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

Abstract

The present invention relates to a positive electrode active material, a positive electrode containing the same, and a lithium secondary battery, wherein the lithium transition metal oxide particles are in single-particle form, the lithium transition metal oxide having an average sphericity of 0.70 or more according to Formula 1 described herein, and the electrode containing the lithium transition metal oxide has an average sphericity of 0.70 or more according to Formula 1 described herein when the electrode is rolled to a porosity of 20%.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2023-0043516 dated April 3, 2023, and all content disclosed in the said Korean Patent Application is incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material for lithium secondary batteries, a positive electrode containing the same, and a lithium secondary battery. [Background technology]

[0003] In recent years, with the rapid proliferation of electronic devices using batteries, such as mobile phones, laptop computers, and electric vehicles, the demand for small, lightweight, and relatively high-capacity rechargeable batteries has been rapidly increasing. In particular, lithium-ion batteries are attracting attention as a power source for portable devices due to their light weight and high energy density. Therefore, research and development and efforts to improve the performance of lithium-ion batteries are being actively pursued.

[0004] In a lithium secondary battery, an organic electrolyte or polymer electrolyte is filled between a positive electrode and a negative electrode, both made of an active material capable of lithium ion intercalation and deintercalation. Electrical energy is produced by oxidation and reduction reactions during lithium ion intercalation / deintercalation at the positive and negative electrodes.

[0005] Lithium-ion rechargeable batteries utilize lithium cobalt oxide (LiCoO2), nickel-based lithium transition metal oxides, lithium manganese oxide (LiMnO2 or LiMn2O4, etc.), and lithium iron phosphate compounds (LiFePO4) as positive electrode active materials. Among these, lithium cobalt oxide (LiCoO2) is widely used due to its advantages of high operating voltage and excellent capacity characteristics, and is applied as a positive electrode active material for high voltage applications. However, due to rising cobalt (Co) prices and unstable supply, there are limitations to its large-scale use as a power source in fields such as electric vehicles, increasing the need for the development of alternative positive electrode active materials.

[0006] Therefore, nickel-based lithium transition metal oxides, such as nickel-cobalt-manganese lithium transition metal oxides, have been developed in which some of the cobalt (Co) is replaced with nickel (Ni).

[0007] On the other hand, conventionally developed nickel-based lithium transition metal oxides have a fine (micro) average particle size (D 50 This is a form of secondary particles formed by the aggregation of fine primary particles having a large surface area and low particle strength. Therefore, when an electrode is manufactured using a positive electrode active material containing secondary particles formed by the aggregation of fine primary particles and then rolled, there is a problem of severe particle cracking, high gas generation during cell operation, and poor stability. In particular, high-content nickel-based (High-Ni) lithium transition metal oxides, in which the nickel (Ni) content is increased to ensure high capacity, have further reduced chemical stability and it is difficult to ensure thermal stability due to the aforementioned structural problems.

[0008] To improve upon the shortcomings of the aforementioned conventional nickel-based lithium transition metal oxides in the form of aggregated secondary particles, the average particle size (D 50 Nickel-based lithium transition metal oxide cathode active materials have been proposed that are in a secondary particle form in which large macro-primary particles are aggregated.

[0009] The nickel-based lithium transition metal oxide cathode active material in the form of secondary particles in which macro primary particles are aggregated has minimized interfaces of the secondary particles, and problems such as thermal stability, lifetime degradation due to side reactions during electrochemical reactions, and gas generation are improved.

[0010] On the other hand, a high-content nickel-based (High-Ni) lithium transition metal oxide cathode active material usually undergoes a water washing process in order to reduce the content of lithium impurities remaining on the surface. Such a water washing process is advantageous for reducing gas generation since it removes lithium by-products on the surface, but it is disadvantageous in terms of lifetime due to surface damage of the cathode active material particles. In particular, the nickel-based lithium transition metal oxide cathode active material in the form of secondary particles in which macro primary particles are aggregated has a problem of inherently inferior lifetime characteristics, but the lifetime characteristics further deteriorate after undergoing the water washing process, and the resistance increases as charge and discharge proceed.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0012] An object of the present invention is to provide a lithium secondary battery with a reduced gas generation amount and improved energy density by developing a cathode active material having a single particle form and suppressed particle cracking.

Means for Solving the Problems

[0013] In order to solve the above problems, the present invention provides a cathode active material, a cathode, and a lithium secondary battery.

[0014] (1) The present invention provides a positive electrode active material comprising lithium transition metal oxide particles in single-particle form, wherein the lithium transition metal oxide has an average sphericity of 0.7 or more according to the following formula 1, and when the electrode containing the lithium transition metal oxide is rolled to have a porosity of 20%, the average sphericity of 0.7 or more according to the following formula 1 is provided.

[0015]

number

[0016] In the above formula 1, A is the area of ​​lithium transition metal oxide particles [μm²] 2 ] and P is the circumference [μm] of the lithium transition metal oxide particle.

[0017] (2) The present invention provides the positive electrode active material described in (1) above, wherein the lithium transition metal oxide has a ratio of 42% or more of particles with a sphericity of 0.7 to 0.8 according to formula 1 to the total number of particles of the lithium transition metal oxide.

[0018] (3) The present invention provides a positive electrode active material according to (1) or (2) above, wherein the lithium transition metal oxide has a ratio of 10% or more of particles with a sphericity of 0.8 to 0.9 according to Formula 1 to the total number of particles of the lithium transition metal oxide.

[0019] (4) The present invention provides a positive electrode active material according to any one of (1) to (3) above, wherein when an electrode containing the lithium transition metal oxide is rolled to have a porosity of 20%, the ratio of the number of particles with a sphericity of 0.7 to 0.8 according to formula 1 to the total number of lithium transition metal oxide particles contained in the electrode is 40% or more.

[0020] (5) The present invention provides a positive electrode active material according to any one of (1) to (4) above, wherein when an electrode containing the lithium transition metal oxide is rolled to have a porosity of 20%, the ratio of the number of particles with a sphericity of 0.8 to 0.9 according to formula 1 to the total number of lithium transition metal oxide particles contained in the electrode is 15% or more.

[0021] (6) The present invention relates to a lithium transition metal oxide having an average particle size (D 50 The present invention provides a positive electrode active material according to any one of (1) to (5) above, wherein the diameter of the ) is 1.5 μm or more and 6 μm or less.

[0022] (7) The present invention provides a positive electrode active material according to any one of (1) to (6) above, wherein the lithium transition metal oxide is represented by the following chemical formula 1.

