Positive electrode active material, method for manufacturing the same, and lithium secondary battery containing the positive electrode active material

Abstract

The present invention relates to a positive electrode active material containing lithium nickel-based transition metal oxide particles that contain 96 mol% or more of nickel, do not contain manganese, and have a ratio of titanium (Ti) substituted in transition metal sites in the crystal structure of 400 ppm to less than 1,000 ppm, wherein the lithium nickel-based transition metal oxide particles include a concentration gradient region in which the concentrations of aluminum (Al) and cobalt (Co) atoms change from the surface toward the center of the particle, and in the concentration gradient region, the absolute value of the slope of change of cobalt atom concentration (A) and the absolute value of the slope of change of aluminum atom concentration (B) satisfy A > B, a method for producing the same, and a secondary battery containing the same.

Description

[Technical 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 producing the same. [Background technology]

[0002] Since its commercialization by Sony in 1991, lithium-ion batteries have seen a surge in demand across a wide range of applications, from small consumer electronics like mobile IT products to medium and large electric vehicles and energy storage systems. In particular, low-cost, high-energy cathode materials are essential for medium and large electric vehicles and energy storage systems, but cobalt, the main raw material for single-crystal LiCoO2 (LCO), the cathode active material currently on the market, is expensive.

[0003] Therefore, recently, LiNi has been used as a positive electrode active material for medium- and large-sized secondary batteries, in which some of the Co is replaced with other transition metals 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 such NCM and NCA-based cathode active materials have the advantages of inexpensive nickel 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, such Ni-based cathode active materials are manufactured by mixing a transition metal compound precursor synthesized by coprecipitation with a lithium source and then synthesizing it in solid phase. However, Ni-based cathode materials synthesized in this way exist in the form of secondary particles in which small primary particles are aggregated, and there is a problem that micro-cracks are generated inside the secondary particles during the long-term charge-discharge process. Micro-cracks induce side reactions with new interfaces of the cathode active material and the electrolyte, resulting in battery performance degradation such as decreased stability due to gas generation and decreased battery performance due to electrolyte depletion. Furthermore, achieving high energy density requires increasing the electrode density (>3.3 g / cc), but this induces the decay of secondary particles and the depletion of the electrolyte due to side reactions with the electrolyte, leading to a sharp decline in the initial lifetime. In short, this means that Ni-based cathode active materials in the form of secondary particles synthesized by the conventional coprecipitation method cannot achieve high energy density.

[0004] To address the problems of the aforementioned secondary particle form of Ni-based cathode active materials, research has recently been conducted on single-particle Ni-based cathode active materials. Single-crystal Ni-based cathode active materials can achieve excellent electrochemical performance without particle breakdown when the electrode density increases (>3.3 g / cc) to realize high energy density. However, such single-crystal Ni-based cathode active materials exhibit unstable Ni during electrochemical evaluation. 3+ Ni 4+ The study revealed that ions can lead to structural and / or thermal instability, resulting in reduced battery stability. As a result, there is still a demand for positive electrode active materials for the development of lithium secondary batteries with high energy density and long lifespan characteristics. [Overview of the project] [Problems that the invention aims to solve]

[0005] The present invention aims to provide a positive electrode active material that ensures high energy density and long lifespan. [Means for solving the problem]

[0006] In one embodiment, the material contains lithium nickel-based transition metal oxide particles that contain 96 mol% or more of nickel, do not contain manganese, and have a ratio of titanium (Ti) substituted at transition metal sites in the crystal structure of less than 400 ppm to 1,000 ppm. The lithium nickel-based transition metal oxide particle includes a concentration gradient region in which the concentrations of aluminum (Al) and cobalt (Co) atoms change from the surface toward the center of the particle. A positive electrode active material is provided such that, in the aforementioned concentration gradient region, the absolute value of the slope of change in cobalt atom concentration (A) and the absolute value of the slope of change in aluminum atom concentration (B) satisfy A > B.

[0007] In another embodiment, a step of mixing a nickel element-containing precursor compound, a lithium element-containing precursor compound, an M1 element-containing precursor compound, an M2 element-containing precursor compound, a sodium precursor compound, and an S element-containing precursor compound, and then performing a first calcination to obtain a lithium nickel-based transition metal oxide precursor compound, The process includes the step of solid-phase mixing the lithium nickel-based transition metal oxide precursor compound, a Co precursor compound, and an Al precursor compound, followed by a second calcination to obtain lithium nickel-based transition metal oxide particles. The lithium nickel-based transition metal oxide particle includes a concentration gradient region in which the concentrations of aluminum (Al) and cobalt (Co) atoms change from the surface toward the center of the particle. A method for producing a positive electrode active material is provided, wherein in the aforementioned concentration gradient region, the absolute value of the slope of change in cobalt atom concentration (A) and the absolute value of the slope of change in aluminum atom concentration (B) satisfy A > B.

[0008] In another embodiment, a positive electrode containing the aforementioned positive electrode active material, The negative electrode and, A lithium secondary battery including an electrolyte is provided.

Advantages of the Invention

[0009] The cathode active material according to one aspect contains 96 mol% or more of nickel, does not contain a manganese element, the ratio of titanium (Ti) substituted at the transition metal site in the crystal structure is from 400 ppm to less than 1,000 ppm, and has a concentration gradient region having a Co and Al concentration gradient. In the concentration gradient region, the absolute value (A) of the change gradient of the cobalt atom concentration and the absolute value (B) of the change gradient of the aluminum atom concentration satisfy A > B, so that particles are not collapsed even at a high electrode density, and by stabilizing Ni ions, it is possible to ensure increased capacity per unit volume and life stability.

