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

Abstract

The present invention relates to a positive electrode active material having low nickel disorder and high particle strength in a crystal structure and capable of realizing a battery having excellent capacity properties and capacity retention rate, and a positive electrode and a lithium secondary battery comprising the same, wherein the positive electrode active material comprises a large-diameter lithium transition metal oxide and a small-diameter lithium transition metal oxide having an average particle diameter (D 50 ) smaller than the large-diameter lithium transition metal oxide, wherein the large-diameter lithium transition metal oxide and the small-diameter lithium transition metal oxide each independently have a composition represented by Formula 1, and have a crystal grain size of 100 nm to 150 nm, wherein the difference in the crystal grain size of the large-diameter lithium transition metal oxide and the small-diameter lithium transition metal oxide is less than 40 nm, and the positive electrode active material has a nickel disorder (Ni-disorder) of 1.5% or less.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2020-0164820, filed with the Korean Intellectual Property Office on November 30, 2020, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This invention relates to positive electrode active materials and positive electrodes and lithium secondary batteries containing the same. Background Technology

[0004] With technological advancements and increasing demands for mobile devices, the need for secondary batteries as an energy source is rapidly growing. Among these secondary batteries, lithium-ion batteries, characterized by high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0005] Lithium transition metal composite oxides are used as positive electrode active materials in lithium-ion batteries. Among these, lithium-cobalt composite oxides, such as LiCoO2, are mainly used due to their high functional voltage and excellent capacity characteristics. However, LiCoO2 suffers from poor thermal performance and is expensive because its crystal structure is unstable due to delithiation. Therefore, the widespread use of LiCoO2 as a power source in fields such as electric vehicles is limited.

[0006] As alternatives to LiCoO2, lithium manganese composite metal oxides (LiMnO2, LiMn2O4, etc.), lithium iron phosphate compounds (LiFePO4, etc.), and lithium nickel composite metal oxides (LiNiO2, etc.) have been developed. Among these materials, lithium nickel composite metal oxides, with their high reversible capacity of approximately 200 mAh / g, have been the subject of more active research and development, facilitating the realization of high-capacity batteries. However, compared to LiCoO2, LiNiO2 exhibits poorer thermal stability. Furthermore, a problem with LiNiO2 is that when an internal short circuit occurs due to external pressure during charging, the positive electrode active material decomposes, leading to battery rupture and fire.

[0007] Therefore, as a method to improve the low thermal stability of LiNiO2 while maintaining its excellent reversible capacity, nickel-cobalt-manganese-based lithium composite transition metal oxides in which part of Ni is replaced by Mn and Co, and nickel-cobalt-aluminum-based lithium composite transition metal oxides in which part of Ni is replaced by Mn and Al have been developed.

[0008] Meanwhile, in the case of lithium composite transition metal oxides with high nickel content, there is an increase in nickel disorder in the crystal structure of the cathode active material. Therefore, the following problems arise: the increased variation in the crystal structure of the cathode active material reduces particle strength, making the particles prone to breakage, and causing NiO with a rock salt structure to form on the particle surface due to side reactions.

[0009] Therefore, there is a need to develop a positive electrode active material that has low nickel disorder and high particle strength in its crystal structure, while containing lithium composite transition metal oxides with high nickel content, and is capable of achieving batteries with excellent capacity characteristics and capacity retention. Summary of the Invention

[0010] [Technical Issues]

[0011] One aspect of the present invention provides a positive electrode active material and a method for preparing the same, wherein the positive electrode active material has low nickel disorder and high particle strength in its crystal structure, and contains lithium composite transition metal oxide with high nickel content, thereby enabling the realization of a battery with excellent capacity characteristics and capacity retention.

[0012] [Technical Solution]

[0013] According to one aspect of the present invention, a positive electrode active material is provided, the positive electrode active material comprising a large-diameter lithium transition metal oxide and a small-diameter lithium transition metal oxide, wherein the average particle size (D) of the small-diameter lithium transition metal oxide is... 50 The average particle size (D) of the large-diameter lithium transition metal oxide is smaller than that of the other two. 50 The large-diameter lithium transition metal oxide and the small-diameter lithium transition metal oxide each independently have the composition represented by Formula 1 below and have a grain size of 100 nm to 150 nm, wherein the difference in grain size between the large-diameter lithium transition metal oxide and the small-diameter lithium transition metal oxide is less than 40 nm.

[0014] [Formula 1]

[0015] Li x1 [Ni a1 Co b1 Mn c11 Al c12 Zr d1 M 1 e1 O2

[0016] In Equation 1 above,

[0017] M 1is one or more selected from B, Mg, Ca, V, Cr, Fe, Zn, Ga, Y, Nb, Mo, Ta, and W, and

[0018] 1.0 < x1 ≤ 1.10, 0.7 ≤ a1 < 1, 0 < b1 < 0.3, 0 < c11 < 0.3, 0.001 < c12 < 0.05, 0.001 ≤ d1 ≤ 0.0065, 0 ≤ e1 ≤ 0.1, and a1 + b1 + c11 + c12 + d1 + e1 = 1.

[0019] According to another aspect of the present invention, a positive electrode including the positive electrode active material and a lithium secondary battery including the positive electrode are provided.

[0020] [Advantageous Effects]

[0021] The present invention provides a positive electrode active material having a high nickel content, low nickel disorder in the crystal structure, and high particle strength. In addition, when the positive electrode active material is applied to a battery, the battery has excellent capacity properties and capacity retention at high temperatures. Detailed Embodiments

[0022] It should be understood that the words or terms used in the description and claims of the present invention should not be construed as being limited to the meanings defined in a common dictionary. It should also be understood that based on the principle that the inventor can appropriately define the meanings of words or terms to best explain the invention, the words or terms should be construed as having meanings consistent with their meanings in the context of the related art and the technical concept of the present invention.

[0023] In this specification, it should be understood that the terms "comprising," "including," or "having" are intended to specify the presence of the stated features, numbers, steps, elements, or combinations thereof, but do not preclude the presence or addition of one or more other features, numbers, steps, elements, or combinations thereof.

[0024] In this specification, "particle" refers to particles in the micrometer unit, which, when observed under magnification, can be divided into "grains" in crystalline form with tens of nanometer units. Upon further magnification and observation of these grains, discrete regions can be identified where atoms form lattice structures in specific directions; these are called "crystal grains." The particle size observed in XRD is defined as the grain size. The grain size can be obtained using XRD data via the Rietveld method. Specifically, the grain size can be obtained as follows: Place the sample in the groove in the center of a standard powder holder, and use a glass slide to flatten the sample surface while ensuring the sample height equals the height of the holder's edge. Then, analyze the measured XRD data (2θ = 15° to 90°, step size = 0.02°, total scan time: 20 minutes) using an X-ray diffractometer (Bruker, D8 Endeavor) with the Fundamental Parameter Approach (built into Bruker's Rietveld-based TOPAS program).

[0025] In this instruction manual, particle strength is measured as follows: Particles are placed on a plate, and then a miniature compression tester (Shimadzu Corporation, MCT-W500) is used to measure the force at which the particles break while increasing the compressive force. The measured force is set as the particle strength value.

[0026] The invention will be described in more detail below.

[0027] Positive electrode active material

[0028] The inventors discovered that although the positive electrode active material has a high nickel content, it also contains large-diameter lithium transition metal oxides and has an average particle size (D...). 50 When the small-diameter lithium transition metal oxide, the large-diameter lithium transition metal oxide, and the small-diameter lithium transition metal oxide each independently have the composition represented by Formula 1 and have a grain size of 100 nm to 150 nm, and the difference in grain size between the large-diameter lithium transition metal oxide and the small-diameter lithium transition metal oxide is less than 40 nm, the nickel disorder in the crystal structure of the positive electrode active material is low and the particle strength of the positive electrode active material is high. When the positive electrode active material is applied to a battery, the capacity characteristics and capacity retention of the battery can be improved, thus completing the present invention.