[0023] [Chemical formula 1] Li(Ni) 1-x-y-z Co x Mn y M z )O2

[0024] In the above chemical formula 1, M is one or more elements selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and x, y, and z are the atomic fractions of independent elements, where 0 <x≦0.25、0<y≦0.25、0≦z<0.1、0<x+y+z≦0.5である。

[0025] (8) The present invention provides a positive electrode for a lithium secondary battery comprising the positive electrode active material described in any one of (1) to (7) above.

[0026] (9) The present invention provides a lithium secondary battery including the positive electrode described in (8) above. [Effects of the Invention]

[0027] The single-particle positive electrode active material produced by the present invention has high sphericity and single-particle degree, and the phenomenon of fine particle generation due to particle fracture is reduced. When used as a positive electrode active material in a lithium secondary battery, it reduces the gas generation phenomenon of the battery and can significantly improve the battery life. [Brief explanation of the drawing]

[0028] [Figure 1] This is a segmentation image of the cross-section of the positive electrode containing the positive electrode active material manufactured in Example 1. [Figure 2] This is a segmentation image of the cross-section of the positive electrode containing the positive electrode active material manufactured in Example 2. [Figure 3] This is a segmentation image of the cross-section of the positive electrode containing the positive electrode active material manufactured in Comparative Example 1. [Figure 4] This graph shows the percentage [%] of the number of particles based on sphericity according to Formula 1 described herein, relative to the total number of lithium transition metal oxide particles in the positive electrode active materials produced in Example 1, Example 2, and Comparative Example 1. [Figure 5] This graph shows the ratio [%] of the number of lithium transition metal oxide particles to the total number of lithium transition metal oxide particles contained in the electrode, based on the sphericity according to Formula 1 described herein, when the electrode containing lithium transition metal oxide was rolled to a porosity of 20% in the positive electrode active material produced in Example 1, Example 2, and Comparative Example 1. [Figure 6] Figures 6(A) and 6(B) are SEM images of the cathode active materials produced in Example 1 and Comparative Example 1, respectively. [Figure 7] Figures 7(A) to 7(C) are SEM images of the cathode active materials produced in Example 1, Example 2, and Comparative Example 1, respectively. [Figure 8] This graph shows the amount of gas generated (ml) over time (weeks) in batteries containing the positive electrode active material produced in Example 1, Example 2, and Comparative Example 1. [Modes for carrying out the invention]

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

[0030] In the description and claims of the present invention, terms and words used should not be construed as being limited to their ordinary or dictionary meanings. The inventors should interpret them in accordance with the meaning and concept consistent with the technical idea of the present invention, following the principle that they can appropriately define the concept of the terms in order to explain their invention in the best way possible.

[0031] Hereinafter, the present invention will be described in detail.

[0032] In the present invention, "primary particle" means the smallest particle unit that can be distinguished as one lump when observing the cross-section of the positive electrode active material with a scanning electron microscope (SEM). It may consist of one crystal grain or a plurality of crystal grains. In the present invention, the average particle size (Dv 50 ) may be measured using a scanning electron microscope (SEM) (JEOL, JSM-7900F). Specifically, in the particle size distribution curve (graph curve of particle size distribution degree) of each particle obtained using a scanning electron microscope (SEM), it can be defined as the particle size corresponding to 50% of the volume cumulative distribution. After taking the volume of a sphere with a radius equal to half of the particle size of the primary particle obtained using a scanning electron microscope (SEM) as the volume of the primary particle, it can be measured by calculating the particle size at the location where the volume cumulative distribution by particle size becomes 50% in the result of calculating the volume of the primary particle. In the present invention, the particle size of the primary particle may be calculated by calculating the area of each primary particle from the number of pixels corresponding to each of the n primary particles present in the SEM image, and using the radius of a circle having the same area as the area of each primary particle to calculate the particle size of each primary particle present on the SEM image.

[0033] In the present invention, "single particle" is a term used to distinguish it from positive electrode active material particles in the form of secondary particles formed by the aggregation of tens to hundreds of primary particles, which have been commonly used in the past. The term encompasses both single particles consisting of one primary particle and aggregate particles of 50 or fewer primary particles.

[0034] In this invention, "average particle size (D 50 The average particle size (D) can be defined as the particle size at the 50% reference level of the volume cumulative particle size distribution and can be measured by the laser diffraction method. Specifically, the average particle size (D) 50 ) After dispersing the target particles in a dispersion medium, they are introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000) and irradiated with ultrasound at approximately 28 kHz with an output of 60 W, and the average particle size (D) at the 50% reference level of the cumulative particle volume distribution by particle size measured by the analyzer is determined. 50 It is possible to calculate ).

[0035] In this invention, "degree of single particle formation" is the average particle size (Dv) of the primary particles that make up the single particle. 50 ), and the average particle size (D) of lithium transition metal oxides which are single particles. 50 This value is adjusted by the average particle size (Dv) of the primary particles that make up the lithium transition metal oxide. 50 ) is the average particle size (D) of lithium transition metal oxides. 50 The closer it is to ), the higher the degree of single-particle separation.

[0036] In this invention, "single crystal" refers to a crystal in which no grain boundaries are present within the particles.

[0037] In this invention, the "area of ​​lithium transition metal oxide particles" and the "perimeter of lithium transition metal oxide particles" can be determined by irradiating the positive electrode with an argon (Ar) ion beam using an ion milling device (JEOL, CP-09IB19520CCP, acceleration voltage: 6kV), cutting the positive electrode using the ion milling method to obtain a cross-section of the positive electrode, taking a scanning electron microscope (SEM) image of the cross-section of the positive electrode, and then performing image processing on the image. Specifically, these can be measured from a two-dimensional segmentation image, partitioned into particle units, obtained by image processing with an image processing program. The segmentation image can be obtained by manufacturing a positive electrode containing the positive electrode active material to be measured, cutting the positive electrode using the ion milling method to obtain a cross-section of the positive electrode, acquiring a scanning electron microscope (SEM) image of the cross-section, inputting the acquired scanning electron microscope image into a deep learning program, identifying multiple objects contained in the image, and then segmenting the SEM image into particle units based on the multiple objects. The "area of ​​lithium transition metal oxide particles" may be calculated using the number of pixels corresponding to each of the n particles present in the segmentation image, and the "perimeter of lithium transition metal oxide particles" may be calculated using the length of the outermost shell boundary corresponding to each of the n particles present in the segmentation image.

[0038] positive electrode active material The positive electrode active material according to the present invention will be described below.

[0039] The positive electrode active material of the present invention contains lithium transition metal oxide particles in single-particle form, wherein the lithium transition metal oxide has an average sphericity of 0.7 or more according to the following formula 1, and is characterized in that when the electrode containing the lithium transition metal oxide is rolled to have a porosity of 20%, the average sphericity of 0.7 or more according to the following formula 1.

