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 cathode active material comprising a lithium metal oxide having a nickel (Ni) containing layered crystal structure in a single particle form and a coating layer coating the entire surface of the lithium metal oxide and containing an aluminum (Al) compound, the lithium metal oxide having a c-axis lattice constant of 14.14 to 14.22 Å when analyzed by X-ray diffraction pattern, the coating layer having an average thickness of 0.5 to 1.5 nm.

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. More specifically, this invention relates to a single-particle series of 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 poor 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 formed from tens to hundreds of primary particles aggregated into spherical secondary particles. However, in the preparation of cathodes, lithium nickel cobalt manganese oxides in this secondary particle form are prone to particle breakage during the pressing process, resulting in the shedding of primary particles. Furthermore, internal cracks can form within the particles 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 poor 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 (the so-called "high-nickel" trend). While increasing the nickel content in cathode active materials 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, resulting in accelerated degradation of the positive electrode active material, poor lifespan characteristics, and reduced 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 lifespan characteristics.

[0006] However, to grow high-nickel-based single-particle lithium transition metal oxides into cathode active materials with particle sizes of several micrometers, high-temperature and long-term calcination is required. However, excessive calcination during this period can lead to defects in the layered crystal structure. Furthermore, due to the relatively high calcination temperature, a rocksalt phase forms on the particle surface, increasing surface resistivity and reducing lithium-ion mobility. This reduced mobility results in an imbalance in lithium-ion migration, causing crystal structure deformation and particle cracking. With continued cycling, this leads to reduced lifespan characteristics, such as capacity degradation. In addition, after the high-nickel-based single-particle cathode material is prepared, the residual lithium content (LiOH and / or Li₂CO₃) on the surface is high, posing a risk to battery safety. Summary of the Invention

[0007] (a) Technical problems to be solved Therefore, the present invention aims to provide a positive electrode active material for lithium secondary batteries, a method for preparing the same, and a lithium secondary battery containing the same. The positive electrode active material, as a single-particle lithium metal oxide, has improved lifespan characteristics and reduced residual lithium.

[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 a single particle containing a nickel (Ni) layered crystal structure and a coating layer covering the entire surface of the lithium metal oxide and containing an aluminum (Al) compound. The lithium metal oxide has a c-axis lattice constant of 14.14 to 14.22 Å in X-ray diffraction pattern analysis, and the coating layer has an average thickness of 0.5 to 1.5 nm.

[0009] When the lithium metal oxide is analyzed by X-ray diffraction, the ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane (I(003) / I(104)) can be 1.44 to 1.6.

[0010] Based on the total weight of the positive electrode active material, the aluminum content in the positive electrode active material can be 500 to 1000 ppm.

[0011] The aluminum compound contains Al2O3, which may be amorphous.

[0012] The residual lithium content of the positive electrode active material can be below 15,000 ppm.

[0013] Based on the total number of moles of metals other than lithium, the nickel content in the lithium metal oxide can be above 80 mol%.

[0014] The lithium metal oxide can be represented by the following chemical formula 1.

[0015] [Chemical Formula 1] Li a [Ni x Co y Mn z M w O2 In the chemical formula 1, 0.8≤a≤1.3, 0.8≤x<1, 0≤y≤0.2, 0≤z≤0.2, 0≤w≤0.2, and x+y+z+w=1, and M is Zr, Al, B, Y, Ti, Nb, W, V, Cr, Mo, Ta, Fe, Cu, Zn, Ga, Ge, Ru, Rh, Sn, Sb, Re, Ir, Pt, Pb, Bi, Na, K, Rb, Cs, Ca, Sr, Ba, Mg, Si, Sc or a combination thereof.

[0016] 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 lithium metal oxide in the form of a single particle containing a nickel (Ni) layered crystal structure; a step of forming a coating layer containing an aluminum compound on the lithium metal oxide by atomic layer deposition; and a step of heat-treating the lithium metal oxide with the coating layer formed at a temperature of 370 to 530°C to form a positive electrode active material.

[0017] The atomic layer deposition can be performed in one cycle.

[0018] One cycle of the atomic layer deposition may include: supplying an aluminum-containing gas to the lithium metal oxide, causing the aluminum-containing gas to be adsorbed onto the lithium metal oxide; and supplying a reactant to the lithium metal oxide with the adsorbed aluminum-containing gas and causing it to react.

[0019] Based on the total weight of the lithium metal oxide, the supply of the aluminum-containing gas can be 0.1 to 2% by weight.

[0020] Based on the total weight of the lithium metal oxide, the amount of reactant supplied can be from 0.001 to 0.01 by weight.