Brief Description of the Drawings

[0010] [Figure 1] It is a SEM photograph of the cathode active materials obtained in Example 1 and Comparative Examples 1 to 7 according to an embodiment of the present invention. [Figure 2] It is a drawing showing the HR-TEM analysis result indicating the ratio of elements in the direction from the surface to the center of particles of the cathode active material obtained in Example 1 according to an embodiment of the present invention. [Figure 3] It is a drawing showing the HR-TEM analysis result indicating the ratio of elements in the direction from the surface to the center of particles of the cathode active material obtained in Comparative Example 1. [Figure 4] It is a schematic diagram of a lithium battery according to an exemplary embodiment.

Modes for Carrying Out the Invention

[0011] The present inventive concept described below can be subjected to various transformations and can have various embodiments. Specific embodiments are illustrated in the drawings and will be described in detail in the detailed description. However, this is not intended to limit the present inventive concept to specific embodiments, and it should be understood to include all transformations, equivalents, or alternatives included in the technical scope of the present inventive concept.

[0012] The terms used below are used solely to describe specific embodiments and are not intended to limit the scope of this original idea.

[0013] A singular expression includes plural expressions unless explicitly stated otherwise in the context. Hereafter, terms such as “includes” or “has” indicate the presence of a feature, number, stage, operation, component, part, ingredient, material, or combination thereof as described in the specification, and should be understood not to preemptively exclude the possibility of the presence or addition of one or more other features, numbers, stages, operations, components, parts, ingredients, materials, or combinations thereof.

[0014] The " / " used below may be interpreted as either "and" or "or," depending on the context.

[0015] As used below, the term "concentration gradient region" should be understood to refer to a region in which the concentration of an atom changes linearly or nonlinearly.

[0016] The term "concentration gradient slope" used below should be understood to refer to the change in atomic concentration from the outer surface of the concentration gradient region toward the center of the particle.

[0017] In the drawings, thicknesses are shown enlarged or reduced to clearly represent various layers and regions. Throughout the specification, similar parts are denoted by the same reference numerals. Throughout the specification, when a layer, film, region, plate, etc., is described as being "on top of" 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., are used to describe various components, but components are not limited by these terms. The terms are used solely to distinguish one component from another.

[0018] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as they would ordinarily be understood by a person of ordinary skill in the art to which this invention pertains. Furthermore, terms defined in commonly used dictionaries should be interpreted to have the meaning consistent with their meaning in the context of the relevant art and the subject matter of this invention, and should not be interpreted ideally or excessively formally.

[0019] While specific embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are not currently anticipated or foreseeable may arise from the applicant or those skilled in the art. Accordingly, the attached claims, which may be filed and amended, are intended to include all such alternatives, modifications, variations, improvements, and substantial equivalents.

[0020] The following describes in more detail a positive electrode active material according to exemplary embodiments, a method for producing the same, and a lithium secondary battery including a positive electrode containing the same.

[0021] A positive electrode active material according to one embodiment includes lithium nickel-based transition metal oxide particles containing 96 mol% or more of nickel, no manganese, and a ratio of titanium (Ti) substituted at transition metal sites in the crystal structure of less than 400 ppm to 1,000 ppm. The lithium nickel-based transition metal oxide particles include a concentration gradient region in which the concentrations of aluminum (Al) and cobalt (Co) atoms change from the surface toward the center of the particle, and in the concentration gradient region, the absolute value of the slope of change of cobalt atom concentration (A) and the absolute value of the slope of change of aluminum atom concentration (B) can satisfy A > B.

[0022] 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 1.5 mol% or less, 1.0 mol% or less, or 0.5 mol% of aluminum atoms.

[0023] According to one embodiment, the lithium nickel-based transition metal oxide particles may contain 2.5 mol% or less of cobalt atoms. For example, the lithium nickel-based transition metal oxide particles may contain 1 mol% to 2 mol%, or 1.5 mol% to 2 mol%, of cobalt atoms.

[0024] According to one embodiment, in the concentration gradient region, the concentrations of aluminum atoms and cobalt atoms can have a concentration gradient that decreases from the outer surface of the concentration gradient region toward the center of the particle.

[0025] According to one embodiment, in the concentration gradient region, the concentration of cobalt atoms is higher than the concentration of aluminum atoms. This significantly improves the lifetime characteristics while minimizing the decrease in initial capacity.

[0026] Lithium transition metal oxide particles according to one embodiment of the present invention include concentration gradient regions in which the concentrations of aluminum and cobalt atoms change in local regions of the particles. Compared to positive electrode active materials having a concentration gradient throughout the particles, this can improve capacity and lifetime characteristics. Furthermore, by making the change in cobalt atom concentration greater than the change in aluminum atom concentration in the concentration gradient region, the particles have structural stability and improved conductivity during charging and discharging, thereby improving lifetime characteristics without reducing initial discharge efficiency due to nickel dissolution or degrading high-power characteristics. Moreover, when the magnitude of the absolute value of the slope of change in cobalt atom concentration and the absolute value of the slope of change in aluminum atom concentration satisfy the aforementioned range, the lifetime characteristic improvement effect can be achieved while suppressing the decrease in output characteristics due to the increase in lithium-ion resistance caused by the increase in the thickness of the concentration gradient region.

