Lithium secondary battery including a positive electrode active material, a method for producing the same, and a positive electrode containing the same

Abstract

The present invention relates to a positive electrode active material comprising lithium transition metal oxide particles containing Ni atoms and Co atoms, in which a portion of Li has been substituted with Na, and a phosphorus-containing coating layer disposed on the surface of the lithium transition metal oxide particles, the lithium transition metal oxide particles comprising a concentration gradient region in which the concentration of Co atoms decreases from the surface toward the center of the particles; a method for producing the same; and a lithium secondary battery equipped with a positive electrode containing the same.

Description

Technical Field

[0001] The present invention relates to a cathode active material having a novel composition, a method for producing the same, and a lithium secondary battery including the cathode containing the same.

[0002] The present invention has been made with the support of funds from the Ministry of Trade, Industry and Energy, with the subject number P0009541 of the title "Development of High-strength / Long-life / High-stability Ni-rich NCA (>210 mAh / g, @4.3V) Cathode Material for Medium and Large Lithium Secondary Batteries".

Background Art

[0003] After the lithium secondary battery was commercialized by Sony in 1991, the demand has been rapidly increasing in various fields from small household appliances such as mobile IT products to medium and large electric vehicles and energy storage systems. In particular, for medium and large electric vehicles and energy storage systems, a low-cost and high-energy cathode material is essential. However, cobalt, which is the main raw material of single-crystalline LiCoO2 (LCO), the currently commercialized cathode active material, is expensive.

[0004] Therefore, recently, as a cathode active material for medium and large secondary batteries, instead of LCO, LiNi in which a part of Co is replaced with another transition metal x Co y Mn z O2 (NCM) (x + y + z = 1) and LiNi x Co y Al zUsing a Ni-based cathode active material represented by O2(NCA)(x + y + z = 1), such NCM-based and NCA-based cathode active materials have the advantages that the price of nickel as a raw material is low and they have a high reversible capacity. In particular, in terms of high capacity, NCM and NCA with a Ni molar ratio of 50 mol% or more have attracted attention. Generally, such Ni-based cathode active materials are manufactured by mixing a transition metal compound precursor synthesized by a coprecipitation method with a lithium source and then performing solid-phase synthesis. However, the Ni-based cathode material synthesized in this way exists in the form of secondary particles in which small primary particles are agglomerated, and there is a problem that micro-cracks occur inside the secondary particles during a long-term charge / discharge process. The micro-cracks induce side reactions between a new interface of the cathode active material and the electrolyte, and as a result, battery performance degradation such as a decrease in stability due to gas generation and a decrease in battery performance due to electrolyte depletion is induced. In addition, in order to realize a high energy density, an increase in electrode density (>3.3 g / cc) is required, which induces the collapse of secondary particles, induces electrolyte depletion due to side reactions with the electrolyte, and induces a sharp drop in the initial life. Eventually, it means that the Ni-based cathode active material in the form of secondary particles synthesized by the existing coprecipitation method cannot realize a high energy density.

[0005] To solve the problems of the aforementioned Ni-based cathode active material in the form of secondary particles, recently, research on single-particle-type Ni-based cathode active materials has been conducted. The single-crystalline Ni-based cathode active material can exhibit excellent electrochemical performance without particle collapse when the electrode density increases (>3.3 g / cc) for realizing its energy density. However, such a single-crystalline Ni-based cathode active material has been reported to have a problem that the battery stability decreases due to structural and / or thermal instability caused by unstable Ni 3+ ions, Ni 4+ ions. Therefore, for the development of high-energy lithium secondary batteries, there is still a need for a technology to stabilize the unstable Ni ions in the single-crystalline Ni-based cathode active material.

Summary of the Invention

Problems to be Solved by the Invention

[0006] According to one aspect, unstable Ni ions in the single-crystalline Ni-based cathode active material as described above are stabilized, and the structural stability of the cathode active material is improved by the Co concentration gradient region in the cathode active material. During charge and discharge, cracking of particles is suppressed, a high energy density is realized, and a cathode active material with improved long-life characteristics is provided.

Means for Solving the Problem

[0007] According to one aspect, a part of Li is substituted with Na, and lithium transition metal oxide particles containing Ni atoms and Co atoms, and a phosphorus-containing coating layer disposed on the surface of the lithium transition metal oxide particles are included, and a cathode active material is provided in which the lithium transition metal oxide particles include a concentration gradient region in which the concentration of Co atoms decreases from the surface toward the particle center.

[0008] According to another aspect, a step of preparing lithium transition metal oxide particles in which a part of Li is substituted with Na and which contain Ni atoms and Co atoms, a step of mixing the lithium transition metal oxide particles, a Co element-containing compound, and a P element-containing compound to obtain a cathode active material precursor, and a step of heat-treating the cathode active material precursor to obtain a cathode active material are included, and a method for manufacturing a cathode active material is provided in which the cathode active material includes a phosphorus-containing coating layer on the surface and includes a concentration gradient region in which the concentration of Co atoms decreases from the surface toward the particle center.

[0009] According to still another aspect, a lithium secondary battery including a cathode including the cathode active material, an anode, and an electrolyte is provided.

Effects of the Invention

[0010] The positive electrode active material according to one aspect of the present invention includes single crystal and single particle lithium transition metal oxide particles, in which a part of the Li element in the single crystal is substituted with Na, and the concentration of Co among the transition metals includes a concentration gradient region that decreases from the surface of the lithium transition metal oxide particles toward the particle center. By doing so, during charge and discharge, the collapse due to cracking of the particles is prevented, the unstable Ni ions present in the high-Ni-based lithium transition metal oxide are stabilized, the capacity per unit volume is increased, and the life stability is improved.

Brief Description of the Drawings

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Modes for Carrying Out the Invention

[0012] The present inventive concept described below can be subjected to various transformations and can have various embodiments, but specific embodiments are illustrated in the drawings and will be described in detail by detailed description. However, it should not be construed as limiting the present inventive concept to specific embodiments, and all transformations, equivalents, or alternatives included in the technical scope of the present inventive concept should be understood to be included.

[0013] The terms used below are used only for explaining specific embodiments and are not intended to limit the present inventive concept. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the following, terms such as "including" or "having" indicate the presence of features, numbers, steps, operations, components, parts, components, materials, or combinations thereof described in the specification, and it should not be understood that the presence or addition of one or more other features, numbers, steps, operations, components, parts, components, materials, or combinations thereof is precluded in advance. " / " used below can be interpreted as "and" or "or" depending on the context.

[0014] In the drawings, to clearly represent various layers and regions, the thickness is shown enlarged or reduced. Throughout the specification, similar parts are denoted by the same reference numerals. Throughout the specification, when a part such as a layer, film, region, or plate is said to be "on" or "above" another part, it includes not only the case where it is directly above the other part but also the case where there are other parts in between. Throughout the specification, terms such as first and second can be used to describe various components, but the components are not limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

[0015] Unless otherwise defined, all terms (including technical and scientific terms) used herein shall have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will also be understood that terms such as those defined in commonly used dictionaries shall be interpreted to have a meaning that coincides with their meaning in the context of the relevant art and this disclosure content, and should not be interpreted in an idealized or overly formal sense.

[0016] "Group" means a group in the periodic table according to the International Union of Pure and Applied Chemistry ("IUPAC") 1-18 group classification system.

[0017] Although specific embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are not currently anticipated or cannot be anticipated may occur to the applicant or one of ordinary skill in the art. Accordingly, the appended claims, which may be amended as filed, are intended to cover all such alternatives, modifications, variations, improvements, and substantial equivalents.

[0018] Hereinafter, a lithium secondary battery including a positive electrode active material, a method for manufacturing the same, and a positive electrode including the same according to exemplary embodiments will be described in more detail.

