Positive electrode active material and positive electrode and lithium secondary battery containing the positive electrode active material

Abstract

This invention relates to a single-particle positive electrode active material capable of exhibiting optimal battery performance, and also to a positive electrode and a lithium secondary battery comprising the positive electrode active material. The positive electrode active material comprises a lithium composite transition metal oxide having the composition shown in Formula 1 as described in this specification and being a single-particle form consisting of 10 or fewer primary particles, wherein the D0 of the primary particles obtained from SEM images... v,50 The particle size is 2.2 μm to 3.7 μm, and the proportion of small particles according to Equation 1 as described in this specification is 5% to 10%.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2023-0151123, 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 and a positive electrode and a lithium secondary battery containing the positive electrode active material, and more specifically, to a single-particle form of a positive electrode active material and a positive electrode and a lithium secondary battery containing the 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] To date, lithium composite transition metal oxides containing two or more transition metals are typically prepared as spherical secondary particles composed of tens to hundreds of primary particles. In recent years, to address the structural and thermal stability issues of these secondary particle-form cathode active materials, the development of single-particle cathode active materials has accelerated. Specifically, when secondary particle-form cathode active materials are applied to lithium-ion batteries, they generate significant amounts of gas, leading to battery volume expansion. Furthermore, increasing the nickel content in the cathode active material to achieve high capacity increases the risk of fire. Therefore, the demand for developing single-particle cathode active materials with excellent stability is growing.

[0007] Single-particle positive electrode active materials are the opposite of spherical secondary particle positive electrode active materials prepared by conventional methods, which are composed of dozens to hundreds of primary particles. They are positive electrode active materials composed of fewer than 10 primary particles. Since the size of the primary particles in single-particle positive electrode active materials has a very significant impact on the performance of the positive electrode active materials, it is necessary to control the size of the primary particles well.

[0008] Meanwhile, when using single-particle positive electrode active materials to manufacture lithium secondary batteries, the particles are prone to cracking and collapse during the rolling process after coating the positive electrode active material onto the positive electrode current collector. Therefore, during the charging and discharging process of lithium secondary batteries, gas is generated due to side reactions between the positive electrode active material and the electrolyte solution, and expansion occurs, leading to battery performance degradation.

[0009] Therefore, there is a need to develop positive electrode active materials in single-particle form that can exhibit optimal battery performance. Summary of the Invention

[0010] Technical issues

[0011] To address the aforementioned problems, one object of the present invention is to provide a single-particle positive electrode active material capable of exhibiting optimal battery performance.

[0012] Another object of the present invention is to provide a lithium secondary battery with improved performance by incorporating the above-mentioned positive electrode active material.

[0013] Technical solution

[0014] To achieve the above objectives, the present invention provides a positive electrode active material, a method for preparing the positive electrode active material, a positive electrode, and a lithium secondary battery.

[0015] (1) The present invention provides a positive electrode active material comprising a lithium composite transition metal oxide having the composition shown in Formula 1 and being a single particle consisting of equal to or less than 10 primary particles, wherein the D of the primary particles obtained from SEM images is... v,50 The particle size is 2.2 μm to 3.7 μm, and the proportion of small particles according to Equation 1 below is 5% to 10%.

[0016] [Formula 1]

[0017] Li 1+x Ni a1 Co b1 Mn c1 Zr d1 Y e1 M f1 O 2-y Ay

[0018] In the above formula (1), M is one or more selected from W, Cu, Sr, Mn, Ti, Mg, Mo, B, Sn, Fe, Zn, Si, and Al, A is one or more selected from F, Cl, Br, I, and S, and -0.1 ≤ x ≤ 0.1, 0 < a1 < 1, 0 < b1 < 1, 0 < c1 < 1, 0 < d1 < 0.01, 0 < e1 < 0.01, 0 ≤ f1 < 0.1, 0 ≤ y ≤ 0.2, and a1 + b1 + c1 + d1 + e1 + f1 = 1, and

[0019] [Equation 1]

[0020] Small particle ratio (%) = (sum of areas of primary particles with a particle size of 1 μm or less obtained from the SEM image / sum of areas of all primary particles obtained from the SEM image) × 100.

[0021] (2) In the above (1), the present invention provides a positive electrode active material, wherein the D of the primary particles obtained from the SEM image v,50 is 2.5 μm to 2.8 μm.

[0022] (3) In the above (1) or (2), the present invention provides a positive electrode active material, wherein the D of the positive electrode active material measured by using a particle size analyzer (PSA) 50 is 3.5 μm to 4 μm.

[0023] (4) In any one of the above (1) to (3), the present invention provides a positive electrode active material, wherein the lithium composite transition metal oxide is doped with 1000 ppm to 4000 ppm of Zr and 1000 ppm to 4000 ppm of Y.

[0024] (5) In any one of the above (1) to (4), the present invention provides a positive electrode active material, wherein the positive electrode active material further includes a coating layer formed on the lithium composite transition metal oxide, and the coating layer includes Al, W, or a combination thereof.

[0025] (6) The present invention provides a positive electrode including the positive electrode active material according to any one of the above (1) to (5).

[0026] (7) The present invention provides a lithium secondary battery including the positive electrode according to the above (6), a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

[0027] Advantageous effects

[0028] The positive electrode active material of the present invention comprises a lithium composite transition metal oxide doped with Zr and Y, and the small particle size ratio and the particle size of the primary particles meet a specific range according to Equation 1 described in this specification, thereby reducing particle breakage and improving the capacity, initial efficiency and resistivity of the lithium secondary battery.

[0029] The positive electrode and lithium secondary battery of the present invention can have excellent capacity, initial efficiency and resistance performance, etc. Attached Figure Description

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

[0031] Figure 2 This is a SEM image of the positive electrode active material of Example 3. Detailed Implementation

[0032] The present invention will now be described in more detail for the purpose of understanding.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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 consisting of 10 or fewer primary particles. Specifically, in this invention, the single-particle form can be a single particle consisting of one primary particle, or it can be a secondary particle form consisting of 2 to 10 primary particles agglomerated together.

[0037] "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.

[0038] In this specification, "D of primary particles derived from SEM images" v,50"It can be obtained by: calculating the area of ​​each primary particle by the number of pixels corresponding to each of the n (at least 50) primary particles present at a specific magnification (e.g., 5000x, 8000x) in the SEM image; calculating the particle size and volume of each primary particle in the SEM image using the radius of a circle with the same area as each primary particle; and calculating the particle size at the 50% point of the cumulative volume distribution based on particle size."

[0039] In this specification, the "sum of the areas of primary particles with a diameter of less than 1 μm obtained from the SEM image" can be obtained as follows: calculate the area of ​​each primary particle by the number of pixels corresponding to each of the n (at least 50) primary particles present at a specific magnification (e.g., 5000x, 8000x) in the SEM image; use the radius value of a circle with the same area as each primary particle to obtain the particle diameter of each primary particle in the SEM image; and then add up the areas of the primary particles with a diameter of less than 1 μm among these primary particles.

