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

Abstract

The present invention relates to a positive electrode active material in which the particle size of primary particles is uniform, so that the amount of fine powder is small, and the particles are rarely crushed in a fine crushing step and a rolling step for manufacturing a lithium secondary battery. The present invention relates to a positive electrode active material, a method for preparing the same, and a positive electrode and a lithium secondary battery comprising the same, in which the positive electrode active material comprises a lithium nickel cobalt manganese-based oxide having a nickel content of 50 mol% or more in all transition metals and being in the form of a single particle consisting of 10 or less primary particles, and a polydispersity index (PDI) value according to Equation 1 described in the specification is 1.0 to 1.8.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2023-0151125, filed on November 3, 2023, with the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This invention relates to a positive electrode active material, a method for preparing the same, and a positive electrode and a lithium secondary battery containing the same positive electrode active material. More specifically, it relates to a positive electrode active material having a uniform particle size, a method for preparing the same, and a positive electrode and a lithium secondary battery containing the same positive electrode active material. Background Technology

[0004] In recent years, with the technological development and increasing demand for mobile devices and electric vehicles, the demand for secondary batteries as energy sources has grown rapidly. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life and low self-discharge rate, have been commercialized and are widely used.

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

[0006] Meanwhile, lithium composite transition metal oxides suffer from poor lifespan at high temperatures. Furthermore, when using lithium composite transition metal oxides as positive electrode active materials in the manufacture of lithium-ion secondary batteries, the particles of the positive electrode active material are prone to cracking and breakage during the coating and rolling process onto the positive electrode current collector. Therefore, during the charging and discharging process of lithium-ion secondary batteries, gas generation and expansion occur due to side reactions between the positive electrode active material and the electrolyte solution, leading to a deterioration in lifespan.

[0007] Therefore, there is a need to develop a positive electrode active material that can improve the stability and lifespan properties of batteries. Summary of the Invention

[0008] Technical problem

[0009] To solve the above problems, an object of the present invention is to provide a positive electrode active material containing a lithium composite transition metal oxide, which can improve the stability and life properties of a battery.

[0010] In addition, another object of the present invention is to provide a preparation method for preparing the positive electrode active material.

[0011] In addition, another object of the present invention is to provide a lithium secondary battery whose performance is improved by including the above positive electrode active material.

[0012] Technical solution

[0013] To achieve the above object, the present invention provides a positive electrode active material, a preparation method for the positive electrode active material, a positive electrode, and a lithium secondary battery.

[0014] (1) The present invention provides a positive electrode active material containing a lithium nickel cobalt manganese-based oxide, wherein the nickel content in all transition metals of the lithium nickel cobalt manganese-based oxide is 50 mol% or more, and it may be in the form of a single particle composed of 10 or less primary particles. Among them, the polydispersity index (PDI) value of the positive electrode active material according to Equation 1 below is 1 to 1.8: [Equation 1] PDI = volume average particle size (μm) of primary particles / number average particle size (μm) of primary particles (2) In the above (1), the present invention provides a positive electrode active material, wherein the lithium nickel cobalt manganese-based oxide has the composition shown in Formula 1 below.

[0015] [Formula 1]

[0016] Li 1+x Ni a1 Co b1 Mn c1 M 1 d1 O2

[0017] Among them, in Formula 1 above, M 1 is one or more selected from Al, W, Co, B, Zr, Y, Ce, Hf, La, Ba, F, P, S, Nb, Ta, Sc, Cr, V, Cu, Sr, Ti, Mg, Mo, Sn, Fe, Zn, and Si, and -0.1 ≤ x ≤ 0.1, 0.5 ≤ a1 < 1, 0 < b1 < 0.5, 0 < c1 < 0.5, 0 ≤ d1 ≤ 0.2, and a1 + b1 + c1 + d1 = 1.

[0018] (3) In (1) or (2) above, the present invention provides a positive electrode active material, wherein the volume average particle size of the primary particles is 0.5 μm to 3.5 μm.

[0019] (4) In any of (1) to (3) above, the present invention provides a positive electrode active material, wherein the number of primary particles has an average particle size of 0.5 μm to 2.0 μm.

[0020] (5) In any one of (1) to (4) above, the present invention provides a positive electrode active material, wherein the positive electrode active material has a D measured by using a particle size analyzer (PSA). 50 The thickness ranges from 3 μm to 5 μm.

[0021] (6) In any of (1) to (5) above, the present invention provides a positive electrode active material, wherein 3 g of the positive electrode active material is placed in a mold with an inner diameter of 13 mm, and then pressed at 9 tons for 1 minute, and the proportion of the number of particles with a particle size of less than 1 μm as measured by PSA (particle size analyzer) to the total number of particles is less than 2.5%.

[0022] (7) The present invention provides a method for preparing a positive electrode active material, wherein the method comprises: (A) mixing a nickel cobalt manganese-based hydroxide with a nickel content of more than 50 mol% in all transition metals with a lithium-containing raw material to prepare a mixture; and (B) sintering the mixture once at 600°C to 900°C in an air atmosphere, continuously heating the mixture to 920°C to 1000°C, and then sintering the mixture a second time at 920°C to 1000°C to prepare a sintered product.

[0023] (8) In (7) above, the present invention provides a method for preparing a positive electrode active material, wherein the nickel cobalt manganese-based hydroxide has the composition shown in Formula 2 below.

[0024] [Equation 2]

[0025] Ni a2 Co b2 Mn c2 M 2 2(OH)2

[0026] In Equation 2 above, M 2is one or more selected from Al, W, Co, B, Zr, Y, Ce, Hf, La, Ba, F, P, S, Nb, Ta, Sc, Cr, V, Cu, Sr, Ti, Mg, Mo, Sn, Fe, Zn, and Si, and 0.5 ≤ a2 < 1, 0 < b2 < 0.5, 0 < c2 < 0.5, 0 ≤ d2 ≤ 0.2, and a2 + b2 + c2 + d2 = 1.

[0027] (9) In the above (7) or (8), the present invention provides a method for preparing a positive electrode active material, wherein the secondary sintering is carried out for 1 hour to 12 hours.

[0028] (10) In any one of the above (7) to (9), the present invention provides a method for preparing a positive electrode active material, wherein the secondary sintering is carried out for 4 hours to 14 hours.

[0029] (11) In any one of the above (7) to (10), the present invention provides a method for preparing a positive electrode active material, wherein the method further includes (C) finely pulverizing the sintered product.

[0030] (12) In the above (11), the present invention provides a method for preparing a positive electrode active material, wherein the fine pulverization is carried out by vortex flow pulverization.

[0031] (13) In the above (12), the present invention provides a method for preparing a positive electrode active material, wherein the vortex flow pulverization is carried out under a pressure of 1 bar to 5 bar.