[0021] The atomic layer deposition can be performed at temperatures ranging from 150 to 300°C.

[0022] The atomic layer deposition can be performed at pressures ranging from 1 to 10 Torr.

[0023] Another embodiment of the present invention provides a lithium secondary battery cathode comprising the aforementioned cathode active material.

[0024] Another embodiment of the present invention provides a lithium secondary battery comprising the positive electrode of the lithium secondary battery.

[0025] (III) Beneficial Effects The lithium secondary battery positive electrode active material according to one embodiment of the present invention is a lithium metal oxide in single-particle form, which can improve lifetime characteristics and reduce residual lithium. Furthermore, the lithium secondary battery positive electrode active material according to one embodiment of the present invention can achieve excellent capacity characteristics. Attached Figure Description

[0026] Figure 1 This is a SEM image of the positive electrode active material prepared according to Example 1. Detailed Implementation

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] Furthermore, unless otherwise specified, % means weight, 1 ppm is 0.0001 wt%.

[0032] 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.

[0033] 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.

[0034] 1. Positive electrode active material According to one embodiment of the present invention, the positive electrode active material for a lithium secondary battery comprises lithium metal oxide in the form of single particles. Compared to conventional secondary particles, the single-particle form of the positive electrode active material has a smaller specific surface area, thereby reducing gas generation caused by side reactions with the electrolyte. Furthermore, due to the high particle strength, particle breakage can be suppressed during pressing, and cracks generated during repeated charging and discharging are reduced. Therefore, it offers superior lifespan and safety compared to secondary particles, and has the advantage of enabling high energy density in the electrode.

[0035] 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 tens 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, resulting in a secondary structure, i.e., a secondary structure.

[0036] Furthermore, a "primary particle" refers to the smallest unit of particle that can be divided into a block when the cross-section of a positive electrode active material is observed using a scanning electron microscope (SEM). It can consist of a single grain or multiple grains. Additionally, a "grain" refers to the separated regions within a primary particle where atoms form a lattice structure with a specific orientation.

[0037] Furthermore, based on the total molar number of metals other than lithium, the nickel content in the lithium metal oxide according to the present invention can be 80 mol% or more, more specifically 85 mol% or more. With such a high nickel content in the lithium metal oxide (so-called "high nickel"), high battery capacity can be achieved.

[0038] However, to grow high-nickel-based single-particle lithium transition metal oxides into cathode active materials with particle sizes of several micrometers, high-temperature and long-term calcination is required. However, excessive calcination during this period can lead to defects in the layered crystal structure. Furthermore, due to the relatively high calcination temperature, a rocksalt phase forms on the particle surface, increasing surface resistivity and reducing lithium-ion mobility. This reduced mobility results in an imbalance in lithium-ion migration, causing crystal structure deformation and particle cracking. With continued cycling, this leads to reduced lifespan characteristics, such as capacity degradation. In addition, after the high-nickel-based single-particle cathode material is prepared, the residual lithium content (LiOH and / or Li₂CO₃) on the surface is high, posing a risk to battery safety.

[0039] Therefore, the positive electrode active material of a lithium secondary battery according to one embodiment of the present invention comprises a coating layer covering the entire surface of a lithium metal oxide and containing an aluminum (Al) compound. That is, the coating layer is a conformal coating layer that uniformly covers the entire surface of a single particle. Therefore, compared to island-type coating layers, the structural stability of the positive electrode active material can be better improved, thereby preferably achieving the desired lifetime characteristics of the positive electrode active material. Furthermore, during the coating of the lithium metal oxide, the coating material reacts with some residual lithium remaining on the surface of the lithium metal oxide to form the coating layer, and this reaction occurs more effectively than with island-type coating layers, thereby more preferably achieving a reduction in residual lithium. On the other hand, the conformal coating layer, as described later, can be obtained by a coating process using atomic layer deposition (ALD).

[0040] At this point, the average thickness of the coating layer can be from 0.5 to 1.5 nm, more specifically from 0.65 to 1.4 nm. If the average thickness of the coating layer is too thin, the coating effect will be negligible, and the improvement in the lifetime characteristics of the positive electrode active material may be negligible. If the average thickness of the coating layer is too thick, the coating layer will act as a resistive element, which may lead to excessive degradation of the capacity characteristics of the positive electrode active material.

