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

Abstract

The present invention relates to a positive electrode active material, in which the degree of long axis orientation of crystal grains DoA is 0.5 to 1, and the ratio of crystal grains A having a degree of c-axis orientation of crystal grains of 0.5 to 1, represented by the cross product value of the c-axis rotation vector Rc of the crystal lattice of the crystal grains and the position unit vector P' of the crystal grains obtained through Electron Backscatter Diffraction (EBSD) analysis, accounts for 25% to 80% of all crystal grains in a cross section of the positive electrode active material particle, and a positive electrode and a lithium secondary battery including the same.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0036940, filed on March 22, 2021, and all contents disclosed in the Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material, a positive electrode including the same, and a lithium secondary battery, and more particularly to a positive electrode active material for a lithium secondary battery having excellent life characteristics and resistance characteristics, and a positive electrode and a lithium secondary battery including the same. [Background technology]

[0003] Recently, with the development of technologies and increasing demand for mobile devices and electric vehicles, the demand for secondary batteries as energy sources has been increasing rapidly. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] As the positive electrode active material for lithium secondary batteries, lithium transition metal oxides such as lithium cobalt oxides like LiCoO2, lithium nickel oxides like LiNiO2, lithium manganese oxides like LiMnO2 or LiMn2O4, and lithium iron phosphate oxides like LiFePO4 have been developed. a Co b Mn c ]O2, Li[Ni a Co b Al c ]O2, Li[Ni a Co b Mn c Al d Lithium composite transition metal oxides containing two or more transition metals, such as ]O2, have been developed and are widely used.

[0005] Lithium composite transition metal oxides containing two or more transition metals developed to date are typically produced in the form of spherical secondary particles formed by the aggregation of tens to hundreds of primary particles, but physical properties such as lithium ion mobility and electrolyte impregnation ability vary depending on the orientation and shape (aspect ratio) of the primary particles. Therefore, research is being conducted to improve the performance of positive electrode active materials by controlling the particle structure of the positive electrode active material particles.

[0006] Korean Patent No. 10-1611784 (Patent Document 1) discloses a positive electrode active material in which the length of the a-axis direction of primary particles is longer than the length of the c-axis direction of primary particles, and the a-axes of the primary particles are radially aligned. In Patent Document 1, the morphology and orientation of the primary particles of the positive electrode active material are analyzed using a scanning electron microscope (SEM) and / or a transmission electron microscope (TEM).

[0007] However, the TEM analysis used in Patent Document 1 only provides information on a partial region of the particle, not the entire particle, making it difficult to represent the overall characteristics of the cathode active material particle. Furthermore, since the physical properties of a cathode active material vary depending not only on the morphology and orientation of the primary particles but also on the morphology and orientation of the crystalline, even if the primary particles have similar morphologies and orientations, they may exhibit different physical properties.

[0008] Therefore, in order to develop a positive electrode active material with better properties, research into the crystalline grain structure of the positive electrode active material is required. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to solve the above problems by providing a positive electrode active material that can realize excellent capacity and life characteristics by including crystal grains in a specific ratio, the crystal grains having specific conditions for the orientation of their major axes and c axes.

[0010] The present invention also provides a positive electrode and a lithium secondary battery comprising the positive electrode active material according to the present invention. [Means for solving the problem]

[0011] According to one embodiment, the present invention provides a positive electrode active material for a lithium secondary battery, in which the degree of long axis orientation of the crystal grains, DoA, represented by the following [Equation 1], is 0.5 to 1, and the proportion of crystal grains A having a degree of c-axis orientation of the crystal grains, represented by the cross product of the c-axis rotation vector Rc of the crystal lattice of the crystal grains and the position unit vector P' of the crystal grains, obtained through electron backscatter diffraction (EBSD) analysis, is 25% to 80% of all crystal grains in a cross section of the positive electrode active material particle.

[0012] [Formula 1]

number

[0013] In the formula 1, λ1 is the long axis vector E of the crystal grain measured from image data obtained by scanning ion microscope analysis of the cross section of the positive electrode active material. I λ2 is the magnitude of the minor axis vector E of the crystal grain measured from image data obtained by analyzing the cross section of the positive electrode active material with a scanning ion microscope. II is the size of C D is the position unit vector P' and the major axis unit vector E of the grain I ' is the dot product value.

[0014] In this case, the scanning ion microscope analysis may involve irradiating a cross section of the positive electrode active material with a focused ion beam to obtain a scanning ion microscope image, obtaining segmented data in units of crystal grains from the scanning ion microscope image using deep learning, and calculating the DoA represented by Equation 1 from the segmented data.

[0015] Meanwhile, the Electron Backscatter Diffraction (EBSD) analysis may be performed by measuring a cross section of the positive electrode active material by EBSD to obtain EBSD Euler map data including position information and Euler angle information of each crystal grain, and then calculating the c-axis rotation vector Rc(x, y, z) of the crystal lattice of the crystal grain using the following Equation 2:

[0016] [Formula 2]

number

[0017] In the above [Equation 2], [X, Y, Z] is (0, 0, 1), and Φ, θ, Ψ are Euler angles obtained from Euler map data.

[0018] Preferably, the positive electrode active material may further include crystal grains B having a degree of c-axis orientation of 0.5 to 1 and a DoA of less than 0.5, crystal grains C having a degree of c-axis orientation of less than 0.5 and a DoA of 0.5 to 1, and crystal grains D having a degree of c-axis orientation of less than 0.5 and a DoA of less than 0.5.