[0040] In this specification, the "sum of the areas of all primary particles obtained from the SEM image" can be obtained as follows: calculate the area of ​​each primary particle by the number of pixels corresponding to each of the n (at least 50) primary particles present at a specific magnification (e.g., 5000x, 8000x) in the SEM image; use the radius value of a circle with the same area as each primary particle to obtain the particle size of each primary particle in the SEM image; and then add up the areas of all primary particles.

[0041] In this specification, "D measured using a particle size analyzer (PSA)" 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.

[0042] Positive electrode active material

[0043] This invention provides a positive electrode active material comprising a lithium composite transition metal oxide having the composition shown in Formula 1 and being a single particle consisting of 10 or fewer primary particles, wherein the D of the primary particles obtained from SEM images is... v,50 The particle size ranges from 2.2 μm to 3.7 μm, and the proportion of small particles according to Equation 1 below is 5% to 10%. Lithium composite transition metal oxides can have a layered structure.

[0044] [Formula 1]

[0045] Li 1+x Ni a1 Co b1 Mn c1 Zr d1 Y e1 M f1 O 2-y A y

[0046] In the above Formula 1, M is selected from one or more of W, Cu, Sr, Mn, Ti, Mg, Mo, B, Sn, Fe, Zn, Si, and Al, A is selected from one or more of F, Cl, Br, I, and S, and -0.1 ≤ x ≤ 0.1, 0 < a1 < 1, 0 < b1 < 1, 0 < c1 < 1, 0 < d1 < 0.01, 0 < e1 < 0.01, 0 ≤ f1 < 0.1, 0 ≤ y ≤ 0.2, and a1 + b1 + c1 + d1 + e1 + f1 = 1, and

[0047] [Equation 1]

[0048] Small particle ratio (%) = (Sum of the areas of primary particles with a particle size of 1 μm or less obtained from the SEM image / Sum of the areas of all primary particles obtained from the SEM image) × 100.

[0049] The present inventors found that if the positive electrode active material contains the above lithium composite transition metal oxide in the form of single particles and doped with Zr and Y, the particle size of the primary particles satisfies a specific range, and the small particle ratio according to Equation 1 described in the present specification is 5% to 10%, then during the roll pressing process for manufacturing a lithium secondary battery, the breakage of the positive electrode active material is reduced, thereby improving the capacity, initial efficiency, and resistance performance of the lithium secondary battery, and thus the present invention was completed.

[0050] According to the present invention, the lithium composite transition metal oxide is doped with Zr and Y. In this case, Zr is stably doped on the transition metal layer, so that even if lithium is repeatedly intercalated and deintercalated due to repeated charging and discharging, a stable structure can be maintained. And, Y acts as a flux material during the sintering process, so that the optimal primary particle size can be achieved even at a relatively low temperature, which is advantageous for the resistance property or rate property.

[0051] Meanwhile, if the lithium composite transition metal oxide is not doped with Zr, the structure retention rate decreases, which is disadvantageous in terms of the life property; if it is not doped with Y, the sintering temperature needs to be further increased to achieve the optimal primary particle size, which is disadvantageous in terms of the resistance property or rate property.

[0052] According to the present invention, in order to enable the lithium complex transition metal oxide to have optimal lifetime and resistivity performance while having the desired primary particle size, the lithium complex transition metal oxide may be doped with 1000 ppm to 4000 ppm of Zr and 1000 ppm to 4000 ppm of Y.

[0053] The Zr content relative to the total weight of lithium complex transition metal oxides can be above 1000 ppm, above 1100 ppm, above 1200 ppm, above 1300 ppm, or above 1400 ppm, and can be below 1500 ppm, below 1600 ppm, below 1700 ppm, below 1800 ppm, below 1900 ppm, below 2000 ppm, below 2100 ppm, below 2200 ppm, below 2300 ppm, below 2400 ppm, below 2500 ppm, below 2600 ppm, below 2700 ppm, below 2800 ppm, below 2900 ppm, below 3000 ppm, below 3100 ppm, below 3200 ppm, below 3300 ppm, below 3400 ppm, below 3500 ppm, below 3600 ppm, below 3700 ppm, below 3800 ppm, below 3900 ppm, or below 4000 ppm.

[0054] The content of Y relative to the total weight of lithium complex transition metal oxides can be above 1000 ppm, above 1100 ppm, above 1200 ppm, above 1300 ppm, above 1400 ppm, above 1500 ppm, above 1600 ppm, above 1700 ppm, above 1800 ppm, above 1900 ppm, above 2000 ppm, above 2100 ppm, above 2200 ppm, above 2300 ppm, above 2400 ppm, above 2500 ppm, above 2600 ppm, above 2700 ppm, above 2800 ppm, or above 2900 ppm, and can be below 3000 ppm, below 3100 ppm, below 3200 ppm, below 3300 ppm, below 3400 ppm, below 3500 ppm, below 3600 ppm, below 3700 ppm, below 3800 ppm, below 3900 ppm, or below 4000 ppm.

[0055] If the Zr content is within the above range, high capacity can be achieved while maintaining excellent structure retention as it changes with charge and discharge; if the Y content is within the above range, optimal primary particle size can be achieved even at relatively low temperatures, thus enabling high capacity to be achieved while being favorable to resistive or rate properties.

[0056] According to the present invention, the particle size ratio of the positive electrode active material according to Equation 1 is 5% to 10%. If the particle size ratio is 5% to 10%, optimal performance is achieved in terms of battery performance, particle breakage, and rolling density.

[0057] Meanwhile, if the proportion of small particles in the positive electrode active material is less than 5%, there will be problems with the battery's efficiency and resistance performance; if it is greater than 10%, there will be problems with particle breakage and deterioration of rolling density.

[0058] According to the present invention, the D of primary particles is derived from SEM images. v,50 The particle size can range from 2.2 μm to 3.7 μm, preferably from 2.5 μm to 2.8 μm. Under these conditions, optimal performance is achieved in terms of battery performance, particle breakage, and rolling density. Simultaneously, if the primary particle size (D...)... v,50 If the thickness is less than 2.2 μm, there will be problems with the battery's rolling density and / or lifespan performance; if it is greater than 3.7 μm, there will be problems with the battery's efficiency and / or resistance performance.

[0059] D of primary particles v,50 The doping elements and their content, the amount of lithium raw material added, and the sintering temperature can be controlled during the preparation of the positive electrode active material.

[0060] According to the present invention, the D of the positive electrode active material is measured by using a particle size analyzer (PSA). 50 The diameter can range from 3.5 μm to 4.0 μm. The D of the positive electrode active material... 50 The particle size can be above 3.50 μm, and can be below 3.80 μm, 3.85 μm, 3.90 μm, 3.95 μm, or 4.0 μm. If the D of the positive electrode active material is measured using 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 3.5 μm, the battery life may be reduced; if D 50 If the diameter is greater than 4.0 μm, the battery capacity may decrease.