[0032] (14) The present invention provides a positive electrode comprising the positive electrode active material according to any one of the above (1) to (6).

[0033] (15) The present invention provides a lithium secondary battery comprising the positive electrode according to the above (14), a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

[0034] Advantageous Effects

[0035] The positive electrode active material of the present invention contains a lithium composite transition metal oxide and has a polydispersity index value within a specific range that satisfies Equation 1 described in this specification, so it has a uniform particle size, thereby reducing particle breakage and improving the life characteristics of the lithium secondary battery.

[0036] Furthermore, the method for preparing the positive electrode active material according to the present invention can effectively prepare the above-mentioned positive electrode active material. Specifically, in the method for preparing the positive electrode active material of the present invention, a mixture comprising a positive electrode active material precursor and a lithium-containing raw material is sintered once at 600°C to 900°C, and the mixture is continuously heated to 920°C to 1000°C, and then sintered a second time at 920°C to 1000°C, thereby improving the particle size uniformity of the primary particles.

[0037] The positive electrode and lithium secondary battery of the present invention can have excellent high-temperature stability and lifespan properties. Attached Figure Description

[0038] Figure 1 This is a graph showing the sintering curves of an embodiment of the present invention.

[0039] Figure 2 This is a SEM image of the positive electrode active material of Example 1.

[0040] Figure 3 This is a SEM image of the positive electrode active material of Example 2.

[0041] Figure 4 This is a SEM image of the positive electrode active material of Comparative Example 1.

[0042] Figure 5 This is a SEM image of the positive electrode active material of Comparative Example 2. Detailed Implementation

[0043] The present invention will now be described in more detail for the purpose of understanding.

[0044] It will be understood that the terms or words used in this specification and claims should not be construed as having the meanings defined in commonly used dictionaries, but should be interpreted as having meanings and concepts consistent with the technical concept of the invention, based on the principle that the inventors can appropriately define the concepts of the terms to best interpret the invention.

[0045] In this specification, it should be understood that the terms “comprising,” “including,” or “having” are intended to specify the presence of the said features, quantities, steps, elements, or combinations thereof, but do not exclude the presence or addition of one or more other features, quantities, steps, elements, or combinations thereof.

[0046] In this specification, the term "on" includes not only the case where one component is directly formed on the upper surface of another component, but also the case where a third component is disposed between the two.

[0047] In this specification, "single-particle form" is the opposite of the concept of spherical secondary particles formed by the agglomeration of dozens to hundreds of primary particles prepared by conventional methods, and refers to a form composed of 10 or fewer primary particles. Specifically, in this invention, single-particle form can refer to a single particle composed of one primary particle, or it can refer to a secondary particle form formed by the agglomeration of several primary particles.

[0048] "Primary particles" refer to the smallest unit of particles identified when observing positive electrode active materials using a scanning electron microscope, while "secondary particles" refer to secondary structures formed by the aggregation of multiple primary particles.

[0049] In this specification, the "volume average particle size of primary particles" is based on the value of Equation 2 below, and this value is obtained by calculating the area of ​​each primary particle using the number of pixels corresponding to each of the n primary particles present in the SEM image, and using the radius (r) of a circle with the same area as each primary particle. i This allows for the calculation of the particle size (D) of each primary particle present in the SEM image. i =2r i ) and volume (V i =4 / 3×πr i 3 The volume calculated for each particle is multiplied by its diameter to obtain the value (V). i D i The sum of the totals divided by the calculated volume (V) i The sum of ).

[0050] [Equation 2]

[0051] Volume average particle size of primary particles

[0052] In Equation 2 above, n is the number of primary particles present in the SEM image, and V i Let V be the volume of one of the n primary particles. i D i The volume (V) of one of n primary particles. i ) and particle size (D i The value obtained by multiplying them.

[0053] In this specification, the "average particle size of the number of primary particles" is obtained as follows: the area of ​​each primary particle is calculated by taking the number of pixels corresponding to each of the n primary particles present in the SEM image, and the radius (r) of a circle with the same area as each primary particle is used. i This allows for the calculation of the particle size (D) of each primary particle present in the SEM image. i =2r iThe total calculated particle size is then divided by the number of particles in a single operation.

[0054] [Equation 3]

[0055] Number of particles per unit area and average particle size

[0056] In Equation 3 above, n is the number of primary particles present in the SEM image, and D... i The particle size (D) of one of n primary particles. i ).

[0057] In this specification, the term "D measured using a particle size analyzer (PSA)" is used. 50 "Refers to the particle size at the 50% point of the volumetric cumulative distribution based on particle size." (D) 50 The particle size distribution can be measured by dispersing the powder to be tested in a dispersion medium and then introducing the mixture into a commercially available laser diffraction particle size measurement device (such as Microtrac's S3500). The particle size distribution is calculated by measuring the difference in the diffraction pattern as the particle passes through the laser beam, and then the particle size at the 50% point of the volumetric cumulative distribution of the particle size in the measurement device is calculated.

[0058] Positive electrode active material

[0059] This invention provides a positive electrode active material comprising a lithium nickel cobalt manganese-based oxide (lithium composite transition metal oxide), wherein the nickel content of the lithium nickel cobalt manganese-based oxide in all transition metals is 50 mol% or more, and it can be in the form of a single particle composed of 10 or fewer primary particles, wherein the polydispersity index (PDI) value of the positive electrode active material according to Equation 1 below is 1 to 1.8. The lithium nickel cobalt manganese-based oxide can have a layered structure.

[0060] [Equation 1]

[0061] PDI = Volume average particle size of primary particles (μm) / Number average particle size of primary particles (μm)

[0062] The inventors discovered that if the positive electrode active material contains the above-mentioned lithium nickel cobalt manganese-based oxide in the form of single particles and has a polydispersity index (PDI) value that satisfies a specific range according to Equation 1 above, the primary particles have a uniform particle size, resulting in fewer fine particles. Furthermore, particle breakage is reduced in the fine grinding and rolling processes used to manufacture lithium secondary batteries, thereby improving the lifespan properties of lithium secondary batteries. Based on this, the present invention was completed.

[0063] According to the present invention, the polydispersity index (PDI) value of the positive electrode active material according to Equation 1 is 1.0 to 1.8. Theoretically, if all primary particles constituting the lithium nickel cobalt manganese-based oxide have the same particle size, the polydispersity index (PDI) value is 1.0, and the more uniform the particle size, the closer this value is to 1.0. Specifically, the polydispersity index value can be 1.0 or higher, 1.1 or higher, 1.2 or higher, 1.3 or higher, 1.4 or higher, 1.5 or higher, or 1.6 or higher, and can be 1.7 or lower or 1.8 or lower. If the polydispersity index value meets the above range, the uniformity of the primary particles can be improved and particle breakage can be reduced. The polydispersity index value is determined by a combination of the preparation method and composition of the positive electrode active material, the size and particle size distribution of the primary particles, etc., and is not determined by any single factor.