[0029] The positive electrode active material of the present invention comprises large-diameter lithium transition metal oxide and small-diameter lithium transition metal oxide, wherein the average particle size (D) of the small-diameter lithium transition metal oxide is... 50)Less than large-diameter lithium transition metal oxides, wherein the large-diameter lithium transition metal oxides and the small-diameter lithium transition metal oxides each independently have a composition represented by Formula 1 below and have a grain size of 100 nm to 150 nm, and the difference in the grain sizes between the large-diameter lithium transition metal oxides and the small-diameter lithium transition metal oxides is less than 40 nm.

[0030] [Formula 1]

[0031] Li x1 [Ni a1 Co b1 Mn c11 Al c12 Zr d1 M 1 e1 O2

[0032] In Formula 1 above,

[0033] M 1 is one or more selected from B, Mg, Ca, V, Cr, Fe, Zn, Ga, Y, Nb, Mo, Ta, and W, and

[0034] 1.0 < x1 ≤ 1.10, 0.7 ≤ a1 < 1, 0 < b1 < 0.3, 0 < c11 < 0.3, 0.001 < c12 < 0.05, 0.001 ≤ d1 ≤ 0.0065, 0 ≤ e1 ≤ 0.1, and a1 + b1 + c11 + c12 + d1 + e1 = 1.

[0035] x1 represents the molar number of lithium when the total molar number of metals other than lithium (Ni, Co, Zr, and M 1 ) contained in the large-diameter or small-diameter lithium transition metal oxides is 1, and can satisfy 1.0 < x1 ≤ 1.10 or 1.03 ≤ x1 ≤ 1.07. When the x1 value is within the above range, Li and Ni are in a competitive relationship in the reaction of occupying the Li positions in the crystal structure, and the nickel disorder in the crystal structure can be reduced by increasing the content ratio of lithium. Therefore, a battery with excellent capacity characteristics and capacity retention rate can be achieved. In addition, when the x1 value is less than 1.0, there is a problem that the nickel disorder in the crystal structure increases as the content ratio of lithium decreases, and when the x1 value is greater than 1.10, the problem is that since the amount of unreacted lithium increases, lithium by-products increase, and since the initial discharge capacity decreases, the initial efficiency decreases. At the same time, when the lithium by-products increase, there is a problem of difficulty in controlling the preparation process of the positive electrode active material.

[0036] a1 represents the atomic fraction of nickel among the metal elements other than lithium in the large-diameter or small-diameter lithium transition metal oxide, and can satisfy 0.7 ≤ a1 < 1, 0.8 ≤ a1 < 1, or 0.85 ≤ a1 ≤ 0.95. When the value of a1 is 0.7 or more, specifically 0.8 or more, that is, when the positive electrode active material has a high nickel content, it has the advantage that the capacity increases as the content of nickel that can participate in the redox reaction increases.

[0037] b1 represents the atomic fraction of cobalt among the metal elements other than lithium in the large-diameter or small-diameter lithium transition metal oxide, and can satisfy 0 < b1 < 0.3, 0 < b1 < 0.2, or 0 < b1 < 0.15.

[0038] c11 represents the atomic fraction of manganese among the metal elements other than lithium in the large-diameter or small-diameter lithium transition metal oxide, and can satisfy 0 < c11 < 0.3, 0 < c11 < 0.2, or 0 < c11 < 0.15.

[0039] c12 represents the atomic fraction of aluminum among the metal elements other than lithium in the large-diameter or small-diameter lithium transition metal oxide, and can satisfy 0.001 < c12 < 0.05, 0.005 < c12 < 0.04, or 0.01 < c12 < 0.03. If the value of c12 is within the above range, it has the advantages of improved thermal safety and improved high-temperature life characteristics. In particular, when aluminum is doped with zirconium atoms in the above content, it has the advantage of further improving the high-temperature life characteristics.

[0040] d1 represents the atomic fraction of zirconium among the metal elements other than lithium in the large-diameter or small-diameter lithium transition metal oxide, and can satisfy 0.001 ≤ d1 ≤ 0.0065, or 0.002 ≤ d1 ≤ 0.0045. When the value of d1 is within the above range, zirconium replaces at the metal site, thereby increasing the binding force with oxygen, and thus has the advantages of improving the crystal structure stability and enhancing the particle strength to increase the high-temperature life. At the same time, when the value of d1 is less than 0.001, that is, when the content of zirconium in the lithium transition metal oxide is less than 940 ppm, this content is too small to exert the effect of improving the structure stability and particle strength. In addition, when the value of d1 is greater than 0.0065, that is, when the content of zirconium in the lithium transition metal oxide is greater than 6000 ppm, there is a problem that the inactive region in the metal site increases and the capacity decreases.

[0041] e1 represents the atomic fraction of element M among the metal elements other than lithium in the large-diameter or small-diameter lithium transition metal oxide 1 and can satisfy 0 ≤ e1 ≤ 0.1 or 0 ≤ e1 ≤ 0.05.

[0042] The grain size of large- or small-diameter lithium transition metal oxides can range from 100 nm to 150 nm, specifically 100 nm to 140 nm, and more specifically 110 nm to 130 nm. Grain sizes within this range offer the advantage of increased structural stability due to less shrinkage and expansion of the crystal structure during charging and discharging. Conversely, when the grain size is less than 100 nm, insufficient crystal development leads to high nickel disorder and low particle strength. When the grain size is greater than 150 nm, increased shrinkage and expansion of the active material particles (especially primary particles) during charging and discharging increases particle breakage and deteriorates structural stability.

[0043] The grain size difference between large-diameter and small-diameter lithium transition metal oxides can be less than 40 nm, specifically less than 30 nm. That is, the grain size difference between large-diameter and small-diameter lithium transition metal oxides can be small. More specifically, the grain size of large-diameter and small-diameter lithium transition metal oxides can be the same. In this case, since excessive breakage of either small-diameter or large-diameter lithium transition metal oxide particles during rolling can be prevented, the battery can exhibit excellent lifespan characteristics when the positive electrode active material is applied.

[0044] Meanwhile, when the grain size difference between large-diameter lithium transition metal oxides and small-diameter lithium transition metal oxides is greater than 40 nm, and when the grain size of small-diameter lithium transition metal oxides is smaller than that of large-diameter lithium transition metal oxides, the small-diameter lithium transition metal oxide particles will be excessively fractured during the rolling process, thereby increasing the amount of small-sized fine powder generated; while when the grain size of large-diameter lithium transition metal oxides is smaller than that of small-diameter lithium transition metal oxides, there is a problem that the conductivity is reduced due to excessive fracture of large-diameter lithium transition metal oxide particles during the rolling process.

[0045] In particular, although the positive electrode active material of the present invention is a high nickel content positive electrode active material, the positive electrode active material includes a specific content of Zr, the molar ratio of lithium to the total number of transition metals contained in the positive electrode active material is greater than 1.0 and less than 1.10, and the grain size of the positive electrode active material satisfies 100nm to 150nm. This results in low nickel disorder in the crystal structure of the positive electrode active material, high particle strength of the positive electrode active material, and reduced shrinkage and expansion amplitude of the active material primary particles during high-temperature charge and discharge. Therefore, when this positive electrode active material is applied to a battery, the capacity retention rate of the battery can be improved.