[0019] A positive electrode active material according to one embodiment includes lithium transition metal oxide particles in which a part of Li is substituted with Na and includes Ni atoms and Co atoms, and a phosphorus-containing coating layer disposed on the surface of the lithium transition metal oxide particles, and the lithium transition metal oxide particles also include a concentration gradient region in which the concentration of Co atoms decreases from the surface toward the particle center.

[0020] When a part of Li in the positive electrode active material is replaced by Na, during charging, the structural deformation due to the desorption of Li ions is suppressed, the long-life characteristics of the positive electrode active material are improved, and the lithium transition metal oxide particles include a concentration gradient region where the concentration of Co atoms decreases from the surface toward the particle center. As a result, the stability of the crystal structure is further improved, and during the charge-discharge process, not only is the crystal collapse suppressed and the life characteristics improved, but also on the surface, the distribution of unstable Ni(III) ions and Ni(IV) ions is reduced, and at the core center, the distribution of Ni(II) ions is increased. This not only suppresses the side reaction between Ni ions and the electrolyte, but also due to the high Ni ion content, a high capacity of the positive electrode active material can be obtained. Therefore, the positive electrode active material has high-capacity characteristics and long-life characteristics.

[0021] According to one embodiment, the concentration gradient region may also include a region up to a distance of 500 nm from the surface of the lithium transition metal oxide particles toward the center.

[0022] For example, the concentration gradient region may also include a region up to a distance of 250 nm from the surface of the lithium transition metal oxide particles toward the center.

[0023] When the concentration gradient region exists up to the distance from the surface of the lithium transition metal oxide particles, the high-capacity characteristics and long-life characteristics of the positive electrode active material are achieved.

[0024] According to one embodiment, in the concentration gradient region, the concentration of Ni atoms may increase from the surface of the lithium transition metal oxide particles toward the particle center.

[0025] According to one embodiment, in the concentration gradient region, from the surface of the lithium transition metal oxide particles toward the particle center, the concentration of Co atoms decreases, and the concentration of Ni atoms may increase.

[0026] When the concentration of Co atoms gradually decreases and the concentration of Ni atoms gradually increases from the surface of the lithium transition metal oxide particles, the high-capacity characteristics and long-life characteristics of the positive electrode active material are achieved.

[0027] According to an embodiment, the lithium transition metal oxide particles also include a lithium transition metal oxide represented by the following Chemical Formula 1: Li 1-x Na x M 1-(α+β+γ) W α Mg β Ti γ O 2-a S a ···(Chemical Formula 1)

[0028] In Chemical Formula 1, M, x, α, β, γ, and a will be specifically described later.

[0029] In the lithium transition metal oxide represented by Chemical Formula 1, a part of Li is substituted with Na, a part of M is substituted with W, Mg, and Ti, and a part of O is substituted with S. During charge and discharge of a lithium secondary battery including the same, the structural stability of the lithium transition metal oxide is improved, the capacity per unit volume is increased, and the life stability is improved.

[0030] Further, in a high-Ni-based lithium transition metal oxide in which M contains Ni, substitution with a small amount of W, Mg, and Ti induces reduction of unstable nickel ions present in the lithium transition metal oxide, for example, Ni 3+ , Ni 4+ to stable nickel ions in the form of Ni 2+ . Thereby, deterioration of the positive electrode active material and capacity reduction due to a side reaction between unstable nickel ions and the electrolytic solution during charge and discharge are suppressed.

[0031] In addition to the concentration gradient region, the lithium transition metal oxide particles contain a small amount of W, Mg, and Ti as transition metals, thereby inducing reduction of unstable nickel ions, for example, Ni 3+ , Ni 4+ present in the lithium transition metal oxide particles to stable nickel ions in the form of Ni 2+ . During charge and discharge, deterioration of the positive electrode active material can be prevented, and capacity reduction can be significantly suppressed.

[0032] According to one embodiment, in Chemical Formula 1, M is also one or more elements selected from among alkali metal elements, alkaline earth metal elements, transition metal elements, post-transition metals, and non-metal elements excluding W, Mg, Ti, Na, and S.

[0033] For example, M is also one or more elements selected from among K, Rb, Cs, Fr, Be, Ca, Sr, Ba, Ra, Sc, Y, La, Zr, Hf, V, Nb, Ta, Cr, Mo, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, B, Al, Ga, In, Tl, C, Si, Ge, Sn, Pb, N, P, As, Sb, Bi, N, P, As, Sb, Bi, Se, Te, and Po.

[0034] According to one embodiment, M is also one or more elements selected from among alkaline earth metal elements, transition metal elements, post-transition metals, and non-metal elements excluding W, Mg, Ti, Na, and S.

[0035] For example, M is also one or more elements selected from among Be, Ca, Sr, Ba, Ra, Sc, Y, La, Zr, Hf, V, Nb, Ta, Cr, Mo, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, B, Al, Ga, In, Tl, C, Si, Ge, Sn, Pb, N, P, As, Sb, Bi, N, P, As, Sb, Bi, Se, Te, and Po.

[0036] According to one embodiment, M is also one or more elements selected from among Ni, Co, Mn, Al, V, Ca, Zr, B, and P.

[0037] For example, M is also one or more elements selected from among Ni, Co, Mn, Al, V, Ca, Zr, B, and P. For example, M is also one or more elements selected from among Ni, Co, Mn, and Al.

[0038] According to one embodiment, x also satisfies 0 < x ≤ 0.01. Here, x represents the substitution molar ratio of Na to Li in the lithium transition metal oxide represented by Chemical Formula 1. By substituting a part of Li in the lithium transition metal oxide represented by Chemical Formula 1 with Na, the structural stability can be improved. When Na substitutes for the lattice space where Li is located, due to the intervention of Na, which has a larger ionic radius than Li, during the desorption of Li in the charged state, the expansion of the crystal structure due to the repulsive force between oxygen atoms in the lithium transition metal oxide is suppressed. As a result, the structural stability of the lithium transition metal oxide is achieved even during repeated charging.

[0039] According to one embodiment, α also satisfies 0 < α ≤ 0.01. Here, α represents the substitution molar ratio of W to the M element in the lithium transition metal oxide represented by Chemical Formula 1. When W is substituted within the above range, the structural stability of the lithium transition metal oxide is improved. When the substitution molar ratio of W exceeds 0.01, a decrease in structural stability due to the deflection of the crystal structure is induced, WO3 is formed as an impurity, and a decrease in electrochemical properties may be caused.

[0040] According to one embodiment, β also satisfies 0 < β ≤ 0.005. Here, β represents the substitution molar ratio of Mg to the M element in the lithium transition metal oxide represented by Chemical Formula 1. When the substitution molar ratio of Mg satisfies the above range, the expansion of the structure of the lithium transition metal oxide can be suppressed in the charged state.

[0041] According to one embodiment, γ also satisfies 0 < γ ≤ 0.005. Here, γ represents the substitution molar ratio of Ti to the M element in the lithium transition metal oxide represented by Chemical Formula 1. When the substitution molar ratio of Ti satisfies the above range, the expansion of the structure of the lithium transition metal oxide can be suppressed in the charged state.

[0042] When the aforementioned W, Mg, and Ti are substituted with the lithium transition metal oxide in the molar ratio, in the charged state, even during lithium desorption, in the lithium transition metal oxide, due to the suppression of the structural expansion of the crystal by the interaction between oxygen atoms, the structural stability is improved and the life characteristics are improved.

[0043] According to one embodiment, the sum of α, β, and γ is also 0 < α + β + γ ≤ 0.02. For example, the sum of α, β, and γ is also 0 < α + β + γ ≤ 0.016. When α + β + γ satisfies the above range, the structural stability of the lithium transition metal oxide is guaranteed. When α + β + γ exceeds 0.02, an impurity phase is formed, which not only acts as a resistance during lithium desorption but also causes the collapse of the crystal structure during repeated charging.

