Positive electrode active material, positive electrode comprising the same, and lithium secondary battery

Abstract

This invention relates to a single-particle positive electrode active material comprising: a single-particle lithium composite transition metal oxide having a layered structure; and a cobalt-containing coating formed on the single-particle lithium composite transition metal oxide, wherein the positive electrode active material satisfies Formula 1 or Formula 2 as described herein. Furthermore, this invention relates to a positive electrode and a lithium secondary battery comprising the aforementioned positive electrode active material.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2023-0172675, filed on December 1, 2023, the entire contents of which are incorporated herein by reference for all purposes. Technical Field

[0003] This invention relates to a positive electrode active material comprising a lithium composite transition metal oxide in the form of single particles, and a positive electrode and a lithium secondary battery comprising the positive electrode active material. Background Technology

[0004] Recently, with the technological development and increasing demand for mobile devices and electric vehicles, the demand for secondary batteries as an energy source is rapidly increasing. Among secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life and low self-discharge rate, have been commercialized and are widely used.

[0005] As positive electrode active materials for lithium secondary batteries, lithium transition metal oxides such as LiCoO2 (lithium cobalt oxides), LiNiO2 (lithium nickel oxides), LiMnO2 or LiMn2O4 (lithium manganese oxides), and LiFePO4 (lithium iron phosphate oxides) have been developed. a Co b Mn c O2, Li[Ni a Co b Al c ]O2 and Li[Ni a Co b Mn c Al d Lithium complex transition metal oxides containing two or more transition metals, such as O2, have recently been developed and are widely used.

[0006] Lithium composite transition metal oxides containing two or more transition metals, developed to date, are typically manufactured as spherical secondary particles comprised of tens to hundreds of primary particles. However, recently, to address the structural and thermal stability issues inherent in secondary particle-type cathode active materials, the development of single-particle cathode active materials is being accelerated. Specifically, when secondary particle-type cathode active materials are applied to lithium-ion batteries, a large amount of gas is generated, leading to battery volume expansion. Increasing the nickel content in the cathode active material to achieve higher capacity also increases the risk of fire. Therefore, the demand for developing single-particle-type cathode active materials with excellent stability is increasing. However, single-particle-type cathode materials suffer from poor resistivity due to their low specific surface area.

[0007] Therefore, there is a need to develop single-particle cathode materials with excellent stability that can improve the initial efficiency and resistance characteristics of batteries when applied to them. Summary of the Invention

[0008] Technical issues

[0009] The present invention aims to solve the above problems and provides a positive electrode active material with excellent structural stability that can improve the initial efficiency and resistance characteristics of batteries when applied to batteries.

[0010] Furthermore, the present invention aims to provide a lithium secondary battery comprising the aforementioned positive electrode active material, thereby having improved initial efficiency, resistance characteristics, etc.

[0011] Technical solution

[0012] To address the aforementioned issues, this invention provides a positive electrode active material, a positive electrode, and a lithium secondary battery.

[0013] (1) The present invention provides a positive electrode active material comprising: a lithium composite transition metal oxide in the form of single particles having a layered structure; and a cobalt-containing coating formed on the lithium composite transition metal oxide, wherein the positive electrode active material satisfies formula 1 or formula 2: [Formula 1]

[0014] [Equation 2]

[0015] in, It is the ratio of the peak intensity corresponding to the LiCoO2 Cu Kα1 diffraction peak position at 37° to 38° in the XRD spectrum of the positive electrode active material to the peak intensity of the (003) plane, and It is the ratio of the peak intensity corresponding to the LiCoO2 Cu Kα1 diffraction peak position at 45° to 45.5° in the XRD spectrum of the positive electrode active material to the peak intensity of the (003) plane.

[0016] (2) The present invention provides a positive electrode active material according to (1) above, wherein the average particle size (D) of the lithium composite transition metal oxide is... 50 The thickness ranges from 1.0 μm to 5.0 μm.

[0017] (3) The present invention provides a positive electrode active material according to (1) or (2) above, wherein the lithium composite transition metal oxide comprises nickel (Ni), cobalt (Co) and manganese (Mn).

[0018] (4) The present invention provides a positive electrode active material according to any one of the above (1) to (3), wherein the lithium composite transition metal oxide has a composition represented by the following Chemical Formula 1: [Chemical Formula 1] Li a Ni b Co c Mn d M 1 e O2 Where: M 1 is at least one selected from Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P, and S, and 0.9 ≤ a ≤ 1.1, 0.8 ≤ b < 1.0, 0 < c < 0.2, 0 < d < 0.2, 0 ≤ e ≤ 0.1, and b + c + d + e = 1.

[0019] (5) The present invention provides a positive electrode active material according to any one of the above (1) to (4), wherein the coating portion has a thin film shape, a discontinuously formed island shape, or a combination thereof.

[0020] (6) The present invention provides a positive electrode active material according to any one of the above (1) to (5), wherein the coating portion is a region in the range of 5 nm to 100 nm in the direction from the surface to the center of the positive electrode active material.

[0021] (7) The present invention provides a positive electrode comprising the positive electrode active material according to any one of the above (1) to (6).

[0022] (8) The present invention provides a lithium secondary battery comprising: the positive electrode according to the above (7); a negative electrode; and a separator interposed between the positive electrode and the negative electrode; and an electrolyte.

