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

Abstract

The present invention relates to a positive electrode active material comprising a lithium transition metal oxide in single-particle form, wherein the lithium transition metal oxide satisfies one or more of the conditions 1 to 3 described herein, a positive electrode containing the same, and a lithium secondary battery.

Description

[Technical Field]

[0001] This application claims priority rights based on Korean Patent Applications No. 10-2023-0043514, No. 10-2023-0043515, and No. 10-2023-0043517 dated April 3, 2023, and all content disclosed in the documents of said Korean Patent Applications 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] Nickel-based lithium transition metal oxide cathode active materials in a secondary particle form, where macro-primary particles are aggregated, minimize the secondary particle interface, improving thermal stability and addressing issues such as life degradation due to side reactions during electrochemical reactions and gas generation.

[0010] On the other hand, high-content nickel-based (High-Ni) lithium transition metal oxide cathode active materials typically undergo a water washing process to reduce the amount of lithium impurities remaining on the surface. While such a water washing process is advantageous in reducing gas generation by removing lithium by-products from the surface, it is disadvantageous in terms of lifespan due to surface damage to the cathode active material particles. In particular, nickel-based lithium transition metal oxide cathode active materials in the form of secondary particles, where macro-primary particles are aggregated, inherently have poor lifespan characteristics. Furthermore, undergoing a water washing process further degrades these characteristics, and resistance increases as charging and discharging progresses. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Korean Patent Publication No. 10-2014-0093529 [Overview of the project] [Problems that the invention aims to solve]

[0012] The objective of the present invention is to provide a lithium secondary battery with reduced gas generation and improved energy density by developing a positive electrode active material that has a single-particle form and suppresses particle fracture. [Means for solving the problem]

[0013] To solve the above problems, the present invention provides a positive electrode active material, a positive electrode, and a lithium secondary battery.

[0014] (1) The present invention provides a positive electrode active material containing a lithium transition metal oxide in a single particle form, wherein the lithium transition metal oxide satisfies any one or more of the following conditions 1 to 3.

[0015] [Condition 1] The lithium transition metal oxide has an average cross-sectional area change rate (ΔX 11 ) of 5% or more and 20% or less according to the following formula (1); [Number] In the formula (1), X 30≦ is the average cross-sectional area [μm 2 of the lithium transition metal oxide particles contained in the electrode containing the lithium transition metal oxide and not subjected to rolling, X 11 is the average cross-sectional area [μm 2 of the lithium transition metal oxide particles contained in the electrode when the electrode is rolled so that the porosity is 11%.

[0016] [Condition 2] The lithium transition metal oxide has a ratio of the number of particles with C 11 [%] exceeding 6% of more than 3% with respect to the total number of all particles of the lithium transition metal oxide contained in the electrode; [Number] In the formula (2), when the electrode containing the lithium transition metal oxide is rolled so that the porosity is x%, a is the cross-sectional area [μm 2 of the cracks formed in the lithium transition metal oxide particles contained in the electrode, and b is the cross-sectional area [μm 2 of the lithium transition metal oxide particles contained in the electrode.

[0017] [Condition 3] The lithium transition metal oxide is such that when an electrode containing the lithium transition metal oxide is rolled to a porosity of 11%, the ratio of the number of particles with cracks to the total number of lithium transition metal oxide particles contained in the electrode is 78% or less;

[0018] (2) The present invention relates to a lithium transition metal oxide that has an average cross-sectional area change rate (ΔX) according to formula (1) described herein. 11 The present invention provides a positive electrode active material as described in (1) above, wherein the content of (1) is 8% or more and 15% or less.

[0019] (3) The present invention relates to the lithium transition metal oxide having an average cross-sectional area change rate (ΔX) according to the following formula (3). 20 The present invention provides a positive electrode active material according to (1) or (2) above, wherein the amount of ) is 1% or more and 15% or less.

[0020]

number

[0021] In the above formula (3), X 30≦ This refers to the average cross-sectional area [μm²] of lithium transition metal oxide particles contained in an electrode that contains lithium transition metal oxide and has not undergone rolling. 2 ] and X 20 When the electrode is rolled to a porosity of 20%, the average cross-sectional area [μm²] of the lithium transition metal oxide particles contained in the electrode is obtained. 2 ]

[0022] (4) In the present invention, when the electrode containing the lithium transition metal oxide is rolled to a porosity of 11%, the cross-sectional area of ​​the total number of lithium transition metal oxide particles contained in the electrode is 3 μm 2 ~4μm 2 The present invention provides a positive electrode active material according to any one of (1) to (3) above, wherein the proportion of particles that are 40% or less.

[0023] (5) The present invention relates to the X 11 is 5 μm 2 More than 10μm 2 The following positive electrode active material is provided, as described in any one of (1) to (4) above.

[0024] (6) The present invention relates to the lithium transition metal oxide, and the C of formula (2) is the total number of lithium transition metal oxide particles contained in the electrode. 20 The present invention provides a positive electrode active material according to any one of (1) to (5) above, wherein the proportion of particles with a percentage exceeding 6% is 0.5% or more.

[0025] (7) The present invention relates to the lithium transition metal oxide, and the C of formula (2) is the total number of lithium transition metal oxide particles contained in the electrode. 11 The present invention provides a positive electrode active material according to any one of (1) to (6) above, wherein the proportion of particles with a [%] of 0% to 1% is 40% or less.

[0026] (8) The present invention relates to the lithium transition metal oxide, and the C of formula (2) is the total number of lithium transition metal oxide particles contained in the electrode. 20 The present invention provides a positive electrode active material according to any one of (1) to (7) above, wherein the proportion of particles with a [%] of 0% to 1% is 45% or less.

[0027] (9) The present invention relates to the lithium transition metal oxide, and the C of formula (2) is the total number of lithium transition metal oxide particles contained in the electrode. 11 The present invention provides a positive electrode active material according to any one of (1) to (8) above, wherein the proportion of particles with a [%] of 1% to 2% is 20% or less.

[0028] (10) The present invention relates to the lithium transition metal oxide, and the C of formula (2) is the total number of lithium transition metal oxide particles contained in the electrode. 20 The present invention provides a positive electrode active material according to any one of (1) to (9) above, wherein the proportion of particles with a [%] of 1% to 2% is 20% or less.

[0029] (11) The present invention provides a positive electrode active material according to any one of (1) to (10) 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 cracks to the total number of lithium transition metal oxide particles contained in the electrode is 70% or less.

[0030] (12) The present invention provides a positive electrode active material according to any one of (1) to (11) above, wherein the lithium transition metal oxide has a ratio of 50% or less of the number of particles with cracks to the total number of particles.

[0031] (13) The present invention provides a positive electrode active material according to any one of (1) to (12) above, wherein when an electrode containing the lithium transition metal oxide is rolled to have a porosity of 11%, the difference in the ratio of the number of cracked particles to the total number of lithium transition metal oxide particles contained in the electrode before and after rolling is 20% or more and 80% or less.

[0032] (14) 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 (13) above, wherein the diameter of the ) is 1.5 μm or more and 6 μm or less.

[0033] (15) The present invention provides a positive electrode active material according to any one of (1) to (14) above, wherein the lithium transition metal oxide is represented by the following chemical formula 1.

