Positive electrode active material for lithium secondary battery, method for preparing same, and lithium secondary battery comprising same

Abstract

The present embodiment relates to a positive electrode active material for a lithium secondary battery, comprising: an inner core of a layered lithium transition metal oxide containing 60 mol% or more of nickel (Ni) based on the total number of moles of transition metal; and a coating layer disposed on the inner core, comprising cobalt (Co), aluminum (Al), or a combination thereof, consisting of single particles, and the coating layer being of an island type.

Description

Technical Field

[0001] The present embodiment relates to a positive electrode active material for a lithium secondary battery, a method for preparing the same, and a lithium secondary battery including the positive electrode active material. More specifically, it relates to a positive electrode active material for a lithium secondary battery composed of single particles, a method for preparing the same, and a lithium secondary battery including the material. Background Art

[0002] Driven by the recent explosive growth in the demand for electric vehicles and the requirement for increased driving range, the development of secondary batteries that meet this demand and have high capacity and high energy density is actively underway globally.

[0003] In particular, to meet this requirement, a high-nickel NCM (nickel-cobalt-manganese) positive electrode material with a high nickel content needs to be used. However, increasing the nickel content results in a decrease in particle strength, the generation of microcracks during charge and discharge, and thus an increase in specific surface area, leading to side reactions with the electrolyte and an increase in gas generation. In addition, due to the unstable structure, unstable Ni 3+ will be reduced to stable Ni 2+ , further generating stable NiO and causing more cation mixing phenomena, making it still difficult to actually apply it as a positive electrode active material for electric vehicles or lithium-ion batteries for energy storage.

[0004] Therefore, the demand for single particles is increasing. By maximizing the size of primary particles, single particles break away from the existing polycrystalline structure in which primary particles aggregate to form secondary particles, and act as active materials in the form of single particles. Single-crystalline particles have a smaller specific surface area than poly-crystalline particles, which can suppress side reactions with the electrolyte and significantly reduce gas generation.

[0005] However, during the preparation of single particles, due to the presence of a resistive layer of nickel oxide on the surface, there are problems of increased initial resistance and degraded life characteristics. Summary of the Invention

[0006] Technical Problem

[0007] Therefore, an object of the present invention is to provide a single-particle positive electrode active material, a method for preparing the same, and a lithium secondary battery including the positive electrode active material, which can improve the capacity and output characteristics of the battery by reducing the initial resistance and improve the life characteristics.

[0008] Technical Solution

[0009] The positive electrode active material for a lithium secondary battery according to an embodiment includes a core of a layered lithium transition metal oxide containing 60 mol% or more of nickel (Ni) based on the total number of moles of transition metals; and a coating disposed on the core and containing cobalt (Co), aluminum (Al), or a combination thereof, which consists of single particles and is of an island type.

[0010] Based on the total number of moles of transition metals, the nickel content is 85 mol% or more.

[0011] The coating further contains lithium and is an oxide.

[0012] The coating has a shape in which convex or hemispherical coating materials are discontinuously distributed on the core.

[0013] The coating has a layered crystal structure.

[0014] The coating is connected to the core in a layered crystal structure.

[0015] The coating contains cobalt and aluminum, and the molar ratio of cobalt to aluminum (Co / Al) is 3 to 18.

[0016] Based on the total weight of the positive electrode active material for the lithium secondary battery, the content of the coating is 1 to 3 wt%.

[0017] The lithium transition metal oxide further contains zirconium (Zr), aluminum (Al), or a combination thereof.

[0018] The lithium transition metal oxide is represented by the following Chemical Formula 1:

[0019] [Chemical Formula 1]

[0020] Li a [Ni x Co y Mn z M1 w1 M2 w2 O2

[0021] In Chemical Formula 1, 0.8 ≤ a ≤ 1.2, 0.6 ≤ x ≤ 0.97, 0 ≤ y ≤ 0.2, 0 < z ≤ 0.2, 0 ≤ w1 ≤ 0.1, 0 ≤ w2 ≤ 0.1, M1 is Zr, Al, or a combination thereof, and M2 is Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

[0022] A method for preparing a positive electrode active material for a lithium secondary battery according to another embodiment includes: a step of preparing a nickel-containing transition metal hydroxide; a step of forming a mixture including the transition metal hydroxide and a lithium raw material, and then firing at a temperature of 710 to 930 °C to form a lithium transition metal oxide; and a step of mixing the lithium transition metal oxide with a coating raw material and then performing heat treatment at a temperature of 670 to 740 °C to form a coating, where the coating raw material includes a cobalt raw material, an aluminum raw material, or a combination thereof.

[0023] In the step of forming the lithium transition metal oxide, the mixture further includes a doping raw material, where the doping raw material includes a zirconium raw material, an aluminum raw material, or a combination thereof.

[0024] In the step of forming the coating, based on the total weight of the lithium transition metal oxide and the doping raw material, the content of the coating is 1 to 3 wt%.

[0025] The coating raw material is fine particles with an average particle size (D50) of 200 to 500 nm.

[0026] A positive electrode for a lithium secondary battery according to another embodiment includes a positive electrode active material layer of the positive electrode active material.

[0027] A lithium secondary battery according to another embodiment may include a positive electrode, a negative electrode, and an electrolyte disposed therebetween. The positive electrode includes the positive electrode active material for the lithium secondary battery.

[0028] Advantageous Effects of the Invention

[0029] In one embodiment of the present invention, the positive electrode active material for a lithium secondary battery is a single particle and includes a coating containing cobalt, aluminum, or a combination thereof; since the coating is of an island type, the initial resistance can be reduced, thereby improving the capacity and output characteristics of the battery and improving the life characteristics.

[0030] A method for preparing a positive electrode active material for a lithium secondary battery according to another embodiment of the present invention can easily prepare a single-particle positive electrode active material having an island-shaped coating by appropriately adjusting the sintering temperature when forming the lithium transition metal oxide and appropriately adjusting the heat treatment temperature when forming the coating. Description of the Drawings

[0031] Figure 1 A schematic diagram of a positive electrode active material for a lithium secondary battery provided by an embodiment of the present invention.

[0032] Figure 2 A schematic diagram of a positive electrode active material for a conventional lithium secondary battery.

[0033] Figure 3It is a SEM image of the surface of a single particle of the positive electrode active material prepared according to Example 1-1.

[0034] Figure 4 It is a SEM image of the surface of a single particle of the positive electrode active material prepared according to Comparative Example 1.

[0035] Figure 5 It is a FIB (Focused Ion Miling) image of the positive electrode active material prepared according to Example 1-1.

[0036] Figure 6 It is a FIB (Focused Ion Milling) image of the positive electrode active material prepared according to Comparative Example 1.

[0037] Figure 7 It is an image obtained by elemental mapping of the positive electrode active material prepared according to Example 1-1 after FIB (Focused Ion Milling).

[0038] Figure 8 It is a graph of the EDS line scan measurement results from the inside to the outside of the active material for Region 1 of the image of the positive electrode active material prepared according to Example 1-1 after FIB (Focused Ion Milling).

[0039] Figure 9 It is a graph of the EDS line scan measurement results from the inside to the outside of the active material for Region 2 of the image of the positive electrode active material prepared according to Example 1-1 after FIB (Focused Ion Milling).