[0023] Advantageous Effects

[0024] The positive electrode active material of the present invention includes a lithium composite transition metal oxide in the form of single particles; and a cobalt-containing coating portion formed in the form of single particles on the lithium composite transition metal oxide, and satisfies Formula 1 or Formula 2 described herein, thereby improving the initial efficiency, resistance characteristics, capacity characteristics, life characteristics, etc. of the lithium secondary battery. Description of the Drawings

[0025] Figure 1 are XRD patterns of the positive electrode active materials of Examples 1 to 3 and Comparative Examples 1 and 2.

[0026] Figure 2This is a SEM image of the calcined product from the preparation example.

[0027] Figure 3 This is a SEM image of the positive electrode active material of Example 1.

[0028] Figure 4 This is a SEM image of the positive electrode active material of Example 2.

[0029] Figure 5 This is a SEM image of the positive electrode active material of Example 3.

[0030] Figure 6 This is a SEM image of the positive electrode active material of Comparative Example 1.

[0031] Figure 7 This is a SEM image of the positive electrode active material of Comparative Example 3.

[0032] Figure 8 This is a SEM image of the positive electrode active material of Comparative Example 4.

[0033] Figure 9 The HAADF-STEM (High Angle Annular Dark Field Scanning Transmission Electron Microscopy) elemental mapping data of a cross-sectional sample of the positive electrode active material of Example 2 are shown. Detailed Implementation

[0034] The invention will be described in more detail below to aid in understanding it.

[0035] The terms or words used in the specification and claims of this application should not be construed as limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts consistent with the technical spirit of the invention, based on the principle that the inventor can adequately define the terms and concepts to best describe his invention.

[0036] It should be understood that the terms “comprising,” “including,” and “having” as used herein are intended to indicate the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0037] In this specification, the term "on" includes not only cases where a component is directly formed on another component, but also cases where a third component is inserted between these components.

[0038] In this specification, "single-particle positive electrode active material" is a concept contrasted with positive electrode active materials formed by the aggregation of dozens to hundreds of primary particles into spherical secondary particles manufactured by conventional methods, and refers to positive electrode active materials composed of 10 or fewer primary particles. Specifically, the single-particle positive electrode active material in this invention can be a single particle composed of one primary particle, or it can be a secondary particle form composed of several primary particles aggregated together.

[0039] "Primary particles" refer to the smallest particle unit identified when observing positive electrode active materials using a scanning electron microscope, while "secondary particles" refer to a secondary structure formed by the aggregation of multiple primary particles.

[0040] In this specification, the term "average particle size (D)" is used. 50 "" refers to the particle size at the 50% point of the cumulative volume distribution based on particle size. Average particle size (D) 50 The determination of particle size distribution can be performed as follows: The powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). The difference between the diffraction pattern corresponding to the particle size and the particle size is measured when the particles pass through the laser beam, thus obtaining the particle size distribution. The particle size at the point where the cumulative volume distribution corresponding to the particle size is 50% is calculated in the analyzer. Specifically, in this specification, D... 50 The values ​​were determined after setting the particle characteristics parameters of Microtrac S3500 to refractive index: 1.55, transparency: transparent, and shape: irregular, adding the test powder and 500 μL of 10% sodium hexametaphosphate aqueous solution to 25 mL of distilled water at a flow rate of 20% and then sonicating for 1 minute.

[0041] In this instruction manual, This refers to the peak intensity at a specific 2θ position after normalizing the XRD spectrum of the positive electrode active material by setting the peak intensity of the (003) plane to 1. That is, It refers to the ratio of the peak intensity at a specific 2θ position in the XRD spectrum of the positive electrode active material to the peak intensity of the (003) surface.

[0042] Positive electrode active material

[0043] This invention provides a positive electrode active material comprising: a lithium composite transition metal oxide in the form of single particles having a layered structure; and a cobalt-containing coating formed on the lithium composite transition metal oxide, wherein the positive electrode active material satisfies either Formula 1 or Formula 2: [Formula 1]

[0044] [Equation 2]

[0045] in: It is the ratio of the peak intensity corresponding to the LiCoO2 Cu Kα1 diffraction peak position at 37° to 38° in the XRD spectrum of the positive electrode active material to the peak intensity of the (003) plane, and It is the ratio of the peak intensity corresponding to the LiCoO2 Cu Kα1 diffraction peak position at 45° to 45.5° in the XRD spectrum of the positive electrode active material to the peak intensity of the (003) plane.

[0046] Here, the peak intensity corresponding to the position of the Cu Kα1 diffraction peak in the XRD spectrum of a specific positive electrode active material is the XRD peak intensity corresponding to the 2θ value corresponding to the position of the Cu Kα1 diffraction peak appearing in the XRD spectrum of LiCoO2.

[0047] The inventors have discovered that when the positive electrode active material comprises a lithium composite transition metal oxide in the form of single particles and a cobalt-containing coating formed on the lithium composite transition metal oxide in the form of single particles, and satisfies Formula 1 or Formula 2 above, the surface degradation that may occur due to high calcination temperature during the manufacturing process of the positive electrode active material in the form of single particles is reduced, and the residual lithium content is low, thereby improving the initial efficiency, resistance characteristics, capacity characteristics, lifespan characteristics, etc. of the lithium secondary battery, thus completing the present invention.

[0048] When the positive electrode active material includes a coating, the amount of residual lithium byproducts can be reduced, and structural stability can be increased, thereby improving the battery's lifespan and resistance characteristics, and also reducing gas generation. Here, the coating can be in the form of a thin film or a discontinuously formed island, and can be formed integrally or partially on a lithium composite transition metal oxide.