[0019] In this case, the combined ratio of crystal grains A and crystal grains C to the total crystal grains in the cross section of the positive electrode active material particle may be 50% to 90%, preferably 50% to 80%. Specifically, to the total crystal grains in the cross section of the positive electrode active material particle, the ratio of crystal grains A may be 25% to 70%, the ratio of crystal grains B may be 5% to 30%, the ratio of crystal grains C may be 20% to 70%, and the ratio of crystal grains D may be 5% to 30%.

[0020] On the other hand, the positive electrode active material may have a crystal grain size of 100 nm to 200 nm, preferably 100 nm to 180 nm, and more preferably 100 nm to 150 nm.

[0021] The positive electrode active material may have a microstrain of 0.04% to 0.25%, preferably 0.06% to 0.15%.

[0022] The positive electrode active material may have an average primary particle size of 0.05 μm to 8 μm, preferably 0.1 μm to 4 μm, and an average secondary particle size of 2 μm to 25 μm, preferably 4 μm to 18 μm.

[0023] Meanwhile, the positive electrode active material may be a lithium composite transition metal oxide represented by the following [Chemical Formula 1]. [Chemical formula 1] Li x [Ni a Co b M 1 c M 2 d ]O 2-y A y In the above [Chemical Formula 1], Said M 1 is one or more elements selected from the group consisting of Mn and Al, 2 is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and A is one or more elements selected from the group consisting of F, Cl, Br, I, At, and S, and 0.98≦x≦1.20, 0 <a<1、0<b<1、0<c<1、0≦d≦0.2、0≦y≦0.2である。

[0024] According to another embodiment, the present invention provides a positive electrode including the positive electrode active material according to the present invention, and a lithium secondary battery including the positive electrode. [Effects of the Invention]

[0025] The positive electrode active material of the present invention contains crystal grains with high long axis and c axis orientation at a specific ratio, and when applied to a secondary battery, can achieve excellent capacity and life characteristics. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 2 is a scanning ion microscope image of a cross section of a positive electrode active material. [Figure 2] 1A and 1B are diagrams illustrating a process of obtaining a segmentation image by analyzing a scanning ion microscope image of a cross section of a positive electrode active material. [Figure 3] FIG. 1 is a diagram showing the long axis orientation of crystal grains and the DoA value. [Figure 4] FIG. 2 is a diagram showing an EBSD Eulerian map obtained by EBSD analysis of a cross section of a positive electrode active material. [Figure 5] FIG. 1 is a diagram showing a c-axis orientation map of crystal grains. DETAILED DESCRIPTION OF THE INVENTION

[0027] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to best explain his / her invention.

[0028] In the present invention, the term "crystal grain" refers to a single-crystal particle unit having a regular atomic arrangement. In the present invention, the crystal grain size can be measured by analyzing X-ray diffraction data of a cross section of the positive electrode active material using Rietveld refinement. For example, the crystal grain size can be obtained by performing X-ray diffraction analysis under the following conditions using an Empyreon XRD system manufactured by Malyer Panalytica to obtain XRD data, and then processing the XRD data using the Highscore program manufactured by Malyer Panalytica. The half-width was determined using the Caglioti equation.

[0029] <X-ray Diffraction Analysis Conditions> Light source: Cu-target, 45 kV, 40 mA output, wavelength = 1.54 Å Detector: GaliPIX3D Sample preparation: A sample of about 5 g was filled into a holder with a diameter of 2 cm and loaded onto a rotation stage (radiation stage). Measurement time: Approximately 30 minutes Measurement range: 2θ = 15° to 85°

[0030] In the present invention, the "primary particle" means the smallest particle unit that can be distinguished as a single mass when observing the cross-section of the positive electrode active material through a scanning electron microscope (SEM). It can consist of one crystal grain or multiple crystal grains. In the present invention, the average particle size of the primary particles can be measured by a method of measuring each particle size distinguished by the SEM data of the cross-section of the positive electrode active material.

[0031] In the present invention, the "secondary particle" means a secondary structure formed by the aggregation of multiple primary particles. The average particle size of the secondary particles can be measured using a particle size analyzer. In the present invention, s3500 of Microtrac was used as the particle size analyzer.

[0032] In the present invention, the "micro strain" is a value measured through Rietveld refinement analysis of X-ray diffraction data and indicates the degree of deformation of the crystal lattice.

[0033] On the other hand, in the present invention, the ratio (%) of each crystal grain means (the number of the crystal grains / the total number of crystal grains present in the cross-section of the positive electrode active material particles) × 100.

[0034] Hereinafter, the present invention will be specifically described.

[0035] The present inventors have conducted extensive research to develop a positive electrode active material that can achieve excellent life and resistance characteristics. As a result, they have found that when the ratio of crystal grains in a positive electrode active material that have a high degree of orientation of the long axis and c axis of the crystal grains satisfies a specific range, the capacity and life characteristics of a secondary battery can be improved, and have completed the present invention.

[0036] positive electrode active material The positive electrode active material according to the present invention is characterized in that the degree of long axis orientation DoA of the crystal grains represented by [Formula 1] is 0.5 to 1, and the proportion of crystal grains A having a degree of c-axis orientation of the crystal grains of 0.5 to 1 satisfies 25% to 80% of the total crystal grains in the cross section of the positive electrode active material particle.

[0037] [Formula 1]

number

[0038] In the above [Equation 1], λ1 is the long axis vector E of the crystal grain measured from image data obtained by scanning ion microscope analysis of the cross section of the positive electrode active material. I λ2 is the magnitude of the minor axis vector E of the crystal grain measured from image data obtained by analyzing the cross section of the positive electrode active material with a scanning ion microscope. II is the size of C D is the position unit vector P' and the major axis unit vector E of the grain I ' is the dot product value.

[0039] First, DoA expressed by the above [Equation 1] will be explained.