[0034] [Chemical formula 1] Li(Ni) 1-x-y-z Co x Mn y M z )O2

[0035] 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, 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。

[0036] (16) The present invention provides a positive electrode for a lithium secondary battery comprising a positive electrode active material described in any one of (1) to (15) above.

[0037] (17) The present invention provides a lithium secondary battery including the positive electrode described in (16) above. [Effects of the Invention]

[0038] The positive electrode active material according to the present invention can reduce the generation of fine particles due to particle cracking, achieve a high degree of single particle formation or a low crack particle rate, and when used as a positive electrode active material in a lithium secondary battery, it can reduce the gas generation phenomenon in the battery, significantly improve the battery life, and exhibit excellent battery performance. [Brief explanation of the drawing]

[0039] [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] Figures 4(A) and 4(B) are SEM images of the cathode active materials produced in Example 1 and Comparative Example 1, respectively. [Figure 5] Figures 5(A) to 5(C) are SEM images of the cathode active materials produced in Example 1, Example 2, and Comparative Example 1, respectively. [Figure 6] This shows the change in particle size distribution of lithium transition metal oxides contained in the positive electrode when the positive electrode containing the positive electrode active material manufactured in Example 1 is pressurized. [Figure 7] This shows the change in particle size distribution of lithium transition metal oxides contained in the positive electrode when the positive electrode containing the positive electrode active material manufactured in Comparative Example 1 is pressurized. [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]

[0040] The present invention will be described in more detail below to facilitate understanding of it.

[0041] The terms and words used in the description and claims of this invention should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather should be interpreted in a manner consistent with the technical idea of ​​this invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0042] The present invention will be described in detail below.

[0043] In the present invention, "primary particle" refers to the smallest particle unit that can be distinguished as a single mass when observing a cross-section of the positive electrode active material with a scanning electron microscope (SEM), and may consist of one crystal grain or multiple crystal grains. In the present invention, the average particle size (Dv) of the primary particle 50The particle size may be measured using a scanning electron microscope (SEM) (JEOL, JSM-7900F). Specifically, it can be defined as the particle size corresponding to 50% of the cumulative volume distribution in the particle size distribution curve (graph curve of particle size distribution) of each particle obtained using a scanning electron microscope (SEM). The particle size can be measured by first taking the volume of a sphere with a radius of half the particle size of the primary particle obtained using a scanning electron microscope (SEM) as the volume of the primary particle, and then calculating the particle diameter at the point where the cumulative volume distribution by particle size is 50% in the result of calculating the volume of the primary particle. In the present invention, the particle size of a primary particle may be calculated by first 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 then using the radius of a circle having the same area as each of the primary particles to calculate the particle size of each primary particle present in the SEM image.

[0044] 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.

[0045] 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 ).

[0046] 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.

[0047] In this invention, "single crystal" refers to a crystal in which no grain boundaries are present within the particles.

[0048] In this invention, the "average cross-sectional area change rate" is the percentage change in the average cross-sectional area of ​​lithium transition metal oxide particles contained in an electrode when the electrode containing lithium transition metal oxide is rolled to have a porosity of x% compared to the unrolled electrode. The "average cross-sectional area" can be measured by calculating the arithmetic mean of the "cross-sectional area".

[0049] In this invention, the "cross-sectional area" can be determined by irradiating the positive electrode with an argon (Ar) ion beam using an ion milling device (JEOL, IB-19520CCP, acceleration voltage: 6kV), cutting the positive electrode by the ion milling method to obtain a cross-section of the positive electrode, capturing a scanning electron microscope (SEM) image of the cross-section of the positive electrode, and then performing image processing on the image. Specifically, it 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 by 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 "cross-sectional area" may be calculated using the number of pixels corresponding to each of the n particles present in the segmentation image.

[0050] In this invention, "crack" refers to a region where the surface of a particle is fractured (broken) in an image observed by a scanning electron microscope (SEM), which is distinguished from interparticle boundaries having a linear shape of a certain size or larger through boundary information learning. Alternatively, "crack" refers to a region that appears black in an image observed by a scanning electron microscope (SEM), or a region that appears darker than adjacent areas. The region that appears dark is determined by the contrast difference with the surrounding area, and only regions that are not interparticle boundaries and have a linear shape of a certain size or larger are identified as cracks. On the other hand, if no cracks are present, they appear white, or a lighter color than cracks in adjacent areas.

[0051] In this invention, the "crack cross-sectional area" and the "particle cross-sectional area" can be confirmed by irradiating the positive electrode with an argon (Ar) ion beam using an ion milling device (JEOL, IB-19520CCP, acceleration voltage: 6kV), cutting the positive electrode by 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 processing the image. Specifically, they 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 by 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 "crack cross-sectional area" is calculated using the number of pixels corresponding to areas that appear black or darker than adjacent areas in the particles present in the segmentation image, while the "particle cross-sectional area" is calculated using the number of pixels corresponding to the particle, and in this case, if a crack exists in the particle, the cross-sectional area of ​​the crack may be included.

[0052] In this invention, the "number of particles with cracks" can be determined by the presence or absence of cracks. The presence or absence of cracks can be determined by visually observing the segmentation image, where areas that are black or relatively darker than adjacent areas are judged to have cracks, and areas that are white or relatively brighter than adjacent areas are judged to not have cracks.

[0053] positive electrode active material The positive electrode active material according to the present invention will be described below.

[0054] The positive electrode active material of the present invention comprises a lithium transition metal oxide, wherein the lithium transition metal oxide is in single-particle form and satisfies one or more of the following conditions 1 to 3.

[0055] [Condition 1] The lithium transition metal oxide has an average cross-sectional area change rate (ΔX) according to the following formula (1). 11 ) is between 5% and 20%;

number

[0056] [Condition 2] The lithium transition metal oxide is C according to the following formula (2) for the total number of lithium transition metal oxide particles contained in the electrode. 11 The proportion of particles with a percentage exceeding 6% is 3% or more;

number

[0057] [Condition 3] The lithium transition metal oxide is such that when an electrode containing the lithium transition metal oxide is rolled to a porosity of 11%, the ratio of the number of particles with cracks to the total number of lithium transition metal oxide particles contained in the electrode is 78% or less;

[0058] 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.

[0059] Lithium transition metal oxides, which are secondary particles, are prone to particle cracking during the electrode rolling process. This increases the 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 rolling for the manufacture of 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.

[0060] In this invention, the problems that occur with lithium transition metal oxides in secondary particle form, as described above, are improved by developing lithium transition metal oxides in single-particle form. In particular, when the positive electrode active material satisfies any one of conditions 1 to 3 of this invention, a secondary battery can be realized that has a single-particle form, suppresses particle cracking, and has excellent high-temperature life characteristics and high-temperature storage performance.

[0061] [Condition 1] In this invention, in order to evaluate and quantitatively show the degree of particle cracking of lithium transition metal oxides before and after rolling, the average cross-sectional area change rate (ΔX) is used. x The concept of the average cross-sectional area change rate (△X) is used. x This index represents how much the average cross-sectional area of ​​lithium transition metal oxide particles contained in an electrode is changed when the electrode containing lithium transition metal oxide is rolled to a porosity of x%, compared to the average cross-sectional area of ​​lithium transition metal oxide particles contained in an electrode that has not undergone rolling.