[0044] According to one embodiment, in Chemical Formula 1, β and γ are also 0 < β ≤ 0.003 and 0 < γ ≤ 0.003, respectively.

[0045] For example, in Chemical Formula 1, β = γ. When β = γ, for example, when the molar ratios of Mg and Ti are the same, during charging and discharging, charge balance is achieved within the lithium transition metal oxide, the collapse of the crystal structure is suppressed, the structural stability is improved, and as a result, the life characteristics are improved.

[0046] According to one embodiment, a is also 0 < a ≤ 0.01. For example, 0 < a ≤ 0.005, 0 < a ≤ 0.003, or 0 < a ≤ 0.001. Here, a represents the substitution molar ratio of S for the O element in the lithium transition metal oxide represented by Chemical Formula 1.

[0047] When a part of the oxygen element is substituted with S, the binding force with the transition metal increases, the transition of the crystal structure of the lithium transition metal oxide is suppressed, and as a result, the structural stability of the lithium transition metal oxide is improved.

[0048] In addition, when the substitution molar ratio of S exceeds 0.01, due to the repulsive force of S anions, the crystal structure becomes unstable and, conversely, the life characteristics deteriorate.

[0049] According to one embodiment, the lithium transition metal oxide is also a single particle. The single particle is a concept that is distinguished from a secondary particle formed by aggregating a plurality of particles or a particle formed by aggregating a plurality of particles and coating the periphery of the aggregate. By having the lithium transition metal oxide in the form of a single particle, particle disintegration can be prevented even at a high electrode density. Therefore, it becomes possible to realize a high energy density of the positive electrode active material containing the lithium transition metal oxide. Also, compared to secondary particles formed by aggregating a plurality of single particles, disintegration is suppressed during rolling, a high energy density can be realized, and deterioration of the lifespan due to particle disintegration can also be prevented.

[0050] According to one embodiment, the lithium transition metal oxide can have a single crystal. The single crystal has a concept that is distinguished from a single particle. The single particle refers to a particle formed into one particle regardless of the type and number of crystals inside, and the single crystal means having only one crystal in the particle. Such a single crystal lithium transition metal oxide not only has very high structural stability, but also has easier lithium ion conduction compared to polycrystals and excellent fast charging characteristics compared to polycrystalline active materials.

[0051] According to one embodiment, the positive electrode active material is a single crystal and a single particle. By being formed by the single crystal and the single particle, it is structurally stable and a high-density electrode can be realized, and a lithium secondary battery containing the same can have improved lifespan characteristics and a high energy density at the same time.

[0052] According to one embodiment, the lithium transition metal oxide is also represented by any one of Chemical Formulas 2 to 4 below. Li 1-x’ Na x’ Ni y1’ Co y2’ Mn y3’ W α’ Mg β’ Ti γ’ O 2-a’S a’ ···(Chemical formula 2) Li 1-x” Na x” Ni y1” Co y2” Al y3” W α” Mg β” Ti γ” O 2-a” S a” ···(Chemical formula 3) Li 1-x’’’ Na x’’’ Ni y1’’’ Co y2’’’ W α’’’ Mg β’’’ Ti γ’’’ O 2-a’’’ S a’’’ ···(Chemical formula 4)

[0053] According to an embodiment, in the chemical formula 2 0 < x’ ≦ 0.01, 0 < α’ ≦ 0.01, 0 < β’ ≦ 0.005, 0 < γ’ ≦ 0.005, 0 < a’ ≦ 0.01, 0 < α’ + β’ + γ’ ≦ 0.02, 0.48 ≦ y1’ < 1, 0 < y2’ ≦ 0.2, 0 < y3’ ≦ 0.3, y1’ + y2’ + y3’ + α’ + β’ + γ’ = 1 also holds.

[0054] In the chemical formula 3 0 < x” ≦ 0.01, 0 < α” ≦ 0.01, 0 < β” ≦ 0.005, 0 < γ” ≦ 0.005, 0 < a” ≦ 0.01, 0 < α” + β” + γ” ≦ 0.02, 0.73 ≦ y1” < 1, 0 < y2” ≦ 0.2, 0 < y3” ≦ 0.05, y1” + y2” + y3” + α” + β” + γ” = 1 also holds.

[0055] In the chemical formula 4 0 < x’’’ ≦ 0.01, 0 < α’’’ ≦ 0.01, 0 < β’’’ ≦ 0.005, 0 < γ’’’ ≦ 0.005, 0 < a’’’ ≦ 0.01, 0 < α’’’ + β’’’ + γ’’’ ≦ 0.02, 0.78 ≦ y1’’’ < 1, 0 < y2’’’ ≦ 0.2, y1’’’ + y2’’’ + α’’’ + β’’’ + γ’’’ = 1 also holds.

[0056] For example, in the chemical formula 2, 0 < β’ ≤ 0.003, 0 < γ’ ≤ 0.003, 0 < α’ + β’ + γ’ ≤ 0.016; in the chemical formula 3, 0 < β” ≤ 0.003, 0 < γ” ≤ 0.003, 0 < α” + β” + γ” ≤ 0.016; and in the chemical formula 4, 0 < β’’’ ≤ 0.003, 0 < γ’’’ ≤ 0.003, 0 < α’’’ + β’’’ + γ’’’ ≤ 0.016.

[0057] The lithium transition metal oxide satisfying the above composition can stabilize unstable Ni ions inside and possess high energy density and long - life stability.

[0058] In the case of a cathode active material containing a general high - nickel lithium nickel cobalt manganese oxide, the stabilization of unstable Ni ions is essential. However, when W, Mg, and Ti are introduced into a part of the transition metal sites in the crystal, the cathode active material can achieve overall charge balance, suppressing the oxidation of Ni(II) ions to unstable Ni(III) or Ni(IV) ions, and the unstable Ni(III) or Ni(IV) is also reduced to Ni(II). On the other hand, the loss of conductivity caused by substituting a part of the transition metal with the heterogeneous elements W, Mg, and Ti is compensated by substituting a part of O with S, and by substituting a part of Li with Na, the decrease in Li conductivity due to structural deformation during charge and discharge is also suppressed, thus obtaining a single - crystal, structurally stable, high - capacity, and long - life cathode active material.

[0059] According to one embodiment, the average particle size (D 50 ) of the lithium transition metal oxide is also 0.1 μm to 20 μm. For example, the average particle size (D 50) is also 0.1 μm to 15 μm, 0.1 μm to 10 μm, 1 μm to 20 μm, 5 μm to 20 μm, 1 μm to 15 μm, 1 μm to 10 μm, 5 μm to 15 μm, or 5 μm to 10 μm. When the average particle size of the lithium transition metal oxide belongs to the above range, the desired energy density per volume can be realized. When the average particle size of the lithium transition metal oxide exceeds 20 μm, it will cause a sharp decrease in the charge and discharge capacity, and when it is 0.1 μm or less, it is difficult to obtain the desired energy density per volume.

[0060] According to one embodiment, the lithium transition metal oxide further includes a coating layer containing a phosphorus-containing compound on the surface.

[0061] For example, the phosphorus-containing compound is also crystalline, amorphous, or a combination thereof. For example, the phosphorus-containing compound contains crystalline Li3PO4 or an amorphous phosphorus-containing compound containing lithium atoms, phosphorus atoms, and oxygen atoms.

[0062] According to one embodiment, in the positive electrode active material, the molar ratio of the phosphorus (P) element is also 0.2 mol% or less in the total elements contained in the positive electrode active material.

[0063] According to one embodiment, the phosphorus-containing compound also includes a compound represented by the following Chemical Formula 5: Li a PbO c ···(Chemical Formula 5) 0 < a ≤ 3, 0 < b ≤ 1, and 0 < c ≤ 4.