[0040]

number

[0041] In the above formula 1, A is the area of ​​lithium transition metal oxide particles [μm²] 2 ] and P is the circumference [μm] of the lithium transition metal oxide particle.

[0042] The lithium transition metal oxide is in a single-particle form consisting of 50 or fewer primary particles. That is, the lithium transition metal oxide is a single particle or a single-particle form in which 2 to 50 particles are aggregated. Specifically, it may be in a form consisting of 2 to 40, 2 to 30, 2 to 20, or 2 to 10 primary particles, preferably 2 to 10. The single-particle form is distinguished from secondary particles in which more than 50 primary particles are aggregated.

[0043] Lithium transition metal oxides, which are secondary particles, are prone to particle cracking during the electrode rolling process. This increases the specific surface area of ​​the active material, leading to a significant decrease in storage performance and lifespan at high temperatures. In particular, lithium metal oxides with a high nickel content are even more susceptible to particle cracking during the rolling process for manufacturing the positive electrode. In this case, side reactions between the lithium metal oxide and the electrolyte increase, potentially degrading the physical properties of the secondary battery.

[0044] This invention improves upon the problems that arise with lithium transition metal oxides in secondary particle form, as described above, by developing lithium transition metal oxides in single-particle form. In particular, the performance of single-particle positive electrode active materials varies greatly depending on the shape of each particle, especially its sphericity. For example, the more spherical a single particle is, the more effectively particle cracking can be suppressed when the single particle is rolled during electrode manufacturing. Therefore, the lithium transition metal oxide particles contained in the positive electrode active material of this invention have a high level of sphericity, thus maintaining a single-particle form while suppressing particle cracking, and enabling excellent high-temperature life characteristics and high-temperature storage performance when used in lithium secondary batteries.

[0045] Specifically, in this invention, the concept of sphericity of lithium transition metal oxides is used to evaluate and quantitatively indicate the degree of particle cracking before and after rolling of lithium transition metal oxides. Sphericity as defined in this invention is a concept used to confirm how close lithium transition metal oxide particles are to a spherical shape, and is calculated by the following formula 1.

[0046]

number

[0047] In the above formula 1, A is the area of ​​lithium transition metal oxide particles [μm²] 2 ] and P is the circumference [μm] of the lithium transition metal oxide particle.

[0048] The sphericity calculated using Equation 1 can be evaluated from the perimeter and area of ​​the lithium transition metal oxide particles, which are calculated from the cross-section of the particles.

[0049] Specifically, after manufacturing an electrode (positive electrode) containing a positive electrode active material containing lithium transition metal oxide particles, the electrode is cut by an ion milling method to obtain a cross-section of the positive electrode, an SEM image of the cross-section of the positive electrode is obtained using an SEM, and the sphericity can be calculated from the area and circumference of the lithium transition metal oxide particles calculated using an image processing program.

[0050] If lithium transition metal oxide particles are perfectly spherical, the sphericity according to Equation 1 is 1. If they deviate from a spherical shape, the perimeter of the particle relative to its area will be longer, and therefore the sphericity value will be less than 1. In other words, the sphericity value is greater than 0 and less than or equal to 1, and the closer the sphericity is to 1, the more similar the particle's shape is to a sphere.

[0051] The lithium transition metal oxide contained in the positive electrode active material of the present invention has an average sphericity of 0.7 or higher according to Formula 1, and when the electrode containing the lithium transition metal oxide is rolled to have a porosity of 20%, the average sphericity of 0.7 or higher according to Formula 1 is obtained.

[0052] In the present invention, the lithium transition metal oxide has an average sphericity of 0.7 or higher, calculated by formula 1. Specifically, the average sphericity may be 0.7 or higher, 0.71 or higher, 0.72 or higher, 0.73 or higher, 0.74 or higher, or 0.75 or higher, and may be 0.8 or lower, 0.9 or lower, or 1 or lower. This means that the sphericity values ​​of the lithium transition metal oxide particles are generally high and show a high average, and since the positive electrode active material of the present invention is manufactured by a solid-phase synthesis method, the firing temperature can be lowered compared to positive electrode active materials manufactured by over-firing using conventional precursors. If the firing temperature is high, the pulverization process after firing is carried out at high pressure, which increases the particle cracking phenomenon and lowers the sphericity. In addition, positive electrode active materials using precursors manufactured by over-firing have low sphericity because they clump together in areas where temperature deviations occur. However, in this invention, since particles are formed and grown using raw material powder without using a precursor, a low calcination temperature is used, the grinding pressure is low, and the particles exhibit high sphericity.

[0053] Furthermore, the lithium transition metal oxide has an average sphericity of 0.7 or higher when the electrode containing the lithium transition metal oxide is rolled to a porosity of 20%. Specifically, the average sphericity may be 0.7 or higher, 0.71 or higher, 0.72 or higher, 0.73 or higher, or 0.74 or higher, and may be 0.8 or lower, 0.9 or lower, or 1 or lower.

[0054] The aforementioned porosity (20%) is calculated using the ratio of the electrode density to the total true density of the solid content of the positive electrode active material.

[0055] Specifically, the manufactured positive electrode active material, carbon black conductive material, and PVdF binder were mixed in an N-methylpyrrolidone solvent in a weight ratio of 95:2:3 to produce a positive electrode composite material (viscosity: 5000 mPa·S). This composite material was then applied to one surface of an aluminum current collector and dried at 130°C to produce the positive electrode. In this process, the porosity of the positive electrode active material layer in the positive electrode was 30% or more, and the porosity of the positive electrode active material layer was adjusted by rolling to a thickness that satisfies the porosity calculated by the following mathematical formula 1.

[0056] [Mathematical formula 1] Porosity (P) = [(True density of positive electrode active material layer (T) - Positive electrode density (D)) / True density of positive electrode active material layer (T)] × 100

[0057] After punching out each positive electrode to a size of 14φ, the mass and thickness of each punched-out positive electrode were measured, and these were used as the mass (M) and thickness (H) of the positive electrode active material layer by subtracting the mass and thickness of the aluminum current collector.

[0058] The density (D) of each positive electrode was calculated by dividing the mass (M) of the positive electrode active material layer by (positive electrode area (S) × thickness (H) of the positive electrode active material layer) (D = M / (S × H)).

[0059] The true density (T) of each positive electrode active material layer was obtained from the sum of the ratio of each component in the positive electrode composite material and the true density of each component (T = [(0.95 × true density of positive electrode active material) + (0.02 × true density of carbon black conductive material) + (0.03 × true density of PVDF binder)]).

