Positive electrode active materials and positive electrodes and lithium secondary batteries containing them

Abstract

This invention relates to a positive electrode active material and a positive electrode and a lithium secondary battery comprising the same, wherein, in the cross-section of the positive electrode active material particles, the ratio of grains with a long axis orientation degree DoA of 0.5 to 1 and grains with a c-axis orientation degree less than 0.5 is in the range of 25% to 70%, wherein the c-axis orientation degree is expressed as the cross product of the grain's position unit vector P' and the c-axis rotation vector Rc of the grain's lattice obtained by electron backscatter diffraction (EBSD) analysis.

Description

Technical Field

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2021-0002838, filed on January 8, 2021, the contents of which are incorporated herein by reference. Technical Field

[0004] This invention relates to a positive electrode active material and a positive electrode and a lithium secondary battery containing the same, and more specifically, to an excellent positive electrode active material for lithium secondary batteries and a positive electrode and a lithium secondary battery containing the same, wherein the positive electrode active material, when used in a secondary battery, can not only improve the capacity characteristics of the secondary battery, but also reduce the amount of gas generated during the charging and discharging of the secondary battery. Background Technology

[0005] With the recent technological advancements and increasing demands for mobile devices and electric vehicles, the demand for secondary batteries as an energy source has increased significantly. Among these secondary batteries, lithium-ion batteries, characterized by high energy density, high voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0006] As positive electrode active materials for lithium-ion secondary batteries, lithium transition metal oxides have been developed, such as: lithium cobalt oxides like LiCoO2; lithium nickel oxides like LiNiO2; lithium manganese oxides like LiMnO2 or LiMn2O4; or lithium iron phosphates like LiFePO4. Recently, lithium composite transition metal oxides containing two or more transition metals, such as Li[Ni], have been developed and widely used. a Co b Mn c O2, Li[Ni a Co b Al c ]O2 and Li[Ni a Co b Mn c Al d O2.

[0007] Lithium transition metal oxides containing two or more transition metals, developed to date, are typically prepared as spherical secondary particles in which tens to hundreds of primary particles aggregate. Physical properties such as lithium-ion mobility or electrolyte permeability vary with the orientation or shape (aspect ratio) of the primary particles. Therefore, efforts are underway to investigate ways to improve the performance of cathode active materials by controlling the particle structure of these particles.

[0008] Korean Patent No. 10-1611784 (Patent Document 1) discloses a positive electrode active material in which the length of the primary particles in the a-axis direction is greater than the length in the c-axis direction, and the a-axis of the primary particles is arranged radially. In Patent Document 1, the shape or orientation of the primary particles of the positive electrode active material is analyzed using scanning electron microscopy (SEM) and / or transmission electron microscopy (TEM).

[0009] However, the TEM analysis used in Patent Document 1 has limitations because it can only obtain information about a partial region rather than the entire particle, making it difficult to represent the properties of the entire positive electrode active material particle. Furthermore, since the physical properties of the positive electrode active material vary with the shape or orientation of the grains and the shape or orientation of the primary particles, even when the shape or orientation of the primary particles is similar, they may exhibit different physical properties.

[0010] Therefore, it is necessary to study the grain structure of positive electrode active materials in order to develop positive electrode active materials with better properties.

[0011] Existing technical documents

[0012] [Patent Literature]

[0013] (Patent Document 1) Korean Patent No. 10-1611784 Summary of the Invention

[0014] Technical issues

[0015] One aspect of the present invention provides a positive electrode active material that can not only improve the capacity characteristics of a secondary battery when used in a secondary battery, but also reduce the amount of gas generated during the charging and discharging process of the secondary battery by including grains, wherein the orientation of the long axis and c-axis of the grains satisfies specific conditions in a specific ratio.

[0016] Another aspect of the present invention provides a positive electrode and a lithium secondary battery comprising a positive electrode active material according to the present invention.

[0017] Technical solution

[0018] According to one aspect of the present invention, a positive electrode active material for lithium secondary batteries is provided, wherein, in all grains of the cross section of the positive electrode active material particles, the ratio of grains C with a long axis orientation degree DoA of 0.5 to 1 as expressed by [Formula 1] and a c-axis orientation degree of less than 0.5 is in the range of 25% to 70%, wherein the c-axis orientation degree is expressed as the cross product of the grain position unit vector P' and the c-axis rotation vector Rc of the grain lattice obtained by electron backscatter diffraction (EBSD) analysis.

[0019] [Formula 1]

[0020]

[0021] In [Formula 1],

[0022] λ1 is the major axis vector E of the corresponding grain. I The size of the material was measured from image data obtained by scanning ion microscopy analysis of the cross-section of the positive electrode active material.

[0023] λ2 is the minor axis vector E of the corresponding grain. II The size of the material was measured from image data obtained by scanning ion microscopy analysis of the cross-section of the positive electrode active material, and

[0024] C D It is the unit vector E of the major axis of the corresponding grain. I The dot product of 'the unit vector P'.

[0025] In this case, scanning ion microscopy analysis can be performed by obtaining a scanning ion microscopy image by irradiating the cross section of the positive electrode active material with a focused ion beam, obtaining data segmented from the scanning ion microscopy image into grain units by using deep learning, and calculating the DoA expressed by [Equation 1] from the segmented data.

[0026] Electron backscatter diffraction (EBSD) analysis can be performed by obtaining EBSD Euler plot data, including the position information and Euler angle information of each grain, through electron backscatter diffraction (EBSD) measurement of the cross section of the positive electrode active material, and obtaining the c-axis rotation vector Rc(x, y, z) of the grain lattice through [Equation 2].

[0027] [Formula 2]

[0028]

[0029] In [Formula 2],

[0030] [X, Y, Z] is (0, 0, 1), and

[0031] ψ, θ, and ф are Euler angles obtained from Euler plot data.