[0064] For example, in Chemical Formula 5, 0 < b ≤ 0.02.

[0065] According to one embodiment, the coating layer is also arranged to cover at least a part of the lithium transition metal oxide. For example, the coating layer can completely cover the surface of the lithium transition metal oxide.

[0066] According to one embodiment, the positive electrode active material may have a peak at 2θ = 20° to 25° in an X-ray diffraction spectrum obtained by XRD (X-ray diffraction) analysis using CuKα rays.

[0067] In the XRD graph, the peak at 2θ = 20° to 25° indicates the presence of Li3PO4.

[0068] According to one embodiment, the coating layer may have a thickness of 250 nm or less. When the thickness of the coating layer is 250 nm or less, it does not act as a resistance layer for lithium migration and has the effect of sufficiently reducing residual lithium.

[0069] Hereinafter, a method for manufacturing a positive electrode active material according to one aspect will be described in detail.

[0070] A method for manufacturing a positive electrode active material according to one embodiment includes preparing lithium transition metal oxide particles in which part of Li is substituted with Na and which contain Ni atoms and Co atoms, mixing the lithium transition metal oxide particles, a Co element-containing compound, and a P element-containing compound to obtain a positive electrode active material precursor, and firing the positive electrode active material precursor to obtain a positive electrode active material. The positive electrode active material includes a phosphorus-containing coating layer on the surface and includes a concentration gradient region in which the concentration of Co atoms decreases from the surface toward the particle center.

[0071] According to one embodiment, the step of preparing the lithium transition metal oxide particles includes mixing a Li element-containing compound, a Na element-containing compound, a W element-containing compound, a Mg element-containing compound, a Ti element-containing compound, an M element-containing compound, and an S element-containing compound to obtain a lithium transition metal oxide precursor, and heat-treating the lithium transition metal oxide precursor to obtain lithium transition metal oxide particles represented by the following Chemical Formula 1: Li 1-x Na x M 1-(α+β+γ) W α Mg β Ti γ O2-a S a ···(Chemical Formula 1) In the Chemical Formula 1, M is one or more elements selected from among alkali metal elements, alkaline earth metal elements, transition metal elements, post-transition metals, and non-metal elements excluding W, Mg, Ti, Na, and S; 0 < x ≤ 0.01, 0 < α ≤ 0.01, 0 < β ≤ 0.005, 0 < γ ≤ 0.005, 0 < a ≤ 0.01, and 0 < α + β + γ ≤ 0.02.

[0072] For specific descriptions related to the Chemical Formula 1, refer to the foregoing.

[0073] The mixing stage includes mechanically mixing the specific element-containing compound. The mechanical mixing is performed in a dry manner. The mechanical mixing applies mechanical force to crush and mix the substances to be mixed, thereby forming a uniform mixture. The mechanical mixing can also be performed using a mixing device such as a ball mill, a planetary mill, a stirred ball mill, or a vibrating mill that utilizes beads that are chemically inert, for example. At this time, in order to maximize the mixing effect, a small amount of alcohol such as ethanol or a higher fatty acid such as stearic acid can be selectively added.

[0074] The mechanical mixing is performed in an oxidizing atmosphere, which is for preventing the reduction of transition metals in the transition metal source (e.g., Ni compound) and realizing the structural stability of the active material.

[0075] The lithium element-containing compound includes, but is not limited to, lithium hydroxide, oxide, nitride, carbonate, or a combination thereof. For example, the lithium precursor can also be LiOH or Li2CO3.

[0076] The Na element-containing compound may include, but is not limited to, hydroxides, oxides, nitrides, carbonates of Na, or combinations thereof. For example, it may also be NaOH, Na2CO3, or a combination thereof.

[0077] The W element-containing compound may include, but is not limited to, hydroxides, oxides, nitrides, carbonates of W, or combinations thereof. For example, it may also be W(OH)6, WO3, or a combination thereof.

[0078] The Mg element-containing compound may include, but is not limited to, hydroxides, oxides, nitrides, carbonates of Mg, or combinations thereof. For example, it may also be Mg(OH)2, MgCO3, or a combination thereof.

[0079] The Ti element-containing compound may include, but is not limited to, hydroxides, oxides, nitrides, carbonates of Ti, or combinations thereof. For example, it may also be Ti(OH)2, TiO2, or a combination thereof.

[0080] The M element-containing compound may include, but is not limited to, hydroxides, oxides, nitrides, carbonates of one or more elements selected from the group consisting of alkali metal elements, alkaline earth metal elements, transition metal elements, metalloid elements, and non-metal elements excluding W, Mg, Ti, Na, and S, or combinations thereof. For example, Ni 0.8 Co 0.1 Mn 0.1 (OH)2, Ni 0.9 Co 0.05 Al 0.05 (OH)2 or Ni 0.9 Co 0.1 (OH)2.

[0081] The S element-containing compound may include, but is not limited to, hydroxides, oxides, nitrides, carbonates, ammonium compounds of S, or combinations thereof. For example, it may also be (NH4)2S.

[0082] According to an embodiment, the step of obtaining the cathode active material precursor may further include a Co element-containing compound and a P element-containing compound as a mixed material.

[0083] The Co element-containing compound is a compound capable of providing a Co element, and includes a hydroxide, oxide, nitride, carbonate, acetate of Co, or a combination thereof. For example, it may also be cobalt acetate.

[0084] The P element-containing compound precursor includes any P element-containing compound capable of providing a P element. For example, the P precursor may also be (NH4)2HPO4.

[0085] In the step of preparing the lithium transition metal oxide particles, the heat treatment step also includes a first heat treatment step and a second heat treatment step. The first heat treatment step and the second heat treatment step may be performed continuously, or may have a rest period after the first heat treatment step. Also, the first heat treatment step and the second heat treatment step may be performed in the same chamber, or may be performed in different chambers from each other.

[0086] The heat treatment temperature in the first heat treatment step is higher than the heat treatment temperature in the second heat treatment step.

[0087] The first heat treatment step may be performed at a heat treatment temperature of 800°C to 1,200°C. The heat treatment temperature may be, for example, 850°C to 1,200°C, 860°C to 1,200°C, 870°C to 1,200°C, 880°C to 1,200°C, 890°C to 1,200°C, or 900°C to 1,200°C, but is not limited thereto, and includes any range formed by selecting any two points within the above range.

[0088] The second heat treatment stage can be carried out at a heat treatment temperature of 700°C to 800°C. The heat treatment temperature can also be 710°C to 800°C, 720°C to 800°C, 730°C to 800°C, 740°C to 800°C, 750°C to 800°C, 700°C to 780°C, 700°C to 760°C, 700°C to 750°C, or 700°C to 730°C, but is not limited thereto, and any range formed by selecting any two points within the above range is included.

[0089] According to an embodiment, the heat treatment time in the first heat treatment stage is shorter than the heat treatment time in the second heat treatment stage.

[0090] For example, in the first heat treatment stage, the heat treatment time can be 3 hours to 5 hours, 4 hours to 5 hours, or 3 hours to 4 hours, but is not limited thereto, and any range formed by selecting any two points within the above range is included.

[0091] For example, in the second heat treatment stage, the heat treatment time can be 10 hours to 20 hours, 10 hours to 15 hours, but is not limited thereto, and any range formed by selecting any two points within the above range is included.

[0092] The first heat treatment stage may also include a stage of heat treatment at a heat treatment temperature of 800°C to 1,200°C for 3 to 5 hours.

[0093] The second heat treatment stage may also include a stage of heat treatment at a heat treatment temperature of 700°C to 800°C for 10 to 20 hours.