[0060] When an electrode containing a lithium transition metal oxide is rolled to a porosity of 20%, the average sphericity calculated by formula 1 being 0.7 or higher indicates that the decrease in sphericity due to particle cracking after rolling is significantly reduced in the lithium transition metal oxide. Thus, the positive electrode active material of the present invention suppresses particle cracking, reduces the content of lithium by-products, and suppresses side reactions with the electrolyte. Furthermore, it enables the realization of excellent physical properties such as high-temperature life characteristics and storage performance in lithium secondary batteries.

[0061] As described above, the positive electrode active material of the present invention was evaluated by its sphericity when an electrode containing a lithium transition metal oxide was rolled to a porosity of 20%. However, the magnitude of the pressure is similar to the magnitude of the pressure used in the rolling process during the manufacture of the positive electrode, and can be understood as a clearer standard for evaluating the particle cracking phenomenon when used in a lithium secondary battery.

[0062] In this invention, the ratio (S) of the number of particles whose sphericity according to formula 1 is a constant value (y) to the total number of lithium transition metal oxide particles is defined as follows: x、y This defines the number of particles whose sphericity is constant relative to the total number of lithium transition metal oxide particles contained in the positive electrode active material of the present invention. More specifically, it represents the number of particles whose sphericity is constant relative to the total number of lithium transition metal oxide particles contained in the electrode when manufacturing an electrode using the positive electrode active material.

[0063] In the present invention, the lithium transition metal oxide may have a ratio of 42% or more of particles with a sphericity of 0.7 to 0.8 according to Formula 1 to the total number of particles of the lithium transition metal oxide, more specifically, 42% or more, 42.5% or more, 43.0% or more, or 43.8% or more, and may be 70% or less, 60% or less, 50% or less, or 45% or less.

[0064] In the present invention, the lithium transition metal oxide may have a ratio of 10% or more of particles with a sphericity of 0.8 to 0.9 according to Formula 1 to the total number of particles of the lithium transition metal oxide, more specifically, 10% or more, 15% or more, 20% or more, 25% or more, or 30% or more, and 70% or less, 60% or less, 50% or less, or 40% or less.

[0065] When lithium transition metal oxides have a sphericity within the above range, there are advantages such as less particle cracking during the rolling process for manufacturing electrodes, resulting in a longer lifespan for the positive electrode active material, suppressed side reactions with the electrolyte during cell operation, and reduced gas generation.

[0066] In the present invention, when an electrode containing the lithium transition metal oxide is rolled to have a porosity of 20%, the ratio of the number of particles with a sphericity of 0.7 to 0.8 according to formula 1 to the total number of lithium transition metal oxide particles contained in the electrode may be 40% or more, more specifically 40% or more, 41% or more, 42% or more, or 42.5% or more, and 70% or less, 60% or less, or 55% or less.

[0067] In the present invention, when an electrode containing the lithium transition metal oxide is rolled to have a porosity of 20%, the ratio of the number of particles with a sphericity of 0.8 to 0.9 according to formula 1 to the total number of lithium transition metal oxide particles contained in the electrode may be 15% or more, more specifically 15% or more, 16% or more, 20% or more, or 25% or more, and may be 70% or less, 60% or less, 50% or less, or 40% or less.

[0068] A significant change in sphericity to a low range after the electrode rolling process can be interpreted as the occurrence of particle cracking. In contrast, the single-particle positive electrode active material of the present invention shows no significant change in sphericity after the rolling process, indicating that particle cracking is suppressed.

[0069] In the present invention, the lithium transition metal oxide has an average particle size (D 50 The size of the septum may be 1.5 μm or more and 6 μm or less, specifically 2 μm or more, 3 μm or more, or 3.5 μm or more, and 6 μm or less, 5 μm or less, or 4.5 μm or less.

[0070] The positive electrode active material of the present invention has the advantage of having a single-particle form, which suppresses particle cracking and reduces gas generation compared to conventional secondary particles in which primary particles are aggregated. Furthermore, by having the average particle size of the lithium transition metal oxide within the above range, side reactions and gas generation due to an increase in specific surface area can be reduced, and the degeneration of the positive electrode active material can be prevented. In addition, the capacity reduction that occurs when the size of the lithium transition metal oxide becomes larger than an appropriate level can also be suppressed.

[0071] In the present invention, the primary particles are defined as having an average particle size (Dv 50 The diameter may be 1.5 μm or larger, specifically 2 μm or larger, 3 μm or larger, or 3.5 μm or larger, and 6 μm or smaller, 5 μm or smaller, or 4.5 μm or smaller.

[0072] The lithium transition metal oxide contained in the positive electrode active material of the present invention has an average particle size (Dv) within the above range. 50 By consisting of primary particles having ), particle strength is increased, particle cracking during rolling can be suppressed, rolling density can be improved, lithium by-products are reduced, and the amount of gas generated by side reactions with the electrolyte can be reduced.

[0073] In the present invention, the lithium transition metal oxide may be represented by the following chemical formula 1.

[0074] [Chemical formula 1] Li(Ni) 1-x-y-z Co x Mn y M z )O2

[0075] In the aforementioned chemical formula 1, M is one or more elements selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo. x, y, and z are the atomic fractions of independent elements, and 0 <x≦0.25、0<y≦0.25、0≦z<0.1、0<x+y+z≦0.5である。

[0076] M is an element substituted for a transition metal site in the oxide represented by Chemical Formula 1, and may include at least one selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo.

[0077] 1 - x - y - z represents the molar ratio of nickel among the metal components excluding lithium in the lithium transition metal oxide represented by Chemical Formula 1, and 0.5 ≦ 1 - x - y - z < 1, preferably 0.8 ≦ 1 - x - y - z ≦ 0.95.

[0078] x represents the molar ratio of cobalt among the metal components excluding lithium in the lithium transition metal oxide represented by Chemical Formula 1, and 0 < x ≦ 0.25, preferably 0.025 ≦ x ≦ 0.1.

[0079] y represents the molar ratio of manganese among the metal components excluding lithium in the lithium transition metal oxide represented by Chemical Formula 1, and 0 < y ≦ 0.25, preferably 0.005 ≦ y ≦ 0.1.

[0080] z represents the molar ratio of M among the metal components excluding lithium in the lithium transition metal oxide represented by Chemical Formula 1, and 0 ≦ z < 0.1, preferably 0 ≦ z ≦ 0.02.

[0081] Further, the positive electrode active material may further include a coating layer formed on the surface, and the coating layer may preferably contain B (boron).

[0082] The coating layer can block the contact between the positive electrode active material and the electrolyte contained in the lithium secondary battery, suppress the occurrence of side reactions, further improve the life characteristics, and increase the packing density of the positive electrode active material.

