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

Abstract

The present invention relates to a positive electrode active material comprising a lithium nickel-based transition metal oxide in the form of secondary particles, the secondary particles being an aggregate of primary particles, in which, for a cross-section at 40-60% of the diameter of the secondary particles, a) the number ratio of primary particles having an aspect ratio of 1.6 or more in the cross-section is 0.81 or more, and b) the number ratio of secondary particles having an aspect ratio of 1.6 or more in the cross-section is 0.81 or more; and b) a K value calculated by the following Equation 1 is 12 to 40. The positive electrode active material having the above-mentioned characteristics can reduce particle fragmentation during a cycle, thereby suppressing deterioration of a battery and improving stability. [Equation 1] K = RAP * NP / AS wherein RAP is the average aspect ratio of the primary particles, NP is the number of the primary particles, and AS is the cross-sectional area of the secondary particles.

Description

[0001] Cross - reference to related applications

[0002] This application claims the priority benefit of Korean Patent Application No. 10 - 2022 - 0184868, filed on December 26, 2022, the disclosure of which is incorporated herein by reference in its entirety. Technical field

[0003] The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode including the same, and a lithium secondary battery. More specifically, the present invention relates to a positive electrode active material including a lithium nickel - based transition metal oxide in the form of secondary particles (which are aggregates of primary particles), a positive electrode including the same, and a lithium secondary battery. Background art

[0004] A lithium secondary battery generally consists of a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode and the negative electrode include active materials capable of intercalating and deintercalating lithium ions.

[0005] As positive electrode active materials for lithium secondary batteries, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMnO4, etc.), lithium iron phosphate compound (LiFePO4), etc. have been used. Among them, lithium cobalt oxide has the advantages of a high working voltage and excellent capacity characteristics, but the price of cobalt as a raw material is high, and its supply is unstable, making it difficult to commercially apply it to large - capacity batteries. Lithium nickel oxide has poor structural stability, making it difficult to achieve sufficient life characteristics. At the same time, lithium manganese oxide has excellent stability, but has a problem of poor capacity characteristics. Therefore, in order to compensate for the problems of lithium transition metal oxides containing only Ni, Co, or Mn, lithium nickel - based transition metal oxides containing two or more transition metals have been developed. In particular, lithium nickel cobalt manganese oxide containing Ni, Co, and Mn is widely used in the field of electric vehicle batteries.

[0006] Recently, the demand for high - power and high - capacity batteries such as batteries for electric vehicles has been increasing, so the nickel content in the positive electrode active material has gradually increased. When the nickel content in the positive electrode active material increases, the initial capacity characteristics are improved, but a large amount of highly reactive Ni +4 ions are generated during electrode rolling or during charging and discharging, resulting in the structural collapse of the positive electrode active material. As a result, surface side reactions increase, and the deterioration rate of the positive electrode active material increases, thereby reducing the life characteristics and battery safety. Summary of the invention

[0007] [Technical problem]

[0008] The present invention aims to solve the above problems and provides a positive electrode active material, which suppresses particle breakage and cracks during electrode manufacturing and during charge / discharge by optimizing the shape of primary particles inside secondary particles, thereby having enhanced durability.

[0009] In addition, the present invention provides a positive electrode and a lithium secondary battery, which have improved high-temperature life characteristics and high-temperature output characteristics by including the above positive electrode active material.

[0010] [Technical Solution]

[0011] To solve the above problems, according to one aspect of the present invention, there is provided a positive electrode active material including a lithium nickel-based transition metal oxide in the form of secondary particles, which are aggregates of primary particles, wherein a cross-section at 40% to 60% of the diameter of the secondary particles satisfies the following conditions a) and b):

[0012] a) The number ratio of primary particles having an aspect ratio of 1.6 or more in the above cross-section is 0.81 or more, and

[0013] b) The K value calculated by the following Equation 1 is 12 to 40:

[0014] [Equation 1]

[0015] K = R AP × N P / A S

[0016] wherein R AP is the average aspect ratio of primary particles, N P is the number of primary particles, and A S is the cross-sectional area of the secondary particles.

[0017] To solve the above problems, according to another aspect of the present invention, there is provided a positive electrode including the positive electrode active material of the present invention.

[0018] To solve the above problems, according to still another aspect of the present invention, there is provided a lithium secondary battery including the positive electrode of the present invention.

[0019] [Advantageous Effects]

[0020] The positive electrode active material for a lithium secondary battery of the present invention includes a lithium nickel-based transition metal oxide in which the shape of primary particles in secondary particles is optimized, thereby reducing particle breakage caused by roll pressing during electrode manufacturing, the crack generation rate of active material particles during charge and discharge, and the amount of fine powder generated, and obtaining excellent durability.

[0021] In addition, the positive electrode active material for a lithium secondary battery of the present invention can minimize particle breakage and crack generation, reduce side reactions on the electrode surface, and suppress its deterioration, thereby having high-temperature life characteristics and high-temperature output characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a scanning electron micrograph of a cross-section of the positive electrode active material particles manufactured in Example 1 of the present invention.

[0023] Figure 2 is a scanning electron micrograph of a cross-section of the positive electrode active material particles manufactured in Comparative Example 1.

[0024] Figure 3 is a scanning electron micrograph of a cross-section of the positive electrode active material particles manufactured in Comparative Example 2. DETAILED DESCRIPTION

[0025] The terms or words used in the specification and claims of the present application should not be construed as limited to their ordinary or dictionary meanings, but should be interpreted based on the principle that the inventor can fully define the concept of the terms to best describe his invention, and should be interpreted as meanings and concepts consistent with the technical spirit of the present invention.