[0064] Meanwhile, if the polydispersity index of the positive electrode active material is greater than 1.8, the primary particle size will be uneven, the number of fine particles will increase, and particle breakage will increase in the fine grinding and rolling processes used to manufacture lithium secondary batteries, thus leading to the problem of deterioration in the life performance of lithium secondary batteries.

[0065] According to the present invention, the volume average particle size of the primary particles can be from 0.5 μm to 3.5 μm. Specifically, the volume average particle size of the primary particles can be 0.5 μm or more, 0.6 μm or more, 0.7 μm or more, 0.8 μm or more, 0.9 μm or more, 1.0 μm or more, 1.1 μm or more, 1.2 μm or more, 1.3 μm or more, 1.4 μm or more, 1.5 μm or more, 1.6 μm or more, 1.7 μm or more, 1.8 μm or more, 1.9 μm or more, 2.0 μm or more, 2.1 μm or more, 2.2 μm or more, or 2.3 μm or more, and can be less than 2.6 μm, less than 2.7 μm, less than 2.8 μm, less than 2.9 μm, or less than 3.0 μm. If the volume average particle size of the primary particles is within the above range, the positive electrode active material can be in the form of single particles, and because it is conducive to lithium ion migration, it can improve the battery's lifespan and capacity properties, thereby optimizing electrochemical performance.

[0066] According to the present invention, the number average particle diameter of the primary particles can be 0.5 μm to 2.0 μm. The number average particle diameter of the primary particles can specifically be 0.5 μm or more, 0.6 μm or more, 0.7 μm or more, 0.8 μm or more, 0.9 μm or more, 1.0 μm or more, 1.1 μm or more, 1.2 μm or more, or 1.3 μm or more, and can be 1.6 μm or less, 1.7 μm or less, 1.8 μm or less, 1.9 μm or less, or 2.0 μm or less. If the number average particle diameter of the primary particles is within the above range, the positive electrode active material can be in the form of single particles, and the life characteristics and capacity characteristics of the battery can be improved, thereby optimizing the electrochemical performance.

[0067] According to the present invention, the nickel content of the lithium nickel cobalt manganese-based oxide among all transition metals can be 50 mol% or more, 51 mol% or more, 52 mol% or more, 53 mol% or more, 54 mol% or more, 55 mol% or more, 56 mol% or more, 57 mol% or more, 58 mol% or more, 59 mol% or more, or 60 mol% or more. That is, the lithium nickel cobalt manganese-based oxide can be a lithium composite transition metal oxide having a high nickel content. In this case, the energy density of the lithium secondary battery can be improved.

[0068] According to the present invention, the lithium nickel cobalt manganese-based oxide can have a composition represented by the following Formula 1.

[0069] [Formula 1]

[0070] Li 1+x Ni a1 Co b1 Mn c1 M 1 d1 O2

[0071] In the above Formula 1, M 1 is one or more selected from Al, W, Co, B, Zr, Y, Ce, Hf, La, Ba, F, P, S, Nb, Ta, Sc, Cr, V, Cu, Sr, Ti, Mg, Mo, Sn, Fe, Zn, and Si, and -0.1 ≤ x ≤ 0.1, 0.5 ≤ a1 < 1, 0 < b1 < 0.5, 0 < c1 < 0.5, 0 ≤ d1 ≤ 0.2, and a1 + b1 + c1 + d1 = 1.

[0072] The aforementioned x can be greater than -0.1, greater than -0.09, greater than -0.08, greater than -0.07, greater than -0.06, greater than -0.05, greater than -0.04, greater than -0.03, greater than -0.02, greater than -0.01, greater than 0, greater than 0, greater than 0.01, greater than 0, greater than 0, greater than 0.02, greater than 0.03, greater than 0.04, or greater than 0.5, and can be less than 0.07, less than 0.08, less than 0.09, or less than 0.1. When x meets the above ranges, high capacity properties and high energy density per unit volume can be achieved.

[0073] According to the present invention, in Formula 1 above, a1 represents the molar ratio of nickel in the metal elements of the lithium nickel cobalt manganese-based oxide, and can be 0.50 or more, 0.51 or more, 0.52 or more, 0.53 or more, 0.54 or more, 0.55 or more, 0.56 or more, 0.57 or more, 0.58 or more, 0.59 or more, or 0.60 or more, and can be 0.70 or less, 0.75 or less, 0.80 or less, 0.85 or less, 0.90 or less, 0.95 or less, or less than 1.0. If a1 satisfies the above range, high energy properties can be achieved, and in particular, if a1 is 0.6 to 0.7, high energy density and high stability can be achieved during high-voltage driving.

[0074] According to the present invention, in Formula 1 above, b1 represents the atomic molar ratio of cobalt in the metal element of the lithium nickel cobalt manganese-based oxide, and can be greater than 0.0 or greater than 0.01, and can be less than 0.15, less than 0.20, less than 0.30, less than 0.40, or less than 0.50. If b1 satisfies the above range, the stability during the charge and discharge process can be improved, and the rate performance can be improved.

[0075] According to the present invention, in Formula 1 above, c1 represents the molar ratio of manganese in the metal element of the lithium nickel cobalt manganese-based oxide, and can be greater than 0.0 or more than 0.01, more than 0.05, more than 0.10, more than 0.15, more than 0.20, more than 0.25, or more than 0.30, and can be less than 0.35, less than 0.40, less than 0.45, or less than 0.50. If c1 meets the above range, high-temperature stability can be improved, and side reactions with electrolyte solution can be relatively reduced.

[0076] According to the present invention, in Formula 1 above, d1 represents the metal element M in the lithium nickel cobalt manganese-based oxide. 1 The molar ratio of the elements can be greater than or equal to 0.0, and can be less than or equal to 0.05, 0.1, or 0.2. When d1 meets the above range, it can improve the crystal structure stability of the positive electrode active material and improve the particle morphology.

[0077] According to the present invention, M is selected from one or more of Al, W, Co, B, Zr, Y, Ce, Hf, La, Ba, F, P, S, Nb, Ta, Sc, Cr, V, Cu, Sr, Ti, Mg, Mo, Sn, Fe, Zn and Si. 1 These are dopants that can improve the crystallinity and single-particle formation of cathode active materials. They are not mandatory, but if M is included... 1 This can improve the battery's capacity and lifespan properties.

