A cathode active material, method of preparing the same, lithium secondary battery comprising the cathode active material

Abstract

The present invention relates to a positive electrode active material comprising: lithium transition metal oxide particles; and coating particles present on the surface of the lithium transition metal oxide particles and comprising tungsten (W) and cobalt (Co) elements, wherein the coating particles comprise a first coating region adjacent to the surface of the lithium transition metal oxide particles and a second coating region present on the first coating region, wherein the first coating region has an elemental ratio of tungsten higher than that of cobalt and the second coating region has an elemental ratio of cobalt higher than that of tungsten, a method for manufacturing the same, and a secondary battery comprising the same.

Description

Technology Field

[0001] This invention relates to a positive electrode active material used in the positive electrode of a lithium secondary battery and a method for manufacturing the same. Background Technology

[0002] Since lithium-ion batteries were commercialized by Sony in 1991, demand has surged across various fields, ranging from small home appliances such as mobile IT products to medium-to-large electric vehicles and energy storage systems. In particular, low-cost, high-energy cathode materials are essential for medium-to-large electric vehicles and energy storage systems, but cobalt, the main raw material for single-crystal LiCoO2 (LCO), a currently commercialized cathode active material, is expensive.

[0003] Therefore, recently, LiNi, in which a portion of Co is substituted with another transition metal, has been used as a cathode active material for medium and large-sized secondary batteries instead of LCO. x Co y Mn z O2(NCM, x+y+z=1) and LiNi x Co y Al zNi-based cathode active materials represented as O2(NCA, x+y+z=1) are used, and these NCM and NCA-based cathode active materials have the advantages of low nickel cost as a raw material and high reversible capacity. In particular, NCM and NCA with a Ni molar ratio of 50 mol% or more are attracting attention in terms of high capacity. Generally, these Ni-based cathode active materials are manufactured by mixing a transition metal compound precursor synthesized by the co-precipitation method with a lithium source and then synthesizing it in a solid state. However, the Ni-based cathode materials synthesized in this way exist in the form of secondary particles consisting of aggregated small primary particles, which presents a problem in that micro-cracks occur within the secondary particles during long-term charge / discharge processes. Micro-cracks induce adverse reactions between the new interface of the cathode active material and the electrolyte, resulting in battery performance degradation such as reduced stability due to gas generation and decreased battery performance caused by electrolyte depletion. Furthermore, achieving high energy density requires an increase in electrode density (>3.3 g / cc), but this induces the decay of secondary particles, leading to electrolyte depletion caused by adverse reactions with the electrolyte and a sharp decline in initial lifespan. Ultimately, this implies that Ni-based cathode active materials in the form of secondary particles synthesized by the conventional co-precipitation method cannot achieve high energy density.

[0004] To address the problems of the aforementioned secondary particle-type Ni-based cathode active materials, research on single-particle Ni-based cathode active materials has recently been conducted. Single-crystal Ni-based cathode active materials can achieve excellent electrochemical performance because particle decay does not occur when electrode density is increased (> 3.3 g / cc) to realize high energy density. However, during electrochemical evaluation, unstable Ni 3+ , Ni 4+ It has been raised that battery stability is degraded due to structural and / or thermal instability caused by ions.

[0005] Accordingly, there is still a demand for cathode active materials for the development of lithium-ion batteries with high energy density and long lifespan characteristics. The problem to be solved

[0006] The present invention is intended to provide a positive electrode active material for ensuring high energy density and long lifespan. means of solving the problem

[0007] According to one aspect, lithium transition metal oxide particles; and

[0008] It comprises a coating layer including coating particles present on the surface of the lithium transition metal oxide particles and containing tungsten (W) and cobalt (Co) elements, and

[0009] The coating layer comprises a first coating region adjacent to the surface of the lithium transition metal oxide particle and a second coating region existing on the first coating region, and

[0010] A positive electrode active material is provided in which the first coating region has an elemental ratio of tungsten higher than the elemental ratio of cobalt, and the second coating region has an elemental ratio of cobalt higher than the elemental ratio of tungsten.

[0011] According to another aspect, a step of providing lithium transition metal oxide particles;

[0012] A step of obtaining a first solid mixture by solid-state mixing the above lithium transition metal oxide particles and a tungsten (W)-containing precursor compound;

[0013] A step of obtaining a second solid mixture by solid-mixing the first solid mixture and a cobalt (Co)-containing precursor compound; and

[0014] A method for manufacturing an anode active material is provided, comprising the step of obtaining the aforementioned anode active material by secondarily calcining the above-mentioned second solid mixture.

[0015] According to another aspect, a cathode comprising the aforementioned cathode active material;

[0016] cathode; and

[0017] Electrolytes;

[0018] A lithium secondary battery including is provided. Effects of the invention

[0019] According to one aspect, the cathode active material comprises a coating layer comprising coating particles containing tungsten and cobalt elements on the surface of nickel-based lithium transition metal oxide particles, wherein the coating layer comprises a first coating region adjacent to the surface of the lithium transition metal oxide particles and a second coating region existing on the first coating region, and wherein the first coating region has a higher elemental ratio of tungsten than of cobalt, so that there is no particle breakage even at high electrode density, and by effectively stabilizing Ni ions, it has the effect of increasing capacity per unit volume, high power output, and increased lifespan stability. Brief explanation of the drawing

[0020] FIGS. 1a to 1f are SEM images of each of the positive electrode active materials of Examples 1 to 6 according to one embodiment of the present invention. Figures 2a to 2h are SEM images of the cathode active materials of Comparative Examples 1 to 8, respectively. Figure 3 is the result of HR-TEM analysis showing the ratio of Ni, Co, and W elements from the surface of the cathode active material of Comparative Example 3 toward the center of the particle. Figure 4 is the HR-TEM analysis result showing the ratio of Ni, Co, and W elements from the surface of the cathode active material of Comparative Example 4 toward the center of the particle. Figure 5 is the result of HR-TEM analysis showing the ratio of Ni, Co, and W elements from the surface of the cathode active material of Comparative Example 5 toward the center of the particle. Figure 6 is the result of HR-TEM analysis showing the ratio of Ni, Co, and W elements from the surface of the cathode active material of Example 1 toward the center of the particle. FIG. 7 is a schematic diagram of a lithium battery according to an exemplary embodiment. <Explanation of symbols for major parts of the drawing> 1: Lithium battery 2: Cathode 3: Positive electrode 4: Separator 5: Battery case 6: Cap Assembly Specific details for implementing the invention

[0021] The present inventive concept described below is subject to various modifications and may have various embodiments, and specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present inventive concept to specific embodiments and should be understood to include all modifications, equivalents, or substitutions that fall within the scope of the description of the present inventive concept.

[0022] The terms used below are used merely to describe specific embodiments and are not intended to limit the creative idea.

[0023] A singular expression includes a plural expression unless the context clearly indicates otherwise. In the following, terms such as "comprising" or "having" are intended to indicate the existence of the features, numbers, steps, actions, components, parts, components, materials, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, components, materials, or combinations thereof.

[0024] The " / " used below may be interpreted as "and" or "or" depending on the context.

[0025] As used below, "concentration gradient" should be understood to refer to the linear or non-linear change in the concentration of atoms or compounds.

[0026] In the drawings, thicknesses have been enlarged or reduced to clearly represent various layers and regions. Throughout the specification, the same reference numerals have been used for similar parts. Throughout the specification, when a part such as a layer, film, region, or plate is described as being "on" or "above" another part, this includes not only cases where it is directly above another part but also cases where there is another part in between. Throughout the specification, terms such as "first," "second," etc., may be used to describe various components, but the components should not be limited by these terms. The terms are used solely for the purpose of distinguishing one component from another.

[0027] Unless otherwise defined, all terms used in this specification (including technical and scientific terms) have the same meaning as generally understood by those skilled in the art to which this disclosure pertains. Furthermore, it will also be understood that terms as defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning within the context of the relevant technology and the content of this disclosure, and should not be interpreted in an idealized or overly formal sense.

[0028] Although specific embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are not currently anticipated or cannot be anticipated may arise to the applicant or those skilled in the art. Accordingly, the appended claims, which may be filed and modified, are intended to include all such alternatives, modifications, variations, improvements, and substantial equivalents.