[0026] It should be understood that the terms "comprising", "including", and "having" used herein are intended to indicate the presence of the implemented features, numbers, steps, components, or combinations thereof, but do not exclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0027] In the present disclosure, a "secondary particle" refers to a particle formed by agglomeration of dozens to hundreds of primary particles. More specifically, a secondary particle is an agglomerate of 50 or more primary particles.

[0028] In the present disclosure, "D 50 " refers to the particle size at 50% of the volume-based cumulative particle size distribution of the positive electrode active material powder. The average particle size D 50 can be measured using the laser diffraction method. For example, the positive electrode active material powder is dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and irradiated with ultrasonic waves of about 28 kHz with an output of 60 W. Thereafter, the average particle size can be determined by obtaining a volume-based cumulative particle size distribution diagram and then obtaining the particle size corresponding to 50% of the volume-based cumulative amount.

[0029] Hereinafter, the present invention will be described in more detail.

[0030] Positive electrode active material

[0031] The positive electrode active material of the present invention includes a lithium nickel-based transition metal oxide in the form of secondary particles, which are aggregates of primary particles. For a cross-section at 40% to 60% of the diameter of the secondary particles, a) the number ratio of primary particles with an aspect ratio of 1.6 or more in the above cross-section is 0.81 or more, and b) the K value calculated by the following Equation 1 is 12 to 40:

[0032] [Equation 1]

[0033] K = R AP ×N P / A S

[0034] where R AP is the average aspect ratio of the primary particles, N P is the number of primary particles, and A S is the cross-sectional area of the secondary particles.

[0035] According to an embodiment of the present invention, the lithium nickel-based transition metal oxide included in the positive electrode active material is characterized in that the above conditions a) and b) are satisfied in a cross-section based on 40% to 60% of the diameter of the secondary particles.

[0036] In this specification, the characteristics obtained from the cross-section of the lithium nickel-based transition metal oxide are values obtained by photographing the cross-section of the oxide particles cut by ion milling with a field emission scanning electron microscope and analyzing it with an image analysis program.

[0037] Condition a) means that, among the primary particles on the cross-section of the secondary particles, the ratio of the number of primary particles with an aspect ratio of 1.6 or more to the total number of primary particles is 0.81 or more. That is, the aspect ratio of 81% or more of the primary particles is 1.6 or more, which may mean that the proportion of primary particles preferably having an elongated shape is high. Preferably, the number ratio may be 0.82 or more, 0.83 or more, 0.84 or more, or 0.85 or more.

[0038] In addition, condition b) means that the range of the K value represented by Equation 1 is 12 to 40. Preferably, the K value may be 15 or more, 17 or more, or 20 or more, and 35 or less, 32 or less, or 28 or less. The K value is the ratio of the product of the aspect ratio and the number of primary particles to the cross-sectional area of the secondary particles. The lower limit of the K value may mean that, relative to the area, when the aspect ratio of the primary particles is the same, it is more preferable that there are more primary particles, and when the number is the same, it is preferable that the aspect ratio is larger. The upper limit may mean that, relative to the area, the aspect ratio and the number of the particles should be at an appropriate level, and when they exceed the appropriate level, particle breakage and cracking may occur.

[0039] On the other hand, the positive electrode active material in the form of secondary particles has a shape in which primary particles are aggregated, and its performance can be determined according to the arrangement of the primary particles, the crystal orientation of the primary particles, etc. Among them, the arrangement of the primary particles can have a greater influence than the crystal orientation of the primary particles because the grain boundaries between the primary particles are regions where lithium ions or electrons move at high speed; since the more the number of primary particles, the more grain boundaries are formed and the better the performance, but on the contrary, cracks are likely to occur; and the grain boundaries are regions where the possibility of side reactions with the electrolyte is the highest. Therefore, the performance of the positive electrode active material, that is, the performance of the lithium secondary battery, can be determined according to the arrangement of the primary particles.

[0040] Specifically, it is preferable that the primary particles have a large aspect ratio. When the number of primary particles in the cross-sectional area of the secondary particles is large, there is a contradiction that, although as described above, due to a large number of grain boundaries, the mobility of lithium ions and electrons can be improved, but on the contrary, the possibility of cracking and side reactions will increase. Therefore, considering these characteristics, the inventors of the present invention intend to solve the above problems by defining the ratio of the number of primary particles having an aspect ratio equal to or greater than a specific value existing in the cross-section of the secondary particles, and the ratio of the product of the aspect ratio and the number of primary particles to the cross-sectional area of the secondary particles.

[0041] According to an embodiment of the present invention, the lithium nickel-based transition metal oxide may further satisfy the following condition: in a cross-section of 40% to 60% based on the diameter of the secondary particles, the short diameter (D S ) of the primary particles and the D 50 of the secondary particles have a ratio of 0.025 or less.

[0042] When the ratio of the short diameter (D S ) of the primary particles to the D 50 of the secondary particles (D S / D 50 ) is 0.025 or less, the primary particles can have an elongated shape and an appropriate size level, and an appropriate number of primary particles can exist in the cross-section of the secondary particles. The ratio of the short diameter of the primary particles to the D 50 of the secondary particles may preferably be 0.023 or less, or 0.020 or less. The lower limit can be controlled by the K value, and may preferably be 0.010 or more, 0.012 or more, or 0.013 or more.