[0078] According to the present invention, the D of the positive electrode active material is measured by a particle size analyzer (PSA). 50 The diameter can range from 3 μm to 5 μm. The D-type of the positive electrode active material... 50 Specifically, the particle size can be 3.00 μm or larger, 3.10 μm or larger, 3.20 μm or larger, 3.30 μm or larger, 3.40 μm or larger, or 3.50 μm or larger, and can be below 4.50 μm, below 4.60 μm, below 4.70 μm, below 4.80 μm, below 4.90 μm or below 5.00 μm. If the D of the positive electrode active material is measured by a particle size analyzer (PSA)... 50 Within the aforementioned range, the lifetime and capacity properties of batteries containing this positive electrode active material can be improved, thereby optimizing electrochemical performance. For reference, if D 50 If the diameter is less than 3 μm, battery life may be reduced, and if D 50 If the thickness is greater than 5 μm, the battery capacity may decrease.

[0079] According to the present invention, 3 g of positive electrode active material is placed in a mold with an inner diameter of 13 mm, and then pressed at 9 tons for 1 minute. The ratio of the number of particles with a diameter less than 1 μm to the total number of particles, as measured by a particle size analyzer (PSA), can be less than 2.5%, less than 2.0%, less than 1.5%, less than 1.4%, less than 1.3%, or less than 1.2%. In this case, the breakage of positive electrode active material particles can be reduced during the rolling process used in the manufacture of lithium secondary batteries, thereby improving the lifespan of the lithium secondary batteries.

[0080] Preparation method of positive electrode active material

[0081] This invention provides a method for preparing the above-mentioned positive electrode active material. Specifically, the positive electrode active material of this invention is prepared by the following method.

[0082] The method for preparing the positive electrode active material of the present invention includes: (A) mixing a nickel-cobalt-manganese-based hydroxide with a nickel content of more than 50 mol% in all transition metals with a lithium-containing raw material to prepare a mixture; and (B) sintering the mixture once at 600°C to 900°C in an air atmosphere, continuously heating the mixture to 920°C to 1000°C, and then sintering the mixture a second time at 920°C to 1000°C to prepare a sintered product.

[0083] The inventors discovered that by sintering the mixture once at 600°C to 900°C, continuously heating it to 920°C to 1000°C, and then sintering it a second time at 920°C to 1000°C, lithium nickel cobalt manganese-based oxide in the form of single particles with uniform primary particle size can be prepared, thereby reducing the breakage of positive electrode active material particles in the rolling process used to manufacture lithium secondary batteries. Based on this, the present invention was completed.

[0084] For example, the positive electrode active material of the present invention can be prepared by the following methods: Figure 1 As shown, the mixture is heated from room temperature to 850°C, and sintered at 850°C for a predetermined time. The mixture is then continuously heated to 950°C, and sintered at 950°C for a predetermined time. Figure 1 This is a graph showing the sintering curve of one embodiment of the present invention.

[0085] Step (A)

[0086] Step (A) above is a step of preparing a mixture by mixing a nickel-cobalt-manganese-based hydroxide (hereinafter referred to as a composite transition metal hydroxide or positive electrode active material precursor) with a nickel content of more than 50 mol% in all transition metals with a lithium-containing raw material.

[0087] According to the present invention, lithium nickel cobalt manganese-based hydroxides may have the composition shown in Formula 2.

[0088] [Equation 2]

[0089] Ni a2 Co b2 Mn c2 M 2 d2 (OH)2

[0090] In Equation 2 above, M 2is one or more selected from Al, W, Co, B, Zr, Y, Ce, Hf, La, Ba, F, P, S, Nb, Ta, Sc, Cr, V, Cu, Sr, Ti, Mg, Mo, Sn, Fe, Zn, and Si, and 0.5 ≤ a2 < 1, 0 < b2 < 0.5, 0 < c2 < 0.5, 0 ≤ d2 ≤ 0.2, and a2 + b2 + c2 + d2 = 1.

[0091] According to the present invention, in Formula 2 above, a2 represents the molar ratio of nickel in the metal elements of the nickel-cobalt-manganese-based hydroxide, and can be 0.50 or more, 0.51 or more, 0.52 or more, 0.53 or more, 0.54 or more, 0.55 or more, 0.56 or more, 0.57 or more, 0.58 or more, 0.59 or more, or 0.60 or more, and can be 0.70 or less, 0.75 or less, 0.80 or less, 0.85 or less, 0.90 or less, 0.95 or less, or less than 1.0. If a2 satisfies the above range, the battery including the positive electrode active material to be prepared can achieve high-capacity properties, and particularly, if a2 is 0.6 to 0.7, the battery including the positive electrode active material to be prepared can exhibit high energy density during high-voltage driving, thereby achieving high-capacity properties.

[0092] According to the present invention, in Formula 2 above, b2 represents the atomic molar ratio of cobalt in the metal elements of the nickel-cobalt-manganese-based hydroxide, and can be greater than 0.0 or 0.01 or more, and can be 0.15 or less, 0.20 or less, 0.30 or less, 0.40 or less, or less than 0.50. If b2 satisfies the above range, the stability of the battery including the positive electrode active material to be prepared during charge and discharge can be improved, and the rate performance can be improved.

[0093] According to the present invention, in Formula 2 above, c2 represents the molar ratio of manganese in the metal elements of the nickel-cobalt-manganese-based hydroxide, and can be greater than 0.0 or 0.01 or more, 0.05 or more, 0.10 or more, 0.15 or more, 0.20 or more, 0.25 or more, or 0.30 or more, and can be 0.35 or less, 0.40 or less, 0.45 or less, or less than 0.50. If c2 satisfies the above range, the battery including the positive electrode active material to be prepared can achieve high-capacity properties. In addition, the high-temperature stability of the battery can be improved, and the side reaction with the electrolyte solution can be relatively reduced.

[0094] According to the present invention, in Formula 2 above, d2 represents the molar ratio of element M in the metal elements of the nickel-cobalt-manganese-based hydroxide 1 and can be 0.0 or more, and can be 0.05 or less, 0.1 or less, or 0.2 or less. If d2 satisfies the above range, the crystal structure stability of the positive electrode active material to be prepared can be improved, and the particle morphology can be improved.

[0095] According to the present invention, the lithium-containing raw materials can be lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, hydroxyoxides, etc., and there are no particular limitations, as long as they are soluble in water. Specifically, the lithium-containing raw materials can be Li₂CO₃, LiNO₃, LiNO₂, LiOH, LiOH·H₂O, LiH, LiF, LiCl, LiBr, LiI, CH₃COOLi, Li₂O, lithium acetate, lithium dicarboxylate, lithium citrate, lithium fatty acid, alkyl lithium, lithium halides, etc., and any one or a mixture of two or more of them can be used.