[0040] The DoA value expressed by the above [Equation 1] indicates the orientation of the long axis of the crystal grains, and can be determined using data obtained through scanning ion microscope analysis.

[0041] Specifically, a cross section of the positive electrode active material is irradiated with a focused ion beam to obtain a scanning ion microscope image, and then segmented data is obtained from the scanning ion microscope image in units of crystal grains using deep learning.The degree of long axis orientation (DoA) of the crystal grains, expressed by Equation 1, can be calculated from the segmented data.

[0042] The method for determining the DoA value through scanning ion microscope analysis will be described in more detail below.

[0043] A scanning ion microscope (SIM) is a device that irradiates an ion beam onto a sample surface and measures the surface structure of the sample through the resulting signal ion image. Because the ion beam exhibits different reflectances at different crystal planes, a SIM can be used to obtain cross-sectional images of positive electrode active material particles, each separated into single crystal grains with the same atomic arrangement. Figure 1 shows a SIM image of the cross section of a positive electrode active material particle. From Figure 1, it can be seen that the cross-sectional image of the positive electrode active material particle is separated into crystal grains.

[0044] Next, the scanning ion microscope image obtained as described above is analyzed to obtain segmented data in units of crystal grains, and the image analysis may be performed using deep learning.

[0045] A process of analyzing a scanning ion microscope image to obtain segmented data information is shown in Figure 2. As shown in Figure 2, the image analysis can be performed by, for example, detecting boundaries from a scanning ion microscope image through deep learning, and then obtaining image data segmented in units of crystal grains using the boundaries.

[0046] In this case, the boundary detection may be performed using an AutoEncoder Neural Network (U-NET) algorithm, and the segmentation may be performed using a watershed segmentation algorithm or the like.

[0047] Since scanning ion microscope images themselves do not contain digitized information, the present invention obtains segmented data information for each crystal grain through deep learning, thereby enabling information such as the shape and position of the crystal grains to be digitized.

[0048] Once segmented data is obtained through the above-described scanning ion microscope image analysis, the position vector, major axis vector, and minor axis vector of the grain to be measured can be obtained from the data, and the DoA value in Equation 1 can be calculated using the obtained vectors.

[0049] [Formula 1]

number

[0050] In the above [Equation 1], λ1 is the long axis vector E of the crystal grain measured from image data obtained by scanning ion microscope analysis of the cross section of the positive electrode active material. I At this time, the magnitude of the major axis vector E I means the vector that passes through the center of gravity of the crystal grain and has the smallest sum of the distance between the vector and each pixel in the crystal grain.

[0051] λ2 is the minor axis vector E of the crystal grain measured from image data obtained by scanning ion microscope analysis of the cross section of the positive electrode active material. II At this time, the magnitude of the minor axis vector E II means the vector that has the largest sum of the distance between the vector and each pixel in the crystal grain among the vectors that pass through the center of gravity of the crystal grain.

[0052] On the other hand, the above C D is the position unit vector P' of the crystal grain and the major axis unit vector E I The position unit vector P′ of the crystal grain is a vector obtained by converting a position vector connecting the center of the cross section of the positive electrode active material particle to the center of gravity of the crystal grain so that the magnitude of the vector becomes 1, and the major axis unit vector E I ' is the major axis vector E I is a vector converted so that its magnitude becomes 1.

[0053] The DoA value calculated using Equation 1 indicates the degree to which the long axis of the crystal grain is inclined relative to a line passing through the center of the positive electrode active material and the center of gravity of the crystal grain, and the closer the DoA value is to 1, the smaller the angle between the long axis of the crystal grain and the line, and the closer the DoA value is to 0, the larger the angle between the long axis of the crystal grain and the line. In other words, the closer the DoA is to 1, the higher the long axis orientation of the crystal grain.

[0054] Figure 3 shows the DoA values ​​obtained through this method and the long axes of the crystal grains. As shown in Figure 3, in the case of crystal grain 1, where the angle between the long axis of the crystal grain and the line passing through the center of the positive active material and the center of gravity of the crystal grain is small, the DoA was 0.965, which is close to 1. However, in the case of crystal grain 2, where the angle between the long axis of the crystal grain and the line passing through the center of the positive active material and the center of gravity of the crystal grain is large, the DoA was small at 0.352.

[0055] Meanwhile, by mapping the longitudinal orientation information of each crystal grain, the ratio of crystal grains having a specific longitudinal orientation value in the cross section of the positive electrode active material particle can be measured.

[0056] Next, the degree of c-axis orientation of crystal grains will be described.

[0057] The degree of c-axis orientation of the crystal grain indicates the orientation of the c-axis of the crystal lattice of the crystal grain, and is the cross product of the c-axis rotation vector Rc of the crystal lattice of the crystal grain obtained through electron backscatter diffraction (EBSD) analysis and the position unit vector P' of the crystal grain.

[0058] Specifically, the degree of c-axis orientation of the crystal grains can be determined by obtaining EBSD Euler map data including position information and Euler angle information of each crystal grain through electron backscatter diffraction (EBSD) measurement of a cross section of the positive electrode active material, calculating the c-axis rotation vector Rc of the crystal lattice using the EBSD Euler map data, and then calculating the cross product of the c-axis rotation vector Rc of the crystal lattice and the position unit vector P' of the crystal grain.

[0059] The method for determining the degree of c-axis orientation of crystal grains according to the present invention will now be described in detail.