[0043] In addition, the lithium nickel-based transition metal oxide may further satisfy the following condition: the ratio of the long diameter (D L ) of the primary particles to the D 50 of the secondary particles (D L / D 50) is from 0.035 to 0.075. This may mean that it is desirable for the primary particles to have a long shape, and in the case of the above range, the primary particles can have such a shape and exist in an appropriate amount. Therefore, preferably, the ratio can be 0.035 or more, 0.038 or more, 0.040 or more, 0.045 or more, 0.050 or more, or 0.055 or more, and 0.070 or less, 0.065 or less, or 0.063 or less.

[0044] According to an embodiment of the present invention, the average aspect ratio of the primary particles in the secondary particles can be from 2.0 to 3.5. Although there is a condition that the ratio of the number of primary particles with an aspect ratio of 1.6 or more to the total amount is 0.81 or more, when the overall average value satisfies the range of 2.0 to 3.5, it can contribute to optimizing the shape of the primary particles, and thus the technical purpose of improving durability can be effectively achieved. The average aspect ratio can be 2.1 or more, 2.2 or more, 2.3 or more, or 2.4 or more, and 3.3 or less, 3.2 or less, or 3.0 or less.

[0045] Meanwhile, according to an example of the present invention, the crystal strain of the secondary particles of the lithium nickel-based transition metal oxide can be 670×10 -6 or less. The crystal strain of the secondary particles represents the degree of deformation of the crystal lattice, and when the degree of deformation of the crystal lattice is large, it means that the structural stability is low. When the above range is not satisfied, the structure may be prone to collapse during electrode rolling or cycling, resulting in electrode deterioration, and thus the high-temperature life and output characteristics may be poor. In addition, the positive electrode containing such a positive electrode active material has an initial efficiency lower than a specific range, and thus there is a problem that there is a difference in rate characteristics with the negative electrode, resulting in a lithium plating phenomenon in which lithium is deposited on the surface of the negative electrode and reducing the energy density. Therefore, the above crystal strain can preferably be 660×10 -6 or less, 655×10 -6 or less, 650×10 -6 or less, or 645×10 -6 or less.

[0046] According to an embodiment of the present invention, the D 50 of the lithium nickel-based transition metal oxide can be from 7.0 μm to 20.0 μm. Preferably, it can be 8.0 μm or more, 9.0 μm or more, 9.5 μm or more, or 10.0 μm or more, and 19.0 μm or less, 18.0 μm or less, 16.0 μm or less, 15.0 μm or less, or 14.0 μm or less. When the D 50 of the secondary particles satisfies the above range, the life characteristics can be improved, and due to excellent lithium mobility and thus improved resistance characteristics, the output can be increased.

[0047] Meanwhile, the positive electrode active material of the present invention may include a lithium nickel-based transition metal oxide. Specifically, it is a lithium nickel-based transition metal oxide having the composition shown in the following Chemical Formula 1:

[0048] [Chemical Formula 1]

[0049] Li 1+x Ni a Co b M 1 c M 2 d O 2-e X e

[0050] Wherein:

[0051] M 1 includes one or more selected from Mn and Al; M 2 includes one or more selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, and Nb; X includes one or more selected from the group consisting of N, P, S, F, and Cl; 0 ≤ x ≤ 0.5, 0.6 ≤ a < 1.0, 0 < b ≤ 0.4, 0 < c ≤ 0.4, 0 ≤ d ≤ 0.05, and 0 ≤ e ≤ 0.05.

[0052] In the above Formula 1, M 1 may include Mn, Al, or a combination thereof, preferably Mn or a combination of Mn and Al; M 2 may include at least one selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably at least one selected from the group consisting of Zr, Y, Mg, and Ti, more preferably Zr, Y, or a combination thereof. M 2 The element is not necessarily included, but when included in an appropriate amount, it can play a role in promoting grain growth or improving the crystal structure stability during calcination. In addition, X is an anion substituting for the oxygen site and may include N, P, S, F, or Cl.

[0053] 1 + x represents the molar ratio of lithium in the lithium nickel-based transition metal oxide and may be 0 ≤ x ≤ 0.50, 0 ≤ x ≤ 0.20, 0 ≤ x ≤ 0.15, or 0 ≤ x ≤ 0.10.

[0054] a represents the molar ratio of nickel among all metals other than lithium in the lithium nickel-based transition metal oxide and may be 0.60 ≤ a < 1.00, 0.65 ≤ a < 1.00, 0.70 ≤ a ≤ 0.99, 0.75 ≤ a ≤ 0.99, or 0.80 ≤ a ≤ 0.99, 0.82 ≤ a ≤ 0.99, 0.84 ≤ a ≤ 0.99, or 0.86 ≤ a ≤ 0.99.

[0055] b represents the molar ratio of cobalt among all metals other than lithium in the lithium nickel-based transition metal oxide, and can be 0 < b ≤ 0.40, 0 < b ≤ 0.30, 0.01 ≤ b ≤ 0.25, 0.01 ≤ b ≤ 0.20, or 0.01 ≤ b ≤ 0.15.

[0056] c represents the molar ratio of M among all metals other than lithium in the lithium nickel-based transition metal oxide 1 and can be 0 < c ≤ 0.40, 0 < c ≤ 0.30, 0.01 ≤ c ≤ 0.25, 0.01 ≤ c ≤ 0.20, or 0.01 ≤ c ≤ 0.15.