[0096] According to the present invention, the mixing ratio of the composite transition metal hydroxide and the lithium-containing raw material can be such that the ratio (M:Li) of the total number of moles of transition metals (M) contained in the composite transition metal hydroxide to the number of moles of lithium (Li) contained in the lithium-containing raw material is 1:1.0 to 1.1, 1:1.01 to 1.09, 1:1.02 to 1.08, 1:1.03 to 1.07, 1:1.04 to 1.07 or 1:1.05 to 1.07.

[0097] Simultaneously, during the mixing process in step (A), raw materials containing doped elements can be further mixed. These doped raw materials can act as fluxes during sintering, thus further improving the lifespan and resistivity properties of the battery containing the positive electrode active material.

[0098] Step (B)

[0099] Step (B) above involves sintering the mixture once at 600°C to 900°C in an air atmosphere, continuously heating the mixture to 920°C to 1000°C, and then sintering the mixture a second time at 920°C to 1000°C to prepare the sintered product.

[0100] According to the present invention, when the mixture is sintered once at 600°C to 900°C, the lithium-containing raw material dissolves and is distributed sufficiently and uniformly on the surface of the positive electrode active material precursor. As a result, lithium reacts effectively with the positive electrode active material precursor, and thus an active material with a uniform primary particle morphology can be finally obtained after secondary sintering. The primary sintering temperature can be specifically above 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, 660℃, 670℃, 680℃, 690℃, 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, or 830℃, and can also be below 870℃, 880℃, 890℃, or 900℃. If the primary sintering temperature is within the above range, the uniformity of the primary particles can be improved. Meanwhile, if the primary sintering temperature is below 600℃, the reaction between lithium and the cathode active material precursor cannot proceed fully. Therefore, during the secondary sintering process, a secondary particle form of cathode active material, consisting of more than 10 primary particles agglomerated together, will be formed, resulting in a deterioration in lifetime properties. Furthermore, if the primary sintering temperature is above 900℃, the primary particles grow rapidly, leading to uneven particle growth during the secondary sintering process and a reduction in capacity.

[0101] According to the present invention, a single sintering can be carried out in an oxygen atmosphere or an air atmosphere.

[0102] According to the present invention, a single sintering process can be carried out for 2 to 12 hours. Under these conditions, the reaction between nickel-cobalt-manganese-based hydroxide and lithium can proceed sufficiently, so that lithium can be uniformly distributed even inside the positive electrode active material, and uniform particle growth can be achieved overall.

[0103] After the first sintering, if the temperature is immediately and continuously raised to 920°C to 1000°C, and a second sintering is performed at 920°C to 1000°C, lithium is embedded in the cathode active material precursor, forming a layered structure. The interfaces of the primary particles bond together, achieving primary particle growth and yielding a sintered product. In this case, the sintered product is a lithium nickel cobalt manganese-based oxide in single-particle form, consisting of fewer than 10 primary particles, with a nickel content of 50 mol% or more in all transition metals. If the second sintering temperature is within the above range, the primary particles grow to a sufficient size, improving structural stability and thus enhancing thermal stability and lifespan. However, if the second sintering temperature is below 920°C, the primary particle size is small, resulting in a non-uniform cathode active material in the form of secondary particles rather than single particles, leading to reduced lifespan. Furthermore, if the second sintering temperature is above 1000°C, the primary particle size is too large, potentially degrading the battery's capacity and performance.

[0104] Secondary sintering can be carried out in a lithium transition metal oxygen atmosphere or an air atmosphere.

[0105] According to the present invention, the secondary sintering can be carried out for 4 to 14 hours. Under these conditions, primary particles with high crystallinity and suitable size can be obtained, and excellent production efficiency can be achieved.

[0106] The present invention divides the sintering process into primary sintering and secondary sintering, wherein the primary sintering temperature is lower than the secondary sintering temperature. This can improve the particle uniformity of the positive electrode active material and ultimately improve the lifespan of the battery containing the positive electrode active material.

[0107] In terms of breaking down large particles that agglomerate together due to weak forces during sintering to form single particles, the method for preparing the positive electrode active material of the present invention may further include (C) finely pulverizing the sintered product.

[0108] According to the present invention, fine grinding can be carried out by vortex flow grinding. In this case, the particles agglomerated during the sintering process can be broken up by the collision of particles in the positive electrode active material, which can improve the uniformity of loading the positive electrode active material during the manufacturing of the electrode.

[0109] According to the present invention, vortex milling can be carried out at a pressure of 1 bar to 5 bar. Under this condition, the amount of fine particles that may be generated due to particle collision during fine milling can be reduced.

[0110] positive electrode

[0111] The present invention provides a positive electrode comprising the above-mentioned positive electrode active material.

[0112] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer may include the aforementioned positive electrode active material.

[0113] The positive electrode current collector can contain a highly conductive metal, and there are no particular limitations, as long as it does not react within the battery's voltage range and the positive electrode active material layer can easily adhere to it. Examples of positive electrode current collectors include stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc. Furthermore, the thickness of the positive electrode current collector can typically range from 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector 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.

[0114] If necessary, in addition to the positive electrode active material, the positive electrode active material layer may optionally include a conductive material and a binder. In this case, the content of the positive electrode active material relative to the total weight of the positive electrode active material layer can be from 80% to 99% by weight, more specifically from 85% to 98.5% by weight, and excellent capacity performance can be exhibited within the above range.

[0115] Conductive materials are used to impart conductivity to the electrodes, and any conductive material can be used without particular restrictions, as long as it is electronically conductive and does not cause chemical changes in the battery to be constructed. Specific examples may include graphite, such as natural or artificial graphite; carbonaceous 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 metal fibers, such as copper, nickel, aluminum, and silver; 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 of these may be used. The content of the conductive material relative to the total weight of the positive electrode active material layer can be from 0.1% by weight to 15% by weight.

[0116] Adhesives are used to improve the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, polymers whose hydrogen atoms are substituted with Li, Na, or Ca, or various copolymers thereof, and any one or a mixture of two or more of them may be used. The adhesive content may be from 0.1% by weight to 15% by weight relative to the total weight of the positive electrode active material layer.

[0117] The positive electrode can be manufactured according to conventional positive electrode manufacturing methods, the difference being the use of the aforementioned positive electrode active material. Specifically, the positive electrode can be manufactured by dissolving or dispersing the aforementioned positive electrode active material, along with optional binders, conductive materials, and dispersants in a solvent to prepare a composition for forming a positive electrode active material layer, coating the composition onto a positive electrode current collector, and then drying and rolling it; or it can be manufactured by casting the composition for forming a positive electrode active material layer onto a separate support, then peeling the film off the support, and stacking the film layer onto the positive electrode current collector.