[0029] A cathode active material according to exemplary embodiments, a method for manufacturing the same, and a lithium secondary battery including a cathode containing the same will be described in more detail below.

[0030] A positive electrode active material according to one aspect comprises: lithium transition metal oxide particles; and a coating layer comprising coating particles present on the surface of the lithium transition metal oxide particles and including tungsten (W) and cobalt (Co) elements, wherein the coating layer comprises a first coating region adjacent to the surface of the lithium transition metal oxide particles and a second coating region present on the first coating region, wherein the elemental ratio of tungsten in the first coating region is higher than the elemental ratio of cobalt, and the elemental ratio of cobalt in the second coating region may be higher than the elemental ratio of tungsten.

[0031] By including coating particles containing cobalt and tungsten elements on the surface of the cathode active material, the crystal of the cathode active material containing lithium transition metal oxide particles is stabilized, and in particular, structural stability is obtained through the stabilization of unstable Ni in high-nickel cathode active materials in which the molar ratio of nickel is 90% or more.

[0032] Furthermore, by including cobalt and tungsten, and by including a first coating region in which the tungsten concentration is higher than the cobalt concentration and a second coating region in which the cobalt concentration is higher than the tungsten concentration, side reactions caused by rapid crystal distortion or the leaching of unstable Ni elements within the crystal during the charging and discharging process can be effectively suppressed, and the lifespan characteristics are improved compared to cases where the cobalt coating layer and the tungsten coating layer are separate or a mixed single coating layer is present.

[0033] According to one embodiment, the coating layer may further include a tungsten coating region between the first coating region and the surface of the lithium transition metal oxide particle, and may further include a cobalt coating region on the second coating region.

[0034] Here, the term "tungsten coating region" means a region within a coating layer containing tungsten and cobalt where cobalt is not substantially distributed, and the term "cobalt coating region" means a region within a coating layer containing tungsten and cobalt where tungsten is not substantially distributed.

[0035] According to one embodiment, the first coating region may have a concentration gradient in which the proportion of cobalt elements increases from the surface of the lithium transition metal oxide particles toward the second coating region.

[0036] For example, the concentration gradient of the first coating region may increase in the direction away from the surface of the lithium transition metal oxide particles, such that the concentrations of cobalt and tungsten elements increase.

[0037] According to one embodiment, the second coating region may have a concentration gradient in which the ratio of the tungsten element decreases in a direction away from the surface of the lithium transition metal oxide particle.

[0038] For example, the concentration gradient of the second coating region may increase the concentration of the cobalt element and decrease the concentration of the tungsten element in a direction away from the surface of the lithium transition metal oxide particle.

[0039] According to one embodiment, the coating particles may further contain Ni element. For example, the concentration of the Ni element contained within the coating particles may have a concentration gradient that decreases in a direction away from the surface of the lithium transition metal oxide particles.

[0040] According to one embodiment, the coating particles are provided on the surface of the lithium transition metal oxide and can become integral with the lithium transition metal oxide during the sintering process. For example, Ni elements contained in the lithium transition metal oxide can diffuse into the interior of the coating particles during the sintering process.

[0041] According to one embodiment, the coating particles may have a diameter of less than 700 nm. For example, the coating particles may have a diameter of 600 nm or less, 500 nm or less, 400 nm or less, 300 nm or less, or 200 nm or less. If the coating particles have a diameter of 700 nm or more, they may act as a resistance layer for lithium ion movement during the charging and discharging process, which may degrade the rate characteristics.

[0042] According to one embodiment, the surface of the lithium transition metal oxide particles may further include tungsten oxide, lithium tungsten oxide, or a combination thereof.

[0043] According to one embodiment, the tungsten may be included in an amount of 1,000 ppm to 8,000 ppm relative to the weight of the lithium transition metal oxide particles. For example, the tungsten may be included in an amount of 1,500 ppm to 8,000 ppm, 2,000 ppm to 8,000 ppm, or 2,500 ppm to 7,500 ppm.

[0044] When the tungsten content satisfies the above range, the leakage of unstable Ni ions to the outside is sufficiently prevented, and capacity loss due to Ni ion side reactions can be suppressed.

[0045] According to one embodiment, the lithium transition metal oxide particles may have a Ni content of 60 mol% or more.

[0046] For example, the lithium transition metal oxide particles may have a Ni content of 65 mol% or more, 70 mol% or more, 75 mol% or more, 80 mol% or more, 85 mol% or more, 91 mol% or more, 92 mol% or more, 93 mol% or more, 94 mol% or more, or 95 mol% or more.

[0047] As the Ni content in the above lithium transition metal oxide particles increases, the amount of unstable Ni ions generated increases. These unstable Ni ions are lost through side reactions with the electrolyte, causing a decrease in capacity. Furthermore, the loss of Ni ions within the crystal leads to crystal deformation and the formation of inactive phases, which degrades lifespan characteristics. Therefore, it is essential to stabilize unstable Ni ions in high-nickel cathode active materials of 90 mol% or more. An cathode active material according to one embodiment of the present invention includes coating particles containing W and Co on the surface of lithium transition metal oxide particles. By forming the aforementioned characteristic concentration gradient within the coating particles, not only is capacity loss low even in high-nickel cathode active materials, but crystal stabilization is also achieved, thereby improving lifespan characteristics.

[0048] According to one embodiment, the lithium transition metal oxide particles may be single crystals. Here, a single crystal means containing a single crystal within the particle. Since single-crystal particles can prevent particle breakage even at high electrode densities, they are advantageous for realizing high energy density of the cathode active material.

[0049] According to one embodiment, the cathode active material may be a single particle. A single particle is a concept distinct from an aggregate (i.e., a secondary particle) formed by the aggregation of multiple particles.

[0050] According to one embodiment, the lithium nickel-based transition metal oxide particles may be secondary particles formed by the aggregation of a plurality of single particles. The secondary particles formed by the aggregation of a plurality of single particles may be in the form of two or more single-crystal single particles aggregated. In this case, the proportion of secondary particles contained in the cathode active material may be less than 30% of the total lithium nickel-based transition metal oxide particles. For example, the proportion of secondary particles contained in the cathode active material may be 29% or less, 28% or less, 27% or less, 26% or less, or 25% or less with respect to the total lithium nickel-based oxide particles.

[0051] According to one embodiment, the cathode active material is a single crystal and a single particle. By being formed as a single crystal and a single particle, it is possible to realize a structurally stable and high-density electrode, so that a lithium secondary battery including the same can simultaneously have improved lifespan characteristics and high energy density.

[0052] According to one embodiment, the average particle size (D) of the positive electrode active material 50 ) may be 0.1㎛ to 20㎛. Here, the average particle size (D 50 ) refers to the particle size of the particles that account for 50% of the smallest particles in the particle size distribution analysis (PSD). For example, the above average particle size (D 50 The particle size may be 0.5㎛ to 20㎛, 1㎛ to 20㎛, 2㎛ to 19㎛, 3㎛ to 18㎛, 4㎛ to 17㎛, 5㎛ to 16㎛, 6㎛ to 15㎛, 7㎛ to 14㎛, 8㎛ to 13㎛, or 9㎛ to 12㎛. When the average particle size of the cathode active material falls within the above range, the desired energy density per volume can be achieved. If the average particle size of the cathode active material exceeds 20㎛, it leads to a rapid decrease in charge / discharge capacity, and if it is 1㎛ or less, it is difficult to obtain the desired energy density per volume.

[0053] According to one embodiment, some of the lithium (Li) elements in the crystals of the lithium transition metal oxide particles may be replaced with sodium (Na) elements, and some of the oxygen (O) elements may be replaced with sulfur (S) elements.

[0054] As some of the lithium atoms are substituted with sodium atoms, crystal collapse is suppressed even when lithium is defused from the crystal structure during the charging process. Additionally, the introduction of sodium atoms increases the crystal volume, thereby increasing lithium mobility and improving output characteristics. Furthermore, as some of the oxygen atoms are substituted with sulfur (S) atoms, the bonding force between the transition metal and the sulfur atom increases. Consequently, the transition of the lithium nickel-based oxide crystal structure is suppressed during the charging and discharging process of the lithium secondary battery, thereby improving the structural stability of the lithium nickel-based oxide crystal. As a result, lifespan characteristics can be improved.