[0083] The coating layer may be formed over the entire surface of the positive electrode active material or partially. Specifically, when the coating layer is partially formed on the surface of the positive electrode active material, it may cover 20% or more but less than 100% of the total specific surface area of ​​the positive electrode active material. When the specific surface area of ​​the coating layer is less than 20%, the effect of improving lifespan characteristics and packing density due to the formation of the coating layer is minimal.

[0084] Furthermore, the positive electrode active material of the present invention can be manufactured by the steps of: (S1) preparing a solid-phase raw material mixture containing lithium raw material powder, nickel raw material powder, cobalt raw material powder, and manganese raw material powder such that the molar ratio of lithium to all transition metals is 0.90 to 1.10; (S2) first firing the solid-phase raw material mixture and then crushing it to produce a primary firing product; and (S3) mixing lithium raw material powder into the primary firing product such that the total molar ratio of lithium to all transition metals is 0.95 to 1.10, and then performing a secondary firing.

[0085] In the above method, the secondary firing temperature may be 500-900°C, 600-850°C, or 700-800°C.

[0086] Furthermore, in step (S1), the solid-phase raw material mixture may further contain M raw material powder (wherein M is one or more selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo).

[0087] The lithium transition metal oxide of the present invention is produced by a solid-phase synthesis method using a solid-phase raw material mixture. The solid-phase synthesis method has the advantage of enabling mass production through a relatively simple synthesis process, and is particularly advantageous for the production of high-content nickel NCM with a high nickel content.

[0088] Furthermore, the grinding and mixing process results in smaller and more uniformly mixed raw material particles, allowing for smoother particle growth at lower temperatures and enabling superior single-particle formation and sphericity.

[0089] In contrast, when a process is used in which a positive electrode active material precursor is prepared first and then used to manufacture a single-particle positive electrode active material slurry, the particle growth may not proceed smoothly, resulting in insufficient single-particle formation. This necessitates an over-calcination process, which may lead to a decrease in battery capacity during use due to reasons such as the formation of a rock salt phase. Furthermore, secondary particle morphologies based on the precursor will coexist, making it impossible to achieve the desired degree of sphericity and single-particle formation in this invention.

[0090] In the present invention, the lithium raw material powder may be, for example, a lithium-containing carbonate (e.g., lithium carbonate), a lithium-containing hydrate (e.g., lithium hydroxide hydrate (LiOH·H2O)), a lithium-containing hydroxide (e.g., lithium hydroxide), a lithium-containing nitrate (e.g., lithium nitrate (LiNO3)), or a lithium-containing chloride (e.g., lithium chloride (LiCl)). Preferably, the first lithium raw material substance may be one or more selected from the group consisting of lithium hydroxide, lithium hydroxide hydrate, and lithium carbonate.

[0091] In the present invention, nickel raw material powder means a raw material powder containing only nickel in order to provide nickel as a transition metal. The nickel raw material powder may be at least one selected from the group consisting of nickel oxide, nickel carbonate, nickel sulfate, nickel hydroxide, nickel phosphate, and nickel nitrate.

[0092] The cobalt raw material powder may be at least one selected from the group consisting of cobalt oxide, cobalt carbonate, cobalt sulfate, cobalt hydroxide, and cobalt phosphate.

[0093] The manganese raw material powder may be at least one selected from the group consisting of manganese dioxide, manganese carbonate, manganese sulfate, and manganese nitrate.

[0094] In the solid-phase raw material mixture produced in step (S1), lithium raw material powder, nickel raw material powder, cobalt raw material powder, and manganese raw material powder are mixed so that the molar ratio of lithium to the total transition metals is 0.90 to 1.10.

[0095] If the molar ratio of lithium is less than 0.90, problems may occur in the formation of the composite transition metal phase by solid-phase synthesis, potentially leading to lithium deficiency, decreased discharge efficiency, and a significant increase in surface resistance. If the mixed molar ratio exceeds 1.10, the residual lithium may increase, potentially leading to a decrease in the performance of the positive electrode active material.

[0096] The molar ratio of lithium is a condition controlled to produce a positive electrode active material with excellent performance, having a single-particle form with a high degree of single-particle formation as in the present invention, and without excessive residual lithium.

[0097] In the present invention, a primary calcined product is produced by first calcining the solid-phase raw material mixture and then grinding it.

[0098] The primary firing may be performed at a temperature of 400 to 900°C. When the primary firing temperature is within the above range, it is possible to prevent the reactivity of the lithium raw material powder and the respective transition metal raw material powders in the solid phase raw material mixture from being low, which can lead to an increase in unreacted residual lithium, or to prevent a shortage of lithium inside the positive electrode active material, which can reduce the battery capacity and lifespan. Furthermore, it is possible to suppress localized over-firing phenomena caused by non-uniform reactions during primary firing, which can degrade the performance of the positive electrode active material and reduce the battery capacity and lifespan.

[0099] In the present invention, the solid-phase raw material mixture is first calcined and then pulverized. By pulverizing, the average particle size (D) of the first calcined product is reduced. 50The particle size can be adjusted to 2-4 μm or 3-4 μm, and the maximum particle size (Dmax) can be adjusted to 30 μm or less or 20 μm or less. Such a grinding process is advantageous in producing the positive electrode active material in the form of single particles of a desired size, and ultimately single particles with a uniform composition can be produced.

[0100] The positive electrode active material of the present invention can be produced by mixing lithium raw material powder into the primary calcined product such that the total molar ratio of lithium to all transition metals is 0.95 to 1.10, and then performing a secondary calcination.

[0101] If the total molar ratio of lithium to the transition metal is less than 0.95 after mixing the lithium raw material powder, problems may occur in the formation of the composite transition metal phase by solid-phase synthesis, potentially leading to lithium deficiency, decreased discharge efficiency, and a significant increase in surface resistance. Furthermore, if the total molar ratio of lithium exceeds 1.10, the residual lithium may increase, potentially leading to a decrease in the performance of the positive electrode active material.

[0102] Furthermore, as in the present invention, in order to produce a positive electrode active material in the form of a single particle with high sphericity, the particles can be packed so that the packing density during firing is 0.7 cc / g or more. When the packing density increases, the distance between particles decreases during firing, which can facilitate particle reaction and growth. In addition, an appropriate lithium molar ratio has a flux effect, which can induce the formation of a highly spherical shape even when firing at low temperatures.

[0103] In this invention, the secondary firing temperature may be 500-900°C, 600-850°C, or 700-800°C. The secondary firing time may be 3-15 hours or 5-12 hours.

[0104] By performing secondary calcination within the above range, thermal energy and additional lithium raw materials can be replenished as needed, compensating for the lack of particle growth during primary calcination. Fine particles generated in the grinding process are grown and absorbed, enabling the production of a positive electrode active material with a suitable particle size and a low crack particle ratio.