[0040] Figure 10 It is a graph of the EDS line scan measurement results from the inside to the outside of the active material for Region 2 of the image of the positive electrode active material prepared according to Comparative Example 1 after FIB (Focused Ion Milling).

[0041] Figure 11 It is a graph of the EELS test results in the coating layer of the positive electrode active material prepared according to Example 1-1.

[0042] Figure 12 It is a graph of the EELS test results in the coating of the positive electrode active material prepared according to Example 1-1.

[0043] Figure 13 It is an SAED pattern analysis image of the core and coating regions of the positive electrode active material prepared according to Example 1-1. Detailed implementation mode

[0044] 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 part, component, region, layer, and / or segment. Therefore, without departing from the scope of the present invention, the first part, component, region, layer, and / or segment described below can also be described as the second part, component, region, layer, and / or segment.

[0045] The terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the present invention. Unless the context clearly dictates otherwise, the singular forms used are also intended to include the plural forms. It should also be understood that the term "comprising" used in the specification can specifically refer to a certain characteristic, region, integer, step, action, element, and / or component, but does not exclude the existence or addition of other characteristics, regions, integers, steps, actions, elements, and / or components.

[0046] If a part is described as being above another part, there may be other parts directly above or between the other parts. When a part is described as being directly above another part, there will be no other parts therebetween.

[0047] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention pertains. For terms defined in a dictionary, they should be interpreted as having a meaning consistent with the relevant technical literature and the content disclosed herein, and should not be interpreted in an idealized or overly formal sense.

[0048] In addition, unless otherwise specifically described, % represents % by weight, and 1 ppm represents 0.0001% by weight.

[0049] In this specification, "combinations thereof" described in a Markush-type expression means one or more mixtures or combinations selected from the group consisting of the constituent elements recited in the Markush-type expression, and means including one or more selected from the group consisting of the above-mentioned constituent elements.

[0050] Hereinafter, embodiments of the present invention will be described in detail so that one of ordinary skill in the art to which the present invention pertains can easily implement the present invention. However, the present invention can be implemented in various different ways and is not limited to the embodiments described herein.

[0051] 1. Positive electrode active material

[0052] According to an embodiment of the present invention, a positive electrode active material for a lithium secondary battery is provided, which includes a core of layered lithium transition metal oxide containing 60 mol% or more of nickel (Ni) based on the total mole number of transition metals; and a coating disposed on the core and containing cobalt (Co), aluminum (Al), or a combination thereof, which is composed of single particles, and the coating is of an island type.

[0053] Figure 1 Schematic diagram of the positive electrode active material for a lithium secondary battery provided by the embodiment of the present invention.

[0054] Referring to Figure 1 , according to an embodiment of the present invention, the positive electrode active material (100) for a lithium secondary battery is composed of a core (10) and a coating (20) disposed on the core.

[0055] According to an embodiment of the present invention, the positive electrode active material (100) for a lithium secondary battery is composed of single particles.

[0056] More specifically, according to whether the primary particles of a unit particle are assembled, the positive electrode active material can be divided into unassembled primary particles or secondary particle forms formed by the aggregation of multiple primary particles. Such a primary particle refers to the smallest particle unit that can be distinguished as a whole when observing the cross-section of the positive electrode active material through a scanning electron microscope (SEM), and it can be composed of one crystal grain or multiple crystal grains.

[0057] According to the present invention, since the positive electrode active material is composed of single particles, the problems caused by secondary particles can be solved: the large specific surface area leads to an increased risk of side reactions with the electrolyte, and during multiple charge and discharge processes, micro-cracks (cracks) will occur between the primary particles, resulting in a decrease in structural stability and deterioration of the life characteristics. In addition, the calendering density can be increased when preparing the electrode, thereby improving the energy density of the electrode.

[0058] However, due to the unstable Ni 3+ , Ni 4+ ions generate a nickel oxide resistance layer on the surface, resulting in an increase in the initial resistance and a decrease in the life characteristics.

[0059] To solve the above problems, in an embodiment of the present invention, the positive electrode active material for a lithium secondary battery includes a coating (20) containing cobalt, aluminum, or a combination thereof on the lithium transition metal oxide core.

[0060] Since the active material includes a coating containing cobalt, aluminum, or a combination thereof, the formation of a nickel oxide resistance layer can be inhibited, thereby reducing the initial resistance, improving the capacity and output characteristics of the battery, and enhancing the life characteristics. Moreover, during the coating formation process, the residual lithium in the lithium transition metal oxide can be reduced, thereby suppressing the degradation of battery performance caused by the residual lithium.

[0061] Figure 1 Schematic diagram of an island coating type positive electrode active material according to an embodiment of the present invention, Figure 2 Schematic diagram of a conformal coating type positive electrode active material.

[0062] In particular, the positive electrode active material coating according to the present invention is of the island type.

[0063] More specifically, the morphology of the positive electrode active material coating can be divided into a conformal coating that uniformly and continuously covers the surface of the positive electrode material and an island coating that covers in a discontinuous dot shape.

[0064] The optimal form of such a coating that can improve battery performance may vary depending on the coating material.

[0065] After multiple studies, the inventors found that when using a coating material containing cobalt, aluminum, or a combination thereof, the island coating method is more effective in improving battery performance. The reason is that when a coating material containing cobalt, aluminum, or a combination thereof forms a coating during heat treatment, a composite oxide material containing lithium and oxygen is generated; if this oxide material belongs to the type of conformal coating that covers the entire positive electrode material, the resistance characteristics of lithium during insertion and deinsertion into the core will increase. Therefore, by reducing the initial resistance of the battery, the battery capacity and output characteristics can be improved, and its life characteristics can be enhanced.

[0066] Specifically, the coating may further contain lithium and may be an oxide. More specifically, the coating may be a composite oxide containing lithium and cobalt, aluminum, or a combination thereof. This is due to the reaction between the residual lithium remaining on the surface during the formation of the lithium transition metal oxide and the coating raw materials during the preparation process.

[0067] More specifically, the coating may be formed by discontinuously distributing a plurality of protrusions or hemispherical coating materials on the core.

[0068] At this time, the size of each of the protrusions or hemispherical coating materials may be 50 to 400 nm. Since the size of each of the protrusions or hemispherical coating materials satisfies the above range, it has the advantage of forming an island random coating.

[0069] By observing the SEM (scanning electron microscope) or TEM (transmission electron microscope) images of the surface of the positive electrode active material, the distribution morphology and size of these coating materials can be confirmed.

[0070] In particular, the coating may have a layered crystal structure. That is, both the core and the coating of the positive electrode active material according to the present invention can have a layered crystal structure. Thus, different from the traditional coating that blocks the path of lithium ions transferring to the core through a general inorganic coating, the layered coating of the present invention has the advantage of serving as a channel for lithium ions to pass through. By performing SAED (Selected Area Electron Diffraction) pattern analysis on the active material, the layered structure of the coating can be confirmed.

[0071] At this time, the coating may be connected to the core in a layered crystal structure. Thus, the enhancement effect of lithium ion conductivity can be maximized. This can be confirmed by performing an EDS line scan on the boundary region between the core and the coating.