[0041] Furthermore, the average thickness of the coating layer can be measured using the following methods. First, the coating layer thickness of a single positive electrode active material particle (a single particle) can be obtained by analyzing a cross-sectional TEM image of the positive electrode active material particle after FIB (Focused Ion Beam) milling, randomly selecting 10 locations on the surface of the positive electrode active material particle, and calculating the average coating layer thickness at the selected locations. Second, the average thickness of the coating layer can be obtained by measuring the coating layer thickness of any 20 positive electrode active material particles in the positive electrode active material powder using the same method as described above, and calculating their average value.

[0042] However, the inventors have confirmed that when a conformal coating layer is formed on a single-particle lithium metal oxide using an atomic layer deposition process, the improvement in lifetime characteristics brought about by the coating is not as expected. Furthermore, due to the full coating of the coating layer with lower electrochemical activity than the lithium metal oxide substrate, the capacity characteristics of the positive electrode active material are poor.

[0043] Therefore, the c-axis lattice constant of the lithium metal oxide according to the present invention is 14.14 to 14.22 Å, more specifically 14.14 to 14.215 Å, when analyzed by X-ray diffraction patterns. The c-axis lattice constant of the lithium metal oxide can refer to the width of the lithium ion migration range within the lithium metal oxide, and thus may have a significant impact on the electrochemical characteristics of the battery. According to the present invention, in addition to the aforementioned coating layer, as the c-axis lattice constant of the lithium metal oxide is further adjusted to the aforementioned range, capacity and lifetime characteristics can preferably be achieved.

[0044] On the other hand, for the c-axis lattice constant in the aforementioned range, as described below, it can be obtained by additional heat treatment within an appropriate temperature range after the coating process.

[0045] Furthermore, the c-axis lattice constant of lithium metal oxides can be estimated using peak broadening from XRD data, and can be quantitatively calculated using the Scherrer equation.

[0046] Furthermore, in the X-ray diffraction pattern analysis of lithium metal oxides according to the present invention, the ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane (I(003) / I(104)) can be from 1.44 to 1.6, more specifically from 1.44 to 1.5. In the X-ray diffraction pattern analysis of lithium metal oxides, the ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane (I(003) / I(104)) can be used as a measure of the so-called cation mixing ratio. In this case, a larger I(003) / I(104) peak intensity ratio indicates a smaller cation mixing ratio. Cation mixing refers to the phenomenon in lithium metal oxides having a layered crystal structure (i.e., a structure in which lithium layers and transition metal layers are alternately stacked) where transition metal cations in the transition metal layers are partially replaced by transition metal cations in the lithium layers. The proportion of transition metal cations replaced in the lithium layers is called the cation mixing ratio. In particular, nickel ions, with ionic radii similar to lithium ions, are typical transition metals that substitute into the lithium layer. In this case, if the cation mixing ratio of the lithium metal oxide is too high, the mobility of lithium ions within the lithium layer decreases, potentially leading to degradation of battery capacity and lifespan characteristics. Therefore, the lithium metal oxide according to the present invention, by ensuring that the I(003) / I(104) peak intensity ratio meets the aforementioned range, can more preferably achieve improved capacity and lifespan characteristics of the positive electrode active material.

[0047] On the other hand, for the I(003) / I(104) peak intensity ratio of lithium metal oxides in the range described below, it can be obtained by additional heat treatment within an appropriate temperature range after the coating process.

[0048] Furthermore, based on the total weight of the positive electrode active material, the aluminum content in the positive electrode active material can be from 500 to 1000 ppm, more specifically from 750 to 950 ppm. When the aluminum content in the positive electrode active material meets the aforementioned range, the average thickness of the coating layer can be appropriately obtained within the scope of this invention. Therefore, the capacity and lifespan of the positive electrode active material can be preferably achieved.

[0049] On the other hand, the aluminum content in the positive electrode active material can be measured by ICP (inductively coupled plasma optical analysis) composition analysis.

[0050] Furthermore, the aluminum compound present within the coating layer comprises Al2O3, which can be amorphous. This improves lithium-ion mobility, thereby allowing for more optimal capacity and output characteristics of the cathode active material. The amorphous nature of the aluminum compound can be confirmed by TEM (transmission electron microscopy) image analysis or X-ray diffraction pattern analysis of the cathode active material.

[0051] Furthermore, the residual lithium content of the positive electrode active material according to the present invention can be below 15,000 ppm. This suppresses gas generation and battery swelling caused by side reactions between residual lithium and the electrolyte, thereby improving battery safety. On the other hand, the residual lithium content within this range can be obtained through additional heat treatment after the coating process, as described below.

[0052] More specifically, the lithium metal oxide according to the present invention can be represented by the following chemical formula 1.