[0046] According to the present invention, the average particle size (D) of large-diameter lithium transition metal oxides50 The diameter can range from 8 μm to 15 μm, specifically from 8 μm to 13 μm. Additionally, the average particle size (D) of small-diameter lithium transition metal oxides... 50 The average particle size (D) can range from 3 μm to 7 μm, specifically from 4 μm to 6 μm. Lithium transition metal oxides can be classified by average particle size (D). 50 Large-diameter lithium transition metal oxides ranging from 8 μm to 15 μm and with an average particle size (D) 50 The composition consists of small-diameter lithium transition metal oxides ranging from 3 μm to 7 μm. The weight ratio of large-diameter lithium transition metal oxides to small-diameter lithium transition metal oxides can be 5:5 to 9:1, specifically 6:2 to 9:1, and more specifically 7:3 to 9:1. In this case, with increasing roll density, it is easy to manufacture products with high loading (20 mg / cm³). 2 The electrodes (above) can reduce particle breakage during rolling.

[0047] Simultaneously, a coating containing B, Zr, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Sr, Ba, Ce, F, P, S, or Y can be formed on the surface of the lithium transition metal oxide. Specifically, a boron coating containing boron can be formed on the surface of the lithium transition metal oxide.

[0048] According to the concept of the present invention, the Ni disorder degree of the positive electrode active material can be less than 1.5%, specifically less than 1.4%, preferably 0 to 1.3%. In this case, although the positive electrode active material of the present invention has a high nickel content, a battery with excellent capacity characteristics and capacity retention can be achieved. Meanwhile, in this specification, the nickel disorder degree value can refer to the irregular Ni at the lithium sites. 2+ The amount (%) of ions was obtained as follows: XRD data were obtained using an X-ray diffraction analyzer (Bruker, D8 Endeavor), and then atomic structure analysis was performed using the Rietveld method to analyze the Ni ions occupying lithium sites. 2+ The relative amount of ions and the relative occupancy of oxygen in oxygen sites.

[0049] According to the present invention, the particle strength of large-diameter lithium transition metal oxides can be from 140 MPa to 180 MPa, specifically from 145 MPa to 180 MPa, and more specifically from 145 MPa to 165 MPa. Furthermore, the particle strength of small-diameter lithium transition metal oxides can be from 110 MPa to 150 MPa, specifically from 115 MPa to 145 MPa, and more specifically from 120 MPa to 145 MPa. In this case, primary particle breakage during charging and discharging is reduced, thereby improving structural stability, thus enabling the realization of batteries with improved capacity retention, particularly at high temperatures.

[0050] The positive electrode active material of the present invention can be prepared by the following method. Specifically, the positive electrode active material of the present invention can be prepared as follows: large-diameter lithium transition metal oxide and small-diameter lithium transition metal oxide are prepared separately and then mixed, wherein the average particle size (D) of the small-diameter lithium transition metal oxide is... 50 Smaller than the average particle size (D) of large-diameter lithium transition metal oxides 50 ).

[0051] Large-diameter lithium transition metal oxides and small-diameter lithium transition metal oxides can each be prepared by a method comprising the following steps: (A) mixing a large-diameter or small-diameter transition metal precursor with a nickel content of 70 mol% or more relative to the total moles of the transition metal, an aluminum-containing raw material, a zirconium-containing raw material, and a lithium-containing raw material to prepare a mixture; and (B) calcining the mixture at a temperature of 720°C to 780°C to prepare the large-diameter or small-diameter lithium transition metal oxide. In this case, the amount of lithium-containing raw material mixed is such that the molar ratio of lithium to the total moles of the transition metal (Li / transition metal) in the large-diameter or small-diameter lithium transition metal oxide to be prepared is greater than 1.0 and less than 1.10; the amount of zirconium-containing raw material mixed is from 940 ppm to 6000 ppm relative to the transition metal precursor; and the amount of aluminum-containing raw material mixed is from 300 ppm to 13700 ppm relative to the transition metal precursor.

[0052] Large-diameter or small-diameter transition metal precursors may each independently have the composition represented by Formula 2 or Formula 3.

[0053] [Equation 2]

[0054] [Ni a2 Co b2 Mn c21 Al c22 M 1 d2 ](OH)2

[0055] [Formula 3]

[0056] [Ni a2 Co b2 Mn c21 Al c22 M 1 d2 ]OOH

[0057] In equations 2 and 3,

[0058] M 1 It is selected from one or more of B, Mg, Ca, V, Cr, Fe, Zn, Ga, Y, Nb, Mo, Ta, and W, and

[0059] 0.7 ≤ a2 < 1, 0 < b2 < 0.3, 0 < c21 < 0.3, 0.001 < c22 < 0.05, 0 ≤ d2 ≤ 0.1, a2 + b2 + c21 + c22 + d2 = 1.

[0060] a2 represents the atomic fraction of nickel in the metal element of the large-diameter or small-diameter transition metal precursor, and can satisfy 0.7 ≤ a2 < 1, 0.8 ≤ a2 < 1, or 0.85 ≤ a2 ≤ 0.95.

[0061] b2 represents the atomic fraction of cobalt in the metal element of the large-diameter or small-diameter transition metal precursor, and can satisfy 0 < b2 < 0.3, 0 < b2 < 0.2, or 0 < b2 < 0.15.

[0062] c21 represents the atomic fraction of manganese in the metal element of the large-diameter or small-diameter transition metal precursor, and can satisfy 0 < c21 < 0.3, 0 < c21 < 0.2, or 0 < c21 < 0.15.

[0063] c22 represents the atomic fraction of aluminum in the metal element of the large-diameter or small-diameter transition metal precursor, and can satisfy 0.001 < c22 < 0.05, 0.005 < c22 < 0.04, or 0.01 < c22 < 0.03.

[0064] d2 represents the atomic fraction of element M in the metal element of the large-diameter or small-diameter transition metal precursor 1 and can satisfy 0 ≤ d2 ≤ 0.1 or 0 ≤ d2 ≤ 0.05.

[0065] The lithium-containing raw material can include one or more selected from lithium hydroxide hydrate, lithium carbonate, and lithium hydroxide. The lithium-containing raw material can specifically be lithium hydroxide hydrate, and more specifically LiOH·H2O. In this case, the reactivity between the precursor having a high nickel atomic fraction (in the metal element of the precursor) and the lithium-containing raw material can be improved.

[0066] The mixing amount of the lithium-containing raw material can be such that the molar ratio of lithium contained in the lithium transition metal oxide to be prepared to the total molar number of transition metals (Li / transition metal) is greater than 1.0 and 1.10 or less, specifically 1.03 to 1.07. When the mixing amount of the lithium-containing raw material is such that the molar ratio of lithium contained in the lithium transition metal oxide to be prepared to the total molar number of transition metals (Li / transition metal) is 1.0 or less, there is a problem that the degree of nickel disorder in the crystal structure increases as the lithium content ratio decreases, and when the mixing amount is greater than 1.10, the problem is that since the amount of unreacted lithium increases, the lithium by-products increase, and the initial efficiency decreases due to the decrease in the initial discharge capacity of the positive electrode active material to be prepared.

[0067] Zirconium-containing raw materials can be zirconium-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or hydroxyoxides. For example, when the zirconium-containing raw material is a zirconium-containing oxide, it can be ZrO2.

[0068] The mixing amount of zirconium-containing feedstock relative to the transition metal precursor can be from 940 ppm to 6000 ppm, specifically from 1000 ppm to 6000 ppm, and more specifically from 2000 ppm to 4000 ppm. When the zirconium-containing feedstock is mixed at a content of less than 940 ppm relative to the transition metal precursor, there is a problem that the zirconium content is too low to exhibit the effect of improving structural stability and particle strength. On the other hand, when the content is mixed at a content of more than 6000 ppm, there is a problem that the inactive regions in the metal sites increase, resulting in a decrease in capacity.