[0057] d represents the molar ratio of the M 2 element among all metals other than lithium in the lithium nickel-based transition metal oxide, and can be 0 ≤ d ≤ 0.05, 0 ≤ d ≤ 0.02 or 0 ≤ d ≤ 0.01.

[0058] e represents the molar ratio of element X among all non-metals other than oxygen in the lithium nickel-based transition metal oxide, and can be 0 ≤ e ≤ 0.05, 0 ≤ e ≤ 0.02, or 0 ≤ e ≤ 0.01.

[0059] Method for manufacturing positive electrode active material

[0060] Next, a method for manufacturing the positive electrode active material powder of the present invention will be described.

[0061] The method for manufacturing the positive electrode active material powder of the present invention includes the following steps: (S1) preparing a positive electrode active material precursor by adding a transition metal-containing solution containing cations of nickel (Ni), cobalt (Co), and M 1 and performing a coprecipitation reaction with an alkaline aqueous solution and an ammonium solution; and (S2) preparing a positive electrode active material powder by mixing the positive electrode active material precursor and a lithium raw material and subjecting the mixture to heat treatment.

[0062] In addition, the manufactured positive electrode active material contains a lithium nickel-based transition metal oxide in the form of secondary particles (wherein dozens to hundreds of primary particles aggregate to form an aggregate).

[0063] Hereinafter, each step of the method for manufacturing the positive electrode active material powder will be described in detail.

[0064] First, a transition metal-containing solution containing cations of nickel (Ni), cobalt (Co), and M 1 is prepared. For example, the transition metal-containing solution may include a nickel raw material, a cobalt raw material, and an M 1 raw material, wherein the M 1 raw material may be a manganese raw material and / or an aluminum raw material.

[0065] Thereafter, a precursor of the positive electrode active material can be prepared by adding a complexing agent containing an ammonium cation and an aqueous alkaline solution to a transition metal solution and performing a coprecipitation reaction.

[0066] The nickel-containing raw material can be, for example, nickel acetate, nickel nitrate, nickel sulfate, nickel halide, nickel sulfide, nickel hydroxide, nickel oxide, nickel oxyhydroxide, etc. Specifically, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, nickel fatty acid salt, nickel halide, or a combination thereof, but not limited thereto.

[0067] The cobalt-containing raw material can be cobalt acetate, cobalt nitrate, cobalt sulfate, cobalt halide, cobalt sulfide, cobalt hydroxide, cobalt oxide, cobalt oxyhydroxide, etc. Specifically, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4, Co(SO4)2·7H2O, or a combination thereof, but not limited thereto.

[0068] The manganese-containing raw material can be, for example, manganese acetate, manganese nitrate, manganese sulfate, manganese halide, manganese sulfide, manganese hydroxide, manganese oxide, manganese oxyhydroxide, or a combination thereof. Specifically, manganese oxides such as Mn2O3, MnO2, Mn3O4, etc.; manganese salts such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese dicarboxylate salt, manganese citrate, manganese fatty acid salt; manganese oxyhydroxide, manganese chloride, or a combination thereof, but not limited thereto.

[0069] The aluminum-containing raw material can be, for example, Al2O3, Al(OH)3, Al(NO3)3, Al2(SO4)3, (HO)2AlCH3CO2, HOAl(CH3CO2)2, Al(CH3CO2)3, aluminum halide, or a combination thereof.

[0070] The transition metal-containing solution can be prepared by the following process: adding a nickel-containing raw material, a cobalt-containing raw material, and an M- 1 containing raw material to a solvent, specifically a mixed solvent of water or an organic solvent that can be uniformly mixed with water (such as alcohol, etc.), or mixing an aqueous solution of a nickel-containing raw material, an aqueous solution of a cobalt-containing raw material, and an M- 1 containing raw material.

[0071] The complexing agent containing an ammonium cation can be, for example, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or a combination thereof, but not limited thereto. At the same time, the complexing agent containing an ammonium cation can be used in the form of an aqueous solution, where the solvent can be water, or a mixture of water and an organic solvent that is uniformly miscible with water (specifically, alcohol, etc.).

[0072] The basic compound can be a hydroxide of an alkali metal or an alkaline earth metal, such as NaOH, KOH or Ca(OH)2, its hydrate, or a combination thereof. The basic compound can also be used in the form of an aqueous solution, where the solvent can be water, or a mixture of water and an organic solvent that is miscible with water (specifically, alcohols, etc.).

[0073] The basic compound is added to adjust the pH of the reaction solution, and the addition amount can be such that the pH of the metal solution is 8 to 12.

[0074] The coprecipitation reaction can be carried out in an inert atmosphere such as nitrogen or argon within a temperature range of 35°C to 80°C.

[0075] Therefore, a precursor of a positive electrode active material containing nickel, cobalt and M 1 cations can be prepared.

[0076] Through the above process, precursor particles of a positive electrode active material of nickel-cobalt-M 1 hydroxide are produced and precipitated in the reaction solution. By controlling the concentrations of the nickel-containing raw material, the cobalt-containing raw material and the M 1 raw material, a precursor of a positive electrode active material with a nickel (Ni) content of 60 mol% or more, 65 mol% or more, 70 mol% or more, 75 mol% or more, preferably 80 mol% or more, more preferably 82 mol% or more in the total metal content can be prepared. The precipitated precursor particles of the positive electrode active material can be separated and dried according to a conventional method to produce a precursor of a positive electrode active material.

[0077] The temperature, time, input amount and order of raw materials, additives used together and pH of the coprecipitation reaction can be appropriately controlled, thereby preparing a positive electrode active material according to an embodiment of the present invention and allowing the shape and arrangement of primary particles in secondary particles to be formed as desired.