[0105] In the present invention, the firing may be carried out in an oxygen or air atmosphere. When firing is carried out in the aforementioned atmosphere, the local oxygen partial pressure increases, improving the crystallinity of the positive electrode active material and making it easier to control the surface phase. In contrast, when firing is carried out in a non-oxidizing atmosphere or an inert gas atmosphere instead of the aforementioned atmosphere, the crystallinity decreases due to the desorption of oxygen during firing, and the surface phase is formed unevenly, making it difficult to control the phase present on the surface.

[0106] Furthermore, the present invention may further include the step of forming a coating layer. Preferably, the coating layer may contain elements such as B or Co, but is not limited to these.

[0107] For example, the coating element may form a coating layer on the surface of the positive electrode active material by heat treatment.

[0108] The heat treatment for forming the coating layer may be performed within a temperature range suitable for the coating material to be applied to the surface of the positive electrode active material, specifically, between 100 and 800°C.

[0109] Furthermore, the present invention provides a positive electrode for a lithium secondary battery containing the positive electrode active material.

[0110] Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector and containing the positive electrode active material.

[0111] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector usually has a thickness of 3 to 500 μm, and the adhesion strength of the positive electrode active material may be increased by forming fine irregularities on the surface of the current collector. For example, various forms such as films, sheets, foils, meshes, porous materials, foams, and nonwoven fabrics are possible.

[0112] The positive electrode active material layer may contain a conductive material and a binder together with the positive electrode active material.

[0113] In this case, the positive electrode active material may be included in an amount of 80 to 99% by weight, more specifically 85 to 98% by weight, relative to the total weight of the positive electrode active material layer. When included within the above content range, excellent capacity characteristics can be observed.

[0114] In this case, the conductive material is used to impart conductivity to the electrodes and can be used in the constructed battery without any particular limitations, as long as it does not cause a chemical change and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these may be used alone, or a mixture of two or more. The conductive material may be included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0115] The binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or as a mixture of two or more. The binder may be included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0116] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except that the positive electrode active material is used. Specifically, the positive electrode composite material, which is prepared by dissolving or dispersing the positive electrode active material and, selectively, a binder and a conductive material in a solvent, can be applied to a positive electrode current collector, followed by drying and rolling. In this case, the types and contents of the positive electrode active material, binder, and conductive material are as described above.

[0117] The solvent can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone, or a mixture of two or more. The amount of solvent used should be sufficient to dissolve or disperse the cathode active material, conductive material, and binder, and to have a viscosity that allows for excellent thickness uniformity during subsequent coating for cathode manufacturing, taking into account the coating thickness and production yield of the slurry.

[0118] Alternatively, the positive electrode may be manufactured by casting the positive electrode composite onto another support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0119] Furthermore, the present invention can be used to manufacture an electrochemical element including the positive electrode. Specifically, the electrochemical element may be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0120] The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, a separator interposed between the positive and negative electrodes, and an electrolyte. As the positive electrode is as described above, a detailed explanation will be omitted, and only the other components will be described in detail below.

[0121] Furthermore, the lithium secondary battery may selectively further include a battery container for housing the electrode assembly comprising the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0122] In the lithium secondary battery described above, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0123] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The negative electrode current collector usually has a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, the bonding force of the negative electrode active material may be strengthened by forming fine irregularities on the surface of the current collector. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0124] The negative electrode active material layer selectively includes a binder and a conductive material together with the negative electrode active material.

[0125] As the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. β Examples include lithium-doped and dedoped metal oxides such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites; any one or more mixtures of these can be used. A metallic lithium thin film may also be used as the negative electrode active material. As for the carbon material, both low-crystallinity carbon and high-crystallinity carbon can be used. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0126] The negative electrode active material may be present in an amount of 80% to 99% by weight relative to the total weight of the negative electrode active material layer.

[0127] The binder is a component that helps to bond the conductive material, the active material, and the current collector, and is usually added in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0128] The conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, specifically 5% by weight or less, relative to the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive, and may be used, for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0129] For example, the negative electrode active material layer may be manufactured by coating a negative electrode composite material, which is prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and then drying it; or it may be manufactured by casting the negative electrode composite material onto another support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0130] On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations, and those with low resistance to ion movement of the electrolyte and excellent electrolyte impregnation ability are particularly preferred. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof can be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separators containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be selectively used as single-layer or multi-layer structures.

[0131] Furthermore, the electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0132] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0133] The organic solvent can be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move, and is not particularly limited. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the cyclic carbonate and the linear carbonate can be mixed in a volume ratio of about 1:1 to about 1:9 to produce an electrolyte with excellent performance.

[0134] The lithium salt can be any compound capable of providing lithium ions for use in lithium secondary batteries, and is not particularly limited. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The lithium salt is preferably used within the range of 0.1 to 2.0 M. When the lithium salt concentration falls within the above range, the electrolyte has appropriate conductivity and viscosity, exhibiting excellent electrolyte performance and allowing lithium ions to move effectively.

[0135] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be present in an amount of 0.1 to 5 parts by weight per 100 parts by weight of the total weight of the electrolyte.

[0136] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent discharge capacity, output characteristics, and life characteristics in a stable manner, making it useful in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the electric vehicle field, such as hybrid electric vehicles (HEVs).

[0137] Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0138] The aforementioned battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0139] The external shape of the lithium secondary battery of the present invention is not particularly limited, but cylindrical, rectangular, pouch-type, or coin-type batteries using a can are possible.

[0140] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also suitably as a unit battery in medium- and large-sized battery modules containing a large number of battery cells.

[0141] Examples and Comparative Examples The present invention will be described in more detail below with reference to examples. However, the following examples are for illustrative purposes only and do not limit the scope of the present invention to these examples alone.

[0142] Example 1 Li, Ni, Co, Mn, and Al raw materials were added to a mixer in amounts such that the molar ratio of Li:Ni:Co:Mn:Al was 0.97:0.93:0.05:0.01:0.01, and the mixture was mixed and pulverized using a high-energy milling apparatus. The raw materials used were LiOH·H2O, Ni(OH)2, Co3O4, and MnO. 2、 And Al3O4 was used.

[0143] The mixed and pulverized raw materials were packed into a crucible at a density of 0.7 g / cc or higher, and subjected to primary calcination at 810°C for 10 hours under an oxygen atmosphere. The resulting primary calcined material was then pulverized using a pneumatic pulverizer. At this stage, the size of the primary calcined material was D 50 2-4 μm, D max It was adjusted to be >20μm.

[0144] The crushed primary calcined material and LiOH·H2O were mixed so that the molar ratio of lithium to the transition metal was 1.00. After secondary calcination at 750°C for 5 hours, the mixture was crushed using a pneumatic pulverizer to produce a positive electrode active material (lithium transition metal oxide).