[0060] Electron backscatter diffraction analysis is a method for measuring the crystallographic phase and crystallographic orientation of a sample using its diffraction pattern and then analyzing the sample's crystallographic information based on this information. When a sample (i.e., a cross-section of a cathode active material) is tilted at a large angle relative to the direction of the electron beam in a scanning electron microscope, the incident electron beam scatters within the sample, creating a diffraction pattern along the sample's surface. This is called an electron backscatter diffraction pattern (EBSP). Because the electron backscatter diffraction pattern responds to the crystallographic orientation of the area irradiated by the electron beam, it can be used to accurately measure the sample's crystallographic orientation. EBSD software can then be used to obtain Euler map data containing various information related to the crystallographic orientation of the entire sample. Figure 4 shows an Euler map obtained by electron backscatter diffraction (EBSD) analysis of a cross-section of a cathode active material particle.

[0061] The EBSD Euler map data includes position vector information and Euler angle information for each crystal grain. By using the Euler angle information, the c-axis rotation vector Rc of the crystal lattice in each crystal grain can be obtained.

[0062] The c-axis rotation vector Rc of the crystal lattice indicates the direction in which the c-axis of the crystal grain rotates with respect to a line passing through the center of gravity of the crystal grain and the center of the positive electrode active material.

[0063] Specifically, the c-axis rotation vector Rc of the crystal lattice can be expressed as (x, y, z) calculated by the following [Equation 2].

[0064] [Formula 2]

number

[0065] In the above [Equation 2], [X, Y, Z] is (0, 0, 1), and the above Φ, θ, and Ψ are the Euler angles of each crystal grain obtained from the Euler map data.

[0066] The degree of orientation of the crystal grains can be calculated using the c-axis rotation vector Rc of the crystal lattice calculated as described above and the position vector information of each crystal grain included in the Euler map data. Specifically, the degree of orientation of the crystal grains can be quantified as the cross product of the c-axis rotation vector Rc of the crystal lattice and the position unit vector P' of the crystal grain.

[0067] In this case, the position unit vector P' means the position vector of the crystal grain converted so that its magnitude is 1. For example, if the position vector of the crystal grain is (a, b, o), the position unit vector is

[0068]

number

[0069] This becomes:

[0070] The position unit vector P' and the c-axis rotation vector Rc of the crystal lattice Cross product value is a numerical value indicating the degree of c-axis orientation of the crystal grain within the positive electrode active material particle. Specifically, when the cross product of the position unit vector P' and the c-axis rotation vector Rc of the crystal lattice is 1, this means that the c-axis of the crystal grain is aligned perpendicular to the line passing through the center of the positive electrode active material particle and the center of gravity of the crystal grain, and when the cross product is 0, this means that the c-axis of the crystal grain is aligned horizontally to the line.

[0071] In positive electrode active materials, the mobility of lithium ions when moving perpendicular to the c-axis is more than 10 times faster than when moving along the c-axis. Therefore, a lithium migration path is formed perpendicular to the c-axis. Furthermore, when the lithium migration path is formed parallel to a line passing through the center of the positive electrode active material particle and the center of gravity of the corresponding crystal grain, the lithium migration distance is minimized, thereby improving lithium conductivity. Therefore, the closer the cross product of the position unit vector P' and the c-axis rotation vector Rc of the crystal lattice is to 1, the better the c-axis orientation of the corresponding crystal grain can be determined.

[0072] Meanwhile, by combining the c-axis orientation of each crystal grain obtained as described above, the c-axis orientation of the entire crystal grain in the cross section of the positive electrode active material particle can be obtained. Figure 5 shows a c-axis orientation map of the crystal grains of the positive electrode active material obtained by combining the c-axis orientation of each crystal grain. In Figure 5, red indicates better c-axis orientation, and blue indicates worse c-axis orientation. Using the c-axis orientation map described above, the percentage of crystal grains that satisfy the c-axis orientation conditions in the cross section of the positive electrode active material particle can be determined.

[0073] According to the inventors' research, the ratio of crystal grains (hereinafter referred to as crystal grains A) having a degree of long axis orientation (DoA) of 0.5 to 1 and a degree of c-axis orientation (DoA) of 0.5 to 1 (represented by [Equation 1]) among all crystal grains in the cross section of a positive electrode active material particle can be 25% to 80%, 25% to 70%, 30% to 70%, 30% to 60%, 30% to 50%, or 30% to 40%. It has been found that when the ratio of crystal grains A satisfies the above range, excellent life and capacity characteristics can be realized. If the ratio of crystal grains A is less than 25%, the improvement in life and resistance characteristics cannot be obtained, and if it exceeds 80%, capacity characteristics are reduced.

[0074] Meanwhile, in addition to the crystal grains A, the positive electrode active material according to the present invention may further include crystal grains having a c-axis orientation of 0.5 to 1 and a long axis orientation DoA of less than 0.5 (hereinafter referred to as crystal grains B), crystal grains having a c-axis orientation of less than 0.5 and a long axis orientation DoA of 0.5 to 1 (hereinafter referred to as crystal grains C), and crystal grains having a c-axis orientation of less than 0.5 and a long axis orientation DoA of less than 0.5 (hereinafter referred to as crystal grains D).

[0075] In this case, the combined ratio of crystal grains A and C to the total crystal grains in the cross section of the positive electrode active material particle is preferably 50% to 90%, specifically 50% to 80%, and more specifically 55% to 65%. When the ratio of crystal grains A and C satisfies the above range, better effects can be obtained in terms of life characteristics, particularly resistance characteristics.

[0076] Specifically, of all the crystal grains in the cross section of the positive electrode active material particle, the proportion of crystal grains A may be 25% to 70%, preferably 30% to 60%, more preferably 30% to 50%, and even more preferably 30% to 50%; the proportion of crystal grains B may be 5% to 30%, preferably 10% to 30%, more preferably 15% to 30%, and even more preferably 15% to 25%; the proportion of crystal grains C may be 20% to 70%, preferably 20% to 50%, and even more preferably 20% to 40%; and the proportion of crystal grains D may be 5% to 30%, preferably 10% to 30%, more preferably 15% to 30%, and even more preferably 10% to 20%.