[0032] Preferably, the positive electrode active material may further comprise: grain A, wherein grain A has a DoA of 0.5 to 1 and a c-axis orientation of 0.5 to 1; grain B, wherein grain B has a DoA of less than 0.5 and a c-axis orientation of 0.5 to 1; and grain D, wherein grain D has a DoA of less than 0.5 and a c-axis orientation of less than 0.5, wherein, in the cross-section of the positive electrode active material particles, the proportion of grain A may be in the range of more than 20% and less than 25%, the proportion of grain B may be in the range of 5% to 30%, the proportion of grain C may be in the range of 25% to 70%, and the proportion of grain D may be in the range of 5% to 30%.

[0033] In this case, the sum of the ratios of grain A and grain C in the cross-section of the positive electrode active material particles can be in the range of 50% to 90%, for example, 50% to 80%.

[0034] The grain size of the positive electrode active material can be 70nm to 200nm, preferably 100nm to 180nm, and more preferably 100nm to 150nm.

[0035] In addition, the positive electrode active material can have micro-strain of 0.04% to 0.25%, for example 0.06% to 0.15%.

[0036] In addition, the positive electrode active material can have an average particle size of primary particles of 0.05 μm to 8 μm, for example 0.1 μm to 4 μm, and an average particle size of secondary particles of 2 μm to 25 μm, for example 4 μm to 18 μm.

[0037] The positive electrode active material can be a lithium composite transition metal oxide represented by [Equation 1].

[0038] [Formula 1]

[0039] Li x [Ni a Co b M 1 c M 2 d ]O 2-y A y

[0040] In [Equation 1],

[0041] M 1 It is at least one element selected from Mn and Al.

[0042] M 2is at least one element selected from 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,

[0043] A is at least one element selected from F, Cl, Br, I, At, and S, and

[0044] 0.98 ≤ x ≤ 1.20, 0 < a < 1, 0 < b < 1, 0 < c < 1, 0 ≤ d ≤ 0.2, and 0 ≤ y ≤ 0.2.

[0045] According to another aspect of the present invention, there is provided a positive electrode including the positive electrode active material according to the present invention and a lithium secondary battery including the positive electrode.

[0046] Advantageous Effects

[0047] Since the positive electrode active material of the present invention includes crystal grains having a specific ratio of high long-axis orientation and low c-axis orientation, excellent capacity characteristics and reduced gas generation characteristics can be achieved when the positive electrode active material is used in a secondary battery. Brief Description of the Drawings

[0048] Figure 1 A scanning ion microscope image showing a cross-section of the positive electrode active material;

[0049] Figure 2 A method for obtaining a segmented image by analyzing a scanning ion microscope image of a cross-section of the positive electrode active material;

[0050] Figure 3 A diagram showing the long-axis orientation and DoA value of the crystal grains;

[0051] Figure 4 An EBSD Euler diagram obtained by performing electron backscatter diffraction (EBSD) analysis on a cross-section of the positive electrode active material;

[0052] Figure 5 A diagram showing the c-axis orientation of the crystal grains. Detailed Description of the Embodiments

[0053] It should be understood that the words or terms used in the specification and claims should not be construed as having the meanings defined in a common dictionary, and it should also be understood that the words or terms should be construed as having meanings consistent with their meanings in the context of the relevant art and the technical idea of the present invention based on the principle that the inventor can appropriately define the meanings of the words or terms to best explain the invention.

[0054] In the present invention, the term "crystal grain" refers to a single crystal unit having a regular atomic arrangement. By analyzing the X-ray diffraction data of the cross-section of the positive electrode active material using the Rietveld refinement method, the size of the crystal grains can be measured. For example, by performing X-ray diffraction analysis using an Empyrean XRD instrument from Malvern Panalytical under the following conditions to obtain XRD data, and then processing the XRD data using the Highscore program from Malvern Panalytical, the crystal grain size can be obtained. In this case, the full width at half maximum is set to be measured using the Caglioti equation.

[0055] <X-ray Diffraction Analysis Conditions>

[0056] X-ray source: Cu-target, 45 kV, 40 mA output,

[0057] Detector: GaliPIX3D

[0058] Sample preparation: Fill approximately 5 g of the sample in a holder with a diameter of 2 cm and load it on a rotating stage.

[0059] Measurement time: Approximately 30 minutes

[0060] Measurement range: 2θ = 15° to 85°

[0061] In the present invention, the term "primary particle" refers to the smallest particle unit that is distinguished as a single entity when observing the cross-section of the positive electrode active material through a scanning electron microscope (SEM), where it can be composed of a single crystal grain or multiple crystal grains. In the present invention, the average particle size of the primary particles is measured by measuring the size of each particle distinguished from the SEM data of the cross-section of the positive electrode active material particles and then calculating the arithmetic mean thereof.

[0062] In the present invention, the term "secondary particle" refers to 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, and in the present invention, Microtrac S3500 is used as the particle size analyzer.

[0063] In the present invention, "microstrain" is a value measured by performing Rietveld refinement analysis on X-ray diffraction data, which is a value representing the degree of lattice deformation.

[0064] The ratio (%) of each crystal grain in the present invention refers to (the number of corresponding crystal grains / the total number of crystal grains present in the cross-section of the positive electrode active material particles) × 100.

[0065] The present invention will be described in detail below.

[0066] As a result of extensive research into developing positive electrode active materials that can not only improve the capacity characteristics of secondary batteries when used in secondary batteries, but also reduce gas generation during the charging and discharging processes of secondary batteries, the inventors have discovered that when the ratio of grains with high long-axis orientation and low c-axis orientation in the grains of the positive electrode active material meets a specific range, the capacity characteristics and gas generation reduction characteristics of the secondary battery can be improved, thus completing the present invention.

