Lithium secondary battery positive electrode active material, method for preparing the same, and lithium secondary battery comprising the same

Abstract

The present invention relates to a lithium secondary battery positive electrode active material comprising a lithium metal oxide in the form of single particles and a coating layer containing cobalt disposed on the surface of the lithium metal oxide, the coating layer being attached to the surface of the lithium metal oxide in the form of islands comprising a plurality of mutually spaced attached particles, the average coating rate of the coating layer being 35 to 48 area% based on the total surface area of the single particles.

Description

Technical Field

[0001] This invention relates to positive electrode active materials for lithium secondary batteries, their preparation methods, and lithium secondary batteries containing the same. Background Technology

[0002] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMnO4, etc.), and lithium iron phosphate compounds (LiFePO4) have been used as positive electrode active materials for lithium-ion batteries. Among these, lithium cobalt oxide has advantages such as high operating voltage and excellent capacity characteristics; however, cobalt, as a raw material, is expensive and its supply is unstable, making it difficult to commercially apply in high-capacity batteries. Lithium nickel oxide suffers from poor structural stability, making it difficult to achieve sufficient lifespan characteristics. On the other hand, while lithium manganese oxide exhibits excellent stability, it suffers from a decline in capacity characteristics. Therefore, to overcome the problems of lithium transition metal oxides containing only Ni, Co, or Mn, lithium composite transition metal oxides containing two or more transition metals have been developed. Among these, lithium nickel cobalt manganese oxide containing Ni, Co, and Mn is widely used in the field of electric vehicle batteries.

[0003] Traditional lithium nickel cobalt manganese oxides are typically in the form of spherical secondary particles formed by the aggregation of tens to hundreds of primary particles. However, in the pressing process during cathode fabrication, these secondary particles are prone to breakage due to primary particle detachment, and internal cracks can form during charge and discharge. When the cathode active material experiences particle breakage or cracking, the contact area with the electrolyte increases, leading to gas generation from side reactions with the electrolyte and accelerated degradation of the active material, thus resulting in a decrease in lifespan characteristics.

[0004] Furthermore, the demand for high-output, high-capacity batteries, such as those used in electric vehicles, is increasing, leading to a gradual increase in the nickel content of cathode active materials. While increasing the nickel content improves initial capacity characteristics, repeated charge-discharge cycles will generate a large amount of highly reactive Ni. +4 The presence of ions leads to the structural collapse of the positive electrode active material, thus accelerating its degradation and resulting in decreased lifespan and battery safety.

[0005] To address the aforementioned issues, a technique is proposed as follows: During the preparation of lithium nickel cobalt manganese oxide, the calcination temperature is increased to produce a single-particle, rather than a secondary-particle, positive electrode active material. Compared to traditional secondary-particle positive electrode active materials, single-particle positive electrode active materials exhibit fewer side reactions with the electrolyte due to their smaller contact area, and possess superior particle strength, resulting in less particle breakage during electrode fabrication. Therefore, using single-particle positive electrode active materials offers advantages such as reduced gas generation and superior lifetime characteristics.

[0006] However, for single-particle cathode active materials, compared to traditional secondary-particle cathode active materials, the primary particles are larger and have fewer interfaces between them, serving as lithium-ion diffusion pathways. Therefore, lithium mobility is lower. Furthermore, because they are prepared at relatively high calcination temperatures, a rocksalt phase forms on the particle surface, resulting in higher surface resistivity. This reduced lithium mobility first leads to a decrease in capacity characteristics, and secondly, it causes uneven lithium-ion migration, leading to crystal structure deformation and particle cracking. This results in a decline in lifetime characteristics, such as increased resistance with cycling. Summary of the Invention

[0007] (a) Technical problems to be solved Therefore, the present invention aims to provide a single-particle form of lithium secondary battery positive electrode active material with excellent capacity characteristics and low resistance increase rate with cycling, a method for preparing the same, and a lithium secondary battery containing the same.

[0008] (II) Technical Solution One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery, comprising a lithium metal oxide in the form of single particles and a coating layer containing cobalt disposed on the surface of the lithium metal oxide. The coating layer is attached to the surface of the lithium metal oxide in the form of an island containing a plurality of spaced-apart attached particles, and the average coating area of ​​the coating layer is 35 to 48% of the total surface area of ​​the single particles.

[0009] The average diameter of the attached particles can be 160 to 240 nm.

[0010] The average thickness of the attached particles can be 50 to 90 nm.

[0011] Based on the total moles of the lithium metal oxide, the cobalt content in the coating layer can be from 0.7 to 4.8 mol.

[0012] When XPS analysis is performed on the outermost surface of the lithium metal oxide, a first peak appears in the region with a binding energy of 775 to 785 eV, and the full width at half maximum (FWHM) of the first peak can be less than 2.5 eV.

[0013] When XPS analysis was performed on the outermost surface of the lithium metal oxide, a second peak appeared in the region with a binding energy of 790 to 800 eV, and the full width at half maximum (FWHM) of the second peak could be less than 2.5 eV.

[0014] When XPS analysis is performed on the lithium metal oxide at a depth of 100 nm from the outermost surface, a third peak appears in the region with a binding energy of 775 to 785 eV, and the full width at half maximum (FWHM) of the third peak can be less than 4 eV.

[0015] When XPS analysis is performed on the lithium metal oxide at a depth of 100 nm from the outermost surface, a fourth peak appears in the region with a binding energy of 790 to 800 eV, and the full width at half maximum (FWHM) of the fourth peak can be less than 4 eV.

[0016] The coating layer may contain CoO, CO3O4, LiCoO2, or a combination thereof.

[0017] The average aspect ratio of the attached particles can be less than 1.5.

[0018] The lithium metal oxide and the coating layer may have a layered crystal structure.

[0019] The lithium metal oxide can be represented by the following chemical formula 1.

[0020] [Chemical Formula 1] Li a [Ni x Co y Mn z M w O2 In the chemical formula 1, 0.8≤a≤1.3, 0.15≤x≤1, 0≤y≤1, 0≤z≤1, 0≤w≤0.1, x+y+z+w≤1, and M is Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, Re, Cr, Ga, Pt, or a combination thereof.

[0021] Another embodiment of the present invention provides a method for preparing a positive electrode active material for a lithium secondary battery, comprising: a step of preparing a metal precursor; a step of mixing the metal precursor and a first lithium raw material and then calcining the mixture to form a lithium metal oxide in the form of single particles; and a step of mixing the lithium metal oxide and a cobalt raw material and then subjecting the mixture to a coating heat treatment to form a cobalt-containing coating layer, wherein the coating layer is attached to the surface of the lithium metal oxide and is in the form of an island containing a plurality of mutually spaced attached particles, and the average coating rate of the coating layer is 35 to 48% of the total surface area of ​​the single particles.

[0022] In the step of forming the coating layer, the amount of cobalt raw material added may be 0.7 to 4.8 mol based on the total moles of the lithium metal oxide.