[0072] On the other hand, the coating may contain only cobalt, may contain only aluminum, or may contain both cobalt and aluminum. More specifically, when the coating contains both cobalt and aluminum, the improvement effect of battery performance can be more effectively achieved.

[0073] When the coating contains both cobalt and aluminum, the molar ratio of cobalt to aluminum (Co / Al) can be 3 to 18, more specifically 4 to 17. Thus, the improvement effect of battery performance can be more effectively achieved.

[0074] Based on the total weight of the positive electrode active material for the lithium secondary battery, the content of the coating can be 1 to 3% by weight, more specifically 1.2 to 2.8% by weight. When the coating content is too low, the reduction of the initial resistance and the improvement effects of capacity, output, and life characteristics brought by the coating may be negligible; while when the coating content is too high, the proportion of the core material will be too small, resulting in a decrease in battery capacity.

[0075] On the other hand, the core contains a layered lithium transition metal oxide. At this time, the content of nickel is 60 mol% or more based on the total molar number of transition metals, and more specifically can reach 85 mol% or more. The higher the content of nickel, the higher the capacity can be achieved, but due to the cation mixing phenomenon, there is a problem of reduced structural stability. At this time, since the positive electrode active material according to the present invention is composed of single particles as described above and includes a coating containing cobalt, aluminum, or a combination thereof, it can achieve high nickel content as described above while ensuring battery stability.

[0076] The lithium transition metal oxide may further contain zirconium (Zr), aluminum (Al), or a combination thereof as a doping element. By including zirconium, aluminum, or a combination thereof as a doping element, the structural stability of the active material can be enhanced, thereby further maximizing the life characteristics of the battery.

[0077] More specifically, since Zr ions occupy the Li site, Zr acts as a pillar, alleviating the contraction of the lithium ion path during charge and discharge, thereby stabilizing the layered structure. This phenomenon means that cation mixing can be reduced and the lithium diffusion coefficient can be increased, thereby extending the cycle life.

[0078] In addition, Al ions move to the tetragonal lattice site, thereby suppressing the degradation of the layered structure into a spinel structure that is not smooth enough for lithium ion migration.

[0079] As a doping element, only Zr may be included, only Al may be included, or both Zr and Al may be included. Preferably, when both Zr and Al are included as doping elements, the improvement effect of the battery life characteristics can be maximized.

[0080] Based on the total molar amount of the transition metal, the content of Zr may be 0.1 to 1 mol%, more specifically, 0.16 to 0.64 mol%.

[0081] Based on the total molar amount of the transition metal, the content of Al may be 0.1 to 4 mol%, more specifically, 0.4 to 2.8 mol%.

[0082] The lithium transition metal oxide may be more specifically represented by the following Chemical Formula 1.

[0083] [Chemical Formula 1]

[0084] Li a [Ni x Co y Mn z M1 w1 M2 w2 O2

[0085] In the chemical formula 1, 0.8 ≤ a ≤ 1.2, 0.6 ≤ x ≤ 0.97, 0 ≤ y ≤ 0.2, 0 < z ≤ 0.2, 0 ≤ w1 ≤ 0.1, 0 ≤ w2 ≤ 0.1, M1 is Zr, Al or a combination thereof, and M2 is Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr or a combination thereof.

[0086] In the lithium transition metal oxide of the chemical formula 1, lithium corresponding to the content of a can be included, that is, 0.8 ≤ a ≤ 1.2. When a is too small, it may lead to a decrease in capacity; when a is too large, the strength of the positive electrode active material after firing increases, making pulverization difficult, and at the same time, due to an increase in lithium by-products, the gas generation amount also increases. Considering the improvement effect of lithium content control on the capacity characteristics of the positive electrode active material and the firing balance during the preparation of the active material, it is more preferable to include lithium with a content of 0.9 ≤ a ≤ 1.1.

[0087] In the lithium transition metal oxide of the chemical formula 1, nickel corresponding to the content of x can be included, that is, 0.6 ≤ x ≤ 0.97 or 0.85 ≤ x ≤ 0.97. If the nickel content is too low, it is difficult to achieve a large capacity of the battery; if the nickel content is too high, the battery life and safety will be reduced due to the decrease in the structural stability of the active material.

[0088] In the lithium transition metal oxide of the chemical formula 1, cobalt corresponding to the content of y can be included, that is, 0 ≤ y ≤ 0.2. If the cobalt content is too low, it is difficult to achieve both sufficient rate characteristics and a high powder density of the active material. If the cobalt content is too high, the overall raw material cost will increase, and the reversible capacity will decrease.

[0089] In the lithium transition metal oxide of the chemical formula 1, manganese corresponding to the content of z can be included, that is, 0 < z ≤ 0.2. If the manganese content is too low, it may lead to an increase in production cost and a decrease in the stability of the active material. If the manganese content is too high, the capacity and output characteristics of the battery may decrease.

[0090] In the lithium transition metal oxide of the chemical formula 1, M1 corresponding to the content of w1 can be included, that is, 0 ≤ w1 ≤ 0.1. M1 is a doping element of Zr, Al or a combination thereof.

[0091] In the lithium transition metal oxide of the chemical formula 1, M2 corresponding to the content of w2 can be included, that is, 0 ≤ w2 ≤ 0.1. M2 is other doping elements, which are Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr or a combination thereof.

[0092] 2. Preparation method of the positive electrode active material

[0093] The present inventors have conducted numerous studies on a simple preparation method for the positive electrode active material having a "island-like" coating for the single particles, and found that controlling the heat treatment temperature during the formation of the coating is crucial, thereby perfecting the preparation method of the active material.

[0094] Another embodiment of the present invention provides a method for preparing a positive electrode active material for a lithium secondary battery. The method includes the steps of preparing a nickel-containing transition metal hydroxide; forming a mixture including the transition metal hydroxide and a lithium raw material, and then firing the mixture at a temperature of 710 to 930 °C to form a lithium transition metal oxide; and mixing the lithium transition metal oxide with a coating raw material, and then performing heat treatment on the mixture at a temperature of 670 to 740 °C to form a coating, where the coating raw material includes a cobalt raw material, an aluminum raw material, or a combination thereof.

[0095] 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 step by step below.

[0096] First, prepare a nickel-containing transition metal hydroxide.

[0097] The transition metal hydroxide is a precursor of the positive electrode active material.

[0098] At this time, doping elements can be doped in the preparation stage of the positive electrode active material precursor.

[0099] For example, the precursor can be prepared by adding an aqueous ammonia solution and a caustic soda solution to a transition metal-containing solution including a nickel raw material, a manganese raw material, and an optional doping raw material including Zr, Al, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof to perform a coprecipitation reaction.

[0100] The nickel raw material is not particularly limited when used in the field for preparing the positive electrode active material precursor. For example, the nickel raw material can be nickel-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, oxyhydroxide, etc. Specifically, it can be NiSO4, NiSO4·6H2O, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, fatty acid nickel salt, nickel halide, or a combination thereof, but is not limited thereto.

[0101] There are no special restrictions on the manganese raw material when it is used in the art to prepare the precursor of the positive electrode active material. For example, the manganese raw material can be manganese-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, oxyhydroxide 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 fatty acid salt, manganese oxides such as Mn2O3, MnO2, Mn3O4, oxyhydroxides, manganese chloride or a combination thereof, but not limited thereto.