[0027] According to one embodiment, in the concentration gradient region, the concentration of nickel atoms may increase from the surface of the particle towards the center of the particle. For example, the concentration of nickel atoms decreases towards the surface of the particle in the concentration gradient region, and the concentration does not change in regions other than the concentration gradient region.

[0028] According to one embodiment, the concentration gradient region may have a thickness of 0.6 or less of the particle radius. For example, the concentration gradient region may have a thickness of 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 satisfies the above thickness range, it does not act as a resistance layer against lithium migration, and therefore does not induce a decrease in output characteristics.

[0029] According to one embodiment, the concentration gradient region can have a thickness of 300 nm or less from the surface of the lithium nickel-based transition metal oxide particle toward the center of the particle. For example, the thickness of the concentration gradient region is 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 center of the particle. When the thickness range is satisfied, it does not act as a resistive layer against lithium migration, so a decrease in output characteristics is not induced.

[0030] According to one embodiment, the lithium nickel-based transition metal oxide particles may further contain sodium (Na) and sulfur (S) atoms.

[0031] According to one embodiment, in the crystal of lithium nickel-based transition metal oxide particles, some of the lithium (Li) atoms are replaced by sodium (Na) atoms, and some of the oxygen (O) atoms are replaced by sulfur (S) atoms.

[0032] The substitution of some lithium atoms with sodium atoms suppresses crystal collapse even when lithium is desorbed from the crystal structure during the charging process. The introduction of sodium atoms increases the crystal volume and thus the lithium mobility, resulting in improved output characteristics. Furthermore, the substitution of some oxygen atoms with sulfur (S) atoms increases the bonding strength between the transition metal and the sulfur atoms, suppressing structural transitions in the lithium nickel oxide crystal during the charging and discharging process of the lithium secondary battery, and improving the structural stability of the lithium nickel oxide crystal. As a result, the lifespan characteristics may be improved.

[0033] According to one embodiment, the total amount of sodium (Na) and sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles is 300 ppm to 1,500 ppm. For example, the total amount of sodium (Na) and sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles is 400 ppm to 1,500 ppm. For example, the total amount of sodium (Na) and sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles is 500 ppm to 1,500 ppm. For example, the total amount of sodium (Na) and sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles is 600 ppm to 1,500 ppm. For example, the total amount of sodium (Na) and sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles is 700 ppm to 1,500 ppm. For example, the total amount of sodium (Na) and sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles is 800 ppm to 1,500 ppm. For example, the total amount of sodium (Na) and sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles is 900 ppm to 1,500 ppm. For example, the total amount of sodium (Na) and sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles is 1,000 ppm to 1,500 ppm. For example, the total amount of sodium (Na) and sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles is 1,100 ppm to 1,500 ppm. For example, the total amount of sodium (Na) and sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles is 1,200 ppm to 1,500 ppm. For example, the total amount of sodium (Na) and sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles is 1,000 ppm to 1,400 ppm. For example, the total amount of sodium (Na) and sulfur (S) atoms is 1,100 ppm to 1,400 ppm. For example, the total amount of sodium (Na) and sulfur (S) atoms is 1,200 ppm to 1,400 ppm.When the total amount of sodium and sulfur atoms satisfies the aforementioned range, crystal breakdown during the charging and discharging process is prevented, and an improvement in lifespan characteristics can be expected.

[0034] According to one embodiment, the ratio of titanium contained in the lithium nickel-based transition metal oxide particles is 500 ppm to 900 ppm, or 500 ppm to 800 ppm.

[0035] According to one embodiment, the lithium nickel-based transition metal oxide particles are single particles or single crystals, and secondary particles formed by the aggregation of multiple single particles.

[0036] For example, the lithium nickel-based transition metal oxide particles may be single particles. A single particle is a concept distinct from a secondary particle formed by the aggregation of multiple particles, or a particle formed by the aggregation of multiple particles with a coating around the aggregate. By having the lithium nickel-based transition metal oxide particles in the form of single particles, particle collapse can be prevented even at high electrode densities. Therefore, not only can a high energy density be realized for the positive electrode active material containing lithium nickel-based transition metal oxide particles, but particle collapse due to rolling during electrode plate formation can also be prevented, resulting in excellent lifetime characteristics.

[0037] According to one embodiment, the lithium nickel-based transition metal oxide particles can have single crystals. A single crystal is a concept distinct from a single particle. A single particle refers to a particle formed as one, regardless of the type and number of crystals inside, while a single crystal simply means having one crystal within the particle. Such single-crystal lithium nickel-based transition metal oxide particles not only have very high structural stability but also conduct lithium ions more easily than polycrystalline materials, thus exhibiting superior fast-charging characteristics compared to polycrystalline active materials.

[0038] According to one embodiment, the lithium nickel-based transition metal oxide particles may be secondary particles in which a plurality of single particles are aggregated. The secondary particles in which a plurality of single particles are aggregated are in a form in which two or more single crystal single particles are aggregated. At this time, the ratio of the secondary particles contained in the positive electrode active material is less than 30% of the entire lithium nickel-based transition metal oxide particles. For example, the ratio of the secondary particles contained in the positive electrode active material is 29% or less, 28% or less, 27% or less, 26% or less, or 25% or less with respect to the entire lithium nickel-based transition metal oxide particles.