[0067] Positive electrode active material

[0068] The positive electrode active material according to the present invention is characterized in that, in all the grains of the cross section of the positive electrode active material particles, the proportion of grains C with a long axis orientation degree DoA of 0.5 to 1 as expressed by [Formula 1] and a c-axis orientation degree of less than 0.5 satisfies 25% to 70%.

[0069] [Formula 1]

[0070]

[0071] In [Formula 1],

[0072] λ1 is the major axis vector E of the corresponding grain. I The size of the material was measured from image data obtained by scanning ion microscopy analysis of the cross-section of the positive electrode active material.

[0073] λ2 is the minor axis vector E of the corresponding grain. II The size of the material was measured from image data obtained by scanning ion microscopy analysis of the cross-section of the positive electrode active material, and

[0074] C D It is the unit vector E of the major axis of the corresponding grain. I The dot product of 'the unit vector P'.

[0075] First, the DoA represented by [Formula 1] will be described.

[0076] The DoA value represented by [Formula 1] is used to indicate the orientation of the grain's long axis, which can be obtained by analyzing data using a scanning ion microscope.

[0077] Specifically, after obtaining a scanning ion microscope image of the cross-section of the positive electrode active material by irradiating it with a focused ion beam, data segmented from the scanning ion microscope image into grain units is obtained by using deep learning, and the grain long axis orientation degree DoA, represented by [Equation 1], can be calculated from the segmented data.

[0078] The method for obtaining DoA values ​​by scanning ion microscopy analysis will be described in more detail below.

[0079] A scanning ion microscope (SI) is a device that measures the surface structure of a sample by scanning the surface with an ion beam and capturing images of the signal ions emitted. In this case, because the reflectivity of the ion beam differs on different crystal planes, a cross-sectional image of the positive electrode active material particles can be obtained using an SI, which is divided into single crystal units with the same atomic arrangement. A SI image of the cross-section of the positive electrode active material particles is shown below. Figure 1 In China. Through Figure 1 It can be confirmed that the cross-sectional image of the positive electrode active material particles is divided into grain units.

[0080] Next, by analyzing the scanning ion microscope images obtained as described above, data segmented into grain units is obtained. In this case, deep learning can be used for image analysis.

[0081] The process of obtaining segmented data information by analyzing scanning ion microscopy images is shown below. Figure 2 In the middle. For example Figure 2 As shown, the image analysis is performed by, for example, obtaining image data of grain units by using the boundary lines after detecting the boundary lines from a scanning ion microscope image using deep learning.

[0082] In this case, the AutoEncoder Neural Network (U-NET) algorithm can be used for boundary line detection, and the Watershed segmentation algorithm can be used for segmentation.

[0083] Since scanning ion microscope images themselves do not contain quantitative information, this invention obtains data information segmented into individual grain units through deep learning, and thereby can quantify information such as the shape and position of the grains.

[0084] If the segmented data is obtained through scanning ion microscopy image analysis as described above, the position vector, major axis vector, and minor axis vector of the grain to be measured from the data can be obtained, and these data can be used to calculate the DoA value of Formula 1.

[0085] [Formula 1]

[0086]

[0087] In [Formula 1],

[0088] λ1 is the major axis vector E of the corresponding grain. IThe size of this is measured from image data obtained by scanning ion microscopy analysis of the cross-section of the positive electrode active material, and in this case, the major axis vector E I It refers to the vector that has the smallest sum of distances between the vector passing through the centroid of the corresponding grain and each pixel in the grain.

[0089] λ2 is the minor axis vector E of the corresponding grain. II The size of this is measured from image data obtained by scanning ion microscopy analysis of the cross-section of the positive electrode active material, and in this case, the minor axis vector E II It refers to the vector that has the largest sum of distances between the vector passing through the centroid of the corresponding grain and each pixel in the grain.

[0090] C D It is the unit vector E of the major axis of the corresponding grain. I The dot product of the position unit vector P' and the position unit vector of the grain, where the grain's position unit vector P' is obtained by converting the position vector with a magnitude of 1 by connecting the centroid of the corresponding grain to the center of the cross-section of the positive electrode active material particle, and the major axis unit vector E I 'is achieved by making the major axis vector E I The vector is obtained by converting it to a value of 1. In this case, the center of the cross-section of the positive electrode active material particle is the centroid in the two-dimensional image (scanning ion microscope image of the cross-section of the positive electrode active material).

[0091] The DoA value calculated using [Formula 1] represents the degree of inclination of the long axis of the corresponding grain relative to a straight line passing through the center of the positive electrode active material and the centroid of the corresponding grain. The closer the DoA value is to 1, the smaller the angle between the long axis of the corresponding grain and the straight line; conversely, the closer the DoA value is to 0, the larger the angle between the long axis of the corresponding grain and the straight line. In other words, it can be said that the closer the DoA value is to 1, the higher the orientation of the grain's long axis.

[0092] A view showing the DoA values ​​obtained by the above method and the corresponding major axes of the grains is presented. Figure 3 In the middle. For example Figure 3 As shown, for grain 1, which has a smaller angle between its long axis and the straight line passing through the center of the positive electrode active material and the corresponding grain centroid, the DoA is 0.965, which is close to 1. However, for grain 2, which has a larger angle between its long axis and the straight line passing through the center of the positive electrode active material and the corresponding grain centroid, the DoA can be understood to be smaller, at 0.352.

[0093] By plotting the long axis orientation information of each of the above grains, the ratio of grains with a specific long axis orientation value in the cross-section of the positive electrode active material particles can be measured.

[0094] Next, the c-axis orientation of the grains will be described.

[0095] The c-axis orientation of a grain is used to represent the c-axis orientation of a grain lattice, where it is the cross product of the grain's unit position vector P' and the c-axis rotation vector Rc of the grain lattice obtained by electron backscatter diffraction (EBSD) analysis.