[0061] 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 (fine particle generation) measured by a particle size analyzer (PSA) can be 2.5% or less, specifically 2.0% or less, 1.5% or less, 1.0% or less, or 0.6% or less. In this case, the specific surface area of ​​the particles in contact with the electrolyte solution is reduced, thus suppressing side reactions, improving capacity retention (lifetime) according to charge-discharge changes, and reducing gas generation.

[0062] According to the present invention, the lithium complex transition metal oxide may contain more than 60 mol% nickel relative to the total molar percentage of metals other than lithium. That is, the lithium complex transition metal oxide may be a high-nickel-based lithium complex transition metal oxide. In this case, the energy density of the lithium secondary battery can be improved.

[0063] According to the present invention, in Formula 1 above, x can be -0.1 or higher, -0.09 or higher, -0.08 or higher, -0.07 or higher, -0.06 or higher, -0.05 or higher, -0.04 or higher, -0.03 or higher, -0.02 or higher, -0.01 or higher, or 0 or higher, and can be 0.06 or lower, 0.07 or lower, 0.08 or lower, 0.09 or lower, or 0.1 or lower. When x satisfies the above range, high capacity properties and high energy density per unit volume can be achieved.

[0064] According to the present invention, in Formula 1 above, a1 represents the atomic fraction of nickel in the metal elements other than lithium in the lithium complex transition metal oxide, and can be 0.6 or more, 0.61 or more, or 0.62 or more, and can be 0.7 or less, 0.71 or less, 0.72 or less, 0.73 or less, 0.74 or less, 0.75 or less, 0.76 or less, 0.77 or less, 0.78 or less, 0.79 or less, 0.8 or less, 0.81 or less, 0.82 or less, 0.83 or less, 0.84 or less, 0.85 or less, 0.86 or less, 0.87 or less, 0.88 or less, 0.89 or less, 0.9 or less, 0.91 or less, 0.92 or less, 0.93 or less, 0.94 or less, 0.95 or less, 0.96 or less, 0.97 or less, 0.98 or less, or less than 1. When a1 meets the above range, high capacity properties can be achieved, and in particular, if a1 is 0.6 to 0.75, high energy density is exhibited during high voltage driving, thus achieving high capacity properties.

[0065] According to the present invention, in Formula 1 above, b1 represents the atomic fraction of cobalt among the metal elements other than lithium in the lithium-based complex transition metal oxide, and can be greater than 0, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, or 0.05 or more, and can be less than 0.10, less than 0.11, less than 0.12, less than 0.13, less than 0.14, less than 0.15, less than 0.16, less than 0.17, or less than 0.18. The values ​​below 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, or less than 0.4. When b1 meets the above ranges, the stability during the charge and discharge process can be improved, and the rate capability can be improved.

[0066] According to the present invention, in Formula 1 above, c1 represents the atomic fraction of manganese among the metal elements other than lithium in the lithium-based complex transition metal oxide, and can be greater than 0, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, 0.1 or more, 0.11 or more, 0.12 or more, 0.13 or more, 0.14 or more, 0.15 or more, or 0.16 or more. The concentrations of c1 can be 0.17 or higher, 0.18 or higher, 0.19 or higher, 0.2 or higher, 0.21 or higher, 0.22 or higher, 0.23 or higher, 0.24 or higher, 0.25 or higher, 0.26 or higher, 0.27 or higher, 0.28 or higher, 0.29 or higher, or 0.30 or higher, and can be below 0.32, below 0.33, below 0.34, below 0.35, below 0.36, below 0.37, below 0.38, below 0.39 or less than 0.4. When c1 meets the above ranges, high capacity properties can be achieved. Furthermore, high-temperature stability can be improved, and side reactions with the electrolyte solution can be relatively reduced.

[0067] According to the present invention, in Formula 1 above, d1 represents the atomic fraction of zirconium in the metal elements other than lithium in the lithium composite transition metal oxide, and can be 0 or more or 0.0005 or more, and can be 0.001 or less, 0.002 or less, 0.003 or less, 0.004 or less, 0.005 or less, 0.006 or less, 0.007 or less, 0.008 or less, 0.009 or less, or 0.01 or less. When d1 satisfies the above range, the crystal structure stability of the positive electrode active material can be improved, and due to the improved structural stability, the resistance and lifespan of the battery can be improved.

[0068] According to the present invention, in Formula 1 above, e1 represents the atomic fraction of yttrium among the metal elements other than lithium in the lithium-based complex transition metal oxide, and can be 0 or more or 0.001 or more, and can be 0.002 or less, 0.003 or less, 0.004 or less, 0.005 or less, 0.006 or less, 0.007 or less, 0.008 or less, 0.009 or less, or 0.01 or less. When e1 satisfies the above range, particle growth can be improved, thereby improving capacity and lifetime.

[0069] According to the present invention, in Formula 1 above, f1 represents the atomic fraction of element M among the metal elements other than lithium in the lithium composite transition metal oxide, and can be 0 or more, or can be 0.01 or less, 0.02 or less, 0.03 or less, 0.04 or less, 0.05 or less, 0.06 or less, 0.07 or less, 0.08 or less, 0.09 or less, or 0.10 or less. When f1 satisfies the above range, the crystal structure stability of the positive electrode active material can be improved, and the particle morphology can be improved.

[0070] According to the present invention, the positive electrode active material may further comprise a coating layer formed on a lithium composite transition metal oxide, wherein the coating layer may comprise Al, W, or a combination thereof. In this case, the battery comprising the positive electrode active material can have optimal capacity and lifespan performance.

[0071] According to the present invention, the Al content in the coating layer can be from 1000 ppm to 2000 ppm relative to the total weight of the positive electrode active material. Specifically, the Al content relative to the total weight of the positive electrode active material can be 1000 ppm or more, 1100 ppm or more, 1200 ppm or more, 1300 ppm or more, or 1400 ppm or more, and can be 1500 ppm or less, 1600 ppm or less, 1700 ppm or less, 1800 ppm or less, 1900 ppm or less, or 2000 ppm or less. In this case, the conductivity of the positive electrode active material can be improved, and the formation of byproducts from side reactions with the electrolyte solution in the battery can be suppressed, thus improving the capacity, resistivity, and lifetime properties of the positive electrode active material.

[0072] According to the present invention, relative to the total weight of the positive electrode active material, the content of W contained in the coating layer can be 2000 ppm to 4000 ppm. Specifically, the content of W can be 2000 ppm or more, 2100 ppm or more, 2200 ppm or more, 2300 ppm or more, 2400 ppm or more, 2500 ppm or more, 2600 ppm or more, 2700 ppm or more, 2800 ppm or more, or 2900 ppm or more, and can be 3000 ppm or less, 3100 ppm or less, 3200 ppm or less, 3300 ppm or less, 3400 ppm or less, 3500 ppm or less, 3600 ppm or less, 3700 ppm or less, 3800 ppm or less, 3900 ppm or less, or 4000 ppm or less. In this case, the conductivity of the positive electrode active material can be improved, and the generation of by-products formed by side reactions with the electrolyte solution in the battery can be suppressed. Therefore, the capacity properties, resistance properties, life properties, etc. of the positive electrode active material can be improved.