[0062] The aforementioned porosity (x%) is calculated using the ratio of the electrode density to the total true density of the solid content of the positive electrode active material.

[0063] 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.

[0064] [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

[0065] 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.

[0066] 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)).

[0067] 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)]).

[0068] The aforementioned average cross-sectional area change rate (△X x A low ) means that when electrodes containing lithium transition metal oxides are rolled at a constant strength, less particle cracking occurs in the lithium transition metal oxides, and the change in the cross-sectional area of ​​the particles is minimal.

[0069] The positive electrode active material of the present invention comprises a lithium transition metal compound, wherein the lithium transition metal oxide is in single-particle form, and the lithium transition metal oxide has an average cross-sectional area change rate (ΔX) according to the following formula (1). 11 ) is between 5% and 20%.

[0070]

number

[0071] In equation (1) above, X 30≦ This refers to the average cross-sectional area [μm²] of lithium transition metal oxide particles contained in an electrode that contains lithium transition metal oxide and has not undergone rolling. 2 ] and X 11 When the electrode is rolled to a porosity of 11%, the average cross-sectional area [μm²] of the lithium transition metal oxide particles contained in the electrode is obtained. 2 ]

[0072] The average cross-sectional area change rate (△X) according to the above formula 1. 11 This value is determined by the change in cross-sectional area when an electrode containing a lithium transition metal oxide is rolled to a porosity of 11%, and since the magnitude of the pressure is similar to or slightly higher than the magnitude of the rolling pressure during the manufacture of the positive electrode, it can be understood as a clearer standard for evaluating the particle cracking phenomenon when used in lithium secondary batteries, and in particular, the trend when the rolling pressure is increased can be confirmed more specifically.

[0073] In the present invention, the lithium transition metal oxide has an average cross-sectional area change rate (ΔX) according to formula 1. 11 ) is 5% or more and 20% or less, more specifically, it may be 5% or more, 6% or more, 7% or more, 8% or more, 9% or more, or 10% or more, and may be 12% or less, 13% or less, 14% or less, 15% or less, 16% or less, 17% or less, 18% or less, 19% or less, or 20% or less, preferably 8% or more and 15% or less.

[0074] When lithium transition metal oxides satisfy the above physical properties, particle strength can be improved, reducing particle cracking during rolling, and the content of lithium by-products can be reduced, suppressing side reactions with the electrolyte. Furthermore, excellent physical properties such as high-temperature life characteristics and storage performance can be achieved in lithium secondary batteries.

[0075] In addition, when the electrode containing the lithium transition metal oxide is rolled to a porosity of 11%, the cross-sectional area of ​​the total number of lithium transition metal oxide particles contained in the electrode is 3 μm². 2 ~4μm 2 The proportion of particles that are 40% or less may be 40% or less, specifically 40% or less, 39% or less, 38% or less, 37% or less, 36% or less, 35% or less, 34% or less, or 33% or less.

[0076] Furthermore, when the electrode containing the lithium transition metal oxide is rolled to a porosity of 11%, the cross-sectional area is 4 μm relative to the total number of lithium transition metal oxide particles contained in the electrode. 2 ~5μm 2 The proportion of particles that are 22% or less may be 22% or less, specifically 22% or less, 21% or less, or 20% or less.

[0077] Furthermore, when the electrode containing the lithium transition metal oxide is rolled to a porosity of 11%, the cross-sectional area relative to the total number of lithium transition metal oxide particles contained in the electrode is 10 μm². 2 The proportion of particles that meet the above criteria may be 5% or more, or 6% or more.

[0078] For lithium transition metal oxides to satisfy the above physical properties means that particle cracking after rolling is suppressed and the proportion distribution of particle cross-sectional area before and after rolling is small. If particles crack easily, the proportion of particles with a smaller cross-sectional area increases, and the cross-sectional area of ​​10 μm... 2 The proportion of particles larger than the above tends to decrease.

[0079] On the other hand, X 11 is 5 μm 2 More than 10μm 2 The following is acceptable. More specifically, 5.0 μm 2 or greater than 5.5 μm 2 The above is sufficient, 6 μm 2 Below, 7μm 2 Below, 8μm 2 Below, 9μm 2 or less, or 10 μm 2 The following is acceptable:

[0080] Furthermore, in the present invention, the lithium transition metal oxide exhibits a lower average cross-sectional area change rate (△X) compared to conventional positive electrode active materials, even when the rolling strength is changed. x ) indicates.

[0081] For example, the lithium transition metal oxide has an average cross-sectional area change rate (ΔX) according to the following formula (3).20 ) may be between 1% and 15%.

[0082]

number

[0083] In the above formula (3), X 30≦ This refers to the average cross-sectional area [μm²] of lithium transition metal oxide particles contained in an electrode that contains lithium transition metal oxide and has not undergone rolling. 2 ] and X 20 When the electrode is rolled to a porosity of 20%, the average cross-sectional area [μm²] of the lithium transition metal oxide particles contained in the electrode is obtained. 2 ]

[0084] Furthermore, the average cross-sectional area change rate (△X) according to formula (3) above. 20 ) may be 2% or more, and may be 12% or less, 11% or less, or 10% or less.

[0085] Furthermore, the lithium transition metal oxide according to the present invention is the ΔX x When defined, the average cross-sectional area change rate (△X 14 ) may be 1% or more and 5% or less, specifically 1% or more, 1.2% or more, or 1.3% or more, and 5% or less, 4% or less, 3% or less, 2% or less, or 1.8% or less.

[0086] Furthermore, the lithium transition metal oxide according to the present invention is the ΔX x When defined, the average cross-sectional area change rate (△X 16 ) may be 3% or more and 15% or less, specifically 3% or more, 5% or more, 7% or more, or 8% or more, and 15% or less, 12% or less, or 10% or less.

[0087] The average cross-sectional area change rate (△X) due to the various rolling strengths mentioned above. xSatisfying any of them means that since the structure is stable and no cracks occur, it is possible to improve problems such as deterioration of battery characteristics due to particle cracking and gas generation and problems of high-temperature stability. Further, when maximizing the porosity to a level without particle cracking, it can have advantages in terms of having a high electrode density and the energy density per volume of the secondary battery.

[0088] [Condition 2] In the present invention, in order to evaluate and quantitatively show the degree of particle cracking before and after rolling of the lithium transition metal oxide, the ratio (C x [%]) of the crack cross-sectional area possessed by the lithium transition metal oxide is used. The C x [%] represents the ratio of the cross-sectional area of cracks generated in the lithium transition metal oxide particles contained in the electrode when the electrode containing the lithium transition metal oxide is rolled so that the porosity becomes x%, and this is an index representing the strength and rolling resistance of the lithium transition metal oxide, and the degree of crack generation and particle cracking.

[0089] For example, a large value of the C x [%] means that a wide-area crack has occurred in the particles of the lithium transition metal oxide due to rolling, and the ratio (A x ) of particles having a C x、y [%] value equal to or higher than a certain value (y) being high means that cracks due to rolling have occurred in that many more particles. The fact that cracks due to rolling have occurred in the particles is a different concept from the occurrence of particle cracking. The fact that cracks have occurred in the particles means that cracks have occurred while the particles resist rolling without cracking, so the higher the number of particles with a high C x [%] value, the higher the strength of the lithium transition metal oxide particles can be interpreted.