[0039] According to one embodiment, the lithium nickel-based transition metal oxide particles are single crystals and single particles. By being formed into single crystals and single particles, they are structurally stable and it is possible to realize a high-density electrode, so that a lithium secondary battery containing the same can have improved life characteristics and high energy density at the same time.

[0040] According to one embodiment, the average particle diameter (D 50 ) of the lithium nickel-based transition metal oxide particles is 0.1 μm to 20 μm. Here, the average particle diameter (D 50 ) means the particle diameter of the particles occupying 50% in ascending order of particle size in particle size distribution analysis (PSD). For example, the average particle diameter (D 50 ) is 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 diameter of the lithium nickel-based transition metal oxide particles belongs to the above range, the desired energy density per volume can be realized. When the average particle diameter of the lithium nickel-based transition metal oxide particles exceeds 20 μm, it causes a sharp decrease in charge-discharge capacity, and when it is 1 μm or less, it is difficult to obtain the desired energy density per volume.

[0041] According to one embodiment, the lithium nickel-based transition metal oxide particles are represented by the following Chemical Formula 1: (Chemical Formula 1) Li 1-a Naa Ni 1-x-y-α-β Co x Al y M1 α M2 β O 2-b S b

[0042] In the aforementioned chemical formula 1, M1 and M2 are one or more elements independently 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である。

[0043] According to one embodiment, M1 is one or more elements selected from the group consisting of Ti, Sr, Ba, Ce, and Bi. For example, M1 is Ti.

[0044] According to one embodiment, M2 is one or more elements selected from the group consisting of Zr, W, B, and Mg. For example, M2 is Zr.

[0045] According to one embodiment, M1 is Ti and M2 is Zr.

[0046] According to one embodiment, a is 0 <a≦0.005または0<a≦0.001である。

[0047] According to one embodiment, b is 0 < β ≤ 0.005 or 0 < β ≤ 0.003.

[0048] According to one embodiment, α is 0 < α ≤ 0.002 or 0 < α ≤ 0.001.

[0049] According to one embodiment, β is 0 < β ≤ 0.002 or 0 < β ≤ 0.001.

[0050] According to one embodiment, α and β are also identical to each other.

[0051] According to one embodiment, x satisfies 0 < x ≤ 0.025 or 0 < x ≤ 0.02.

[0052] According to one embodiment, y satisfies 0 < y ≤ 0.009, 0 < y ≤ 0.008, 0 < y ≤ 0.007, 0 < y ≤ 0.006, or 0 < y ≤ 0.005.

[0053] According to one embodiment, 0 < x ≤ 0.02 and 0 < y ≤ 0.005.

[0054] When the lithium nickel-based transition metal oxide particles according to one embodiment of the present invention satisfy the chemical formula 1, improvement in life characteristics can be expected without reduction in capacity and output characteristics.

[0055] Hereinafter, a method for manufacturing a positive electrode active material according to one aspect will be described in detail.

[0056] A method for manufacturing a positive electrode active material according to one aspect includes mixing a nickel element-containing precursor compound, a lithium element-containing precursor compound, a M1 element-containing precursor compound, and a M2 element-containing precursor compound, and then performing a first firing to obtain a lithium nickel-based transition metal oxide precursor compound; and solid-phase mixing the lithium nickel-based transition metal oxide precursor compound with a Co precursor compound and an Al precursor compound, and then performing a second firing to obtain lithium nickel-based transition metal oxide particles. At this time, the lithium nickel-based transition metal oxide particles include a concentration gradient region in which the concentrations of aluminum (Al) and cobalt (Co) atoms change from the surface of the particles toward the center of the particles, and in the concentration gradient region, the absolute value (A) of the change gradient of the cobalt atom concentration and the absolute value (B) of the change gradient of the aluminum atom concentration can satisfy A > B.

[0057] Refer to the foregoing content regarding the lithium nickel-based transition metal oxide particles.

[0058] According to one embodiment, a nickel element-containing precursor compound is a compound that can provide nickel element and includes, but is not limited to, nickel hydroxide, oxide, nitride, carbonite, acetate, or a combination thereof. For example, the nickel element-containing precursor compound is NiO, Ni(OH)2, NiCO3, or a combination thereof. Furthermore, the nickel element-containing precursor compound may contain Na element in an amount greater than 0 and less than or equal to 300 ppm, and S element in an amount of 300 to 1200 ppm. For example, the nickel element-containing precursor compound may contain Na element in an amount of 100 to 300 ppm and S element in an amount of 400 to 1200 ppm. For example, the nickel element-containing precursor compound may contain Na element in an amount of 100 to 300 ppm and S element in an amount of 600 to 1200 ppm. For example, the nickel element-containing precursor compound may contain Na element in an amount of 100 to 300 ppm and S element in an amount of 700 to 1200 ppm. For example, the nickel element-containing precursor compound contains 100 to 300 ppm of sodium and 800 to 1200 ppm of sulfur. For example, the nickel element-containing precursor compound contains 100 to 300 ppm of sodium and 900 to 1200 ppm of sulfur. For example, the nickel element-containing precursor compound contains 100 to 300 ppm of sodium and 1000 to 1200 ppm of sulfur.

[0059] According to one embodiment, the lithium element-containing precursor compound includes, but is not limited to, lithium hydroxide, oxide, nitride, carbonite, or a combination thereof. For example, the lithium element-containing precursor compound is LiOH·H2O, Li2CO3, or a combination thereof.