[0023] In the step of forming the coating layer, the coating heat treatment can be carried out at a temperature of 620 to 700°C.

[0024] The sphericity of the cobalt raw material can be 0.8 or higher.

[0025] In the step of forming the coating layer, a second lithium raw material may be further mixed.

[0026] The amount of the second lithium raw material added can be less than 4 mol%, based on the total moles of the lithium metal oxide.

[0027] The cobalt raw material can be Co(OH)2, CoCl2, CoO, CoF3, CoSO4·xH2O, CoSO4·7H2O, (CH3CoO)2Co·4H2O, Co(NO3)2·6H2O, (CH3CO2)2Co, CoCO3· x H2O, Co3(PO4)2 or a combination thereof.

[0028] A water washing process may not be required after the step of forming lithium metal oxide and before the step of forming the coating layer.

[0029] Another embodiment of the present invention provides a lithium secondary battery cathode comprising the aforementioned cathode active material.

[0030] Another embodiment of the present invention provides a lithium secondary battery comprising the positive electrode of the lithium secondary battery.

[0031] (III) Beneficial Effects According to one embodiment of the present invention, the positive electrode active material of a lithium secondary battery, which is a lithium metal oxide in the form of a single particle, contains a cobalt-containing coating layer in the form of an island. By appropriately controlling the structure of the coating layer, it can have excellent capacity characteristics and a low rate of increase in resistance due to cycling. Attached Figure Description

[0032] Figure 1 and Figure 2 This is a SEM image of the positive electrode active material prepared according to Example 2.

[0033] Figure 3 These are TEM and SAED pattern analysis images of the positive electrode active material prepared according to Example 2.

[0034] Figure 4 The graph shows the XPS analysis results of the positive electrode active material prepared according to Example 2.

[0035] Figure 5 The graph shows the XPS analysis results of the positive electrode active material prepared according to Comparative Example 1. Detailed Implementation

[0036] The terms "first," "second," "third," etc., are used to describe various parts, components, regions, layers, and / or segments, but these parts, components, regions, layers, and / or segments should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, and / or segment from another. Therefore, without departing from the scope of the invention, the first part, component, region, layer, and / or segment described below can also be described as a second part, component, region, layer, and / or segment.

[0037] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular forms used are intended to include the plural forms as well. It should also be understood that the term "comprising" as used in the specification can specifically refer to a particular feature, domain, integer, step, action, element, and / or component, and does not exclude the presence or addition of other features, domains, integers, steps, actions, elements, and / or components.

[0038] If one part is described as being on top of another part, then other parts may exist directly on top of or in between the other part. If one part is described as being directly on top of another part, then no other parts exist in between.

[0039] Although not otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in dictionaries should be interpreted as having the same meaning as disclosed in relevant technical literature and herein, and should not be interpreted in an idealized or overly formal sense.

[0040] In addition, unless otherwise specified, % means weight, 1ppm means 0.0001 wt%.

[0041] In this specification, the term "combination" as used in the Markush form refers to a mixture or combination of one or more of the constituent elements described in the Markush form, which means including one or more of the constituent elements described above.

[0042] The embodiments of the present invention will be described in detail below to enable those skilled in the art to implement the invention. However, the present invention can be implemented in various different ways and is not limited to the embodiments described herein.

[0043] 1. Positive electrode active material The positive electrode active material for a lithium secondary battery according to one embodiment of the present invention comprises lithium metal oxide in the form of single particles. Compared with conventional secondary particles, the single-particle form of the positive electrode active material has a smaller specific surface area, thereby reducing the amount of gas generated due to side reactions with the electrolyte. Furthermore, due to the high particle strength, particle breakage can be suppressed during rolling, and cracks generated by repeated charging and discharging can be reduced. Therefore, it has superior lifespan and safety compared to secondary particles, and offers the advantage of achieving high energy density in the electrode.

[0044] In this specification, "single particle" is a term used to distinguish it from the commonly used term for positive electrode active material particles, which are formed by the aggregation of dozens to hundreds of primary particles. The concept includes single particles consisting of one primary particle and aggregates of 30 or fewer primary particles. Furthermore, "secondary particle" refers to an aggregate formed by the physical or chemical bonding between primary particles, without any deliberate aggregation or granulation process, i.e., a secondary structure.

[0045] However, for single-particle cathode active materials, compared to traditional secondary-particle cathode active materials, the primary particles are relatively large in size and have fewer interfaces between them, serving as lithium-ion diffusion pathways. Therefore, lithium mobility is lower. Furthermore, due to the relatively high calcination temperature, a rocksalt phase forms on the particle surface, resulting in higher surface resistivity. This reduced lithium mobility first leads to a decrease in capacity characteristics, and secondly, it causes uneven lithium-ion migration, leading to crystal structure deformation and particle cracking. This results in a decline in lifetime characteristics, such as increased resistance with cycling.

[0046] Therefore, the positive electrode active material of a lithium secondary battery according to one embodiment of the present invention comprises a cobalt-containing coating layer disposed on the surface of a lithium metal oxide. In this case, the coating layer adheres to the surface of the lithium metal oxide in an island-like form comprising a plurality of spaced-apart attached particles. Since the positive electrode active material according to the present invention comprises a cobalt-containing coating layer in an island-like form, capacity can be improved and the rate of increase in resistance due to cycling can be reduced. Traditionally, to improve the electrochemical properties of the positive electrode active material, a conformal coating layer covering the entire surface of the lithium metal oxide is typically formed. However, to achieve a conformal coating layer, high-temperature coating heat treatment processes are required, resulting in high process costs and difficulty in achieving good thickness uniformity, leading to increased resistance. On the other hand, the positive electrode active material according to the present invention comprises an island-like coating layer, thus saving process costs. Furthermore, an island-like coating layer comprising unit attached particles of uniform size and thickness can be achieved, thereby improving capacity and reducing the rate of increase in resistance due to cycling.

[0047] On the other hand, in this specification, "attached particles" refers to the smallest particle unit that is attached to the surface of lithium metal oxide and spaced apart from each other, and is classified as a block when the surface of lithium metal oxide is observed by scanning electron microscopy (SEM).

[0048] The shape of the attached particles is amorphous, although there are no particular restrictions, but more specifically they can be dot shapes with an average aspect ratio of 1.5 or less. In this specification, "aspect ratio" refers to the ratio of the longest side to the shortest side within the attached particle, and the "average aspect ratio" can be obtained by averaging any 20 attached particles observed on a 30,000x SEM image.

[0049] At this point, the lithium metal oxide and the coating layer can have a layered crystal structure. That is, the positive electrode active material according to the present invention not only has a layered crystal structure in the bulk lithium metal oxide, but the coating layer can also have a layered crystal structure. Since both the bulk and the coating layer have a layered crystal structure, the diffusion of lithium ions within the layered structure can be maintained in both the bulk and the coating layer, thereby achieving the aforementioned improved electrochemical properties more effectively.