[0118] The solvent can be one commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, water, etc., and any one or a mixture of two or more of them can be used. The amount of solvent used is sufficient to achieve the following effects: considering the coating thickness and manufacturing yield of the slurry, it can dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, and subsequently, it gives the slurry a viscosity that exhibits excellent thickness uniformity when coated to manufacture the positive electrode.

[0119] Lithium secondary batteries

[0120] The present invention provides a lithium secondary battery comprising the above-mentioned positive electrode, negative electrode, separator disposed between the positive electrode and the negative electrode, and electrolyte.

[0121] The lithium secondary battery may also optionally include a battery case for housing an electrode assembly consisting of a positive electrode, a negative electrode, and a separator, as well as a sealing component for sealing the battery case.

[0122] The negative electrode may include a negative electrode current collector and a layer of negative electrode active material located on the negative electrode current collector.

[0123] There are no particular limitations on the negative electrode current collector, as long as it has high conductivity and will not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. Furthermore, the thickness of the negative electrode current collector can typically range from 3 μm to 500 μm, and similar to the positive electrode current collector, fine irregularities can be formed on its surface 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.

[0124] If necessary, in addition to the negative electrode active material, the negative electrode active material layer may optionally include an adhesive and a conductive material.

[0125] As negative electrode active materials, compounds capable of reversibly inserting and deintercalating lithium ions can be used. Specific examples can include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metallic compounds that can form alloys 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 dedoped with lithium, such as SiO₂. β (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing metal compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of them can be used. Furthermore, lithium metal films can be used as anode active materials. In addition, low-crystallinity carbon, high-crystallinity carbon, etc., can all be used as carbon materials. Representative examples of low-crystallinity carbon can include soft carbon and hard carbon, and representative examples of high-crystallinity carbon can 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 calcined carbon such as petroleum or coal tar pitch-derived coke. Based on the total weight of the anode active material layer, the content of the anode active material can be from 80% to 99% by weight.

[0126] The binder for the negative electrode active material layer is a component used to assist in the bonding between the conductive material, the active material, and the current collector, and its addition amount is typically from 0.1% to 10% by weight, based on the total weight of the negative electrode active material layer. Examples of binders may include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0127] The conductive material in the negative electrode active material layer is a component used to further improve the conductivity of the negative electrode active material, and its addition amount can be less than 10% by weight, preferably less than 5% by weight, based on the total weight of the negative electrode active material layer. There are no particular limitations on the conductive material, as long as it is conductive and will 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; fluorocarbons; 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; or conductive polymers, such as polyphenylene derivatives, etc.

[0128] The negative electrode can be prepared by dissolving or dispersing the negative electrode active material and optionally the binder and conductive material in a solvent to prepare a composition for forming a negative electrode active material layer, coating the composition onto the negative electrode current collector, and then drying; or it can be prepared by casting the composition for forming a negative electrode active material layer onto a separate support, then peeling the film off the support, and stacking the film layer onto the negative electrode current collector.

[0129] The separator is used to separate the negative electrode from the positive electrode and provide a migration path for lithium ions. Any separator can be used without particular limitations, as long as it is a separator commonly used in lithium secondary batteries. In particular, separators with excellent electrolyte retention and low resistance to ion migration in the electrolyte are preferred. Specifically, porous polymer membranes can be used, for example, porous polymer membranes made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures having two or more of these layers. Alternatively, conventional porous nonwoven fabrics can be used, such as nonwoven fabrics made from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Furthermore, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can optionally be used in single-layer or multi-layer structures.

[0130] Electrolytes can be organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., but are not limited to these, and can be used to manufacture lithium secondary batteries. As a specific example, an electrolyte can contain an organic solvent and a lithium salt.

[0131] As organic solvents, any organic solvent can be used without particular restrictions, as long as it can serve as a medium through which ions participating in the electrochemical reactions of the battery can migrate. 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 solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), 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, and may contain double-bonded aromatic rings or ether bonds); amides such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane. Among them, carbonate solvents are preferred, and even more preferred are mixtures of cyclic carbonates (such as ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant and low viscosity linear carbonate compounds (such as ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) that can improve the charge and discharge performance of the battery.

[0132] As a lithium salt, any compound can be used without particular restrictions, as long as it can provide the lithium ions used in lithium secondary batteries. Specifically, the anion of the lithium salt can be selected from F... - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N -At least one of the components in the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc., can be used as lithium salts. The lithium salts can be used in concentration ranges from 0.1 M to 2.0 M. If the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, thus exhibiting excellent electrolyte performance, and lithium ions can migrate effectively.

[0133] To improve battery life, suppress battery capacity reduction, and improve battery discharge capacity, the electrolyte may also contain one or more additives, such as halogenated alkylene carbonates like difluorocarbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexamethylphosphoryltriamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidinanes, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. In this case, the content of the additives relative to the total weight of the electrolyte can be from 0.1% by weight to 5% by weight.

[0134] The lithium secondary battery containing the above-described positive electrode active material of the present invention has excellent performance and can therefore be used in portable devices such as mobile phones, laptops and digital cameras, and in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0135] 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.

[0136] The lithium secondary battery of the present invention can be used as a single cell for powering small devices, and can also preferably be used as a unit cell in a medium or large battery module comprising multiple single cells.

[0137] Therefore, the present invention provides a battery module comprising the lithium secondary battery as a unit cell, and a battery pack comprising the battery module.

[0138] Battery modules or battery packs can be used as power sources for one or more medium to large-sized devices in power tools, electric vehicles (including electric vehicles (EVs), hybrid electric vehicles and plug-in hybrid electric vehicles (PHEVs)), or energy storage systems.

[0139] Embodiments of the present invention

[0140] The embodiments of the present invention will now be described in detail 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.

[0141] Examples and Comparative Examples

[0142] Example 1

[0143] A composite transition metal hydroxide in the form of secondary particles (composition: Ni) consisting of dozens to hundreds of primary particles aggregated together. 0.60 Co 0.05 Mn 0.35 (OH)2, D 50 Li2CO3 and Ni+Co+Mn were added to an acoustic mixer to make the ratio of the total number of moles of transition metals (Ni+Co+Mn) in the composite transition metal hydroxide to the number of moles of lithium (Li) in Li2CO3 ((Ni+Co+Mn):Li) 1:1.05. The mixture was then prepared by mixing at 40 g (g: gravitational acceleration) for 2 minutes, at 80 g for 1 minute, and at 50 g for 2 minutes.

[0144] The mixture was added to a circular alumina crucible (75 mm × 75 mm) and sintered at 850 °C for 4 hours in air atmosphere. Then, the temperature was continuously increased to 950 °C (heating rate: 10 °C / min) and sintered again at 950 °C for 14 hours to prepare the sintered product.

