Positive electrode active material, manufacturing method thereof and lithium secondary battery comprising positive electrode active material

Abstract

The present invention relates to a positive electrode active material, a method for manufacturing the same, and a lithium secondary battery comprising the same, the positive electrode active material comprising: lithium nickel-based transition metal oxide particles containing 96 mol% or more of nickel and not containing manganese element, the proportion of titanium (Ti) substituted to a transition metal site in the crystal structure being 400 ppm to less than 1000 ppm; and a concentration gradient region in which the concentrations of aluminum (Al) and cobalt (Co) atoms change from the surface of the lithium nickel-based transition metal oxide particles toward the center of the particles, in which the absolute value (A) of the slope of change of the cobalt atom concentration and the absolute value (B) of the slope of change of the aluminum atom concentration in the concentration gradient region satisfy Agt; b.

Description

Technical Field

[0001] The invention relates to a positive electrode active material for a lithium secondary battery positive electrode and a manufacturing method thereof. Background Art

[0002] Since Sony Corporation commercialized lithium-ion secondary batteries in 1991, demand has rapidly increased across a wide range of applications, from small home appliances like mobile IT products to mid- to large-sized electric vehicles and energy storage systems. In particular, these applications require low-cost, high-energy cathode materials. However, cobalt, a component of single-crystal LiCoO2 (LCO), is currently a commercially available cathode active material and is expensive.

[0003] Therefore, as the positive electrode active material of medium and large secondary batteries, LiNi is used in which a part of Co is replaced by other transition metals. x Co y Mn z O2(NCM, x+y+z=1) and LiNi x Co y Al z Nickel-based positive electrode active materials represented by O2(NCA, x+y+z=1) are used to replace LCO, and the advantages of these NCM and NCA-based positive electrode active materials are that nickel as the main raw material is cheap and has a high reversible capacity. In particular, NCM and NCA with a molar ratio of Ni greater than or equal to 50 mol% have attracted attention in terms of high capacity. Generally, such Ni-based positive electrode active materials are made by mixing a transition metal compound precursor synthesized by a co-precipitation method with a lithium source and then conducting solid-phase synthesis. However, the Ni-based positive electrode material synthesized in this way exists in the form of secondary particles formed by aggregation of small primary particles, and micro-cracks (micro-cracks) are generated inside the secondary particles during the charge / discharge process. Microcracks cause side reactions between the new interface of the positive electrode active material and the electrolyte, thereby leading to degradation of battery performance, such as decreased stability due to the generation of gas, and degradation of battery performance due to depletion of the electrolyte. Furthermore, achieving high energy density requires increasing electrode density (>3.3 g / cc), but this leads to the collapse of secondary particles, which in turn depletes the electrolyte due to side reactions with the electrolyte, resulting in a sharp decrease in initial lifespan. Consequently, Ni-based cathode active materials in the form of secondary particles synthesized by existing coprecipitation methods cannot achieve high energy density.

[0004] To solve the above-mentioned problems of Ni-based cathode active materials in the form of secondary particles, single-particle Ni-based cathode active materials are being studied recently. Single-crystal Ni-based cathode active materials can achieve excellent electrochemical performance because the particles do not collapse when the electrode density is increased (>3.3g / cc) to achieve high energy density. However, in electrochemical evaluation, such single-crystal Ni-based cathode active materials have a poor electrochemical performance due to the unstable Ni 3+ 、Ni 4+ ions, resulting in structural and / or thermal instability, leading to deterioration of battery stability.

[0005] Therefore, there is still a need for a positive electrode active material for a lithium secondary battery having characteristics for developing high energy density and long life. Summary of the Invention

[0006] Technical issues

[0007] The present invention provides a positive electrode active material for ensuring high energy density and long life.

[0008] Technical Solution

[0009] In one aspect, a positive electrode active material is provided, comprising: lithium nickel-based transition metal oxide particles containing greater than or equal to 96 mol % nickel and no manganese, wherein the proportion of titanium (Ti) substituted into transition metal sites in the crystal structure is 400 ppm to less than 1000 ppm; and

[0010] A concentration gradient region, wherein the concentrations of aluminum (Al) atoms and cobalt (Co) atoms change from the surface of the lithium nickel-based transition metal oxide particle to the center of the particle,

[0011] The absolute value of the slope of the change in the cobalt atom concentration (A) and the absolute value of the slope of the change in the aluminum atom concentration (B) in the concentration gradient region satisfy A>B.

[0012] On the other hand, a method for manufacturing a positive electrode active material is provided, comprising: mixing a precursor compound containing a nickel element, a precursor compound containing a lithium element, a precursor compound containing an M1 element, a precursor compound containing an M2 element, a sodium precursor compound, and a precursor compound containing an S element, and then obtaining a lithium nickel-based transition metal oxide precursor by a first calcination; and

[0013] After solid-phase mixing of the lithium nickel-based transition metal oxide precursor compound, the Co precursor compound, and the Al precursor compound, lithium nickel-based transition metal oxide particles are obtained by a second calcination.

[0014] The positive electrode active material includes a concentration gradient region, wherein the concentration of aluminum (Al) atoms and cobalt (Co) atoms changes from the surface of the lithium nickel-based transition metal oxide particle to the center of the particle,

[0015] The absolute value of the slope of the change in the cobalt atom concentration (A) and the absolute value of the slope of the change in the aluminum atom concentration (B) in the concentration gradient region satisfy A>B.

[0016] Another aspect provides a lithium secondary battery comprising:

[0017] a positive electrode comprising the positive electrode active material;

[0018] a negative electrode; and

[0019] electrolytes.

[0020] Beneficial effects

[0021] According to one aspect, the positive electrode active material contains greater than or equal to 96 mol% nickel and does not contain manganese, the proportion of titanium (Ti) substituted to the transition metal site in the crystal structure is 400 ppm to less than 1000 ppm, and includes a concentration gradient region with a concentration gradient of Co concentration and Al concentration, and the absolute value of the slope of the change of the cobalt atom concentration (A) and the absolute value of the slope of the change of the aluminum atom concentration (B) in the concentration gradient region satisfy A>B, thereby preventing particle breakage and stabilizing nickel ions even at high electrode density, thereby obtaining an increase in capacity per unit volume and a life stability effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 are scanning electron microscope (SEM) images of positive electrode active materials obtained through Example 1 and Comparative Examples 1 to 7 according to one embodiment of the present invention.