[0069] Aluminum-containing raw materials can be aluminum-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or hydroxyoxides. For example, when the aluminum-containing raw material is an aluminum oxide, it can be Al2O3.

[0070] The mixing amount of aluminum-containing raw materials relative to the transition metal precursor can be from 300 ppm to 13700 ppm, specifically from 1400 ppm to 11000 ppm, and more specifically from 2800 ppm to 8300 ppm. When aluminum-containing raw materials are mixed at a content of less than 300 ppm relative to the transition metal precursor, there is a problem that the aluminum content is too low to exhibit the effect of improving thermal and structural stability. When mixed at a content of more than 13700 ppm, there is a problem that the inactive regions in the metal sites increase, resulting in a decrease in capacity.

[0071] As needed, step (B) above may also include a process of cleaning the calcined product obtained by calcining the mixture at a temperature of 720°C to 780°C with a cleaning solution and then drying it, and may also include a process of mixing the dried calcined product with a raw material containing coating elements and heat-treating it to form a coating.

[0072] Firing can be carried out at temperatures between 720°C and 780°C. Specifically, the firing temperature can be between 730°C and 770°C, and more specifically, between 740°C and 760°C. When the firing temperature is within this range, crystals of appropriate size can be formed, and the process cost is not high. In particular, lithium transition metal oxides with grain sizes of 100 nm to 150 nm can be prepared.

[0073] Meanwhile, the sintering temperature for preparing large-diameter lithium transition metal oxides can be higher than that for preparing small-diameter lithium transition metal oxides. Therefore, it is possible to prepare cathode active materials with grain size differences of less than 40 nm, especially less than 30 nm, and even more particularly 0 nm. Specifically, the sintering temperature for preparing large-diameter lithium transition metal oxides can be 10°C to 50°C higher than that for preparing small-diameter lithium transition metal oxides.

[0074] Firing can be carried out in an oxygen atmosphere. Under these conditions, fired products with structurally stable phases can be formed.

[0075] Cleaning is a process of removing residual lithium and other impurities using a cleaning solution such as deionized water or distilled water, while drying is a process of removing moisture from the positive electrode active material that contains moisture due to washing, and can be performed by methods known in the art.

[0076] In addition, the coating formation process is a process of forming a coating on the surface of a lithium transition metal oxide, which can also be carried out using methods known in the art.

[0077] positive electrode

[0078] Furthermore, the present invention can provide a positive electrode for a lithium secondary battery, the positive electrode comprising a positive electrode active material prepared by the above method.

[0079] Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector and containing the aforementioned positive electrode active material.

[0080] There are no particular restrictions on the positive electrode current collector as long as it is conductive and does not cause chemical changes within the battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, or silver can be used. Furthermore, the thickness of the positive electrode current collector is typically from 3 μm to 500 μm, and micro-irregularities can be formed on its surface to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0081] The positive electrode active material layer may include conductive materials, binders, and positive electrode active materials.

[0082] 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% by weight. When contained within the above content range, excellent capacity characteristics can be exhibited.

[0083] Conductive materials are used to impart conductivity to the electrodes, and any conductive material can be used without particular limitation, as long as it is conductive without causing a chemical change in the battery to be constructed. Specific examples may 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, thermally cracked carbon black, and carbon fibers; metal powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one or a mixture of two or more of these can be used. Based on the total weight of the positive electrode active material layer, the content of the conductive material can be from 1% by weight to 30% by weight.

[0084] 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, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one or a mixture of two or more thereof may be used. Based on the total weight of the positive electrode active material layer, the adhesive content can be from 1% by weight to 30% by weight.

[0085] In addition to using the aforementioned positive electrode active materials, positive electrodes can be manufactured using common methods for manufacturing positive electrodes. Specifically, a positive electrode can be manufactured by coating a positive electrode active material layer forming composition onto a positive electrode current collector and subsequently drying and rolling it. This positive electrode active material layer forming composition is prepared by dissolving or dispersing the aforementioned positive electrode active material, along with optional binders and conductive materials, in a solvent. In this case, the types and amounts of the positive electrode active material, binder, and conductive material are as described above.

[0086] The solvent can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, or water. Any one or a mixture of two or more of these solvents can be used. Considering the coating thickness and preparation yield of the slurry, the amount of solvent used is sufficient if it can dissolve and disperse the positive electrode active material, binder, and conductive material, and achieves a viscosity that exhibits excellent thickness uniformity in subsequent coating processes used to manufacture the positive electrode.

[0087] Alternatively, in other methods, the positive electrode can be manufactured by casting a positive electrode active material layer forming composition onto a separate support, and then stacking the film layer obtained by peeling it off from the support onto the positive electrode current collector.

[0088] Lithium secondary batteries

[0089] Furthermore, the present invention can manufacture an electrochemical device including the aforementioned positive electrode. Specifically, the electrochemical device can be a battery, a capacitor, etc., and more specifically, a lithium secondary battery.

[0090] Specifically, a lithium secondary battery includes a positive electrode, a negative electrode disposed opposite to the positive electrode, a separator placed between the positive and negative electrodes, and an electrolyte. The positive electrode is the same as described above, so its detailed description will be omitted. In the following text, only the remaining components will be described in detail.

[0091] In addition, the lithium secondary battery may optionally include a battery case for housing an electrode assembly consisting of a positive electrode, a negative electrode and a separator, and a sealing member for sealing the battery case.

[0092] In a lithium secondary battery, the negative electrode includes a negative electrode current collector and a layer of negative electrode active material located on the negative electrode current collector.

[0093] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and does not cause chemical changes within the battery. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, or silver, as well as aluminum-cadmium alloys, can be used. Furthermore, the thickness of the negative electrode current collector is typically from 3 μm to 500 μm, and similar to the positive electrode current collector, micro-irregularities can be formed on the surface of the negative electrode current collector to improve the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0094] In addition to the negative electrode active material, the negative electrode active material layer may optionally include a binder and a conductive material.

[0095] As anode active materials, compounds capable of reversibly inserting and de-intercalating lithium can be used. Specific examples of anode active materials can include: carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metallic substances 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 that can be doped and de-doped with lithium, such as SiO₂. β(0<β<2), SnO2, vanadium oxide, lithium vanadium oxide; or a composite containing the aforementioned metallic substances and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more thereof can be used. Furthermore, lithium metal films can be used as negative electrode active materials. In addition, low-crystallinity carbon, high-crystallinity carbon, etc., can all be used as carbon materials. Representative examples of low-crystallinity carbon may include soft carbon and hard carbon, and representative examples of high-crystallinity carbon may include irregular, planar, 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 sintered carbon, such as coke derived from petroleum or coal tar pitch.

[0096] 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.

[0097] Adhesives are components used to facilitate the bonding between conductive materials, active materials, and current collectors, and are typically added in amounts ranging from 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of adhesives include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0098] Conductive materials are components that further enhance the conductivity of the negative electrode active material, and their addition amount relative to the total weight of the negative electrode active material layer can be less than 10% by weight, specifically less than 5% by weight. The conductive material is not particularly limited, as long as it is conductive and does not cause chemical changes in the battery. For example, graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; conductive fibers, such as carbon fibers and metal fibers; metal powders, such as fluorocarbon powder, aluminum powder, and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; or conductive materials, such as polyphenylene derivatives; and so on.