[0060] According to one embodiment, the M1 element-containing precursor compound includes, but is not limited to, hydroxides, oxides, nitrides, carbonides, or combinations thereof of one or more elements selected from the group consisting of Ti, Sr, Ba, Ce, and Bi. For example, the M1 element-containing precursor compound is TiO2, Sr(OH)2, BaO, Ce2O3, Bi(OH)3, or a combination thereof.

[0061] According to one embodiment, the M2 element-containing precursor compound includes, but is not limited to, hydroxides, oxides, nitrides, carbonides, 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 is ZrO2, WO3, B2O3, MgO, or a combination thereof.

[0062] According to one embodiment, the mixing is performed as solid-phase mixing, and includes mechanical mixing. The mechanical mixing is performed dry. The mechanical mixing involves applying mechanical force to crush and mix the substances to be mixed, forming a homogeneous mixture. The mechanical mixing is performed using a mixing device such as a ball mill, planetary mill, stirred ball mill, or vibrating mill that uses chemically inert beads. In this case, small amounts of alcohol such as ethanol or volatile higher fatty acids such as stearic acid can be selectively added to maximize the mixing effect.

[0063] The aforementioned mechanical mixing is carried out in an oxidizing atmosphere, which prevents the reduction of the transition metal in the transition metal source (e.g., Ni compound) and ensures the structural stability of the active material.

[0064] According to one embodiment, the first and second firings are performed at different temperatures, with the temperature for the first firing being higher than the temperature for the second firing. This allows for the production of lithium nickel-based transition metal oxide precursor particles in single crystal and single particle form through the first firing, and by performing the second firing at a lower temperature than the first firing, a concentration gradient region can be formed from the outer surface of the precursor particles without excessive crystal growth of the particles.

[0065] According to one embodiment, the first firing may be carried out at a temperature of 700°C to 800°C for 13 to 20 hours. For example, the first firing may be carried out at a temperature of 710°C to 790°C, 720°C to 780°C, or 730°C to 770°C. For example, the first firing may be carried out for 14 to 19 hours, or 15 to 18 hours.

[0066] According to one embodiment, the second firing may be carried out at a temperature of 650°C to 750°C for 8 to 12 hours. For example, the second firing may be carried out 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 carried out for 8 to 11 hours, or 9 to 11 hours.

[0067] According to one embodiment, the first firing is performed at 700°C to 800°C, and the second firing is performed at 650°C to 750°C.

[0068] The lithium nickel-based transition metal oxide particles produced by the aforementioned method have single crystal and single-particle forms, and by including concentration gradient regions of Co and Al elements on their surfaces, unstable Ni ions (Ni(III), Ni(IV)) are stabilized, resulting in a positive electrode active material with long-life characteristics.

[0069] In another embodiment, a positive electrode containing the aforementioned positive electrode active material is provided.

[0070] In yet another embodiment, a lithium secondary battery is provided, comprising the positive electrode, the negative electrode, and the electrolyte.

[0071] According to one embodiment, the electrolyte is a liquid electrolyte, a semi-solid electrolyte, or a solid electrolyte. See below for details on electrolytes.

[0072] The positive electrode and the lithium secondary battery containing it are manufactured by the following method.

[0073] First, the positive electrode is prepared.

[0074] For example, a positive electrode active material composition is prepared by mixing the aforementioned positive electrode active material, conductive material, binder, and solvent. The positive electrode active material composition is directly coated onto a metal current collector to produce a positive electrode plate. Alternatively, the positive electrode active material composition may be cast onto a separate support, and then the film peeled off the support is laminated onto a metal current collector to produce a positive electrode plate. The positive electrode is not limited to the above-described form and may take other forms.

[0075] The aforementioned conductive materials include graphite such as natural graphite and artificial graphite; carbon black; conductive tubes such as carbon nanotubes; conductive whiskers such as fluorocarbons, zinc oxide, and potassium titanate; and conductive metal oxides such as titanium oxide. However, the materials are not limited to these, and any material that can be used as a conductive material in the relevant technical field can be used.

[0076] Examples of binders used include vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene, mixtures thereof, metal salts, or styrene-butadiene rubber polymers, but are not limited to these; any binder usable in the relevant art can be used. Other examples of binders include lithium salts, sodium salts, calcium salts, or Na salts of the aforementioned polymers.

[0077] The aforementioned solvent may be N-methylpyrrolidone, acetone, or water, but is not limited to these; any solvent usable in the art can be used.

[0078] The content of the positive electrode active material, conductive material, binder, and solvent is at levels typically used in lithium batteries. Depending on the application and configuration of the lithium battery, one or more of the conductive material, binder, and solvent may be omitted.

[0079] Next, the negative electrode is prepared.

[0080] For example, a negative electrode active material, a conductive material, a binder, and a solvent are mixed to prepare a negative electrode active material composition. The negative electrode active material composition is directly coated onto a metal current collector having a thickness of 3 μm to 500 μm and dried to produce a negative electrode plate. Alternatively, the negative electrode active material composition may be cast onto a separate support, and then the film peeled off the support is laminated onto a metal current collector to produce a negative electrode plate.

[0081] The negative electrode current collector is not particularly limited as long as it is conductive without inducing a chemical change in the battery, and for example, copper, nickel, or copper surface-treated with carbon can be used.

[0082] The negative electrode active material can be any material that is usable as a negative electrode active material for lithium batteries in the art. 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.

[0083] For example, metals that can be alloyed with lithium include Si, Sn, Al, Ge, Pb, Bi, Sb, Si-Y alloys (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 not Si), and Sn-Y alloys (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 not Sn). The element Y includes Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, R u, 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.