[0090] On the other hand, in the present invention, the ratio (A x ) of particles having a C x、y [%] equal to a certain value (y) is defined. The C x[%] The value is the ratio of the cross-sectional area of cracks formed in the lithium transition metal oxide particles contained in the electrode when the electrode containing the lithium transition metal oxide is rolled so that the porosity is x%, so C x [%] The ratio (A x、y ) of the particles having a constant value (y) is the number of particles among the total number of lithium transition metal oxide particles contained in the electrode, among which C x [%] represents the concept of the number of particles having a constant value (y).

[0091] The positive electrode active material of the present invention contains a lithium transition metal compound, and the lithium transition metal oxide is C according to the following formula (2) with respect to the total number of lithium transition metal oxide particles contained in the electrode 11 [%] The ratio of the number of particles exceeding 6% is 3% or more.

[0092]

Equation

[0093] In the above formula (2), When the electrode containing the lithium transition metal oxide is rolled so that the porosity is x%, a is the cross-sectional area of cracks formed in the lithium transition metal oxide particles contained in the electrode [μm 2 , and b is the cross-sectional area of the lithium transition metal oxide particles contained in the electrode [μm 2 .

[0094] C according to the above formula (2) 11 [%] is a value determined by the cross-sectional area of crack generation in each particle of the lithium transition metal oxide contained in the electrode when the electrode containing the lithium transition metal oxide is rolled so that the porosity is 11%. Since the magnitude of the pressure is similar to or slightly higher than the magnitude of the pressure in rolling during the manufacture of the positive electrode, it can be understood as a clearer criterion for evaluating the particle cracking phenomenon when used in a lithium secondary battery. In particular, the tendency when the pressure of rolling increases can be more specifically confirmed.

[0095] In the present invention, the lithium transition metal oxide is the C of formula (2) relative to the total number of lithium transition metal oxide particles contained in the electrode. 11 The percentage of particles with a [%] exceeding 6% is 3% or more, specifically 3% or more, 3.5% or more, 4.0% or more, or 4.5% or more. This means that rolling-induced cracks occurred in a certain percentage or more of lithium transition metal oxide particles, and in particular, C 11 A percentage exceeding 6% indicates that a large number of particles have developed cracks of a broader morphology.

[0096] Thus, the lithium transition metal oxide of the present invention suppresses particle cracking by generating cracks in resistance to rolling pressure, thereby reducing the content of lithium by-products and suppressing 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.

[0097] Furthermore, in the present invention, the lithium transition metal oxide is C according to formula (2) above, relative to the total number of lithium transition metal oxide particles contained in the electrode. 11 The proportion of particles with a percentage of 0% to 1% may be 40% or less, more specifically, 25% or more, 28% or more, or 30% or more, and 40% or less.

[0098] Furthermore, in the present invention, the lithium transition metal oxide is C according to formula (2) above, relative to the total number of particles. 11 The proportion of particles with a percentage of 1% to 2% may be 20% or less, more specifically, 5% or more, 6% or more, 7% or more, 8% or more, 9% or more, 10% or more, or 11% or more, and may be 20% or less.

[0099] Furthermore, in the present invention, the ratio of the crack cross-sectional area according to formula (2) when rolling is not performed after manufacturing the positive electrode is C 30If defined as ≤[%], then C is the number of lithium transition metal oxide particles contained in the electrode relative to the total number of lithium transition metal oxide particles. 30 The proportion of particles whose ≤[%] is between 0% and 1% (A 30≦、0-1 ) is more than the C of equation (2) with respect to the total number of lithium transition metal oxide particles contained in the electrode. 11 [%] represents the proportion of particles where the percentage is between 0% and 1% (A 11≦、0-1 ) can appear at a high level. Also, C relative to the total number of lithium transition metal oxide particles contained in the electrode 30≦ [%] represents the percentage of particles where the percentage exceeds 6% (A 30≦、6< ) is more than the C of equation (2) with respect to the total number of lithium transition metal oxide particles contained in the electrode. 11 [%] represents the percentage of particles where the percentage exceeds 6% (A 11≦、6< ) can appear at a high level.

[0100] In particular, the lithium transition metal oxide of the present invention exhibits increased crack formation instead of particle splitting during rolling, resulting in a higher proportion of particles with small-area cracks, as described above.

[0101] Specifically, the ratio of C to the total number of lithium transition metal oxide particles contained in the electrode 30≦ [%] represents the proportion of particles where the percentage is between 0% and 1% (A 30≦、0-1 ) and the C according to formula (2) above, for the total number of lithium transition metal oxide particles contained in the electrode. 11 [%] represents the proportion of particles where the percentage is between 0% and 1% (A 11、0-1 The difference between this and ) may be 15% or more, specifically 15% or more, 18% or more, or 20% or more.

[0102] Specifically, the ratio of C to the total number of lithium transition metal oxide particles contained in the electrode 30≦ [%] represents the percentage of particles where the percentage exceeds 6% (A 30≦、6< ) and the C according to formula (2) above, for the total number of lithium transition metal oxide particles contained in the electrode. 11 [%] represents the percentage of particles where the percentage exceeds 6% (A 11、6<The difference between this and the given value may be 3% or more, specifically 3% or more, 3.5% or more, 4.0% or more, or 4.5% or more.

[0103] This indicates that even lithium transition metal oxide particles contained in the positive electrode active material of the present invention, which do not have cracks when not rolled, develop cracks when the electrode containing lithium transition metal oxide is rolled. From this, it can be seen that particle cracks occur at a high frequency instead of particle splitting phenomena.

[0104] Furthermore, in the present invention, the lithium transition metal oxide is C according to formula (2) above, relative to the total number of lithium transition metal oxide particles contained in the electrode. 20 The proportion of particles whose [%] is between 0% and 1% may be 45% or less, more specifically, 20% or more, or 25% or more, and may be 45% or less, 40% or less, 39% or less, 38% or less, 37% or less, 36% or less, 35% or less, or 34% or less.

[0105] Furthermore, in the present invention, the lithium transition metal oxide is C according to formula (2) above, relative to the total number of lithium transition metal oxide particles contained in the electrode. 20 The proportion of particles with a percentage of 1% to 2% may be 20% or less, more specifically, 5% or more, 6% or more, 7% or more, 8% or more, 9% or more, 10% or more, 11% or more, 12% or more, or 15% or more, and may be 20% or less.

[0106] Furthermore, in the present invention, the lithium transition metal oxide is C according to formula (2) above, relative to the total number of lithium transition metal oxide particles contained in the electrode. 20 The percentage of particles with a percentage exceeding 6% may be 0.5% or more, 0.6% or more, or 0.8% or more, and 1.5% or less.

[0107] In particular, the lithium transition metal oxide of the present invention exhibits increased crack formation instead of particle splitting during rolling, resulting in a higher proportion of particles with small-area cracks, as described above.

[0108] Furthermore, in the present invention, the lithium transition metal oxide is C relative to the total number of lithium transition metal oxide particles contained in the electrode. 11 [%] represents the proportion of particles where the percentage is between 1% and 2% (A 11、1-2 ) is more important than the total number of lithium transition metal oxide particles contained in the electrode, C 20 [%] represents the percentage of particles where the percentage is 1-2% (A 20、1-2 ) can appear at a high level.