[0094] The first heat treatment step causes the lithium transition metal oxide to form a cathode active material with a layered structure, induces the growth of particles, and makes them form a single crystal shape. In the first heat treatment step, each primary particle within the secondary particle-shaped lithium transition metal oxide grows rapidly and cannot withstand the interparticle stress. As a result, while the interior of the primary particles appears, they fuse with each other, and it is considered that a single crystal cathode active material for a secondary battery is formed. The second heat treatment step increases the crystallinity of the layered structure generated in the first heat treatment step by performing heat treatment at a temperature lower than that of the first heat treatment step for a long period of time. Through the first heat treatment step and the second heat treatment step, a high nickel-based cathode active material of a single phase, single crystal, and single particle is obtained.

[0095] According to one embodiment, the firing step can be carried out at a temperature of 500 °C to 900 °C. According to one embodiment, the firing step can be carried out for 1 hour to 6 hours.

[0096] According to one embodiment, the firing step can be carried out at a temperature of 500 °C to 900 °C for 1 hour to 6 hours. By firing the cathode active material precursor at the aforementioned firing temperature and time, a cathode active material is obtained in which Co atoms have a concentration gradient and a coating layer containing a phosphorus-containing compound is formed on the surface of the lithium transition metal oxide particles.

[0097] According to one embodiment, the lithium transition metal oxide produced by the manufacturing method is a single crystal and a single particle, and the single crystal can have a layered structure. Further, the average particle size of the lithium transition metal oxide is also 0.1 μm to 20 μm.

[0098] Further, in the lithium transition metal oxide produced by the manufacturing method of the cathode active material, the W, Mg, and Ti elements are substituted at the sites of the M element in the structure, the S element is substituted at the O site, and the Na element is substituted at the Li site, thereby not only suppressing the oxidation of existing Ni 2+ but also existing unstable Ni 3+ ions of Ni 2+Reduction to ions is induced, and a structurally stable and high-density lithium transition metal oxide is obtained. Also, the reduced Ni 2+ ions and Li + ions have similar ionic radii, promoting Li / Ni disordering. When Li is desorbed, Ni ions fill the vacant lattice sites, thereby achieving the structural stability of the crystal.

[0099] Furthermore, by including a Co concentration gradient region and a phosphorus-containing coating layer, the capacity characteristics and life characteristics are improved compared to the case where existing transition metals are substituted.

[0100] According to another aspect, a positive electrode including the aforementioned positive electrode active material is provided.

[0101] According to still another aspect, a lithium secondary battery including the positive electrode, a negative electrode, and an electrolyte is provided.

[0102] The positive electrode and the lithium secondary battery including the same are also manufactured by the following method.

[0103] First, a positive electrode is prepared.

[0104] For example, a positive electrode active material composition in which the aforementioned positive electrode active material, a conductive material, a binder, and a solvent are mixed is prepared. The positive electrode active material composition is directly coated on a metal current collector to manufacture a positive electrode plate. As an alternative, after the positive electrode active material composition is cast on a separate support, the film peeled off from the support is laminated on a metal current collector to manufacture a positive electrode plate. The positive electrode is not limited to the aforementioned form and may also be in other forms.

[0105] Examples of the conductive material include, but are not limited to, 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. Any material that can be used as a conductive material in the relevant technical field can be used.

[0106] Examples of the binder include, but are not limited to, vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene, and their mixtures·metal salts, or styrene-butadiene rubber-based polymers. Any material that can be used as a binder in the relevant technical field can be used. Further examples of other binders include lithium salts, sodium salts, calcium salts, or Na salts of the aforementioned polymers.

[0107] Examples of the solvent include, but are not limited to, N-methylpyrrolidone, acetone, or water. Any material that can be used in the relevant technical field can be used.

[0108] The contents of the aforementioned positive electrode active material, conductive material, binder, and solvent are at levels generally 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 can be omitted.

[0109] Next, a negative electrode is prepared.

[0110] 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 on a metal current collector having a thickness of 3 μm to 500 μm and dried to manufacture a negative electrode plate. As an alternative, after the negative electrode active material composition is cast on a separate support, a film peeled off from the support is laminated on a metal current collector to manufacture a negative electrode plate.

[0111] The negative electrode current collector is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, copper, nickel, or a material obtained by surface-treating the surface of copper with carbon can be used.

[0112] Any negative electrode active material can be used as long as it can be used as a negative electrode active material for a lithium battery in the relevant technical field. For example, it may contain one or more selected from the group consisting of lithium metal, a metal alloyable with lithium, transition metal oxides, non-transition metal oxides, and carbon-based materials.

[0113] For example, the metal alloyable with lithium includes Si, Sn, Al, Ge, Pb, Bi, Sb, 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 Si), 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 Sn), and the like. Examples of the element Y also include 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.

[0114] For example, the transition metal oxide also includes lithium titanate, vanadium oxide, lithium vanadate, and the like.

[0115] For example, the non-transition metal oxide is also SnO2, SiO x (0 < x < 2), etc.

[0116] The carbon-based material is also crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon is also graphite such as amorphous, plate-shaped, flaky, spherical or fibrous natural graphite or artificial graphite, and the amorphous carbon is also soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0117] In the negative electrode active material composition, the conductive material, binder and solvent can be the same as those in the case of the positive electrode active material composition.

[0118] The contents of the aforementioned negative electrode active material, conductive material, binder and solvent are at levels generally used in lithium batteries. Depending on the use and configuration of the lithium battery, one or more of the aforementioned conductive material, binder and solvent can be omitted.

[0119] Next, a separator inserted between the positive electrode and the negative electrode is prepared.

[0120] If the separator is one generally used in a lithium battery, any of them can be used. One with low resistance to the ion movement of the electrolyte and excellent electrolyte moisture retention ability can be used. The separator can be a single film or a multilayer film, and is, for example, selected from among glass fiber, polyester, Teflon (registered trademark), polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in the form of a nonwoven fabric or a woven fabric. Also, a mixed multilayer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator can be used. For example, a wound separator such as polyethylene or polypropylene is used for a lithium-ion battery, and a separator with excellent impregnation ability for an organic electrolyte can be used for a lithium-ion polymer battery. For example, the separator is also manufactured by the following method.

[0121] A polymer resin, a filler, and a solvent are mixed to prepare a separator composition. The separator composition can be directly coated on the upper part of the electrode and dried to form a separator. Or, after the separator composition is cast on a support and dried, the separator film peeled from the support is laminated on the upper part of the electrode to form a separator.

[0122] The polymer resin used for manufacturing the separator is not particularly limited, and any substance used as a binder for the electrode plate can be used. For example, a vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or a mixture thereof can be used.

[0123] Next, an electrolyte is prepared.

[0124] For example, the electrolyte is also an organic electrolyte solution. Further, the electrolyte is also a solid. For example, it may be a boron oxide, a lithium oxynitride, etc., but is not limited thereto, and any material can be used as long as it can be used as a solid electrolyte in the technical field. The solid electrolyte is also formed on the negative electrode by a method such as a sputtering method.

[0125] For example, the organic electrolyte solution is also produced by dissolving a lithium salt in an organic solvent.

[0126] Any of the organic solvents can be used as long as they can be used as organic solvents in the technical field. For example, cyclic carbonates such as propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate; esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone; ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, 2-methyltetrahydrofuran; nitriles such as acetonitrile; amides such as dimethylformamide, etc. They can be used alone or in combination of multiple. For example, a solvent obtained by mixing a cyclic carbonate and a chain carbonate can be used.

[0127] Further, a gel-phase polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide or polyacrylonitrile with an electrolyte solution, LiI, Li3N, Li x Ge y P z S α 、Li x Ge y P z S α X δInorganic solid electrolytes such as (where X is F, Cl, Br) can be used.