[0073] Preparation method of positive electrode active material

[0074] The positive electrode active material of the present invention can be prepared by the following method for preparing a positive electrode active material. However, the present invention is not limited thereto.

[0075] The method for preparing the positive electrode active material in the form of single particles of the present invention includes: (A) mixing a positive electrode active material precursor having the composition shown in the following formula 2, a zirconium-containing raw material, a yttrium-containing raw material, and a lithium-containing raw material to prepare a mixture; and (B) subjecting the mixture to a first sintering at 600°C to 850°C, a second sintering at 960°C to 970°C, and then a third sintering at 500°C to 850°C in an air atmosphere to prepare a sintered product.

[0076] [Formula 2]

[0077] Ni a2 Co b2 Mn c2 M 1 d2 (OH)2

[0078] In the above formula 2, M 1 is selected from one or more of Zr, Y, W, Cu, Sr, Mn, Ti, Mg, Mo, B, Sn, Fe, Zn, Si, and Al, and 0 < a2 < 1, 0 < b2 < 1, 0 < c2 < 1, 0 ≤ d2 < 0.1, and a2 + b2 + c2 + d2 = 1.

[0079] The inventors discovered that if a mixture of a positive electrode active material precursor and zirconium-containing raw materials, yttrium-containing raw materials, and lithium-containing raw materials is sintered sequentially at 800°C to 900°C once, at 940°C to 970°C twice, and then at 550°C to 650°C three times, a positive electrode active material with uniform particle size can be prepared. Furthermore, during the rolling process used in the manufacture of lithium secondary batteries, the breakage of the positive electrode active material particles is reduced. Based on this, the present invention was completed.

[0080] Step (A)

[0081] Step (A) above is a step of preparing a mixture by mixing a positive electrode active material precursor having the composition shown in Formula 2 above, a zirconium-containing raw material, a yttrium-containing raw material and a lithium-containing raw material.

[0082] According to the present invention, the cathode active material precursor may contain more than 60 mol% nickel (Ni) relative to the total number of moles of transition metals contained in the cathode active material precursor. In this case, the energy density of the lithium secondary battery can be improved.

[0083] According to the present invention, in Formula 2 above, a2 represents the atomic fraction of nickel in the metal element in the composite transition metal hydroxide, and can be 0.6 or more, 0.61 or more, or 0.62 or more, and can be 0.7 or less, 0.71 or less, 0.72 or less, 0.73 or less, 0.74 or less, 0.75 or less, 0.76 or less, 0.77 or less, 0.78 or less, 0.79 or less, 0.8 or less, 0.81 or less, 0.82 or less, 0.83 or less, 0.84 or less, 0.85 or less, 0.86 or less, 0.87 or less, 0.88 or less, 0.89 or less, 0.9 or less, 0.91 or less, 0.92 or less, 0.93 or less, 0.94 or less, 0.95 or less, 0.96 or less, 0.97 or less, 0.98 or less, or less than 1. When a2 meets the above range, the battery containing the finally prepared positive electrode active material can achieve high capacity properties, and in particular, if a2 is 0.6 to 0.75, the battery containing the finally prepared positive electrode active material can exhibit high energy density during high voltage driving, thereby achieving high capacity properties.

[0084] According to the present invention, in Formula 2 above, b2 represents the atomic fraction of cobalt in the metal element of the composite transition metal hydroxide, and can be greater than 0, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, or 0.05 or more, and can be less than 0.10, less than 0.11, less than 0.12, less than 0.13, less than 0.14, less than 0.15, less than 0.16, less than 0.17, less than 0.18, etc. The values ​​are below 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, or less than 0.4. When b2 meets the above ranges, the stability of the battery containing the finally prepared positive electrode active material during the charge and discharge process can be improved, and the rate performance can be improved.

[0085] According to the present invention, in Formula 2 above, c2 represents the atomic fraction of manganese in the metal element of the composite transition metal hydroxide, and can be greater than 0, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, 0.1 or more, 0.11 or more, 0.12 or more, 0.13 or more, 0.14 or more, 0.15 or more, 0.16 or more, 0 The concentration of c2 can be 0.17 or higher, 0.18 or higher, 0.19 or higher, 0.2 or higher, 0.21 or higher, 0.22 or higher, 0.23 or higher, 0.24 or higher, 0.25 or higher, 0.26 or higher, 0.27 or higher, 0.28 or higher, 0.29 or higher, or 0.30 or higher, and can be 0.32 or lower, 0.33 or lower, 0.34 or lower, 0.35 or lower, 0.36 or lower, 0.37 or lower, 0.38 or lower, 0.39 or lower, or less than 0.4. When c2 meets the above ranges, the battery containing the finally prepared positive electrode active material can achieve high capacity properties. Furthermore, the high-temperature stability of the battery can be improved, and side reactions with the electrolyte solution can be relatively reduced.

[0086] According to the present invention, in Formula 2 above, d2 represents the metal element M in the composite transition metal hydroxide. 1 The atomic fraction of the element can be greater than or equal to 0, and can be less than or equal to 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.10. When d2 meets the above range, the crystal structure stability of the finally prepared positive electrode active material can be improved, and the particle morphology can be improved.

[0087] 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, Li2SO4, CH3COOLi, Li3C6H5O7, etc., and any one or a mixture of two or more of them can be used.

[0088] According to the present invention, the mixing ratio of the positive electrode active material precursor and the lithium-containing raw material can be such that the ratio (M:Li) of the total molar number of transition metals (M) contained in the positive electrode active material precursor to the molar number of lithium (Li) contained in the lithium-containing raw material is 1:1.03 to 1.07. Under this condition, the finally prepared positive electrode active material can have the desired primary particle size and can improve the battery life and resistivity properties.

[0089] According to the present invention, the zirconium (Zr)-containing raw material can be selected from Zr(OH)4, ZrO2, Zr(NO3)4, ZrCl4, ZrS2, Zr(SO4)2 and C8H 12 One or more of O8Zr, specifically, one or more of ZrO2, Zr(OH)4 and Zr(NO3)4, more specifically ZrO2.

[0090] According to the present invention, the amount of zirconium-containing raw material added can be such that the zirconium content is 1000 ppm to 4000 ppm relative to the total weight of the positive electrode active material precursor. Specifically, the amount of zirconium-containing raw material added can be such that, relative to the total weight of the complex transition metal hydroxide, zirconium is 1000 ppm or more, 1100 ppm or more, 1200 ppm or more, 1300 ppm or more, or 1400 ppm or more, and can be below 1500 ppm, below 1600 ppm, below 1700 ppm, below 1800 ppm, below 1900 ppm, below 2000 ppm, below 2100 ppm, below 2200 ppm, below 2300 ppm, below 2400 ppm, below 2500 ppm, below 2600 ppm, below 2700 ppm, below 2800 ppm, below 2900 ppm, below 3000 ppm, below 3100 ppm, below 3200 ppm, below 3300 ppm, below 3400 ppm, below 3500 ppm, or below 3600 ppm. Below ppm, below 3700 ppm, below 3800 ppm, below 3900 ppm, or below 4000 ppm. Under these conditions, Zr is stably doped onto the transition metal layer, thus maintaining a stable structure even if lithium is repeatedly inserted and extracted due to repeated charging and discharging.