[0099] For example, the negative electrode active material layer can be prepared by coating a negative electrode mixture material onto a negative electrode current collector and then drying it, wherein the negative electrode mixture material is prepared by dissolving or dispersing the negative electrode active material and optionally a binder and conductive material in a solvent. Alternatively, the negative electrode active material layer can be prepared by casting the negative electrode mixture material onto a separate support and then laminating the film layer peeled off from the support onto the negative electrode current collector.

[0100] The negative electrode active material layer can be prepared by coating a negative electrode mixture material onto a negative electrode current collector and then drying it, wherein the negative electrode mixture material is prepared by dissolving or dispersing the negative electrode active material and optionally a binder and conductive material in a solvent. Alternatively, the negative electrode active material layer can be prepared by casting the negative electrode mixture material onto a separate support and then laminating the film layer peeled off from the support onto the negative electrode current collector.

[0101] Meanwhile, in lithium secondary batteries, the separator is used to separate the negative and positive electrodes and provide a pathway for lithium ions to move. Any separator can be used without particular limitation, as long as it is commonly used as a separator in lithium secondary batteries. In particular, separators with high electrolyte retention capacity and low resistance to the movement of electrolyte ions are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes made from polyolefin polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers), or laminated structures of two or more layers can be used. Furthermore, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Additionally, coated separators including ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0102] In addition, the electrolyte used in this invention can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc., all of which can be used to manufacture lithium secondary batteries, but are not limited thereto.

[0103] Specifically, electrolytes may include organic solvents and lithium salts.

[0104] Any organic solvent can be used without particular limitation, as long as it can serve as a medium through which ions participating in the battery electrochemical reaction can move. Specifically, as organic solvents, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone can be used; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic C2 to C20 hydrocarbon group, which may contain double bonds, aromatic rings, or ether bonds); amides such as dimethylformamide; dioxolane solvents such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant and low viscosity chain carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred, as these mixtures can improve the charge / discharge performance of the battery. In this case, when cyclic carbonates and chain carbonates are mixed in a volume ratio of about 1:1 to about 1:9, the electrolyte solution can exhibit excellent performance.

[0105] Any compound can be used as a lithium salt without particular limitation, as long as it can provide lithium ions for lithium secondary batteries. Specifically, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, and LiN(CF3SO2) 2. LiCl, LiI, LiB(C₂O₄)₂, etc. Lithium salts can be used in concentration ranges from 0.1M to 2.0M. When the concentration of lithium salts is within this range, the electrolyte exhibits suitable conductivity and viscosity, thus demonstrating excellent performance, and lithium ions can move efficiently.

[0106] In order to improve battery life characteristics, suppress battery capacity decline, and increase battery discharge capacity, the electrolyte may also include one or more additives, such as halogenated alkyl carbonate compounds (e.g., ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, etc. In this case, the content of the additives can be from 0.1% by weight to 5% by weight, based on the total weight of the electrolyte.

[0107] Lithium secondary batteries containing the positive electrode active material of the present invention as described above stably exhibit excellent discharge capacity, output characteristics, and lifespan characteristics, and are therefore suitable for use in portable devices such as mobile phones, laptops, and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs).

[0108] Therefore, the present invention can provide a battery module including the lithium secondary battery as a unit cell, and a battery pack including the battery module.

[0109] The battery module or battery pack can be used as a power source for one or more medium to large-sized devices, such as power tools, electric vehicles (e.g., electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs)), or energy storage systems.

[0110] The shape of the lithium secondary battery of the present invention is not particularly limited, and it can be cylindrical, square, bag-shaped, coin-shaped, etc.

[0111] The lithium secondary battery of the present invention can be used in battery cells used as power sources for small devices, and can also preferably be used as cell cells in medium and large battery modules comprising multiple battery cells.

[0112] The embodiments of the present invention will be described in detail below to enable those skilled in the art to readily implement the invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

[0113] Preparation Example

[0114] Preparation Example 1

[0115] Nickel sulfate, cobalt sulfate, and manganese sulfate were mixed in deionized water at a molar ratio of 87:6:7 to prepare a 2M aqueous solution of the metal salt. Separately, a 4M NaOH aqueous solution and a 7% NH4OH aqueous solution were prepared.

[0116] Containers containing aqueous solutions of a metal salt, NaOH, and NH4OH were connected to a batch reactor (capacity: 5L) set to 60°C. 3L of deionized water was added to the reactor, and nitrogen gas was then introduced at a rate of 2L / min to remove dissolved oxygen from the deionized water, thus creating a non-oxidizing atmosphere within the reactor. Subsequently, NaOH aqueous solution was introduced at 60°C to maintain pH 12.0. Then, the aqueous solutions of the metal salt, NaOH, and NH4OH were introduced at rates of 180ml / hr, 180ml / hr, and 10ml / hr, respectively, to conduct a co-precipitation reaction for 10 hours, thereby preparing Ni-containing materials with an average particle size of 10μm. 0.87 Co 0.06 Mn 0.07 (OH)2 is a large-diameter transition metal precursor.

[0117] Preparation Example 2

[0118] The average particle size of Ni was prepared in the same manner as in Preparation Example 1. 0.87 Co 0.06 Mn 0.07 The small-diameter transition metal precursor of (OH)2 differs in that the co-precipitation reaction is carried out for 3 hours.

[0119] Examples and Comparative Examples

[0120] Example 1

[0121] (1) Preparation of large-diameter lithium transition metal oxides

[0122] A mixture was prepared by uniformly mixing the large-diameter transition metal precursor prepared in Preparation Example 1, LiOH·H2O as a lithium-containing raw material, and ZrO2 and Al2O3 as raw materials containing doping elements. LiOH·H2O was introduced in an amount such that the molar ratio of lithium to the total molar amount of transition metal in the large-diameter lithium transition metal oxide to be prepared (Li / transition metal) was 1.05:1, ZrO2 was introduced in an amount of 3000 ppm relative to the large-diameter transition metal precursor, and Al2O3 was introduced in an amount of 4700 ppm relative to the large-diameter transition metal precursor.

[0123] The mixture was calcined at 760°C for 16 hours in an oxygen atmosphere to prepare a calcined product. The calcined product was washed with deionized water, then the moisture was removed using a vacuum pump and the product was dried. The dried calcined product was mixed with 0.1 wt% boric acid (H3BO3), and the mixture was heat-treated at 400°C for 5 hours to prepare a large-diameter lithium transition metal oxide (average particle size: 10.0 μm, composition: Li) with a boron coating formed on its surface. 1.05 (Ni 0.87 Co0.06 Mn 0.07 ) 0.98 Zr 0.0032 Al 0.017 O2, grain size: 120nm).

[0124] (2) Preparation of small-diameter lithium transition metal oxides

[0125] Small-diameter lithium transition metal oxides (average particle size: 5.0 μm, composition: Li) with a boron coating formed on their surface were prepared in the same manner as in Example 1 (1). 1.05 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.98 Zr 0.0032 Al 0.017 O2 (grain size: 120 nm), the difference being that the small-diameter transition metal precursor prepared in Preparation Example 2 was used instead of the large-diameter transition metal precursor prepared in Preparation Example 1, and the firing temperature was adjusted to 740 °C.

[0126] (3) Preparation of positive electrode active materials

[0127] A positive electrode active material was prepared by mixing large-diameter lithium transition metal oxide and small-diameter lithium transition metal oxide at a weight ratio of 8:2.