[0102] The ammonia solution can be used as a complexing agent, such as NH3, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3 or a combination thereof, but not limited thereto. On the other hand, the ammonia solution can also be used in the form of an aqueous solution. In this case, the solvent used can be water, or a mixture of water and an organic solvent (specifically, alcohols, etc.) that can be uniformly mixed with water.

[0103] The caustic soda solution can be used as a precipitant or a pH regulator, and can contain alkaline compounds such as hydroxides of alkali metals or alkaline earth metals such as NaOH, KOH or Ca(OH)2, their hydrates or a combination thereof. The caustic soda solution can also be used as an aqueous solution. In this case, water, or a mixture of water and an organic solvent (such as alcohols) that can be uniformly mixed with water can be used as the solvent.

[0104] The coprecipitation reaction can be carried out in an inert atmosphere such as nitrogen or argon.

[0105] In the coprecipitation reaction, the temperature in the reactor can be in the range of 30 to 70 °C, specifically it can be in the range of 40 to 60 °C, and more specifically it can be in the range of 45 to 55 °C.

[0106] Nickel-manganese (-doped element) hydroxide particles are generated through the above process and precipitated in the reaction solution. After the precipitated precursor particles are separated and dried according to a conventional method, a precursor can be obtained. The precursor can be secondary particles formed by aggregation of primary particles.

[0107] By adjusting the concentrations of the nickel-containing raw material and the manganese-containing raw material, a precursor with a nickel (Ni) content of 60 mol% or more or 85 mol% or more in the total metal content can be prepared. In other words, based on the total molar number of the transition metals in the transition metal hydroxide, the nickel content can be 60 mol% or 85 mol% or more, thereby realizing the large capacity of the battery.

[0108] Next, after forming a mixture containing the transition metal hydroxide and the lithium raw material, firing is carried out at a temperature of 710 to 930 °C to form a lithium transition metal oxide.

[0109] At this time, the mixture may further include a doping raw material, which may include a zirconium raw material, an aluminum raw material, or a combination thereof.

[0110] Moreover, the doping raw material may further include other doping raw materials including Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

[0111] Specifically, the firing temperature is 710 to 930 °C, more specifically 720 to 920 °C. If the firing temperature is too low, it is difficult to form the positive electrode active material in a single particle form, and the growth of the particle size may also be insufficient; if the firing temperature is too high, the structural stability of the positive electrode active material will decrease, resulting in a reduction in performance such as the reversible capacity.

[0112] The firing time can be carried out between 2 and 36 hours, more specifically, it can be carried out between 20 and 30 hours. If the firing time is too short, the synthesis reaction may not proceed sufficiently or the crystal structure may not develop sufficiently; if the firing time is too long, the production efficiency may decrease.

[0113] The firing can be carried out in an oxygen atmosphere. When firing a high-concentration (Ni-rich) positive electrode active material with a high Ni content at a high temperature for a long time, due to the cation mixing phenomenon caused by Ni occupancy in the lithium layer of the layered crystal structure during the firing process, in order to prevent this phenomenon, it is preferably to synthesize the positive electrode active material in an oxygen atmosphere. 2+ occupancy, so in order to prevent this phenomenon, it is preferred to synthesize the positive electrode active material in an oxygen atmosphere.

[0114] The firing can be divided into a first firing and a second firing as needed.

[0115] Next, after mixing the lithium transition metal oxide with the coating raw material, heat treatment is carried out at a temperature of 670 to 740 °C to form a coating.

[0116] The coating raw material includes a cobalt raw material, an aluminum raw material, or a combination thereof.

[0117] The coating raw material may further include a lithium raw material.

[0118] The cobalt raw material may be any cobalt-containing substance without particular limitation, and Co(OH)2 is preferably used.

[0119] The aluminum raw material may be any aluminum-containing substance without particular limitation, and Al(OH)3 is preferably used.

[0120] The lithium raw material may be any lithium-containing substance without particular limitation, and LiOH·H2O is preferably used.

[0121] In particular, when forming the coating, the heat treatment temperature can be between 670 and 740°C, more specifically, between 680 and 730°C. If the heat treatment temperature is too low, it may be difficult to smoothly form the coating. If the heat treatment temperature is too high, a full-surface (conformal) coating may be formed instead of an island coating, or the coating raw materials Co or Al may diffuse excessively into the interior of the positive electrode material instead of the surface, resulting in the coating having little effect on improving battery performance.

[0122] The coating material content can be 1 to 3 weight percent, more specifically 1.2 to 2.8 weight percent, based on the total weight of the lithium transition metal oxide and the coating material. If the coating material content is too low, the coating layer content is also too low, resulting in a less pronounced effect of reducing initial resistance and improving lifespan characteristics. If the coating material content is too high, the coating layer content may be insufficient for the core content, ultimately leading to a decrease in battery capacity.

[0123] More specifically, the content of the cobalt raw material is 1 to 2 wt % based on the total weight of the lithium transition metal oxide and the coating raw material.

[0124] Furthermore, the content of the aluminum raw material is 0.2 to 0.8 wt % based on the total weight of the lithium transition metal oxide and the coating raw material.

[0125] Alternatively, the coating material may be microparticles having an average particle size (D50) of 200 to 500 nm. If the microparticle size is too small, agglomeration may occur during dry mixing of the coating materials, resulting in uneven coating. If the microparticle size is too large, the coating particles may become too large, leading to increased resistance.

[0126] 3. Positive electrode and lithium secondary battery

[0127] Another embodiment of the present invention provides a positive electrode including the positive electrode active material for a lithium secondary battery.

[0128] Specifically, the positive electrode includes a positive electrode current collector, and a positive electrode active material layer including the positive electrode active material is disposed on the positive electrode current collector.

[0129] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. can be used. In addition, the thickness of the positive electrode current collector is generally 3 to 500 μm, and fine concave and convex surfaces can be formed on the positive electrode current collector to enhance the adhesion of the positive electrode active material. For example, the positive electrode current collector can take various forms, such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabrics, and the like.

[0130] The positive electrode active material layer may further include the above positive electrode active material, a binder, and / or a conductive material.

[0131] At this time, the binder serves to enhance 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), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, sodium carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM rubber), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc. One of them can be used alone or two or more can be used in combination, but not limited thereto. The binder may account for 1 to 30% by weight of the total weight of the positive electrode active material layer.

[0132] In addition, the conductive material is used to impart conductivity to the electrode. In the assembled battery, as long as it has electronic conductivity and does not cause chemical changes, it can be used without special restrictions. Specific examples include graphite such as natural graphite or artificial graphite; carbon materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, summer black, carbon fiber, etc.; metal powders or metal fibers such as copper, nickel, aluminum, silver, etc.; conductive whiskers such as zinc oxide, potassium titanate, etc.; conductive metal oxides such as titanium oxide, etc.; or conductive polymers such as polystyrene derivatives, etc. One of these materials can be used alone or two or more can be used in combination, but not limited thereto. The conductive material is usually included in an amount of 1 to 30% by weight of the total weight of the positive electrode active material layer.