[0077] Meanwhile, the crystal grain ratio of a positive electrode active material varies depending on the composition of a precursor used in preparing the positive electrode active material, the shape and orientation of the crystal grains of the precursor, the type of doping element, and / or the firing temperature, etc. Therefore, a positive electrode active material satisfying the crystal grain ratio of the present invention can be prepared by appropriately adjusting the type of precursor, the doping element, the firing temperature, etc.

[0078] On the one hand, the positive electrode active material according to the present invention can be a lithium composite transition metal oxide containing two or more transition metals, and for example, can be a lithium composite transition metal oxide represented by the following [Chemical Formula 1].

[0079] [Chemical Formula 1] Li x [Ni a Co b M 1 c M 2 d O 2-y A y

[0080] In the above [Chemical Formula 1], the M 1 can be one or more elements selected from the group consisting of Mn and Al.

[0081] The M 2 can be one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo.

[0082] Also, the A can be one or more elements selected from the group consisting of F, Cl, Br, I, At, and S.

[0083] The x represents the molar ratio of Li to the total number of moles of transition metals, and can be 0.98 ≤ x ≤ 1.20, preferably 0.99 ≤ x ≤ 1.10, more preferably 1.0 ≤ x ≤ 1.10.

[0084] The a represents the molar ratio of Ni to the total number of moles of transition metals, and can be 0 < a < 1, preferably 0.3 ≤ a < 1, more preferably 0.6 ≤ a < 1, still more preferably 0.8 ≤ a < 1.

[0085] The b represents the molar ratio of Co to the total number of moles of transition metals, and can be 0 < b < 1, preferably 0 < b < 0.7, more preferably 0 < b < 0.4, still more preferably 0 < b < 0.2.

[0086] c represents the molar ratio of M to the total number of moles of transition metals, where 0 < c < 1, preferably 0 < c < 0.7, more preferably 0 < c < 0.4, and even more preferably 0 < c < 0.2. 1 It can be 0 < c < 1, preferably 0 < c < 0.7, more preferably 0 < c < 0.4, and even more preferably 0 < c < 0.2.

[0087] d represents the molar ratio of M to the total number of moles of transition metals, where 0 ≤ d ≤ 0.2, preferably 0 ≤ d ≤ 0.15, and more preferably 0 ≤ d ≤ 0.10. 2 It can be 0 ≤ d ≤ 0.2, preferably 0 ≤ d ≤ 0.15, and more preferably 0 ≤ d ≤ 0.10.

[0088] y represents the molar ratio of the A element substituted at the oxygen position, where 0 ≤ y ≤ 0.2, preferably 0 ≤ y ≤ 0.15, and more preferably 0 ≤ y ≤ 0.10.

[0089] On the other hand, the positive electrode active material may have a crystal grain size of 100 nm to 200 nm, preferably 100 nm to 180 nm, and more preferably 100 nm to 150 nm. If the crystal grain size becomes too large, a rock salt phase may be formed, resulting in a decrease in resistance characteristics and life characteristics. If the crystal grain size becomes too small, the contact area with the electrolyte increases, and degradation may occur early.

[0090] Also, the positive electrode active material may have a microstrain of 0.04% to 0.25%, preferably 0.06 to 0.15%. If the microstrain is too large, the life characteristics will decline, and if it is too small, the lithium ion mobility will decline.

[0091] Also, the positive electrode active material may have an average primary particle diameter of 0.05 μm to 4 μm, preferably 0.1 μm to 2 μm. If the average primary particle diameter is too large, a rock salt phase may be formed, resulting in a decrease in resistance characteristics and life characteristics. If the average primary particle diameter is too small, the contact area with the electrolyte increases, and degradation may occur early.

[0092] In addition, the positive electrode active material may have an average secondary particle size of 2 μm to 25 μm, preferably 4 μm to 18 μm. When the average secondary particle size satisfies this range, it is possible to prevent the positive electrode active material particles from cracking during the rolling process and to prevent a decrease in processability during slurry preparation.

[0093] positive electrode Next, the positive electrode according to the present invention will be described.

[0094] The positive electrode includes a positive electrode active material according to the present invention. Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, the positive electrode active material layer including the positive electrode active material according to the present invention.

[0095] Here, since the positive electrode active material is the same as that described above, a detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0096] The positive electrode current collector may include a highly conductive metal, and is not particularly limited as long as it easily adheres to the positive electrode active material layer and is non-reactive within the battery voltage range. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum or stainless steel whose surfaces are surface-treated with carbon, nickel, titanium, silver, etc. The positive electrode current collector typically has a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0097] The positive electrode active material layer may optionally contain a conductive material, a binder, and a dispersant in addition to the positive electrode active material, as needed.

[0098] The positive electrode active material may be contained in an amount of 80 to 99 wt %, more specifically 85 to 98.5 wt %, based on the total weight of the positive electrode active material layer, and excellent capacity characteristics can be exhibited when contained in this range.

[0099] The conductive material is used to impart conductivity to the electrode and can be any material that does not cause chemical changes in the resulting battery 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 fibers, such as copper, nickel, aluminum, and silver; conductive tubes, such as carbon nanotubes; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials can be used alone or in combination. The conductive material can be present in an amount of 0.1 to 15 wt % based on the total weight of the positive electrode active material layer.