[0023] Figure 2 1 is a result of HR-TEM analysis showing the element ratio in the direction from the surface toward the center of the particle of the positive electrode active material obtained in Example 1 according to one embodiment of the present invention.

[0024] Figure 3 1 is a result of HR-TEM analysis showing the element ratio of the positive electrode active material obtained in Comparative Example 1 in a direction from the surface toward the center of the particle.

[0025] Figure 4 is a schematic diagram of a lithium battery according to an exemplary embodiment.

[0026] <Description of Reference Numerals>

[0027] 1: Lithium battery 2: Negative electrode

[0028] 3: positive electrode 4: separator

[0029] 5: Battery case 6: Cover assembly DETAILED DESCRIPTION

[0030] The inventive concept described below may be subjected to various modifications and has various embodiments, and specific embodiments are shown in the drawings and described in detail. However, this is not intended to limit the inventive concept to a specific implementation form, and it should be understood that the inventive concept technology includes all modifications, equivalents or alternatives within its scope.

[0031] The terms used below are only used to describe specific embodiments and are not intended to limit the present inventive concept.

[0032] Singular expressions include dependent expressions unless the context clearly dictates otherwise. Hereinafter, terms such as “include,” “have,” or “have” indicate the presence of features, numbers, steps, operations, constituent elements, parts, ingredients, materials, or combinations thereof described in the specification, but it should be understood that they do not preclude the presence or addition of one or more other features, numbers, steps, operations, constituent elements, parts, ingredients, materials, or combinations thereof.

[0033] The “ / ” used below can be interpreted as “and” or “or” depending on the specific situation.

[0034] It should be understood that "concentration gradient region" as used hereinafter refers to a region where the concentration of atoms changes linearly or nonlinearly.

[0035] As used herein, the term "concentration gradient slope" should be understood to refer to the amount of change in atomic concentration from the outer surface of a concentration gradient region to the center of the particle.

[0036] To clearly represent the various layers and regions in the drawings, the thickness is exaggerated or reduced. Throughout this specification, similar parts are given the same reference numerals. Throughout this specification, when a layer, film, region, plate, or other part is described as being "above" or "over" another part, this includes not only the part being directly above the other part, but also the presence of another part between the two parts. Throughout this specification, terms such as first and second may be used to describe various components, but the components are not limited by the terms. Terms are used only to distinguish one component from another.

[0037] All terms used in this specification (including technical and scientific terms) have the same meanings as those commonly understood by those skilled in the art to which this disclosure belongs. In addition, conventional terms such as dictionary definitions should be interpreted as having meanings consistent with the meanings in the context of the relevant technology and this disclosure, and should not be interpreted as idealized or overly formal meanings.

[0038] Although specific embodiments have been described, the applicant or a person skilled in the art may implement currently unforeseen or unforeseen alternatives, modifications, variations, improvements, and substantial equivalents. Therefore, the appended claims, as they will be filed or as they may be amended, include all alternatives, modifications, variations, improvements, and substantial equivalents.

[0039] Hereinafter, a positive electrode active material, a method of manufacturing the same, and a lithium secondary battery including a positive electrode of the positive electrode active material according to exemplary embodiments are described in detail.

[0040] According to one aspect, the positive electrode active material may include: lithium nickel-based transition metal oxide particles, which contain greater than or equal to 96 mol% nickel and do not contain manganese, and the proportion of titanium (Ti) substituted to the transition metal site in the crystal structure is 400 ppm to less than 1000 ppm; and a concentration gradient region, in which the concentration of aluminum (Al) and cobalt (Co) atoms changes from the surface of the lithium nickel-based transition metal oxide particles to the center of the particles, wherein the absolute value of the slope of the change of the cobalt atom concentration (A) and the absolute value of the slope of the change of the aluminum atom concentration (B) in the concentration gradient region satisfy A>B.

[0041] According to one embodiment, the lithium nickel-based transition metal oxide particles may contain less than 2 mol% of aluminum atoms. For example, the lithium nickel-based transition metal oxide particles may contain less than or equal to 1.5 mol%, less than or equal to 1.0 mol%, or 0.5 mol% of aluminum atoms.

[0042] According to one embodiment, the lithium nickel-based transition metal oxide particles may contain less than or equal to 2.5 mol% of cobalt atoms. For example, the lithium nickel-based transition metal oxide particles may contain greater than or equal to 1 mol% and less than or equal to 2 mol%, or greater than or equal to 1.5 mol% and less than or equal to 2 mol% of cobalt atoms.

[0043] According to one embodiment, the concentration gradient region may have a concentration gradient in which the concentrations of aluminum atoms and cobalt atoms decrease from the outer surface of the concentration gradient region toward the center of the particle.

[0044] According to one embodiment, the concentration of cobalt atoms in the concentration gradient region may be greater than the concentration of aluminum atoms. This minimizes the decrease in initial capacity, significantly improving lifespan characteristics.

[0045] According to one embodiment of the present invention, the lithium transition metal oxide particles include a concentration gradient region, wherein the concentrations of aluminum atoms and cobalt atoms vary in a localized region of the particle, thereby improving capacity and lifespan characteristics compared to a positive electrode active material having a concentration gradient throughout the particle. Furthermore, by making the change in cobalt atom concentration in the concentration gradient region greater than the change in aluminum atom concentration, the particles can be provided with structural stability and improved conductivity during the charge and discharge process, thereby improving lifespan characteristics in the presence of a decrease in initial discharge efficiency and degradation of high-power characteristics due to nickel dissolution. Furthermore, when the absolute values of the slopes of the change in cobalt atom concentration and the absolute values of the slopes of the change in aluminum atom concentration fall within the aforementioned ranges, the decrease in output characteristics caused by the increase in lithium ion resistance due to the increase in the thickness of the concentration gradient region is suppressed, thereby improving lifespan characteristics.

[0046] According to one embodiment, the concentration of nickel atoms in the concentration gradient region may increase from the particle surface toward the particle center. For example, the concentration of nickel atoms decreases toward the particle surface in the concentration gradient region, while remaining unchanged in regions outside the concentration gradient region.

[0047] According to one embodiment, the thickness of the concentration gradient region can be 0.6 or less of the particle radius. For example, the thickness of the concentration gradient region can be 0.5 or less, 0.4 or less, 0.3 or less, or 0.2 or less of the particle radius. When the concentration gradient region meets the above thickness range, it will not become a resistance layer for lithium migration, thereby not causing a decrease in output characteristics.

