A 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 containing lithium transition metal oxide particles containing Ni atoms and Co atoms, in which a portion of Li has been substituted with Na, and in which the lithium transition metal oxide particles contain a concentration gradient region in which the concentration of Co atoms decreases from the surface toward the center of the particle, 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 manufacturing the same, and a lithium secondary battery including the cathode.

[0002] The present invention has been made with the support of funds from the Ministry of Industry, Trade and Resources under Project Serial Number P0009541 titled "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 being commercialized by Sony in 1991, the demand for lithium secondary batteries 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 raw material nickel is inexpensive and has 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 the new interface of the cathode active material and the electrolyte, resulting in battery performance degradation such as a decrease in stability due to gas generation and a decrease in battery performance due to electrolyte depletion. In addition, in order to realize a high energy density, an increase in electrode density (>3.3 g / cc) is required, which induces the disintegration 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. Single-crystalline Ni-based cathode active materials can exhibit excellent electrochemical performance without particle disintegration when the electrode density increases (>3.3 g / cc) for realizing their energy density. However, such single-crystalline Ni-based cathode active materials have 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 single-crystalline Ni-based cathode active materials. 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 Problems

[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 are included. There is provided a cathode active material 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, there is provided a method for producing a cathode active material including the steps 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, mixing the lithium transition metal oxide particles and a Co element-containing compound to obtain a cathode active material precursor, and firing the cathode active material precursor to obtain a cathode active material, wherein the cathode active material includes a concentration gradient region in which the concentration of Co atoms decreases from the surface toward the particle center of the lithium transition metal oxide particles.

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

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, 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 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 subject to various transformations and can have various embodiments, but specific embodiments are illustrated in the drawings and are described in detail by a detailed description. However, it should not be construed as limiting the inventive concept to specific embodiments, and should be understood to include all transformations, equivalents, or alternatives included in the technical scope of the inventive concept.

[0013] The terms used below are only used for the purpose of describing specific embodiments and are not intended to limit the 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, elements, materials, or combinations thereof described in the specification, and it should not be understood to preclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, elements, materials, or combinations thereof. As used below, " / " may be construed as "and" or "or" depending on the context.

[0014] In the drawings, in order 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 "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 only used 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, and should not be interpreted in an idealized or overly formal sense.

[0016] "Group" means a group of 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 include all such alternatives, modifications, variations, improvements, and substantial equivalents.

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

[0019] A cathode 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 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 direction.

[0020] When a part of Li in the positive electrode active material is substituted with 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, the crystal collapse is suppressed during the charge-discharge process, and not only the life characteristics are improved, but also on the surface, the distribution of unstable Ni(III) ions and Ni(IV) ions is reduced, and at the core center, by increasing the distribution of Ni(II) ions, not only the side reaction between the Ni ions and the electrolytic solution is suppressed, but also a high capacity of the positive electrode active material can be obtained due to the high Ni ion content. Therefore, the positive electrode active material has high-capacity characteristics and long-life characteristics. Further, as will be described later, by additionally doping transition metals such as W, Mg, and Ti, unstable Ni(III) and Ni(IV) are reduced, so that the structural stability is further improved and the life characteristics are remarkably improved.

[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] From the surface of the lithium transition metal oxide particles, the concentration of Co atoms gradually decreases and the concentration of Ni atoms gradually increases, thereby achieving the high-capacity characteristics and long-life characteristics of the positive electrode active material.

[0027] According to one embodiment, the lithium transition metal oxide particles also contain 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 by Na, a part of M is substituted by W, Mg, and Ti, and a part of O is substituted by S. During charge and discharge of a lithium secondary battery containing it, 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 of a small amount of W, Mg, and Ti induces reduction of unstable nickel ions existing in the lithium transition metal oxide, for example, Ni 3+ , Ni 4+ to the form of stable nickel ions Ni 2+ , thereby suppressing deterioration of the positive electrode active material and capacity reduction due to side reactions between unstable nickel ions and the electrolytic solution during charge and discharge.

[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, so that unstable nickel ions distributed in the lithium transition metal oxide particles, for example, Ni 3+ , Ni 4+to induce the reduction to Ni in the form of stable nickel ions, prevent the deterioration of the positive electrode active material during charge and discharge, and significantly suppress the capacity reduction. 2+

[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 may also be one or more elements selected from among Ni, Co, Mn, Al, V, Ca, Zr, B, and P. For example, M may also be 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. When a part of Li in the lithium transition metal oxide represented by Chemical Formula 1 is substituted 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 lithium desorption 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 bending 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 foregoing W, Mg, and Ti are substituted for the lithium transition metal oxide in the molar ratio, in the charged state, even when lithium is desorbed, in the lithium transition metal oxide, due to suppression of structural expansion of the crystal by the interaction between oxygen, 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, charge balance within the lithium transition metal oxide is achieved during charging and discharging, 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 means 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, the repulsive force of S anions makes the crystal structure unstable, and conversely, the life characteristics are deteriorated.