[0128] Example 2

[0129] (1) Preparation of large-diameter lithium transition metal oxides

[0130] Large-diameter lithium transition metal oxides (average particle size: 10.0 μm, composition: Li) with a boron coating formed on their surface were prepared in the same manner as in Example 1 (1). 1.07 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.98 Zr 0.0032 Al 0.017 O2 (grain size: 130nm), the difference being that LiOH·H2O is introduced in an amount such that the molar ratio (Li / transition metal) of lithium to the total number of moles of transition metal in the large-diameter lithium transition metal oxide to be prepared is 1.07:1.

[0131] (2) Preparation of small-diameter lithium transition metal oxides

[0132] Small-diameter lithium transition metal oxides (average particle size: 5.0 μm, composition: Li) with a boron coating formed on their surface were prepared in the same manner as in Example 1 (2). 1.07 (Ni 0.87Co 0.06 Mn 0.07 ) 0.98 Zr 0.0032 Al 0.017 O2 (grain size: 130nm), the difference being that LiOH·H2O is introduced in an amount such that the molar ratio (Li / transition metal) of lithium to the total number of moles of transition metal in the small-diameter lithium transition metal oxide to be prepared is 1.07:1.

[0133] (3) Preparation of positive electrode active materials

[0134] A positive electrode active material was prepared by mixing large-diameter lithium transition metal oxide and small-diameter lithium transition metal oxide at a weight ratio of 8:2.

[0135] Example 3

[0136] (1) Preparation of large-diameter lithium transition metal oxides

[0137] Large-diameter lithium transition metal oxides (average particle size: 10.0 μm, composition: Li) with a boron coating formed on their surface were prepared in the same manner as in Example 1 (1). 1.03 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.98 Zr 0.0032 Al 0.017 O2 (grain size: 110nm), the difference being that LiOH·H2O is introduced in an amount such that the molar ratio of lithium to the total number of moles of transition metal in the large-diameter lithium transition metal oxide to be prepared (Li / transition metal) is 1.03:1.

[0138] (2) Preparation of small-diameter lithium transition metal oxides

[0139] Small-diameter lithium transition metal oxides (average particle size: 5.0 μm, composition: Li) with a boron coating formed on their surface were prepared in the same manner as in Example 1 (2). 1.03 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.98 Zr 0.0032 Al 0.017 O2 (grain size: 110nm), the difference being that LiOH·H2O is introduced in an amount such that the molar ratio (Li / transition metal) of lithium to the total number of moles of transition metal in the small-diameter lithium transition metal oxide to be prepared is 1.03:1.

[0140] (3) Preparation of positive electrode active materials

[0141] A positive electrode active material was prepared by mixing large-diameter lithium transition metal oxide and small-diameter lithium transition metal oxide at a weight ratio of 8:2.

[0142] Comparative Example 1

[0143] (1) Preparation of large-diameter lithium transition metal oxides

[0144] Large-diameter lithium transition metal oxides (average particle size: 10.0 μm, composition: Li) with a boron coating formed on their surface were prepared in the same manner as in Example 1 (1). 1.05 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.9825 Zr 0.00053 Al 0.017 The difference is that ZrO2 (grain size: 120 nm) is introduced at an amount of 500 ppm relative to the large-diameter transition metal precursor.

[0145] (2) Preparation of small-diameter lithium transition metal oxides

[0146] Small-diameter lithium transition metal oxides (average particle size: 5.0 μm, composition: Li) with a boron coating formed on their surface were prepared in the same manner as in Example 1 (2). 1.05 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.9825 Zr 0.00053 Al 0.017 The difference is that ZrO2 (grain size: 120 nm) is introduced at an amount of 500 ppm relative to the small-diameter transition metal precursor.

[0147] (3) Preparation of positive electrode active materials

[0148] A positive electrode active material was prepared by mixing large-diameter lithium transition metal oxide and small-diameter lithium transition metal oxide at a weight ratio of 8:2.

[0149] Comparative Example 2

[0150] (1) Preparation of large-diameter lithium transition metal oxides

[0151] Large-diameter lithium transition metal oxides (average particle size: 10.0 μm, composition: Li) with a boron coating formed on their surface were prepared in the same manner as in Example 1 (1). 1.05 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.975 Zr 0.0081 Al0.017 The difference is that ZrO2 (grain size: 120 nm) is introduced at an amount of 7500 ppm relative to the large-diameter transition metal precursor.

[0152] (2) Preparation of small-diameter lithium transition metal oxides

[0153] Small-diameter lithium transition metal oxides (average particle size: 5.0 μm, composition: Li) with a boron coating formed on their surface were prepared in the same manner as in Example 1 (2). 1.05 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.975 Zr 0.0081 Al 0.017 The difference is that ZrO2 (grain size: 120 nm) is introduced at an amount of 7500 ppm relative to small-diameter transition metal precursors.

[0154] (3) Preparation of positive electrode active materials

[0155] A positive electrode active material was prepared by mixing large-diameter lithium transition metal oxide and small-diameter lithium transition metal oxide at a weight ratio of 8:2.

[0156] Comparative Example 3

[0157] (1) Preparation of large-diameter lithium transition metal oxides

[0158] Large-diameter lithium transition metal oxides (average particle size: 10.0 μm, composition: Li) with a boron coating formed on their surface were prepared in the same manner as in Example 1 (1). 1.0 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.98 Zr 0.0032 Al 0.017 O2 (grain size: 120nm), the difference is that LiOH·H2O is introduced in an amount such that the molar ratio of lithium to the total number of transition metal moles in the large-diameter lithium transition metal oxide to be prepared (Li / transition metal) is 1:1.0, and the firing temperature is adjusted to 770℃.

[0159] (2) Preparation of small-diameter lithium transition metal oxides

[0160] Small-diameter lithium transition metal oxides (average particle size: 5.0 μm, composition: Li) with a boron coating formed on their surface were prepared in the same manner as in Example 1 (2). 1.0 (Ni 0.87 Co 0.06 Mn 0.07 )0.98 Zr 0.0032 Al 0.017 O2 (grain size: 120nm), the difference is that LiOH·H2O is introduced in an amount such that the molar ratio of lithium to the total number of transition metal moles in the small-diameter lithium transition metal oxide to be prepared (Li / transition metal) is 1:1.0, and the firing temperature is adjusted to 750℃.

[0161] (3) Preparation of positive electrode active materials

[0162] A positive electrode active material was prepared by mixing large-diameter lithium transition metal oxide and small-diameter lithium transition metal oxide at a weight ratio of 8:2.

[0163] Comparative Example 4

[0164] (1) Preparation of large-diameter lithium transition metal oxides

[0165] Large-diameter lithium transition metal oxides (average particle size: 10.0 μm, composition: Li) with a boron coating formed on their surface were prepared in the same manner as in Example 1 (1). 1.11 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.98 Zr 0.0032 Al 0.017 The difference is that LiOH·H2O is introduced to make the molar ratio of lithium to the total number of transition metal moles (Li / transition metal) in the large-diameter lithium transition metal oxide to be prepared 1.11:1, and the firing temperature is adjusted to 740℃.

[0166] (2) Preparation of small-diameter lithium transition metal oxides

[0167] Small-diameter lithium transition metal oxides (average particle size: 5.0 μm, composition: Li) with a boron coating formed on their surface were prepared in the same manner as in Example 1 (2). 1.11 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.98 Zr 0.0032 Al 0.017 O2 (grain size: 120nm), the difference is that LiOH·H2O is introduced in an amount such that the molar ratio of lithium to the total number of transition metal moles in the small-diameter lithium transition metal oxide to be prepared (Li / transition metal) is 1.11:1, and the firing temperature is adjusted to 720℃.

[0168] (3) Preparation of positive electrode active materials

[0169] A positive electrode active material was prepared by mixing large-diameter lithium transition metal oxide and small-diameter lithium transition metal oxide at a weight ratio of 8:2.