[0109] This indicates that when the rolling strength of the lithium transition metal oxide contained in the positive electrode active material of the present invention is increased, the proportion of particles in which cracks are formed increases, and that even at a certain level of high pressure, particle cracks occur at a high frequency instead of particle splitting.

[0110] [Condition 3] In this invention, the concept of crack particle percentage [%] of the lithium transition metal oxide contained in the electrode is used to evaluate and quantitatively indicate the degree of particle cracking before and after rolling of the lithium transition metal oxide. The crack particle percentage [%] is expressed as a percentage of the number of particles with cracks relative to the total number of lithium transition metal oxide particles contained in the electrode. In this invention, when the electrode is rolled, the lithium transition metal oxide has a low percentage of particles with cracks, suppressing side reactions with the electrolyte and preventing problems such as gas generation and deterioration of battery cycle characteristics.

[0111] The crack particle rate [%] can be calculated from the ratio of the number of particles (c) containing cracks to the total number of lithium transition metal oxide particles (d) contained in the electrode. C and D can be calculated by manufacturing an electrode (positive electrode) containing a positive electrode active material containing lithium transition metal oxide particles, cutting the electrode by an ion milling method to obtain a cross-section, obtaining an SEM image of the cross-section of the positive electrode using an SEM, and determining the presence or absence of cracks using an image processing program.

[0112] The aforementioned crack particle ratio is a value determined by whether or not cracks occur in each particle when an electrode containing lithium transition metal oxide is rolled to a porosity of 11%, and the magnitude of the pressure is similar to or slightly higher than the magnitude of the rolling pressure during the manufacture of the positive electrode. Therefore, it can be understood as a clearer standard for evaluating the particle cracking phenomenon when used in lithium secondary batteries, and in particular, the trend when the rolling pressure is increased can be confirmed more specifically.

[0113] In the present invention, when an electrode containing the lithium transition metal oxide is rolled to have a porosity of 11%, the ratio of the number of particles with cracks to the total number of lithium transition metal oxide particles contained in the electrode is 78% or less, specifically 78% or less, or 77% or less. This means that the proportion of lithium transition metal oxide particles with cracks remains low even after rolling, indicating that particle cracking has been improved.

[0114] Thus, the lithium transition metal oxide of the present invention can suppress particle cracking phenomena, reduce the content of lithium by-products, and suppress side reactions with the electrolyte. Furthermore, it can achieve excellent physical properties such as high-temperature life characteristics and storage performance in lithium secondary batteries.

[0115] Furthermore, 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 cracks to the total number of lithium transition metal oxide particles contained in the electrode may be 70% or less, more specifically, 70% or less, 69% or less, or 68% or less, or 50% or more, or 52% or more.

[0116] In the present invention, the lithium transition metal oxide may have a ratio of 50% or less of the number of particles with cracks to the total number of particles, more specifically, 5% or more, 10% or more, 12% or more, or 15% or more, and may be 50% or less, 45% or less, 40% or less, 35% or less, or 30% or less.

[0117] In the present invention, when an electrode containing the lithium transition metal oxide is rolled to have a porosity of 11%, the difference in the ratio of the number of cracked particles to the total number of lithium transition metal oxide particles contained in the electrode before and after rolling may be 20% or more and 80% or less, more specifically, 20% or more, 30% or more, or 40% or more, and may be 80% or less, 70% or less, 65% or less, or 60% or less.

[0118] In the present invention, the lithium transition metal oxide has an average particle size (D 50 The diameter may be 1.5 μm or larger, specifically 1.5 μm or larger, 2 μm or larger, 3 μm or larger, or 3.5 μm or larger, and 6 μm or smaller, 4.5 μm or smaller, or 4 μm or smaller.

[0119] 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, when the average particle size of the single particles is within the above range, it is possible to prevent a decrease in performance due to a low rolling density and suppress an increase in resistance.

[0120] In the present invention, the lithium transition metal oxide may be represented by the following Chemical Formula 1.

[0121] [Chemical Formula 1] Li(Ni 1-x-y-z Co x Mn y M z )O2

[0122] In 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 atomic fractions of independent elements, respectively, and 0 < x ≤ 0.25, 0 < y ≤ 0.25, 0 ≤ z < 0.1, 0 < x + y + z ≤ 0.5.

[0123] M is an element substituted for a transition metal site in the oxide represented by Chemical Formula 1, and may contain at least one or more selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo.

[0124] 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 may be 0.5 ≤ 1 - x - y - z < 1, preferably 0.8 ≤ 1 - x - y - z ≤ 0.95.

[0125] [[ID=3④]] 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 may be 0 < x ≤ 0.25, preferably 0.025 ≤ x ≤ 0.1.

[0126] 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 may be 0 < y ≤ 0.25, preferably 0.005 ≤ x ≤ 0.1.

[0127] The value of z represents the molar ratio of M among the metal components excluding lithium in the lithium transition metal oxide represented by the chemical formula 1, and may be 0 ≤ z < 0.1, preferably 0 ≤ z ≤ 0.02.

[0128] Furthermore, the positive electrode active material may further include a coating layer formed on its surface, and the coating layer may preferably contain B (boron).

[0129] The coating layer prevents contact between the positive electrode active material and the electrolyte contained in the lithium secondary battery, thereby suppressing the occurrence of side reactions, which further improves the lifespan characteristics and increases the packing density of the positive electrode active material.

[0130] 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 surface area of ​​the positive electrode active material. When the 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.

[0131] 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.

[0132] In the above method, the secondary firing temperature may be 500°C to 900°C, 600°C to 850°C, or 700°C to 800°C.

[0133] 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).

[0134] Method for manufacturing positive electrode active material 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.

[0135] 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.

[0136] 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 be smooth, 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 degree of sphericization and single-particle formation targeted by this invention.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] The solid-phase raw material mixture produced in step (S1) contains 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 the total transition metals is 0.90 to 1.10.

[0142] 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.

[0143] 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.

[0144] In the present invention, the solid-phase raw material mixture is first calcined and then pulverized.

[0145] The primary firing may be performed at a temperature of 400°C to 900°C. When the primary firing temperature is within the above range, it is possible to prevent the lithium raw material powder and each transition metal raw material powder in the solid phase raw material mixture from being too reactive, which can lead to an increase in unreacted residual lithium, or a deficiency of lithium inside the positive electrode active material, which can reduce the battery's 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's capacity and lifespan.

[0146] 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. 50 The 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.

[0147] The product can be manufactured by mixing lithium raw material powder with the result of step (S2) such that the total molar ratio of lithium to all transition metals is 0.95 to 1.10, and then performing a secondary calcination.

[0148] If the total molar ratio of lithium to the transition metal is less than 0.95 after mixing the lithium raw materials, 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, there is a risk of increased residual lithium and a decrease in the performance of the positive electrode active material.

[0149] In the present invention, the secondary firing temperature may be 500°C to 900°C, 600°C to 850°C, or 700°C to 800°C. The secondary firing time may be 5 to 15 hours, or 7 to 12 hours.

[0150] 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 high degree of single particle formation.

[0151] 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.

[0152] 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.

[0153] For example, the coating element may form a coating layer on the surface of the positive electrode active material by heat treatment.

[0154] 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.

[0155] Furthermore, the present invention provides a positive electrode for a lithium secondary battery containing the positive electrode active material.