[0145] The sintered product was finely pulverized at a rate of 12 g / min at 3.5 bar using an air jet mill (Isaac ENC) to prepare the positive electrode active material.

[0146] Example 2

[0147] The mixture prepared in Example 1 was added to a circular alumina crucible (75 mm × 75 mm) and sintered at 850 °C for 4 hours in an air atmosphere. Then, the temperature was continuously increased to 940 °C (heating rate: 10 °C / min), and then sintered again at 940 °C for 14 hours to prepare the sintered product.

[0148] The sintered product was finely pulverized at a rate of 12 g / min at 3.5 bar using an air jet mill (Isaac ENC) to prepare the positive electrode active material.

[0149] Comparative Example 1

[0150] The mixture prepared in Example 1 was added to a circular alumina crucible (75 mm × 75 mm) and sintered at 950°C for 14 hours in an air atmosphere to prepare the sintered product.

[0151] The sintered product was finely pulverized at a rate of 12 g / min at 3.5 bar using an air jet mill (Isaac ENC) to prepare the positive electrode active material.

[0152] Comparative Example 2

[0153] The mixture prepared in Example 1 was added to a circular alumina crucible (75 mm × 75 mm) and sintered at 950°C for 14 hours in air atmosphere. Then, the temperature was continuously lowered to 850°C (cooling rate: 10°C / min), and then sintered again at 850°C for 4 hours to prepare the sintered product.

[0154] The sintered product was finely pulverized at a rate of 12 g / min at 3.5 bar using an air jet mill (Isaac ENC) to prepare the positive electrode active material.

[0155] Experimental Example

[0156] Experimental Example 1: (1) Analysis of positive electrode active materials

[0157] SEM images of the positive electrode active materials prepared in the examples and comparative examples were obtained using SEM (FEI Corporation, Inspect F). Then, the boundaries of the primary particles present in the SEM images were delineated using an image processing program (LG Chem Corporation, DX program) to obtain images displayed in random colors.

[0158] At the same time, Figure 2 (Example 1) Figure 3 (Example 2) Figure 4 (Comparative Example 1) and Figure 5 (Comparative Example 2) shows SEM images of the positive electrode active materials of Examples 1 and 2, and Comparative Examples 1 and 2, respectively. (Refer to...) Figure 2 and Figure 3 It can be confirmed that the positive electrode active materials in Examples 1 and 2 are in single-particle form.

[0159] Using an image obtained by dividing the boundaries of primary particles and displaying it in random colors, the area of ​​each primary particle is calculated by counting the number of pixels in each of the n primary particles (averaging over 50,000 primary particles). The area is then calculated using the radius (r) of a circle with the same area as each primary particle. iThe particle size (D) of each primary particle present in the SEM image was calculated. i =2r i ) and volume (V i =4 / 3×πr i 3 The volume (V) of each primary particle is calculated and then multiplied by its diameter to obtain the value. i D i The sum of the totals divided by the calculated volume (V) i The sum of the calculated particle sizes is used to obtain the volume average particle size of the primary particles; the sum of the calculated particle sizes is divided by the number of primary particles to obtain the number average particle size of the primary particles; then the PDI value is obtained according to Equation 1 of the present invention, and all the above results are shown in Table 1 below.

[0160] Experimental Example 2: (2) Analysis of Positive Electrode Active Materials

[0161] Take 0.01 g of each positive electrode active material (powder) prepared in the examples and comparative examples, place it in a vial containing 30 mL of ultrapure water and 500 μL of dispersant, disperse it using an ultrasonicator for 1 minute, and then analyze it in a PSA (Microtrac, S3500) to determine D. 50 As shown in Table 1 below.

[0162] At this time, D 50 It refers to the particle size at the 50% point of the volumetric cumulative distribution of particle size.

[0163] Experimental Example 3: Evaluation of Fine Particle Generation

[0164] Take 3 g of each positive electrode active material (powder) prepared in the examples and comparative examples, place it in a mold with an inner diameter of 13 mm, press it at 9 tons for 1 minute, and then use PSA (Microtrac, S3500) to determine the number of particles with a diameter less than 1 μm. In addition, calculate the ratio of the number of particles with a diameter less than 1 μm to the total number of particles (fine particle generation), and show it in Table 1 below.

[0165] [Table 1]

[0166] Referring to Table 1 above, compared with the positive electrode active materials of Comparative Example 1 and Comparative Example 2, the PDI values ​​of the positive electrode active materials of Example 1 and Example 2 are closer to 1, thus confirming that their primary particle size is more uniform. Furthermore, it can be confirmed that the positive electrode active materials of Example 1 and Example 2 have a lower amount of fine particles formed.

[0167] In the positive electrode active materials of Comparative Example 1 and Comparative Example 2, it is believed that the primary particles begin to grow before the lithium melts and diffuses uniformly. Therefore, some particles grow excessively due to the excess lithium, while other particles grow smaller due to insufficient lithium, resulting in uneven growth.

[0168] Experiment Example 4: Battery Performance Evaluation

[0169] (1) Assessment of volume change rate

[0170] The positive electrode active materials, carbon black conductive materials, and polyvinylidene fluoride (PVDF) binders prepared in the examples and comparative examples were mixed in N-methylpyrrolidone (NMP) solvent at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was coated onto one surface of an aluminum current collector, dried at 130°C, and then rolled to manufacture the positive electrode.

[0171] A negative electrode slurry was prepared by mixing a negative electrode active material (natural graphite and artificial graphite in a 5:5 weight ratio), a Super C conductive material, a binder (ZEON, BML302), and an additive (Daicel, DAICEL2200) in water at a weight ratio of 95.6:1.0:2.3:1.1. The negative electrode slurry was then coated onto one surface of a copper current collector, dried at 130°C, and subsequently rolled to manufacture the negative electrode.

[0172] A porous polyethylene diaphragm is placed between the positive and negative electrodes manufactured above to prepare an electrode assembly. This electrode assembly is then laminated at 80°C to ensure complete electrode bonding. Aluminum and nickel tabs are welded together, and the assembly is placed in an aluminum bag and injected with an electrolyte solution to manufacture a single battery cell. The electrolyte solution used here is an organic solvent prepared by dissolving 0.7 M LiPF6 in a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 3:7.

[0173] Each of the manufactured single cells was charged at 25°C with a constant current of 0.1 C for 3 hours, followed by vacuum degassing by opening one side of the bag and resealing. The charge-discharge cycle was then repeated three times with a constant current of 0.33 C, followed by charging with a constant current of 0.33 C. The charged single cells were opened and the negative electrode separated. Two positive electrodes and two separators were then alternately stacked and placed in an aluminum bag. An electrolyte solution was injected into the bag to manufacture a cell for volume measurement. The electrolyte solution used was prepared by dissolving 0.7 M LiPF6 in an organic solvent formed by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7.