[0091] According to the present invention, the yttrium (Y)-containing raw material may be selected from one or more of YCl3, Y2O3, Y(NO3)3, Y(OH)3, YSZ, Y2(SO4)3 and Y2S3, specifically selected from one or more of Y2O3, Y(OH)3 and YSZ, and more specifically Y2O3.

[0092] According to the present invention, the amount of yttrium-containing raw material added can be such that the yttrium content is 1000 ppm to 4000 ppm relative to the total weight of the positive electrode active material precursor. Specifically, the amount of yttrium-containing raw material added can be such that, relative to the total weight of the complex transition metal hydroxide, yttrium is 1000 ppm or higher, 1100 ppm or higher, 1200 ppm or higher, 1300 ppm or higher, 1400 ppm or higher, 1500 ppm or higher, 1600 ppm or higher, 1700 ppm or higher, 1800 ppm or higher, 1900 ppm or higher, 2000 ppm or higher, 2100 ppm or higher, 2200 ppm or higher, 2300 ppm or higher, 2400 ppm or higher, 2500 ppm or higher, 2600 ppm or higher, 2700 ppm or higher, 2800 ppm or higher, or 2900 ppm or higher, and can be below 3000 ppm, below 3100 ppm, below 3200 ppm, below 3300 ppm, below 3400 ppm, below 3500 ppm, or below 3600 ppm. Below ppm, below 3700 ppm, below 3800 ppm, below 3900 ppm, or below 4000 ppm. In this case, Y acts as a fluxing agent during sintering, thus achieving optimal primary particle size even at relatively low temperatures, which is beneficial for resistivity or rate capability.

[0093] Step (B)

[0094] Step (B) above involves sintering the mixture once at 600°C to 850°C, a second time at 960°C to 970°C, and a third time at 500°C to 850°C in an air atmosphere to prepare the sintered product.

[0095] According to the present invention, when the mixture is sintered once at 600°C to 850°C, the lithium-containing raw material dissolves and is sufficiently and uniformly distributed on the precursor surface. As a result, lithium reacts effectively with the precursor, thus enabling the preparation of an active material with a uniform primary particle morphology. Specifically, the primary sintering temperature can be above 600°C, above 650°C, above 700°C, or above 750°C, and can be below 800°C or below 850°C. If the primary sintering temperature is within the above range, the lithium-containing raw material can dissolve and be sufficiently and uniformly distributed on the precursor surface. However, if the primary sintering temperature is below 600°C, there is a problem that the lithium-containing raw material cannot dissolve sufficiently; if it is above 850°C, the lithium-containing raw material may embed itself in the precursor before dissolving and being sufficiently and uniformly distributed, potentially resulting in an active material with a relatively non-uniform morphology.

[0096] According to the present invention, in terms of the uniform distribution of lithium-containing raw materials, the first sintering is carried out in an air atmosphere.

[0097] According to the present invention, a single sintering process can be carried out for 1 to 8 hours. Under these conditions, the lithium-containing raw material can be dissolved and distributed sufficiently and uniformly on the precursor surface.

[0098] After the first sintering, if the temperature is immediately and continuously raised to 960°C to 970°C, and a second sintering is performed at 960°C to 970°C, lithium is embedded in the precursor, forming a layered structure, and the interfaces of the primary particles bond together, achieving primary particle growth. If the second sintering temperature is within this range, the optimal primary particle size can be achieved, thus the battery's capacity, resistance, lifespan, particle breakage, and roll density can also exhibit optimal performance. Conversely, if the second sintering temperature is below 960°C, the primary particle size decreases, leading to problems with particle breakage and deterioration in roll density; if the temperature is above 970°C, the primary particle size increases, resulting in problems with deterioration in efficiency and resistance performance.

[0099] For proper growth of the primary particles, secondary sintering is carried out in an air atmosphere.

[0100] According to the present invention, the secondary sintering can be carried out for 3 to 12 hours. In this case, lithium can be fully embedded in the precursor, and the growth of primary particles can also be appropriately achieved.

[0101] If the temperature is immediately and continuously raised to 500℃ to 850℃ after the second sintering, and a third sintering is carried out at 500℃ to 850℃, the crystal structure defects of the active material caused by the high temperature of the second sintering can be alleviated, thereby obtaining a sintered product with fewer structural defects. The specific sintering temperatures can be above 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, or 600℃, and can be below 650℃, 660℃, 670℃, 680℃, 690℃, 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, 830℃, 840℃, or 850℃. In these conditions, the sintered product is a single-particle lithium composite transition metal oxide. If the sintering temperatures are within the above ranges, structural defects can be effectively mitigated. Meanwhile, if the sintering temperature is below 500℃ or above 850℃, it may not be able to effectively alleviate structural defects.

[0102] In terms of minimizing structural defects, the third sintering is carried out in an air atmosphere.

[0103] According to the present invention, the three sintering processes can be carried out for 1 to 8 hours. Under these conditions, defects in the crystal structure can be minimized.

[0104] Regarding efficient electrode fabrication and efficient reaction at the active material-electrolyte interface, the preparation method of the positive electrode active material of the present invention may further include (C) fine pulverization of the sintered product. Fine pulverization enables the D of the positive electrode active material, as measured by a particle size analyzer (PSA), to be more efficient. 50 The thickness ranges from 3.5 μm to 4.0 μm.

[0105] According to the present invention, fine grinding can be carried out by vortex flow grinding. In this case, compared with conventional physical grinding, not only is the grinding efficiency good, but no heat is generated, thus suppressing the denaturation of the active material surface.

[0106] According to the present invention, vortex milling can be carried out at a pressure of 1 bar to 5 bar. Under this condition, the target particle size can be effectively achieved.

[0107] The method for preparing the positive electrode active material of the present invention may further include (C') mixing the sintered product with one or more selected from aluminum raw materials and tungsten raw materials, and then heat-treating the mixture to form a coating layer comprising one or more selected from Al and W on the sintered product. In this case, a coating portion comprising one or more selected from Al and W is formed on the sintered product (lithium composite transition metal oxide in single-particle form).

[0108] According to the present invention, the aluminum raw material may be selected from one or more of Al2O3, Al(OH)3, AlCl3, AlF3 and Al2(SO4)3, specifically selected from one or more of Al2O3, Al(OH)3 and AlF3, and more specifically Al2O3.