[0048] According to one embodiment, the concentration gradient region may have a thickness of less than or equal to 300 nm from the surface of the lithium nickel-based transition metal oxide particle toward the particle center. For example, the concentration gradient region may have a thickness of 50 nm to 300 nm, 100 nm to 250 nm, or 150 nm to 200 nm from the surface of the lithium nickel-based transition metal oxide particle toward the particle center. When the thickness falls within the above range, it does not become a resistance layer for lithium migration, thereby preventing a decrease in output characteristics.

[0049] According to one embodiment, the lithium nickel-based transition metal oxide particles may further contain sodium (Na) and sulfur (S) atoms.

[0050] According to one embodiment, some lithium (Li) atoms in the crystals of the lithium nickel-based transition metal oxide particles may be substituted by sodium (Na) atoms, and some oxygen (O) atoms may be substituted by sulfur (S) atoms.

[0051] Since some of the lithium atoms are replaced by sodium atoms, crystal collapse can be suppressed even when lithium is deintercalated in the crystal structure during charging. The introduction of sodium atoms increases the crystal volume, thereby increasing the mobility of lithium, thereby improving output characteristics. In addition, since some of the oxygen atoms are replaced by sulfur (S) atoms, the binding force between the transition metal and the sulfur atoms is increased, which suppresses the migration of the lithium nickel-based oxide crystal structure during the charge and discharge process of the lithium secondary battery, thereby improving the crystal structure stability of the lithium nickel-based oxide. As a result, the life characteristics can be improved.

[0052] According to one embodiment, the total amount of the sodium (Na) and the sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles may be 300 ppm to 1500 ppm. For example, the total amount of the sodium (Na) and the sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles may be 400 ppm to 1500 ppm. For example, the total amount of the sodium (Na) and the sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles may be 500 ppm to 1500 ppm. For example, the total amount of the sodium (Na) and the sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles may be 600 ppm to 1500 ppm. For example, the total amount of the sodium (Na) and the sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles may be 700 ppm to 1500 ppm. For example, the total amount of the sodium (Na) and the sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles may be 800 ppm to 1500 ppm. For example, the total amount of the sodium (Na) and the sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles may be 900 ppm to 1500 ppm. For example, the total amount of the sodium (Na) and the sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles may be 1000 ppm to 1500 ppm. For example, the total amount of the sodium (Na) and the sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles may be 1100 ppm to 1500 ppm. For example, the total amount of the sodium (Na) and the sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles may be 1200 ppm to 1500 ppm. For example, the total amount of the sodium (Na) and the sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles may be 1000 ppm to 1400 ppm. For example, the total amount of the sodium (Na) and the sulfur (S) atoms may be 1100 ppm to 1400 ppm. For example, the total amount of sodium (Na) and sulfur (S) atoms may be 1200 ppm to 1400 ppm. When the total amount of sodium and sulfur atoms satisfies the above range, crystal collapse during charge and discharge can be prevented, thereby improving lifespan characteristics.

[0053] According to one embodiment, the ratio of titanium included in the lithium nickel-based transition metal oxide particles may be 500 ppm to 900 ppm or 500 ppm to 800 ppm.

[0054] According to one embodiment, the lithium nickel-based transition metal oxide particles may be single particles or single crystals, and secondary particles formed by aggregation of a plurality of single particles.

[0055] For example, the lithium nickel-based transition metal oxide particles can be single particles. Single particles are a concept different from secondary particles formed by the aggregation of multiple particles or particles formed by the aggregation of multiple particles with the outer edges of the aggregates coated. Because the lithium nickel-based transition metal oxide particles have a single particle morphology, particle breakage can be prevented even at high electrode density. Therefore, not only can a high energy density of the positive electrode active material containing lithium nickel-based transition metal oxide particles be achieved, but breakage caused by winding during the formation of the electrode plate can also be prevented, thereby achieving excellent life characteristics.

[0056] According to one embodiment, the lithium nickel-based transition metal oxide particles may comprise single crystals. The concepts of single crystal and single particle are distinct. A single particle refers to a particle consisting of a single particle, regardless of the internal crystal type or orientation, while a single crystal refers to a particle containing only one crystal. Such single-crystal lithium nickel-based transition metal oxide particles have high structural stability and conduct lithium ions more readily than polycrystalline particles, resulting in superior high-speed charging characteristics compared to polycrystalline active materials.

[0057] According to one embodiment, the lithium nickel-based transition metal oxide particles may be secondary particles formed by the aggregation of multiple single particles. The secondary particles formed by the aggregation of multiple single particles may be in the form of an aggregation of two or more single crystal particles. In this case, the proportion of secondary particles contained in the positive electrode active material may be less than 30% of the lithium nickel-based transition metal oxide particles. For example, relative to the overall nickel-based oxide particles, the proportion of secondary particles contained in the positive electrode active material may be less than or equal to 29%, less than or equal to 28%, less than or equal to 27%, less than or equal to 26%, or less than or equal to 25%.

[0058] According to one embodiment, the lithium nickel-based transition metal oxide particles can be single crystals and single particles. By forming them into single crystals and single particles, a structurally stable and high-density electrode can be achieved, thereby allowing a lithium secondary battery including the electrode to have both improved lifespan characteristics and high energy density.

[0059] According to one embodiment, the average particle size (D 50 ) can be 0.1 μm to 20 μm. 50) refers to the particle size of the particles that account for 50% starting from the smallest particle size in the particle size distribution analysis (PSD). For example, the average particle size (D 50 ) can be 0.5 μm to 20 μm, 1 μm to 20 μm, 2 μm to 19 μm, 3 μm to 18 μm, 4 μm to 17 μm, 5 μm to 16 μm, 6 μm to 15 μm, 7 μm to 14 μm, 8 μm to 13 μm, or 9 μm to 12 μm. When the average particle size of the lithium nickel-based transition metal oxide particles is within the above range, the required energy density per unit volume can be achieved. When the average particle size of the lithium nickel-based transition metal oxide particles is greater than 20 μm, the charge-discharge capacity drops sharply, and when it is less than or equal to 1 μm, it is difficult to obtain the required energy density per unit volume.

[0060] According to one embodiment, the lithium nickel-based transition metal oxide particles can be represented by the following Chemical Formula 1.