[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 secondary particles formed by aggregation of a plurality of particles or particles formed by aggregation of a plurality of particles and coating around 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. Further, compared with secondary particles in which a plurality of single particles are aggregated, disintegration is suppressed during rolling, a high energy density can be realized, and life deterioration 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 easy lithium ion conduction compared with polycrystals and excellent high-rate charging characteristics compared with 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 life characteristics and high energy density at the same time.

[0052] According to one embodiment, the lithium transition metal oxide is represented by any one of the following Chemical Formulas 2 to 4. Li 1-x’ Na x’ Ni y1’ Co y2’ Mny3’ 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. For example, in Chemical Formula 2, 0 < β’ ≦ 0.003, 0 < γ’ ≦ 0.003, 0 < α’ + β’ + γ’ ≦ 0.016; in Chemical Formula 3, 0 < β” ≦ 0.003, 0 < γ” ≦ 0.003, 0 < α” + β” + γ” ≦ 0.016; and in Chemical Formula 4, 0 < β’’’ ≦ 0.003, 0 < γ’’’ ≦ 0.003, 0 < α’’’ + β’’’ + γ’’’ ≦ 0.016.

[0056] The lithium transition metal oxide satisfying the above composition can stabilize unstable Ni ions inside and possess high energy density and long - life stability.

[0057] In the case of a cathode active material containing a general high - nickel - based lithium nickel cobalt manganese oxide, 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, thereby obtaining a single - crystal, structurally stable, high - capacity, and long - life cathode active material.

[0058] 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-discharge capacity, and when it is 0.1 μm or less, it is difficult to obtain the desired energy density per volume.

[0059] Hereinafter, the manufacturing method of the positive electrode active material according to one embodiment will be described in detail.

[0060] The manufacturing method of the positive electrode active material according to one embodiment includes the steps of preparing lithium transition metal oxide particles in which a part of Li is substituted with Na and containing Ni atoms and Co atoms, mixing the lithium transition metal oxide particles and a Co 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 concentration gradient region in which the concentration of Co atoms decreases from the surface toward the particle center.

[0061] According to one embodiment, the step of preparing the lithium transition metal oxide particles includes the steps of 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 O 2-a S a ···(Chemical Formula 1)

[0062] 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.

[0063] For the specific description regarding Chemical Formula 1, refer to the foregoing.

[0064] The mixing step also includes mechanically mixing the specific element-containing compound. The mechanical mixing is carried out dry. The mechanical mixing applies mechanical force to crush and mix the substances to be mixed, forming a uniform mixture. Mechanical mixing can also be carried out using a mixing device such as a ball mill, planetary mill, stirred ball mill, or vibrating mill that utilizes beads which are chemically inert, for example. At this time, in order to maximize the mixing effect, a small amount of an alcohol such as ethanol or a higher fatty acid such as stearic acid can be selectively added.

[0065] The mechanical mixing is carried out 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.

[0066] The lithium element-containing compound also 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.

[0067] The Na element-containing compound also includes, but is not limited to, sodium hydroxide, oxide, nitride, carbonate, or a combination thereof. For example, it can also be NaOH, Na2CO3, or a combination thereof.

[0068] The W element-containing compound may include, but is not limited to, hydroxides, oxides, nitrides, carbon oxides of W, or combinations thereof. For example, it may also be W(OH)6, WO3, or combinations thereof.

[0069] The Mg element-containing compound may include, but is not limited to, hydroxides, oxides, nitrides, carbon oxides of Mg, or combinations thereof. For example, it may also be Mg(OH)2, MgCO3, or combinations thereof.

[0070] The Ti element-containing compound may include, but is not limited to, hydroxides, oxides, nitrides, carbon oxides of Ti, or combinations thereof. For example, it may also be Ti(OH)2, TiO2, or combinations thereof.

[0071] The M element-containing compound may include, but is not limited to, hydroxides, oxides, nitrides, carbon oxides of one or more elements selected from 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.

[0072] The S element-containing compound may include, but is not limited to, hydroxides, oxides, nitrides, carbon oxides, ammonium compounds of S, or combinations thereof. For example, it may also be (NH4)2S.