[0055] According to one embodiment, the positive active material can be represented by the following chemical formula 1.

[0056] <Chemical Formula 1>

[0057] Li 1-a Na a Ni 1-α M α O 2-b S b

[0058] In the above chemical formula 1, M comprises Co and W, and further comprises Ti, Mg, Y, Sr, Ba, Ce, Bi, Zr, B, Mn, Al, or any combination thereof, and

[0059] The above Co and W originate from coating particles present on the surface of the lithium transition metal oxide particles, and

[0060] 0 <a≤0.01, 0<α≤0.05, 0<b≤0.01이다.

[0061] According to one embodiment, the positive active material can be represented by the following chemical formula 2.

[0062] <Chemical Formula 2>

[0063] Li 1-a Na a Ni 1-β-γ-δ Co β W γ M1 δ O 2-b S b

[0064] In the above chemical formula 2,

[0065] The above M1 includes Al, Mn, Ti, Mg, Y, Sr, Ba, Ce, Bi, Zr, B, or any combination thereof, and

[0066] The above Co and W originate from coating particles present on the surface of the lithium transition metal oxide particles, and

[0067] 0 <a≤0.01, 0<β≤0.03, 0<γ≤0.003, 0<γ≤0.017, 0 <b≤0.01이다.

[0068] For example, the above M1 may include Al, Mn, Ti, Mg, Y, Zr, B, or any combination thereof. For example, the above M1 may include Al, Zr, Mn, or any combination thereof.

[0069] According to one embodiment, M1 may include Al, Ti, Mg, Y, Sr, Ba, Ce, Bi, Zr, B, or any combination thereof. For example, M1 may include Al, Mn, Zr, B, Mg, Ti, Y, or any combination thereof. For example, M1 may include Al, Mn, Zr, or any combination thereof.

[0070] According to one embodiment, 0 < γ ≤ 0.025 and 0 < γ ≤ 0.0175.

[0071] When the positive electrode active material according to one embodiment of the present invention satisfies Formula 1 or Formula 2, an improvement in lifespan characteristics can be expected without a decrease in the capacity and output characteristics of the high-nickel positive electrode active material.

[0072] Hereinafter, a method for manufacturing a positive electrode active material according to one aspect is described in detail.

[0073] A method for manufacturing a positive electrode active material according to one aspect comprises the steps of: providing lithium transition metal oxide particles; solid-state mixing of the lithium transition metal oxide particles and a tungsten (W)-containing precursor compound to obtain a first solid-state mixture; solid-state mixing of the first solid-state mixture and a cobalt (Co)-containing precursor compound to obtain a second solid-state mixture; and second-state calcining of the second solid-state mixture to obtain a positive electrode active material, wherein the lithium transition metal oxide comprises coating particles containing tungsten (W) and cobalt (Co) elements on the surface of the particles, and the coating particles comprise a first coating region adjacent to the surface of the lithium transition metal oxide particles and a second coating region existing on the first coating region, wherein the first coating region has an elemental ratio of tungsten higher than the elemental ratio of cobalt, and the second coating region has an elemental ratio of cobalt higher than the elemental ratio of tungsten.

[0074] In the description of the manufacturing method, details regarding lithium transition metal oxide particles and cathode active materials that overlap with previously explained content are omitted.

[0075] According to one embodiment, the step of providing the lithium transition metal oxide particles may include the step of obtaining lithium transition metal oxide particles by mixing two or more precursor compounds among a nickel element-containing precursor compound; a lithium element-containing precursor compound; a sodium (Na) element-containing precursor compound; a sulfur (S) element-containing precursor compound; an aluminum (Al) element-containing precursor compound; a zirconium (Zr) element-containing precursor compound; and a manganese (Mn) element-containing precursor compound, and then performing a first calcination.

[0076] According to one embodiment, the nickel element-containing precursor compound is a compound capable of providing nickel element and may include, but is not limited to, nickel hydroxide, oxide, nitride, carbonate, acetate salt, or a combination thereof. For example, the nickel element-containing precursor compound may be NiO, Ni(OH)2, NiCO3, or a combination thereof.

[0077] According to one embodiment, the lithium element-containing precursor compound may include, but is not limited to, lithium hydroxides, oxides, nitrides, carbonates, or combinations thereof. For example, the lithium element-containing precursor compound may be LiOH·H2O, Li2CO3, or a combination thereof.

[0078] According to one embodiment, the sodium element-containing precursor compound may include, but is not limited to, sodium hydroxides, oxides, nitrides, carbonates, or combinations thereof. For example, it may be NaOH, Na2CO3, or a combination thereof.

[0079] According to one embodiment, the sulfur element-containing precursor compound may include, but is not limited to, a hydroxide, oxide, nitride, carbonate, ammonium compound, or combination thereof of sulfur (S). For example, it may be (NH4)2SO4.

[0080] According to one embodiment, the aluminum element-containing precursor compound may include, but is not limited to, aluminum hydroxides, oxides, nitrides, carbonates, acetate salts, or combinations thereof. For example, the aluminum-based compound may be Al(OH)3, Al2(CO3)3, Al2O3, or a combination thereof.

[0081] According to one embodiment, the zirconium element-containing precursor compound may include, but is not limited to, zirconium hydroxides, oxides, nitrides, carbonates, or combinations thereof. For example, it may be Zr(OH)4, Zr2(CO3)4, or a combination thereof.

[0082] According to one embodiment, the manganese element-containing precursor compound may include, but is not limited to, a manganese hydroxide, oxide, nitride, carbonate, or combination thereof. For example, it may be Mn(OH)2, MnCO3, or a combination thereof.

[0083] According to one embodiment, the tungsten-containing precursor compound may include tungsten hydroxide, oxide, nitride, carbonate, acetate salt, or a combination thereof, but is not limited thereto. For example, it may be WO3, W(OH)3, W2(CO3)3, or a combination thereof.

[0084] According to one embodiment, the cobalt-containing precursor compound may include, but is not limited to, a hydroxide, oxide, nitride, carbonate, acetic acid salt of cobalt. For example, the cobalt-based compound may be Co(OH)2, CoCO3, or a combination thereof.

[0085] According to one embodiment, solid mixing includes performing mechanical mixing. The mechanical mixing is performed dry. The mechanical mixing involves applying mechanical force to crush and mix the materials to be mixed to form a uniform mixture. Mechanical mixing can be performed using a mixing device such as a ball mill, planetary mill, stirred ball mill, or vibrating mill, for example, using chemically inert beads. At this time, to maximize the mixing effect, a small amount of alcohol such as ethanol or a volatile higher fatty acid such as stearic acid may be optionally added.

[0086] The above mechanical mixing is performed in an oxidizing atmosphere to prevent the reduction of the transition metal in the lithium transition metal oxide particles, thereby ensuring the structural stability of the active material.

[0087] According to one embodiment, the time for the second solid-state mixing may be shorter than the time for the first solid-state mixing. Accordingly, the tungsten-containing precursor compound provided in the first solid-state mixing and the cobalt-containing precursor compound provided in the second solid-state mixing are sequentially positioned on the surface of the lithium transition metal oxide particles, and a first coating region and a second coating region can be formed by subsequent calcination. If the second solid-state mixing time is excessively long, the tungsten-containing precursor compound and the cobalt-containing precursor compound are randomly mixed on the surface of the lithium transition metal oxide particles, making it difficult to obtain the desired first coating region and second coating region even if calcination is performed.

[0088] According to one embodiment, the first solid mixing may be performed for 8 to 12 minutes. For example, the first solid mixing may be performed for 9 to 11 minutes each.

[0089] According to one embodiment, the second solid mixing may be performed for 3 to 7 minutes. For example, the second solid mixing may be performed for 4 to 6 minutes each.