[0050] Furthermore, the average coating percentage of the coating layer, based on the total surface area of ​​a single lithium metal oxide particle, can be 35% to 48% of the area, more specifically 38% to 46% of the area. If the average coating percentage is too high, the surface inert resistance of the active material increases, and the capacity and resistance increase rate characteristics due to cycling may deteriorate. If the average coating percentage is too low, the residual lithium removal rate is low, surface cation mixing increases, and the capacity and resistance increase rate characteristics due to cycling may deteriorate. In this specification, the coating percentage can refer to the proportion of the area of ​​the lithium metal oxide surface covered by multiple attached particles. This average coating percentage can be measured by the following method. First, the coating percentage of the coating layer for a single positive electrode active material particle can be obtained by calculating the percentage value of the total area of ​​the attached particles relative to the total surface area of ​​the observed lithium metal oxide particles when observing the surface of the lithium metal oxide using a 30,000x SEM (scanning electron microscope). Furthermore, the average coating rate of the coating layer can be obtained by calculating the coating rate of any 20 positive electrode active material particles in the positive electrode active material powder using the method described above, and then calculating the average value of the coating rate.

[0051] Furthermore, the average diameter of the attached particles can be from 160 to 240 nm, more specifically from 170 to 230 nm. If the average diameter of the attached particles is too small, the coating effect, such as surface protection, will be poor, and the capacity and the rate of increase in resistance due to cycling may deteriorate. If the average diameter of the attached particles is too large, the surface inert resistance of the active material will increase, and the capacity and the rate of increase in resistance due to cycling may deteriorate. In this specification, the diameter of the attached particles may refer to the length of the longest side within the attached particle. This average diameter of the attached particles can be obtained by calculating the average length of the longest side of any 20 attached particles observed when viewing the positive electrode active material using a 30,000x SEM.

[0052] Furthermore, the average thickness of the attached particles can be 50 to 90 nm, more specifically 55 to 85 nm. If the average thickness of the attached particles is too small, the coating effect, such as surface protection, will be poor, and the capacity and resistance increase rate characteristics due to cycling may deteriorate. If the average thickness of the attached particles is too large, the surface inert resistance of the active material will increase, and the capacity and resistance increase rate characteristics due to cycling may deteriorate. In this specification, the thickness of the attached particles can refer to the height of the attached particles with the lithium metal oxide surface as the reference plane. This average thickness of the attached particles can be measured by the following methods. First, the thickness of the attached particles of a single positive electrode active material particle can be obtained by measuring the thickness of any attached particle seen when observing the cross-section of the positive electrode active material particle using a 500,000x TEM (transmission electron microscope). Second, the average thickness of the attached particles can be obtained by calculating the thickness of the attached particles of any 20 positive electrode active material particles in the positive electrode active material powder using the method described above, and then averaging the results.

[0053] Based on the total moles of lithium metal oxide, the cobalt content in the coating layer can be from 0.7 to 4.8 mol%, more specifically from 0.8 to 4 mol%. When the cobalt content in the coating layer meets the above range, the average coating rate, average particle size of the attached particles, and average thickness of the attached particles can be more easily obtained within the range described in this invention.

[0054] In this case, the coating layer may contain CoO, CO3O4, LiCoO2, or a combination thereof. CoO, CO3O4, or LiCoO2, due to their favorable structural and phase stability characteristics, can more ideally achieve the aforementioned improvements in electrochemical properties. The presence of CoO, CO3O4, or LiCoO2, as described later, can be confirmed by XPS analysis of the outermost surface of the lithium metal oxide.

[0055] Furthermore, when XPS analysis is performed on the outermost surface of the lithium metal oxide, a first peak may appear in the region with a binding energy of 775 to 785 eV. In this case, the full width at half maximum (FWHM) of the first peak may be below 2.5 eV, more specifically below 2.4 eV. The first peak in this region may refer to Co2p3 / 2. As the FWHM of the first peak satisfies this range, electrochemically active CoO, CO3O4, or LiCoO2 crystal phases can be well formed, thereby achieving the aforementioned improvement in electrochemical properties more effectively. On the other hand, in this specification, XPS refers to X-ray photoelectron spectroscopy.

[0056] Furthermore, when XPS analysis is performed on the outermost surface of the lithium metal oxide, a second peak may appear in the region with a binding energy of 790 to 800 eV. In this case, the full width at half maximum (FWHM) of the second peak may be below 2.5 eV, more specifically below 2.4 eV. The second peak in this region may refer to Co2p1 / 2. With the FWHM of the second peak satisfying this range, electrochemically active CoO, CO3O4, or LiCoO2 crystal phases can be well formed, thus achieving the aforementioned improvement in electrochemical properties more effectively.

[0057] Furthermore, when XPS analysis is performed at a depth of 100 nm from the outermost surface of the lithium metal oxide, a third peak may appear in the region with a binding energy of 775 to 785 eV. In this case, the full width at half maximum (FWHM) of the third peak may be below 4 eV, more specifically below 3.5 eV. The third peak in this region may refer to Co2p3 / 2. With the FWHM of the third peak satisfying this range, electrochemically active CoO, Co3O4, or LiCoO2 crystal phases can be well formed, thus achieving the aforementioned improvement in electrochemical properties more effectively.

[0058] When XPS analysis is performed on the lithium metal oxide at a depth of 100 nm from its outermost surface, a fourth peak may appear in the region with a binding energy of 790 to 800 eV. In this case, the full width at half maximum (FWHM) of the fourth peak may be below 4 eV, more specifically below 3.5 eV. The fourth peak in this region may refer to Co2p1 / 2. With the FWHM of the fourth peak satisfying this range, electrochemically active CoO, CO3O4, or LiCoO2 crystal phases can be well formed, thus achieving the aforementioned improvement in electrochemical properties more effectively.

[0059] Furthermore, the residual lithium content of the lithium metal oxide according to the present invention can be less than 5000 ppm, more specifically less than 4500 ppm, 4000 ppm, 3500 ppm, or 3200 ppm. The inventors have confirmed that when the average coating ratio and other physical properties of the coating layer are adjusted to the range described in the present invention, the residual lithium content is significantly reduced. Residual lithium can generate gas due to side reactions with the electrolyte, thereby leading to a decrease in battery safety and lifespan characteristics. Therefore, as the residual lithium content of the lithium metal oxide according to the present invention meets the aforementioned range, safety and lifespan characteristics can be improved.

[0060] The lithium metal oxide can be more specifically represented by the following chemical formula 1.

[0061] [Chemical Formula 1] Li a [Ni x Co y Mn z Mw O2 In the chemical formula 1, 0.8≤a≤1.3, 0.15≤x≤1, 0≤y≤1, 0≤z≤1, 0≤w≤0.1, x+y+z+w≤1, and M is Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, Re, Cr, Ga, Pt, or a combination thereof.