[0073] According to one embodiment, in the step of obtaining the cathode active material precursor, a Co element-containing compound may be further included as a mixed material.

[0074] The Co element-containing compound is a compound capable of providing the Co element, and includes a hydroxide, oxide, nitride, carbonate, acetate of Co, or a combination thereof. For example, it may also be cobalt acetate.

[0075] 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 carried out 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 carried out in the same chamber, or may be carried out in different chambers from each other.

[0076] The heat treatment temperature in the first heat treatment step is higher than the heat treatment temperature in the second heat treatment step.

[0077] The first heat treatment step may be carried out 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 any range formed by selecting any two points within the above range is included.

[0078] The second heat treatment step may be carried out at a heat treatment temperature of 700°C to 800°C. The heat treatment temperature may 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.

[0079] According to an embodiment, the heat treatment time in the first heat treatment step is shorter than the heat treatment time in the second heat treatment step.

[0080] For example, in the first heat treatment stage, the heat treatment time is 3 to 5 hours, 4 to 5 hours, or 3 to 4 hours, but is not limited thereto, and any range constituted by selecting any two points within the above range is included.

[0081] For example, in the second heat treatment stage, the heat treatment time is 10 to 20 hours, 10 to 15 hours, but is not limited thereto, and any range constituted by selecting any two points within the above range is included.

[0082] The first heat treatment stage also includes a stage of heat treating at a heat treatment temperature of 800°C to 1,200°C for 3 to 5 hours.

[0083] The second heat treatment stage also includes a stage of heat treating at a heat treatment temperature of 700°C to 800°C for 10 to 20 hours.

[0084] In the first heat treatment stage, the lithium transition metal oxide forms a layered-structured positive electrode active material, induces the growth of particles, and makes them form a single crystal shape. In the first heat treatment stage, each primary particle in the lithium transition metal oxide of secondary particle shape grows rapidly and cannot withstand the inter-particle stress, so that while the inside of the primary particle appears, they are fused with each other, and it is considered that a single crystal positive electrode active material for a secondary battery is formed. The second heat treatment stage increases the crystallinity of the layered structure generated in the first heat treatment stage by performing heat treatment at a lower temperature than the first heat treatment stage for a long period of time. Through the first heat treatment stage and the second heat treatment stage, a high-nickel-based positive electrode active material of single phase, single crystal, and single particle can be obtained.

[0085] According to an embodiment, in the step of obtaining the positive electrode active material precursor, the Co element-containing compound is also included in an organic solvent. For example, the organic solvent is also a volatile solvent. For example, the organic solvent is a solvent that is volatile at a temperature of 80° C. or lower, such as methanol or ethanol.

[0086] According to an embodiment, the firing step can be carried out at a temperature of 500° C. to 900° C. For example, the firing step can be carried out at a temperature of 600° C. to 900° C. According to an embodiment, the firing step can be carried out for 1 hour to 6 hours. For example, the firing step can be carried out for 2 hours to 4 hours.

[0087] According to an 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 positive electrode active material precursor at the aforementioned firing temperature and time, a positive electrode active material in which a concentration gradient region having a concentration gradient of Co atoms is formed can be obtained.

[0088] According to an embodiment, the concentration gradient region also includes a region of 500 nm or less from the surface of the lithium transition metal oxide particles toward the center. In the process of firing the positive electrode active material precursor, it is considered that a concentration gradient region of Co element is formed in the process of Co element penetrating the surface of the lithium transition metal oxide particles and diffusing inside.

[0089] According to an 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 diameter of the lithium transition metal oxide is also 0.1 μm to 20 μm.

[0090] Further, in the lithium transition metal oxide produced by the manufacturing method of the positive electrode active material, W, Mg, and Ti elements are substituted at the site of M element in the structure, S element is substituted at the O site, and Na element is substituted at the Li site, so that not only the oxidation of existing Ni 2+ is suppressed, but also the existing unstable Ni3+ Ni ions 2+ Reduction to ions is induced, and structurally stable and high-density lithium transition metal oxides are obtained. Also, the reduced Ni 2+ ions and Li + ions have similar ionic radii, promoting Li / Ni disordering. When Li desorbs, Ni ions fill the vacant lattice sites, achieving the structural stability of the crystal.

[0091] Furthermore, by further including a Co concentration gradient region, the structural stability is improved compared to the case where only transition metals are additionally substituted, and the capacity characteristics and life characteristics are improved.