[0049] Meanwhile, if the positive electrode active material of the present invention does not satisfy the above formula 1 or formula 2, there is a problem that the deterioration layer and residual lithium existing on the surface of the positive electrode active material in the form of single particles cannot be improved.

[0050] Specifically, when according to the value of Equation 1 ( ) is less than 0 and when according to the value of equation 2 ( When the value is 1 or less, there is no cobalt coating and therefore a deteriorated portion still exists on the surface of the positive electrode active material in the form of single particles. In addition, when the value according to Formula 1 is greater than 15 and the value according to Formula 2 is greater than 10, cobalt diffuses and exists inside the positive electrode active material in the form of single particles. Therefore, even in this case, there is a problem that there is almost no cobalt coating on the surface of the positive electrode active material and therefore a deteriorated portion still exists on the surface of the positive electrode active material.

[0051] The values ​​of Equations 1 and 2 above are determined by the complex interactions of factors such as the presence or absence of a cobalt-containing coating, the manufacturing method of the positive electrode active material, the amount of cobalt-containing coating material added during the manufacturing process of the positive electrode active material, and the heat treatment temperature, rather than by a single factor.

[0052] According to the present invention, the average particle size (D) of lithium composite transition metal oxides 50 The average particle size (D) of lithium composite transition metal oxides can range from 1.0 μm to 5.0 μm, specifically, it can be greater than 1.0 μm, greater than 1.5 μm, greater than 2.0 μm, greater than 2.5 μm, or greater than 3.0 μm, and can be less than 4.5 μm or less than 5.0 μm. 50 Within the above range, the amount of gas generated during charging and discharging can be minimized, and high capacity can be achieved.

[0053] According to the present invention, lithium composite transition metal oxides may include nickel (Ni), cobalt (Co) and manganese (Mn).

[0054] Based on the total molar amount of metals other than lithium, lithium complex transition metal oxides can contain 60 mol% or more, specifically 80 mol% or more, and more specifically 85 mol% or more of nickel. That is, lithium complex transition metal oxides can be high-nickel lithium complex transition metal oxides. In this case, the energy density of lithium secondary batteries can be improved.

[0055] According to the present invention, the lithium complex transition metal oxide can have a composition represented by the following chemical formula 1. In this case, the lithium complex transition metal oxide has a layered structure.

[0056] [Chemical Formula 1]

[0057] Li a Ni b Co c Mn d M 1 e O2

[0058] in: M 1is at least one selected from Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P, and S, and 0.9 ≤ a ≤ 1.1, 0.8 ≤ b < 1.0, 0 < c < 0.2, 0 < d < 0.2, 0 ≤ e ≤ 0.1, and b + c + d + e = 1.

[0059] b refers to the atomic fraction of nickel among the metal elements in the lithium composite transition metal oxide, which can be 0.80 or more, 0.81 or more, 0.82 or more, 0.83 or more, 0.84 or more, 0.85 or more, 0.86 or more, 0.87 or more, 0.88 or more, 0.89 or more, or 0.90 or more, and can be 0.95 or less, 0.96 or less, 0.97 or less, 0.98 or less, 0.99 or less, or less than 1.0.

[0060] c refers to the atomic fraction of cobalt among the metal elements in the lithium composite transition metal oxide, which can be greater than 0, 0.001 or more, 0.002 or more, 0.003 or more, 0.004 or more, 0.005 or more, 0.006 or more, 0.007 or more, 0.008 or more, 0.009 or more, or 0.01 or more, and can be 0.05 or less, 0.06 or less, 0.07 or less, 0.08 or less, 0.09 or less, 0.10 or less, 0.11 or less, 0.12 or less, 0.13 or less, 0.14 or less, 0.15 or less, 0.16 or less, 0.17 or less, 0.18 or less, 0.19 or less, or less than 0.20.

[0061] d refers to the atomic fraction of manganese among the metal elements in the lithium composite transition metal oxide, which can be greater than 0, 0.005 or more, 0.01 or more, 0.015 or more, or 0.02 or more, and can be 0.04 or less, 0.05 or less, 0.06 or less, 0.07 or less, 0.08 or less, 0.09 or less, 0.10 or less, 0.11 or less, 0.12 or less, 0.13 or less, 0.14 or less, 0.15 or less, 0.16 or less, 0.​​​​​​​

[0064] According to the present invention, the coating portion may comprise a lithium cobalt-based oxide having a cobalt content higher than that of the lithium composite transition metal oxide. That is, the coating portion may comprise a lithium cobalt-based oxide having the same layered structure as the lithium composite transition metal oxide, and having a composition derived from LiCo... 1-x M x O2 represents the composition (where M is Ni, Co, Mn, Al or a combination thereof, and x is 0 or more and less than 1.0).

[0065] According to the present invention, the coating portion may include a thin film shape, a discontinuously formed island shape, or a combination thereof. Furthermore, when the coating portion is a thin film, the thin film may have a wrinkled form. In this case, forming a coating portion containing appropriate cobalt on the surface of the positive electrode active material improves the surface degradation layer, thereby further improving the battery's capacity, initial efficiency, and resistance.

[0066] According to the present invention, the coating portion can be a region ranging from 5 nm to 100 nm in the direction from the surface of the positive electrode active material to its center. That is, the coating portion can be a region ranging from the surface to a specific point in the direction from the center of the positive electrode active material to a point ranging from 5 nm to 100 nm. In this case, a coating portion containing appropriate cobalt is formed on the surface of the positive electrode active material, thereby improving the surface degradation layer and thus further improving the battery capacity, initial efficiency, and resistance.