[0174] The initial volume of the battery cell was measured, and then it was stored in an oven at 60°C for 8 weeks. The volume of the battery cell after 8 weeks was measured, and the volume change rate was calculated as ([(initial volume) - (cell volume after 8 weeks)] / (initial volume) × 100). The results are shown in Table 2 below.

[0175] (2) Capacity retention assessment

[0176] The positive electrode active materials, carbon black conductive materials, and polyvinylidene fluoride (PVDF) binders prepared in the examples and comparative examples were mixed in an N-methylpyrrolidone (NMP) solvent at a ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was coated onto one surface of an aluminum current collector, dried at 130°C, and then rolled to manufacture the positive electrode.

[0177] A lithium metal electrode is used as the negative electrode, and a porous polyethylene separator is placed between the positive and negative electrodes to prepare an electrode assembly. The electrode assembly is then placed inside the battery casing, and an electrolyte solution is injected to manufacture a semi-cell. The electrolyte solution is prepared by dissolving 1.0 M LiPF6 in an organic solvent formed by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:3:4.

[0178] Each half of the manufactured cells was charged at 45°C using a CC-CV method (0.5 C) to 4.45 V, and then discharged using a CC method (1 C) to 2.5 V. This process was defined as one cycle, and the cycle was repeated a total of 50 times to measure the capacity of the lithium secondary battery. The percentage of the discharge capacity at the 50th cycle relative to the discharge capacity at the 1st cycle was defined as the capacity retention rate, and the results are shown in Table 2 below.

[0179] [Table 2]

[0180] Referring to Tables 1 and 2 above, compared with the batteries that each contained the positive electrode active materials of Comparative Example 1 and Comparative Example 2, the PDI values ​​of the positive electrode active materials of Example 1 and Example 2 are closer to 1, and the amount of fine particles generated is less. Therefore, it is confirmed that the batteries containing the above-mentioned positive electrode active materials have smaller volume changes due to gas generation and higher capacity retention.

[0181] As a result, according to the method for preparing the positive electrode active material of the present invention, if a mixture comprising a positive electrode active material precursor and a lithium-containing raw material is sintered once at 600°C to 900°C, continuously heated to 920°C to 1000°C, and then sintered again at 920°C to 1000°C, a positive electrode active material in the form of single particles with uniform primary particle size can be prepared, and the amount of fine particles generated is small. Furthermore, the positive electrode active material of the present invention contains a single-particle form of lithium nickel cobalt manganese-based oxide with a nickel content of 50 mol% or more in all transition metals, and a PDI value of 1 to 1.8, thus improving the high-temperature stability and lifespan properties of lithium secondary batteries.

Claims

1. A positive electrode active material comprising a lithium nickel cobalt manganese-based oxide having a nickel content of 50 mol% or more among all transition metals, and the lithium nickel cobalt manganese-based oxide being in the form of a single particle composed of 10 or fewer primary particles, in, The polydispersity index (PDI) value of the positive electrode active material according to the following Equation 1 is 1 to 1.8: [Equation 1] PDI = volume average particle size (μm) of primary particles / number average particle size (μm) of primary particles.

2. The positive electrode active material as described in claim 1, wherein, The lithium nickel cobalt manganese-based oxide has a composition represented by the following Formula 1: [Formula 1] Li 1+x Ni a1 Co b1 Mr c1 M 1 d1 O2 Among them, in Equation 1 above, M 1 is one or more selected from Al, W, Co, B, Zr, Y, Ce, Hf, La, Ba, F, P, S, Nb, Ta, Sc, Cr, V, Cu, Sr, Ti, Mg, Mo, Sn, Fe, Zn, and Si, and -0.1 ≤ x ≤ 0.1, 0.5 ≤ a1 < 1, 0 < b1 < 0.5, 0 < c1 < 0.5, 0 ≤ d1 ≤ 0.2, and a1 + b1 + c1 + d1 = 1.

3. The positive electrode active material as described in claim 1, wherein, The volume average particle size of the primary particles is 0.5 μm to 3.5 μm.

4. The positive electrode active material as described in claim 1, wherein, The number average particle size of the primary particles is 0.5 μm to 2.0 μm.

5. The positive electrode active material as described in claim 1, wherein, The positive electrode active material has a particle size distribution (D) measured using a PSA particle size analyzer. 50 The thickness ranges from 3 μm to 5 μm.

6. The positive electrode active material as described in claim 1, wherein, After putting 3 g of the positive electrode active material into a mold with an inner diameter of 13 mm, pressing it at 9 tons for 1 minute, the proportion of the number of particles with a particle size less than 1 μm measured by PSA (particle size analyzer) relative to the total number of particles is 2.5% or less.

7. A method for preparing the positive electrode active material according to claim 1, the method comprising: (A) Mixing a nickel cobalt manganese-based hydroxide having a nickel content of 50 mol% or more among all transition metals with a lithium-containing raw material to prepare a mixture; and (B) Subjecting the mixture to a first sintering at 600°C to 900°C in an air atmosphere, continuously heating the mixture to 920°C to 1000°C, and then subjecting the mixture to a second sintering at 920°C to 1000°C to prepare a sintered product.

8. The method of claim 7, wherein, The nickel cobalt manganese-based hydroxide has a composition represented by the following Formula 2: [Formula 2] Ni a2 What b2 Mn c2 M 2 d2 (OH)2 wherein, in the above Formula 2, M 2 It is selected from one or more of Al, W, Co, B, Zr, Y, Ce, Hf, La, Ba, F, P, S, Nb, Ta, Sc, Cr, V, Cu, Sr, Ti, Mg, Mo, Sn, Fe, Zn, and Si, and 0.5 ≤ a2 < 1, 0 < b2 < 0.5, 0 < c2 < 0.5, 0 ≤ d2 ≤ 0.2, and a2 + b2 + c2 + d2 = 1.

9. The method of claim 7, wherein, The first sintering is carried out for 1 hour to 12 hours.

10. The method of claim 7, wherein, The second sintering is carried out for 4 hours to 14 hours.

11. The method according to claim 7, the method further comprising (C) finely pulverizing the sintered product.

12. The method of claim 11, wherein, The fine pulverization is carried out by vortex flow pulverization.

13. The method of claim 12, wherein, The vortex flow pulverization is carried out at a pressure of 1 bar to 5 bar.

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

15. A lithium secondary battery comprising: The positive electrode according to claim 14; A negative electrode; A separator disposed between the positive electrode and the negative electrode; and An electrolyte.

Images