[0062] 2. Preparation method of positive electrode active material Another embodiment of the present invention provides a method for preparing a positive electrode active material for a lithium secondary battery, comprising: a step of preparing a metal precursor; a step of mixing the metal precursor and a first lithium raw material and then calcining the mixture to form a lithium metal oxide in the form of single particles; and a step of mixing the lithium metal oxide and a cobalt raw material and then subjecting the mixture to a coating heat treatment to form a cobalt-containing coating layer, wherein the coating layer is attached to the surface of the lithium metal oxide and is in the form of an island containing a plurality of mutually spaced attached particles, and the average coating rate of the coating layer is 35 to 48% of the total surface area of ​​the single particles.

[0063] The preparation method of a positive electrode active material for a lithium secondary battery according to another embodiment of the present invention is described below step by step.

[0064] First, prepare the metal precursor.

[0065] The metal precursor may more specifically be a metal hydroxide.

[0066] The metal precursor can be prepared, for example, by adding a complexing agent solution and a pH adjuster solution to a metal-containing solution containing nickel, manganese, or cobalt raw materials to carry out a co-precipitation reaction.

[0067] There are no particular limitations on the nickel raw material used in the preparation of precursors for positive electrode active materials in this technical field. For example, the nickel raw material can be a nickel-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or hydroxyoxide, etc. Specifically, it can be NiSO4, NiSO4·6H2O, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, nickel salts of fatty acids, nickel halides, or combinations thereof, but is not limited thereto.

[0068] There are no particular limitations on the cobalt raw material used in the preparation of cathode active material precursors in this technical field. For example, the cobalt raw material can be a cobalt-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or hydroxyoxide, specifically CoSO4, CoSO4·7H2O, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, or combinations thereof, but it is not limited to these.

[0069] There are no particular limitations on the manganese raw material used in the preparation of precursors for positive electrode active materials in this technical field. For example, the manganese raw material can be a manganese-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, hydroxy oxide, or a combination thereof. Specifically, it can be manganese salts such as MnSO4, MnCO3, Mn(NO3)2, manganese acetate, manganese dicarboxylate, manganese citrate, and manganese salts of fatty acids, manganese oxides such as Mn2O3, MnO2, and Mn3O4, hydroxy oxides, manganese chloride, or a combination thereof, but is not limited to these.

[0070] The metal-containing solution can be prepared by adding a nickel, manganese, or cobalt raw material to a solvent, specifically water or a mixture of water and an organic solvent (e.g., an alcohol) that can be uniformly mixed with water.

[0071] The complexing agent-containing solution serves to form a complex. The complexing agent may include, for example, NH3, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or combinations thereof, but is not limited thereto. Alternatively, the complexing agent-containing solution can be used in the form of an aqueous solution. In this case, water or a mixture of water and an organic solvent (e.g., an alcohol) that is homogeneous with water can be used as the solvent.

[0072] The pH-adjusting solution acts as a precipitant or pH adjuster and may contain a basic compound, which is an alkali metal or alkaline earth metal hydroxide, such as NaOH, KOH, or Ca(OH)₂, its hydrate, or a combination thereof. Alternatively, the pH-adjusting solution can also be used in the form of an aqueous solution, in which case water or a mixture of water and an organic solvent (e.g., an alcohol) that is homogeneous with water can be used as the solvent. In this case, the pH-adjusting solution can be added to the reaction solution to achieve a pH of 10 to 13.

[0073] The coprecipitation reaction can be carried out in an inert atmosphere such as nitrogen or argon, at a temperature of 30 to 70°C, and at a pH of 10 to 13.

[0074] Nickel (or manganese-cobalt) hydroxide particles are generated using the process described above and precipitated in the reaction solution. The precipitated precursor particles can be separated using conventional methods and obtained by washing with water and drying. The precursor can be secondary particles formed from primary particle aggregation.

[0075] At this point, the molar ratio of nickel, cobalt, or manganese in the precursor can be adjusted by regulating the concentration of the nickel, cobalt, or manganese raw materials. In other words, the concentrations of the nickel, cobalt, and manganese raw materials can be adjusted so that the molar ratio of nickel, cobalt, or manganese in the final lithium metal oxide product is within the range described in this invention.

[0076] Next, the metal precursor and the first lithium raw material are mixed and calcined to form lithium metal oxide in the form of single particles.

[0077] At this point, the first lithium raw material can be any lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or hydroxyl oxide, etc., as long as it is soluble in water, there are no particular restrictions. Specifically, the lithium raw material can be Li₂CO₃, LiNO₃, LiNO₂, LiOH, LiOH·H₂O, LiH, LiF, LiCl, LiBr, LiI, CH₃COOLi, Li₂O, Li₂SO₄, CH₃COOLi, Li₃C₆H₅O₇ or a combination thereof, but is not limited to these.

[0078] Furthermore, the calcination can be carried out at a temperature of 800 to 1000°C. If the calcination temperature is too low, lithium metal oxide in single-particle form may not form. If the calcination temperature is too high, over-calcination will result in crystal structure defects, which may lead to a decrease in electrochemical properties.

[0079] Furthermore, the calcination can be carried out for 5 to 20 hours. If the calcination time is too short, lithium metal oxide in single-particle form may not be formed. If the calcination time is too long, crystal structure defects caused by over-calcination may occur, which may lead to a decrease in electrochemical properties.

[0080] Furthermore, the atmosphere during calcination is not particularly limited; for example, it can be carried out in an oxygen (O2) or air atmosphere.

[0081] At this point, a water washing process may be omitted after the step of forming the lithium metal oxide and before the step of forming the coating layer. Water washing is typically performed to remove residual lithium from the surface of the synthesized lithium metal oxide. However, the present invention allows the residual lithium remaining after synthesis to react together with the cobalt raw material described later through a coating heat treatment, thereby forming a layered coating layer with good electrochemical activity based on the lithium cobalt oxide composition, and achieving a good average coating coverage within the scope described in the present invention.

[0082] Next, the lithium metal oxide and cobalt raw materials are mixed and then coated with heat to form a cobalt-containing coating layer.

[0083] At this time, the amount of cobalt raw material added can be 0.7 to 4.8 mol%, based on the total moles of the lithium metal oxide. When the content of the cobalt raw material meets the range, the content of the raw materials used to form the coating layer is appropriately adjusted, thereby making it easier to obtain the above-mentioned average coating rate and other physical properties of the coating layer within the range described in this invention.

[0084] Furthermore, the coating heat treatment can be performed at a temperature of 620 to 700°C, more specifically at a temperature of 640 to 690°C. If the coating heat treatment temperature is too low, the coating layer will not form sufficiently, and the average coating coverage, average diameter of the attached particles, or thickness of the obtained coating layer may be too small. If the coating heat treatment temperature is too high, a conformal coating layer may be formed instead of an island-like structure.