[0090] When the time for performing the first solid-state mixing with the tungsten-containing precursor compound and the time for performing the second solid-state mixing with the cobalt-containing precursor compound are performed within the aforementioned range of time, the lithium transition metal oxide may include coating particles containing tungsten (W) and cobalt (Co) elements on the particle surface, and may include a first coating region adjacent to the surface of the lithium transition metal oxide particles and a second coating region existing on the first coating region, wherein the first coating region has a higher elemental ratio of tungsten than the elemental ratio of cobalt, and the second coating region has a higher elemental ratio of cobalt than the elemental ratio of tungsten, thereby obtaining a structure. However, if the first solid-state mixing is performed for 15 minutes exceeding 12 minutes, a coating layer formed by the tungsten-containing precursor compound is formed, and in the subsequent calcination, a layer separate from the element introduced in the second solid-state mixing is formed, and a concentration gradient region is not formed. Meanwhile, when the first solid-state mixing is performed with a cobalt element-containing precursor compound, a separate coating layer is formed due to the heat generated by the shear force during the first solid-state mixing time, because the cobalt element-containing precursor compound has a lower melting point than the tungsten element-containing precursor compound. Accordingly, the elemental composition of the coating area varies depending on the element and the time of the solid-state mixing.

[0091] According to one embodiment, the first and second sintering are performed at different temperatures, and the temperature for the first sintering may be higher than the temperature for the second sintering. Accordingly, lithium nickel-based transition metal oxide particles in the form of single crystals and single particles are obtained through the first sintering, and by performing the second sintering at a lower temperature than the first sintering, coating particles are attached to the surface of the particles and coating elements are diffused, thereby forming a coating layer containing coating particles on the surface of the lithium transition metal oxide particles. At this time, if coating elements are added simultaneously and solid-state mixing is performed without the aforementioned first and second solid-state mixing, it is difficult to form the first coating region and the second coating region, as in the cathode active material of the present invention, even if the sintering process is undergone.

[0092] According to one embodiment, the first firing may be performed at a temperature of 750°C to 800°C for 8 to 12 hours. For example, the first firing may be performed at a temperature of 760°C to 800°C, or 770°C to 790°C. For example, the first firing may be performed for 9 to 11 hours.

[0093] According to one embodiment, the second firing may be performed at a temperature of 650°C to 750°C for 8 to 12 hours. For example, the second firing may be performed at a temperature of 660°C to 740°C, 670°C to 730°C, 680°C to 720°C, or 690°C to 710°C. For example, the second firing may be performed for 8 to 11 hours, or 9 to 11 hours.

[0094] According to one embodiment, the first firing may be performed at 760°C to 790°C, and the second firing may be performed at 670°C to 720°C.

[0095] The cathode active material manufactured by the above-described method has a single crystal and single particle shape and includes coating particles containing tungsten (W) and cobalt (Co) elements on its surface, and the coating particles include a first coating region adjacent to the surface of the lithium transition metal oxide particles and a second coating region existing on the first coating region, wherein the elemental ratio of tungsten in the first coating region is higher than the elemental ratio of cobalt, and the elemental ratio of cobalt in the second coating region is higher than the elemental ratio of tungsten, thereby obtaining a cathode active material having long life characteristics in which unstable Ni ions (Ni(III)) and Ni(IV) are stabilized.

[0096] According to another aspect, a cathode comprising the aforementioned cathode active material is provided.

[0097] According to another aspect, a lithium secondary battery comprising the anode; cathode; and electrolyte is provided.

[0098] According to one embodiment, the electrolyte may be a liquid electrolyte, a semi-solid electrolyte, or a solid electrolyte. Refer to the description below regarding the electrolyte.

[0099] The above-mentioned positive electrode and the lithium secondary battery containing it can be manufactured in the following way.

[0100] First, the positive electrode is prepared.

[0101] For example, a positive active material composition is prepared by mixing the aforementioned positive active material, conductive material, binder, and solvent. The positive active material composition is directly coated onto a metal current collector to manufacture a positive plate. Alternatively, the positive active material composition may be cast onto a separate support, and then a film peeled from the support is laminated onto a metal current collector to manufacture a positive plate. The positive electrode is not limited to the forms listed above and may be in a form other than those listed above.

[0102] The above conductive materials may include graphite such as natural graphite and artificial graphite; carbon black; conductive tubes such as carbon nanotubes; conductive whiskers such as fluorocarbon, zinc oxide, and potassium titanate; conductive metal oxides such as titanium oxide; but are not limited to these, and any material that can be used as a conductive material in the relevant technical field may be used.

[0103] The above binder may include vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene, mixtures thereof, metal salts, or styrene butadiene rubber-based polymers, but is not limited to these, and any that can be used as a binder in the relevant technical field may be used. Other examples of binders include lithium salts, sodium salts, calcium salts, or Na salts of the aforementioned polymers.

[0104] The above solvent may be N-methylpyrrolidone, acetone, or water, but is not limited to these; any solvent that can be used in the relevant technical field may be used.

[0105] The content of the above-mentioned positive active material, conductive material, binder, and solvent is at a level typically used in lithium batteries. Depending on the application and composition of the lithium battery, one or more of the above-mentioned conductive material, binder, and solvent may be omitted.

[0106] Next, the cathode is prepared.

[0107] For example, a negative electrode active material composition is prepared by mixing a negative electrode active material, a conductive material, a binder, and a solvent. The negative electrode active material composition is directly coated and dried on a metal current collector having a thickness of 3 μm to 500 μm to manufacture a negative electrode plate. Alternatively, the negative electrode active material composition may be cast onto a separate support, and then a film peeled from the support is laminated onto a metal current collector to manufacture a negative electrode plate.

[0108] The above-mentioned negative current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, copper, nickel, or copper surface treated with carbon may be used.

[0109] The above-mentioned negative electrode active material may be any material that can be used as a negative electrode active material for a lithium battery in the relevant technical field. For example, it may include one or more selected from the group consisting of lithium metal, metals alloyable with lithium, transition metal oxides, non-transition metal oxides, and carbon-based materials.

[0110] For example, the metals that can be alloyed with the lithium may be Si, Sn, Al, Ge, Pb, Bi, Sb Si-Y alloys (wherein Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element, or a combination thereof, and is not Si), Sn-Y alloys (wherein Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element, or a combination thereof, and is not Sn), etc. The above element Y may be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, or Te.

[0111] For example, the transition metal oxide may be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, etc.

[0112] For example, the above non-transfer metal oxides are SnO2, SiO2 x (0 <x<2) 등일 수 있다.

[0113] The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be graphite such as natural graphite or artificial graphite in amorphous, plate-like, flake-like, spherical, or fibrous form, and the amorphous carbon may be soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0114] In the cathode active material composition, the conductive material, binder, and solvent may be the same as those used in the anode active material composition.

[0115] The content of the above-mentioned negative electrode active material, conductive material, binder, and solvent is at a level typically used in lithium batteries. Depending on the application and composition of the lithium battery, one or more of the above-mentioned conductive material, binder, and solvent may be omitted.

[0116] Next, a separator to be inserted between the anode and cathode is prepared.

[0117] Any separator commonly used in lithium batteries may be used. One that exhibits low resistance to ion movement of the electrolyte and excellent electrolyte wettability may be used. The separator may be a single film or a multilayer film, and may be selected from, for example, glass fiber, polyester, Teflon, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene (PTFE), or combinations thereof, and may be in the form of a nonwoven or woven fabric. In addition, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may be used. For example, a windable separator such as polyethylene or polypropylene is used in lithium-ion batteries, and a separator with excellent organic electrolyte impregnation capability may be used in lithium-ion polymer batteries. For example, the separator may be manufactured according to the following method.

[0118] A separator composition is prepared by mixing a polymer resin, a filler, and a solvent. The separator composition may be directly coated and dried on the electrode to form a separator. Alternatively, the separator composition may be cast and dried on a support, and then a separator film peeled from the support may be laminated onto the electrode to form a separator.

[0119] The polymer resin used in the manufacture of the above separator is not particularly limited, and any material used as a binder for the electrode plate may be used. For example, vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or mixtures thereof may be used.

[0120] Next, the electrolyte is prepared.

[0121] For example, the electrolyte may be a liquid electrolyte, a semi-solid electrolyte, or a solid electrolyte.

[0122] The above liquid electrolyte may be an organic electrolyte. For example, the organic electrolyte may be prepared by dissolving a lithium salt in an organic solvent.

[0123] The above organic solvent may be any organic solvent that can be used in the relevant technical field. For example, cyclic carbonates such as propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate; esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone; ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, 2-methyltetrahydrofuran; nitriles such as acetonitrile; amides such as dimethylformamide. These can be used individually or in combination. For example, a solvent mixed with cyclic carbonates and chain carbonates can be used.