[0100] The binder serves to improve adhesion between particles of the positive electrode active material and between the positive electrode active material and the current collector. Specific examples of the binder include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, polymers in which hydrogen is substituted with Li, Na, or Ca, or various copolymers thereof, and the like. One or a mixture of two or more of these may be used. The binder may be included in an amount of 0.1 to 15 wt % based on the total weight of the positive electrode active material layer.

[0101] The dispersant can include a water-based dispersant or an organic dispersant such as N-methyl-2-pyrrolidone.

[0102] The positive electrode may be fabricated by a conventional method for fabricating a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode may be fabricated by dissolving or dispersing the positive electrode active material and, optionally, a binder, a conductive material, and a dispersant in a solvent to prepare a positive electrode slurry composition, which is then coated on a positive electrode current collector, followed by drying and rolling.

[0103] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethyl formamide (DMF), acetone, or water, and may be used alone or in combination. The amount of the solvent used may be sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, taking into consideration the coating thickness of the slurry and the manufacturing yield, and to provide a viscosity that allows excellent thickness uniformity when the slurry is subsequently applied to manufacture a positive electrode.

[0104] Alternatively, the positive electrode may be manufactured by casting the positive electrode slurry composition on a separate support, peeling the film from the support, and laminating the film on a positive electrode current collector.

[0105] secondary battery The present invention also provides an electrochemical device including the positive electrode, which may be, for example, a battery or a capacitor, and more specifically, a lithium secondary battery.

[0106] The lithium secondary battery may include a positive electrode, a negative electrode facing the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is the same as that described above, detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0107] The lithium secondary battery may optionally further include a battery container that houses an electrode assembly including the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0108] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0109] The negative electrode current collector may be any material having high conductivity without inducing chemical changes in the battery, and may be, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy. The negative electrode current collector may typically have a thickness of 3 μm to 500 μm, and, like the positive electrode current collector, the current collector surface may be provided with fine irregularities to enhance the binding strength of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0110] The negative electrode active material layer includes a negative electrode active material, and optionally a binder and a conductive material.

[0111] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. 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, and Al alloys; metal oxides capable of doping and dedoping lithium, such as SiOβ(0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; and composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. A mixture of any one or more of these may also be used. A metallic lithium thin film may also be used as the negative electrode active material. Carbon materials may include both low-crystalline carbon and high-crystalline carbon. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, scaly, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-fired carbons such as petroleum or coal tar pitch-derived cokes.

[0112] The negative electrode active material may be included in an amount of 80 wt % to 99 wt % based on the total weight of the negative electrode active material layer.

[0113] The binder is a component that aids in bonding between the conductive material, active material, and current collector, and is typically added in an amount of 0.1 to 10 wt % based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0114] 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 wt % or less, preferably 5 wt % or less, based on the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; carbon fluoride; metal powder such as 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.

[0115] The negative electrode may be manufactured by coating a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector and drying the coating, or by casting the negative electrode slurry composition on a separate support, peeling it off from the support, and laminating the resulting film on the negative electrode current collector.

[0116] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without any particular restrictions. In particular, a separator that exhibits low resistance to electrolyte ion movement and excellent electrolyte humidification capability is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fiber or polyethylene terephthalate fiber, can also be used. Separators coated with ceramic components or polymeric materials to ensure heat resistance or mechanical strength can also be used, and can be used in either a single-layer or multi-layer structure.

[0117] Furthermore, examples of the electrolyte used in the present invention include 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 production of lithium secondary batteries, but are not limited to these.

[0118] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0119] The organic solvent may be any solvent capable of acting as a medium through which ions involved in the electrochemical reaction of the battery can move. Specific examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC) and diethylcarbonate (DEC). ,workman Examples of suitable solvents include carbonate-based solvents such as ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, and may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can enhance the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred. In this case, the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, which can provide excellent electrolyte performance.

[0120] The lithium salt may be any compound capable of providing lithium ions used in a lithium secondary battery, without any particular limitation. Specifically, the anion of the lithium salt may be F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - The lithium salt may be at least one selected from the group consisting of: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The lithium salt may be used at a concentration in the range of 0.1 to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, thereby exhibiting excellent electrolyte performance and allowing lithium ions to migrate effectively.

[0121] As described above, the lithium secondary battery including the cathode active material according to the present invention exhibits excellent capacity and life characteristics and can be usefully used in various fields such as portable devices such as mobile phones, laptops, and digital cameras, and electric vehicles.

[0122] Hereinafter, the present invention will be described in detail with reference to examples. However, the examples according to the present invention can be modified in various ways, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art. [Example]

[0123] Preparation Example 1 - Preparation of Positive Electrode Active Material Precursor A NiSO4, CoSO4, and MnSO4 were mixed in distilled water in amounts such that the molar ratio of nickel:cobalt:manganese was 90:5:5 to prepare a 2.4 M transition metal aqueous solution.

[0124] Next, deionized water was added to the reactor, and nitrogen gas was purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor. Then, 7.96 M NaOH was added to maintain the pH inside the reactor at 11.9.

[0125] Then, the aqueous solution of transition metals was added to the reactor at a rate of 850 mL / hr, and the aqueous NaOH solution was added at a rate of 510 mL / hr and the aqueous NH4OH solution was added at a rate of 160 mL / hr. The reaction was carried out for 40 hours under the conditions of a reaction temperature of 50°C, pH 11.4, and a stirring speed of 600 rpm to obtain Ni. 0.9 Co 0.05 Mn 0.05 A positive electrode active material precursor represented by (OH)2 was prepared.

[0126] Preparation Example 2 - Preparation of Positive Electrode Active Material Precursor B NiSO4, CoSO4, and MnSO4 were mixed in distilled water in amounts such that the molar ratio of nickel:cobalt:manganese was 90:5:5 to prepare a 2.4 M transition metal aqueous solution.