[0067] Meanwhile, based on the total molar number of metals other than lithium contained in the lithium composite transition metal oxide, the cobalt content in the coated portion can be from 0.5 mol% to 3 mol%. In this case, residual lithium byproducts can be further reduced, and lifetime and resistivity characteristics can be further improved.

[0068] The positive electrode active material of the present invention can be manufactured by a method comprising the following steps: (A) mixing a positive electrode active material precursor, which is a composite transition metal hydroxide, a composite transition metal hydroxyl oxide or a combination thereof, with a lithium-containing raw material to prepare a mixture; (B) calcining the mixture to prepare a calcined product; and (C) mixing the calcined product with a cobalt-containing coating material and then subjecting it to heat treatment.

[0069] As a lithium-containing raw material, any water-soluble lithium sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or hydroxyl oxide is acceptable, with no particular restrictions. Specifically, the lithium-containing raw material can be Li₂CO₃, LiNO₃, LiNO₂, LiOH, LiOH·H₂O, LiH, LiF, LiCl, LiBr, LiI, CH₃COOLi, Li₂O, Li₂SO₄, CH₃COOLi, or Li₃C₆H₅O₇, or any one or a mixture of two or more of them.

[0070] The composite transition metal hydroxide, composite transition metal hydroxyl oxide or combination thereof and the lithium-containing raw material may be mixed in such a way that the ratio (Li / M) of the number of moles of lithium (Li) contained in the lithium-containing raw material to the total number of moles of transition metal (M) contained in the composite transition metal hydroxide, composite transition metal hydroxyl oxide or combination thereof is 1.0 or more, 1.01 or more, or 1.02 or more, and 1.05 or less, 1.06 or less, 1.07 or less, 1.08 or less, 1.09 or less, or 1.10 or less.

[0071] When preparing the mixture in step (A), raw materials containing doped elements, such as zirconium-containing raw materials or yttrium-containing raw materials, may be further mixed.

[0072] Step (B) can also be a step of preparing a calcined product by sequentially subjecting the mixture to a first calcination at 800°C to 900°C and a second calcination at 700°C to 800°C under normal pressure. In this case, the second calcination can be carried out at a temperature lower than that of the first calcination.

[0073] The cobalt-containing coating material can be Co(OH)2 and can be mixed in an appropriate amount that can react with the residual lithium present in the calcined product, for example, in an amount equivalent to 2 mol% to 5 mol%, specifically 2 mol% to 3 mol%, based on the total moles of the calcined product.

[0074] The heat treatment can be performed at 650°C to 800°C, specifically 670°C to 770°C, so that cobalt can react fully only on the surface. Simultaneously, the heat treatment can include a first heat treatment at 650°C to 800°C, specifically 670°C to 770°C, followed by a second heat treatment at 450°C to 550°C (similar to an annealing process) to remove defects on the surface of the positive electrode active material.

[0075] positive electrode

[0076] The present invention provides a positive electrode comprising the aforementioned positive electrode active material.

[0077] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer may include a positive electrode active material.

[0078] The positive electrode current collector can contain a highly conductive metal, as long as the positive electrode active material layer can easily adhere to it and it is non-reactive within the battery's voltage range; there are no particular limitations. Examples of positive electrode current collectors include stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatments such as carbon, nickel, titanium, or silver. Furthermore, the thickness of the positive electrode current collector is typically from 3 μm to 500 μm. To improve the adhesion of the positive electrode active material, fine irregularities can be formed on the surface of the current collector. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0079] If desired, the positive electrode active material layer may optionally include conductive materials and binders together with the positive electrode active material. In this case, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be from 80% to 99% by weight, more specifically from 85% to 98.5% by weight, and can exhibit excellent capacity characteristics within this range.

[0080] Conductive materials are used to impart conductivity to the electrodes. They can be any material as long as they possess electronic conductivity without causing a chemical change in the resulting battery; there are no particular limitations. Specific examples include graphite, such as natural or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, and carbon fibers; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Any one or a mixture of two or more of these materials may also be used. Based on the total weight of the positive electrode active material layer, the content of the conductive material can range from 0.1% by weight to 15% by weight.

[0081] Adhesives are used to improve the bonding between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, polymers wherein hydrogen is substituted by Li, Na, or Ca, or various copolymers thereof, and any one or a mixture of two or more of them may be used. Based on the total weight of the positive electrode active material layer, the adhesive content can be from 0.1% by weight to 15% by weight.

[0082] In addition to using the aforementioned positive electrode active material, the positive electrode can be manufactured according to conventional positive electrode manufacturing methods. Specifically, the aforementioned positive electrode active material and, as needed, a binder, conductive material, and dispersant can be dissolved or dispersed in a solvent to prepare a composition for forming a positive electrode active material layer. This composition is then coated onto a positive electrode current collector, followed by drying and rolling to manufacture the positive electrode. Alternatively, the positive electrode can be manufactured by casting the composition for forming a positive electrode active material layer onto a separate support, peeling off the support to obtain a film, and then laminating the film onto the positive electrode current collector.

[0083] The solvent can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, water, etc., and any one or a mixture of two or more thereof can be used. Considering the coating thickness and manufacturing yield of the slurry, the solvent can be used in an amount sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, and allows the slurry to have a viscosity that exhibits excellent thickness uniformity when coated in subsequent positive electrode manufacturing.