[0128] Any of the above lithium salts can also be used as long as they can be used as lithium salts in the 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 a mixture thereof, etc.

[0129] As can be seen from FIG. 8, the lithium battery 1 includes a positive electrode 3, a negative electrode 2, and a separator 4. The aforementioned positive electrode 3, negative electrode 2, and separator 4 are wound or folded and housed in a battery case 5. Next, an organic electrolyte is injected into the battery case 5, sealed with a cap assembly 6, and the lithium battery 1 is completed. The battery case 5 can also be cylindrical, rectangular, portable, coin-shaped, or thin-film type, etc. For example, the lithium battery 1 is also a thin-film battery. The lithium battery 1 is also a lithium-ion battery.

[0130] A separator can be disposed between the positive electrode and the negative electrode to form a battery structure. After the battery structure is laminated into a bicell structure, impregnated with an organic electrolyte, and the resulting product is housed and sealed in a port, a lithium-ion polymer battery is completed.

[0131] Also, a plurality of the battery structures are laminated to form a battery pack, and such a battery pack can be used in all devices that require high capacity and high output. For example, it can be used in notebook computers, smartphones, electric vehicles (EVs), etc.

[0132] In addition, since the lithium battery is excellent in life characteristics and high-rate characteristics, it can be used in electric vehicles. For example, it can be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). Also, it can be used in fields where a large amount of power storage is required. For example, it can be used in electric bicycles, electric tools, power storage systems, etc.

[0133] The present invention will be described in more detail through the following production examples, examples and comparative examples. However, these examples are only for illustrating the present invention, and the scope of the present invention is not limited only by them.

[0134] (Production of Cathode Active Material) Example 1 100 g of Ni 0.8 Co 0.1 Mn 0.1 (OH)2, and 41.8 g of Li2CO3, 3.0 g of WO3, 0.27 g of MgCO3, 0.24 g of TiO2, 0.45 g of NaOH, and 0.75 g of (NH4)2 S are mechanically mixed for about 15 minutes. The mixed powder is heat-treated at 1,000 °C for 4 hours and at 700 °C for 10 hours to obtain lithium transition metal oxide particles. Next, 100 g of the lithium transition metal oxide particles are added to a mixed solution in which 2 g of cobalt acetate and 2 g of (NH4)2HPO4 are dissolved in ethanol, followed by stirring for 30 minutes, drying at 80 °C to remove ethanol, and then firing at 800 °C for 3 hours to obtain a cathode active material. The specific composition of the obtained cathode active material can be confirmed in Table 1.

[0135] Example 2 100 g of Ni 0.90 Co 0.05 Al 0.05 (OH)2, and 42.4 g of Li2CO3, 3.0 g of WO3, 0.27 g of MgCO3, 0.24 g of TiO2, 0.45 g of NaOH, and 0.75 g of (NH4)2 SMix mechanically for about 15 minutes. The mixed powder was heat-treated at 970 °C for 4 hours and at 700 °C for 10 hours to obtain lithium transition metal oxide particles. Next, 100 g of the lithium transition metal oxide particles were added to a mixed solution obtained by dissolving 2 g of cobalt acetate and 2 g of (NH4)2HPO4 in ethanol, followed by stirring for 30 minutes, drying at 80 °C to remove ethanol, and then firing at 800 °C for 3 hours to obtain a positive electrode active material. The specific composition of the obtained positive electrode active material can be confirmed in Table 1.

[0136] Example 3 100 g of Ni 0.9 Co 0.1 (OH)2, and 42.0 g of Li2CO3, 3.0 g of WO3, 0.27 g of MgCO3, 0.24 g of TiO2, 0.45 g of NaOH, and 0.75 g of (NH4)2S were mechanically mixed for about 15 minutes. The mixed powder was heat-treated at 970 °C for 4 hours and at 700 °C for 10 hours to obtain lithium transition metal oxide particles. Next, 100 g of the lithium transition metal oxide particles were added to a mixed solution obtained by dissolving 2 g of cobalt acetate and 2 g of (NH4)2HPO4 in ethanol, followed by stirring for 30 minutes, drying at 80 °C to remove ethanol, and then firing at 800 °C for 3 hours to obtain a positive electrode active material. The specific composition of the obtained positive electrode active material can be confirmed in Table 1.

[0137] Comparative Example 1 100 g of Ni 0.8 Co 0.1 Mn 0.1 (OH)2, and 41.8 g of Li2CO3, 3.0 g of WO3, 0.27 g of MgCO3, 0.24 g of TiO2, 0.45 g of NaOH, and 0.75 g of (NH4)2 S were mechanically mixed for about 15 minutes. The mixed powder was heat-treated at 1,000 °C for 4 hours and at 700 °C for 10 hours to obtain a positive electrode active material. The specific composition of the obtained positive electrode active material can be confirmed in Table 1.

[0138] Comparative Example 2 100 g of Ni0.8 Co 0.1 Mn 0.1 (OH)2, and 41.8 g of Li2CO3, 0.27 g of MgCO3, and 0.24 g of TiO2 are mechanically mixed for about 15 minutes. The mixed powder is heat-treated at 1,000 °C for 4 hours and at 700 °C for 10 hours to obtain a positive electrode active material. The specific composition of the obtained positive electrode active material can be confirmed in Table 1.

[0139] Comparative Example 3 100 g of Ni 0.8 Co 0.1 Mn 0.1 (OH)2, and 41.8 g of Li2CO3, 0.27 g of MgCO3, and 0.45 g of NaOH are mechanically mixed for about 15 minutes. The mixed powder is heat-treated at 1,000 °C for 4 hours and at 700 °C for 10 hours to obtain a positive electrode active material. The specific composition of the obtained positive electrode active material can be confirmed in Table 1.

[0140] Comparative Example 4 100 g of Ni 0.8 Co 0.1 Mn 0.1 (OH)2, and 41.8 g of Li2CO3, 0.75 g of (NH4)2S are mechanically mixed for about 15 minutes. The mixed powder is heat-treated at 1,000 °C for 4 hours and at 700 °C for 10 hours to obtain a positive electrode active material. The specific composition of the obtained positive electrode active material can be confirmed in Table 1.

[0141] Comparative Example 5 100 g of Ni 0.8 Co 0.1 Mn 0.1 (OH)2, and 41.8 g of Li2CO3, 0.27 g of MgCO3, and 0.45 g of NaOH are mechanically mixed for about 15 minutes. The mixed powder is heat-treated at 1,000 °C for 4 hours and at 700 °C for 10 hours to obtain lithium transition metal oxide particles. Next, 100 g of lithium transition metal oxide particles were added to a solution in which 2 g of (NH4)2HPO4 was dissolved in ethanol, and then stirred for 30 minutes. Next, it was dried at 80 °C to remove the ethanol solvent, and then calcined at 800 °C for 3 hours to obtain a positive electrode active material. The specific composition of the obtained positive electrode active material can be confirmed in Table 1.

[0142] Comparative Example 6 100 g of Ni 0.8 Co 0.1 Mn 0.1 (OH)2 and 41.8 g of Li2CO3 are mechanically mixed for about 15 minutes. The mixed powder is heat-treated at 1,000 °C for 4 hours and at 700 °C for 10 hours to obtain lithium transition metal oxide particles. Next, 100 g of lithium transition metal oxide particles were added to a solution in which 2 g of cobalt acetate was dissolved in ethanol, and stirred for 30 minutes. Next, it was dried at 80 °C to remove the ethanol solvent, and then calcined at 800 °C for 3 hours to obtain a positive electrode active material. The specific composition of the obtained positive electrode active material can be confirmed in Table 1.