[0061] <Chemical Formula 1>

[0062] Li 1-a Na a Ni 1-x-y-α-β Co x Al y M1 α M2 β O 2-b S b

[0063] In the above Chemical Formula 1,

[0064] M1 and M2 are each independently one or more elements selected from the group consisting of Zr, W, Ti, Sr, Ba, Ce, B, Mg, and Bi,

[0065] 0 < a ≤ 0.01, 0 < α ≤ 0.003, 0 < β ≤ 0.003, 0 < x ≤ 0.03, 0 < y ≤ 0.01, 0 < b ≤ 0.01.

[0066] According to one embodiment, M1 can be one or more elements selected from the group consisting of Ti, Sr, Ba, Ce, and Bi. For example, M1 can be Ti.

[0067] According to one embodiment, M2 can be one or more elements selected from the group consisting of Zr, W, B, and Mg. For example, M2 can be Zr.

[0068] According to one embodiment, M1 can be Ti and M2 can be Zr.

[0069] According to one embodiment, a can be 0 < a ≤ 0.005 or 0 < a ≤ 0.001.

[0070] According to one embodiment, b can be 0 < β ≤ 0.005 or 0 < β ≤ 0.003.

[0071] According to one embodiment, α can be 0 < α ≤ 0.002, or 0 < α ≤ 0.001.

[0072] According to one embodiment, β can be 0 < β ≤ 0.002, or 0 < β ≤ 0.001.

[0073] According to one embodiment, the α and β can be the same as each other.

[0074] According to one embodiment, x can be 0 < x ≤ 0.025 or 0 < x ≤ 0.02.

[0075] According to one embodiment, y can be 0 < y ≤ 0.009, 0 < y ≤ 0.008, 0 < y ≤ 0.007, 0 < y ≤ 0.006, or 0 < y ≤ 0.005.

[0076] According to one embodiment, it can be 0 < x ≤ 0.02, 0 < y ≤ 0.005.

[0077] When the lithium nickel-based transition metal oxide particles according to one embodiment of the present invention satisfy the above Chemical Formula 1, it can be expected that the life characteristics are improved without a decrease in capacity and output characteristics.

[0078] Hereinafter, a method for manufacturing a positive electrode active material according to one aspect will be described in detail.

[0079] A method for manufacturing a positive electrode active material according to one aspect of the present invention includes: after mixing a precursor compound containing a nickel element, a precursor compound containing a lithium element, a precursor compound containing an M1 element, and a precursor compound containing an M2 element, obtaining a lithium nickel-based transition metal oxide precursor by first calcination; and

[0080] After solid-phase mixing of the lithium nickel-based transition metal oxide precursor compound and a Co precursor compound and an Al precursor compound, obtaining lithium nickel-based transition metal oxide particles by second calcination. At this time, there is a concentration gradient region in which the concentrations of aluminum (Al) atoms and cobalt (Co) atoms change in the direction from the surface of the lithium nickel-based transition metal oxide particles toward the particle center, and the absolute value (A) of the change slope of the cobalt atom concentration and the absolute value (B) of the change slope of the aluminum atom concentration in the concentration gradient region can satisfy A > B.

[0081] The content regarding the lithium nickel-based transition metal oxide particles is as described above.

[0082] According to one embodiment, the nickel-containing element precursor compound is a compound that can provide nickel element, which may include but is not limited to nickel hydroxide, oxide, nitride, carbonate, acetic acid or a combination thereof. For example, the nickel-containing element precursor compound may be NiO, Ni(OH)2, NiCO3 or a combination thereof. In addition, the nickel-containing element precursor compound may contain greater than 0ppm to less than or equal to 300ppm of Na element, 300ppm to 1200ppm of S element. For example, the nickel-containing element precursor compound may contain 100ppm to 300ppm of Na element, 400ppm to 1200ppm of S element. For example, the nickel-containing element precursor compound may contain 100ppm to 300ppm of Na element, 600ppm to 1200ppm of S element. For example, the nickel-containing element precursor compound may contain 100ppm to 300ppm of Na element, 700ppm to 1200ppm of S element. For example, the nickel-containing precursor compound may contain 100 ppm to 300 ppm of Na element and 800 ppm to 1200 ppm of S element. For example, the nickel-containing precursor compound may contain 100 ppm to 300 ppm of Na element and 900 ppm to 1200 ppm of S element. For example, the nickel-containing precursor compound may contain 100 ppm to 300 ppm of Na element and 1000 ppm to 1200 ppm of S element.

[0083] In one embodiment, the lithium-containing precursor compound may include, but is not limited to, lithium hydroxide, oxide, nitride, carbonate, or a combination thereof. For example, the lithium-containing precursor compound may be LiOH·H2O, Li2CO3, or a combination thereof.

[0084] According to one embodiment, the precursor compound containing the M1 element may include, but is not limited to, hydroxides, oxides, nitrides, carbonates, or combinations thereof of one or more elements selected from the group consisting of Ti, Sr, Ba, Ce, and Bi. For example, the precursor compound containing the M1 element may be TiO2, Sr(OH)2, BaO, Ce2O3, Bi(OH)3, or combinations thereof.

[0085] According to one embodiment, the M2 element-containing precursor compound may include, but is not limited to, hydroxides, oxides, nitrides, carbonates, or combinations thereof of one or more elements selected from the group consisting of Zr, W, B, and Mg. For example, the M2 element-containing precursor compound may be ZrO2, WO3, B2O3, MgO, or combinations thereof.

[0086] According to one embodiment, the mixing may be solid phase mixing, including mechanical mixing. The mechanical mixing is performed in a dry process. The mechanical mixing refers to the process of crushing and mixing the materials to be mixed by applying mechanical force to form a uniform mixture. Mechanical mixing can be performed using a mixing device, such as a ball mill using chemically inactivated beads, a planetary mill, a stirred ball mill, a vibrating mill, etc. At this time, in order to maximize the mixing effect, a small amount of alcohol such as ethanol, or a volatile higher fatty acid such as stearic acid can be selectively added.

[0087] The mechanical mixing is performed in an oxidizing atmosphere in order to prevent reduction of the transition metal in the transition metal supply source (eg, Ni compound), thereby achieving structural stability of the active material.

[0088] According to one embodiment, the first calcination and the second calcination are performed at different temperatures, and the temperature of the first calcination may be higher than that of the second calcination. Thus, single-crystal and single-particle lithium nickel-based transition metal oxide precursor particles can be obtained through the first calcination, and by performing the second calcination at a temperature lower than that of the first calcination, a concentration gradient region can be formed on the outer surface of the precursor particles without excessive crystal growth of the particles.