[0084] For example, the transition metal oxides include lithium titanium oxide, vanadium oxide, and lithium vanadium oxide.

[0085] For example, the non-transition metal oxides are SnO2, SiO2 x (0 <x<2)などである。

[0086] The carbon-based material is crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon is graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, while the amorphous carbon is soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, calcined coke, etc.

[0087] In the negative electrode active material composition, the conductive material, binder, and solvent can be the same as those used in the positive electrode active material composition.

[0088] The aforementioned concentrations of the negative electrode active material, conductive material, binder, and solvent are at levels typically used in lithium batteries. Depending on the application and configuration of the lithium battery, one or more of the aforementioned conductive material, binder, and solvent may be omitted.

[0089] Next, a separator is prepared to be inserted between the positive electrode and the negative electrode.

[0090] Any separator commonly used in lithium batteries can be used. A separator with low resistance to electrolyte ion movement and excellent electrolyte moisture absorption capacity is used. The separator is a single or multilayer film, selected from, for example, glass fiber, polyester, Teflon®, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in nonwoven or woven form. Mixed multilayer films such as polyethylene / polypropylene two-layer separators, polyethylene / polypropylene / polyethylene three-layer separators, and polypropylene / polyethylene / polypropylene three-layer separators may also be used. For example, a rollable separator such as polyethylene or polypropylene is used in lithium-ion batteries, and a separator with excellent organic electrolyte impregnation capacity is used in lithium-ion polymer batteries. For example, the separator is manufactured by the following method.

[0091] A separator composition is prepared by mixing a polymer resin, a filler, and a solvent. The separator composition is directly coated onto the top of the electrode and dried to form a separator. Alternatively, the separator composition may be cast onto a support, dried, and then the separator film, peeled off the support, is laminated onto the top of the electrode to form a separator.

[0092] The polymer resin used in the manufacture of the separator is not particularly limited, and any substance used as a binder for electrode plates can be used. For example, vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or mixtures thereof can be used.

[0093] Next, electrolytes are prepared.

[0094] For example, the electrolyte may also be an organic electrolyte. Furthermore, the electrolyte may also be a solid. For example, boron oxide, lithium oxynitride, etc., but it is not limited to these; any material usable as a solid electrolyte in the relevant art can be used. The solid electrolyte may be formed on the negative electrode by methods such as sputtering.

[0095] For example, organic electrolytes are produced by dissolving lithium salts in organic solvents.

[0096] Any organic solvent that is usable as an organic solvent in the art can be used. Examples include cyclic carbonates such as propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, and vinylene carbonate; linear carbonates such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl 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; and amides such as dimethylformamide. These can be used individually or in combination. For example, a solvent mixture of cyclic carbonates and linear carbonates can be used.

[0097] Furthermore, there are gel-like polymer electrolytes such as polyethylene oxide and polyacrylonitrile impregnated with an electrolyte solution, as well as LiI, Li3N, and Li x Ge y P z S α Li x Ge y P z S α X δInorganic solid electrolytes such as (X is F, Cl, Br) can be used.

[0098] Any of the aforementioned lithium salts can be used as lithium salts in the relevant art. 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.

[0099] As shown in Figure 4, 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 wound or folded and housed in a battery case 5. Next, 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 can be cylindrical, rectangular, pouch-type, coin-type, or thin-film type. For example, the lithium battery 1 is a thin-film type battery. The lithium battery 1 is also a lithium-ion battery.

[0100] A separator can be placed between the positive electrode and the negative electrode to form a battery structure. After the battery structure is stacked in a bicell structure, it is impregnated with an organic electrolyte, and the resulting product is contained in a pouch and sealed to complete a lithium-ion polymer battery.

[0101] Furthermore, multiple battery structures can be stacked to form a battery pack, and such battery packs can be used in all devices that require high capacity and high output. For example, they can be used in notebook computers, smartphones, electric vehicles (EVs), and the like.

[0102] Furthermore, because the lithium battery exhibits excellent lifespan and high efficiency 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). It can also be used in fields requiring large amounts of power storage. For example, it can be used in electric bicycles, power tools, and power storage systems.

[0103] The present invention will be described in more detail through the following manufacturing examples, embodiments, and comparative examples. However, the embodiments are for illustrative purposes only and do not limit the scope of the present invention.

[0104] (Manufacturing of positive electrode active material) Example 1 1000 g of Ni(OH)2 precursor compound (containing 132 ppm of Na and 1093 ppm of S in the precursor) was mechanically mixed with 462.7 g of LiOH·H2O, 2 g of ZrO2, and 1.09 g of TiO2 for about 15 minutes. The mixed powder was 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 to synthesize the next product.

[0105] Comparative Example 1 1000 g of Ni(OH)2 precursor compound (containing 135 ppm of Na and 1060 ppm of S in the precursor) was mechanically mixed with 462.7 g of LiOH·H2O and 1.09 g of TiO2 for approximately 15 minutes. The mixed powder was calcined at 760°C for 16 hours to synthesize lithium transition metal oxide particles.

[0106] Comparative Example 2 1000 g of Ni(OH)2 precursor compound (containing 133 ppm of Na and 1130 ppm of S in the precursor) was mechanically mixed with 462.7 g of LiOH·H2O and 2 g of ZrO2 for approximately 15 minutes. The mixed powder was calcined at 760°C for 16 hours to synthesize lithium transition metal oxide particles.