[0085] Furthermore, the sphericity of the cobalt raw material can be 0.8 or higher, more specifically 0.85 or 0.9 or higher. If the sphericity of the cobalt raw material is too small, the average coverage of the obtained coating layer will be too small, while the average diameter or average thickness of the obtained coating layer may be too large. On the other hand, in this specification, sphericity is a numerical expression of the degree to which a particle is close to a sphere, and is the value obtained by dividing the circumference of a corresponding circle with the same area as the particle's projected shape by the actual circumference of the particle's projected shape using a flow cytometry particle analyzer. This sphericity can be measured using an analyzer (Fluid Imaging Technologies, Flowcam 8100) for acquiring optical images and analysis software (visual spreadsheet).

[0086] Furthermore, in the step of forming the coating layer, a second lithium raw material can be further mixed. By further mixing the second lithium raw material, a layered structure based on lithium cobalt oxide components with good electrochemical activity can be well formed, and the average coating coverage and other physical properties of the coating layer can be better achieved within the scope described in this invention.

[0087] Furthermore, based on the total moles of the lithium metal oxide, the amount of the second lithium raw material added can be less than 4 mol%, more specifically less than 3.5 mol% or 3 mol%. If the amount of the second lithium raw material added is too large, the average coating rate and other physical properties of the coating layer may deviate from the scope of the present invention.

[0088] The cobalt raw material can be Co(OH)2, CoCl2, CoO, CoF3, CoSO4·xH2O, CoSO4·7H2O, (CH3CoO)2Co·4H2O, Co(NO3)2·6H2O, (CH3CO2)2Co, CoCO3· x H2O, Co3(PO4)2 or combinations thereof, but not necessarily limited to these.

[0089] Therefore, the coating layer having the above-described structure according to the present invention can be well formed.

[0090] 3. Positive electrode and lithium secondary battery Another embodiment of the present invention provides a lithium secondary battery cathode comprising the aforementioned cathode active material.

[0091] More specifically, the positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector and containing the aforementioned positive electrode active material.

[0092] There are no particular limitations on the positive electrode current collector, as long as it does not cause chemical changes in the battery while maintaining conductivity. For example, it can be made of stainless steel, aluminum, nickel, titanium, calcined carbon, or materials such as carbon, nickel, titanium, or silver used to surface-treat aluminum or stainless steel. Furthermore, the positive electrode current collector can typically have a thickness of 3 to 500 μm, and fine irregularities can be formed on its surface to improve the adhesion of the positive electrode active material. For example, it can be in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0093] The positive electrode active material layer may contain a binder and / or a conductive agent together with the aforementioned positive electrode active material.

[0094] At this point, the adhesive serves to improve the adhesion between the positive electrode active material particles and the bonding force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), PVDF-co-HFP copolymer, polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof. These can be used individually or in mixtures of two or more, but are not limited thereto. The adhesive may comprise 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0095] Furthermore, the conductive agent is used to impart conductivity to the electrode, and its use is not particularly restricted as long as it does not cause chemical changes and has electronic conductivity in the constructed battery. Specific examples include graphite such as natural or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, and carbon fiber; metal powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. These can be used alone or in mixtures of two or more, but are not limited to these. The content of the conductive agent relative to the total weight of the positive electrode active material layer is typically 1 to 30% by weight.

[0096] In addition to using the aforementioned positive electrode active material, the positive electrode can be prepared according to conventional positive electrode preparation methods.

[0097] Specifically, the positive electrode can be prepared by coating a positive electrode current collector with a composition for forming a positive electrode active material layer, comprising the aforementioned positive electrode active material and, as needed, an optional binder, conductive agent, or solvent, followed by drying and pressing. In this case, the types and amounts of the positive electrode active material, binder, and conductive agent are as described above.

[0098] The solvent can be one commonly used in this field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. These can be used alone or in mixtures of two or more. Considering the coating thickness and yield of the slurry, the amount of solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive agent, and binder, resulting in a viscosity that exhibits excellent thickness uniformity during subsequent coating preparation of the positive electrode.

[0099] Alternatively, the positive electrode can also be prepared by casting the positive electrode active material layer forming composition onto a separate support, peeling it off from the support to obtain a thin film, and then laminating the thin film onto the positive electrode current collector.

[0100] Another embodiment of the present invention provides a lithium secondary battery comprising the aforementioned lithium secondary battery positive electrode.

[0101] More specifically, the lithium secondary battery may include a positive electrode, a negative electrode, a separator, and an electrolyte.

[0102] The lithium secondary battery may optionally further include a battery container housing an electrode assembly consisting of the positive electrode, negative electrode, and separator, and a sealing component for sealing the battery container.

[0103] The negative electrode may include a negative electrode current collector and a layer of negative electrode active material located on the negative electrode current collector.

[0104] For the negative electrode current collector, there are no particular restrictions as long as it does not cause chemical changes in the battery while maintaining high conductivity. For example, materials such as copper, stainless steel, aluminum, nickel, titanium, calcined carbon, materials that have undergone surface treatment of copper or stainless steel with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. Furthermore, the negative electrode current collector can typically have a thickness of 3 to 500 μm, similar to the positive electrode current collector. Fine irregularities can also be formed on the surface of the current collector to enhance the adhesion of the negative electrode active material. For example, various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics can be used.

[0105] The negative electrode active material layer may optionally include a binder and a conductive agent together with the negative electrode active material. As an example, the negative electrode active material layer may also be prepared by coating a negative electrode active material layer forming composition comprising the negative electrode active material and a selected binder and conductive agent onto the negative electrode current collector and drying it, or by casting the negative electrode forming composition onto a separate support, peeling it off from the support to obtain a film, and then laminating the film onto the negative electrode current collector.

[0106] As the negative electrode active material, compounds capable of reversibly inserting and deintercalating lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metallic compounds that can be alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; lithium-doped and dedoped metal oxides such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the aforementioned metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites. Any one or a mixture of two or more of these can be used. Furthermore, a thin film of metallic lithium can also be used as the negative electrode active material. Additionally, both low-crystallinity carbon and high-crystallinity carbon can be used as carbon materials. As low-crystallinity carbon, soft carbon and hard carbon are representative examples. As highly crystalline carbon, amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon from petroleum or coal tar pitch-derived cokes are representative examples.

[0107] The adhesive and conductive agent may be the same as those previously described in the positive electrode.

[0108] The separator is used to separate the negative and positive electrodes and provide a migration channel for lithium ions. Any separator commonly used in lithium secondary batteries can be used without particular restrictions, especially those with low resistance to electrolyte ion migration and excellent electrolyte wetting ability. Specifically, porous polymer films can be used, such as porous polymer films made from polyolefin polymers like polyethylene homopolymer, polypropylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminates of two or more layers thereof. Alternatively, conventional porous nonwoven fabrics can be used, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers. Furthermore, to ensure heat resistance or mechanical strength, coated separators containing ceramic components or polymeric substances can be used, optionally in single-layer or multi-layer structures.