[0089] According to one embodiment, the first calcination may be performed at a temperature of 700° C. to 800° C. for 13 to 20 hours. For example, the first calcination may be performed at a temperature of 710° C. to 790° C., 720° C. to 780° C., or 730° C. to 770° C. For example, the first calcination may be performed for 14 to 19 hours, or 15 to 18 hours.

[0090] According to one embodiment, the second calcination may be performed at a temperature of 650° C. to 750° C. for 8 to 12 hours. For example, the second calcination 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 calcination may be performed for 8 to 11 hours, or 9 to 11 hours.

[0091] According to one embodiment, the first calcination may be performed at 700°C to 800°C, and the second calcination may be performed at 650°C to 750°C.

[0092] The lithium nickel-based transition metal oxide particles prepared by the above method have a single crystal and single particle shape, and by containing a concentration gradient region of Co element and Al element on the surface, unstable Ni ions (Ni(III), Ni(IV)) can be obtained to stabilize a positive electrode active material with long life characteristics.

[0093] According to another aspect, a positive electrode including the positive electrode active material is provided.

[0094] According to another aspect, a lithium secondary battery is provided, comprising the positive electrode, a negative electrode, and an electrolyte.

[0095] According to one embodiment, the electrolyte may be a liquid electrolyte, a semi-solid electrolyte or a solid electrolyte. The electrolyte is described below.

[0096] The positive electrode and the lithium secondary battery including the positive electrode can be manufactured by the following method.

[0097] First, prepare the anode.

[0098] For example, a positive electrode active material composition is prepared by mixing the above-mentioned positive electrode active material, a conductive material, a binder, and a solvent. A positive electrode plate is produced by directly coating the positive electrode active material composition on a metal current collector. Alternatively, a positive electrode plate can be produced by coating the positive electrode active material composition on a separate support and then laminating a film peeled from the support onto a metal current collector. The positive electrode is not limited to the forms listed above and may have forms other than those listed above.

[0099] The above-mentioned conductive materials can use graphite such as natural graphite, artificial graphite; carbon black; conductive tubes such as carbon nanotubes; conductive whiskers such as fluorocarbon, zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide; etc., but are not limited to these, and any material that can be used as a conductor in the relevant technical field can be used.

[0100] The binder may include, but is not limited to, vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene, mixtures thereof, metal salts, or styrene-butadiene rubber polymers. Any material known in the art as a binder may be used. As another example of a binder, lithium salts, sodium salts, calcium salts, or Na salts of the aforementioned polymers may be used.

[0101] The solvent may be N-methylpyrrolidone, acetone, or water, but is not limited thereto. Any material available in the art may be used.

[0102] The contents of the positive electrode active material, conductive material, binder, and solvent are at conventional levels used in lithium batteries. Depending on the use and configuration of the lithium battery, at least one of the conductive material, binder, and solvent may be omitted.

[0103] Then, a cathode is prepared.

[0104] For example, an anode active material composition is prepared by mixing an anode active material, a conductive material, a binder, and a solvent. The anode plate is formed by directly coating the anode active material composition on a metal current collector with a thickness of 3 μm to 500 μm and then drying it. Alternatively, the anode plate can be formed by coating the anode active material composition on a separate support and then laminating the film peeled from the support onto the metal current collector.

[0105] The anode current collector is not particularly limited as long as it does not cause a chemical change to the battery and has conductivity. For example, copper, nickel, or a material with a carbon surface treatment on the surface of copper can be used.

[0106] Any material available in the art as an anode active material for a lithium battery can be used as the anode active material. For example, it may include one or more selected from the group consisting of lithium metal, a metal alloyable with lithium, a transition metal oxide, a non-transition metal oxide, and a carbon-based material.

[0107] For example, the metal alloyable with lithium may be Si, Sn, Al, Ge, Pb, Bi, Sb, a Si-Y alloy (where 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 silicon), a Sn-Y alloy (where 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 tin), etc. The 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.

[0108] For example, the transition metal oxide may be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, etc.

[0109] For example, the non-transition metal oxide may be SnO2, SiO x (0 < x < 2), etc.

[0110] The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be amorphous, plate-like, flaky, spherical, or fibrous graphite such as natural graphite or artificial graphite, and the amorphous carbon may be soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, or the like.

[0111] The conductive material, binder, and solvent in the negative electrode active material composition may be the same as those used in the positive electrode active material composition.

[0112] The contents of the negative electrode active material, conductive material, binder and solvent are at conventional levels used in lithium batteries. Depending on the use and configuration of the lithium battery, at least one of the conductive material, binder and solvent may be omitted.

[0113] Then, a separator to be inserted between the positive electrode and the negative electrode is prepared.

[0114] The diaphragm can use any material commonly used in lithium batteries. A material with low resistance to the movement of electrolyte ions and excellent electrolyte wetting ability can be used. The diaphragm can be a single-layer film or a multilayer film, for example, can be selected from glass fiber, polyester, polytetrafluoroethylene, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene (PTFE) or a combination thereof, and can be a non-woven fabric or a woven fabric shape. In addition, a mixed multilayer film can be used, for example, a polyethylene / polypropylene double-layer diaphragm, a polyethylene / polypropylene / polyethylene three-layer diaphragm, a polypropylene / polyethylene / polypropylene three-layer diaphragm, etc. For example, a lithium ion battery can use a rollable diaphragm such as polyethylene, polypropylene, and a lithium ion polymer battery can use a diaphragm with excellent organic electrolyte wetting ability. For example, the diaphragm can be made according to the following method.

[0115] A separator composition is prepared by mixing a polymer resin, a filler, and a solvent. The separator composition is applied directly onto an electrode and then dried to form a separator. Alternatively, the separator composition is applied to a support and then dried, and the separator, peeled from the support, is laminated onto an electrode to form a separator.

[0116] The polymer resin used to manufacture the separator is not particularly limited, and any material used as an electrode plate binder can be used, for example, vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or a mixture thereof.

[0117] Then, prepare the electrolyte.

[0118] For example, the electrolyte may be an organic electrolyte. Alternatively, the electrolyte may be a solid. Examples include boron oxide and lithium oxynitride, but are not limited thereto. Any material known in the art as a solid electrolyte may be used. The solid electrolyte may be formed on the negative electrode by sputtering or other methods.