[0053] [Chemical Formula 1] Li a [Ni x Co y Mn z M w O2 In the chemical formula 1, 0.8≤a≤1.3, 0.8≤x<1, 0≤y≤0.2, 0≤z≤0.2, 0≤w≤0.2, and x+y+z+w=1, and M is Zr, Al, B, Y, Ti, Nb, W, V, Cr, Mo, Ta, Fe, Cu, Zn, Ga, Ge, Ru, Rh, Sn, Sb, Re, Ir, Pt, Pb, Bi, Na, K, Rb, Cs, Ca, Sr, Ba, Mg, Si, Sc or a combination thereof.

[0054] In the lithium metal oxide of Formula 1, lithium may contain a content corresponding to 'a' (i.e., 0.8 ≤ a ≤ 1.3). If 'a' is too small, the capacity may decrease; if 'a' is too large, the strength of the calcined positive electrode active material will increase, making it difficult to pulverize, and the gas production may increase due to the increase in lithium by-products. Considering the effect of lithium content control on improving the capacity characteristics of the positive electrode active material and the sintering balance during the preparation of the active material, the lithium content is more preferably 0.9 ≤ a ≤ 1.1.

[0055] In the lithium metal oxide of chemical formula 1, nickel can contain a content corresponding to x (i.e., 0.8 ≤ x < 1). When the nickel content meets the range, high battery capacity can be achieved.

[0056] In the lithium metal oxide of Formula 1, cobalt may be present in an amount corresponding to y (i.e., 0 ≤ y ≤ 0.2). If the cobalt content is too low, grain size growth may be hindered, and output characteristics may decrease. If the cobalt content is too high, preparation costs increase, and reversible capacity may decrease.

[0057] In the lithium metal oxide of Formula 1, manganese may be present in a content corresponding to z (i.e., 0 ≤ z ≤ 0.2). If the manganese content is too low, production costs may increase, and the stability of the active material may decrease. If the manganese content is too high, the battery capacity and output characteristics may be poor.

[0058] In the lithium metal oxide of Formula 1, the other dopant element M can have a content corresponding to w (i.e., 0 ≤ w1 ≤ 0.2). In this case, M can be Zr, Al, B, Y, Ti, Nb, W, V, Cr, Mo, Ta, Fe, Cu, Zn, Ga, Ge, Ru, Rh, Sn, Sb, Re, Ir, Pt, Pb, Bi, Na, K, Rb, Cs, Ca, Sr, Ba, Mg, Si, Sc, or combinations thereof. The content of other dopant elements can be appropriately selected as needed to achieve other doping effects.

[0059] 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 lithium metal oxide in the form of a single particle containing a nickel (Ni) layered crystal structure; a step of forming a coating layer containing an aluminum compound on the lithium metal oxide by atomic layer deposition; and a step of heat-treating the lithium metal oxide with the coating layer formed at a temperature of 370 to 530°C to form a positive electrode active material.

[0060] The preparation method of the positive electrode active material for a lithium secondary battery according to another embodiment of the present invention will be described in detail below.

[0061] First, prepare lithium metal oxides in single-particle form with a nickel (Ni) layered crystal structure.

[0062] More specifically, for the single-particle form of lithium metal oxide, after preparing the metal precursor, the metal precursor is mixed with lithium raw material and calcined, and then crushed to prepare the single-particle form of lithium metal oxide.

[0063] More specifically, the metal precursor may be a metal hydroxide.

[0064] 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.

[0065] There are no particular limitations on the nickel raw material used in the preparation of cathode active material precursors in this technical field. For example, the nickel raw material can be a nickel-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or hydroxyoxide, specifically 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 it is not limited to these.

[0066] There are no particular limitations on the cobalt raw material used in the preparation of precursors for positive electrode active materials 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] For the lithium raw material, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or hydroxyoxides can be used, as long as they are 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 combinations thereof, but is not limited to these.

[0075] Furthermore, the calcination can be carried out at a temperature of 750 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 poor electrochemical properties.

[0076] 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 form. If the calcination time is too long, over-calcination will result in crystal structure defects, which may lead to poor electrochemical properties.

[0077] Furthermore, the atmosphere during calcination is not particularly limited; for example, it can be carried out in an oxygen (O2) or air atmosphere.

[0078] The disintegration process can be carried out according to conventional disintegration processes in the art, such as using an air jet mill.

[0079] Next, the lithium metal oxide in single-particle form prepared according to the above series of methods can be washed with water. This reduces the residual lithium remaining on the surface of the lithium metal oxide after calcination.

[0080] Next, an aluminum compound-containing coating layer is formed on the lithium metal oxide using atomic layer deposition.