[0145] Example 2 The cathode active material (lithium transition metal oxide) was produced in the same manner as in Example 1, except that the primary firing was performed at a temperature of 830°C.

[0146] Comparative Example 1 Nickel-cobalt-manganese hydroxide, Li raw material, and Al raw material were added to a mixer in amounts such that the molar ratio of Li:Ni:Co:Mn:Al was 0.97:0.93:0.05:0.01:0.01, and then mixed. In this process, LiOH·H2O and Ni were used as raw materials. 0.94 Co 0.05 Mn 0.01 (OH)2 and Al2O3 were used.

[0147] The mixed raw materials were packed into a crucible at a density of 0.7 g / cc or higher, and subjected to primary calcination at 760°C for 12 hours under an oxygen atmosphere. The resulting primary calcined material was then pulverized using a pneumatic pulverizer. At this stage, the size of the primary calcined material was D 50 2-4 μm, D max It was adjusted to be >20μm.

[0148] Experimental Example 1 - Unrolled conditions After manufacturing electrodes (positive electrodes) containing the positive electrode active material produced in the above examples and comparative examples, the electrodes were cut by ion milling to obtain cross-sections, and SEM images (approximately 5K magnification) of the cross-sections of the positive electrodes were obtained using an SEM (JEOL, JSM-7900F). Using an image processing program, the area and perimeter of the lithium transition metal oxide particles produced in the examples and comparative examples were confirmed, and the sphericity was calculated and is shown in Tables 1 to 3 below.

[0149] Specifically, 95% by weight of the positive electrode active material produced in the examples and comparative examples, 2.0% by weight of carbon black as a conductive material, and 3.0% by weight of polyvinylidene fluoride (PVDF) as a binder were mixed in an N-methylpyrrolidone (NMP) solvent to produce a positive electrode slurry. The produced positive electrode slurry was then applied to one surface of an aluminum current collector and dried at 130°C to produce a positive electrode.

[0150] Using an ion milling apparatus (JEOL, CP-09IB19520CCP, acceleration voltage: 6kV), the positive electrode was irradiated with an argon (Ar) ion beam and cut by the ion milling method to obtain a cross-section of the positive electrode. Then, an SEM image (approximately 5K magnification) of the cross-section of the positive electrode was taken using a SEM (JEOL, JSM-7900F). Subsequently, using an image processing program (deep learning program, Mask-RCNN model), a two-dimensional segmentation image was obtained in which the boundaries of lithium transition metal oxide particles present in the SEM image were separated and shown in random colors, as shown in Figures 1 and 2.

[0151] For reference, image processing work includes methods where researchers classify images themselves, and image classification methods using deep learning. In this invention, an image classification method using deep learning is used, but the invention is not limited to this.

[0152] The area of ​​the lithium transition metal oxide particles is calculated using the number of pixels corresponding to each of the n particles (approximately 100 to 200) present in the segmentation image. The circumference of the lithium transition metal oxide particles is calculated using the length of the outermost shell boundary corresponding to each of the n particles (approximately 100 to 200) present in the segmentation image. Then, the sphericity is calculated using Equation 1, and the average sphericity and the ratio of the number of unrolled particles for each sphericity (S) are calculated. 30≦、y The following calculations (e.g., [%]) were performed and are shown in Tables 1-3 and Figure 4 below.

[0153] However, the area of ​​the particles captured in the resulting image is 3 μm. 2 Particles that fall under the following categories, or whose overall pattern is not observed in the image, were excluded because they may impair the representativeness of the sample.

[0154] Figure 1 is a segmentation image of the cross-section of the positive electrode containing the positive electrode active material manufactured in Example 1.

[0155] Figure 2 is a segmentation image of the cross-section of the positive electrode containing the positive electrode active material manufactured in Example 2.

[0156] Figure 4 is a graph showing the ratio [%] of the number of particles based on sphericity according to Equation 1 to the total number of lithium transition metal oxide particles in the positive electrode active materials produced in Example 1, Example 2, and Comparative Example 1.

[0157] - Rolling conditions A positive electrode slurry was prepared by mixing 95% by weight of the positive electrode active material produced in the examples and comparative examples, 2.0% by weight of carbon black as a conductive material, and 3.0% by weight of polyvinylidene fluoride (PVDF) as a binder in an N-methylpyrrolidone (NMP) solvent. The prepared positive electrode slurry was then applied to one surface of an aluminum current collector, dried at 130°C, and then rolled to a porosity of 20% to produce a positive electrode. The process was carried out in the same manner as the unrolled conditions described above, except that a two-dimensional segmentation image was obtained and shown in Figure 3. The average sphericity when an electrode containing lithium transition metal oxide is rolled to a porosity of 20%, and the percentage of particle numbers (S) due to rolling (porosity: 20%). 20、y The following were calculated (e.g., [%]) and are shown in Tables 1-3 and Figure 5 below.

[0158] Figure 3 is a segmentation image of the cross-section of the positive electrode containing the positive electrode active material manufactured in Comparative Example 1.

[0159] Figure 5 is a graph showing the ratio [%] of the number of particles based on the sphericity according to Formula 1 described herein to the total number of lithium transition metal oxide particles contained in the positive electrode active material produced in Example 1, Example 2, and Comparative Example 1, when the electrode containing lithium transition metal oxide is rolled to a porosity of 20%.

[0160] [Table 1]

[0161] [Table 2]

[0162] [Table 3]