[0124] Any of the above lithium salts that can be used as lithium salts in the relevant technical field may be used. For example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2)(where x and y are natural numbers), LiCl, LiI, or mixtures thereof, etc.

[0125] The above electrolyte may be a semi-solid electrolyte. For example, the above semi-solid electrolyte may be a gel-type polymer electrolyte obtained by impregnating an electrolyte solution into a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or LiI, Li3N, Li x Ge y P z S α , Li x Ge y P z S α X δ Inorganic solid electrolytes such as (X=F, Cl, Br) can be used.

[0126] The above electrolyte may be a solid electrolyte. For example, it may be boron oxide, lithium oxynitride, etc., but is not limited to these; any that can be used as a solid electrolyte in the relevant technical field may be used. The above solid electrolyte may be formed on the cathode by a method such as sputtering.

[0127] As shown in FIG. 7, the lithium battery (1) comprises a positive electrode (3), a negative electrode (2), and a separator (4). The aforementioned positive electrode (3), negative electrode (2), and separator (4) are wound or folded and accommodated in a battery case (5). Subsequently, an organic electrolyte is injected into the battery case (5) and sealed with a cap assembly (6) to complete the lithium battery (1). The battery case (5) may be cylindrical, prismatic, pouch-type, coin-type, or thin-film type. For example, the lithium battery (1) may be a thin-film battery. The lithium battery (1) may be a lithium-ion battery.

[0128] A separator may be placed between the anode and cathode to form a battery structure. The battery structure is then stacked in a bicell structure, impregnated with an organic electrolyte, and the resulting product is contained in a pouch and sealed to complete a lithium-ion polymer battery.

[0129] In addition, the above-mentioned battery structures are stacked in multiple units to form a battery pack, and such a battery pack can be used in any device requiring high capacity and high output. For example, it can be used in laptops, smartphones, electric vehicles, etc.

[0130] In addition, the lithium battery has excellent lifespan and high-rate characteristics, so it can be used in electric vehicles (EVs). For example, it can be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). In addition, it can be used in fields requiring a large amount of power storage. For example, it can be used in electric bicycles, power tools, power storage systems, etc.

[0131] The present invention is explained in more detail through the following manufacturing examples, embodiments, and comparative examples. However, the embodiments are intended to illustrate the present invention and do not limit the scope of the present invention solely to these embodiments.

[0132] (Manufacturing of cathode active material)

[0133] Example 1

[0134] 1000g of Ni(OH)2, 481.6g of LiOH · H2O, 8.87g of Zr(OH)4, 0.437g of NaOH, 1.52g of MnCO3, 38.52g of Al(OH)3, and 1.44g of (NH4)2SO4 were mechanically mixed for approximately 15 minutes. The mixed powder was 780 o Lithium transition metal oxide particles were synthesized by calcining at 700°C for 10 hours. 500g of the synthesized lithium transition metal oxide particles were first mechanically mixed with 1.25g of WO3 for 10 minutes, then 10g of Co(OH)2 was added and mechanically mixed for 5 minutes, and then calcined at 700°C for 10 hours to synthesize the cathode active material shown in Table 1 below.

[0135] Example 2

[0136] 1000g of Ni(OH)2, 481.6g of LiOH · H2O, 8.87g of Zr(OH)4, 0.437g of NaOH, 1.52g of MnCO3, 38.52g of Al(OH)3, and 1.44g of (NH4)2SO4 were mechanically mixed for approximately 15 minutes. The mixed powder was 780 o Lithium transition metal oxide particles were synthesized by calcining at C for 10 hours. 500g of the synthesized lithium transition metal oxide particles were first mechanically mixed with 2.5g of WO3 for 10 minutes, then 10g of Co(OH)2 was added and mechanically mixed for 5 minutes, and then calcined at 700°C for 10 hours to synthesize the cathode active material shown in Table 1 below.

[0137] Example 3

[0138] 1000g of Ni(OH)2, 481.6g of LiOH · H2O, 8.87g of Zr(OH)4, 0.437g of NaOH, 1.52g of MnCO3, 38.52g of Al(OH)3, and 1.44g of (NH4)2SO4 were mechanically mixed for approximately 15 minutes. The mixed powder was 780 o Lithium transition metal oxide particles were synthesized by calcining at 700°C for 10 hours. 500g of the synthesized lithium transition metal oxide particles were first mechanically mixed with 3.75g of WO3 for 10 minutes, then 10g of Co(OH)2 was added and mechanically mixed for 5 minutes, and then calcined at 700°C for 10 hours to synthesize the cathode active material shown in Table 1 below.

[0139] Example 4

[0140] 1000g of Ni(OH)2, 481.6g of LiOH · H2O, 8.87g of Zr(OH)4, 0.437g of NaOH, 1.52g of MnCO3, 8.52g of Al(OH)3, and 1.44g of (NH4)2SO4 were mechanically mixed for approximately 15 minutes. The mixed powder was 780 oLithium transition metal oxide particles were synthesized by calcining at 700°C for 10 hours. 500g of the synthesized lithium transition metal oxide particles were first mechanically mixed with 1.25g of WO3 for 10 minutes, then 12.5g of Co(OH)2 was added and mechanically mixed for 5 minutes, and then calcined at 700°C for 10 hours to synthesize the cathode active material shown in Table 1 below.

[0141] Example 5

[0142] 1000g of Ni(OH)2, 481.6g of LiOH · H2O, 8.87g of Zr(OH)4, 0.437g of NaOH, 1.52g of MnCO3, 8.52g of Al(OH)3, and 1.44g of (NH4)2SO4 were mechanically mixed for approximately 15 minutes. The mixed powder was 780 o Lithium transition metal oxide particles were synthesized by calcining at 700°C for 10 hours. 500g of the synthesized lithium transition metal oxide particles were mechanically mixed with 1.25g of WO3 for 10 minutes, then 27.5g of Co(OH)2 was added and mechanically mixed for 5 minutes, and then calcined at 700°C for 10 hours to synthesize the cathode active material shown in Table 1 below.

[0143] Example 6

[0144] 1000g of Ni(OH)2, 481.6g of LiOH · H2O, 8.87g of Zr(OH)4, 0.437g of NaOH, 1.52g of MnCO3, 8.52g of Al(OH)3, and 1.44g of (NH4)2SO4 were mechanically mixed for approximately 15 minutes. The mixed powder was 780 o Lithium transition metal oxide particles were synthesized by calcining at 700°C for 10 hours. 500g of the synthesized lithium transition metal oxide particles were first mechanically mixed with 1.25g of WO3 for 10 minutes, then 15g of Co(OH)2 was added and mechanically mixed for 5 minutes, and then calcined at 700°C for 10 hours to synthesize the cathode active material shown in Table 1 below.

[0145] Example 7

[0146] 1000g of Ni(OH)2, 481.6g of LiOH · H2O, 8.87g of Zr(OH)4, 0.437g of NaOH, 39.47g of Al(OH)3, and 1.44g of (NH4)2SO4 were mechanically mixed for approximately 15 minutes. The mixed powder was 780 o Lithium transition metal oxide particles were synthesized by calcining at 700°C for 10 hours. 500g of the synthesized lithium transition metal oxide particles were mechanically mixed with 1.25g of WO3 for 10 minutes, then 10g of Co(OH)2 was added and mechanically mixed for 5 minutes, and then calcined at 700°C for 10 hours to obtain the cathode active material shown in Table 1 below.

[0147] Comparative Example 1

[0148] 1000g of Ni(OH)2, 481.6g of LiOH · H2O, 8.87g of Zr(OH)4, 0.437g of NaOH, 1.52g of MnCO3, 8.52g of Al(OH)3, and 1.44g of (NH4)2SO4 were mechanically mixed for approximately 15 minutes. The mixed powder was 780 o Lithium transition metal oxide particles were synthesized by calcining at 700°C for 10 hours. 500g of the synthesized lithium transition metal oxide particles were mechanically mixed with 10g of Co(OH)2 for 15 minutes, and then calcined at 700°C for 10 hours to synthesize the cathode active material shown in Table 1.

