepared were mixed with PVdF (polyvinylidene fluoride) (KF9700, Solef5130) as a binder, nitrile butadiene rubber (H-NBR) (HPD01) as a dispersant, and carbon black (B.CNT, SFG6L) and single-wall carbon nanotubes as conductive materials in a weight ratio of 97.02:1.87:0.002:0.18:0.60:0.30:0.01 to produce a cathode slurry with a solid content of 67% by weight.

[0157] Specifically, the viscosity measuring slurry was manufactured by mixing at 45°C and a speed of 2500 rpm for 75 minutes under dry room conditions.

[0158] The viscosity of each cathode slurry was measured using a viscometer (rheometers manufactured by TA Instruments). The measurement results are shown in Table 1 below.

[0159] [Table 1]

[0160] As shown in Table 1, we were able to confirm that the viscosity change rate of the positive electrode active materials produced in Examples 1 to 3 was significantly lower than that of the positive electrode active materials produced in Comparative Examples 1 to 4.

[0161] Experimental Example 6 - Electrochemical property analysis of lithium secondary batteries The initial efficiency, initial resistance, and high-temperature lifetime characteristics of half-cells of lithium secondary batteries manufactured as described above were analyzed using the respective positive electrode active materials produced in Examples 4-5 and Comparative Example 5. The analysis results are shown in Table 2 below.

[0162] <Manufacturing of lithium-ion secondary batteries> The positive electrode active material, conductive material (Carbon Black, Denka), and PVDF binder prepared in Examples 4-5 and Comparative Example 5 were mixed in N-methylpyrrolidone in a weight ratio of 95:2:3 to produce a positive electrode slurry. The positive electrode slurry was applied to one surface of an aluminum current collector, dried at 500°C, and then rolled to produce a positive electrode.

[0163] The negative electrode used lithium metal.

[0164] After manufacturing an electrode assembly by interposing a separator between the positive and negative electrodes produced by the method described above, this assembly was placed inside a battery case, and an electrolyte was injected into the case to produce a battery cell. The electrolyte was prepared by dissolving 0.6 M LiPF6 in a mixed organic solvent of ethylene carbonate (EC):dimethyl carbonate (DMC):ethyl methyl carbonate (EMC) in a volume ratio of 1:2:1, and adding 2% by weight of vinylene carbonate (VC).

[0165] <Analysis of initial efficiency, initial resistance, and high-temperature lifetime characteristics> The lithium secondary batteries manufactured as described above were subjected to charging and discharging.

[0166] Specifically, the initial efficiency was determined by performing one charge-discharge cycle at 25°C in CC-CV mode, charging to 4.25V at 0.2C and discharging to 2.5V at 0.2C. The initial efficiency was derived using the following calculation.

[0167] Initial efficiency (%) = (Discharge capacity per charge / discharge cycle / Charge capacity per charge / discharge cycle) × 100

[0168] Specifically, the initial resistance was calculated based on the discharge capacity during one charge / discharge cycle measured at 0.2C. It was then calculated using the voltage change rate when a 1.0C current was applied for 10 seconds after setting the SOC to 95% at 0.2C during two charge / discharge cycles. Additionally, the voltage change rate after setting the SOC to 50% and after setting the SOC to 10% during two charge / discharge cycles were also used for calculations.

[0169] Specifically, the high-temperature life characteristics were evaluated by charging to 4.25V at 0.5C and discharging to 2.5V at 1.0C in CC-CV mode at 45°C, with one charge / discharge cycle being defined as 50 cycles, after which the capacity retention rate was measured and evaluated. The capacity retention rate was derived by the following calculation.