[0163] From Tables 1-3, it was confirmed that the positive electrode active materials produced in Examples 1 and 2 had an average sphericity of 0.70 or higher according to Formula 1 described herein, and that when electrodes containing lithium transition metal oxides were rolled to a porosity of 20%, the average sphericity of 0.70 or higher according to Formula 1 described herein was also confirmed. Furthermore, the ratio of the number of particles with a sphericity of 0.7 to 0.8 according to Formula 1 described herein to the total number of lithium transition metal oxide particles (S 30≦、0.7-0.8 ) is 42% or more, and the ratio of the number of particles with a sphericity of 0.8 to 0.9 according to Equation 1 to the total number of lithium transition metal oxide particles (S 30≦、0.8-0.9 ) is 10% or more, and when an electrode containing lithium transition metal oxide is rolled to a porosity of 20%, the ratio of the number of particles with a sphericity of 0.7 to 0.8 according to formula 1 to the total number of lithium transition metal oxide particles contained in the electrode is (S 20、0.7-0.8 ) is 40% or more, and the ratio of the number of particles with a sphericity of 0.8 to 0.9 according to Equation 1 to the total number of lithium transition metal oxide particles contained in the electrode is (S 20、0.8-0.9 It was confirmed that the sphericity (S) was 15% or more. In comparison, the positive electrode active material produced in Comparative Example 1 had an average sphericity of less than 0.70 according to Formula 1 described herein, and it was confirmed that when the electrode containing lithium transition metal oxide was rolled to a porosity of 20%, the average sphericity (S) according to Formula 1 described herein was less than 0.70. Furthermore, the ratio of the number of particles with a sphericity of 0.7 to 0.8 according to Formula 1 described herein to the total number of lithium transition metal oxide particles (S) 30≦、0.7-0.8 ) is less than 42%, and the ratio of the number of particles with a sphericity of 0.8 to 0.9 according to Equation 1 to the total number of lithium transition metal oxide particles (S 30≦、0.8-0.9 ) is less than 10%, and when an electrode containing lithium transition metal oxide is rolled to a porosity of 20%, the ratio of the number of particles with a sphericity of 0.7 to 0.8 according to formula 1 to the total number of lithium transition metal oxide particles contained in the electrode is (S 20、0.7-0.8) is less than 40%, and the ratio of the number of particles with a sphericity of 0.8 to 0.9 according to Equation 1 to the total number of lithium transition metal oxide particles contained in the electrode is (S 20、0.8-0.9 We confirmed that the percentage was less than 15%.

[0164] Experimental Example 2 SEM (JEOL, JSM-7900F) was used to obtain SEM images of the positive electrode active materials produced in the above examples and comparative examples, which are shown in Figures 6 and 7.

[0165] Figures 6(A) and 6(B) are SEM images of the cathode active materials produced in Example 1 and Comparative Example 1, respectively.

[0166] Figures 7(A) to 7(C) are SEM images of the cathode active materials produced in Example 1, Example 2, and Comparative Example 1, respectively.

[0167] Figures 6 and 7 show that the positive electrode active material produced in Example 1 has a high degree of single-particle formation and is in a single-particle form, while the positive electrode active material produced in Comparative Example 1 has a low degree of single-particle formation. Furthermore, it was confirmed that the positive electrode active material produced in Example 1 has a single-particle form consisting of 2 to 10 primary particles, and compared to the positive electrode active material produced in Comparative Example 1, it has fewer grain boundaries and a higher degree of spheroidization, resulting in stronger particle strength and less particle cracking during electrode rolling.

[0168] Experimental Example 3 A positive electrode slurry was prepared by mixing the positive electrode active material produced in the above example or comparative example with a conductive material (Denka Black) and a binder (PVDF) in an N-methyl-2-pyrrolidone (NMP) solvent in a weight ratio of 95:2:3. The positive electrode slurry was applied to an aluminum current collector, dried, and then rolled to produce a positive electrode.

[0169] Next, a negative electrode slurry was prepared by mixing a negative electrode active material (natural graphite), a conductive material (carbon black), and a binder (SBR+CMC) with water in a weight ratio of 95.6:1.0:3.4. The negative electrode slurry was applied to a copper current collector, dried, and then rolled to produce the negative electrode.

[0170] An electrode assembly was manufactured by interposing a separator between the positive and negative electrodes, and after positioning it inside the battery case, two monocells with an electrode size of 3 cm x 4 cm were produced by injecting an electrolyte. In this process, the electrolyte used was an organic solvent in which ethylene carbonate and ethyl methyl carbonate were mixed in a volume ratio of 3:7, and 0.7 M LiPF6 and 0.3 M LiFSI were dissolved in it.

[0171] The two monocells were charged to 4.2V at 25°C with a constant current of 0.33C and a cutoff of 0.05C, after which the positive electrodes were separated. The separated positive electrodes were placed in cell pouches, electrolyte was added, and the pouches were sealed to prepare the samples. The samples were stored at 60°C for 12 weeks, and the amount of gas generated was measured. The amount of gas generated at 12 weeks is shown in Table 4 and Figure 8 below.

[0172] Figure 8 is a graph showing the amount of gas generated (ml) over time (weeks) in batteries containing the positive electrode active material produced in Example 1, Example 2, and Comparative Example 1.

[0173] [Table 4]

[0174] Table 4 confirms that the secondary battery using the positive electrode active material according to the present invention exhibits excellent gas generation reduction.

Claims

1. A positive electrode active material containing lithium transition metal oxide particles in single-particle form, The lithium transition metal oxide is a positive electrode active material having an average sphericity of 0.7 or more according to the following formula 1, and when the electrode containing the lithium transition metal oxide is rolled to have a porosity of 20%, the average sphericity of 0.7 or more according to the following formula 1. [Math 1] (In formula 1 above, A is the area of ​​lithium transition metal oxide particles [μm²] ２ ] and P is the circumference [μm] of the lithium transition metal oxide particle.

2. The positive electrode active material according to claim 1, wherein the lithium transition metal oxide has a sphericity of 0.7 to 0.8 according to formula 1 as a ratio of 42% or more of the total number of particles of the lithium transition metal oxide.

3. The positive electrode active material according to claim 1, wherein the lithium transition metal oxide has a sphericity of 0.8 to 0.9 according to formula 1 as the ratio of the number of particles with a sphericity of 0.8 to 0.9 relative to the total number of particles of the lithium transition metal oxide, with respect to 10% or more.

4. The positive electrode active material according to claim 1, wherein when an electrode containing the lithium transition metal oxide is rolled to a porosity of 20%, the ratio of the number of particles with a sphericity of 0.7 to 0.8 according to formula 1 to the total number of lithium transition metal oxide particles contained in the electrode is 40% or more.

5. The positive electrode active material according to claim 1, wherein when an electrode containing the lithium transition metal oxide is rolled to a porosity of 20%, the ratio of the number of particles with a sphericity of 0.8 to 0.9 according to formula 1 to the total number of lithium transition metal oxide particles contained in the electrode is 15% or more.

6. The lithium transition metal oxide has an average particle size (D ５０ The positive electrode active material according to claim 1, wherein the diameter of the ) is 1.5 μm or more and 6 μm or less.

7. The positive electrode active material according to claim 1, wherein the lithium transition metal oxide is represented by the following chemical formula 1. [Chemical formula 1] L) １－ｘ－ｙ－ｚ Co ｘ Mn ｙ M ｚ )O ２ (In the above chemical formula 1, M is one or more selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo.) x, y, and z are the atomic fractions of independent elements, where 0 < x ≤ 0.25, 0 < y ≤ 0.25, 0 ≤ z < 0.1, and 0 < x + y + z ≤ 0.

5.

8. A positive electrode for a lithium secondary battery, comprising the positive electrode active material described in any one of claims 1 to 7.

9. A lithium secondary battery comprising a positive electrode for a lithium secondary battery as described in claim 8.

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