[0127] Next, deionized water was added to the reactor, and nitrogen gas was purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor. Then, 7.96 M NaOH was added to maintain the pH inside the reactor at 11.9.

[0128] Then, the aqueous solution of transition metals was added to the reactor at a rate of 850 mL / hr, and the aqueous NaOH solution was added at a rate of 510 mL / hr and the aqueous NH4OH solution was added at a rate of 540 mL / hr. The reaction was carried out for 40 hours under the conditions of a reaction temperature of 50°C, pH 11.4, and a stirring speed of 600 rpm to obtain Ni. 0.9 Co 0.05 Mn 0.05 A positive electrode active material precursor represented by (OH)2 was prepared.

[0129] Example 1 The positive electrode active material precursor A prepared in Preparation Example 1 and LiOH were mixed so that the molar ratio of Li:transition metal (Ni+Co+Mn) was 1.05:1, and the mixture was fired at 770° C. for 13 hours to obtain Li[Ni 0.9 Co 0.05 Mn 0.05 ]O2 was produced.

[0130] Next, the Li[Ni 0.9 Co 0.05 Mn 0.05 ]O2 was washed with water, dried, and then mixed with 500 ppm of boric acid and heat-treated at 300°C to prepare B-coated positive electrode active material 1.

[0131] Example 2 The cathode active material precursor A prepared in Preparation Example 1 and LiOH were mixed so that the molar ratio of Li:transition metal (Ni+Co+Mn) was 1.05:1, and Ta2O5 was added thereto so that the molar ratio of transition metal:Ta was 99.75:0.25, and the mixture was then calcined at 770°C for 13 hours to obtain Li[Ni 0.9 Co 0.05 Mn 0.05 ] 0.9975 Ta 0.0025 O2 was produced.

[0132] Next, the Li[Ni 0.9 Co 0.05 Mn 0.05 ] 0.9975 Ta 0.0025 O2 was washed with water, dried, and then mixed with 500 ppm of boric acid and heat-treated at 300°C to prepare B-coated positive electrode active material 2.

[0133] Example 3 The cathode active material precursor A prepared in Preparation Example 1 and LiOH were mixed so that the molar ratio of Li:transition metal (Ni+Co+Mn) was 1.05:1, and Nb2O3 was added thereto so that the molar ratio of transition metal:Nb was 99.75:0.25, and the mixture was then calcined at 770°C for 13 hours to obtain Li[Ni 0.9 Co 0.05 Mn 0.05 ] 0.9975 Nb 0.0025 O2 was produced.

[0134] Next, the Li[Ni 0.9 Co 0.05 Mn 0.05 ] 0.9975 Nb 0.0025 O2 was washed with water, dried, and then mixed with 500 ppm of boric acid and heat-treated at 300° C. to prepare B-coated positive electrode active material 3.

[0135] Comparative Example 1 The positive electrode active material precursor B prepared in Preparation Example 2 and LiOH were mixed so that the molar ratio of Li:transition metal (Ni+Co+Mn) was 1.05:1, and the mixture was fired at 770° C. for 13 hours to obtain Li[Ni 0.9 Co 0.05 Mn 0.05 ]O2 was produced.

[0136] Next, the Li[Ni 0.9 Co 0.05 Mn 0.05 ]O2 was washed with water, dried, and then mixed with 500 ppm of boric acid and heat-treated at 300°C to prepare B-coated positive electrode active material 4.

[0137] Comparative Example 2 The positive electrode active material precursor B prepared in Preparation Example 2 and LiOH were mixed so that the molar ratio of Li:transition metal (Ni+Co+Mn) was 1.05:1, and the mixture was fired at 760° C. for 13 hours to obtain Li[Ni 0.9 Co 0.05 Mn 0.05 ]O2 was produced.

[0138] Next, the Li[Ni 0.9 Co 0.05 Mn 0.05 ]O2 was washed with water, dried, and then mixed with 500 ppm of boric acid and heat-treated at 300°C to prepare B-coated positive electrode active material 5.

[0139] Comparative Example 3 The positive electrode active material precursor B prepared in Preparation Example 2 and LiOH were mixed so that the molar ratio of Li:transition metal (Ni+Co+Mn) was 1.05:1, and the mixture was fired at 780° C. for 13 hours to obtain Li[Ni 0.9 Co 0.05 Mn 0.05 ]O2 was produced.

[0140] Next, the Li[Ni 0.9 Co 0.05 Mn 0.05 ]O2 was washed with water, dried, and then mixed with 500 ppm of boric acid and heat-treated at 300°C to prepare B-coated positive electrode active material 6.

[0141] Experimental Example 1 Using an ion milling system (Hitachi, IM4000), the cathode active materials 1 to 6 prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were cross-sectioned, and then the above-mentioned scanning ion microscope analysis and electron backscatter diffraction (EBSD) analysis were performed to measure the ratios of crystal grains A, B, C, and D.

[0142] In addition, XRD data of the cathode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were measured using Malvern Panalytical's Empyrean equipment, and the crystal size and microstrain of each cathode active material were measured using the Reitveld refinement method built into Malvern Panalytical's Highscore program.

[0143] The measurement results are shown in Table 1 below.

[0144] [Table 1] [Table 1]

[0145] Experimental Example 2: Evaluation of battery characteristics The positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3, respectively, a conductive material (denka black), and a binder (PVDF) were mixed in a weight ratio of 97.5:1:1.5 in N-methyl-2-pyrrolidone (NMP) solvent to prepare positive electrode slurries. The positive electrode slurries were applied to one side of an aluminum current collector, dried, and then rolled to prepare positive electrodes.