[0109] The electrolytes mentioned include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the preparation of lithium secondary batteries.

[0110] Specifically, the organic liquid electrolyte may contain an organic solvent and a lithium salt.

[0111] The organic solvents mentioned herein can be used without particular restriction, as long as they can act as a medium for the migration of ions participating in the electrochemical reaction of the battery. Specifically, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone can be used as organic solvents; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Carbonate solvents such as carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (where R is a C2 to C20 straight-chain, branched, or cyclic hydrocarbon group, which may contain aromatic rings or ether bonds); amides such as dimethylformamide; dioxolane solvents such as 1,3-dioxolane; or sulfolane solvents. Among these, carbonate solvents are preferred, and more preferably, a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate, etc.) with high ionic conductivity and high dielectric constant, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) that can improve battery charge-discharge performance is preferred. In this case, using a mixture of cyclic carbonates and linear carbonates at a volume ratio of about 1:1 to about 1:9 results in an electrolyte exhibiting excellent performance.

[0112] For the lithium salt, any compound capable of inducing lithium ions for use in lithium-ion secondary batteries can be used without particular restriction. Specifically, as the lithium salt, 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., can be used. The concentration of the lithium salt is preferably in the range of 0.1 to 2.0 M. If the concentration of the lithium salt is within this range, the electrolyte has appropriate conductivity and viscosity, thus exhibiting excellent electrolyte performance, and lithium ions can migrate effectively.

[0113] To improve battery life characteristics, suppress battery capacity reduction, and increase battery discharge capacity, in addition to the electrolyte components, the electrolyte may further contain one or more additives, such as halogenated alkylene carbonates like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether (glyme), hexamethylphosphoryltriamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidinanes, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, etc. In this case, the additives may be present in amounts from 0.1 to 5% by weight relative to the total weight of the electrolyte.

[0114] As described above, lithium secondary batteries containing the positive electrode active material according to the present invention stably exhibit excellent discharge capacity, output characteristics and capacity retention, and are therefore very useful in portable devices such as mobile phones, laptops, and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs).

[0115] Accordingly, another embodiment of the present invention provides a battery module comprising the lithium secondary battery as a unit battery and a battery pack comprising the same.

[0116] The battery module or battery pack can be used as a power tool; an electric vehicle including pure electric vehicles (EVs), hybrid electric vehicles and plug-in hybrid electric vehicles (PHEVs); or a power source for any one or more medium and large-sized equipment / devices in an energy storage system.

[0117] The embodiments of the present invention will be further described in detail below through examples. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0118] Example 1 (1) Preparation of positive electrode active materials (Preparation of metal precursors) First, Ni was prepared. 0.89 Co 0.037 Mn 0.073 Metal precursor of (OH)2.

[0119] (Calcination) Subsequently, the metal precursor was mixed with LiOH·H2O, which served as the first lithium raw material, and calcined at 860°C for 10 hours under an oxygen atmosphere to form lithium metal oxide in single-particle form. At this time, no separate water washing process was performed after the formation of the lithium metal oxide.

[0120] (Coating Heat Treatment) Subsequently, the lithium metal oxide was mixed with Co(OH)₂ (a cobalt raw material that had been ground and had a sphericity of 0.9) and LiOH·H₂O (a second lithium raw material), and then subjected to a coating heat treatment at 680°C to form a coating layer. At this time, the amount of Co(OH)₂ added was 1.0 mol% based on the total moles of lithium metal oxide, and the amount of the second lithium raw material added was 1.0 mol% based on the total moles of lithium metal oxide.

[0121] (2) Preparation of lithium secondary batteries For the slurry used in electrode preparation, the positive electrode active material, conductive agent (carbon black), and binder (PVDF, KF1100) were mixed in a ratio of 92.5:3.5:4 wt%, and NMP (N-methyl-2-pyrrolidone) was added to adjust the viscosity so that the solid content was approximately 30%. The prepared slurry was coated onto a 15 μm thick aluminum foil using a doctor blade, and then dried and pressed. The electrode loading was 14.6 mg / cm³. 2 The compressed density (25℃, 20kN) is 3.1 g / cm³. 3 .

[0122] For the electrolyte, 1M LiPF6 was dissolved in EC:DMC:EMC=3:4:3 (volume%) and 3.0 volume% VC was added relative to the total electrolyte volume. Coin cells were fabricated using a PP separator and a lithium anode (200 μm, Honzometal).

[0123] Example 2 In the coating heat treatment step, the amount of Co(OH)2 added was set to 2.0 mol% based on the total moles of lithium metal oxide, and the amount of the second lithium raw material added was set to 2.0 mol% based on the total moles of lithium metal oxide. Otherwise, the positive electrode active material and the lithium secondary battery were prepared by the same implementation method as in Example 1.

[0124] Comparative Example 1 Except for the absence of a coating heat treatment step, a positive electrode active material and a lithium secondary battery were prepared using the same implementation method as in Example 1.

[0125] Comparative Example 2 In the coating heat treatment step, the amount of Co(OH)2 added was set to 0.5 mol% based on the total moles of lithium metal oxide, and the amount of the second lithium raw material added was set to 2.0 mol% based on the total moles of lithium metal oxide. Otherwise, the positive electrode active material and the lithium secondary battery were prepared by the same implementation method as in Example 1.

[0126] Comparative Example 3 In the coating heat treatment step, the amount of Co(OH)2 added was set to 5.0 mol% based on the total moles of lithium metal oxide, and the amount of the second lithium raw material added was set to 2.0 mol% based on the total moles of lithium metal oxide. Otherwise, the positive electrode active material and the lithium secondary battery were prepared by the same implementation method as in Example 1.

[0127] Comparative Example 4 In the coating heat treatment step, the amount of Co(OH)2 added was set to 2.0 mol% based on the total moles of lithium metal oxide, the amount of the second lithium raw material added was set to 2.0 mol% based on the total moles of lithium metal oxide, and the coating heat treatment temperature was set to 600°C. Otherwise, the positive electrode active material and the lithium secondary battery were prepared by the same implementation method as in Example 1.

[0128] Comparative Example 5 In the coating heat treatment step, the amount of Co(OH)2 added was set to 2.0 mol% based on the total moles of lithium metal oxide, the amount of the second lithium raw material added was set to 2.0 mol% based on the total moles of lithium metal oxide, and the coating heat treatment temperature was set to 750°C. Otherwise, the positive electrode active material and the lithium secondary battery were prepared by the same implementation method as in Example 1.

[0129] Comparative Example 6 In the coating heat treatment step, the amount of Co(OH)2 added was set to 2.0 mol% based on the total moles of lithium metal oxide. Since it was not ground, the sphericity of Co(OH)2 was 0.6. The amount of the second lithium raw material added was set to 2.0 mol% based on the total moles of lithium metal oxide. Otherwise, the positive electrode active material and the lithium secondary battery were prepared by the same implementation method as in Example 1.