[0084] Lithium secondary batteries

[0085] The present invention provides a lithium secondary battery, comprising: a positive electrode; a negative electrode; and a separator and an electrolyte between the positive electrode and the negative electrode.

[0086] The lithium secondary battery may optionally further include a battery container for housing an electrode assembly formed of a positive electrode, a negative electrode, and a separator, and a sealing member for sealing the battery container.

[0087] The negative electrode may include a negative electrode current collector and a layer of negative electrode active material disposed on the negative electrode current collector.

[0088] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and possesses high conductivity. For example, it can be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or copper or stainless steel, aluminum-cadmium alloys, etc., that have undergone surface treatment with carbon, nickel, titanium, silver, etc. Furthermore, the negative electrode current collector typically has a thickness from 3 μm to 500 μm and, similar to the positive electrode current collector, can have fine non-uniformities formed on its surface to increase the adhesion of the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabrics.

[0089] The negative electrode active material layer may optionally include an adhesive and a conductive material together with the negative electrode active material.

[0090] As negative electrode active materials, compounds capable of reversibly inserting and deintercalating lithium can be used. Specifically, examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metal compounds that can be alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and metal oxides capable of lithium doping and dedoping, such as SiO₂. β (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composite materials containing metal compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or more mixtures thereof. Alternatively, lithium metal films can be used as the negative electrode active material. Additionally, low-crystallinity carbon, high-crystallinity carbon, etc., can be used as the carbon material. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, sheet-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch, and high-temperature calcined carbon such as coke from petroleum or coal tar pitch. Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material can be from 80% to 99% by weight.

[0091] The binder for the negative electrode active material layer is a component that facilitates the bonding between the conductive material, the active substance, and the current collector, and is typically added in an amount from 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0092] The conductive material in the negative electrode active material layer is a component that further improves the conductivity of the negative electrode active material. Based on the total weight of the negative electrode active material layer, it can be added in an amount of 10% by weight or less, preferably 5% by weight or less. As a conductive material, there are no particular restrictions as long as it is conductive without causing a chemical change in the battery. For example, it can be graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black; conductive fibers such as carbon fiber and metal fiber; fluorinated carbon; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0093] A composition for forming a negative electrode active material layer can be prepared by dissolving or dispersing the negative electrode active material and optionally a binder and conductive material in a solvent. This composition can then be coated onto a negative electrode current collector and dried to manufacture a negative electrode. Alternatively, a negative electrode can be manufactured by casting the composition for forming a negative electrode active material layer onto a separate support, peeling the film off the support, and then laminating the film onto the negative electrode current collector.

[0094] The separator is used to separate the negative and positive electrodes and provide a channel for the movement of lithium ions. Any separator can be used, as long as it is commonly used in lithium secondary batteries, without particular limitations. In particular, separators with low resistance to electrolyte ion migration and excellent electrolyte moisture retention are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes composed of polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures with two or more layers can be used. Alternatively, existing porous nonwoven fabrics can be used, such as nonwoven fabrics composed of high-melting-point glass fibers and polyethylene terephthalate fibers. Furthermore, to ensure heat resistance or mechanical strength, coated separators containing ceramic components or polymer materials can be used, and can optionally be used in single-layer or multi-layer structures.

[0095] Electrolytes can be organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used to prepare lithium secondary batteries, but are not limited to these. As a specific example, electrolytes can include organic solvents and lithium salts.

[0096] As an organic solvent, any solvent can be used as long as it can serve as a medium through which the ions involved in the electrochemical reaction of the battery can move; there are no particular restrictions. Specifically, organic solvents can be ester solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene or fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethanol or isopropanol; nitriles, such as R-CN (R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include double bonds, aromatic rings, or ether bonds); amides such as dimethylformamide; dioxolane such as 1,3-dioxolane; or sulfolane. Among them, carbonate solvents are preferred, and mixtures of cyclic carbonates (such as ethylene carbonate, propylene carbonate, etc.) with high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery and low viscosity linear carbonate compounds (such as ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) are more preferred.

[0097] As a lithium salt, there are no particular restrictions as long as it can provide lithium ions for use in lithium secondary batteries; it can be any compound. Specifically, the anion of the lithium salt can be selected from F... - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N -At least one of the following lithium salts is used: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. The lithium salt is preferably used at a concentration of 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, thereby exhibiting excellent electrolyte performance, and lithium ions can move efficiently.

[0098] To improve battery life characteristics, suppress battery capacity reduction, and increase battery discharge capacity, in addition to the electrolyte components mentioned above, the electrolyte may also contain one or more additives, such as alkylene carbonate compounds like difluorocarbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-ethylene glycol dimethyl ether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidinanes, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive content can be from 0.1% to 5% by weight, based on the total weight of the electrolyte.

[0099] Lithium secondary batteries incorporating the positive electrode active material of the present invention have excellent initial efficiency, resistance characteristics, capacity characteristics and lifespan characteristics, and are therefore useful in portable devices such as mobile phones, laptops, and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs) and electric vehicles (EVs).

[0100] The shape of the lithium secondary battery of the present invention is not particularly limited, and it can be cylindrical, prismatic, pouch-shaped or coin-shaped.

[0101] The lithium secondary battery according to the present invention can be used not only as a battery cell for powering small devices, but also preferably as a unit cell in medium to large battery modules containing multiple battery cells.

[0102] Therefore, a battery module including a lithium secondary battery as a unit cell and a battery pack including the battery module are provided.