[0149] Comparative Example 2

[0150] 1000g of Ni(OH)2, 481.6g of LiOH · H2O, 8.87g of Zr(OH)4, 0.437g of NaOH, 1.52g of MnCO3, 8.52g of Al(OH)3, and 1.44g of (NH4)2SO4 are mechanically mixed for approximately 15 minutes. The mixed powder is 780 o Lithium transition metal oxide particles were synthesized by calcining at 700°C for 10 hours. 500g of the synthesized lithium transition metal oxide particles were mechanically mixed with 1.25g of WO3 for 15 minutes, and then calcined at 700°C for 10 hours to synthesize the cathode active material shown in Table 1.

[0151] Comparative Example 3

[0152] 1000g of Ni(OH)2, 481.6g of LiOH · H2O, 8.87g of Zr(OH)4, 0.437g of NaOH, 1.52g of MnCO3, 38.52g of Al(OH)3, and 1.44g of (NH4)2SO4 were mechanically mixed for approximately 15 minutes. The mixed powder was 780 o Lithium transition metal oxide particles were synthesized by calcining at 700°C for 10 hours. 500g of the synthesized lithium transition metal oxide particles were first mechanically mixed with 1.25g of WO3 for 20 minutes, then 10g of Co(OH)2 was added and mechanically mixed for 5 minutes, and then calcined at 700°C for 10 hours to synthesize the cathode active material shown in Table 1.

[0153] Comparative Example 4

[0154] 1000g of Ni(OH)2, 481.6g of LiOH · H2O, 8.87g of Zr(OH)4, 0.437g of NaOH, 1.52g of MnCO3, 38.52g of Al(OH)3, and 1.44g of (NH4)2SO4 were mechanically mixed for approximately 15 minutes. The mixed powder was 780 o Lithium transition metal oxide particles were synthesized by calcining at 700°C for 10 hours. 500g of the synthesized lithium transition metal oxide particles were first mechanically mixed with Co(OH)2 for 10 minutes, then 1.25g of WO3 was added and mechanically mixed for 5 minutes, and then calcined at 700°C for 10 hours to synthesize the cathode active material shown in Table 1.

[0155] Comparative Example 5

[0156] 1000g of Ni(OH)2, 481.6g of LiOH · H2O, 8.87g of Zr(OH)4, 0.437g of NaOH, 1.52g of MnCO3, 38.52g of Al(OH)3, and 1.44g of (NH4)2SO4 were mechanically mixed for approximately 15 minutes. The mixed powder was 780 oLithium transition metal oxide particles were synthesized by calcining at 700°C for 10 hours. 500g of the synthesized lithium transition metal oxide particles were mechanically mixed with 10g of Co(OH)2 and 1.25g of WO3 for 15 minutes, and then calcined at 700°C for 10 hours to synthesize the cathode active material shown in Table 1.

[0157] Comparative Example 6

[0158] 1000g of Ni(OH)2, 481.6g of LiOH · H2O, 8.87g of Zr(OH)4, 0.437g of NaOH, 1.52g of MnCO3, 38.52g of Al(OH)3, and 1.44g of (NH4)2SO4 were mechanically mixed for approximately 15 minutes. The mixed powder was 780 o Lithium transition metal oxide particles were synthesized by calcining at 700°C for 10 hours. 500g of the synthesized lithium transition metal oxide particles were mechanically mixed with 10g of Co(OH)2 and 0.5g of WO3 for 15 minutes, and then calcined at 700°C for 10 hours to synthesize the cathode active material shown in Table 1.

[0159] Comparative Example 7

[0160] 1000g of Ni(OH)2, 481.6g of LiOH · H2O, 8.87g of Zr(OH)4, 0.437g of NaOH, 1.52g of MnCO3, 38.52g of Al(OH)3, and 1.44g of (NH4)2SO4 were mechanically mixed for approximately 15 minutes. The mixed powder was 780 o Lithium transition metal oxide particles were synthesized by calcining at 700°C for 10 hours. 500g of the synthesized lithium transition metal oxide particles were mechanically mixed with 10g of Co(OH)2 and 5g of WO3 for 15 minutes, and then calcined at 700°C for 10 hours to synthesize the cathode active material shown in Table 1.

[0161] Comparative Example 8

[0162] 1000g of Ni(OH)2, 481.6g of LiOH · H2O, 8.87g of Zr(OH)4, 0.437g of NaOH, 1.52g of MnCO3, 38.52g of Al(OH)3, and 1.44g of (NH4)2SO4 were mechanically mixed for approximately 15 minutes. The mixed powder was 780 o Lithium transition metal oxide particles were synthesized by calcining at 700°C for 10 hours. 500g of the synthesized lithium transition metal oxide particles were mechanically mixed with 10g of Co(OH)2 and 10g of WO3 for 15 minutes, and then calcined at 700°C for 10 hours to synthesize the cathode active material shown in Table 1.

[0163] furtherance Comparative Example 1 Li 0.99 So 0.01 Ni 0.965 Co 0.02 Mr 0.001 Al 0.009 Zr 0.005 O 1.99 S 0.01 Comparative Example 2 Li 0.99 Na 0.01 Ni 0.9842 W 0.0008 Mn 0.001 Al 0.009 Zr 0.005 O 1.99 S 0.01 Comparative Example 3 Li 0.99 So 0.01 Ni 0.9642 Co 0.02 W 0.0008 Mr 0.001 Al 0.009 Zr 0.005 O 1.99 S 0.01 Comparative Example 4 Li 0.99 So 0.01 Ni 0.9642 Co 0.02 W 0.0008 Mr 0.001 Al 0.009 Zr 0.005 O 1.99 S 0.01 Comparative Example 5 Li 0.99 So 0.01 Ni 0.9642 Co 0.02 W 0.0008 Mr 0.001 Al 0.009 Zr 0.005 O 1.99 S 0.01 Comparative Example 6 Li 0.99 So 0.01 Ni 0.9647 Co 0.02 W 0.0003 Mr 0.001 Al 0.009 Zr 0.005 O 1.99 S 0.01 Comparative Example 7 Li 0.99 So 0.01 Ni 0.962 Co 0.02 W 0.003 Mr 0.001 Al 0.009 Zr 0.005 O 1.99 S 0.01 Comparative Example 8 Li 0.99 So 0.01 Ni 0.959 Co 0.02 W 0.006 Mr 0.001 Al 0.009 Zr 0.005 O 1.99 S 0.01 Example 1 Li 0.99 So 0.01 Ni 0.9642 Co 0.02 W 0.0008 Mr 0.001 Al 0.009 Zr 0.005 O 1.99 S 0.01 Example 2 Li 0.99 So 0.01 Ni 0.9634 Co 0.02 W 0.0016 Mr 0.001 Al 0.009 Zr 0.005 O 1.99 S 0.01 Example 3 Li 0.99 So 0.01 Ni 0.9626 Co 0.02 W 0.0024 Mr 0.001 Al 0.009 Zr 0.005 O 1.99 S 0.01 Example 4 Li 0.99 So 0.01 Ni 0.9592 Co 0.025 W 0.0008 Mr 0.001 Al 0.009 Zr 0.005 O 1.99 S 0.01 Example 5 Li 0.99 So 0.01 Ni 0.9692 Co 0.015 W 0.0008 Mr 0.001 Al 0.009 Zr 0.005 O 1.99 S 0.01 Example 6 Li 0.99 So 0.01 Ni 0.9542 Co 0.030 W 0.0008 Mr 0.001 Al 0.009 Zr 0.005 O 1.99 S 0.01 Example 7 Li 0.99 So 0.01 Ni 0.9642 Co 0.02 W 0.0008 Al 0.01 Zr 0.005 O 1.99 S 0.01

[0164] (Manufacturing of half-cells)

[0165] Example 8

[0166] A slurry was prepared by mixing the cathode active material, conductive material, and binder obtained in Example 1 in a weight ratio of 96:2:2. Here, the conductive material (Super-P) was used, and polyvinylidene fluoride (PVdF) dissolved in N-methyl-2-pyrrolidone solvent was used as the binder.

[0167] The above slurry was uniformly coated onto an Al current collector and dried at 110°C for 2 hours to prepare an anode electrode. The loading level of the electrode plate was 15.0 mg / cm². 2 And, the electrode density was 3.71 g / cc.