[0109] According to the present invention, the amount of aluminum raw material added can be such that the aluminum content relative to the total weight of the sintered product is 1000 ppm to 2000 ppm. Specifically, the amount of aluminum raw material added can be such that the aluminum content relative to the total weight of the sintered product is 1000 ppm or more, 1100 ppm or more, 1200 ppm or more, 1300 ppm or more, or 1400 ppm or more, and can be 1500 ppm or less, 1600 ppm or less, 1700 ppm or less, 1800 ppm or less, 1900 ppm or less, or 2000 ppm or less.

[0110] In this case, the capacity retention rate based on charge and discharge can be improved.

[0111] According to the present invention, the tungsten raw material may be selected from one or more of WO3, WC and H2WO4, and more specifically may be WO3.

[0112] According to the present invention, the amount of tungsten raw material added can be such that, relative to the total weight of the sintered product, tungsten is between 2000 ppm and 4000 ppm. Specifically, the amount of tungsten raw material added can be such that, relative to the total weight of the sintered product, tungsten is 2000 ppm or more, 2100 ppm or more, 2200 ppm or more, 2300 ppm or more, 2400 ppm or more, 2500 ppm or more, 2600 ppm or more, 2700 ppm or more, 2800 ppm or more, or 2900 ppm or more, and can be 3000 ppm or less, 3100 ppm or less, 3200 ppm or less, 3300 ppm or less, 3400 ppm or less, 3500 ppm or less, 3600 ppm or less, 3700 ppm or less, 3800 ppm or less, 3900 ppm or less, or 4000 ppm or less. In this case, the output performance during battery operation can be improved.

[0113] According to the present invention, heat treatment can be performed at 400°C to 600°C. Under these conditions, the lifetime properties of the positive electrode active material can be further improved.

[0114] According to the present invention, the heat treatment is carried out in an air atmosphere for surface stabilization.

[0115] According to the present invention, the heat treatment can be performed for 3 to 12 hours. In this case, by stabilizing the surface of the positive electrode active material, the side reactions between the positive electrode active material and the electrolyte solution caused by repeated charging and discharging are suppressed, thereby improving the battery's lifespan properties.

[0116] positive electrode

[0117] The present invention provides a positive electrode comprising the above-mentioned positive electrode active material.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] Lithium secondary batteries

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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).

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] Embodiments of the present invention

[0146] 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.

[0147] Examples and Comparative Examples

[0148] Example 1

[0149] A composite transition metal hydroxide in the form of secondary particles (composition: Ni) consisting of dozens to hundreds of primary particles aggregated together. 0.62 Co 0.06 Mn 0.32 (OH)2, D 50 3.5 μm of ZrO2 (in an amount such that Zr is 1500 ppm relative to the total weight of the composite transition metal hydroxide) and 3000 ppm of Y2O3 (in an amount such that Y is 3000 ppm relative to the total weight of the composite transition metal hydroxide) were introduced into an acoustic mixer and mixed sequentially at 40 g (g: gravitational acceleration) for 2 minutes, at 80 g for 1 minute, and at 50 g for 2 minutes. Then, Li2CO3 was introduced into the acoustic mixer such that the ratio of the total moles of transition metals (Ni+Co+Mn) in the composite transition metal hydroxide to the moles of lithium (Li) in Li2CO3 ((Ni+Co+Mn):Li) was 1:1.05, and then mixed sequentially at 40 g (g: gravitational acceleration) for 2 minutes, at 80 g for 1 minute, and at 50 g for 2 minutes to prepare a mixture.

[0150] The mixture was introduced into a square alumina crucible (150 mm × 150 mm) and sintered for 4 hours at 850 °C in air. After continuously heating to 965 °C (heating rate: 1.3 °C / min), it was sintered for 6 hours at 965 °C. Then, after continuously cooling to 600 °C (cooling rate: 4 °C / min), it was sintered for 3 hours at 600 °C to prepare the sintered product.

[0151] The sintered product was finely ground for 10 minutes at 4 bar using an air jet mill (2-inch air jet mill, Isaac ENC).

[0152] The finely pulverized sintered product was mixed with Al2O3 (in an amount such that Al is 1500 ppm relative to the total weight of the sintered product) and WO3 (in an amount such that W is 3000 ppm relative to the total weight of the sintered product), and then heat-treated at 500°C in an air atmosphere to prepare a positive electrode active material containing an Al and W coating layer.

[0153] Example 2

[0154] A composite transition metal hydroxide in the form of secondary particles (composition: Ni) consisting of dozens to hundreds of primary particles aggregated together. 0.62 Co 0.06 Mn 0.32 (OH)2 (D50: 3.5 μm), ZrO2 (in an amount such that Zr is 1500 ppm relative to the total weight of the composite transition metal hydroxide), and Y2O3 (in an amount such that Y is 3000 ppm relative to the total weight of the composite transition metal hydroxide) were introduced into an acoustic mixer and mixed sequentially at 40 g (g: gravitational acceleration) for 2 minutes, at 80 g for 1 minute, and at 50 g for 2 minutes. Then, Li2CO3 was introduced into the acoustic mixer such that the ratio of the total moles of transition metals (Ni+Co+Mn) in the composite transition metal hydroxide to the moles of lithium (Li) in Li2CO3 ((Ni+Co+Mn):Li) was 1:1.04. The mixture was then mixed sequentially at 40 g (g: gravitational acceleration) for 2 minutes, at 80 g for 1 minute, and at 50 g for 2 minutes to prepare a mixture.

[0155] The mixture was introduced into a square alumina crucible (150 mm × 150 mm) and sintered for 4 hours at 850 °C in air. After continuously heating to 965 °C (heating rate: 1.3 °C / min), it was sintered for 6 hours at 965 °C. Then, after continuously cooling to 600 °C (cooling rate: 4 °C / min), it was sintered for 3 hours at 600 °C to prepare the sintered product.

[0156] The sintered product was finely ground for 10 minutes at 4 bar using an air jet mill (2-inch air jet mill, Isaac ENC).

[0157] The finely pulverized sintered product was mixed with Al2O3 (in an amount such that Al is 1500 ppm relative to the total weight of the sintered product) and WO3 (in an amount such that W is 3000 ppm relative to the total weight of the sintered product), and then heat-treated at 500°C in an air atmosphere to prepare a positive electrode active material containing an Al and W coating layer.

[0158] Example 3

[0159] A composite transition metal hydroxide in the form of secondary particles (composition: Ni) consisting of dozens to hundreds of primary particles aggregated together. 0.62 Co 0.06 Mn 0.32(OH)2 (D50: 3.5 μm), ZrO2 (in an amount such that Zr is 1500 ppm relative to the total weight of the composite transition metal hydroxide), and Y2O3 (in an amount such that Y is 3000 ppm relative to the total weight of the composite transition metal hydroxide) were introduced into an acoustic mixer and mixed sequentially at 40 g (g: gravitational acceleration) for 2 minutes, at 80 g for 1 minute, and at 50 g for 2 minutes. Then, Li2CO3 was introduced into the acoustic mixer such that the ratio of the total moles of transition metals (Ni+Co+Mn) in the composite transition metal hydroxide to the moles of lithium (Li) in Li2CO3 ((Ni+Co+Mn):Li) was 1:1.06, and then mixed sequentially at 40 g (g: gravitational acceleration) for 2 minutes, at 80 g for 1 minute, and at 50 g for 2 minutes to prepare a mixture.