[0103] Battery modules or battery packs can be used as a power source for any one or more medium and large-sized devices in power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, plug-in hybrid electric vehicles (PHEVs); or systems for energy storage.

[0104] Implementation

[0105] Hereinafter, embodiments of the present invention will be described in detail to enable those skilled in the art to readily implement the invention. However, the present invention can be implemented in various forms and is not limited to the examples described herein.

[0106] Preparation Example

[0107] Tens to hundreds of primary particles (composition: Ni) 0.96 Co 0.01 Mn 0.03 (OH)2, average particle size (D) 50 ZrO2 and Al(OH)3 were mixed at a molar ratio of 1:0.003, and LiOH·H2O was mixed to make the ratio of the total molar number of transition metals (Ni+Co+Mn) in the composite transition metal hydroxide to the molar number of lithium (Li) in LiOH ((Ni+Co+Mn):Li) 1:1.025. Then, ZrO2 was additionally mixed at a weight of 1500 ppm relative to the total weight of the composite transition metal hydroxide, and Y2O3 was additionally mixed at a weight of 300 ppm relative to the total weight of the composite transition metal hydroxide to prepare a mixture. The mixture was heated from room temperature to 835°C at a rate of 5°C / min, and calcined for 6 hours while maintaining the temperature at 835°C. Then, the temperature was lowered to 770°C, and calcined for 12.5 hours while maintaining the temperature at 770°C to prepare a calcined product. The calcined product was non-exothermicly pulverized using an air jet mill to achieve an average particle size (D... 50 The particle size becomes 3.6 μm, thus yielding a lithium composite transition metal oxide (composition: Li) with a layered structure and in single-particle form. 1.025 Ni 0.9550 Co 0.0099 Mn 0.0298 Al 0.0034 Zr 0.0015 Y 0.0003 O2).

[0108] Examples and Comparative Examples

[0109] Example 1

[0110] The lithium composite transition metal oxide prepared in the preparation example and Co(OH)₂ were mixed at a molar ratio of 1:0.03, and Al(OH)₃ was mixed to make the Al content based on the total weight of the lithium composite transition metal oxide 500 ppm, thereby preparing a mixture. Under an oxygen atmosphere, the mixture was heated from room temperature to 675°C at a rate of 5°C / min, subjected to a first heat treatment at 675°C for 5 hours, then cooled to 500°C, and subjected to a second heat treatment at 500°C for 3 hours, thereby preparing a positive electrode active material with a coating containing cobalt and aluminum formed on the lithium composite transition metal oxide (composition: Li). 1.0004 Ni 0.9341 Co 0.0298 Mn 0.0292 Al 0.0051 Zr 0.0015 Y 0.0003 O2, average particle size (D) 50 (3.8 μm).

[0111] Example 2

[0112] The lithium composite transition metal oxide prepared in the preparation example and Co(OH)₂ were mixed at a molar ratio of 1:0.03, and Al(OH)₃ was mixed to make the Al content based on the total weight of the lithium composite transition metal oxide 500 ppm, thereby preparing a mixture. Under an oxygen atmosphere, the mixture was heated from room temperature to 715°C at a rate of 5°C / min, subjected to a first heat treatment at 715°C for 5 hours, then cooled to 500°C, and subjected to a second heat treatment at 500°C for 3 hours, thereby preparing a positive electrode active material with a coating containing cobalt and aluminum formed on the lithium composite transition metal oxide (composition: Li). 1.0004 Ni 0.9341 Co 0.0298 Mn 0.0292 Al 0.0051 Zr 0.0015 Y 0.0003 O2, average particle size (D) 50 (3.8 μm).

[0113] Example 3

[0114] The lithium composite transition metal oxide prepared in the preparation example and Co(OH)₂ were mixed at a molar ratio of 1:0.03, and Al(OH)₃ was mixed to make the Al content based on the total weight of the lithium composite transition metal oxide 500 ppm, thereby preparing a mixture. Under an oxygen atmosphere, the mixture was heated from room temperature to 765°C at a rate of 5°C / min, subjected to a first heat treatment at 765°C for 5 hours, then cooled to 500°C, and subjected to a second heat treatment at 500°C for 3 hours, thereby preparing a positive electrode active material with a coating containing cobalt and aluminum formed on the lithium composite transition metal oxide (composition: Li). 1.0004 Ni 0.9341 Co 0.0298 Mn 0.0292 Al 0.0051 Zr 0.0015 Y 0.0003 O2, average particle size (D) 50 (3.8 μm).

[0115] Comparative Example 1

[0116] Without any coating material, the lithium composite transition metal oxide prepared in the preparation example was heated from room temperature to 715°C at a rate of 5°C / min. After a first heat treatment at 715°C for 5 hours, it was cooled to 500°C and then subjected to a second heat treatment at 500°C for 3 hours, thereby preparing the positive electrode active material (composition: Li). 1.025 Ni 0.9550 Co 0.0099 Mn 0.0298 Al 0.0034 Zr 0.0015 Y 0.0003 O2, average particle size (D) 50 (3.8 μm).

[0117] Comparative Example 2

[0118] The lithium composite transition metal oxide prepared in the preparation example was mixed with LiCoO2 (Aladin, Avention) at a molar ratio of 1:0.03 to prepare a cathode material.