[0081] At this point, the atomic layer deposition can be performed once. If the number of cycles exceeds the specified range during atomic layer deposition, excessive coating will result in an excessively thick coating layer, which may lead to poor capacity characteristics of the positive electrode active material.

[0082] More specifically, one cycle of the atomic layer deposition may include: supplying an aluminum-containing gas to the lithium metal oxide, causing the aluminum-containing gas to be adsorbed onto the lithium metal oxide; and supplying a reactant to the lithium metal oxide with the adsorbed aluminum-containing gas and causing it to react.

[0083] At this point, based on the total weight of the lithium metal oxide, the supply amount of the aluminum-containing gas can be 0.1 to 2% by weight, more specifically 0.1 to 1% by weight or 0.1 to 0.5% by weight. When the supply amount of the aluminum-containing gas meets the above range, aluminum coating can be appropriately performed in each cycle, measured in atomic layer thickness. Thus, the average thickness of the coating layer can be appropriately achieved within the scope of this invention, and more preferably, the capacity and lifetime characteristics of the positive electrode active material can be achieved.

[0084] Furthermore, based on the total weight of the lithium metal oxide, the supply amount of the reactant can be 0.001 to 0.01% by weight, more specifically 0.001 to 0.005% by weight. When the supply amount of the reactant meets the above range, aluminum coating can be appropriately performed in each cycle, measured in atomic layer thickness. Thus, the average thickness of the coating layer can be appropriately achieved within the scope of the present invention, and more preferably, the capacity and lifetime characteristics of the positive electrode active material can be achieved.

[0085] The aluminum-containing gas may be, for example, trimethoxy aluminum (TMA).

[0086] The reactants may be, for example, water (H2O) or ozone (O3).

[0087] The atomic layer deposition can be performed at a temperature between 150 and 300°C. When the atomic layer deposition temperature falls within this range, the reaction between the aluminum-containing gas and the reactants proceeds smoothly, thereby easily forming an aluminum coating layer. Consequently, the average thickness of the coating layer can be appropriately achieved within the scope of this invention, and more preferably, the capacity and lifetime characteristics of the positive electrode active material can be realized.

[0088] The atomic layer deposition can be performed at a pressure of 1 to 10 Torr. When the atomic layer deposition pressure meets this range, the reaction between the aluminum-containing gas and the reactants proceeds smoothly, thereby easily forming an aluminum coating layer. Thus, the average thickness of the coating layer can be appropriately achieved within the scope of this invention, and more preferably, the capacity and lifetime characteristics of the positive electrode active material can be achieved.

[0089] Next, the lithium metal oxide with the coating layer is heat-treated at a temperature of 370 to 530°C to form a positive electrode active material.

[0090] At this point, the heat treatment can be performed at a temperature of 370 to 530°C, more specifically at a temperature of 380 to 520°C. By performing additional heat treatment within the temperature range following the atomic layer deposition coating process, the c-axis lattice constant of the lithium metal oxide and the ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane (I(003) / I(104)) can be appropriately achieved within the scope of this invention. Thus, the capacity and lifetime characteristics of the positive electrode active material can be preferably achieved. The inventors believe that this is because performing additional heat treatment within an appropriate temperature range allows for better regulation of the layered crystal structure of the lithium metal oxide. Furthermore, by performing additional heat treatment after the coating process, the residual lithium reduction effect of the positive electrode active material can be maximized.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] The positive electrode active material layer may contain a binder and / or a conductive agent together with the aforementioned positive electrode active material.

[0095] At this point, the adhesive serves to improve the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), PVDF-co-HFP, 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.

[0096] 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 in the constructed battery and has electronic conductivity. 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 metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. 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.

[0097] In addition to using the aforementioned positive electrode active material, the positive electrode can be prepared according to conventional positive electrode preparation methods.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] Another embodiment of the present invention provides a lithium secondary battery comprising the aforementioned lithium secondary battery positive electrode.

[0102] More specifically, the lithium secondary battery may include a positive electrode, a negative electrode, a separator, and an electrolyte.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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 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.

[0107] 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.

[0108] The adhesive and conductive agent may be the same as those previously described in the positive electrode.

[0109] 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 restriction, 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 as single-layer or multi-layer structures.

[0110] 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.

[0111] Specifically, the organic liquid electrolyte may contain an organic solvent and a lithium salt.

[0112] 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 double bonds, 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) with high ionic conductivity and high dielectric constant, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate), which 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.