[0170] Comparative Example 5

[0171] (1) Preparation of large-diameter lithium transition metal oxides

[0172] Large-diameter lithium transition metal oxides (average particle size: 10.0 μm, composition: Li) with a boron coating formed on their surface were prepared in the same manner as in Example 1 (1). 1.05 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.98 Zr 0.0032 Al 0.017 O2 (grain size: 90nm), the difference is that the firing temperature is adjusted to 730℃.

[0173] (2) Preparation of small-diameter lithium transition metal oxides

[0174] Small-diameter lithium transition metal oxides (average particle size: 5.0 μm, composition: Li) with a boron coating formed on their surface were prepared in the same manner as in Example 1 (2). 1.05 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.98 Zr 0.0032 Al 0.017 O2 (grain size: 90nm), the difference is that the firing temperature is adjusted to 710℃.

[0175] (3) Preparation of positive electrode active materials

[0176] A positive electrode active material was prepared by mixing large-diameter lithium transition metal oxide and small-diameter lithium transition metal oxide at a weight ratio of 8:2.

[0177] Comparative Example 6

[0178] (1) Preparation of large-diameter lithium transition metal oxides

[0179] Large-diameter lithium transition metal oxides (average particle size: 10.0 μm, composition: Li) with a boron coating formed on their surface were prepared in the same manner as in Example 1 (1). 1.05 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.98 Zr 0.0032 Al 0.017O2 (grain size: 160nm), the difference is that the firing temperature is adjusted to 790℃.

[0180] (2) Preparation of small-diameter lithium transition metal oxides

[0181] Small-diameter lithium transition metal oxides (average particle size: 5.0 μm, composition: Li) with a boron coating formed on their surface were prepared in the same manner as in Example 1 (2). 1.05 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.98 Zr 0.0032 Al 0.017 O2 (grain size: 160nm), the difference is that the firing temperature is adjusted to 760℃.

[0182] (3) Preparation of positive electrode active materials

[0183] A positive electrode active material was prepared by mixing large-diameter lithium transition metal oxide and small-diameter lithium transition metal oxide at a weight ratio of 8:2.

[0184] Comparative Example 7

[0185] The large-diameter lithium transition metal oxide (average particle size: 10.0 μm, composition: Li) prepared in Example 2 (1) was used. 1.07 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.98 Zr 0.0032 Al 0.017 O2, grain size: 130 nm) and the small-diameter lithium transition metal oxide (average grain size: 5.0 μm, composition: Li) prepared in Comparative Example 5 (2) and Comparative Example 5 (2) 1.05 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.98 Zr 0.003 Al 0.017 O2 (crystal size: 90nm) was mixed at a weight ratio of 8:2 to prepare a positive electrode active material.

[0186] Comparative Example 8

[0187] The large-diameter lithium transition metal oxide (average particle size: 10.0 μm, composition: Li) prepared in Comparative Example 5 (1) was compared with the large-diameter lithium transition metal oxide (average particle size: 10.0 μm, composition: Li). 1.05 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.98 Zr 0.003 Al 0.017O2, grain size: 90 nm) and the small-diameter lithium transition metal oxide (average particle size: 5.0 μm, composition: Li) prepared in Example 2 (2) 1.07 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.98 Zr 0.0032 Al 0.017 O2 (crystal size: 130nm) was mixed at a weight ratio of 8:2 to prepare a positive electrode active material.

[0188] Comparative Example 9

[0189] (1) Preparation of large-diameter lithium transition metal oxides

[0190] Large-diameter lithium transition metal oxides (average particle size: 10.0 μm, composition: Li) with a boron coating formed on their surface were prepared in the same manner as in Example 1 (1). 1.05 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.9958 Zr 0.0032 Al 0.001 The difference is that Al2O3 is introduced in an amount of 280 ppm relative to the large-diameter transition metal precursor (O2, grain size: 120 nm).

[0191] (2) Preparation of small-diameter lithium transition metal oxides

[0192] Small-diameter lithium transition metal oxides (average particle size: 5.0 μm, composition: Li) with a boron coating formed on their surface were prepared in the same manner as in Example 1 (2). 1.05 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.9958 Zr 0.0032 Al 0.001 The difference is that Al2O3 is introduced in an amount of 280 ppm relative to the small-diameter transition metal precursor (O2, grain size: 120 nm).

[0193] (3) Preparation of positive electrode active materials

[0194] A positive electrode active material was prepared by mixing large-diameter lithium transition metal oxide and small-diameter lithium transition metal oxide at a weight ratio of 8:2.

[0195] Comparative Example 10

[0196] (1) Preparation of large-diameter lithium transition metal oxides

[0197] Large-diameter lithium transition metal oxides (average particle size: 10.0 μm, composition: Li) with a boron coating formed on their surface were prepared in the same manner as in Example 1 (1). 1.05 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.9469 Zr 0.0032 Al 0.05 The difference is that Al2O3 is introduced in an amount of 13,700 ppm relative to the large-diameter transition metal precursor (O2, grain size: 120 nm).

[0198] (2) Preparation of small-diameter lithium transition metal oxides

[0199] Small-diameter lithium transition metal oxides (average particle size: 5.0 μm, composition: Li) with a boron coating formed on their surface were prepared in the same manner as in Example 1 (2). 1.05 (Ni 0.87 Co 0.06 Mn 0.07 ) 0.9468 Zr 0.0032 Al 0.05 O2 (grain size: 120nm), the difference being that Al2O3 is introduced in an amount of 13700ppm relative to the small-diameter transition metal precursor.

[0200] (3) Preparation of positive electrode active materials

[0201] A positive electrode active material was prepared by mixing large-diameter lithium transition metal oxide and small-diameter lithium transition metal oxide at a weight ratio of 8:2.

[0202] Experimental Example

[0203] Experimental Example 1: Evaluation of Ni Disorder

[0204] For each positive electrode active material prepared in Examples 1 to 3 and Comparative Examples 1 to 10, XRD data were obtained using an X-ray diffraction analyzer (Bruker, D8 Endeavor), and atomic structure analysis was performed using the Rietveld method to analyze the Ni occupying lithium sites. 2+ The relative amounts of ions and the relative occupancy of oxygen in the oxygen sites are then used to determine the irregular Ni content in the lithium sites. 2+ The amount (%) of ions was set as the nickel disorder value, as shown in Table 1 below.

[0205] Experimental Example 2: Evaluation of Particle Strength

[0206] For the large-diameter lithium transition metal oxide and small-diameter lithium transition metal oxide particles prepared in Examples 1 to 3 and Comparative Examples 1 to 10, the force at which the particles were broken was measured using a Micro compression tester (Shimadzu Corporation, MCT-W500) while increasing the compression force. The measured force was set as the particle strength value, as shown in Table 1 below.

[0207] [Table 1]

[0208]

[0209] Experiment Example 3: Evaluation of Half-Cell Characteristics

[0210] Using the positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 10, coin-shaped half-cells were fabricated, and the initial charge capacity, initial discharge capacity, and capacity retention of each cell were evaluated.

[0211] Specifically, the positive electrode active materials, carbon black conductive materials, and PVdF binders prepared in Examples 1 to 3 and Comparative Examples 1 to 10 were mixed in NMP solvent at a weight ratio of 97.5:1.0:1.5 to prepare a positive electrode slurry. The positive electrode slurry was coated on one surface of an aluminum current collector, dried at 130°C, and then rolled to manufacture a positive electrode. Simultaneously, a Li metal disc was used as the negative electrode active material. A separator was placed between the above-prepared positive electrode and the Li metal disc negative electrode to form an electrode assembly. The electrode assembly was placed in a battery case, and then an electrolyte solution was injected into the case to form a coin-shaped half-cell. At this time, an electrolyte solution containing 1 M LiPF6 dissolved in an organic solvent of EC / EMC / DEC (3 / 3 / 4, vol%) was used as the electrolyte solution.