[0078] Thereafter, the precursor of the positive electrode active material and a lithium raw material are mixed and heat-treated.

[0079] The lithium raw material can be a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or hydroxyoxide, but there is no particular limitation as long as it is soluble in water. Specifically, the lithium raw material can be Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, or Li3C6H5O7, and any one or a mixture of two or more thereof can be used.

[0080] The precursor of the positive electrode active material and the lithium raw material can be mixed at a molar ratio of 1:1 to 1:1.1. The precursor of the positive electrode active material and the lithium raw material can be mixed, for example, at a molar ratio of about 1:1, about 1:1.02, about 1:1.05, about 1:1.07, or about 1:1.10, but not limited thereto.

[0081] In the case of a high-Ni NCM-based lithium composite transition metal oxide with a Ni content of 60 mol% or more, the heat treatment can be carried out in the temperature range of 750 °C to 1000 °C. The heat treatment can preferably be carried out, for example, in the temperature range of 800 °C to 925 °C, and more preferably in the temperature range of 850 °C to 910 °C.

[0082] Therefore, the manufactured positive electrode active material can have reduced particle breakage and strain in the crystal structure during the roll pressing process or during the charging and discharging of the lithium secondary battery containing the same, and can have improved initial resistance characteristics.

[0083] The heat treatment can be carried out in an air or oxygen atmosphere for, for example, 4 to 12 hours. Specifically, the heat treatment can be carried out, for example, for 4 hours or more, 6 hours or more, 8 hours or more, 10 hours or more, and 12 hours or less, 10 hours or less, 8 hours or less, 6 hours or less.

[0084] The firing process can be carried out by dividing it into a primary firing and a secondary firing, and can be appropriately controlled according to the nickel content at a temperature within the above range, where the firing time can be appropriately controlled according to the shape or structure of the positive electrode active material to be prepared. By controlling such firing process conditions, the positive electrode active material of one embodiment of the present invention can be prepared.

[0085] Meanwhile, when preparing a lithium nickel-based transition metal oxide containing M 2 metal, a raw material containing M 2 metal can be additionally mixed during the coprecipitation reaction or in the firing step. In this case, the raw material containing M 2 metal can be an acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide of M 2 metal.

[0086] On the other hand, when it is desired to form a coating on the surface of the lithium nickel-based transition metal oxide, after the above heat treatment, a step of mixing the lithium nickel-based transition metal oxide prepared by the heat treatment with a coating raw material and then heat-treating the mixture can be further carried out. In this case, the mixing can be completed by solid-phase mixing or liquid-phase mixing, and the heat treatment can be carried out at an appropriate temperature according to the coating raw material. For example, the heat treatment of the coating process can be carried out in the temperature range of 200 °C to 700 °C, or 300 °C to 600 °C, but not limited thereto.

[0087] Positive electrode

[0088] The positive electrode of the present invention comprises the positive electrode active material powder of the present invention as described above. Specifically, the positive electrode includes 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 includes the positive electrode active material powder of the present invention. Since the positive electrode active material powder has been described above, its detailed description will be omitted, and only the remaining components will be described in detail below.

[0089] The positive electrode current collector may comprise a highly conductive metal and is not particularly limited as long as the positive electrode active material layer can be easily adhered thereto and is not reactive within the voltage range of the battery. The positive electrode current collector may be, for example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. Additionally, the positive electrode current collector generally may have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to improve the adhesion of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0090] If necessary, the positive electrode active material layer may optionally include a conductive material and a binder in addition to the positive electrode active material powder.

[0091] In this case, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material powder may be 80% by weight to 99% by weight, more specifically 85% by weight to 98.5% by weight, and when included within the above content range, excellent capacity characteristics can be exhibited.

[0092] The conductive material is used to impart conductivity to the electrode and can be any material without particular limitation as long as it has electron conductivity and does not cause chemical changes in the battery to be constructed. Specific examples thereof may include: graphite, such as natural graphite 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 fiber; powders or fibers of metals such as copper, nickel, aluminum, silver, etc.; conductive tubes, such as carbon nanotubes; 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 thereof can be used. Based on the total weight of the positive electrode active material layer, the content of the conductive material may be 0.1% by weight to 15% by weight.

[0093] Binders are used to improve the binding between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples thereof 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 in which hydrogen is replaced by Li, Na or Ca, 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 content of the binder may be from 0.1% by weight to 15% by weight.

[0094] In addition to using the above positive electrode active material powder, the positive electrode can be manufactured according to a conventional positive electrode manufacturing method. Specifically, the above positive electrode active material powder and, if necessary, a binder, a conductive material, and a dispersant are dissolved or dispersed in a solvent to prepare a positive electrode slurry composition. The slurry composition can be coated on a positive electrode current collector, and then dried and roll-pressed to manufacture the positive electrode.

[0095] The solvent can be any solvent commonly used in the art, for example, dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, etc., and any one or a mixture of two or more thereof can be used. The amount of the solvent can be sufficient to dissolve or disperse the positive electrode active material, the conductive material, the binder, and the dispersant (taking into account the coating thickness of the slurry and the manufacturing yield), and allow the viscosity of the slurry to be such that excellent thickness uniformity is exhibited during the subsequent coating for manufacturing the positive electrode.

[0096] Alternatively, the positive electrode can be manufactured by the following process: casting the positive electrode slurry composition on a separate support, peeling the film from the support, and then laminating the film on the positive electrode current collector.