[0146] A lithium metal electrode was used as the negative electrode.

[0147] The electrode assembly was fabricated by interposing a separator between the positive and negative electrodes, and then placed inside a battery case. An electrolyte solution was then injected to fabricate a lithium secondary battery. The electrolyte solution was prepared by dissolving 1M LiPF6 in an organic solvent containing ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a volume ratio of 3:3:4.

[0148] Next, the secondary batteries were charged at a constant current of 0.1 C at 25° C. up to 4.2 V. Thereafter, they were discharged at a constant current of 0.1 C down to 3 V, and the initial charge capacity and the initial discharge capacity were measured.

[0149] In addition, the secondary batteries were each charged to 4.2 V at 45° C. with a constant current of 0.33 C and then discharged to 3 V with a constant current of 0.33 C, which was defined as one charge-discharge cycle. This cycle was repeated 30 times, and then the capacity retention rate and the resistance increase rate were measured.

[0150] The capacity retention rate and the resistance increase rate were calculated using the following [Equation 3] and [Equation 4].

[0151] [Formula 3] Capacity retention rate (%) = {Discharge capacity after 30 cycles / Discharge capacity after 1 cycle} x 100

[0152] [Formula 4] Resistance increase rate (%) = {(resistance after 30 cycles - resistance after 1 cycle) / resistance after 1 cycle} x 100

[0153] The measurement results are shown in Table 2 below.

[0154] [Table 2] [Table 2]

[0155] As shown in Table 2, the secondary batteries using the cathode active materials of Examples 1 to 3, in which the ratio of crystal grain A satisfies the range of the present invention, exhibited superior capacity characteristics and life characteristics compared to the secondary batteries using the cathode active materials of Comparative Examples 1 to 3.

Claims

1. The degree of orientation of the long axis of the crystal grains, DoA, represented by the following [Equation 1], is 0.5 to 1, and the proportion of crystal grains A having a degree of orientation of the c-axis of the crystal grains, represented by the cross product of the c-axis rotation vector Rc of the crystal lattice of the crystal grains and the position unit vector P' of the crystal grains, obtained through electron backscatter diffraction (EBSD) analysis, is 25% to 80% of all crystal grains in the cross section of the positive electrode active material particle, A positive electrode active material which is a lithium composite transition metal oxide represented by the following [Chemical Formula 1]: [Formula 1] [Equation 1] In the formula 1, λ １ is the long axis vector E of the crystal grain measured from image data obtained by analyzing the cross section of the positive electrode active material with a scanning ion microscope. Ｉ is the size of λ ２ is the minor axis vector E of the crystal grain measured from image data obtained by analyzing the cross section of the positive electrode active material with a scanning ion microscope. ＩＩ is the size of Said C Ｄ is the position unit vector P' and the major axis unit vector E of the crystal grain Ｉ ' is the dot product value. [Chemical formula 1] Li x [Nia Co b M 1 c M 2 d ] O 2-y A y In the [Chemical Formula 1], M 1 is one or more elements selected from the group consisting of Mn and Al; M2 is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; A is one or more elements selected from the group consisting of F, Cl, Br, I, At, and S, 0.98≦x≦1.20, 0<a<1, 0<b<1, 0<c<1, 0≦d≦0.2, 0≦y≦0.

2.

2. 2. The cathode active material of claim 1, wherein the scanning ion microscope analysis involves irradiating a cross section of the cathode active material with a focused ion beam to obtain a scanning ion microscope image, then using deep learning to obtain segmentation data in units of crystal grains from the scanning ion microscope image, and calculating the DoA expressed by Equation 1 from the segmented data.

3. 3. The cathode active material of claim 1, wherein the EBSD analysis involves obtaining EBSD Euler map data including position information and Euler angle information of each crystal grain through EBSD measurement of a cross section of the cathode active material, and calculating a c-axis rotation vector Rc(x, y, z) of a crystal lattice of the crystal grain using the following Equation 2: [Formula 2] [Equation 2] In the formula 2, [X, Y, Z] is (0, 0, 1), and the Φ, θ, and Ψ are Euler angles obtained from Euler map data.

4. The positive electrode active material is Crystal grains B having a DoA of less than 0.5 and a degree of c-axis orientation of the crystal grains of 0.5 to 1; Crystal grains C having a DoA of 0.5 to 1 and a degree of c-axis orientation of the crystal grains of less than 0.5; and The positive electrode active material according to claim 1 , further comprising crystal grains D having the DoA of less than 0.5 and a degree of c-axis orientation of the crystal grains of less than 0.

5.

5. 5. The positive electrode active material according to claim 4, wherein the combined ratio of crystal grains A and crystal grains C to all crystal grains in the cross section of the positive electrode active material particle is 50% to 90%.

6. 6. The cathode active material according to claim 4, wherein, of all the crystal grains in a cross section of the cathode active material particle, a ratio of crystal grains A is 25% to 70%, a ratio of crystal grains B is 5% to 30%, a ratio of crystal grains C is 20% to 70%, and a ratio of crystal grains D is 5% to 30%.

7. The positive electrode active material according to any one of claims 1 to 6, wherein the size of the crystal grains of the positive electrode active material is 100 nm to 200 nm.

8. The positive electrode active material according to any one of claims 1 to 7, wherein the positive electrode active material has a microstrain of 0.04% to 0.25%.

9. 9. The cathode active material according to claim 1, wherein the average particle size of the primary particles of the cathode active material is 0.05 μm to 8 μm.

10. The cathode active material according to any one of claims 1 to 9, wherein the average particle size of the secondary particles of the cathode active material is 2 µm to 25 µm.

11. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 10.

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

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