[0092] According to another aspect, a positive electrode including the aforementioned positive electrode active material is provided.

[0093] According to still another aspect, a lithium secondary battery including the positive electrode, a negative electrode, and an electrolyte is provided.

[0094] The positive electrode and the lithium secondary battery including the same are also manufactured by the following method.

[0095] First, a positive electrode is prepared.

[0096] For example, a positive electrode active material composition in which the aforementioned positive electrode active material, conductive material, binder, and 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 and then peeled off from the support, the film 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.

[0097] 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; conductive metal oxides such as titanium oxide; etc. Any material that can be used as a conductive material in the relevant technical field can be used.

[0098] 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.

[0099] 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.

[0100] The contents of the aforementioned positive electrode active material, conductive material, binder, and solvent are at levels commonly 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 may be omitted.

[0101] Next, a negative electrode is prepared.

[0102] 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, the film peeled off from the support may be laminated on a metal current collector to manufacture a negative electrode plate.

[0103] 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.

[0104] Any of the negative electrode active materials can be used as long as they can be used as a negative electrode active material for a lithium battery in the relevant technical field. For example, those containing 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 are also acceptable.

[0105] For example, the metals alloyable 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 is not Si), 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 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, Tl, Ge, P, As, Sb, Bi, S, Se, or Te.

[0106] For example, the transition metal oxides include lithium titanate, vanadium oxide, lithium vanadate, and the like.

[0107] For example, the non-transition metal oxide is also SnO2, SiO x (where 0 < x < 2) and the like.

[0108] The carbon-based material is also crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon is also graphite such as amorphous, plate-like, 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.

[0109] In the negative electrode active material composition, the same conductive material, binder and solvent as those in the case of the positive electrode active material composition can be used.

[0110] 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 may be omitted.

[0111] Next, a separator inserted between the positive electrode and the negative electrode is prepared.

[0112] If the separator is one generally used in lithium batteries, any of them can be used. One with low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention ability can be used. The separator can be a single membrane or a multilayer membrane. For example, it can be selected from among glass fiber, polyester, Teflon (registered trademark), polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene (PTFE), or combinations thereof, and can be in the form of a non-woven fabric or a woven fabric. Also, a mixed multilayer membrane 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 lithium-ion batteries, and a separator with excellent impregnation ability for organic electrolytes can be used for lithium-ion polymer batteries. For example, the separator can also be manufactured by the following method.

[0113] 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 off from the support is laminated on the upper part of the electrode to form a separator.

[0114] The polymer resin used in the manufacture of the separator is not particularly limited, and any substance used as a binder for the electrode plate can be used. For example, vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or a mixture thereof can be used.

[0115] Next, an electrolyte is prepared.

[0116] 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 of those that can be used as a solid electrolyte in the technical field can be used. The solid electrolyte is also formed on the negative electrode by a method such as sputtering.

[0117] For example, the organic electrolyte solution is also produced by dissolving a lithium salt in an organic solvent.

[0118] 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. are available. They can be used alone or in combination of a plurality. For example, a solvent obtained by mixing a cyclic carbonate and a chain carbonate can be used.

[0119] Further, a gel-phase polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide or polyacrylonitrile with an electrolyte solution, and 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.

[0120] Any of the above lithium salts can 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.

[0121] 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 can also be a thin-film battery. The lithium battery 1 can also be a lithium-ion battery.

[0122] 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 pouch, a lithium-ion polymer battery is completed.

[0123] Also, a plurality of the battery structures can be 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.

[0124] In addition, since the lithium battery has excellent 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, power tools, power storage systems, etc.

[0125] 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.

[0126] (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 solution in which 2 g of cobalt acetate is dissolved in ethanol, stirred for 30 minutes, the mixed solution is left at 80 °C, and after evaporating the ethanol, the obtained powder is fired 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.

[0127] 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 solution in which 2 g of cobalt acetate was dissolved in ethanol, stirred for 30 minutes, the mixed solution was left at 80 °C, and after evaporating the ethanol, the obtained powder was 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.

[0128] 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 mixed 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 solution in which 2 g of cobalt acetate was dissolved in ethanol, stirred for 30 minutes, the mixed solution was left at 80 °C, and after evaporating the ethanol, the obtained powder was 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.

[0129] 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 mixed mechanically 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.

[0130] Comparative Example 2 100 g of Ni 0.8 Co0.1 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.

[0131] 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.

[0132] 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.