[0096] Specifically, by performing electron backscatter diffraction (EBSD) measurements on the cross-section of the positive electrode active material, EBSD Euler diagram data including the position information and Euler angle information of each grain is obtained. The c-axis rotation vector Rc of the lattice is obtained by using the EBSD Euler diagram data, and the c-axis orientation of the grain can be obtained by the cross product of the c-axis rotation vector Rc of the lattice and the position unit vector P' of the corresponding grain.

[0097] The method for obtaining the c-axis orientation of grains according to the present invention will be described in detail below.

[0098] Electron backscattering diffraction (EBSD) analysis is a method that uses the diffraction pattern of a sample to measure its grain structure and orientation, and analyzes its grain structure information accordingly. When a sample (i.e., a cross-section of the cathode active material) is tilted at a large angle relative to the incident direction of the electron beam in a scanning electron microscope, a diffraction pattern appears on the surface of the sample as the incident electron beam is scattered within it; this pattern is called the electron backscattering diffraction pattern (EBSP). Because the EBSP pattern responds to the grain structure orientation of the region irradiated by the electron beam, it can be used to accurately measure the grain structure orientation of the sample, and Euler plot data containing various information related to the grain structure orientation of the entire sample can be obtained using EBSD software. The Euler plot obtained by performing electron backscattering diffraction (EBSD) analysis on the cross-section of the cathode active material is shown in [the figure]. Figure 4 middle.

[0099] EBSD Euler plot data includes the position vector information and Euler angle information of each grain. The c-axis rotation vector Rc of the lattice in each grain can be obtained using the Euler angle information.

[0100] The c-axis rotation vector Rc of the lattice indicates the direction of rotation of the c-axis of the corresponding grain relative to the straight line passing through the center of the positive electrode active material and the centroid of the corresponding grain.

[0101] Specifically, the c-axis rotation vector Rc of the lattice can be calculated as (x, y, z) using the following [Formula 2].

[0102] [Formula 2]

[0103]

[0104] In [Formula 2], [X, Y, Z] is (0, 0, 1), and ψ, θ, and ф are the Euler angles of each grain obtained from Euler plot data.

[0105] Grain orientation can be obtained by using the c-axis rotation vector Rc of the lattice obtained as described above and the position vector information of each grain contained in the Euler plot data. Specifically, grain orientation can be quantified as the value obtained by the cross product of the c-axis rotation vector Rc of the lattice and the unit position vector P' of the grain.

[0106] In this context, the position unit vector P' refers to the vector that transforms the position vector of the corresponding grain in such a way that its magnitude is 1. For example, if the position vector of the corresponding grain is (a, b, 0), then the position unit vector becomes...

[0107] The cross product of the lattice position unit vector P' and the c-axis rotation vector Rc is a numerical value indicating the c-axis orientation of the corresponding grain in the cathode active material particles. Specifically, when the cross product of the lattice position unit vector P' and the c-axis rotation vector Rc is 1, it means that the c-axis of the corresponding grain is set perpendicular to a straight line passing through the center of the cathode active material and the centroid of the corresponding grain, while when the cross product is 0, it means that the c-axis of the corresponding grain is set horizontally relative to the straight line.

[0108] In cathode active materials, the mobility of lithium ions moving along the direction perpendicular to the c-axis is more than 10 times that moving along the c-axis. Therefore, lithium paths are formed along the direction perpendicular to the c-axis. Furthermore, because the lithium migration distance is shortest when the lithium path is formed parallel to a straight line passing through the center of the cathode active material and the centroid of the corresponding grain, the conductivity of lithium is improved. Therefore, it can be considered that the closer the cross product of the position unit vector P' and the c-axis rotation vector Rc of the lattice is to 1, the better the c-axis orientation of the corresponding grain.

[0109] When the c-axis orientation degrees of the individual grains obtained as described above are combined, the c-axis orientation degrees of all grains in the cross-section of the cathode active material particle can be obtained. The c-axis orientation of the cathode active material grains obtained by combining the c-axis orientation degrees of the individual grains is illustrated in the figure below. Figure 5 In. Figure 5 In the diagram, the closer the color is to red, the better the c-axis orientation; conversely, the closer the color is to blue, the worse the c-axis orientation. Using the c-axis orientation diagram described above, the ratio of grains satisfying the c-axis orientation condition in the cross-section of the positive electrode active material particles can be obtained.

[0110] According to the inventors' research, the proportion of grains with a long axis orientation degree DoA of 0.5 to 1 and a c-axis orientation degree of less than 0.5 (hereinafter referred to as grains C) in the total number of grains in the cross-section of the positive electrode active material particles can be in the range of 25% to 70%, preferably 25% to 60%, more preferably 30% to 65%, for example, in the range of 30% to 45%. When the proportion of grains C meets the above range, it has been found that excellent capacity characteristics and gas generation reduction characteristics can be achieved. When the proportion of grains C is less than 25%, it may not be possible to obtain the effect of improving capacity characteristics and gas generation characteristics, while when the proportion of grains C is greater than 70%, not only are the lifetime characteristics deteriorated, but it may also be impossible to obtain the effect of improving gas generation characteristics.

[0111] In addition to grain C, the positive electrode active material according to the present invention may also include grains with a c-axis orientation degree of 0.5 to 1 and a long axis orientation degree DoA of 0.5 to 1 (hereinafter referred to as grain A), grains with a c-axis orientation degree of 0.5 to 1 and a long axis orientation degree DoA of less than 0.5 (hereinafter referred to as grain B), and grains with a c-axis orientation degree of less than 0.5 and a long axis orientation degree DoA of less than 0.5 (hereinafter referred to as grain D). Among all grains in the cross-section of the positive electrode active material particles, the proportion of grain A can be in the range of 20% or more and less than 25%, the proportion of grain B can be in the range of 5% to 30%, the proportion of grain C can be in the range of 25% to 70%, and the proportion of grain D can be in the range of 5% to 30%.