[0130] Comparative Example 7 In the coating heat treatment step, the amount of Co(OH)2 added was set to 2.0 mol% based on the total moles of lithium metal oxide. No second lithium raw material was added. Otherwise, the positive electrode active material and lithium secondary battery were prepared by the same implementation method as in Example 1.

[0131] Comparative Example 8 In the coating heat treatment step, the amount of Co(OH)2 added was set to 5.0 mol% based on the total moles of lithium metal oxide, and the amount of the second lithium raw material added was set to 5.0 mol% based on the total moles of lithium metal oxide. Otherwise, the positive electrode active material and the lithium secondary battery were prepared by the same implementation method as in Example 1.

[0132] Table 1 below summarizes the aforementioned process conditions.

[0133] Table 1 In Table 1 above, w (with) means that a second lithium feedstock was added, and w / o (without) means that no second lithium feedstock was added. Experimental Example 1: Evaluation of the shape and crystal structure of the positive electrode active material SEM (scanning electron microscope) images of the positive electrode active material prepared according to Example 2 were observed and are shown below. Figure 1 and Figure 2 Furthermore, the surface crystal structure of the positive electrode active material prepared according to Example 2 was evaluated by TEM (transmission electron microscopy) and SAED (selected area electron diffraction) pattern analysis, and is shown in the figure. Figure 3 .

[0134] Reference Figures 1 to 2 It can be confirmed that the positive electrode active material according to the present invention forms an island-like coating layer on the surface of lithium metal oxide, which is composed of a plurality of spaced-apart dot-shaped attached particles. Furthermore, it has been confirmed that the average aspect ratio of the plurality of attached particles is approximately 1.

[0135] Reference Figure 3It can be confirmed that the bulk portion (core portion) and the coating layer of the positive electrode active material according to the present invention both have a layered crystal structure.

[0136] Experiment Example 2: Evaluation of the physical properties of positive electrode active materials (1) Evaluation of the coating form The coating morphology (conformal or island-like) was evaluated by observing SEM (scanning electron microscope) images of the positive electrode active materials of the examples and comparative examples.

[0137] (2) Evaluation of the average coverage rate of the coating layer First, the coating coverage of a single positive electrode active material particle was calculated as a percentage of the total area of ​​the attached particles relative to the total surface area of ​​the observed lithium metal oxide particles when observing the surface of the lithium metal oxide using a 30,000x SEM (scanning electron microscope). The average coating coverage was evaluated by calculating the coating coverage of any 20 positive electrode active material particles within the powder using the same method and then averaging the results.

[0138] (3) Evaluate the average thickness of the attached particles First, the thickness of the attached particles of a single positive electrode active material particle is determined by calculating the thickness of any attached particle as observed when the cross-section of the positive electrode active material particle is viewed using a 500,000x TEM (transmission electron microscope). Second, the average thickness of the attached particles is calculated by taking the thickness of the attached particles of any 20 positive electrode active material particles within the positive electrode active material powder using the same method and then averaging the results.

[0139] (4) Evaluate the average particle size of the attached particles The average particle size of the attached particles was evaluated by calculating the average length of the longest side of any 20 attached particles observed when using a 30,000x SEM.

[0140] (5) Evaluation of peak values ​​during X-ray photoelectron spectroscopy (XPS) analysis XPS analysis was used to analyze the binding energy peaks (first and second peaks) at the outermost surface of the lithium metal oxide. Furthermore, the same analysis was used to analyze the binding energy peaks (third and fourth peaks) at a depth of 100 nm from the outermost surface of the lithium metal oxide. Figure 4 and Figure 5 The analysis results of Example 2 and Comparative Example 1 are shown in graphs.

[0141] (6) Evaluation of residual lithium After adding distilled water to the positive electrode active material, residual lithium was extracted using a stirrer, and then the positive electrode active material powder and the extract were separated using a filtration device. Subsequently, the residual lithium was evaluated by measuring the extract through neutralization titration using a Metrohm potentiometric titrator.

[0142] Table 2 Table 3 Referring to Tables 2 and 3, for the embodiments where process conditions such as the content of the coating raw material and the coating heat treatment temperature were appropriately controlled, it can be confirmed that the specific structural properties of the coating layer, including the average coating ratio, were appropriately obtained within the range described in this invention. Furthermore, in the embodiments, the full width at half maximum (FWHM) of the first to fourth peaks was sufficiently small, confirming the good formation of a crystalline phase with good electrochemical activity. Additionally, in the embodiments, it can be confirmed that the residual lithium content was significantly reduced. On the other hand, for Comparative Examples 2 and 3, where the content of the cobalt raw material was too low or too high, it can be confirmed that various properties, including the average coating ratio, deviated from the range described in this invention.

[0143] Furthermore, in Comparative Example 4, where the coating heat treatment temperature was too low, it was confirmed that various physical properties, including the average coating rate, deviated from the range described in this invention.

[0144] Furthermore, in Comparative Example 5, where the coating heat treatment temperature was too high, it was confirmed that a non-island-like coating layer, rather than a conformal coating layer, was formed.

[0145] Furthermore, in Comparative Example 6, where the cobalt raw material has a low sphericity, it can be confirmed that various physical properties, including the average coating rate, deviate from the range described in this invention.

[0146] Furthermore, in Comparative Example 7, where LiOH was not added separately after the coating heat treatment, it was confirmed that various physical properties, including the average coating rate, deviated from the range described in this invention.

[0147] Furthermore, in Comparative Example 8, where excessive amounts of LiOH were added during the coating heat treatment, it was confirmed that various physical properties, including the average coating rate, deviated from the range described in this invention.

[0148] Experiment Example 3: Evaluation of the Electrochemical Characteristics of Lithium Secondary Batteries (1) Evaluate the initial capacity and initial efficiency After fabricating the lithium secondary battery half-cells, they were aged at 25°C for 12 hours, followed by charge-discharge tests at 25°C. For initial capacity evaluation, using 200 mAh / g as the baseline capacity, the cells were charged to 4.25V at a constant current of 0.1C, then switched to a constant voltage and charged until the cutoff current reached 0.05C. After charging, the cells were allowed to rest for 10 minutes, and then discharged at a constant current of 0.1C using 200 mAh / g as the baseline capacity until 2.5V was reached.

[0149] (2) Evaluation of high-temperature life characteristics (45℃, 50 cycles) After fabricating the lithium secondary battery half-cell, it was charged at 45°C with a constant current of 0.5C to 4.25V, and then charged with a constant voltage until the cutoff current reached 0.05C. After charging, it was allowed to rest for 10 minutes, and then discharged with a constant current of 1.0C until it reached 2.5V. Fifty charge-discharge cycles were performed under these conditions, and the capacity retention rate of the 50th cycle relative to the first cycle was calculated.