[0160] The mixture was introduced into a square alumina crucible (150 mm × 150 mm) and sintered for 4 hours at 850 °C in air. After continuously heating to 965 °C (heating rate: 1.3 °C / min), it was sintered for 6 hours at 965 °C. Then, after continuously cooling to 600 °C (cooling rate: 4 °C / min), it was sintered for 3 hours at 600 °C to prepare the sintered product.

[0161] The sintered product was finely ground for 10 minutes at 4 bar using an air jet mill (2-inch air jet mill, Isaac ENC).

[0162] The finely pulverized sintered product was mixed with Al2O3 (in an amount such that Al is 1500 ppm relative to the total weight of the sintered product) and WO3 (in an amount such that W is 3000 ppm relative to the total weight of the sintered product), and then heat-treated at 500°C in an air atmosphere to prepare a positive electrode active material containing an Al and W coating layer.

[0163] Comparative Example 1

[0164] A composite transition metal hydroxide in the form of secondary particles (composition: Ni) consisting of dozens to hundreds of primary particles aggregated together. 0.62 Co 0.06 Mn 0.32(OH)2 (D50: 3.5 μm), ZrO2 (in an amount such that Zr is 1500 ppm relative to the total weight of the composite transition metal hydroxide), and Y2O3 (in an amount such that Y is 3000 ppm relative to the total weight of the composite transition metal hydroxide) were introduced into an acoustic mixer and mixed sequentially at 40 g (g: gravitational acceleration) for 2 minutes, at 80 g for 1 minute, and at 50 g for 2 minutes. Then, Li2CO3 was introduced into the acoustic mixer such that the ratio of the total moles of transition metals (Ni+Co+Mn) in the composite transition metal hydroxide to the moles of lithium (Li) in Li2CO3 ((Ni+Co+Mn):Li) was 1:1.05, and then mixed sequentially at 40 g (g: gravitational acceleration) for 2 minutes, at 80 g for 1 minute, and at 50 g for 2 minutes to prepare a mixture.

[0165] The mixture was introduced into a square alumina crucible (150 mm × 150 mm) and sintered for 4 hours at 850 °C in air. After continuously heating to 955 °C (heating rate: 1.3 °C / min), it was sintered for 6 hours at 955 °C. Then, after continuously cooling to 600 °C (cooling rate: 4 °C / min), it was sintered for 3 hours at 600 °C to prepare the sintered product.

[0166] The sintered product was finely ground for 10 minutes at 4 bar using an air jet mill (2-inch air jet mill, Isaac ENC).

[0167] The finely pulverized sintered product was mixed with Al2O3 (in an amount such that Al is 1500 ppm relative to the total weight of the sintered product) and WO3 (in an amount such that W is 3000 ppm relative to the total weight of the sintered product), and then heat-treated at 500°C in an air atmosphere to prepare a positive electrode active material containing an Al and W coating layer.

[0168] Comparative Example 2

[0169] A composite transition metal hydroxide in the form of secondary particles (composition: Ni) consisting of dozens to hundreds of primary particles aggregated together. 0.62 Co 0.06 Mn 0.32(OH)2 (D50: 3.5 μm), ZrO2 (in an amount such that Zr is 1500 ppm relative to the total weight of the composite transition metal hydroxide), and Y2O3 (in an amount such that Y is 3000 ppm relative to the total weight of the composite transition metal hydroxide) were introduced into an acoustic mixer and mixed sequentially at 40 g (g: gravitational acceleration) for 2 minutes, at 80 g for 1 minute, and at 50 g for 2 minutes. Then, Li2CO3 was introduced into the acoustic mixer such that the ratio of the total moles of transition metals (Ni+Co+Mn) in the composite transition metal hydroxide to the moles of lithium (Li) in Li2CO3 ((Ni+Co+Mn):Li) was 1:1.05, and then mixed sequentially at 40 g (g: gravitational acceleration) for 2 minutes, at 80 g for 1 minute, and at 50 g for 2 minutes to prepare a mixture.

[0170] The mixture was introduced into a square alumina crucible (150 mm × 150 mm) and sintered for 4 hours at 850 °C in air. After continuously heating to 975 °C (heating rate: 1.3 °C / min), it was sintered for 6 hours at 975 °C. Then, after continuously cooling to 600 °C (cooling rate: 4 °C / min), it was sintered for 3 hours at 600 °C to prepare the sintered product.

[0171] The sintered product was finely ground for 10 minutes at 4 bar using an air jet mill (2-inch air jet mill, Isaac ENC).

[0172] The finely pulverized sintered product was mixed with Al2O3 (in an amount such that Al is 1500 ppm relative to the total weight of the sintered product) and WO3 (in an amount such that W is 3000 ppm relative to the total weight of the sintered product), and then heat-treated at 500°C in an air atmosphere to prepare a positive electrode active material containing an Al and W coating layer.

[0173] Experimental Example

[0174] Experimental Example 1: Morphological Analysis of Positive Electrode Active Materials

[0175] SEM images of the positive electrode active materials prepared in Examples 1 and 3 were obtained using SEM (FEI Corporation, Inspect F). Then, the SEM image of the positive electrode active material of Example 1 was... Figure 1 The image shows the SEM image of the positive electrode active material in Example 3. Figure 2 As shown in the image.

[0176] Reference Figure 1As shown in Figure 3, the positive electrode active materials of Examples 1 and 3 are in single-particle form.

[0177] Experimental Example 2: ICP Analysis

[0178] Take 0.1 g of each sintered product prepared in the Examples and Comparative Examples (hereinafter referred to as lithium complex transition metal oxides), add 1 mL of hydrochloric acid, and then heat to dissolve the lithium complex transition metal oxides. Subsequently, to accelerate the reaction, a small amount of aqueous hydrogen peroxide solution is added to completely dissolve the lithium complex transition metal oxides, thereby preparing a solution. The solution is then diluted with deionized water to a total volume of 10 mL, thereby preparing the analytical sample. The weight ratios of the constituent elements present in the analytical sample, the composition of the lithium complex transition metal oxides, and the Zr and Y contents (ppm) present in the lithium complex transition metal oxides were measured using an ICP instrument (ICP-OES; Agilent 5110, Agilent Technologies), as shown in Table 1 below.

[0179] [Table 1]

[0180] As shown in Table 1 above, the lithium composite transition metal oxides prepared in Examples 1 to 3 are confirmed to have the composition shown in Formula 1 as described in this specification, and contain doping elements Zr and Y.

[0181] Experimental Example 3: (1) Particle size analysis of positive electrode active material

[0182] SEM images of the positive electrode active materials prepared in the examples and comparative examples were obtained by 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.