[0112] In this case, it is desirable that the sum of the ratios of grain A and grain C in the cross-section of the positive electrode active material particles be in the range of 50% to 90%, particularly 50% to 80%, and even more particularly 55% to 65%. When the ratio of grain A to grain C meets the above range, better performance can be obtained in terms of capacity characteristics and lifetime characteristics, especially lifetime characteristics.

[0113] Because the grain ratio of the positive electrode active material varies with the composition of the precursor used in the preparation of the positive electrode active material, the grain shape and orientation of the precursor, the type of dopant element and / or the sintering temperature, a positive electrode active material with a grain ratio that meets the requirements of the present invention can be prepared by appropriately adjusting the type of precursor, the dopant element and the sintering temperature.

[0114] The positive electrode active material according to the present invention can be a lithium composite transition metal oxide containing two or more transition metals, for example, it can be a lithium composite transition metal oxide represented by the following [Formula 1].

[0115] [Formula 1]

[0116] Li x [Ni a Co b M 1 c M 2 d O 2-y A y

[0117] In [Formula 1],

[0118] M 1 may be at least one element selected from Mn and Al.

[0119] M 2 may be at least one element selected from 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.

[0120] In addition, A may be at least one element selected from F, Cl, Br, I, At, and S.

[0121] x represents the ratio of the mole number of Li to the total mole number of transition metals, where x may satisfy 0.98 ≤ x ≤ 1.20, preferably 0.99 ≤ x ≤ 1.10, and more preferably 1.0 ≤ x ≤ 1.10.

[0122] a represents the ratio of the mole number of Ni to the total mole number of transition metals, where a may satisfy 0 < a < 1, preferably 0.3 ≤ a < 1, more preferably 0.6 ≤ a < 1, for example 0.8 ≤ a < 1.

[0123] b represents the ratio of the mole number of Co to the total mole number of transition metals, where b may satisfy 0 < b < 1, preferably 0 < b < 0.7, more preferably 0 < b < 0.4, for example 0 < b < 0.2.

[0124] c represents the ratio of the mole number of M 1 to the total mole number of transition metals, where c may satisfy 0 < c < 1, preferably 0 < c < 0.7, more preferably 0 < c < 0.4, for example 0 < c < 0.2.

[0125] d represents the ratio of the mole number of M 2 to the total mole number of transition metals, where d may satisfy 0 ≤ d ≤ 0.2, preferably 0 ≤ d ≤ 0.15, and more preferably 0 ≤ d ≤ 0.10.

[0126] y represents the ratio of the mole number of element A substituted at the oxygen site, where y may satisfy 0 ≤ y ≤ 0.2, preferably 0 ≤ y ≤ 0.15, and more preferably 0 ≤ y ≤ 0.10.

[0127] The positive electrode active material can have a grain size of 70nm to 200nm, preferably 100nm to 180nm, and more preferably 100nm to 150nm. If the grain size is increased too much, a rock salt phase may be formed, which will reduce the resistivity and lifetime characteristics. If the grain size is decreased too much, the contact area with the electrolyte may increase, which will cause rapid deterioration.

[0128] Furthermore, the micro-strain of the positive electrode active material can be 0.04% to 0.25%, for example, 0.06% to 0.15%. If the micro-strain is too large, the lifetime characteristics will deteriorate, while if the micro-strain is too small, the lithium-ion mobility will decrease.

[0129] Furthermore, the positive electrode active material can have an average primary particle size of 0.05 μm to 4 μm, for example, 0.1 μm to 2 μm. If the average primary particle size is too large, a rock salt phase may form, reducing resistivity and lifetime characteristics. Conversely, if the average primary particle size is too small, the contact area with the electrolyte may increase, leading to rapid degradation.

[0130] Furthermore, the positive electrode active material can have an average particle size of secondary particles ranging from 2 μm to 25 μm, for example, from 4 μm to 18 μm. When the average particle size of the secondary particles meets the above range, it can prevent the particles of the positive electrode active material from breaking during the rolling process or reducing the processability during the slurry preparation process.

[0131] positive electrode

[0132] Next, the positive electrode according to the present invention will be described.

[0133] The positive electrode comprises the positive electrode active material according to the present invention. Specifically, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material according to the present invention.

[0134] In this case, since the positive electrode active material is the same as described above, its detailed description will be omitted, and only the remaining structure will be described in detail below.

[0135] The positive electrode current collector can include a highly conductive metal, and there are no particular limitations, as long as it is non-reactive within the battery's voltage range and the positive electrode active material layer can easily adhere to it. Examples of materials that can be used as the positive electrode current collector include: stainless steel, aluminum, nickel, titanium, calcined carbon; or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. Furthermore, the positive electrode current collector typically has a thickness of 3μm to 500μm, and fine irregularities can be formed on its surface to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various shapes such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0136] In addition to the positive electrode active material, the positive electrode active material layer may optionally also include conductive materials, binders, and dispersants, if desired.

[0137] In this case, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be 80% to 99% by weight, for example, 85% to 98.5% by weight. When the content of the positive electrode active material is within the above range, excellent capacity characteristics can be obtained.

[0138] Conductive materials are used to provide conductivity to the electrodes. Any conductive material can be used without particular restriction, as long as it has suitable electronic conductivity and does not cause adverse chemical changes in the battery. Specific examples of conductive materials include: graphite such as natural or artificial graphite; carbon materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, and carbon fibers; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and any one or a mixture of two or more of them can be used. Based on the total weight of the positive electrode active material layer, the content of the conductive material can be from 0.1% to 15% by weight.

[0139] The adhesive improves the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples of the adhesive can be 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 monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid and polymers whose hydrogen is replaced by Li, Na, or Ca, or various copolymers thereof, and any one or a mixture of two or more thereof can be used. Based on the total weight of the positive electrode active material layer, the adhesive content can be from 0.1% to 15% by weight.