[0107] Comparative Example 3 1000 g of Ni(OH)2 precursor compound (containing 132 ppm of Na and 1125 ppm of S in the precursor) was mechanically mixed with 462.7 g of LiOH·H2O, 2 g of ZrO2, and 1.09 g of TiO2 for approximately 15 minutes. The mixed powder was calcined at 760°C for 16 hours to synthesize lithium transition metal oxide particles.

[0108] Comparative Example 4 1000 g of Ni(OH)2 precursor compound (containing 136 ppm of Na and 1090 ppm of S in the precursor) was mechanically mixed with 462.7 g of LiOH·H2O, 2 g of ZrO2, and 1.09 g of TiO2 for about 15 minutes. The mixed powder was 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 for 15 minutes, and then calcined at 700°C for 10 hours to synthesize the next product.

[0109] Comparative Example 5 1000 g of Ni(OH)2 precursor compound (containing 135 ppm of Na and 1088 ppm of S in the precursor) was mechanically mixed with 462.7 g of LiOH·H2O, 2 g of ZrO2, and 1.09 g of TiO2 for about 15 minutes. The mixed powder was 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 to synthesize the next product.

[0110] Comparative Example 6 1000 g of Ni(OH)2 precursor compound (containing 130 ppm of Na and 1103 ppm of S in the precursor) was mechanically mixed with 462.7 g of LiOH·H2O, 2 g of ZrO2, and 1.09 g of TiO2 for about 15 minutes. The mixed powder was 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 to synthesize the next product.

[0111] Comparative Example 7 1000 g of Ni(OH)2 precursor compound (containing 129 ppm of Na and 1020 ppm of S in the precursor) was mechanically mixed with 462.7 g of LiOH·H2O, 2 g of ZrO2, and 1.09 g of TiO2 for about 15 minutes. The mixed powder was 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 to synthesize the next product.

[0112] (Half-cell manufacturing) Example 2 A slurry was prepared by mixing the positive electrode 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 as the binder, polyvinylidene fluoride (PVDF) dissolved in N-methyl-2-pyrrolidone solvent was used. The slurry was uniformly applied to an Al current collector and dried at 110°C for 2 hours to produce the positive electrode. The loading level of the electrode plate was 11.0 mg / cm². 2 The electrode density was 3.71 g / cc. Using the manufactured positive electrode as the working electrode and lithium foil as the relative electrode, a CR2032 half cell was prepared using a liquid electrolyte prepared by adding 2% by weight of vinylene carbonate (VC) to a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3 / 7, and then adding LiPF6 as a lithium salt to a concentration of 1M.

[0113] Comparative Examples 8-14 Half-cells were prepared in the same manner 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.

[0114] [Table 1]

[0115] Evaluation Example 1: Composition evaluation of positive electrode active material ICP (inductively coupled plasma) analysis was performed on the cathode active materials synthesized in Example 1 and Comparative Examples 1-7 using a 700-ES (Varian) system, and the results are shown in Table 2 below.

[0116] Referring to Table 2, the ICP analysis results for Comparative Examples 1-7 and Example 1 show that the introduction of Co and Al concentration gradient layers on the surface of the single-particle Ni-based cathode active material resulted in substitution with other transition metals in the active material, increasing the Co and Al content and decreasing the number of moles of other transition metals. During ICP analysis, even when analysis is performed under vacuum, the influx of trace amounts of oxygen and carbon dioxide from the atmosphere makes it difficult to analyze the stoichiometric value of oxygen contained in the material.

[0117] [Table 2]

[0118] Evaluation Example 2: Visual Appearance Evaluation of Cathode Active Material Scanning electron microscopy (SEM) images of Example 1 and Comparative Examples 1-7 are shown in Figure 1. Referring to Figure 1, it can be seen that Comparative Examples 1-3 all have similar particle sizes depending on the type of doping material, and that a concentration gradient region was created on the surface of the cathode material when Co or Al coating was applied.

[0119] Evaluation Example 3: Evaluation of the concentration gradient region of the positive electrode active material 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 energy-dispersive X-ray spectroscopy (EDX) analysis was performed. The results are shown in Figure 2 (Example 1) and Figure 3 (Comparative Example 1).

[0120] Referring to Figures 2 and 3, it can be seen that in Comparative Example 1, the concentration of transition metals is constant on the surface of the active material, while in Example 1, the concentrations of cobalt and aluminum decrease as you move from the surface to the interior of the active material, while the concentration of nickel tends to increase as you move from the surface to the interior. Also, referring to Figure 2, it can be seen that in the lithium transition metal oxide particles of Example 1, the rate of change in cobalt ion concentration is more rapid than the rate of change in aluminum ion concentration within the concentration gradient region. Although not bound by theory, this is thought to have occurred because an excessive amount of Co coating material was used compared to the Al coating material in the synthesis process of Example 1. When the content of the Al coating material is applied to be equal to or greater than the content of the Co coating material, the initial capacity of the cathode material decreases and the energy density decreases. Among the transition metals, cobalt and aluminum ions are known to contribute to the structural stability of cathode active materials with a layered structure compared to nickel ions, and a cathode active material containing an excess of relatively stable cobalt on the surface of the active material will have a positive effect on its electrochemical performance.