[0133] When using the positive electrode active material, the positive electrode can be prepared according to a conventional positive electrode preparation method.

[0134] Specifically, the positive electrode is prepared by coating a composition for forming a positive electrode active material layer, which includes the positive electrode active material and, optionally, a binder, a conductive material, or a solvent as needed, on the positive electrode current collector, and then drying and rolling. At this time, the types and contents of the positive electrode active material, the binder, and the conductive material are as described above.

[0135] The solvent can be a solvent commonly used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or water. These solvents can be used alone or in combination of two or more. The amount of the solvent used should take into account the coating thickness and preparation yield of the slurry to dissolve or disperse the positive electrode active material, conductive agent and binder, and to achieve the viscosity required for excellent thickness uniformity of the coating used for subsequent positive electrode preparation.

[0136] In addition, another method is to cast the composition for preparing the positive electrode active material layer on an independent support, and then peel it from the support to obtain a thin film, and laminate it onto a positive electrode current collector to prepare a positive electrode.

[0137] Another embodiment of the present invention includes a positive electrode including the positive electrode active material, thereby providing a lithium secondary battery.

[0138] The lithium secondary battery specifically includes a positive electrode, a negative electrode opposite to the positive electrode, a separator placed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is as described above.

[0139] In addition, the lithium secondary battery may further optionally include a battery container for accommodating an electrode assembly including a positive electrode, a negative electrode, and a separator, and a sealing member for sealing the battery container.

[0140] In the lithium secondary battery, the negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0141] The negative electrode current collector is not particularly limited to a specific material; it only requires that it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or aluminum-cadmium alloys can be used. Furthermore, the negative electrode current collector typically has a thickness of 3 to 500 μm. Similar to the positive electrode current collector, microscopic irregularities can be formed on the current collector surface to enhance the binding force of the negative electrode active material. For example, various forms such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabrics can be used.

[0142] The negative electrode active material layer may optionally include a negative electrode active material, a binder, and a conductive agent. As an example, the negative electrode active material layer may be prepared by coating a composition for forming a negative electrode active material layer, including a negative electrode active material and optionally a binder and a conductive agent, on a negative electrode current collector and drying the coating, or by casting the negative electrode active material layer on a separate support, peeling the resulting film from the support, and laminating the film on the negative electrode current collector.

[0143] As the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as synthetic graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides capable of lithium insertion and extraction such as SiO β (0 < β < 2), SnO2, vanadium oxides, lithium vanadium oxides, etc.; or composites including the above metal compounds and carbonaceous materials such as Si-C composites or Sn-C composites. Any single material or a mixture of two or more of these can be used. In addition, as the negative electrode active material, a thin film of metallic lithium can also be used. In addition, as the carbon material, low-crystalline carbon and high-crystalline carbon can be used. As the low-crystalline carbon, soft carbon and hard carbon are representative; as the high-crystalline carbon, it includes amorphous, flaky, needle-shaped, spherical, or fibrous natural graphite or synthetic graphite, Kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature fired carbons such as petroleum or coal tar pitch-derived cokes.

[0144] The binder and the conductive agent can be the same as those described in the foregoing positive electrode description.

[0145] In addition, in a lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a channel for the movement of lithium ions. If it is a separator commonly used in lithium secondary batteries, it can be used without any special restrictions. Particularly preferred is a separator with low resistance to the movement of electrolyte ions and excellent electrolyte moisturizing ability. Specifically, a porous polymer film can be used, such as a porous polymer film made of polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof. Also, a conventional porous non-woven fabric can be used, such as a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. In addition, a coated separator containing a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and a single-layer or multi-layer structure can be adopted as needed.

[0146] In addition, in the lithium secondary battery, as the electrolyte, an organic solvent electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc., which can be used in the preparation of the lithium secondary battery, can be used, and the present invention is not limited thereto.

[0147] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0148] The organic solvent can be used without special limitation as long as it can serve as a medium for ions to migrate in the battery electrochemical reaction. Specifically, the following substances can be used as the organic solvent. Ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone, etc.; ether solvents such as dibutyl ether or tetrahydrofuran, etc.; ketone solvents such as cyclohexanone, etc.; aromatic hydrocarbon solvents such as benzene, fluorobenzene, etc.; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), etc.; alcohol solvents such as ethanol, isopropanol, etc.; nitriles such as R-CN (where R is a straight-chain, branched-chain or cyclic hydrocarbon group having 2 to C 20 and may contain a double bond, an aromatic ring or an ether bond), etc.; amides such as dimethylformamide, etc.; dioxolane such as 1,3-dioxolane, etc.; or sulfolane, etc. Among them, carbonate solvents are preferred, and more preferably a mixture of a cyclic carbonate (such as ethylene carbonate or propylene carbonate, etc.) having a high ionic conductivity and a high dielectric constant and capable of improving the charge and discharge performance of the battery and a low-viscosity chain carbonate compound (such as methylethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.). In this case, by mixing the cyclic carbonate and the chain carbonate in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte can be excellent.

[0149] Regarding the lithium salt, any compound that can provide lithium ions for use in a lithium secondary battery can be used without particular limitation. Specifically, the lithium salts include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably used in the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance, and lithium ions can migrate effectively.

[0150] In the electrolyte, in addition to the components of the electrolyte, for the purposes of improving the life characteristics of the battery, suppressing the reduction of the battery capacity, and increasing the battery discharge capacity, etc., one or more additives such as halogenated alkyl carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphate, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidinones, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride may be further included. In addition, the additives may be included in a proportion of 0.1 to 5% by weight based on the total weight of the electrolyte.

[0151] As described above, since the lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, it is useful for portable devices such as mobile phones, laptop computers, and digital cameras, as well as for electric vehicle fields such as hybrid electric vehicles (HEV).

[0152] Therefore, according to another embodiment of the present invention, there is also provided a battery module using the lithium secondary battery as a single cell, and a battery pack including the battery module.

[0153] The battery module or battery pack can be used as a power tool; an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power supply for any one or more medium and large-sized devices in a power storage system.

[0154] Hereinafter, the implementation example of the present invention will be described in more detail through the examples. However, the following example is only a preferred embodiment of the present invention, and the present invention is not limited thereto.

[0155] Example 1-1

[0156] (1) Preparation of positive electrode active material

[0157] (Preparation of Precursor)

[0158] The precursor is prepared into spherical transition metal hydroxide particles by co-precipitation. As synthetic raw materials, NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O are dissolved in deionized water, and NH4(OH) is added as a co-precipitation chelating agent, and NaOH is used for pH adjustment. To prevent oxidation of Ni during the co-precipitation process, N2 is introduced and the reaction temperature is maintained at 50°C. The prepared precursor is filtered (filtering), washed with deionized water (DI water), and dried in an oven at 100°C for 24 hours. The average particle size (D50) of the obtained metal hydroxide precursor is about 3 to 5um. The metal composition of the precursor is (Ni 0.88 Co 0.07 Mn 0.05 )(OH)2.