[0140] The dispersant may contain aqueous dispersants or organic dispersants such as N-methyl-2-pyrrolidone.

[0141] In addition to using the aforementioned positive electrode active material, a positive electrode can be prepared according to typical methods for preparing a positive electrode. Specifically, a positive electrode slurry composition prepared by dissolving or dispersing the aforementioned positive electrode active material, along with optional binders, conductive materials, and dispersants in a solvent as needed, can be coated onto a positive electrode current collector. The coated positive electrode current collector can then be dried and rolled to produce a positive electrode.

[0142] The solvent can be one commonly used in the art and can include dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, and any one of them or a mixture of two or more thereof can be used. The amount of solvent used may be sufficient if, taking into account the coating thickness and manufacturing yield of the slurry, the solvent can dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, and can result in a viscosity that provides excellent thickness uniformity during subsequent coating for the preparation of the positive electrode.

[0143] In addition, as another method, the positive electrode can be prepared by casting the positive electrode slurry composition onto a separate carrier and then pressing the membrane layer separated from the carrier onto the positive electrode current collector.

[0144] Secondary batteries

[0145] Furthermore, in this invention, an electrochemical device comprising the aforementioned positive electrode can be prepared. Specifically, the electrochemical device can be a battery or a capacitor, such as a lithium secondary battery.

[0146] A lithium secondary battery may specifically include a positive electrode, a negative electrode facing the positive electrode, a separator disposed between the positive and negative electrodes, and an electrolyte. Since the positive electrode is the same as described above, its detailed description will be omitted, and only the remaining structures will be described in detail below.

[0147] In addition, the lithium secondary battery may optionally include a battery container that houses an electrode assembly of a positive electrode, a negative electrode and a separator, and a sealing member that seals the battery container.

[0148] In a lithium secondary battery, the negative electrode includes a negative electrode current collector and a layer of negative electrode active material disposed on the negative electrode current collector.

[0149] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and does not cause adverse chemical changes in the battery. Materials used include, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon; copper or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc.; and aluminum-cadmium alloys. Furthermore, the negative electrode current collector can typically have a thickness of 3μm to 500μm, and similar to the positive electrode current collector, fine irregularities can be formed on its surface to improve the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various shapes such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0150] In addition to the negative electrode active material, the negative electrode active material layer optionally also includes a binder and a conductive material.

[0151] Compounds capable of reversibly inserting and deintercalating lithium can be used as anode active materials. Specific examples of anode active materials include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; (semi-)metallic materials capable of forming alloys with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and (semi-)metal oxides that can be doped or undoped with lithium, such as SiO2. β (0<β<2), SnO2, vanadium oxide and lithium vanadium oxide; or composite materials containing (semi-)metallic materials and carbonaceous materials such as Si-C composite materials or Sn-C composite materials, and any one of them or a mixture of two or more thereof can be used. Additionally, lithium metal thin films can be used as the negative electrode active material. Furthermore, both low-crystallinity carbon and high-crystallinity carbon can be used as carbon materials. Typical examples of low-crystallinity carbon can be soft carbon and hard carbon, and typical examples of high-crystallinity carbon can be irregular, planar, sheet-like, spherical or fibrous natural or artificial graphite, condensed graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch and high-temperature sintered carbon such as coke derived from petroleum or coal tar pitch.

[0152] Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material can be 80% to 99% by weight.

[0153] The adhesive is a component that facilitates the bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of adhesives include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0154] The conductive material is a component used to further improve the conductivity of the negative electrode active material, wherein the conductive material can be added in an amount of less than 10% by weight, for example, less than 5% by weight, based on the total weight of the negative electrode active material layer. There are no particular limitations on the conductive material, as long as it is conductive and will not cause adverse chemical changes in the battery, and conductive materials such as: graphite such as natural or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; conductive fibers such as carbon fibers or metal fibers; fluorocarbons; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or polyphenylene derivatives.

[0155] As an example, a negative electrode active material layer can be prepared by coating a negative electrode slurry composition, which is prepared by dissolving or dispersing the negative electrode active material and optionally a binder and conductive material in a solvent, onto a negative electrode current collector and drying the coated negative electrode current collector. Alternatively, the negative electrode active material layer can be prepared by casting the negative electrode slurry composition onto a separate carrier and then pressing the film layer separated from the carrier onto the negative electrode current collector.

[0156] In lithium-ion secondary batteries, the separator separates the negative and positive electrodes and provides a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is commonly used in lithium-ion secondary batteries. In particular, separators with high electrolyte retention capacity and low resistance to electrolyte ion transfer can be used. Specifically, porous polymer membranes can be used, such as porous polymer membranes prepared from polyolefin polymers like ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers; or laminated structures having two or more layers. Furthermore, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers. Additionally, separators coated with ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and separators with single-layer or multi-layer structures can optionally be used.

[0157] Furthermore, the electrolyte used in this invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, or molten inorganic electrolytes that can be used to prepare lithium secondary batteries, but this invention is not limited thereto.

[0158] Specifically, the electrolyte may contain organic solvents and lithium salts.

[0159] Any organic solvent can be used without particular limitation, as long as it serves as a medium through which ions participating in the battery electrochemical reaction can move. Specifically, the following substances can be used as the organic solvent: 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 solvents such as benzene and fluorobenzene; or carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (where R is a linear, branched, or cyclic C2-C20 hydrocarbon group and may contain double bonds, aromatic rings, or ether bonds); amides such as dimethylformamide; dioxolane such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate solvents can be used. For example, a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant, which can improve the charge / discharge performance of the battery, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) can be used. In this case, when cyclic carbonates and linear carbonates are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte can be excellent.