[0113] For the lithium salt, any compound capable of providing lithium ions for use in lithium 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 falls within this range, the electrolyte has appropriate conductivity and viscosity, thus exhibiting excellent electrolyte performance, and lithium ions can migrate effectively.

[0114] 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.

[0115] 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).

[0116] 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.

[0117] 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 a power storage system.

[0118] 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.

[0119] Example 1 (1) Preparation of positive electrode active materials (Preparation of lithium metal oxide) A composition of LiNi was prepared. 0.88 Co 0.095 Mn 0.025 Lithium metal oxide in single-particle form of O2.

[0120] Subsequently, the lithium metal oxide was washed with distilled water.

[0121] The (coated) atomic layer deposition reactor employs a fluidized bed configuration and maintains low vacuum conditions to keep the reaction temperature at 150–300 °C and the chamber pressure at 1–10 Torr. Trimethylaluminum (TMA, Al(CH3)3) was used as the aluminum-containing gas, and water (H2O) was used as the reactant.

[0122] The prepared lithium metal oxide is placed in an atomic layer deposition reactor and injected with TMA along with N2 gas. This allows TMA to undergo chemisorption on the lithium metal oxide substrate until saturation. Then, H2O is injected to induce a chemical reaction, forming an aluminum-containing compound coating layer. Furthermore, based on the total weight of the lithium metal oxide, the amount of TMA added per cycle is 0.2% by weight. Based on the total weight of the lithium metal oxide, the amount of H2O added per cycle is 0.002% by weight.

[0123] This series of processes is called 1 cycle, and a total of 1 cycle is performed.

[0124] (Heat treatment) Subsequently, the lithium metal oxide coated with the coating layer was heat treated at a temperature of 400°C.

[0125] (2) Preparation of lithium secondary batteries For the slurry used in electrode preparation, the positive electrode active material, conductive agent (denka black), and binder (PVDF, KF1100) were mixed in a ratio of 96.5:1.5:2 wt%, and NMP (N-methyl-2-pyrrolidone) was added to adjust the viscosity, resulting in a solids content of approximately 30%. The prepared slurry was coated onto a 20 μm thick aluminum foil using a doctor blade, followed by drying and pressing. The electrode loading was 15.4 mg / cm³. 2 The compressed density (25℃, 20kN) is 3.6 g / cm³.3 .

[0126] 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, Honzo metal).

[0127] Example 2 In the heat treatment step, heat treatment was carried out at a temperature of 450°C. Otherwise, the positive electrode active material and the lithium secondary battery were prepared by the same implementation method as in Example 1.

[0128] Example 3 In the heat treatment step, heat treatment was carried out at a temperature of 500°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 1 Without performing coating and heat treatment steps, a positive electrode active material and a lithium secondary battery were prepared using the same implementation method as in Example 1.

[0130] Comparative Example 2 Without performing a heat treatment step, a positive electrode active material and a lithium secondary battery were prepared using the same implementation method as in Example 1.

[0131] Comparative Example 3 In the heat treatment step, heat treatment was carried out at a temperature of 250°C. Otherwise, the positive electrode active material and the lithium secondary battery were prepared by the same implementation method as in Example 1.

[0132] Comparative Example 4 In the heat treatment step, heat treatment was carried out at a temperature of 300°C. Otherwise, the positive electrode active material and the lithium secondary battery were prepared by the same implementation method as in Example 1.

[0133] Comparative Example 5 In the heat treatment step, heat treatment was carried out at a temperature of 350°C. Otherwise, the positive electrode active material and the lithium secondary battery were prepared by the same implementation method as in Example 1.

[0134] Comparative Example 6 In the heat treatment step, heat treatment was carried out at a temperature of 550°C. Otherwise, the positive electrode active material and the lithium secondary battery were prepared by the same implementation method as in Example 1.

[0135] Comparative Example 7 In the heat treatment step, heat treatment was carried out at a temperature of 600°C. Otherwise, the positive electrode active material and the lithium secondary battery were prepared by the same implementation method as in Example 1.

[0136] Comparative Example 8 In the heat treatment step, heat treatment was carried out at a temperature of 750°C. Otherwise, the positive electrode active material and the lithium secondary battery were prepared by the same implementation method as in Example 1.

[0137] Comparative Example 9 In the coating step, the atomic layer deposition cycle was performed twice, and no heat treatment step was performed. Otherwise, the positive electrode active material and the lithium secondary battery were prepared by the same implementation method as in Example 1.

[0138] Comparative Example 10 In the coating step, the atomic layer deposition cycle was performed twice, and in the heat treatment step, the heat treatment was performed at a temperature of 450°C. Otherwise, the positive electrode active material and the lithium secondary battery were prepared by the same implementation method as in Example 1.