[0133] Comparative Example 5 100 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 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 were added to a solution in which 2 g of cobalt acetate was dissolved in ethanol, and the mixture was stirred for 30 minutes. The mixed solution was left at 80°C to evaporate ethanol, and then the obtained powder was 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.

[0134] Comparative Example 6 100 g of Ni 0.9 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 S 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 a positive electrode active material. The specific composition of the obtained positive electrode active material can be confirmed in Table 1.

[0135] Comparative Example 7 100 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.

[0136] (Manufacture of Half Cell) Example 4 The positive electrode active material obtained in Example 1, the conductive material, and the 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 manufacture a positive electrode. The loading level of the electrode plate was 11.0 mg / cm2 and the electrode density was 3.6 g / cc. Using the manufactured positive electrode as a working electrode, a lithium foil as a counter electrode, and a liquid electrolyte in which LiPF6 was added as a lithium salt to a mixed solvent obtained by mixing ethylene carbonate (EC) / EMC (ethyl methyl carbonate) / DEC (diethyl carbonate) at a volume ratio of 3 / 4 / 3 to a concentration of 1.3 M, a CR2032 half cell was fabricated by a generally known process.

[0137] Examples 5 and 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.

[0138] Comparative Examples 8 to 14 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.

[0139] [Table 1]

[0140] Evaluation Example 1: Composition Evaluation of Positive Electrode Active Material For the positive electrode active materials synthesized in Example 1 and Comparative Example 1, ICP (inductively coupled plasma) analysis was performed using a 700-ES (Varian) instrument, and the results are shown in Table 2 below.

[0141] Referring to Table 2, it can be seen that in 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 positive electrode active material increased the ratio of Co element in the positive electrode active material by about 1 mol% due to substitution with other transition metals in the positive electrode active material, and the number of moles of other transition metals decreased. Also, during ICP analysis, even when the analysis is performed 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.

[0142]

Table 2

[0143] Evaluation Example 2: Particle Size Evaluation of Cathode Active Material The appearances of the cathode active materials synthesized in Example 1 and Comparative Example 1 were obtained using the equipment of Verios 460 (FEI) to obtain SEM (scanning electron microscope) images, which are shown in Fig. 1. Also, using the equipment of Cilas 1090 (Scinco), the particle size distribution was measured and shown in Table 3 below and Fig. 2.

[0144] Referring to Table 3 and Figs. 1 and 2, for the single-particle type cathode active material of Example 1, although a Co concentration gradient region is introduced, no significant change in particle size is observed compared to the single-particle type cathode active material of Comparative Example 1, suggesting that the Co-containing compound penetrated into the lithium transition metal oxide particles to form a concentration gradient region.

[0145]

Table 3

[0146] Evaluation Example 3: Concentration Gradient Region Evaluation of Cathode Active Material For the cathode active materials obtained in Example 1 and Comparative Example 1, photographs were taken using a high-resolution transmission electron microscope (HR-TEM: high resolution transmission electron microscopy), and energy dispersive X-ray spectroscopy (EDX) was carried out. The results are shown in Table 4 and Table 5 below, and Figs. 3 and 4.

[0147]

Table 4

[0148]

Table 5

[0149] Referring to Table 4 and FIG. 3, it can be seen that the concentrations of transition metals such as Ni, Co, and Mn in the positive electrode active material are substantially maintained constant in the surface and central directions of the positive electrode active material.

[0150] Referring to Table 5 and FIG. 4, it was confirmed that in the transition metals in the positive electrode active material, the concentration of Co decreased from the surface to the central direction of the positive electrode active material, and the concentration of Ni tended to increase conversely. Also, it was found that the Co concentration gradient layer was about 500 nm. Without being bound by a specific theory, in 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.

[0151] Evaluation Example 4: Room Temperature Life Evaluation The half cells prepared in Examples 4 to 6 and Comparative Examples 8 to 14 were allowed to rest for 10 hours, then charged in CC mode to 4.3 V at 0.1 C, and then charged in CV mode to a current corresponding to 0.05 C. Next, discharge was performed in CC mode to 3.0 V at 0.1 C to complete the formation process. Next, at room temperature (25°C), after charging in CC mode to 4.3 V at 0.5 C, charging was continued in CV mode to a current corresponding to 0.05 C. Next, discharge was advanced in CC mode to 3.0 V at 1 C, and this process was repeated a total of 50 times. For the initial capacity, the capacity retention rates after 50 charges and discharges were calculated, and the results are shown in Table 7 below. Also, graphs showing the capacity retention rate by cycle are shown in FIGS. 5 to 7.