[0160] Lithium salts can be used without particular restrictions, as long as they are compounds capable of providing lithium ions used in lithium secondary batteries. Specifically, the anion of the lithium salt can be at least one selected from the following: 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 following substances can be used as the lithium salt: 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 can be used in a concentration range of 0.1 M to 2.0 M. If the concentration of the lithium salt is included in the above range, excellent electrolyte performance can be obtained because the electrolyte can have appropriate conductivity and viscosity, and lithium ions can move efficiently.

[0161] As described above, lithium secondary batteries containing the positive electrode active material according to the present invention stably exhibit excellent capacity characteristics and reduced gas generation characteristics, and are suitable for various fields such as portable devices such as mobile phones, laptops, digital cameras; and electric vehicles.

[0162] Methods of implementing the present invention

[0163] The invention will be described in detail below with reference to specific examples. However, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these exemplary embodiments are provided to make this specification thorough and complete and to fully convey the scope of the invention to those skilled in the art.

[0164] Example

[0165] Preparation Example 1 - Preparation of Precursor A for Positive Electrode Active Material

[0166] NiSO4, CoSO4, and MnSO4 were mixed in distilled water in amounts such that the molar ratio of nickel:cobalt:manganese was 92:4:4 to prepare a 2.4 M aqueous solution of transition metals.

[0167] Subsequently, after adding deionized water to the reactor, dissolved oxygen in the water was removed by purging the reactor with nitrogen to create a non-oxidizing atmosphere. Then, 7.96M NaOH was added to maintain the pH in the reactor at 11.9.

[0168] Subsequently, while adding aqueous solutions of transition metals, NaOH, and NH4OH at rates of 850 mL / h, 510 mL / h, and 160 mL / h, respectively, to the reactor, the reaction was carried out at a reaction temperature of 50 °C, a pH of 11.4, and a stirring speed of 600 rpm for 40 hours to prepare the average particle size (D). 50 The value is 13 μm and it is made of Ni 0.92 Co 0.04 Mn 0.04(OH)2 represents precursor A of the positive electrode active material.

[0169] Preparation Example 2 - Preparation of Precursor B for Positive Electrode Active Material

[0170] Except for carrying out the coprecipitation reaction for 12 hours, the average particle size (D) was prepared in the same manner as in Preparation Example 1. 50 ) is 4μm and is made of Ni 0.92 Co 0.04 Mn 0.04 (OH)2 represents precursor B of the positive electrode active material.

[0171] Example 1

[0172] The positive electrode active material precursor A prepared in Preparation Example 1 was mixed with LiOH such that the molar ratio of Li to transition metal was 1.05:1, and Nb2O3 was further mixed with it such that the molar ratio of Nb to transition metal was 0.00125:1. The mixture was then sintered at 760°C for 13 hours to prepare Li[Ni] 0.92 Co 0.04 Mn 0.04 ] 0.99875 Nb 0.00125 O2.

[0173] Then, in Li[Ni 0.92 Co 0.04 Mn 0.04 ] 0.99875 Nb 0.00125 After washing and drying with water, O2 is mixed with 500 ppm of boric acid and heat-treated at 300 °C to prepare B-coated positive electrode active material 1.

[0174] Example 2

[0175] Except that Nb2O3 was further mixed in such a way that the molar ratio of Nb to transition metal was 0.0025:1, the positive electrode active material 2 was prepared in the same manner as in Example 1.

[0176] Comparative Example 1

[0177] The positive electrode active material precursor A prepared in Example 1 was mixed with LiOH and sintered at 760°C for 13 hours to prepare Li[Ni], such that the molar ratio of Li to transition metal was 1.05:1. 0.92 Co 0.04 Mn 0.04 O2.

[0178] Then, in Li[Ni 0.92 Co 0.04 Mn 0.04After washing and drying with water, O2 is mixed with 500 ppm of boric acid and heat-treated at 300 °C to prepare B-coated positive electrode active material 3.

[0179] Comparative Example 2

[0180] The positive electrode active material precursor A prepared in Preparation Example 1 was mixed with LiOH such that the molar ratio of Li to transition metal was 1.05:1, and then Ta₂O₃ was further mixed with it such that the molar ratio of Ta to transition metal was 0.0025:1. The mixture was then sintered at 760°C for 13 hours to prepare Li[Ni] 0.92 Co 0.04 Mn 0.04 ] 0.9975 Ta 0.0025 O2.

[0181] Then, in Li[Ni 0.92 Co 0.04 Mn 0.04 ] 0.9975 Ta 0.0025 After washing and drying with water, O2 is mixed with 500 ppm of boric acid and heat-treated at 300 °C to prepare B-coated positive electrode active material 4.

[0182] Comparative Example 3

[0183] The positive electrode active material precursor B prepared in Preparation Example 2 was mixed with LiOH such that the molar ratio of Li to transition metal was 1.05:1, and Nb2O3 was further mixed with it such that the molar ratio of Nb to transition metal was 0.0025:1. The mixture was then sintered at 770°C for 13 hours to prepare Li[Ni] 0.92 Co 0.04 Mn 0.04 ] 0.9975 Nb 0.0025 O2.

[0184] Then, in Li[Ni 0.92 Co 0.04 Mn 0.04 ] 0.9975 Nb 0.0025 After washing and drying with water, O2 is mixed with 500 ppm of boric acid and heat-treated at 300 °C to prepare B-coated positive electrode active material 5.

[0185] Experimental Example 1: Analysis of Positive Electrode Active Materials

[0186] After cross-sectioning of various positive electrode active materials 1 to 5 prepared by Examples 1 and 2 and Comparative Examples 1 to 3 using an ion milling system (Hitachi, IM4000), the above-mentioned scanning ion microscopy analysis and electron backscatter diffraction (EBSD) analysis were performed to measure the ratio of grains A, B, C and D.

[0187] In addition, XRD data of the positive electrode active materials 1-5 prepared in Examples 1 and 2 and Comparative Examples 1-3 were measured using an Empyrean instrument from Malvern Panalytical, and the grain size and microstrain of various positive electrode active materials were measured using the Rietveld refinement method built into the Highscore program of Malvern Panalytical.