[0159] (Preparation of Lithium Transition Metal Oxides)

[0160] Afterwards, the prepared precursor was uniformly mixed with LiOH·H2O as a lithium source in a stoichiometric ratio so that the Li / Me ratio was slightly greater than 1. At this time, in order to improve the structural stability and prolong the service life, 0.003 mol of Zr and 0.01 mol of Al were added and fired at 890°C for 24 hours to synthesize LiNi 0.87 Co 0.07 Mn 0.05 Al 0.01 A single-particle positive electrode active material of a lithium transition metal oxide composed of O2. In this case, the amount of Zr added is extremely small, so it is not listed in the composition.

[0161] (forming a coating)

[0162] Subsequently, the prepared lithium transition metal oxide is dry-mixed with Co(OH)2 as the cobalt raw material, Al(OH)3 as the aluminum raw material, and LiOH·H2O as the lithium raw material. At this time, the content of Co(OH)2 is mixed to 1.5 wt% based on the total weight of the lithium transition metal oxide, cobalt raw material, aluminum raw material, and lithium raw material. At the same time, the content of Al(OH)3 is mixed to 0.5 wt% based on the total weight of the lithium transition metal oxide, cobalt raw material, aluminum raw material, and lithium raw material. The content of LiOH·H2O is mixed to 0.1 wt% based on the total weight of the lithium transition metal oxide, cobalt raw material, aluminum raw material, and lithium raw material. At this time, both Co(OH)2 and Al2O3 are in the form of microparticles with a size of 200 to 500 nm. Subsequently, heat treatment is carried out at 710 °C to form a coating, thereby preparing the positive electrode active material. At this time, the Co / Al molar ratio of the formed coating is 4, and the content of the coating is 1.5 wt% relative to the positive electrode active material.

[0163] (2) Preparation of Lithium Secondary Battery

[0164] Mix the prepared positive electrode active material, conductive agent (carbon black), and binder (PVDF, KF1120) in a weight ratio of 96.5:1.5:2 to make a slurry for manufacturing an electrode plate, and add N-methyl-2-pyrrolidone (NMP) to adjust the viscosity of the slurry to maintain the solid content at about 30%. Coat the slurry on an aluminum foil (Al foil, thickness: 15 μm) as the positive electrode current collector with a doctor blade, dry and calender it to prepare the positive electrode. The loading amount of the positive electrode is about 14.6 mg / cm 2 , and the calendered density (25 °C, 20 kN) is 3.7 g / cm 3 .

[0165] The electrolyte used is 1 M LiPF6 (EC:DMC:EMC = 3:4:3 (volume%)). A coin-type half-cell is prepared using a polypropylene separator and a lithium metal negative electrode (300 μm, MTI), and then aged at room temperature for 10 hours.

[0166] Example 1-2

[0167] The same lithium transition metal oxide as in Example 1-1 was used, with only the coating manufacturing conditions being different. The content of Co(OH)2 was mixed to 1.8 wt% based on the total weight of the lithium transition metal oxide, cobalt raw material, aluminum raw material, and lithium raw material. At the same time, the content of Al(OH)3 was mixed to 0.05 wt% based on the total weight of the lithium transition metal oxide, cobalt raw material, aluminum raw material, and lithium raw material. The content of LiOH·H2O was mixed to 0.1 wt% based on the total weight of the lithium transition metal oxide, cobalt raw material, aluminum raw material, and lithium raw material. At this time, both Co(OH)2 and Al2O3 were prepared as microparticles with a size of 200 to 500 nm. Subsequently, a heat treatment was performed at 710°C to form a coating, thereby preparing a positive electrode active material. At this time, the Co / Al molar ratio of the formed coating was 17, and the content of the coating was 2.0 wt% relative to the positive electrode active material.

[0168] Example 2

[0169] In addition to the precursor composition of Ni 0.92 Co 0.05 Mn 0.03 (OH)2, and when preparing lithium transition metal oxide, the firing temperature is set to 770 ° C to form a LiNi 0.91 Co 0.05 Mn 0.03 Al 0.01 A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1-1, except for the lithium transition metal oxide having an O2 composition (the Zr doping amount was extremely small and was not described in the composition).

[0170] Example 3

[0171] In addition to the precursor composition of Ni 0.96 Co 0.03 Mn 0.01 (OH)2, and when preparing lithium transition metal oxide, the firing temperature is set to 750 ° C to form a LiNi 0.95 Co 0.03 Mn 0.01 Al 0.01 A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1-1, except for the lithium transition metal oxide having an O2 composition (the Zr doping amount was extremely small and was not described in the composition).

[0172] Example 4

[0173] In addition to the precursor composition of Ni 0.98 Co 0.01 Mn 0.01(OH)2, and when preparing lithium transition metal oxide, the firing temperature is set to 730 ° C to form a LiNi 0.97 Co 0.01 Mn 0.01 Al 0.01 A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1-1, except for the lithium transition metal oxide having an O2 composition (the Zr doping amount was extremely small and was not described in the composition).

[0174] Example 5

[0175] In addition to the precursor composition of Ni 0.86 Co 0.09 Mn 0.05 (OH)2, and when preparing lithium transition metal oxide, the firing temperature is set to 910 ° C to form a LiNi 0.85 Co 0.09 Mn 0.05 Al 0.01 A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1-1, except for the lithium transition metal oxide having an O2 composition (the Zr doping amount was extremely small and was not described in the composition).

[0176] Comparative Example 1

[0177] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1-1, except that the heat treatment temperature was set to 760° C. when forming the coating layer.

[0178] Comparative Example 2

[0179] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 2, except that the heat treatment temperature was set to 760° C. when forming the coating layer.

[0180] Comparative Example 3

[0181] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 3, except that the heat treatment temperature was set to 760° C. when forming the coating layer.

[0182] Comparative Example 4

[0183] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 4, except that the heat treatment temperature was set to 760° C. when forming the coating layer.

[0184] Comparative Example 5

[0185] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 5, except that the heat treatment temperature was set to 760° C. when forming the coating layer.

[0186] Reference Example 1

[0187] Except as follows, a positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1-1. When forming the coating, no aluminum raw material was added, and the content of Co(OH)2 was mixed to 1.5% by weight based on the total weight of the lithium transition metal oxide, cobalt raw material, and lithium raw material. The content of LiOH·H2O was mixed to 0.07% by weight based on the total weight of the lithium transition metal oxide, cobalt raw material, and lithium raw material.

[0188] Reference Example 2

[0189] Except as follows, a positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1-1. When forming the coating, no cobalt raw material was added, and the content of Al(OH)3 was mixed to 1.5% by weight based on the total weight of the lithium transition metal oxide, aluminum raw material, and lithium raw material. The content of LiOH·H2O was mixed to 0.07% by weight based on the total weight of the lithium transition metal oxide, cobalt raw material, aluminum raw material, and lithium raw material.

[0190] Reference Example 3

[0191] Except as follows, a positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1-1. When forming the coating, by adjusting the weight ratio of the contents of Co(OH)2, Al(OH)3, and LiOH·H2O, the molar ratio of Co / Al in the coating was made 2.

[0192] Reference Example 4

[0193] Except as follows, a positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1-1. When forming the coating, by adjusting the weight ratio of the contents of Co(OH)2, Al(OH)3, and LiOH·H2O, the molar ratio of Co / Al in the coating was made 1.