[0150] (3) Evaluation of the increase rate of high temperature resistance (45℃, 50 cycles) After fabricating the half-cell of a lithium-ion secondary battery, it was charged at 45°C with a constant current of 0.5C to 4.25V, and then charged with a constant voltage until the cutoff current reached 0.05C. After charging, it was allowed to rest for 10 minutes, and then discharged with a constant current of 1.0C until it reached 2.5V. Fifty charge-discharge cycles were performed under these conditions, and the rate of increase in resistance in the 50th cycle relative to the first cycle was calculated.

[0151] Table 4 Referring to Table 4, for the embodiments where the coating layer of the positive electrode active material is in the form of an island and the specific structure of the coating layer, including the average coating ratio, satisfies the scope of the present invention, it can be confirmed that the initial charging capacity and discharging capacity are excellent, and the resistance increase rate is very low. On the other hand, for Comparative Example 5 where the coating layer of the positive electrode active material is in the form of a conformal shape, it can be confirmed that the initial charging capacity and discharging capacity are lower than those of the embodiments, and the resistance increase rate is higher.

[0152] Furthermore, in Comparative Examples 1 to 4, 6 to 8, where the coating layer of the positive electrode active material is in the form of an island, but the specific structural properties of the coating layer, including the average coating rate, deviate from the range described in this invention, it can also be confirmed that the initial charging capacity and discharging capacity are lower than those of the Examples, and the high temperature resistance increase rate is higher.

[0153] While preferred embodiments of the present invention have been described above, the present invention is not limited thereto. Various modifications can be made within the scope of the claims, specification, and drawings, and these modifications also fall within the scope of the present invention.

[0154] Therefore, the substantive scope of the present invention is defined by the claims and their equivalents.

Claims

1. A positive electrode active material for lithium secondary batteries, wherein, The positive electrode active material comprises lithium metal oxide in the form of single particles and a cobalt-containing coating layer disposed on the surface of the lithium metal oxide. The lithium metal oxide and the coating layer have a layered crystal structure. The coating layer adheres to the surface of the lithium metal oxide and takes the form of an island containing multiple spaced-apart attached particles. The average coverage of the coating layer is 35% to 48% of the total surface area of ​​the single particle.

2. The lithium secondary battery positive electrode active material according to claim 1, wherein, The average diameter of the attached particles is 160 to 240 nm.

3. The lithium secondary battery positive electrode active material according to claim 1, wherein, The average thickness of the attached particles is 50 to 90 nm.

4. The lithium secondary battery positive electrode active material according to claim 1, wherein, The cobalt content in the coating layer is 0.7 to 4.8 mol, based on the total moles of the lithium metal oxide.

5. The lithium secondary battery positive electrode active material according to claim 1, wherein, When XPS analysis was performed on the outermost surface of the lithium metal oxide, a first peak appeared in the region with a binding energy of 775 to 785 eV, and the full width at half maximum (FWHM) of the first peak was less than 2.5 eV.

6. The lithium secondary battery positive electrode active material according to claim 1, wherein, When XPS analysis was performed on the outermost surface of the lithium metal oxide, a second peak appeared in the region with a binding energy of 790 to 800 eV, and the full width at half maximum (FWHM) of the second peak was less than 2.5 eV.

7. The lithium secondary battery positive electrode active material according to claim 1, wherein, When XPS analysis was performed on the lithium metal oxide at a depth of 100 nm from the outermost surface, a third peak appeared in the region with a binding energy of 775 to 785 eV, and the full width at half maximum (FWHM) of the third peak was less than 4 eV.

8. The lithium secondary battery positive electrode active material according to claim 1, wherein, When XPS analysis was performed on the lithium metal oxide at a depth of 100 nm from the outermost surface, a fourth peak appeared in the region with a binding energy of 790 to 800 eV, and the full width at half maximum (FWHM) of the fourth peak was less than 4 eV.

9. The lithium secondary battery positive electrode active material according to claim 1, wherein, The coating layer comprises CoO, CO3O4, LiCoO2, or a combination thereof.

10. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The average aspect ratio of the attached particles is less than 1.

5.

11. The lithium secondary battery positive electrode active material according to claim 1, wherein, The residual lithium content is below 5000 ppm.

12. The lithium secondary battery positive electrode active material according to claim 1, wherein, The lithium metal oxide is represented by the following chemical formula 1. [Chemical Formula 1] Li a [Ni x Co y Mr z M w ]O2 In the chemical formula 1, 0.8≤a≤1.3, 0.15≤x≤1, 0≤y≤1, 0≤z≤1, 0≤w≤0.1, x+y+z+w≤1, and M is Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, Re, Cr, Ga, Pt, or a combination thereof.

13. A method for preparing a positive electrode active material for a lithium secondary battery, comprising: Steps for preparing metal precursors; The steps include: mixing the metal precursor and the first lithium raw material and then calcining them to form lithium metal oxide in single-particle form; and... The step of mixing the lithium metal oxide and cobalt raw materials and then subjecting them to a coating heat treatment to form a cobalt-containing coating layer. The coating layer is attached to the surface of the lithium metal oxide and is in the form of an island containing multiple spaced-apart attached particles. The average coating area of ​​the coating layer is 35% to 48% of the total surface area of ​​the single particle.

14. The method for preparing the positive electrode active material of a lithium secondary battery according to claim 13, wherein, In the step of forming the coating layer, The amount of cobalt raw material added is 0.7 to 4.8 mol, based on the total moles of the lithium metal oxide.

15. The method for preparing the positive electrode active material of a lithium secondary battery according to claim 13, wherein, In the step of forming the coating layer, The coating heat treatment is carried out at a temperature of 620 to 700°C.

16. The method for preparing the positive electrode active material of a lithium secondary battery according to claim 13, wherein, The sphericity of the cobalt raw material is 0.8 or higher.

17. The method for preparing the positive electrode active material of a lithium secondary battery according to claim 13, wherein, In the step of forming the coating layer, Further mix the second lithium feedstock material.

18. The method for preparing the positive electrode active material of a lithium secondary battery according to claim 17, wherein, The amount of the second lithium raw material added is less than 4 mol% based on the total moles of the lithium metal oxide.

19. The method for preparing the positive electrode active material of a lithium secondary battery according to claim 13, wherein, The cobalt raw materials are Co(OH)2, CoCl2, CoO, CoF3, CoSO4·xH2O, CoSO4·7H2O, (CH3CoO)2Co·4H2O, Co(NO3)2·6H2O, (CH3CO2)2Co, CoCO3· x H2O, Co3(PO4)2 or a combination thereof.

20. The method for preparing the positive electrode active material of a lithium secondary battery according to claim 13, wherein, No water washing process is performed after the step of forming lithium metal oxide and before the step of forming the coating layer.

21. A lithium secondary battery cathode comprising the cathode active material as described in claim 1.

22. A lithium secondary battery comprising the positive electrode of the lithium secondary battery as described in claim 21.

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