[0119] For example, an organic electrolyte can be prepared by dissolving a lithium salt in an organic solvent.

[0120] The organic solvent can be any material that can be used as an organic solvent in the relevant technical field. For example, cyclic carbonates such as propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, and dibutyl carbonate; esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone; ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, and 2-methyltetrahydrofuran; nitriles such as acetonitrile; amides such as dimethylformamide, and the like. These can be used alone or in combination. For example, a solvent containing a mixture of cyclic carbonates and chain carbonates can be used.

[0121] In addition, a gel polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or a polymer electrolyte such as LiI, Li3N, or Li x Ge y P z S α 、Li x Ge y P z S α X δ (X=F, Cl, Br) and other inorganic solid electrolytes.

[0122] The lithium salt can also be any material that can be used as a lithium salt in the relevant technical field. For example, it can be 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) (x, y are natural numbers), LiCl, LiI or a mixture thereof, etc.

[0123] like Figure 4As shown, the lithium battery 1 includes a positive electrode 3, a negative electrode 2, and a separator 4. The positive electrode 3, negative electrode 2, and separator 4 are contained in a battery case 5 by winding or folding. Then, an organic electrolyte is injected into the battery case 5 and sealed with a cap assembly 6, thereby completing the lithium battery 1. The shape of the battery case 5 can be cylindrical, square, pouch, coin, or film. For example, the lithium battery 1 can be a thin-film battery. The lithium battery 1 can be a lithium-ion battery.

[0124] A battery structure can be formed by placing a separator between the positive electrode and the negative electrode. When the battery structure is laminated in a bi-cell structure and then immersed in an electrolyte, the resulting product is housed in a bag and sealed, a lithium ion polymer battery can be completed.

[0125] Furthermore, the battery structure can be stacked to form a battery pack, which can be used in any device requiring high capacity and high output, such as laptop computers, smartphones, and electric vehicles.

[0126] Furthermore, because the lithium battery has excellent lifespan and high-rate characteristics, 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). Furthermore, it can be used in fields requiring large amounts of power storage, such as electric bicycles, power tools, and power storage systems.

[0127] The present invention will be described in further detail by the following preparation examples, examples, and comparative examples. However, the examples are provided to exemplify the present invention and the present invention is not limited thereto.

[0128] (Manufacturing positive electrode active material)

[0129] Example 1

[0130] 1000 g of a Ni(OH)2 precursor compound (containing 132 ppm of Na and 1093 ppm of S), 462.7 g of LiOH·H2O, 2 g of ZrO2, and 1.09 g of TiO2 were mechanically mixed for approximately 15 minutes. The mixed powder was then calcined at 760°C for 16 hours to synthesize lithium transition metal oxide precursor particles. 500 g of the lithium transition metal oxide precursor particles were mechanically mixed with 10 g of Co(OH)2 and 2.5 g of Al(OH)3 for 15 minutes and then calcined at 700°C for 10 hours.

[0131] Comparative Example 1

[0132] 1000 g of a Ni(OH)2 precursor compound (containing 135 ppm of Na and 1060 ppm of S), 462.7 g of LiOH·H2O, and 1.09 g of TiO2 were mechanically mixed for approximately 15 minutes. The mixed powder was then calcined at 760°C for 16 hours to synthesize lithium transition metal oxide particles.

[0133] Comparative Example 2

[0134] 1000 g of a Ni(OH)2 precursor compound (containing 133 ppm of Na and 1130 ppm of S), 462.7 g of LiOH·H2O, and 2 g of ZrO2 were mechanically mixed for approximately 15 minutes. The mixed powder was then calcined at 760°C for 16 hours to synthesize lithium transition metal oxide particles.

[0135] Comparative Example 3

[0136] 1000 g of a Ni(OH)2 precursor compound (containing 132 ppm of Na and 1125 ppm of S), 462.7 g of LiOH·H2O, 2 g of ZrO2, and 1.09 g of TiO2 were mechanically mixed for approximately 15 minutes. The mixed powder was then calcined at 760°C for 16 hours to synthesize lithium transition metal oxide particles.

[0137] Comparative Example 4

[0138] 1000 g of a Ni(OH)2 precursor compound (containing 136 ppm of Na and 1090 ppm of S), 462.7 g of LiOH·H2O, 2 g of ZrO2, and 1.09 g of TiO2 were mechanically mixed for approximately 15 minutes. The mixed powder was then calcined at 760°C for 16 hours to synthesize lithium transition metal oxide precursor particles. 500 g of the lithium transition metal oxide precursor particles and 10 g of Co(OH)2 were mechanically mixed for 15 minutes and then calcined at 700°C for 10 hours.

[0139] Comparative Example 5

[0140] 1000 g of a Ni(OH)2 precursor compound (containing 135 ppm of Na and 1088 ppm of S), 462.7 g of LiOH·H2O, 2 g of ZrO2, and 1.09 g of TiO2 were mechanically mixed for approximately 15 minutes. The mixed powder was then calcined at 760°C for 16 hours to synthesize lithium transition metal oxide precursor particles. 500 g of the lithium transition metal oxide precursor particles were mechanically mixed with 2.5 g of Al(OH)3 for 15 minutes and then calcined at 700°C for 10 hours.

[0141] Comparative Example 6

[0142] 1000 g of a Ni(OH)2 precursor compound (containing 130 ppm of Na and 1103 ppm of S), 462.7 g of LiOH·H2O, 2 g of ZrO2, and 1.09 g of TiO2 were mechanically mixed for approximately 15 minutes. The mixed powder was then calcined at 760°C for 16 hours to synthesize lithium transition metal oxide precursor particles. 500 g of the lithium transition metal oxide precursor particles were mechanically mixed with 10 g of Co(OH)2 and 10 g of Al(OH)3 for 15 minutes and then calcined at 700°C for 10 hours.

[0143] Comparative Example 7

[0144] 1000 g of a Ni(OH)2 precursor compound (containing 129 ppm of Na and 1020 ppm of S), 462.7 g of LiOH·H2O, 2 g of ZrO2, and 1.09 g of TiO2 were mechanically mixed for approximately 15 minutes. The mixed powder was then calcined at 760°C for 16 hours to synthesize lithium transition metal oxide precursor particles. 500 g of the lithium transition metal oxide precursor particles were mechanically mixed with 2.5 g of Co(OH)2 and 10 g of Al(OH)3 for 15 minutes and then calcined at 700°C for 10 hours.