[0097] Electrochemical device (lithium secondary battery)

[0098] Next, the electrochemical device of the present invention will be described. The electrochemical device of the present invention includes the positive electrode of the present invention described above. Specifically, the electrochemical device can be a battery, a capacitor, etc., and more specifically, a lithium secondary battery.

[0099] Specifically, the lithium secondary battery includes a positive electrode, a negative electrode disposed opposite to the positive electrode, and a separator and an electrolyte disposed between the positive electrode and the negative electrode. Since the positive electrode is the same as the above, its detailed description is omitted, and only the remaining components will be described in detail below.

[0100] In addition, the lithium secondary battery may optionally include a battery container that houses an electrode assembly formed of a positive electrode, a negative electrode, and a separator, and a sealing member that seals the battery container.

[0101] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector.

[0102] The negative electrode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery, and may be, for example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, or silver, or an aluminum-cadmium alloy, etc. Additionally, the negative electrode current collector generally may have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to improve the adhesion of the negative electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric, etc.

[0103] In addition to the negative electrode active material, the negative electrode active material layer may optionally include a binder and a conductive material.

[0104] As the negative electrode active material, a compound capable of reversibly inserting and extracting lithium can be used. Specific examples thereof may include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal materials capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides capable of doping and dedoping lithium such as SiO β (0 < β < 2), SnO2, vanadium oxides, and lithium vanadium oxides; or composites containing metal materials 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. Moreover, a thin film of metallic lithium can also be used as the negative electrode active material. Additionally, as the carbon material, all of low-crystalline carbon or high-crystalline carbon, etc. can be used. Representative examples of low-crystalline carbon may include soft carbon and hard carbon, and representative examples of high-crystalline carbon may include irregular, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase carbon microspheres, mesophase pitch, and high-temperature heat-treated carbon such as coke derived from petroleum or coal tar pitch.

[0105] Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material may be 80 wt% to 99 wt%.

[0106] The binder is a component that helps in the bonding between the conductive material, the active material, and the current collector, and the addition amount is generally 0.1 wt% to 10 wt% 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.

[0107] The conductive material is a component that further improves the conductivity of the negative electrode active material, and the addition amount can be 10 wt% or less, preferably 5 wt% or less based on the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery, and examples thereof can be: graphite, such as natural graphite or 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 fibers and metal fibers; carbon fluoride; 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; polyphenylene derivatives and other conductive materials.

[0108] The negative electrode active material and optionally the binder and the conductive material are dissolved or dispersed in a solvent to prepare a negative electrode slurry composition, which can be coated on the negative electrode current collector and dried to manufacture the negative electrode active material layer. Alternatively, the negative electrode active material layer can be manufactured by the following process: casting the negative electrode slurry composition on a separate support, peeling the film from the support, and then laminating the film on the negative electrode current collector.

[0109] Meanwhile, in a lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a movement path for lithium ions. Any separator can be used without particular limitation as long as it is generally used as a separator in a lithium secondary battery. In particular, a separator having excellent moisture retention ability for the electrolyte and low resistance to the movement of electrolyte ions is preferred. Specifically, a porous polymer film can be used, for example, a porous polymer film made of polyolefin polymers (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer), or a laminated structure having two or more layers thereof. In addition, a conventional porous non-woven fabric can also be used, for example, a non-woven fabric made of high melting point glass fibers or polyethylene terephthalate fibers. Furthermore, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material can also be used, and it can optionally be used in a single-layer or multi-layer structure.

[0110] In addition, the electrolyte used in the present invention may be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten-type inorganic electrolyte, etc. that can be used to prepare a lithium secondary battery, but is not limited thereto.

[0111] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0112] As the organic solvent, any organic solvent can be used without particular limitation as long as it can serve as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, the organic solvent may 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 (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC) or propylene carbonate (PC); alcohol solvents such as ethanol or isopropanol; nitriles such as R-CN (where R is a linear, branched or cyclic C2 to C20 hydrocarbon group and may include a double bond aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among them, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate, propylene carbonate, etc.) having a high ionic conductivity and a high dielectric constant and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) that can improve the charge / discharge performance of the battery is more preferred.

[0113] The lithium salt may be any compound without particular limitation as long as it can provide lithium ions used in the lithium secondary battery. Specifically, the anion of the lithium salt may 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 at least one selected from the group consisting of (CF3CF2SO2)2N - The lithium salt may be at least one selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The lithium salt is preferably used at a concentration of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, whereby excellent electrolyte performance can be exhibited and lithium ions can move effectively.

[0114] In order to improve the life characteristics of the battery, suppress the reduction of the battery capacity, and increase the discharge capacity of the battery, in addition to the above electrolyte components, the electrolyte may further contain one or more additives, for example, halogenated alkylene carbonate compounds (such as ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, based on the total weight of the electrolyte, the content of the additive may be 0.1 wt% to 5 wt%.

[0115] Example

[0116] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in various forms and is not limited to the embodiments described herein.

[0117] Example 1

[0118] 4 liters of distilled water was placed in a co-precipitation reactor with a capacity of 20 L, and then it was maintained at a temperature of 50 °C while continuously adding a transition metal solution with a concentration of 3.2 mol / L to the reactor at 300 mL / hr (where NiSO4, CoSO4, and MnSO4 were mixed so that the molar ratio of nickel: cobalt: manganese was 0.83:0.11:0.06), and continuously adding a 28 wt% ammonia water solution at 42 mL / hr. The stirring speed of the impeller was set at 400 rpm, and a 40 wt% sodium hydroxide solution was added to maintain the pH at 9.3. Then, a co-precipitation reaction was carried out for 10 hours to form precursor particles, which were separated and washed, and then dried in an oven at 130 °C to prepare a precursor (tap density: 1.8 g / cc).