[0139] Table 1 below is a table summarizing the process conditions of the embodiments and comparative examples.

[0140] [Table 1] Tables 2 and 3 below are tables summarizing the evaluation results of the physical properties of the positive electrode active materials and the electrochemical characteristics of lithium secondary batteries.

[0141] [Table 2] [Table 3] Experimental Example 1: Evaluation of SEM Images of Positive Electrode Active Materials SEM (scanning electron microscope) images of the positive electrode active material prepared according to Example 1 were observed and are shown below. Figure 1 middle.

[0142] Reference Figure 1 It can be confirmed that the positive electrode active material of Example 1 is in the form of a single particle, and no multiple spaced coated particles were observed on the particle surface. It can be confirmed that the coating layer is a conformal type that uniformly covers the entire surface of the particle.

[0143] Experiment Example 2: Evaluation of the physical properties of positive electrode active materials (1) Evaluation of the average thickness of the coating layer First, the coating thickness of a single positive electrode active material particle (a single particle) is determined by analyzing a cross-sectional TEM image of the particle after FIB (Focused Ion Beam) milling, randomly selecting 10 locations on the surface of the particle, and calculating the average coating thickness at these selected locations. Second, the average coating thickness is determined by measuring the coating thickness of any 20 positive electrode active material particles in the powder using the same method, and calculating their average value.

[0144] (2) Evaluation of the peak intensity ratio of I(003) / I(104) The intensity ratio of the I(003) / I(104) peaks was evaluated by X-ray diffraction pattern analysis.

[0145] (3) Evaluation of c-axis lattice constant The c-axis lattice constant was evaluated by X-ray diffraction pattern analysis and Rietveld refinement.

[0146] (4) Evaluate the Al content in the positive electrode active material The Al content in the positive electrode active material was evaluated by ICP (inductively coupled plasma optical analysis).

[0147] (5) Evaluate the residual lithium content 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 was separated from the extract using a filtration device. Subsequently, the residual lithium was evaluated by measuring the extract through neutralization titration using a Metrohm potentiometric titrator.

[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. To evaluate the initial capacity, a baseline capacity of 200 mAh / g was used, and the cells were charged at a constant current of 0.1C to 4.25V. Then, a constant voltage was applied 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 the same baseline capacity of 200 mAh / g until reaching 2.5V.

[0149] (2) Evaluation of high-temperature capacity retention (45℃, 30 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 at 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. Thirty charge-discharge cycles were performed under the conditions described above, and the capacity retention rate of the 30th cycle relative to the 1st cycle was calculated.

[0150] Referring to Tables 1 to 3, for Examples 1 to 3, where the various process conditions according to the present invention (such as atomic layer deposition coating process, heat treatment at an appropriate temperature after coating process, number of atomic layer deposition cycles, etc.) were appropriately controlled, it can be confirmed that various physical properties (such as average thickness of the coating layer, c-axis lattice constant of lithium metal oxide, I(003) / I(104) peak intensity ratio, etc.) were appropriately obtained within the scope of the present invention. Furthermore, compared to Comparative Example 1, which served as the lithium metal oxide substrate, it can be confirmed that residual lithium was reduced and lifetime characteristics were improved. Moreover, compared to Comparative Example 1, it can be confirmed that capacity characteristics were slightly reduced, but compared to other comparative examples, excellent capacity characteristics were exhibited.

[0151] On the other hand, Comparative Example 1, which is used as a lithium metal oxide substrate, can be confirmed to have poor lifetime characteristics and excessive residual lithium content.

[0152] For Comparative Example 2, which did not undergo a heat treatment process, it was confirmed that the c-axis lattice constant and I(003) / I(104) peak intensity ratio of the positive electrode active material exceeded the range of the present invention, and the residual lithium content was excessive. Furthermore, it was confirmed that the battery's capacity and lifespan characteristics were lower than those of the Examples.

[0153] For Comparative Examples 3 to 5, where a heat treatment process was performed but the heat treatment temperature was too low, it was confirmed that the c-axis lattice constant and I(003) / I(104) peak intensity ratio of the positive electrode active material exceeded the range of the present invention, and the residual lithium content was excessive. Furthermore, it was confirmed that the battery capacity and lifespan characteristics were lower than those of the Examples.