[0194] Reference Example 5

[0195] Except as follows, a positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1-1. When forming the coating, the weight ratio of the contents of Co(OH)2, Al(OH)3, and LiOH·H2O was kept unchanged, but the content of each coating raw material was reduced so that the content of the formed coating was 0.8% by weight relative to the positive electrode active material.

[0196] Reference Example 6

[0197] The positive electrode active material and the lithium secondary battery were prepared in the same manner as in Example 1-1, except as follows. When forming the coating, the weight ratio of the content of Co(OH)2, the content of Al(OH)3, and the content of LiOH·H2O remained unchanged, but the content of each coating raw material was increased so that the content of the formed coating was 3.2% by weight based on the positive electrode active material.

[0198] Table 1 below summarizes the positive electrode active materials and process conditions of Examples 1-1 to 5, Comparative Examples 1 to 5, and Reference Examples 1 to 6.

[0199]

Table 1

[0200]

[0201] Experimental Example 1: SEM Image Analysis of Active Material

[0202] SEM (scanning electron microscope) images of the positive electrode active materials manufactured according to Example 1-1 and Comparative Example 1 were taken, and the results are as shown in Figure 3 (Example 1-1) and Figure 4 (Comparative Example 1).

[0203] Referring to Figure 3 and Figure 4 , in Example 1-1, it was confirmed that coating materials in the form of protrusions or hemispheres with sizes of 100 to 300 nm discontinuously existed on the surface of the lithium transition metal oxide. Thus, an island-like coating was formed.

[0204] On the contrary, in the case of Comparative Example 1, the coating formed a very smooth front coating in the form of spreading on the surface.

[0205] Experimental Example 2: Image Analysis after FIB (Focused Ion Milling) of Active Material

[0206] Images were taken after FIB (focused ion milling) of the positive electrode active materials prepared according to Example 1-1 and Comparative Example 1, and the results are as shown in Figure 5 (Example 1-1) and Figure 6 (Comparative Example 1).

[0207] Referring to Figure 5 and Figure 6 , in the case of Example 1-1, it was confirmed that the coating particles discontinuously existed on the surface of the lithium transition metal oxide substrate.

[0208] On the contrary, in the case of Comparative Example 1, it was confirmed that the coating particles continuously and uniformly coated the surface.

[0209] Experimental Example 3: Image Element Mapping Analysis after FIB (Focused Ion Milling) of Active Material

[0210] The elements mapping was performed on the image of the positive electrode active material prepared according to Example 1-1 after FIB (focused ion milling). The results are as follows: Figure 7 shown.

[0211] like Figure 7 As shown in the figure, it can be confirmed that the doping elements nickel, manganese and zirconium are distributed throughout the structure of the lithium transition metal oxide. At the same time, it can be confirmed that the coating elements cobalt and aluminum are mainly present on the surface of the lithium transition metal oxide.

[0212] Experimental Example 4: EDS Line Scan Analysis of Images After FIB (Focused Ion Milling) of Active Materials

[0213] According to Example 1-1, after FIB (focused ion milling) of the positive electrode active material, EDS line scan was measured from the inside to the outside of area 1 in the image. The results are as follows: Figure 8 After FIB (focused ion milling) of the positive electrode active material, EDS line scan was measured from the inside to the outside of area 2, and the results were as follows: Figure 9 In addition, after FIB (focused ion milling) was performed on the positive electrode active material prepared according to Comparative Example 1, EDS line scan was measured from the inside to the outside of area 1 in the image, and the results were as follows: Figure 10 shown.

[0214] refer to Figure 8 and Figure 9 In the case of Example 1-1, it can be confirmed that cobalt and aluminum exist in both region 1 and region 2, which is consistent with Figure 7 The elemental distribution analysis images are consistent with those of the . Furthermore, it can be confirmed that the concentration gradients of cobalt and aluminum persist, confirming that the layered crystal structures of the coating and core are well connected and that there is no distortion of the crystal structure.

[0215] On the other hand, refer to Figure 10 It can be confirmed that, unlike Example 1-1, the cobalt content in Comparative Example 1 is low, and almost no aluminum is detected. This can be explained by the fact that during the coating heat treatment at high temperature, cobalt and aluminum diffuse into the positive electrode material, resulting in a reduction in the coating effect.

[0216] Experimental Example 5: ELLS Analysis of Active Material Coating

[0217] The coating of the positive electrode active material prepared according to Example 1-1 was subjected to ELLS (electron energy loss spectroscopy) analysis, and the results were as follows: Figure 11 shown.

[0218] refer to Figure 11, the presence of lithium in the coating was confirmed. It can be seen from this that the coating has a composition of lithium cobalt aluminum composite oxide, which is formed by the reaction of the remaining lithium during the formation of lithium transition metal oxide with the coated raw materials cobalt and aluminum.

[0219] Experimental Example 6: TEM Image Analysis of the Cross-Section of the Active Material

[0220] TEM (transmission electron microscope) image analysis was performed on the cross-section of the positive electrode active material manufactured according to Example 1-1, and the results are as Figure 12 shown.

[0221] Reference Figure 12 , it was confirmed that the positive electrode active material of Example 1-1 has a lithium transition metal oxide core and a formed island-like coating.

[0222] Experimental Example 7: SAED Pattern Analysis of the Inner Core and Coating of the Active Material

[0223] SAED (selected area electron diffraction) pattern analysis was performed on the positive electrode active material prepared according to Example 1-1, and the results are as Figure 13 shown. Figure 13 (a) shows the results of SAED pattern analysis of the inner core region, Figure 13 (b) shows the results of SAED pattern analysis of the coating region.

[0224] Reference Figure 13 , it was confirmed that the positive electrode active material of Example 1-1 has a good layered structure both in the inner core and the coating. It can be seen from this that the coating has a layered structure composed of lithium, cobalt, and aluminum composite oxide.

[0225] Experimental Example 8: Evaluation of the Electrochemical Characteristics of Lithium Secondary Batteries

[0226] The electrochemical characteristics of the lithium secondary batteries prepared according to Examples 1-1 to 5, Comparative Examples 1 to 5, and Reference Examples 1 to 4 were evaluated, and the results are shown in Table 2 below. The specific experimental method is as follows.

[0227] (1) Evaluation of the Initial Discharge Capacity and Initial Efficiency

[0228] The capacity evaluation was based on a reference capacity of 200 mAh / g, and the charge-discharge conditions were CC / CV from 2.5 V to 4.25 V, with a 1 / 20C cut-off. The initial capacity was measured by charging at 0.1C / discharging at 0.1C.

[0229] (2) Evaluation of the Initial Resistance (25 °C)

[0230] The room temperature resistance (DC-iR) was calculated by applying a discharge current after fully charging at 4.25 V under the condition of 25 °C and measuring the voltage after 60 seconds.

[0231] (3) High-temperature (45°C) and room-temperature (25°C) life characteristic evaluation (50 cycles)

[0232] The high-temperature life characteristics were measured 50 times under the conditions of charging at 0.3C and discharging at 0.3C at 45°C.

[0233] The room-temperature life characteristics were measured 50 times at 25°C under the conditions of charging at 0.3C and discharging at 0.3C.