[0156] 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.

[0157] 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.

[0158] The positive electrode active material layer may contain a conductive material and a binder together with the positive electrode active material.

[0159] In this case, the positive electrode active material may be present 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 present within the above content range, excellent capacity characteristics can be observed.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] 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.

[0170] The negative electrode active material layer selectively includes a binder and a conductive material together with the negative electrode active material.

[0171] 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.

[0172] The aforementioned 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.

[0173] 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.

[0174] 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.

[0175] 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.

[0176] 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.

[0177] 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.

[0178] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0179] 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.

[0180] 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.

[0181] 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.

[0182] 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).

[0183] 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.

[0184] 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.

[0185] 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.

[0186] 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.

[0187] 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.

[0188] 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.

[0189] 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.

[0190] 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).

[0191] 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.

[0192] 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.

[0193] 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.

[0194] Experimental example Experimental Example 1: Regarding Condition 1 (1) Measurement of cross-sectional area and calculation of average cross-sectional area After manufacturing electrodes (cathodes) containing the cathode active materials produced in the above Examples and Comparative Examples, the electrodes were cut by an ion milling method to obtain cross-sections of the cathodes, and SEM images (at approximately 5K magnification) of the cross-sections of the cathodes were obtained using a SEM (JEOL, JSM-7900F). The cross-sectional areas of the particles were measured using an image processing program, and the average cross-sectional areas were calculated and shown in Tables 1 to 3 below.

[0195] Specifically, 95% by weight of the cathode active materials 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 respective cathode slurries. After applying the produced cathode slurries to one surface of an aluminum current collector, the cathodes were manufactured by drying at 130°C, and rolling was not performed or rolling was performed so that the porosity became x%.

[0196] Using an ion milling apparatus (JEOL, CP-09IB19520CCP, acceleration voltage: 6 kV), the cathode was irradiated with an argon (Ar) ion beam to cut the cathode by an ion milling method to obtain a cross-section of the cathode. Then, a SEM image (at approximately 5K magnification) of the cross-section of the cathode was taken using a SEM (JEOL, JSM-7900F). Thereafter, using an image processing program (a deep learning program, Mask-RCNN model), a two-dimensional segmentation image was obtained in which the boundaries of the particles present in the SEM image were separated and shown in random colors, as shown in FIGS. 1 to 3.

[0197] For reference, image processing operations include methods such as those classified by researchers themselves and image classification methods by deep learning. In the present invention, an image classification method by deep learning is used, but it is not limited thereto.

[0198] The cross-sectional area of ​​each particle is calculated using the number of pixels corresponding to each of the n particles (approximately 100 to 200) present in the segmentation image. The total number of lithium transition metal oxide particles contained in the electrode (total number of particles [particles]) and the ratio of the number of particles present in each cross-sectional area (z) to the total number of lithium transition metal oxide particles contained in the electrode (B x、z [%]), and the average cross-sectional area (X) of the particles present in the segmentation image. x [μm 2 The ]) was calculated and is shown in Tables 1-3 below. However, the cross-sectional area of ​​the particles captured in the resulting images was 3 μm. 2 Particles that were smaller than a certain size or whose overall pattern was not observed in the image were excluded because they could impair the representativeness of the sample.

[0199] Figure 1 is a segmentation image of the cross-section of the positive electrode containing the positive electrode active material manufactured in Example 1.

[0200] Figure 2 is a segmentation image of the cross-section of the positive electrode containing the positive electrode active material manufactured in Example 2.

[0201] 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.

[0202] Figures 1 to 3 show that the positive electrode active materials produced in Examples 1 and 2 have a high degree of single-particle formation, 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 materials produced in Examples 1 and 2 have a single-particle formation consisting of 2 to 10 primary particles, and compared to the positive electrode active material produced in Comparative Example 1, they have fewer grain boundaries and a higher degree of spheroidization, resulting in stronger particle strength and less particle cracking during electrode rolling.

[0203] (2) Calculation of average cross-sectional area change rate For the positive electrode active materials of the above examples and comparative examples, the average cross-sectional area was calculated by method (1) above, either unrolled or under different rolling conditions during electrode manufacturing, and the average cross-sectional area change rate [%] was calculated by the method described below.

number

[0204] The aforementioned X 30≦ This refers to the average cross-sectional area [μm²] of lithium transition metal oxide particles contained in an electrode that contains lithium transition metal oxide and has not undergone rolling. 2 ] and X 11 When the electrode is rolled to a porosity of 11%, the average cross-sectional area [μm²] of the lithium transition metal oxide particles contained in the electrode is obtained. 2 ] and X 14 When the electrode is rolled to a porosity of 14%, the average cross-sectional area [μm²] of the lithium transition metal oxide particles contained in the electrode is obtained. 2 ] and X 16 When the electrode is rolled to a porosity of 16%, the average cross-sectional area [μm²] of the lithium transition metal oxide particles contained in the electrode is obtained. 2 ] and X 20 When the electrode is rolled to a porosity of 20%, the average cross-sectional area [μm²] of the lithium transition metal oxide particles contained in the electrode is obtained. 2 ]

[0205] [Table 1]

[0206] [Table 2]

[0207] [Table 3]

[0208] From Tables 1-3, the positive electrode active material of Examples 1 and 2 has an average cross-sectional area change rate (ΔX) according to formula (1) described herein. 11The ratio of the average cross-sectional area change rate (△X) is 8% or more and 15% or less, and the ratio of the average cross-sectional area change rate (△X) is calculated using formula (3) described herein. 20 It was confirmed that the porosity was between 1% and 15%. Furthermore, in the positive electrode active materials of Examples 1 and 2, when an electrode containing lithium transition metal oxide was rolled to a porosity of 11%, the cross-sectional area relative to the total number of lithium transition metal oxide particles contained in the electrode was 3 μm². 2 ~4μm 2 The proportion of the number of particles (B 11、3-4 ) confirm that it is 40% or less, X 11 is 5 μm 2 More than 10μm 2 I confirmed the following:

[0209] In contrast, the positive electrode active material of Comparative Example 1 has an average cross-sectional area change rate (ΔX) according to formula (1) described herein. 11 ) exceeds 20%, and the average cross-sectional area change rate (△X) according to formula (3) described herein is greater than 20%. 20 It was confirmed that the ratio exceeds 20%. Furthermore, in Comparative Example 1, when the positive electrode active material containing lithium transition metal oxide was rolled to a porosity of 11%, the cross-sectional area relative to the total number of lithium transition metal oxide particles contained in the electrode was 3 μm². 2 ~4μm 2 The proportion of the number of particles (B 11、3-4 ) confirms that it exceeds 40%, X 11 is 5 μm 2 I confirmed that it was less than [amount].

[0210] This means that the positive electrode active material according to the present invention exhibits improved particle cracking during rolling and a low rate of change in cross-sectional area.

[0211] Experimental Example 2: Regarding Condition 2 After manufacturing an electrode (positive electrode) containing the positive electrode active material produced in the above Examples and Comparative Examples, it was cut by an ion milling method to obtain a cross-section of the positive electrode, and a SEM image (approx. 5K magnification) of the cross-section of the positive electrode was taken using a SEM (JEOL, JSM-7900F). Then, using an image processing program, the cross-sectional area of cracks and the cross-sectional area of particles were measured, and C x and A x、y were calculated and shown in Tables 4 to 6 below.