[0145] (Manufacturing half-cells)

[0146] Example 2

[0147] The positive electrode active material obtained in Example 1, a conductive material, and a binder were mixed at a weight ratio of 96:2:2 to prepare a slurry. The conductive material (Super-P) was used, and polyvinylidene fluoride (PVdF) dissolved in N-methyl-2-pyrrolidone was used as the binder.

[0148] The slurry was evenly coated on the Al current collector and dried at 110°C for 2 hours to prepare the positive electrode. The loading of the plate was 11.0 mg / cm 2 , the electrode density is 3.71g / cc.

[0149] The positive electrode prepared as above was used as the working electrode, lithium foil was used as the counter electrode, and a liquid electrolyte was prepared by adding 2 wt % of vinylene carbonate (VC) to a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3 / 7, followed by adding LiPF6 as a lithium salt to a concentration of 1 M. The CR2032 half-cell was prepared according to conventional known methods.

[0150] Comparative Examples 8 to 14

[0151] Half cells were prepared by the same method as in Example 2, except that the positive electrode active materials obtained in Comparative Examples 1 to 7 were used instead of the positive electrode active material obtained in Example 1.

[0152] [Table 1]

[0153] composition Comparative Example 1 <![CDATA[Li 0.9995 Now 0.0005 In 0.999 Of 0.001 SHE 1.997 S 0.003 ]]> Comparative Example 2 <![CDATA[Li 0.9995 On 0.0005 There is no 0.999 Zr 0.001 About 1.997 With 0.003 ]]> Comparative Example 3 <![CDATA[Li 0.9995 On 0.0005 Nor 0.998 Zr 0.001 You 0.001 ON 1.997 WITH 0.003 ]]> Comparative Example 4 <![CDATA[Li 0.9995 On 0.0005 There is no 0.9787 What 0.0193 Zr 0.001 You 0.001 About 1.997 With 0.003 ]]> Comparative Example 5 <![CDATA[Li 0.9995 On 0.0005 There is no 0.9954 Al 0.0026 Zr 0.001 You 0.001 About 1.997 With 0.003 ]]> Comparative Example 6 <![CDATA[Li 0.9995 On 0.0005 There is no 0.952 What 0.026 Al 0.020 Zr 0.001 You 0.001 About 1.997 With 0.003 ]]> Comparative Example 7 <![CDATA[Li 0.9995 On 0.0005 There is no 0.9746 What 0.0024 Al 0.021 Zr 0.001 You 0.001 About 1.997 With 0.003 ]]> Example 1 <![CDATA[Li 0.9995 On 0.0005 There is no 0.9761 What 0.0193 Al 0.0026 Zr 0.001 You 0.001 About 1.997 With 0.003 ]]>

[0154] Evaluation Example 1: Evaluation of the composition of the positive electrode active material

[0155] Inductively coupled plasma (ICP) analysis was performed on the positive electrode active materials prepared in Example 1 and Comparative Examples 1 to 7 using a 700-ES (Varian) instrument. The results are shown in Table 2 below.

[0156] Referring to Table 2, the ICP analysis results for Comparative Examples 1 to 7 and Example 1 demonstrate that the introduction of Co and Al concentration gradient layers on the surface of the single-particle Ni-based positive electrode active material causes substitution of other transition metals in the active material, thereby increasing the Co and Al content and reducing the molar ratio of other transition metals. Even in vacuum analysis, ICP analysis is difficult to determine the stoichiometric value of oxygen in the material due to trace amounts of oxygen and carbon dioxide introduced into the atmosphere.

[0157] [Table 2]

[0158]

[0159] Evaluation Example 1: Evaluation of the appearance of the positive electrode active material

[0160] The scanning electron microscope (SEM) images of Example 1 and Comparative Examples 1 to 7 are shown in FIG. Figure 1 . Reference Figure 1 , Comparative Examples 1 to 3 all exhibit similar particle sizes according to the type of dopant, and when Co or Al coating is applied, a concentration gradient region is generated on the surface of the positive electrode material.

[0161] Evaluation Example 3: Evaluation of the concentration gradient region of the positive electrode active material

[0162] The positive electrode active materials obtained in Example 1 and Comparative Example 1 were photographed using a high resolution transmission electron microscope (HR-TEM) and analyzed by energy dispersive X-ray spectroscopy (EDX). Figure 2 (Example 1) and Figure 3(Comparative Example 1)

[0163] See also Figure 2 and Figure 3 In Comparative Example 1, the transition metal concentration on the active material surface is constant, but in Example 1, the concentrations of cobalt and aluminum decrease from the active material surface to the inside, while the concentration of nickel increases from the active material surface to the inside. Figure 2 , it can be confirmed that in the concentration gradient region of the lithium transition metal oxide particles of Example 1, the rate of change of the cobalt ion concentration is much greater than the rate of change of the aluminum ion concentration. Although not limited by theory, this should be due to the use of an excess of Co coating material compared to the Al coating material during the synthesis process of Example 1. Compared with the content of the Co coating material, when the content of the applicable Al coating material is equal to or greater than this, the initial capacity of the positive electrode material decreases, resulting in a decrease in energy density. It is known that cobalt ions and aluminum ions in transition metals are more conducive to the structural stability of positive electrode active materials with a layered structure than nickel ions. Therefore, a positive electrode active material containing an excess of relatively stable cobalt on the surface of the active material is beneficial to electrochemical performance.

[0164] Evaluation Example 4: Evaluation of high temperature life

[0165] The half-cells prepared in Example 2 and Comparative Examples 8 to 14 were left to rest for 10 hours, then charged to 4.3 V at 0.1 C in CC mode, and then charged in CV mode to a current corresponding to 0.05 C. The formation process was then completed by discharging to 3.0 V at 0.1 C in CC mode.

[0166] Then, it was charged to 4.3 V at 0.5 C in CC mode at high temperature (45°C), and charged in CV mode to a current corresponding to 0.05 C. It was then discharged to 3.0 V at 1 C in CC mode, and this process was repeated 50 times.

[0167] The initial charge capacity and initial discharge capacity were measured, and the initial efficiency was calculated based on them. The capacity retention rate relative to the initial discharge capacity after 50 charge and discharge cycles was calculated and shown in Table 3 below.