[0212] The battery prepared as described above was charged at 25°C with a constant current of 0.1C to a voltage of 4.25V, and then charged at a constant voltage (CV) until the charging current reached 0.05mAh. Thereafter, the battery was discharged at a constant current of 0.1C to a voltage of 3.0V. The initial charge capacity and initial discharge capacity values ​​are shown in Table 2.

[0213] In addition, the discharge capacity of the lithium secondary battery was measured by repeating 50 charge and discharge cycles at a constant current of 1C within the range of 3.0V to 4.25V at 45°C. In particular, the ratio of the discharge capacity of the 50th cycle to the discharge capacity of the 1st cycle was set as the capacity retention rate, as shown in Table 2 below.

[0214] [Table 2]

[0215]

[0216] Referring to Tables 1 and 2, it can be confirmed that the positive electrode active material of the present invention has low nickel disorder and high particle strength in its crystal structure, and when the positive electrode active material is applied to a battery, the battery has excellent capacity characteristics and capacity retention at high temperatures.

[0217] From the above, it can be confirmed that the cathode active material of Comparative Example 1, with a small Zr atomic fraction, has low particle strength due to its low doping content, while the cathode active material of Comparative Example 2, with a large Zr atomic fraction, has low initial charge / discharge capacity due to the increased inactive region of the metal sites. Furthermore, it can be confirmed that the cathode active material of Comparative Example 3, with a Li / Me ratio of 1.0, suffers from high Ni disorder, while the cathode active material of Comparative Example 4, with a Li / Me ratio of 1.11, suffers from difficulty in process control and low initial discharge capacity due to increased lithium byproducts. Additionally, it can be confirmed that the cathode active material of Comparative Example 5, with a grain size of 90 nm, suffers from high Ni disorder and low particle strength due to insufficient crystal growth, while the cathode active material of Comparative Example 6, with a grain size of 160 nm, suffers from increased particle breakage due to excessive shrinkage and expansion of primary particles during charging and discharging. Furthermore, it can be confirmed that in the positive electrode active material of Comparative Example 7, the difference in grain size between the large-diameter lithium transition metal oxide and the small-diameter lithium transition metal oxide is 40 nm or more, and the grain size of the small-diameter lithium transition metal oxide is smaller than that of the large-diameter lithium transition metal oxide. This results in an increase in the amount of small-sized fine powder and consequently, a low capacity retention rate. Similarly, it can be confirmed that in the positive electrode active material of Comparative Example 8, the difference in grain size between the large-diameter lithium transition metal oxide and the small-diameter lithium transition metal oxide is 40 nm or more, and the grain size of the large-diameter lithium transition metal oxide is smaller than that of the small-diameter lithium transition metal oxide. Due to excessive fragmentation of the large-sized lithium transition metal oxide particles, the conductivity decreases, resulting in a low capacity retention rate. In Comparative Example 9, with low aluminum doping, the low capacity retention rate is attributed to deteriorated driving stability. In Comparative Example 10, with high aluminum doping, the initial charge and discharge capacities decrease due to the increase in the inactive region of the metal sites.

[0218] Experimental Example 4: Evaluation using Differential Scanning Calorimetry (DSC)

[0219] Differential scanning calorimetry (DSC) was used to evaluate the coin-shaped half-cells manufactured in Experimental Example 3 that used the positive electrode active materials of Example 1 and Comparative Examples 9 and 10.

[0220] Specifically, using a Setaram HP-DSC device, a coin cell (CHC) was charged to 4.25V (SOC100). Specifically, the coin cell was charged at 25°C with a constant current of 0.1C to 4.25V, and then charged at a constant voltage until the charging current reached 0.05mAh. Subsequently, the battery was discharged at a constant current of 0.1C to 3.0V. The battery was then charged again at a constant current of 0.1C to 4.25V, and then charged at a constant voltage until the charging current reached 0.05mAh. Afterwards, the electrodes were removed, cleaned with dimethyl carbonate (DMC), stamped to a diameter of 5mm, and placed in a high-pressure PAN containing 20μl of electrolyte solution. The temperature was increased from room temperature to 400°C at a rate of 10°C / min, and the exothermic onset temperature was measured.

[0221] [Table 3]

[0222] Example 1 228 Comparative Example 9 218 Comparative Example 10 233

[0223] As can be seen from the results in Tables 2 and 3 above, in Comparative Example 9 with a small Al atomic fraction, there is a problem of increased capacity but decreased capacity retention and DSC thermal stability, while in Comparative Example 10 with a large Al atomic fraction, there is a problem of improved capacity retention and DSC thermal stability but significantly decreased capacity.

Claims

1. A positive electrode active material, the positive electrode active material comprising: Large-diameter lithium transition metal oxide; and Small-diameter lithium transition metal oxides, wherein the average particle size D of the small-diameter lithium transition metal oxides is... 50 The average particle size D of the large-diameter lithium transition metal oxide is smaller than that of the other two. 50 , in, The large-diameter lithium transition metal oxide and the small-diameter lithium transition metal oxide each independently have a composition represented by the following formula 1 and have a grain size of 100 nm to 150 nm, wherein the difference in grain size between the large-diameter lithium transition metal oxide and the small-diameter lithium transition metal oxide is less than 40 nm, and The positive electrode active material has a nickel disorder degree (Ni-disorder degree) of 1.5% or less: [Formula 1] Li x1 [Ni a1 Co b1 Mr c11 Al c12 Zr d1 M 2 e1 ]O2 Wherein in the above formula 1, M 2 It is selected from one or more of B, Mg, Ca, V, Cr, Fe, Zn, Ga, Y, Nb, Mo, Ta, and W, and 1.03 ≤ x1 ≤ 1.07, 0.7 ≤ a1 < 1, 0 < b1 < 0.3, 0 < c11 < 0.3, 0.001 < c12 < 0.03, 0.00 < d1 ≤ 0.0065, 0 ≤ e1 ≤ 0.1, and a1 + b1 + c11 + c12 + d1 + e1 = 1.

2. The positive electrode active material as described in claim 1, wherein, a1 satisfies 0.8 ≤ a1 < 1.

3. The positive electrode active material as described in claim 1, wherein, d1 satisfies 0.002 ≤ d1 ≤ 0.0045.

4. The positive electrode active material as described in claim 1, wherein, The large-diameter lithium transition metal oxide and the small-diameter lithium transition metal oxide each independently have a grain size of to 140 nm.

5. The positive electrode active material as described in claim 1, wherein, The large-diameter lithium transition metal oxide has a particle strength of 140 Mpa to 180 MPa.

6. The positive electrode active material as described in claim 1, wherein, The small-diameter lithium transition metal oxide has a particle strength of 110 Mpa to 150 MPa.

7. The positive electrode active material as described in claim 1, wherein, The large-diameter lithium transition metal oxide has an average particle size D of 8 μm to 15 μm. 50 .

8. The positive electrode active material as described in claim 1, wherein, The small-diameter lithium transition metal oxide has an average particle size D of 3 μm to 7 μm. 50 .

9. The positive electrode active material as described in claim 1, wherein, The weight ratio of the large-diameter lithium transition metal oxide to the small-diameter lithium transition metal oxide is 5:5 to 9:

1.

10. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 9.

11. A lithium secondary battery comprising the positive electrode according to claim 10.

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