[0121] Evaluation Example 4: High-Temperature Life Evaluation After allowing the half-cells prepared in Example 2 and Comparative Examples 8-14 to rest for 10 hours, they were charged in CC mode to 4.3V at 0.1C, and then charged in CV mode to a current corresponding to 0.05C. Subsequently, they were discharged in CC mode to 3.0V at 0.1C to complete the chemical conversion process. Next, at a high temperature (45°C), the battery was charged in CC mode at 0.5C up to 4.3V, and then charged in CV mode to a current corresponding to 0.05C. Subsequently, it was discharged in CC mode at 1C up to 3.0V, and this process was repeated a total of 50 times. The initial charge capacity and initial discharge capacity were measured, and based on these, the initial efficiency was calculated. The capacity retention rate relative to the initial discharge capacity after 50 charge and discharge cycles was then calculated and is shown in Table 3 below.

[0122] [Table 3]

[0123] Referring to Comparative Examples 8-10, there was no difference in the initial capacity of the positive electrode active material depending on the type of doping material. Next, we examined the effects of introducing a concentration gradient layer. In Comparative Example 11, which introduced a Co concentration gradient layer, the initial discharge capacity and initial efficiency improved, but in Comparative Example 12, which introduced an Al concentration gradient layer, the initial discharge capacity and initial efficiency decreased. Furthermore, in Comparative Example 13, which used a positive electrode active material manufactured 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 manufactured by adding Al at an even higher content than Co, the capacity retention rate was found to be insufficient.

[0124] On the other hand, in Example 2, when using a positive electrode active material containing both Co and Al elements in a concentration gradient layer, and both elements having a concentration gradient, the initial discharge capacity and initial efficiency decreased slightly compared to the Co-only concentration gradient sample. However, in terms of 45°C lifetime, it was confirmed that there was a significant improvement compared to the Co-only concentration gradient sample (Comparative Example 11), the Al-only concentration gradient sample (Comparative Example 12), the sample with equal amounts of Co and Al added (Comparative Example 13), and the sample with a higher content of Al compared to Co added (Comparative Example 14).

[0125] This improvement in lifespan characteristics is thought to be a remarkable effect derived from the concentrations of Co and Al, as well as their concentration gradients.

[0126] Preferred embodiments of the present invention have been described above with reference to the drawings and examples, but these are merely illustrative, and a person with ordinary skill in the art will understand that a variety of modifications and equivalent other embodiments are possible therefrom. Therefore, the scope of protection of the present invention must be determined by the claims. [Explanation of symbols]

[0127] 1 Lithium battery 2 negative electrode 3 Positive electrode 4 Separators 5 Battery case 6 Cap Assembly

Claims

1. It contains lithium nickel-based transition metal oxide particles that contain 96 mol% or more nickel, do not contain manganese, and have a ratio of titanium (Ti) substituted at transition metal sites in the crystal structure of 400 ppm to less than 1,000 ppm. The lithium nickel-based transition metal oxide particle includes a concentration gradient region in which the concentrations of aluminum (Al) and cobalt (Co) atoms change from the surface toward the center of the particle. In the aforementioned concentration gradient region, the absolute value of the slope of change in cobalt atom concentration (A) and the absolute value of the slope of change in aluminum atom concentration (B) satisfy A > B, which is the positive electrode active material.

2. The positive electrode active material according to claim 1, wherein in the concentration gradient region, the concentrations of aluminum atoms and cobalt atoms have a concentration gradient that decreases 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 comprise sodium (Na) and sulfur (S) atoms.

5. The positive electrode active material according to claim 4, wherein the total amount of sodium (Na) and sulfur (S) atoms contained in the lithium nickel-based transition metal oxide particles is 300 ppm to 1,500 ppm.

6. The positive electrode active material according to claim 4, wherein in the crystal of lithium nickel-based transition metal oxide particles, some of the lithium (Li) atoms are substituted with sodium (Na) atoms, and some of the oxygen (O) atoms are substituted with 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 surface of the particle toward the center of the particle.

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

9. The positive electrode active material according to claim 1, wherein the concentration gradient region has a thickness of 300 nm or less 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 the 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 layer exists on the surface 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 lithium nickel-based transition metal oxide particles are represented by the following chemical formula 1, the positive electrode active material according to claim 1: (Chemical formula 1) Li １－ａ Na ａ Ni １－ｘ－ｙ－α－β Co ｘ Al ｙ M1 α M2 β O ２－ｂ S ｂ In the aforementioned chemical formula 1, M1 and M2 are one or more elements independently 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 and 0 < y ≤ 0.

005.

16. The process involves mixing a nickel-containing precursor compound, a lithium-containing precursor compound, an M1-containing precursor compound, and an M2-containing precursor compound, followed by a first calcination to obtain a lithium nickel-based transition metal oxide precursor. The process includes the step of solid-phase mixing the lithium nickel-based transition metal oxide precursor compound, a Co precursor compound, and an Al precursor compound, followed by a second calcination to obtain lithium nickel-based transition metal oxide particles. The lithium nickel-based transition metal oxide particle includes a concentration gradient region in which the concentrations of aluminum (Al) and cobalt (Co) atoms change from the surface toward the center of the particle. A method for producing a positive electrode active material, wherein in the concentration gradient region, the absolute value of the slope of change in cobalt atom concentration (A) and the absolute value of the slope of change in aluminum atom concentration (B) satisfy A > B.

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

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

19. A positive electrode comprising the positive electrode active material described in any one of claims 1 to 15, The negative electrode and, A lithium secondary battery containing an electrolyte.

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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