[0168] [Table 3]

[0169]

[0170] Referring to Comparative Examples 8 to 10, the initial capacity of the positive electrode active material did not differ depending on the type of dopant. Subsequently, the results of confirming the effect of introducing a concentration gradient layer showed that in Comparative Example 11, which introduced a Co concentration gradient layer, the initial discharge capacity and initial efficiency increased, but in Comparative Example 12, which introduced an Al concentration gradient layer, the initial discharge capacity and initial efficiency decreased. Furthermore, it was confirmed that in Comparative Example 13, which used a positive electrode active material prepared by adding equal amounts of Co and Al, the initial discharge capacity decreased, and in Comparative Example 14, which used a positive electrode active material prepared by adding an Al content higher than Co, the capacity retention rate was insufficient.

[0171] In addition, it was confirmed that in Example 2, when a positive electrode active material was used in which the concentration gradient layer contained both Co and Al elements and the two elements had a concentration gradient, the initial discharge capacity and initial efficiency decreased slightly relative to the Co concentration gradient sample alone, but from the perspective of life at 45°C, they were significantly improved compared to the Co concentration gradient sample alone (Comparative Example 11), the Al concentration gradient sample alone (Comparative Example 12), the sample with equal amounts of Co and Al added (Comparative Example 13), and the sample with Al added at a content higher than Co (Comparative Example 14).

[0172] This improvement in life characteristics should be due to the significant effect of the concentration of Co and Al and their concentration gradient.

[0173] The preferred embodiments of the present invention have been described above with reference to the accompanying drawings and examples, but these are merely illustrative and those skilled in the art will appreciate that various modifications and equivalent embodiments may be implemented. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A positive electrode active material comprising: Lithium nickel-based transition metal oxide particles comprising greater than or equal to 96 mol % nickel and no manganese, wherein the proportion of titanium (Ti) substituted into transition metal sites in the crystal structure is from 400 ppm to less than 1000 ppm; and A concentration gradient region, wherein the concentrations of aluminum (Al) atoms and cobalt (Co) atoms change from the surface of the lithium nickel-based transition metal oxide particle to the center of the particle, The absolute value of the slope of the change in the cobalt atom concentration (A) and the absolute value of the slope of the change in the aluminum atom concentration (B) in the concentration gradient region satisfy A>B.

2. The positive electrode active material according to claim 1, wherein It has a concentration gradient in which the concentrations of aluminum atoms and cobalt atoms in the concentration gradient region decrease from the outer surface of the concentration gradient region toward the center of the particle.

3. The positive electrode active material according to claim 1, wherein In the concentration gradient region, the concentration of cobalt atoms is higher than the concentration of aluminum atoms.

4. The positive electrode active material according to claim 1, wherein The lithium nickel-based transition metal oxide particles further include sodium (Na) atoms and sulfur (S) atoms.

5. The positive electrode active material according to claim 4, wherein The total amount of the sodium (Na) atoms and the sulfur (S) atoms included in the lithium nickel-based transition metal oxide particles is 300 ppm to 1500 ppm.

6. The positive electrode active material according to claim 4, wherein In the crystals of the lithium nickel-based transition metal oxide particles, some lithium (Li) atoms are replaced by sodium (Na) atoms, and some oxygen (O) atoms are replaced by sulfur (S) atoms.

7. The positive electrode active material according to claim 1, wherein In the concentration gradient region, the concentration of nickel atoms increases from the particle surface toward the particle center.

8. The positive electrode active material according to claim 1, wherein The thickness of the concentration gradient region is 0.6 or less of the particle radius.

9. The positive electrode active material according to claim 1, wherein The concentration gradient region has a thickness less than or equal to 300 nm from the surface of the lithium nickel-based transition metal oxide particle toward the center of the particle.

10. The positive electrode active material according to claim 1, wherein The lithium nickel-based transition metal oxide particles are single particles or single crystals and secondary particles formed by aggregation of multiple single particles.

11. The positive electrode active material according to claim 11, wherein In the secondary particles formed by the aggregation of the plurality of single particles, a cobalt coating exists on the surfaces of the plurality of single particles.

12. The positive electrode active material according to claim 1, wherein The average particle size of the lithium nickel-based transition metal oxide particles is 0.1 μm to 20 μm.

13. The positive electrode active material according to claim 1, wherein The lithium nickel-based transition metal oxide particles are represented by the following chemical formula 1: <Chemical Formula 1> Li 1-a So a Ni 1-x-y-α-β Co x Al y M1 α M2 β O 2-b S b In the chemical formula 1, M1 and M2 are each independently one or more elements selected from the group consisting of Zr, W, Ti, Sr, Ba, Ce, B, Mg and Bi, 0 <a≤0.01、0<α≤0.003、0<β≤0.003、0<x≤0.03、0<y≤0.01、0<b≤0.01。 14. The positive electrode active material according to claim 13, wherein M1 is Ti and M2 is Zr.

15. The positive electrode active material according to claim 1, wherein 0 <x≤0.02、0<y≤0.005。 16. A method for producing a positive electrode active material, comprising: After mixing a precursor compound containing nickel, a precursor compound containing lithium, a precursor compound containing M1, and a precursor compound containing M2, a lithium nickel-based transition metal oxide precursor is obtained by a first calcination; as well as After solid-phase mixing of the lithium nickel-based transition metal oxide precursor compound, the Co precursor compound, and the Al precursor compound, lithium nickel-based transition metal oxide particles are obtained by a second calcination. The positive electrode active material includes a concentration gradient region, wherein the concentration of aluminum (Al) atoms and cobalt (Co) atoms changes from the surface of the lithium nickel-based transition metal oxide particle to the center of the particle, The absolute value of the slope of the change in the cobalt atom concentration (A) and the absolute value of the slope of the change in the aluminum atom concentration (B) in the concentration gradient region satisfy A>B.

17. The method for producing a positive electrode active material according to claim 16, wherein: The temperature of the first calcination is higher than the temperature of the second calcination.

18. The method for producing a positive electrode active material according to claim 16, wherein: The first calcination is performed at 700°C to 800°C, and the second calcination is performed at 650°C to 750°C.

19. A lithium secondary battery comprising: A positive electrode comprising the positive electrode active material according to any one of claims 1 to 15; negative electrode; as well as electrolytes.

20. The lithium secondary battery according to claim 19, wherein The electrolyte is a liquid electrolyte, a semi-solid electrolyte or a solid electrolyte.

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