[0152]

Table 6

[0153] Referring to Table 6 and FIG. 5, according to the normal temperature life results of Example 4 and Comparative Example 8, when the concentration gradient region is included (Example 4), compared with the case where the concentration gradient region is not included, at 50 cycles, a life maintenance rate improved by about 3% was shown. This is considered to be because cobalt, which contributes to the structural stabilization of the layered structure, is relatively excessively distributed on the surface of the cathode active material, thereby suppressing the deterioration of the cathode active material. Furthermore, in the case of the half cell of Example 4, compared with Comparative Examples 9 to 11 in which a cathode active material not containing a concentration gradient region and not containing one or more elements among Na element, W element, Mg element, Ti element and S element was applied, at 50 cycles, a life maintenance rate improved by up to about 7% was shown. Furthermore, when the concentration gradient region is included but one or more elements among Na, W, Mg, Ti, and S are not introduced, for example, compared with Comparative Example 12 in which a cathode active material not containing Ti element was applied, a life maintenance rate improved by about 3% was shown.

[0154] Through such data, it was confirmed that when the Na element, W element, Mg element, Ti element and S element and the concentration gradient region are included, excellent life characteristics can be obtained due to the synergistic effect between them.

[0155] Also, in addition to the nickel-cobalt-manganese (NCM)-based cathode active material, in the case of the nickel-cobalt-aluminum (NCA)-based cathode active material and the nickel-cobalt (NC)-based cathode active material, it was confirmed that when the concentration gradient region is included, the life characteristics are improved by about 2 to 3%.

[0156] In the above, with reference to the drawings and examples, the desirable embodiments according to the present invention have been described, 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 from them. Therefore, the protection scope of the present invention is defined by the scope of the claims.

Claims

1. A positive electrode active material comprising high-Ni lithium transition metal oxide particles which are single particles represented by the following Chemical Formula 1, wherein the high-Ni lithium transition metal oxide particles include a concentration gradient region in which the concentration of Co atoms decreases from the particle 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, 0 < α + β + γ ≤ 0.02, and Ni is 73 mol% or more based on the whole of M.

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

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

4. The positive electrode active material according to Claim 1, wherein the concentration gradient region includes 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. The positive electrode active material according to Claim 1, wherein in the Chemical Formula 1, β and γ are each 0 < β ≤ 0.003 and 0 < γ ≤ 0.

003.

6. The positive electrode active material according to Claim 1, wherein the high-Ni lithium transition metal oxide particles are 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, In the Chemical Formula 4, 0 < β''' ≤ 0.003, 0 < γ''' ≤ 0.003, 0 < α''' + β''' + γ''' ≤ 0.

016. The positive electrode active material according to Claim 6.

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

9. 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 and a Co element-containing compound to obtain a positive electrode active material precursor; Firing the positive electrode active material precursor to obtain a positive electrode active material, wherein the positive electrode active material includes a concentration gradient region in which the concentration of Co atoms decreases from the surface of the high-Ni lithium transition metal oxide particles toward the particle center, and a method for manufacturing 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, and 0 < α + β + γ ≤ 0.02, and Ni is 73 mol% or more with respect to the whole of M.

10. The method for manufacturing a positive electrode active material according to claim 9, wherein M further includes one or more elements selected from Mn, Al, V, Ca, Zr, B, and P.

11. The step of preparing the high-Ni 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 a positive electrode active material including the high-Ni lithium transition metal oxide particles represented by the chemical formula 1, and the method for manufacturing a positive electrode active material according to claim 9.

12. The method for manufacturing a positive electrode active material according to claim 11, wherein the mixing step includes mechanical mixing.

13. The heat treatment step includes a first heat treatment step and a second heat treatment step, and the heat treatment temperature of the first heat treatment step is higher than the heat treatment temperature of the second heat treatment step, and the method for manufacturing a positive electrode active material according to claim 11.

14. In the step of obtaining the positive electrode active material precursor, the Co element-containing compound is contained in an organic solvent, and the method for manufacturing a positive electrode active material according to claim 9.

15. The method for manufacturing a positive electrode active material according to claim 9, wherein the concentration gradient region includes a region of 500 nm or less from the surface of the lithium transition metal oxide particles toward the center.

16. The firing step is performed at a temperature of 500°C to 900°C for 1 hour to 6 hours, and the method for manufacturing a positive electrode active material according to claim 9.

17. A positive electrode including the positive electrode active material according to any one of claims 1 to 8; a negative electrode; A lithium secondary battery comprising an electrolyte and...

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