[0119] The Ni 0.83 Co 0.11 Mn 0.06 (OH)2 precursor synthesized by coprecipitation reaction is mixed with LiOH so that the molar ratio of Li / Me (Ni + Co + Mn) is 1.05, and heat-treated in an oxygen atmosphere at 870 °C for 10 hours to prepare a positive electrode active material having a composition of LiNi 0.83 Co 0.11 Mn 0.06 O2.

[0120] Examples 2 to 4 and Comparative Examples 1 to 4

[0121] Prepare a positive electrode active material having the particle size characteristics shown in Table 1 below.

[0122] Experimental Example 1: Measurement of characteristics of positive electrode active material

[0123] 1) Particle characteristics on the cross-section of the positive electrode active material: For each positive electrode active material prepared in the above examples and comparative examples, by Ar ion milling, using an analytical device, dual-beam FIB (Helios 450F1 / FEI), in the SIM (scanning ion microscope) / ETD (Everyhart-Thornley SE detector) mode, under the conditions of an acceleration voltage of 30 kV, a current of 24 pA, a working distance of 13 mm, and a magnification of 12,000 to 15,000 times, an image of the particle cross-section at about 50% of the diameter is obtained. Thereafter, using an image analysis program, the cross-sectional area (AS) of the secondary particles, the long diameter (D 1 max ) and short diameter (D 1 min ) of the primary particles are averaged, the number (N p ) is analyzed, the aspect ratio (R AR ) of each primary particle and its average value are analyzed, and the K value is calculated by the following Equation 1 and listed in Table 1 below. For the reliability of the data, the above characteristics were analyzed for 50 particles, and their average values were used. Representatively, cross-sectional photographs of Example 1 and Comparative Examples 1 and 2 are shown in Figures 1 to 3 .

[0124] [Equation 1]

[0125] K = R AR x N P / A S

[0126] Where R AR is the average aspect ratio of the primary particles, N P is the number of primary particles, and A Sis the cross-sectional area of the secondary particles.

[0127] 2) Particle size characteristics of the positive electrode active material: 0.005 g of each positive electrode active material prepared in the above Examples and Comparative Examples was dispersed in H2O as a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device (PSD, Malvern, Mastersizer 3000), and irradiated with ultrasonic waves at an output of 60 W and a frequency of about 28 kHz to obtain a volume-based particle size distribution diagram of each positive electrode active material. Using this diagram, the D of the secondary particles was measured. 50 The results are shown in Table 1 below.

[0128] 3) Crystal strain: Measured by analyzing the XRD data obtained by X-ray diffraction analysis of the positive electrode active material powder by the Rietveld refinement method. In this case, a Bruker D8 Endeavor equipped with a LynxEye XE-T position-sensitive detector was used (light source: Cu-Kα, ). The sample was placed in the groove of a general powder holder, and a cover glass was used to make the surface of the sample uniform. The sample was filled so that its height was consistent with the edge of the holder, and then the above X-ray diffraction analysis was performed under the conditions of a step size of 0.02° and a total scanning time of about 20 minutes for the FDS 0.5°, 2θ = 15° to 90° region. For the measured data, considering the charge at each site (the metal at the transition metal site is +3, and Ni at the Li site is +2) and cation mixing, Rietveld refinement was performed. Specifically, when analyzing the crystal strain, the instrumental broadening was used with the FPA (fundamental parameter method) implemented in the Bruker TOPAS program, and all peaks in the measurement range were used for fitting. Among the peak types available in TOPAS, only the Lorentz contribution was used as the FP (first principle) to fit the peak shape.

[0129] 4) Fine powder generation rate (volume %): For the above Examples and Comparative Examples, a pressure of 6 tons was applied to the positive electrode active material using a roller press densitometer (Carver Pellet Press) and roller pressing was performed, and then the fine powder increase rate in the region below 1 μm was calculated using the value obtained from particle size analysis (PSD).

[0130] [Table 1]

[0131]

[0132] Referring to Table 1 above, it was confirmed that compared with Examples 1 to 4, Comparative Examples 1 to 4 did not satisfy the K value in the range of 12 to 40, and the number ratio of primary particles with an aspect ratio of 1.6 or more was also small.

[0133] <Manufacture of Lithium Secondary Battery>

[0134] The positive electrode active materials, carbon black conductive materials, and PVDF binders prepared in Examples 1 to 4 and Comparative Examples 1 to 4 were mixed at a weight ratio of 95:2:3 in N-methylpyrrolidone 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 roll-pressed to prepare a positive electrode.

[0135] Graphite as the negative electrode active material, super C as the conductive material, and SBR / CMC as the binder were mixed at a weight ratio of 95.6:1.0:3.4 to prepare a negative electrode slurry. The negative electrode slurry was coated on one surface of a copper current collector, dried at 130 °C, and roll-pressed to prepare a negative electrode.

[0136] A separator was placed between the positive electrode and the negative electrode to prepare an electrode assembly, which was placed inside a battery case. Thereafter, an electrolyte was injected into the case to prepare a lithium secondary battery. The electrolyte was prepared by the following process: LiPF6 was dissolved at a concentration of 1 M in a mixed organic solvent in which ethylene carbonate / dimethyl carbonate / diethyl carbonate were mixed at a volume ratio of 1:2:1, and 2 wt% of vinylene carbonate (VC) was added.