[0119] Comparative Example 3

[0120] The lithium composite transition metal oxide prepared in the preparation example and Co(OH)₂ were mixed at a molar ratio of 1:0.03, and Al(OH)₃ was mixed to make the Al content based on the total weight of the lithium composite transition metal oxide 500 ppm, thereby preparing a mixture. Under an oxygen atmosphere, the mixture was heated from room temperature to 615°C at a rate of 5°C / min, subjected to a first heat treatment at 615°C for 5 hours, then cooled to 500°C, and subjected to a second heat treatment at 500°C for 3 hours, thereby preparing a positive electrode active material with a coating containing cobalt and aluminum formed on the lithium composite transition metal oxide (composition: Li). 1.0004 Ni 0.9341 Co 0.0298 Mn 0.0292 Al 0.0051 Zr 0.0015 Y 0.0003 O2, average particle size (D) 50 (3.8 μm).

[0121] Comparative Example 4

[0122] The lithium composite transition metal oxide prepared in the preparation example and Co(OH)₂ were mixed at a molar ratio of 1:0.03, and Al(OH)₃ was mixed to make the Al content based on the total weight of the lithium composite transition metal oxide 500 ppm, thereby preparing a mixture. Under an oxygen atmosphere, the mixture was heated from room temperature to 815°C at a rate of 5°C / min, subjected to a first heat treatment at 815°C for 5 hours, then cooled to 500°C, and subjected to a second heat treatment at 500°C for 3 hours, thereby preparing a positive electrode active material with a coating containing cobalt and aluminum formed on the lithium composite transition metal oxide (composition: Li). 1.0004 Ni 0.9341 Co 0.0298 Mn 0.0292 Al 0.0051 Zr 0.0015 Y 0.0003 O2, average particle size (D) 50 (3.8 μm).

[0123] Experimental Example

[0124] Experimental Example 1: Analysis of Positive Electrode Active Materials

[0125] XRD analysis

[0126] The XRD spectra of the positive electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 4 were obtained and analyzed using XRD (Bruker, D8 Endeavor). The XRD measurement conditions are as follows: - Voltage: 40 kV - Current: 40 mA - Power: 1600 W - Element: Cu - Angle: 15° to 50°, increment: 0.02° (10s per step) The XRD spectra of each positive electrode active material are shown in Figure 1 In the XRD spectrum, the peak intensity of the (003) plane, the peak intensity corresponding to the LiCoO2 Cu Kα1 diffraction peak position at 37° to 38°, and the peak intensity corresponding to the LiCoO2 Cu Kα1 diffraction peak position at 45° to 45.5° were confirmed. The values ​​according to Equations 1 and 2 were calculated and are shown in Table 1 below. Here, the peak intensity corresponding to the LiCoO2 Cu Kα1 diffraction peak position in the XRD spectrum of a specific positive electrode active material is the XRD peak intensity corresponding to the 2θ value corresponding to the position of the Cu Kα1 diffraction peak of LiCoO2 appearing in the XRD spectrum of Comparative Example 2. Specifically, it is the XRD peak intensity corresponding to the position of the Cu Kα1 diffraction peak of LiCoO2 appearing in the XRD spectrum of Comparative Example 2. Figure 1 The XRD peak intensity corresponding to the 2θ value of the position of the larger peak in the XRD spectrum of Comparative Example 2, which appears between 37° and 38° or 45° and 45.5°.

[0127] [Table 1]

[0128] Referring to Table 1, it can be confirmed that the positive electrode active materials of Examples 1 to 3 satisfy Formula 1 or Formula 2 of the present invention, while the positive electrode active materials of Comparative Examples 1 to 4 deviate from them.

[0129] Speciation analysis of positive electrode active material and Co element

[0130] SEM images of the calcined products of the preparation examples, the positive electrode active materials of Examples 1 to 3, and Comparative Examples 1, 3, and 4 were obtained using an electron probe microanalyzer (JEOL, JXA-iHP200F) (accelerating voltage: 15 kV, probe current: 20 nA, residence time: 20 ms), and are shown below. Figure 2 (Calcination product of the preparation example) Figure 3 (Example 1) Figure 4 (Example 2) Figure 5 (Example 3) Figure 6 (Comparative Example 1) Figure 7 (Comparative Example 3) and Figure 8 (Comparative Example 4)

[0131] In addition, HAADF-STEM EDS (energy-dispersive X-ray spectroscopy) elemental mapping data of the cross-sectional sample of the positive electrode active material of Example 2 were obtained using a Thermo Fisher Scientific Titan G2 ChemiSTEM 80-200 instrument, and are shown in the figure. Figure 9 Meanwhile, cross-sectional samples of the positive electrode active material were prepared by Ar ion milling for 2 hours using an Ar ion milling system (Hitachi, IM-5000) (accelerating voltage: 6 kV).

[0132] Reference Figures 2 to 6 It can be confirmed that the positive electrode active materials of Examples 1 to 3 have a coating portion on the surface, while the positive electrode active material of Comparative Example 1 does not have a coating portion on the surface.

[0133] Reference Figure 9 It can be confirmed that Co is coated on the surface in the form of a thin film (a wrinkled film), and Al is coated in the form of islands. In addition, it can be confirmed that a thin coating is formed in a region ranging from the surface of the positive electrode active material to the center in the direction of 100 nm.

[0134] Experimental Example 2: Evaluation of Battery Characteristics

[0135] Manufacturing of half-cells

[0136] In N-methylpyrrolidone (NMP) (Daejung Chemicals & Metals) as a solvent, positive electrode active materials prepared in Examples 1, 3 and Comparative Examples 1 to 4, carbon black (Denka, DenkaBlack) as a conductive material, and PVdF (Kureha, KF1300) as a binder were added in a weight ratio of 95:3:2 to prepare a composition for forming a positive electrode active material layer.