[0143] Comparative Example 7 100 g of Ni 0.90 Co 0.05 Al 0.05 (OH)2, 42.4 g of Li2CO3, 3.0 g of WO3, 0.27 g of MgCO3, 0.24 g of TiO2, 0.45 g of NaOH, and 0.75 g of (NH4)2S are mechanically mixed for about 15 minutes. The mixed powder is heat-treated at 970 °C for 4 hours and at 700 °C for 10 hours to obtain lithium transition metal oxide particles. The specific composition of the obtained positive electrode active material can be confirmed in Table 1.

[0144] Comparative Example 8 100 g of Ni 0.9 Co 0.1(OH)2, and 42.0 g of Li2CO3, 3.0 g of WO3, 0.27 g of MgCO3, 0.24 g of TiO2, 0.45 g of NaOH, and 0.75 g of (NH4)2S are mechanically mixed for about 15 minutes. The mixed powder is heat-treated at 970 °C for 4 hours and at 700 °C for 10 hours to obtain lithium transition metal oxide particles. The specific composition of the obtained positive electrode active material can be confirmed in Table 1.

[0145] (Manufacture of Half Cell) Example 4 The positive electrode active material obtained in Example 1, a conductive material, and a binder were mixed at a weight ratio of 94:3:3 to produce a slurry. Here, carbon black was used as the conductive material, and polyvinylidene fluoride (PVdF) was dissolved in an N-methyl-2-pyrrolidone solvent and used as the binder. The slurry was uniformly applied to an Al current collector and dried at 110 °C for 2 hours to produce a positive electrode. The loading level of the electrode plate was 11.0 mg / cm 2 and the electrode density was 3.6 g / cc. Using the manufactured positive electrode as a working electrode and a lithium foil as a counter electrode, a liquid electrolyte in which LiPF6 was added as a lithium salt to a mixed solvent of ethylene carbonate (EC) / EMC (ethyl methyl carbonate) / DEC (diethyl carbonate) mixed at a volume ratio of 3 / 4 / 3 to a concentration of 1.3 M was used, and a CR2032 half cell was fabricated by a generally known process.

[0146] Examples 5, 6 A half cell was fabricated in the same manner as in Example 4, except that the positive electrode active materials obtained in Examples 2 and 3 were used instead of the positive electrode active material obtained in Example 1.

[0147] Comparative Examples 9 to 16 A half cell was fabricated in the same manner as in Example 4, 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.

[0148]

Table 1

[0149] Evaluation Example 1: Composition Evaluation of Cathode Active Material For the cathode active materials synthesized in Example 1 and Comparative Example 1, ICP (inductively coupled plasma) analysis was carried out using a 700-ES (Varian) instrument, and the results are shown in Table 2 below.

[0150] Referring to Table 2, it can be seen that for the ICP analysis results of Comparative Example 1 and Example 1, the introduction of the Co concentration gradient region on the surface of the single-particle type Ni-based cathode active material increased the ratio of Co element in the cathode active material by 1.6 mol% through substitution with other transition metals in the cathode active material, and the number of moles of other transition metals was reduced. Also, Li x PO y Due to the introduction of the coating layer, the P content in the active material is 0.2 mol%. In view of the fact that it does not affect the stoichiometric values of transition metals or Li, it is suggested that the coating layer contains P element. Also, during ICP analysis, even when the analysis is carried out in a vacuum, due to the inflow of trace amounts of oxygen and carbon dioxide in the atmosphere, the stoichiometric value of oxygen contained in the substance is difficult to analyze.

[0151]

Table 2

[0152] Evaluation Example 2: Particle Size Evaluation of Cathode Active Material The appearance of the cathode active materials synthesized in Example 1 and Comparative Example 1 was observed using a Verios 460 (FEI) instrument to obtain SEM (scanning electron microscope) images, which are shown in Figure 1. Also, the particle size distribution was measured using a Cilas 1090 (Scinco) instrument, and the results are shown in Table 3 and Figure 2 below.

[0153] Referring to Table 3 and Figures 1 and 2, the single-particle type cathode active material of Example 1 has a Co concentration gradient region and Lix PO y A coating layer of PO is introduced, but no significant change in particle size is observed compared to the single-particle type cathode active material of Comparative Example 1. On the surface of the cathode active material of Example 1, it was confirmed that the Li x PO y compound exists as particles with a size of several hundred nanometers.

[0154]

Table 3

[0155] Evaluation Example 3: Residual Lithium Evaluation of Cathode Active Material 10 g of the cathode active material synthesized in each of Example 1 and Comparative Example 1 and a deionized water (D.I.W) solution were stirred at 350 rpm for 30 minutes. After filtering 40 g of the solution, 100 g of deionized water (D.I.W) was further added, and the measurement was carried out using a potentiometric titrator (888 Titrando, Metrohm). The results are shown in Table 4 below.

[0156]

Table 4

[0157] It can be seen that the residual lithium compounds (Li2CO3, LiOH) present on the surface of the cathode active material are reduced by about 30% in Example 1 compared to Comparative Example 1. This is because the lithium remaining on the surface of the cathode active material reacts with the phosphorus-containing compound to form a Li x PO y coating layer. It can be understood that this is for the formation of the coating layer. Together with the Co concentration gradient region, the Li x PO y coating layer can prevent the direct exposure of the electrolyte and the cathode active material during electrochemical evaluation and contribute to the life stability.

[0158] Evaluation Example 4: Evaluation of Concentration Gradient Region and Coating Layer of Cathode Active Material Regarding the positive electrode active materials obtained in Example 1 and Comparative Example 1, photographs were taken using a high resolution transmission electron microscope (HR-TEM), and energy dispersive X-ray spectroscopy (EDX) was performed. The results are shown in Tables 5 and 6 below, and Figures 3 and 4A, B.

[0159]

Table 5

[0160]

Table 6

[0161] Referring to Table 5 and Figure 3, it can be seen that the concentrations of transition metals in the positive electrode active material, such as Ni, Co, and Mn, are substantially maintained constant in the surface and central directions of the positive electrode active material.

[0162] Referring to Table 6 and Figure 4A, it was confirmed that in the transition metals in the positive electrode active material, the concentration of Co decreases from the surface to the central direction of the positive electrode active material, and the concentration of Ni increases conversely. Also, it was found that the Co concentration gradient layer is about 500 nm. Without being bound by a specific theory, among the transition metals, cobalt ions contribute to the structural stability of the positive electrode active material having a layered structure compared to nickel ions. Therefore, due to the excessive inclusion of relatively stable cobalt on the surface of the positive electrode active material, it is considered that the structural stability of the positive electrode active material is improved during charge and discharge, and the long-life characteristics are improved.

[0163] Also, referring to Figure 4B, it was confirmed from the EDX analysis results of the particle surface in Example 1 that there is a coating layer containing phosphorus (P) of about 250 nm or less on the particle surface.

[0164] Evaluation Example 5: Room Temperature Life Evaluation The half-cells fabricated in Examples 4 to 6 and Comparative Examples 8 to 14 were allowed to rest for 10 hours, then charged in CC mode at 0.1C up to 4.3V, and then the charging was continued in CV mode up to a current corresponding to 0.05C. Next, discharging was carried out in CC mode at 0.1C down to 3.0V to complete the formation process. Next, at room temperature (25°C), after charging in CC mode at 0.5C up to 4.3V, the charging was continued in CV mode up to a current corresponding to 0.05C. Next, discharging was carried out in CC mode at 1C down to 3.0V, and this process was repeated a total of 50 times. Regarding the initial capacity, the capacity retention rates after 50 charge and discharge cycles were calculated, and the results are shown in Table 7 below. Also, graphs showing the capacity retention rates by cycle are shown in FIGS. 5 to 7.