[0154] For Comparative Examples 6 to 8, although a heat treatment process was performed, the heat treatment temperature was too high. It was confirmed that the c-axis lattice parameters and, in some cases, the I(003) / I(104) peak intensity ratio exceeded the scope of the present invention. Furthermore, although the residual lithium content was good, it was confirmed that the battery capacity and lifespan characteristics were lower than those of the examples. On the other hand, for Comparative Examples 6 to 8, it was confirmed that when the heat treatment temperature was too high, the average thickness of the coating layer also became too thick, which also had an adverse effect on the positive electrode active material.

[0155] For Comparative Example 9, which did not undergo a heat treatment process, it was confirmed that the c-axis lattice constant and I(003) / I(104) peak intensity ratio of the positive electrode active material exceeded the scope of the present invention. Furthermore, it was confirmed that the battery capacity and lifespan characteristics were lower than those of the Examples.

[0156] For Comparative Example 10, which underwent heat treatment at an appropriate temperature but had only two atomic layer deposition cycles, it was confirmed that not only was the average thickness of the coating layer excessively thick, but the c-axis lattice constant and I(003) / I(104) peak intensity ratio of the positive electrode active material also exceeded the scope of the present invention. Furthermore, it was confirmed that the battery's capacity and lifespan characteristics were lower than those of the Examples.

[0157] 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.

[0158] 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 a lithium metal oxide in the form of single particles with a nickel-containing layered crystal structure and a coating layer containing an aluminum compound covering the entire surface of the lithium metal oxide. The lithium metal oxide exhibits a c-axis lattice constant of 14.14 to 14.22 Å in X-ray diffraction pattern analysis. The average thickness of the coating layer is 0.5 to 1.5 nm.

2. The lithium secondary battery positive electrode active material according to claim 1, wherein, When the lithium metal oxide is analyzed by X-ray diffraction, the ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane, I(003) / I(104), is 1.44 to 1.

6.

3. The lithium secondary battery positive electrode active material according to claim 1, wherein, Based on the total weight of the positive electrode active material, the aluminum content in the positive electrode active material is 500 to 1000 ppm.

4. The lithium secondary battery positive electrode active material according to claim 1, wherein, The aluminum compound contains Al2O3, which is amorphous.

5. The lithium secondary battery positive electrode active material according to claim 1, wherein, The residual lithium content is below 15,000 ppm.

6. The lithium secondary battery positive electrode active material according to claim 1, wherein, Based on the total molar number of metals other than lithium, the nickel content in the lithium metal oxide is above 80 mol%.

7. 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, 0.8≤x<1, 0≤y≤0.2, 0≤z≤0.2, 0≤w≤0.2, and x+y+z+w=1, and M is Zr, Al, B, Y, Ti, Nb, W, V, Cr, Mo, Ta, Fe, Cu, Zn, Ga, Ge, Ru, Rh, Sn, Sb, Re, Ir, Pt, Pb, Bi, Na, K, Rb, Cs, Ca, Sr, Ba, Mg, Si, Sc or a combination thereof.

8. A method for preparing a positive electrode active material for a lithium secondary battery, comprising: Steps for preparing lithium metal oxides with nickel-containing layered crystal structures in single-particle form; The steps of forming an aluminum compound-containing coating layer on the lithium metal oxide by atomic layer deposition; and The step of heat-treating the lithium metal oxide with the coating layer at a temperature of 370 to 530°C to form a positive electrode active material.

9. The method for preparing the positive electrode active material of a lithium secondary battery according to claim 8, wherein, The atomic layer deposition is performed in one cycle.

10. The method for preparing the positive electrode active material of a lithium secondary battery according to claim 9, wherein, One cycle of atomic layer deposition includes: The steps of supplying aluminum-containing gas to the lithium metal oxide, causing the aluminum-containing gas to be adsorbed onto the lithium metal oxide; and The steps of supplying reactants to lithium metal oxides that have adsorbed aluminum-containing gas and causing them to react.

11. The method for preparing the positive electrode active material of a lithium secondary battery according to claim 10, wherein, Based on the total weight of the lithium metal oxide, the supply of the aluminum-containing gas is 0.1 to 2% by weight.

12. The method for preparing the positive electrode active material of a lithium secondary battery according to claim 10, wherein, Based on the total weight of the lithium metal oxide, the amount of reactant supplied is 0.001 to 0.01 by weight.

13. The method for preparing the positive electrode active material of a lithium secondary battery according to claim 8, wherein, The atomic layer deposition is performed at temperatures ranging from 150 to 300°C.

14. The method for preparing the positive electrode active material of a lithium secondary battery according to claim 8, wherein, The atomic layer deposition was carried out under a pressure of 1 to 10 Torr.

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

16. A lithium secondary battery comprising the positive electrode of the lithium secondary battery as described in claim 15.

Images