[0137] A composition for forming a positive electrode active material layer was coated on one side of an aluminum foil current collector with a thickness of 20 μm, and dried at 135°C for 3 hours to form a positive electrode active material layer. Next, a roll forming method was used to roll-press the positive electrode active material layer to achieve a porosity of 20% by volume, thereby manufacturing the positive electrode.

[0138] A half-cell is manufactured using lithium metal as the negative electrode together with the aforementioned positive electrode.

[0139] Evaluation of the initial characteristics of the battery

[0140] The fabricated half-cells were charged at 25°C with a constant current (CC) of 0.2 C to 4.25 V, and then charged with a constant voltage (CV) of 4.25 V until the charging current became 0.005 mAh (cutoff current). After resting for 20 minutes, they were discharged with a constant current of 0.2 C to 2.5 V. The initial charge capacity and initial discharge capacity were measured, and the DC internal resistance (DCIR) was calculated, as shown in Table 2 below. For reference, the DCIR value is calculated by dividing the difference between the initial voltage and the voltage after 60 seconds of discharge at a constant current of 0.2 C by the applied current.

[0141] Evaluation of battery cycle characteristics

[0142] The prepared half-cell was charged at 25°C with a constant current (CC) of 0.2 C to 4.25 V, and then charged with a constant voltage (CV) of 4.25 V until the charging current became 0.005 mAh (cutoff current). After resting for 20 minutes, it was discharged with a constant current of 0.2 C to 2.5 V.

[0143] Subsequently, the battery was transferred to a 45°C room and charged at a constant current of 0.5 C to 4.25 V, then charged at a constant voltage (CV) of 4.25 V until the charging current became 0.005 mAh (cutoff current), and then discharged at a constant current of 1.0 C to 2.5 V. This constituted one cycle, and 50 charge-discharge cycles were performed. In this case, the percentage of the discharge capacity of the 50th cycle relative to the discharge capacity of the 1st cycle is shown in Table 2 below as the capacity retention rate. Additionally, the percentage of the DCIR value of the 50th cycle relative to the DCIR value of the 1st cycle is shown in Table 2 below as the resistance increase rate. For reference, the DCIR value of the nth cycle is calculated by dividing the difference between the voltage at full charge and the voltage 60 seconds after the start of discharge by the current obtained when discharging at a constant current of 1.0 C to 2.5 V in the nth cycle.

[0144] [Table 2]

[0145] Referring to Table 2, it can be confirmed that, compared with the batteries containing the positive electrode active materials of Comparative Examples 1 to 4, the batteries containing the positive electrode active materials of Examples 1 to 3 all have excellent initial efficiency, resistance characteristics and lifetime performance.

[0146] As a result, it can be seen that when the positive electrode active material contains lithium composite transition metal oxide in the form of single particles and a cobalt-containing coating formed on the lithium composite transition metal oxide in the form of single particles, and satisfies Formula 1 or Formula 2 described herein, the surface degradation that may occur due to high calcination temperature during the manufacture of positive electrode active material in the form of single particles is reduced, and the residual lithium content is low, thereby improving the initial efficiency, resistance characteristics, capacity characteristics, lifetime characteristics, etc. of lithium secondary batteries.

Claims

1. A positive electrode active material, comprising: A lithium composite transition metal oxide in the form of single particles having a layered structure; and A cobalt-containing coating formed on the lithium composite transition metal oxide, wherein, The positive electrode active material satisfies the following formula 1 or formula 2: [Formula 1] [Formula 2] Where: It is the ratio of the peak intensity corresponding to the LiCoO2 Cu Kα1 diffraction peak position at 37° to 38° in the XRD spectrum of the positive electrode active material to the peak intensity of the (003) plane, and It is the ratio of the peak intensity corresponding to the LiCoO2 Cu Kα1 diffraction peak position at 45° to 45.5° in the XRD spectrum of the positive electrode active material to the peak intensity of the (003) plane.

2. The positive electrode active material according to claim 1, wherein, The average particle size (D) of the lithium composite transition metal oxide 50 The thickness ranges from 1.0 μm to 5.0 μm.

3. The positive electrode active material according to claim 1, wherein, The lithium composite transition metal oxide contains nickel (Ni), cobalt (Co), and manganese (Mn).

4. The positive electrode active material according to claim 1, wherein, The lithium composite transition metal oxide has a composition represented by the following Chemical Formula 1: [Chemical Formula 1] Li a Ni b Co c Mr d M 1 e O2 Where: M 1 It is selected from at least one of Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P, and S, and 0.9 ≤ a ≤ 1.1, 0.8 ≤ b < 1.0, 0 < c < 0.2, 0 < d < 0.2, 0 ≤ e ≤ 0.1, and b + c + d + e = 1.

5. The positive electrode active material according to claim 1, wherein, The coating portion includes a thin film form, discontinuously formed island form, or a combination thereof.

6. The positive electrode active material according to claim 1, wherein, The coating portion is an area in the range of 5 nm to 100 nm in the direction from the surface to the center of the positive electrode active material.

7. A positive electrode, comprising the positive electrode active material according to any one of claims 1 to 6.

8. A lithium secondary battery, comprising: The positive electrode according to claim 7; A negative electrode; And A separator interposed between the positive electrode and the negative electrode; And An electrolyte.

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