[0212] Specifically, similar to Experimental Example 1, a positive electrode was manufactured and the cross-section of the positive electrode was photographed, and a two-dimensional segmentation image was obtained using an image processing program. In each of the n (approx. 100 to 200) lithium transition metal oxide particles present in the segmentation image, a region that appears black or a region that appears darker than adjacent sites was defined as a crack. Using the number of pixels corresponding to the crack, the cross-sectional area [μm 2 of the crack formed in the lithium transition metal oxide particle was calculated, and using the number of pixels corresponding to the lithium transition metal oxide particle including the cross-sectional area of the crack, the cross-sectional area of the lithium transition metal oxide particle was calculated. The percentage (C x [%]) of the cross-sectional area of the crack formed in the lithium transition metal oxide particle with respect to the cross-sectional area of the lithium transition metal oxide particle, the ratio (A x [%]) of the particles for which C x、y is a constant value (y) according to formula (2) described herein with respect to the total number of particles of the lithium transition metal oxide contained in the electrode, the number of particles with cracks [pieces], and the total number of particles [pieces] are shown in Tables 4 to 6 below.

[0213]

Table 4

[0214]

Table 5

[0215]

Table 6

[0216] From Tables 4-6, the positive electrode active material of Examples 1 and 2 is C according to formula (2) described herein, relative to the total number of lithium transition metal oxide particles contained in the electrode. 11 [%] represents the percentage of particles where the percentage exceeds 6% (A 11、6< It was confirmed that the amount of ) was 3% or more. In addition, the amount of C according to formula (2) described herein was calculated relative to the total number of lithium transition metal oxide particles contained in the electrode. 20 [%] represents the percentage of particles that make up more than 6% (A 20、6< ) is 0.5% or more, and the C is calculated according to formula (2) described herein, relative to the total number of lithium transition metal oxide particles contained in the electrode. 11 [%] represents the proportion of particles that are between 0% and 1% (A 11、0-1 ) is 40% or less, and the C is calculated using formula (2) described herein with respect to the total number of lithium transition metal oxide particles contained in the electrode. 20 [%] represents the proportion of particles that are between 0% and 1% (A 20、0-1 ) is 45% or less, and the C is calculated using formula (2) described herein with respect to the total number of lithium transition metal oxide particles contained in the electrode. 11 [%] represents the proportion of particles that make up 1% to 2% (A 11、1-2 ) is 20% or less, and the C is calculated according to formula (2) described herein with respect to the total number of lithium transition metal oxide particles contained in the electrode. 20 [%] represents the proportion of particles that make up 1% to 2% (A 20、1-2 We confirmed that the percentage was 20% or less.

[0217] In contrast, the positive electrode active material of Comparative Example 1 has a C content of formula (2) described herein relative to the total number of lithium transition metal oxide particles contained in the electrode. 11 [%] represents the percentage of particles that make up more than 6% (A 11、6< It was confirmed that the amount of ) was less than 3%. In addition, the amount of C according to formula (2) described herein was calculated relative to the total number of lithium transition metal oxide particles contained in the electrode. 20 [%] represents the percentage of particles that make up more than 6% (A 20、6<) is less than 0.5%, and the C content is less than 0.5% of the total number of lithium transition metal oxide particles contained in the electrode, according to formula (2) described herein. 11 [%] represents the proportion of particles that are between 0% and 1% (A 11、0-1 ) exceeds 40%, and C according to formula (2) described herein with respect to the total number of lithium transition metal oxide particles contained in the electrode. 20 [%] represents the proportion of particles that are between 0% and 1% (A 20、0-1 ) exceeds 45%, and C according to formula (2) described herein with respect to the total number of lithium transition metal oxide particles contained in the electrode. 11 [%] represents the proportion of particles that make up 1% to 2% (A 11、1-2 ) exceeds 20%, and C according to formula (2) described herein with respect to the total number of lithium transition metal oxide particles contained in the electrode. 20 [%] represents the proportion of particles that make up 1% to 2% (A 20、1-2 We confirmed that the percentage exceeds 20%.

[0218] This means that the lithium transition metal oxide contained in the positive electrode active material of the present invention increases the generation of cracks instead of particle splitting during rolling, resulting in a higher proportion of particles with small-area cracks. Furthermore, the lithium transition metal oxide contained in the positive electrode active material shows that the proportion of particles with cracks increases even more when the rolling strength is increased, and that even at a certain level of high pressure, particle cracks occur at a high frequency instead of particle splitting.

[0219] Experimental Example 3: Regarding Conditions 2-3 The positive electrode active materials produced in the above examples and comparative examples were placed in a circular mold, pressurized with a pressure of 0 to 9 tons, and then the compressed pellets were crushed in a mortar to confirm the particle distribution.

[0220] Figure 6 shows the change in particle size distribution of lithium transition metal oxides contained in the positive electrode after pressurizing the positive electrode containing the positive electrode active material manufactured in Example 1, specifically at pressures of 0 tons, 3 tons, 6 tons, and 9 tons. Specifically, it is a graph of the cumulative distribution function (Q[%]) with respect to particle size [μm], showing the change in particle size distribution.

[0221] Figure 7 shows the change in particle size distribution of lithium transition metal oxides contained in the positive electrode after pressurizing the positive electrode containing the positive electrode active material manufactured in Comparative Example 1, specifically at pressures of 0 tons, 3 tons, 6 tons, and 9 tons. Specifically, it is a graph of the cumulative distribution function (Q[%]) with respect to particle size [μm], showing the change in particle size distribution.

[0222] Figures 6 and 7 show that in Example 1, the positive electrode active material produced showed almost no shift in the distribution curve due to particle cracking when the pressure was increased. However, in Comparative Example 1, particle cracking occurred as the pressure increased, and the particle distribution shifted to the left overall. In conclusion, it can be seen that in the positive electrode active material according to the present invention, cracks occur instead of particles cracking when pressurized.

[0223] Experimental Example 4: Regarding Condition 3 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 taken using an SEM (JEOL, JSM-7900F). Subsequently, the number of lithium transition metal oxide particles with cracks was determined using an image processing program, and the crack particle ratio was calculated and is shown in Tables 7 to 9 below.

[0224] Specifically, the positive electrode was manufactured and its cross-section was photographed in the same manner as in Experimental Example 1, and a two-dimensional segmentation image was obtained using an image processing program. Each of the n (approximately 100 to 200) lithium transition metal oxide particles present in the segmentation image was visually observed, and the presence or absence of cracks was confirmed by determining whether a crack was present in areas that were black or relatively dark compared to adjacent areas, and whether a crack was absent in areas that were white or relatively bright compared to adjacent areas. When the electrode containing lithium transition metal oxide was rolled to a porosity of x%, the total number of lithium transition metal oxide particles (d[particles]) and the number of particles with cracks (c[particles]) contained in the electrode were calculated, and the percentage of the number of particles with cracks (c[particles]) relative to the total number of lithium transition metal oxide particles (d[particles]) was calculated as the crack particle ratio (D x [%]) is shown in Tables 7-9 below.