[0168] A CR2032 half-cell was fabricated according to a commonly known process using the above-mentioned anode as the working electrode, a lithium foil as the counter electrode, and a liquid electrolyte in which LiPF6 was added as a lithium salt to a mixed solvent of ethylene carbonate (EC) / diethyl carbonate (DEC) / dimethyl carbonate (DMC) in a volume ratio of 3 / 4 / 3 to a concentration of 1.3 M.

[0169] Examples 9 to 14

[0170] A half cell was fabricated in the same manner as in Example 8, except that the cathode active materials obtained in Examples 2 to 7 were used instead of the cathode active material obtained in Example 1.

[0171] Comparative Examples 9 to 16

[0172] A half-cell was fabricated in the same manner as in Example 8, except that the cathode active materials obtained in Comparative Examples 1 to 8 were used instead of the cathode active material obtained in Example 1.

[0173] Evaluation Example 1: Evaluation of the appearance of the cathode active material

[0174] Scanning electron microscopy (SEM) images of the cathode active materials obtained in Examples 1 to 6 and Comparative Examples 1 to 8 were taken and are shown in FIGS. 1 and 2.

[0175] Referring to Figures 1 and 2, it was confirmed that the cathode active materials obtained in Examples 1 to 6 are single particles that do not differ significantly on the sample surface even when Co and W concentration gradients are introduced.

[0176] Evaluation Example 2: Evaluation of the composition of the cathode active material

[0177] Inductively coupled plasma (ICP) analysis was performed on the cathode active materials synthesized in Examples 1 to 7 and Comparative Examples 1 to 8 using a 700-ES (Varian) instrument, and the results are listed in Table 2 below.

[0178] Referring to Table 2, the ICP analysis results of Comparative Examples 1 to 8 and Examples 1 to 7 show that the introduction of first and second coating regions of Co and W on the surface of the single-particle Ni-based cathode active material causes substitution with other transition metals within the active material, increasing the content of Co and W and decreasing the moles of other transition metals. When performing ICP analysis, even if the analysis is conducted under vacuum, it is difficult to analyze the stoichiometric value of oxygen contained in the material due to the influx of trace amounts of atmospheric oxygen and carbon dioxide.

[0179] Li (mol%) Na (mol%) Ni (mol%) Co(mol%) Mn(mol.%) Al (mol%) W (mol%) Zr(mol%) S(mol%) Comparative Example 1 99 1 96.5 2 0.1 0.9 - 0.5 1 Comparative Example 2 99 1 98.42 - 0.1 0.9 0.08 0.5 1 Comparative Example 3 99 1 96.42 2 0.1 0.9 0.08 0.5 1 Comparative Example 4 99 1 96.42 2 0.1 0.9 0.08 0.5 1 Comparative Example 5 99 1 96.42 2 0.1 0.9 0.08 0.5 1 Comparative Example 6 99 1 96.47 2 0.1 0.9 0.03 0.5 1 Comparative Example 7 99 1 96.2 2 0.1 0.9 0.3 0.5 1 Comparative Example 8 99 1 95.9 2 0.1 0.9 0.6 0.5 1 Example 1 99 1 96.42 2 0.1 0.9 0.08 0.5 1 Example 2 99 1 96.34 2 0.1 0.9 0.16 0.5 1 Example 3 99 1 96.26 2 0.1 0.9 0.24 0.5 1 Example 4 99 1 95.92 2.5 0.1 0.9 0.08 0.5 1 Example 5 99 1 96.92 1.5 0.1 0.9 0.08 0.5 1 Example 6 99 1 95.42 3.0 0.1 0.9 0.08 0.5 1 Example 7 99 1 96.42 2.0 0 1.0 0.08 0.5 1

[0180] Evaluation Example 3: Evaluation of the coating region of the cathode active material

[0181] For the cathode active materials obtained in Example 1 and Comparative Examples 3 to 5, the surface of the cathode material was analyzed using high resolution transmission electron microscopy (HR-TEM), and the results are shown in Fig. 3 (Comparative Example 3), Fig. 4 (Comparative Example 4), Fig. 5 (Comparative Example 5), and Fig. 6 (Example 1).

[0182] Referring to FIG. 3, it was confirmed that Comparative Example 3 has a first coating layer composed of W on the surface of the active material and a second coating layer composed of Co thereon. Referring to FIG. 4, it was confirmed that Comparative Example 4 has a first coating layer composed of Co and a second coating layer composed of W thereon on the surface of the active material. It was confirmed that in the active material of Comparative Example 4, Co(OH)2 forms a coating layer structure before calcination due to the shear heat generated during mechanical mixing, and thus W elements are not mixed into the Co coating layer even when solid-state mixing is subsequently performed with WO3. Referring to FIG. 5, it was confirmed that a single coating layer composed of Co and W is present on the surface of the active material.

[0183] In contrast, referring to FIG. 6, it was confirmed that Example 1 includes a coating layer comprising tungsten (W) and cobalt (Co), comprising a first coating region in which the tungsten content is greater than the cobalt content, and a second coating region thereon in which the cobalt content is greater than the tungsten content. Tungsten and cobalt are present in the first coating region, and tungsten contributes to improving electrochemical properties by facilitating lithium migration from the interior of the cathode active material to the surface. At this time, the presence of cobalt together with tungsten reduces the area where tungsten comes into contact with the electrolyte, thereby preventing loss of tungsten. In the second coating region, since cobalt is included as the main element, side reactions with the electrolyte are effectively suppressed, and tungsten included as a minor element further improves electrochemical properties by facilitating lithium migration from the surface. In contrast, when only a cobalt coating layer exists as the outermost coating layer, the cobalt coating layer does not contain tungsten, so the cobalt coating layer acts as a resistance layer for lithium ion movement, resulting in a relative decrease in electrochemical properties. When a tungsten coating layer is included as the outermost coating layer, the tungsten coating layer comes into direct contact with the electrolyte, causing the coating layer to be lost due to side reactions, which leads to electrochemical losses. Additionally, when only a mixed coating layer of cobalt and tungsten is included, the surface area where tungsten reacts with the electrolyte is larger than in the example, causing the coating layer to be lost due to side reactions, which leads to electrochemical losses. Accordingly, the present embodiment includes tungsten (W) and cobalt (Co), and includes a first coating region in which the content of tungsten is greater than the content of cobalt, and a second coating region thereon in which the content of cobalt is greater than the content of tungsten. Therefore, side reactions between tungsten and the electrolyte are sufficiently suppressed so that lithium migration operates smoothly, and as the concentration of cobalt increases toward the outermost layer, the structural stability of the cathode active material is also improved, thereby improving electrochemical performance.

[0184] Evaluation Example 4: High-temperature life evaluation

[0185] After resting the half-cells prepared in Examples 8 to 14 and Comparative Examples 9 to 16 for 10 hours, they were charged in CC mode at 0.2C to 4.25V, and then charged in CV mode to a current corresponding to 0.05C. Next, the formation process was completed by discharging in CC mode at 0.2C to 2.5V.

[0186] Next, the device was charged in CC mode at 0.5C to 4.25V at a high temperature (45℃), and then charged in CV mode to a current corresponding to 0.05C. Next, it was discharged in CC mode at 1C to 2.5V, and this process was repeated a total of 50 times. The HPPC (Hybrid pulse power characterization) evaluation protocol for the cathode active material is shown in Table 3.

[0187] Step C-rate voltage mode Step 1 charge 0.2C 4.25V CC+0.05C CV discharge of electricity 0.2C 2.5V CC charge 1C 4.25V CC+0.05C CV Step 2 discharge of electricity 1C Step 1: Discharge to 10% capacity CC+0.05C CV Step 3 Rest - - 1 hour Step 4 Discharge pulse 2C - 10sec Step 5 Rest - - 40sec Step 6 Charge pulse 3.75C 10sec Step 7 Rest - - 40sec Step 8 Charge pulse 1.25C - 10sec Step 9 Repeat Steps 2-8 to SOC 10–90%

[0188] The initial charge capacity and initial discharge capacity were measured, and the initial efficiency was calculated based on this. The capacity retention rate relative to the initial discharge capacity after 50 charge and discharge cycles was calculated and is shown in Table 4 below.