[0137] Experimental Example 2: Measurement of performance of positive electrode active material

[0138] 1) High temperature performance: The lithium secondary battery manufactured above was subjected to 200 charge and discharge cycles at a temperature of 45 °C under the condition of 0.33C / 0.33C, and then the capacity retention rate (%) of the single cell was measured as the charge / discharge efficiency. When evaluating the life under the above method and conditions, the voltage and current during discharge were used to calculate the resistance ((V0 - V1) / I, where V0 is the initial discharge voltage, V1 is the voltage after 10 seconds of discharge, and I is the applied current), and the resistance increase rate was calculated using the resistance after cycling compared to the initial resistance. The results are shown in Table 3 below.

[0139] 2) Difference in crack area (%) before and after deterioration: For the above positive electrode, the cross-section of the positive electrode before and after cycling was analyzed. A reference region was set at a depth of 20 μm and a planar direction of 200 μm from the surface of the active material layer, and the area was obtained by dividing the crack region and the particle region in this region. The crack region is the part where the particles are broken, and the particle region is the part where the particles are not broken. An image was obtained by photographing the cross-section of the electrode cut by ion milling using a field emission scanning electron microscope (FESEM, JEOL JSM-IT800SHL) under the conditions of an acceleration voltage of 5 kV, an emission current of 10 μA, a working distance of 10 mm, and a detector BED.

[0140] For the FESEM cross-sectional images, the crack area and the particle area were quantified by an image analysis program based on digital transformation. Additionally, to improve the accuracy, more than 50 reference areas were specified for the positive electrode cross-section to obtain the crack area and its average value for each area.

[0141] [Table 2]

[0142]

[0143] Referring to Table 3, when the shape of the primary particles is optimized as in Examples 1 to 4 of an embodiment of the present invention, it can be confirmed that the life characteristics are excellent because the electrode deterioration is low and the capacity retention rate at high temperatures is high, and the output characteristics are excellent because the resistance increase rate is low. However, as in Comparative Example 1, when the aspect ratio of the primary particles is small and the number of primary particles is not large compared to the area of the secondary particles as compared with the examples, it can be confirmed that the incidence of breakage or cracks in the active material particles is high, which can easily lead to electrode deterioration, and thus the performance is poor. Additionally, in the case of Comparative Example 2, although the aspect ratio is similar to that of the examples, both the major diameter and the minor diameter of the primary particles are larger than those of the examples, and the number is too small relative to the area of the secondary particles, so the K value range is not satisfied, which means that the size of the primary particles themselves is large. In such a shape, it can be confirmed that the output characteristics are poor because the resistance increase is large. Additionally, Comparative Example 3 has a shape opposite to that of Comparative Example 2, with a large aspect ratio, but the primary particles are very small, so the K value is not satisfied. In this case, there is a problem that cracks are generated in the active material particles even during electrode rolling. On the contrary, the degree of deterioration before and after cycling is small, but very poor results are shown in terms of life and output characteristics. It can be seen from this that the degree of particle breakage is large.

Claims

1. A positive electrode active material comprising a lithium nickel-based transition metal oxide in the form of secondary particles, wherein the secondary particles are aggregates of primary particles, and for a cross-section at 40% to 60% of the diameter of the secondary particles, the following conditions a) and b) are satisfied: a) The number ratio of primary particles having an aspect ratio of 1.6 or more in the above cross-section is 0.81 or more, and b) The K value calculated by the following Equation 1 is 12 to 40: [Equation 1] K = R AP × N P / A S where R AP is the average aspect ratio of the primary particles, N P is the number of primary particles, and A S is the dimensionless number of the cross-sectional area (μm 2 ) of the secondary particles.

2. The positive electrode active material according to claim 1, wherein The short diameter of the primary particles and D of the secondary particles 50 have a ratio of 0.025 or less.

3. The positive electrode active material according to claim 1, wherein, The ratio of the long diameter of the primary particle to D of the secondary particle 50 is from 0.035 to 0.

075.

4. The positive electrode active material according to claim 1, wherein The average aspect ratio of the primary particles in the secondary particles is 2.0 to 3.

5.

5. The positive electrode active material according to claim 1, wherein, The D of the secondary particles 50 is from 7 μm to 20 μm.

6. The positive electrode active material according to claim 1, wherein, The crystal strain of the secondary particles should be 670×10 -6 or less.

7. The positive electrode active material according to claim 6, wherein, The crystal strain of the secondary particles should be 645×10 -6 or less.

8. The positive electrode active material according to claim 1, wherein The lithium nickel-based transition metal oxide is represented by the following Chemical Formula 1: [Chemical Formula 1] Li 1+x Ni a Co b M 1 c M 2 d O 2-e X e Among them, M 1 includes one or more selected from Mn and Al; M 2 includes one or more selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, and Nb; X includes one or more selected from the group consisting of N, P, S, F, and Cl; 0 ≤ x ≤ 0.5, 0.6 ≤ a < 1, 0 < b ≤ 0.4, 0 < c ≤ 0.4, 0 ≤ d ≤ 0.05, and 0 ≤ e ≤ 0.

05.

9. The positive electrode active material according to claim 8, wherein, In Chemical Formula 1, 0.75 ≤ a ≤ 0.

99.

10. A positive electrode comprising the positive electrode active material according to claim 1.

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

Images