[0225] [Table 7]

[0226] [Table 8]

[0227] [Table 9]

[0228] From Tables 7-9, the positive electrode active materials of Examples 1 and 2, when an electrode containing lithium transition metal oxide is rolled to a porosity of 11%, have a ratio (D) of the number of cracked particles to the total number of lithium transition metal oxide particles contained in the electrode. 11It was confirmed that the porosity (D) was 78% or less. Furthermore, the positive electrode active material of Examples 1 and 2 was found to have a porosity of 20% when an electrode containing lithium transition metal oxide was rolled, and the ratio of the number of cracked particles to the total number of lithium transition metal oxide particles contained in the electrode was 78% or less. 20 We confirmed that the percentage of particles with cracks was 70% or less, and that the ratio of the number of cracked particles to the total number of lithium transition metal oxide particles was 50% or less.

[0229] In contrast, the positive electrode active material of Comparative Example 1, when an electrode containing lithium transition metal oxide is rolled to a porosity of 11%, has a ratio (D) of the number of cracked particles to the total number of lithium transition metal oxide particles contained in the electrode. 11 It was confirmed that the ratio of cracked particles to the total number of lithium transition metal oxide particles contained in the electrode (D) exceeded 78%. Furthermore, in Comparative Example 1, when the electrode containing lithium transition metal oxide was rolled to a porosity of 20%, the positive electrode active material was found to have a ratio of cracked particles to the total number of lithium transition metal oxide particles contained in the electrode (D). 20 We confirmed that the percentage of particles with cracks exceeded 70%, and that the ratio of the number of cracked particles to the total number of lithium transition metal oxide particles exceeded 50%.

[0230] This indicates that, when the rolling strength of the lithium transition metal oxide contained in the positive electrode active material of the present invention is increased, the proportion of particles in which cracks are formed increases relatively little, meaning that particle cracking is less likely to occur even at a certain level of high pressure.

[0231] Experimental Example 5 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 4 and 5.

[0232] Figures 4(A) and 4(B) are SEM images of the cathode active materials produced in Example 1 and Comparative Example 1, respectively.

[0233] Figures 5(A) to 5(C) are SEM images of the cathode active materials produced in Example 1, Example 2, and Comparative Example 1, respectively.

[0234] Figures 4 and 5 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.

[0235] Experimental Example 6 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.

[0236] 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.

[0237] 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.

[0238] 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 10 and Figure 8 below.

[0239] 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.

[0240] [Table 10]

[0241] Table 10 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 a lithium transition metal oxide in single-particle form, The lithium transition metal oxide is a positive electrode active material that satisfies one or more of the following conditions 1 to 3. [Condition 1] The lithium transition metal oxide has an average cross-sectional area change rate (ΔX) according to the following formula (1). １１ ) is between 5% and 20%; [Math 1] (In formula (1) above, X ３０≦ This refers to the average cross-sectional area [μm²] of lithium transition metal oxide particles contained in an electrode that contains lithium transition metal oxide and has not undergone rolling. ２ ] and X １１ When the electrode is rolled to have a porosity of 11%, the average cross-sectional area [μm²] of the lithium transition metal oxide particles contained in the electrode is obtained. ２ ] [Condition 2] The lithium transition metal oxide is C according to the following formula (2) for the total number of lithium transition metal oxide particles contained in the electrode. １１ The proportion of particles with a percentage exceeding 6% is 3% or more; [Math 2] (In the above formula (2), When an electrode containing lithium transition metal oxide is rolled to a porosity of x%, a is the cross-sectional area [μm²] of the cracks formed in the lithium transition metal oxide particles contained in the electrode. ２ ], where b is the cross-sectional area of ​​the lithium transition metal oxide particles contained in the electrode [μm ２ ] [Condition 3] The lithium transition metal oxide is such that when an electrode containing the lithium transition metal oxide is rolled to a porosity of 11%, the ratio of the number of particles with cracks to the total number of lithium transition metal oxide particles contained in the electrode is 78% or less;

2. The lithium transition metal oxide has an average cross-sectional area change rate (ΔX １１ ) of 8% or more and 15% or less according to the formula (1), and the positive electrode active material according to claim 1.

3. The lithium transition metal oxide has an average cross-sectional area change rate (ΔX) calculated using the following formula (3). ２０ The positive electrode active material according to claim 1, wherein the amount of ) is 1% or more and 15% or less. [Math 3] (In the above formula (3), X ３０≦ This refers to the average cross-sectional area [μm²] of lithium transition metal oxide particles contained in an electrode that contains lithium transition metal oxide and has not undergone rolling. ２ ] and X ２０ When the electrode is rolled to a porosity of 20%, the average cross-sectional area [μm²] of the lithium transition metal oxide particles contained in the electrode is obtained. ２ ]

4. When the electrode containing the lithium transition metal oxide is rolled to a porosity of 11%, the cross-sectional area of ​​the total number of lithium transition metal oxide particles contained in the electrode is 3 μm. ２ ~4μm ２ The positive electrode active material according to claim 1, wherein the proportion of particles that are 40% or less.

5. The aforementioned X １１ 5 μm ２ 10 μm or more ２ The positive electrode active material according to claim 1, which is as follows:

6. The lithium transition metal oxide is calculated as C according to formula (2) with respect to the total number of lithium transition metal oxide particles contained in the electrode. ２０ The positive electrode active material according to claim 1, wherein the proportion of particles with a percentage exceeding 6% is 0.5% or more.

7. The lithium transition metal oxide is calculated as C according to formula (2) with respect to the total number of lithium transition metal oxide particles contained in the electrode. １１ The positive electrode active material according to claim 1, wherein the proportion of particles whose [%] is between 0% and 1% is 40% or less.

8. The lithium transition metal oxide is calculated as C according to formula (2) with respect to the total number of lithium transition metal oxide particles contained in the electrode. ２０ The positive electrode active material according to claim 1, wherein the proportion of particles whose [%] is between 0% and 1% is 45% or less.

9. The lithium transition metal oxide is calculated as C according to formula (2) with respect to the total number of lithium transition metal oxide particles contained in the electrode. １１ The positive electrode active material according to claim 1, wherein the proportion of particles with a percentage of 1% to 2% is 20% or less.

10. The lithium transition metal oxide is calculated as C according to formula (2) with respect to the total number of lithium transition metal oxide particles contained in the electrode. ２０ The positive electrode active material according to claim 1, wherein the proportion of particles with a percentage of 1% to 2% is 20% or less.

11. 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 cracks to the total number of lithium transition metal oxide particles contained in the electrode is 70% or less.

12. The positive electrode active material according to claim 1, wherein the lithium transition metal oxide has a ratio of 50% or less of the number of particles with cracks relative to the total number of particles.

13. The positive electrode active material according to claim 1, wherein when an electrode containing the lithium transition metal oxide is rolled to have a porosity of 11%, the difference in the ratio of the number of cracked particles to the total number of lithium transition metal oxide particles contained in the electrode before and after rolling is 20% or more and 80% or less.

14. 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.

15. 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 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, where 0 < x ≤ 0.25, 0 < y ≤ 0.25, 0 ≤ z < 0.1, and 0 < x + y + z ≤ 0.

5.

16. A positive electrode for a lithium secondary battery, comprising the positive electrode active material described in any one of claims 1 to 15.

17. A lithium secondary battery comprising a positive electrode for a lithium secondary battery as described in claim 16.

Images