[0183] 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 based on the number of pixels corresponding to each of the n primary particles (averaging more than 50,000 primary particles). The particle size (Di=2ri) of each primary particle in the SEM image is obtained using the radius (ri) of a circle with the same area as each primary particle. The areas of primary particles with a particle size of less than 1 μm are added together to obtain the sum of the areas of primary particles with a particle size of less than 1 μm. The sum of the areas of all primary particles is then obtained. Subsequently, the small particle ratio is obtained according to Equation 1 described in this specification, as shown in Table 2 below.

[0184] Furthermore, 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 based on the number of pixels corresponding to each of the n primary particles (averaging over 50,000 primary particles). The particle size (Di = 2ri) and volume (Vi = 4 / 3 × πri³) of each primary particle in the SEM image are obtained using the radius (ri) of a circle with the same area as each primary particle. Additionally, the particle size at the 50% point of the cumulative volume distribution based on particle size is calculated, thus obtaining the D of the primary particle. v,50 The values ​​are shown in Table 2 below.

[0185] Experimental Example 4: (2) Particle size analysis of positive electrode active material

[0186] 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 the positive electrode active material using an ultrasonic instrument for 1 minute, and then analyze it in a PSA (Microtrac, S3500) to determine D. 50 As shown in Table 2 below.

[0187] At this time, D 50 It refers to the particle size at the 50% point in the cumulative volume distribution of particle size.

[0188] Experimental Example 5: Evaluation of Fine Particle Generation

[0189] 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 determine the number of particles with a diameter less than 1 μm by using PSA (Microtrac, S3500). 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 amount), as shown in Table 2 below.

[0190] Experiment Example 6: Roller Density Measurement

[0191] Take 5 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 20 mm, press it under 2 tons for 1 minute, and then measure the height of the mold after pressing. Calculate the volume of 5 g of positive electrode active material after pressing based on this height, and obtain the weight of active material per unit volume after pressing (i.e., the roll density), as shown in Table 2 below.

[0192] [Table 2]

[0193] Referring to Table 2 above, it can be confirmed that the small particle ratio of the positive electrode active materials in Examples 1 to 3 meets the range of 5% to 10%, and the D of the primary particles is...v,50 It meets the range of 2.2 μm to 3.7 μm; while the positive electrode active material of Comparative Example 1 has a small particle ratio greater than 10%, and the primary particle D v,50 Less than 2.2 μm. Furthermore, it can be confirmed that the small particle ratio of the positive electrode active material in Comparative Example 2 is less than 5%, and the primary particle size (D0.05) is less than 2.2 μm. v,50 Greater than 3.7 μm.

[0194] Generally, a lower amount of fine particles results in a smaller specific surface area between the particles and the electrolyte solution, which suppresses side reactions, improves capacity retention during charge and discharge, and reduces gas generation—all of which are advantageous. Simultaneously, a higher roll density allows for a greater amount of active material coated per unit volume during electrode manufacturing, which is also advantageous. However, since there is a trade-off between the amount of fine particles and the roll density, it is necessary to consider combining other performance factors to find the optimal conditions.

[0195] Experiment Example 7: Battery Performance Evaluation

[0196] The positive electrode active materials, FX35 conductive materials, and polyvinylidene fluoride (PVDF) binder prepared in the examples and comparative examples were mixed in N-methylpyrrolidone (NMP) solvent at a weight ratio of 95:3:2 to prepare a positive electrode slurry. The positive electrode slurry was coated onto one surface of an aluminum current collector, dried at 130°C for at least 10 minutes, and then rolled to manufacture the positive electrode.

[0197] 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 placed inside a battery case, and then an electrolyte solution is injected into the battery case 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 diethyl carbonate (DEC) in a volume ratio of 3:4:3.

[0198] Each half of the battery cell manufactured in the above manner was charged to 4.5 V at 25°C using CC-CV mode with 0.1 C, and then discharged to 2.5 V with a constant current of 0.1 C. During this process, the initial charge capacity and initial discharge capacity were measured, and the initial charge / discharge capacity, initial efficiency, and DC internal resistance (DCIR) were calculated, as shown in Table 3 below. For reference, the initial efficiency value is the percentage of the initial discharge capacity relative to the initial charge capacity, and the DCIR value is calculated by dividing the difference between the voltage at 60 seconds and the initial voltage when the cell is discharged with a constant current of 0.1 C by the applied current.

[0199] [Table 3]

[0200] Referring to Tables 2 and 3 above, the proportion of small particles in each positive electrode active material of Examples 1 to 3 is in the range of 5% to 10%, and the D of the primary particles is... v,50 The range of 2.2 μm to 3.7 μm is met. Therefore, when the battery contains the above-mentioned positive electrode active material, it performs better in terms of battery capacity, initial efficiency and resistance performance compared with the batteries containing each of the positive electrode active materials of Comparative Example 1 and Comparative Example 2.

Claims

1. A positive electrode active material, which comprises a lithium composite transition metal oxide having a composition represented by the following formula 1 and in the form of a single particle composed of 10 or fewer primary particles, in, D of the primary particles derived from SEM images v,50 The particle size is 2.2 μm to 3.7 μm, and the proportion of small particles according to Equation 1 below is 5% to 10%: [Formula 1] Li 1+x Ni a1 Co b1 Mr c1 Zr d1 Y e1 M f1 O 2-y A y wherein, in the above formula 1, M is one or more selected from W, Cu, Sr, Mn, Ti, Mg, Mo, B, Sn, Fe, Zn, Si, and Al, A is one or more selected from F, Cl, Br, I, and S, and -0.1 ≤ x ≤ 0.1, 0 < a1 < 1, 0 < b1 < 1, 0 < c1 < 1, 0 < d1 < 0.01, 0 < e1 < 0.01, 0 ≤ f1 < 0.1, 0 ≤ y ≤ 0.2, and a1 + b1 + c1 + d1 + e1 + f1 = 1, [Equation 1] Small particle ratio (%) = (Sum of the areas of primary particles with a particle size of 1 μm or less obtained from the SEM image / Sum of the areas of all primary particles obtained from the SEM image) × 100.

2. The positive electrode active material as described in claim 1, wherein, D of the primary particles derived from SEM images v,50 The thickness ranges from 2.5 μm to 2.8 μm.

3. The positive electrode active material as described in claim 1, wherein, The D of the positive electrode active material was measured using a particle size analyzer (PSA). 50 The thickness ranges from 3.5 μm to 4 μm.

4. The positive electrode active material as described in claim 1, wherein, The lithium composite transition metal oxide is doped with 1000 ppm to 4000 ppm of Zr and 1000 ppm to 4000 ppm of Y.

5. The positive electrode active material as described in claim 1, wherein, The positive electrode active material further comprises a coating layer formed on the lithium composite transition metal oxide, wherein the coating layer comprises Al, W, or a combination thereof.

6. A positive electrode, which comprises the positive electrode active material according to any one of claims 1 to 5.

7. A lithium secondary battery, which comprises: The positive electrode according to claim 6; A negative electrode; A separator disposed between the positive electrode and the negative electrode; and An electrolyte.

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