[0234] (4) High-temperature resistance increase rate evaluation

[0235] The high-temperature resistance growth rate is evaluated by taking the resistance value initially measured at 45°C as the reference, measuring the resistance after 50 cycles of life using the same method as the initial resistance measurement, and then converting its growth rate into a percentage (%).

[0236] (5) Differential Scanning Calorimetry (DSC) thermal analysis evaluation

[0237] For DSC analysis, after charging the prepared coin cell to 4.25V under the initial 0.1C charging condition, the cell was disassembled and the positive electrode was taken out separately. After washing it 5 times with DMC, it was prepared. When performing DSC measurement, the electrolyte and the electrode sheet were placed together in the DSC crucible for impregnation, and then the measurement was carried out during the heating process. The DSC equipment used was the DSC1 star system of Mettler toledo company.

[0238] (6) Output characteristic evaluation (2C / 0.1C)

[0239] The evaluation method of the output characteristics is to divide the capacity at 2C by the capacity at 0.1C and convert it into a percentage (%).

[0240]

Table 2

[0241]

[0242] Referring to Table 2, the battery capacities, initial efficiencies, initial resistances, high-temperature and room-temperature life characteristics, high-temperature resistance increase rates, DSC peak temperature characteristics, and output characteristics of Examples 1-1 to 5 are all significantly superior to those of Comparative Examples 1 to 5, which only differ in the heat treatment temperature during the coating formation process. This can be explained by the fact that the coatings of Examples 1-1 to 5 are island-shaped, while the coatings of Comparative Examples 1 to 5 are conformal, and cobalt and aluminum diffuse excessively into the active material, thereby reducing the coating effect. In addition, the cobalt addition amount in Example 1-2 is increased compared with that in Example 1-1, while the aluminum content is decreased. However, the excellent conductivity and life characteristic improvement effect of cobalt elements can compensate for the characteristic deterioration caused by the insufficient aluminum content, especially the deterioration of life characteristics.

[0243] Meanwhile, in Reference Example 1, it has been confirmed that the high-temperature and room-temperature life characteristics, high-temperature resistance increase rate, and DSC peak temperature characteristics are all lower than those of Example 1-1. In addition, in Reference Example 2, it has been confirmed that the battery capacity, initial efficiency, initial resistance, high-temperature and room-temperature life characteristics, high-temperature resistance increase rate, DSC peak temperature characteristics, and output characteristics are all lower than those of Example 1-1. It can be seen from this that the coating elements preferably include two heterogeneous elements, Co and Al, rather than a single Co or Al element.

[0244] Meanwhile, for Reference Examples 3 and 4, it is confirmed that the battery capacity, initial efficiency, initial resistance, high-temperature and room-temperature life characteristics, high-temperature resistance increase rate, and output characteristics (except for the DSC peak temperature characteristic) are all lower than those of Example 1-1. It is thus confirmed that when the Co / Al molar ratio of the coating is too small, the battery performance is poor.

[0245] Meanwhile, the high-temperature and room-temperature life characteristics, high-temperature resistance increase rate, DSC peak temperature characteristics, and output characteristics of Reference Example 5 are all lower than those of Example 1-1; the battery capacity, initial efficiency, initial resistance, high-temperature resistance increase rate, DSC peak temperature characteristics, and output characteristics of Reference Example 6 are all lower than those of Example 1-1. It can be seen from this that too little or too much coating content will lead to a decline in battery performance.

[0246] Although the 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 patent claims, the detailed description of the invention, and the drawings, and these modifications also fall within the scope of the present invention.

[0247] Therefore, the substantial scope of the present invention is defined by the appended claims and their equivalents.

[0248] [Symbol Description]

[0249] 100: Positive active material 10: Core

[0250] 20: Coating

Claims

1. A positive electrode active material for a lithium secondary battery, the positive electrode active material for a lithium secondary battery comprising: A core of a layered lithium transition metal oxide containing 60 mol% or more of nickel (Ni) based on the total mole number of transition metals; And a coating disposed on the core and containing cobalt (Co), aluminum (Al), or a combination thereof, Composed of single particles, and the coating is of an island type.

2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein Based on the total mole number of transition metals, the nickel content is 85 mol% or more.

3. The positive electrode active material for a lithium secondary battery according to claim 1, wherein The coating further contains lithium and is an oxide.

4. The positive electrode active material for a lithium secondary battery according to claim 1, wherein The coating is in a shape in which coating materials in a convex or hemispherical shape are discontinuously distributed on the core.

5. The positive electrode active material for a lithium secondary battery according to claim 1, wherein The coating has a layered crystal structure.

6. The positive electrode active material for a lithium secondary battery according to claim 1, wherein The coating is connected to the core in a layered crystal structure.

7. The positive electrode active material for a lithium secondary battery according to claim 1, wherein The coating contains cobalt and aluminum, and the molar ratio of cobalt to aluminum (Co / Al) is 3 to 18.

8. The positive electrode active material for a lithium secondary battery according to claim 1, wherein Based on the total weight of the positive electrode active material for a lithium secondary battery, the content of the coating is 1 to 3 wt%.

9. The positive electrode active material for a lithium secondary battery according to claim 1, wherein The lithium transition metal oxide further contains zirconium (Zr), aluminum (Al), or a combination thereof.

10. The positive electrode active material for a lithium secondary battery according to claim 1, wherein The lithium transition metal oxide is represented by the following Chemical Formula 1: [Chemical Formula 1] Li a [Ni x Co y Mn z M1 w1 M2 w2 O2 In Chemical Formula 1, 0.8 ≤ a ≤ 1.2, 0.6 ≤ x ≤ 0.97, 0 ≤ y ≤ 0.2, 0 < z ≤ 0.2, 0 ≤ w1 ≤ 0.1, 0 ≤ w2 ≤ 0.1, M1 is Zr, Al, or a combination thereof, and M2 is Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

11. A method for preparing a positive electrode active material for a lithium secondary battery, the preparation method comprising: A step of preparing a nickel-containing transition metal hydroxide; A step of forming a mixture containing the transition metal hydroxide and a lithium raw material, and then firing at a temperature of 710 to 930 °C to form a lithium transition metal oxide; and A step of mixing the lithium transition metal oxide with a coating raw material and then performing heat treatment at a temperature of 670 to 740 °C to form a coating, The coating raw material includes a cobalt raw material, an aluminum raw material, or a combination thereof.

12. The method for preparing a positive electrode active material for a lithium secondary battery according to claim 11, wherein In the step of forming the lithium transition metal oxide, The mixture further comprises a doping raw material, The doping raw material includes a zirconium raw material, an aluminum raw material or a combination thereof.

13. The method for preparing a positive electrode active material for a lithium secondary battery according to claim 11, wherein, in the step of forming the coating, based on the total weight of the lithium transition metal oxide and the coating raw material, the content of the coating raw material is 1 to 3% by weight.

14. The method for preparing a positive electrode active material for a lithium secondary battery according to claim 11, wherein, the coating raw material is fine particles with an average particle size (D50) of 200 to 500 nm.

15. A positive electrode, which comprises the positive electrode active material according to any one of claims 1 to 10.

16. A lithium secondary battery, which comprises: a positive electrode, which comprises the positive electrode active material according to any one of claims 1 to 10.

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