[0170] Capacity retention rate (%) = (Discharge capacity after n charge / discharge cycles / Discharge capacity after one charge / discharge cycle) × 100

[0171] [Table 2]

[0172] As shown in Table 2, D 50 A lithium secondary battery containing the positive electrode active material of Comparative Example 5, which has a diameter exceeding 6.0 μm, is D 50Compared to lithium secondary batteries containing positive electrode active materials of Examples 4-5, where the particle size is 3.7 μm to 6.0 μm, it can be confirmed that these batteries have lower initial efficiency, higher initial resistance, and lower capacity retention. 50 For positive electrode active materials with a particle size exceeding 6.0 μm, the mobility of lithium decreases as the diffusion distance within the lithium ion particle increases, resulting in an increased initial resistance of lithium secondary batteries containing such materials. Furthermore, the charge transfer resistance and diffusion resistance increase, leading to inferior initial efficiency and capacity retention.

Claims

1. A positive electrode active material comprising a lithium nickel-based oxide containing nickel (Ni) and cobalt (Co), wherein the molar ratio of Ni to the total transition metals is 80 mol% or more, and a cobalt-containing coating layer formed on the surface of the lithium nickel-based oxide, The lithium nickel oxide is in the form of a single particle consisting of one single nodule or a pseudo-single particle which is a composite of 30 or fewer nodules. The cobalt-containing coating layer is contained in an amount of 2.0 mol% or more per 100 moles of the lithium nickel-based oxide. The positive electrode active material is D ５０ A positive electrode active material having a diameter of 3.7 μm to 6.0 μm, a residual LiOH content of 0.20% by weight or less, and a Co / Ni ratio of 0.15 to 0.40 at a depth of 45 nm from the surface.

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

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

4. The positive electrode active material is residual Li ２ CO ３ The positive electrode active material according to claim 1, wherein the content of is 0.40% by weight or less.

5. The positive electrode active material is D ｍｉｎ The positive electrode active material according to claim 1, wherein the diameter is 1.0 μm or larger.

6. The aforementioned lithium nickel oxide is represented by the following chemical formula 1, [Chemical formula 1] Li ａ Ni ｂ Co ｃ M １ ｄ M ２ ｅ O ２ In the above chemical formula 1, M １ is at least one selected from the group consisting of Mn and Al, and M ２ The positive electrode active material according to claim 1, wherein is at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo, and satisfies 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 positive electrode active material and a binder according to any one of claims 1 to 6.

8. The amount of the binder adsorbed onto the positive electrode active material is 25.0 mg / m². ２ The positive electrode slurry according to claim 7 is as follows:

9. The viscosity change rate calculated by formula 1 below at 25°C is 1,000% or less. [Math 1] The positive electrode slurry according to claim 7.

10. The process involves mixing a lithium nickel-based transition metal hydroxide precursor containing nickel (Ni) and cobalt (Co) with a lithium raw material and performing primary calcination to form a lithium nickel-based oxide. A method for producing a positive electrode active material, comprising the steps of mixing the lithium nickel oxide with a cobalt-containing raw material and performing secondary calcination to form a positive electrode active material including a cobalt-containing coating layer, The positive electrode active material comprises a lithium nickel oxide in which the molar ratio of Ni to the total transition metal is 80 mol% or more, and a cobalt-containing coating layer formed on the surface of the lithium nickel oxide. The lithium nickel oxide is in the form of a single particle consisting of one single nodule or a pseudo-single particle which is a composite of 30 or fewer nodules, and the positive electrode active material is D ５０ The particle size is 3.7 μm to 6.0 μm, the residual LiOH content is 0.20% by weight or less, and the cobalt-containing coating layer is present in an amount of 2.0 mol% or more per 100 moles of the lithium nickel oxide. The aforementioned secondary firing is performed at 600°C to 700°C, and this is a method for producing a positive electrode active material.

11. The aforementioned cobalt-containing raw material is Co(OH) ２ , CoOOH, Co(OCOCH ３ ) ２ 4H ２ O, Co (NO ３ ) ２ 6H ２ O, CoSO ４ , and Co(SO ４ ) ２ 7H ２ A method for producing a positive electrode active material according to claim 10, comprising at least one selected from the group consisting of O.

12. The method for producing a positive electrode active material according to claim 10, wherein the primary firing is performed at 750°C to 880°C.

13. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 6.

14. A lithium secondary battery comprising the positive electrode described in claim 13.

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