[0165]

Table 7

[0166] Referring to Table 7 and FIG. 5, according to the room temperature life results of Example 4 and Comparative Example 9, in the case of including a coating layer containing a phosphorus-containing compound and a concentration gradient region (Example 4), compared with the case of not including the coating layer and the concentration gradient region, a life retention rate improved by about 2% is shown at 50 cycles, and compared with the case of not containing a phosphorus-containing compound (Comparative Example 14), a life retention rate improved by about 3% is shown at 50 cycles. Furthermore, in the case of the half-cell of Example 4, compared with Comparative Examples 10 to 13 where a cathode active material to which one or more of the elements Na, W, Mg, Ti, and S are not introduced is applied, a life retention rate improved by up to about 8% is shown at 50 cycles.

[0167] Through such data, it was confirmed that when the elements Na, W, Mg, Ti, and S, the Co concentration gradient region, and a coating layer containing a phosphorus-containing compound are applied simultaneously, the most excellent life characteristics can be obtained.

[0168] Furthermore, in addition to nickel-cobalt-manganese (NCM)-based cathode active materials, it was confirmed that the introduction of a coating layer containing a concentration gradient region and a phosphorus-containing compound also improved the life characteristics by about 4 to 5% in the case of nickel-cobalt-aluminum (NCA)-based cathode active materials and nickel-cobalt (NC)-based cathode active materials.

[0169] As described above, the desirable embodiments according to the present invention have been described with reference to the drawings and the examples, but they are merely exemplary, and those having ordinary knowledge in the relevant technical field will be able to understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the protection scope of the present invention is defined by the scope of the claims.

Claims

1. High-Ni lithium transition metal oxide particles which are single particles represented by the following Chemical Formula 1, and a phosphorus-containing coating layer disposed on the surface of the high-Ni lithium transition metal oxide particles, and the high-Ni lithium transition metal oxide particles include a concentration gradient region in which the concentration of Co atoms decreases from the surface toward the particle center, a positive electrode active material. Li １－ｘ Na ｘ M １－（α＋β＋γ） W α Mg β Ti γ O ２－ａ S ａ ... (Chemical formula 1) In the Chemical Formula 1, M includes Ni atoms and Co atoms, 0 < x ≤ 0.01, 0 < α ≤ 0.01, 0 < β ≤ 0.005, 0 < γ ≤ 0.005, 0 < a ≤ 0.01, 0 < α + β + γ ≤ 0.02, Ni is 73 mol% or more with respect to the whole of M.

2. The M further includes one or more elements selected from Mn, Al, V, Ca, Zr, B, and P, characterized in that, The positive electrode active material according to Claim 1.

3. The concentration gradient region is a positive electrode active material according to Claim 1, in which the concentration of Ni atoms increases from the surface of the high-Ni lithium transition metal oxide particles toward the particle center.

4. The concentration gradient region is a positive electrode active material according to Claim 1, including a region up to a distance of 500 nm from the surface of the high-Ni lithium transition metal oxide particles toward the center.

5. In the Chemical Formula 1, β and γ are respectively 0 < β ≤ 0.003, 0 < γ ≤ 0.003, the positive electrode active material according to Claim 1.

6. The high-Ni lithium transition metal oxide particles are a positive electrode active material according to Claim 1, represented by the following Chemical Formula 3 or 4. Li １－ｘ” Na ｘ” Ni ｙ１” Co ｙ２” Al ｙ３” W α” Mg β” Ti γ” O ２－ａ” S ａ” ... (Chemical formula 3) Li １－ｘ’’’ Na ｘ’’’ Ni ｙ１’’’ Co ｙ２’’’ W α’’’ Mg β’’’ Ti γ’’’ O ２－ａ’’’ S ａ’’’ ... (Chemical formula 4) In the Chemical Formula 3, 0 < x” ≤ 0.01, 0 < α” ≤ 0.01, 0 < β” ≤ 0.005, 0 < γ” ≤ 0.005, 0 < a” ≤ 0.01, 0 < α” + β” + γ” ≤ 0.02, 0.73 ≤ y1” < 1, 0 < y2” ≤ 0.2, 0 < y3” ≤ 0.05, y1” + y2” + y3” + α” + β” + γ” = 1, In the Chemical Formula 4, 0 < x’’’ ≤ 0.01, 0 < α’’’ ≤ 0.01, 0 < β’’’ ≤ 0.005, 0 < γ’’’ ≤ 0.005, 0 < a’’’ ≤ 0.01, 0 < α’’’ + β’’’ + γ’’’ ≤ 0.02, 0.78 ≤ y1’’’ < 1, 0 < y2’’’ ≤ 0.2, y1’’’ + y2’’’ + α’’’ + β’’’ + γ’’’ = 1.

7. In the Chemical Formula 3, 0 < β” ≤ 0.003, 0 < γ” ≤ 0.003, 0 < α” + β” + γ” ≤ 0.016, The cathode active material according to claim 6, wherein in the chemical formula 4, 0 < β''' ≤ 0.003, 0 < γ''' ≤ 0.003, and 0 < α''' + β''' + γ''' ≤ 0.

016.

8. The average particle diameter (D ５０ ) of the high-Ni-based lithium transition metal oxide particles is measured using a Cilas 1090 (Scinco) instrument and is from 0.1 μm to 20 μm. The positive electrode active material according to claim 1.

9. The cathode active material according to claim 1, wherein the phosphorus-containing coating layer contains a compound represented by the following chemical formula 5: Li ａ P ｂ O ｃ ... (Chemical formula 5) 0 < a ≤ 3, 0 < b ≤ 1, and 0 < c ≤ 4.

10. The cathode active material according to claim 1, wherein the phosphorus-containing coating layer has a thickness of 250 nm or less.

11. Preparing high-Ni lithium transition metal oxide particles which are single particles represented by the following chemical formula 1; Mixing the high-Ni lithium transition metal oxide particles, a Co element-containing compound, and a P element-containing compound to obtain a cathode active material precursor; Firing the cathode active material precursor to obtain a cathode active material, The method for manufacturing a cathode active material, wherein the cathode active material includes a phosphorus-containing coating layer on the surface and includes a concentration gradient region in which the concentration of Co atoms decreases from the surface toward the particle center. Li １－ｘ Na ｘ M １－（α＋β＋γ） W α Mg β Ti γ O ２－ａ S ａ ... (Chemical formula 1) In the chemical formula 1, M includes Ni atoms and Co atoms, 0 < x ≤ 0.01, 0 < α ≤ 0.01, 0 < β ≤ 0.005, 0 < γ ≤ 0.005, 0 < a ≤ 0.01, and 0 < α + β + γ ≤ 0.02, Ni is 73 mol% or more with respect to the whole of M.

12. The M further includes one or more elements selected from Mn, Al, V, Ca, Zr, B, and P. The method for manufacturing a cathode active material according to claim 11.

13. The step of preparing the high-Ni lithium transition metal oxide particles Mixing a Li element-containing compound, a Na element-containing compound, a W element-containing compound, a Mg element-containing compound, a Ti element-containing compound, an M element-containing compound, and an S element-containing compound to obtain a lithium transition metal oxide precursor; The method for manufacturing a cathode active material according to claim 11, including heat-treating the lithium transition metal oxide precursor to obtain a cathode active material including high-Ni lithium transition metal oxide particles represented by the following chemical formula 1.

14. The mixing step includes a step of mechanical mixing. The method for manufacturing a cathode active material according to claim 13.

15. The heat treatment step includes a first heat treatment step and a second heat treatment step, The heat treatment temperature of the first heat treatment step is higher than the heat treatment temperature of the second heat treatment step. The method for manufacturing a cathode active material according to claim 13.

16. The firing step is performed at a temperature of 500°C to 900°C for 1 to 6 hours, and the method for producing a positive electrode active material according to claim 11.

17. A positive electrode containing the positive electrode active material according to any one of claims 1 to 10, a negative electrode, and an electrolyte, and a lithium secondary battery comprising the same.

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