[0189] Initial charge capacity (mAh / g) Initial discharge capacity (mAh / g) Initial efficiency (%) 50 cycle retention(%) Comparative Example 9 253.4 218.9 86.4 76.3 Comparative Example 10 253.1 216.2 85.4 82.3 Comparative Example 11 253.9 218.8 86.2 79.3 Comparative Example 12 252.9 219.1 86.6 77.1 Comparative Example 13 254.1 219.6 86.4 73.5 Comparative Example 14 252.6 217.9 86.3 76.5 Comparative Example 15 250.6 216.9 86.6 84.5 Comparative Example 16 249.8 214.9 86.0 87.9 Example 8 255.1 220.9 86.6 91.9 Example 9 254.7 220.4 86.5 90.7 Example 10 254.1 220.6 86.8 90.3 Example 11 253.9 220.1 86.7 90.2 Example 12 253.7 220.7 87.0 91.1 Example 13 252.9 219.9 87.0 90.1 Example 14 253.6 221.2 87.2 92.3

[0190] Referring to Table 4, in Examples 8 to 14, as Co and W concentration gradients were introduced in the first coating region and the second coating region, respectively, the initial discharge capacity and initial efficiency of the positive electrode active material were significantly improved compared to cases where there was no Co and W concentration gradient (Comparative Examples 11 to 12), where a single layer of mixed Co and W was present (Comparative Examples 13 to 16), or where only a Co coating layer or a W coating layer was present (Comparative Examples 9, 10).

[0191] This suggests that introducing a coating layer containing tungsten and cobalt on the surface of the cathode active material, wherein the elemental ratio of tungsten is higher than that of cobalt and a first coating region in which the elemental ratio of cobalt is higher than that of tungsten, and a second coating region in which the elemental ratio of cobalt is higher than that of tungsten, is advantageous in terms of cathode active material capacity and efficiency.

[0192] Evaluation Example 5: Output Evaluation

[0193] HPPC (Hybrid pulse power characterization) evaluation was performed on the half-cells prepared in Example 8 and Comparative Examples 11 to 13, and the results are shown in Table 5 below.

[0194] DC-IR (Ω) SOC 10% SOC 50% SOC 90% Comparative Example 11 24.31 12.11 10.89 Comparative Example 12 25.97 12.67 11.34 Comparative Example 13 22,15 10.67 9.82 Example 8 18.76 9.47 9.12

[0195] Referring to Table 5, it was confirmed that the output characteristics were improved, with lower resistance at SOC 10%, 50%, and 90% of the half-cell of Example 8 compared to Comparative Examples 11 to 13. This suggests that introducing a coating layer containing tungsten and cobalt on the surface of the cathode active material, specifically a first coating region in which the elemental ratio of tungsten is higher than that of cobalt and a second coating region in which the elemental ratio of cobalt is higher than that of tungsten, is effective in improving the output characteristics of the cathode active material.

[0196] Although preferred embodiments according to the present invention have been described above with reference to the drawings and embodiments, this is merely illustrative, and those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible therefrom. Accordingly, the scope of protection of the present invention should be determined by the appended claims.

Claims

Claim 1 A positive electrode active material comprising: lithium transition metal oxide particles; and a coating layer comprising coating particles present on the surface of the lithium transition metal oxide particles and comprising tungsten (W) and cobalt (Co) elements, wherein the coating layer comprises a first coating region adjacent to the surface of the lithium transition metal oxide particles and a second coating region present on the first coating region, wherein the first coating region has an elemental ratio of tungsten higher than the elemental ratio of cobalt, and the second coating region has an elemental ratio of cobalt higher than the elemental ratio of tungsten. Claim 2 A positive electrode active material according to claim 1, wherein the first coating region has a concentration gradient in which the ratio of cobalt elements increases from the surface of the lithium transition metal oxide particles toward the second coating region. Claim 3 In claim 1, the anode active material having a second coating region having a concentration gradient in which the tungsten element ratio decreases. Claim 4 In claim 1, the anode active material, wherein the coating particles further comprise the Ni element. Claim 5 In claim 1, the anode active material, wherein the coating particles have a diameter of less than 700 nm. Claim 6 A positive electrode active material according to claim 1, wherein the surface of the lithium transition metal oxide particles further comprises tungsten oxide, lithium tungsten oxide, or a combination thereof. Claim 7 A positive electrode active material according to claim 1, wherein the tungsten comprises 1,000 ppm to 8,000 ppm relative to the weight of the lithium transition metal oxide particles. Claim 8 In claim 1, the lithium transition metal oxide particles are a positive electrode active material having a Ni content of 60 mol% or more. Claim 9 In claim 1, the lithium transition metal oxide particles are single crystals, forming an anode active material. Claim 10 A positive electrode active material according to claim 9, wherein a portion of the lithium (Li) element in the crystal of the lithium transition metal oxide particles is replaced with a sodium (Na) element, and a portion of the oxygen (O) element is replaced with a sulfur (S) element. Claim 11 In claim 1, the cathode active material is represented by the following chemical formula 1, cathode active material: <Chemical Formula 1>Li 1-a Na a Ni 1-α M α O 2-b S b In the above chemical formula 1, M comprises Co and W, and further comprises Ti, Mg, Y, Sr, Ba, Ce, Bi, Zr, B, Mn, Al, or any combination thereof, and Co and W are derived from coating particles present on the surface of the lithium transition metal oxide particles, and 0 <a≤0.01, 0<α≤0.05, 0<b≤0.01이다. Claim 12 In claim 1, the cathode active material is represented by the following chemical formula 2, cathode active material: <Chemical Formula 2>Li 1-a Na a Ni 1-β-γ-δ Co β W γ M1 δ O 2-b S b In the above chemical formula 2, M1 comprises Al, Mn, Ti, Mg, Y, Sr, Ba, Ce, Bi, Zr, B, or any combination thereof, and Co and W are derived from coating particles present on the surface of the lithium transition metal oxide particles, and 0 <a≤0.01, 0<β≤0.03, 0<γ≤0.003, 0<γ≤0.017, 0 <b≤0.01이다. Claim 13 In claim 12, the above M1 is a positive active material comprising Al, Ti, Mg, Y, Sr, Ba, Ce, Bi, Zr, B, or any combination thereof. Claim 14 A method for manufacturing an anode active material comprising: a step of providing lithium transition metal oxide particles; a step of solid-state mixing the lithium transition metal oxide particles and a tungsten (W)-containing precursor compound to obtain a first solid-state mixture; a step of solid-state mixing the first solid-state mixture and a cobalt (Co)-containing precursor compound to obtain a second solid-state mixture; and a step of second-state calcining the second solid-state mixture to obtain an anode active material, wherein the lithium transition metal oxide comprises coating particles containing tungsten (W) and cobalt (Co) elements on the surface of the particles, and the coating particles comprise a first coating region adjacent to the surface of the lithium transition metal oxide particles and a second coating region existing on the first coating region, wherein the first coating region has an elemental ratio of tungsten higher than the elemental ratio of cobalt, and the second coating region has an elemental ratio of cobalt higher than the elemental ratio of tungsten. Claim 15 A method for manufacturing a positive electrode active material according to claim 14, wherein the step of providing the lithium transition metal oxide particles comprises: a step of mixing two or more precursor compounds selected from a nickel element-containing precursor compound; a lithium element-containing precursor compound; a sodium (Na) element-containing precursor compound; a sulfur (S) element-containing precursor compound; an aluminum (Al) element-containing precursor compound; a zirconium (Zr) element-containing precursor compound; and a manganese (Mn) element-containing precursor compound, and then performing a first calcination to obtain lithium transition metal oxide particles. Claim 16 A method for manufacturing an anode active material according to claim 15, wherein the first calcination is performed at a temperature of 750°C to 800°C. Claim 17 A method for manufacturing an anode active material according to claim 14, wherein the secondary calcination is performed at a temperature of 650°C to 750°C. Claim 18 A method for manufacturing an anode active material according to claim 14, wherein the solid mixing comprises mechanical mixing, and the mechanical mixing comprises a ball mill, planetary mill, stirred ball mill, vibrating mill, or a combination thereof using chemically inert beads. Claim 19 A lithium secondary battery comprising: a positive electrode comprising a positive active material according to any one of claims 1 to 13; a negative electrode; and an electrolyte. Claim 20 In paragraph 19, the above electrolyte is a lithium secondary battery, which is a liquid electrolyte, a semi-solid electrolyte, or a solid electrolyte.

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