[0188] The measurement results are shown in Table 1 below.

[0189] [Table 1]

[0190]

[0191] Experimental Example 2: Battery Characteristic Evaluation

[0192] Various positive electrode active materials, conductive materials (Denka Black), and binders (PVDF) prepared in Examples 1 and 2 and Comparative Examples 1-3 were mixed in N-methyl-2-pyrrolidone (NMP) solvent at a weight ratio of 97.5:1:1.5 to prepare a positive electrode slurry. The positive electrode slurry was coated onto one surface of an aluminum current collector, dried, and then rolled to prepare the positive electrode.

[0193] A lithium metal electrode is used as the negative electrode.

[0194] Various lithium-ion secondary batteries were fabricated by placing an electrode assembly between the positive and negative electrodes, housing the electrode assembly in a battery casing, and then injecting an electrolyte. In this case, an electrolyte in which 1 M LiPF6 was dissolved in an organic solvent containing ethylene carbonate, ethyl carbonate, and diethyl carbonate in a volume ratio of 3:3:4 was used as the electrolyte.

[0195] Then, the various secondary batteries were charged to 4.2V at a constant current of 0.1C at 25°C. Subsequently, the various secondary batteries were discharged to 3V at a constant current of 0.1C to determine the initial charge capacity and initial discharge capacity, and the results are shown in Table 2 below.

[0196] In addition, various positive electrode active materials, conductive materials (Denka Black), and binders (PVDF) prepared in Examples 1 and 2 and Comparative Examples 1-3 were mixed in N-methyl-2-pyrrolidone (NMP) solvent at a weight ratio of 97.5:1:1.5 to prepare a positive electrode slurry. The positive electrode slurry was coated on one surface of an aluminum current collector, dried, and then rolled to prepare the positive electrode.

[0197] Next, the negative electrode active material (natural graphite), conductive material (carbon black), and binder (PVDF) were mixed in an N-methyl-2-pyrrolidone (NMP) solvent at a weight ratio of 95.6:1:3.4 to prepare a negative electrode slurry. The negative electrode slurry was coated onto one surface of a copper current collector, dried, and then rolled to prepare the negative electrode.

[0198] Various lithium-ion secondary batteries were fabricated by placing an electrode assembly between the positive and negative electrodes, housing the electrode assembly in a battery casing, and then injecting an electrolyte. In this case, an electrolyte in which 1 M LiPF6 was dissolved in an organic solvent containing ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7 was used as the electrolyte.

[0199] Then, the various secondary batteries were charged to 4.2V at a constant current of 0.1C at 25°C. Subsequently, the various secondary batteries were discharged to 3V (1 cycle) at a constant current of 0.1C, followed by 200 charge-discharge cycles at 45°C within the range of 3V to 4.2V at a constant current of 0.33C. In this case, the capacity retention rate (%) was calculated by dividing the discharge capacity of the 200th cycle by the discharge capacity of the 1st cycle and then multiplying by 100, and the results are shown in Table 2 below.

[0200] Secondary batteries undergoing one charge-discharge cycle and 200 charge-discharge cycles were punctured in a vacuum chamber to expel internal gases. The gases were collected in the vacuum chamber, and the amount of gas generated was quantitatively analyzed using gas chromatography-flame ionization detector (GC-FID). The gas generation from the secondary battery undergoing 200 charge-discharge cycles was then divided by the gas generation from the secondary battery undergoing one charge-discharge cycle to calculate the gas increase (%), and the results are shown in Table 2 below.

[0201] [Table 2]

[0202]

[0203] As shown in [Table 2], it can be confirmed that the secondary batteries using the positive electrode active materials of Examples 1 and 2, wherein the ratio of crystallite C satisfies the scope of the present invention, have better capacity characteristics and gas generation reduction characteristics than the secondary batteries using the positive electrode active materials of Comparative Examples 1 to 3. Furthermore, it can be confirmed that the secondary batteries using the positive electrode active materials of Examples 1 and 2 have lifespan characteristics equal to or better than those using the positive electrode active materials of Comparative Examples 1 to 3.

Claims

1. A positive electrode active material, wherein, among all the grains in the cross-section of the positive electrode active material particles, the proportion of grains C with a long axis orientation degree DoA of 0.5 to 1 (as expressed by [Formula 1]) and a c-axis orientation degree of less than 0.5 is in the range of 25% to 70%. The positive electrode active material is a lithium composite transition metal oxide represented by [Formula 1]. The c-axis orientation of the grain is expressed as the cross product of the grain's position unit vector P' and the c-axis rotation vector Rc of the grain's lattice obtained through electron backscatter diffraction (EBSD) analysis. [Formula 1] in, In [Formula 1], λ1 is the major axis vector E of the corresponding grain. I The size of the material is measured from image data obtained by scanning ion microscopy analysis of the cross-section of the positive electrode active material. λ2 is the minor axis vector E of the corresponding grain. II The size of the material is measured from image data obtained by scanning ion microscopy analysis of the cross-section of the positive electrode active material. C D It is the unit vector E of the major axis of the corresponding grain. I The dot product of 'and the unit vector P' at position, [Formula 1] Li x [Ni a Co b M 1 c M 2 d ]O 2-y A y In [Equation 1], M 1 It is at least one element selected from Mn and Al. M 2 For Nb, A is at least one element selected from F, Cl, Br, I, At, and S, and 0.98≤x≤1.20, 0 <a<1,0<b<1,0<c<1,0.00125≤d≤0.2,0≤y≤0.2。 2. The positive electrode active material according to claim 1, wherein the scanning ion microscopy analysis is performed in the following manner: Scanning ion microscopy images were obtained by irradiating the cross-section of the positive electrode active material with a focused ion beam. Data segmented into grain units from the scanning ion microscope image was obtained using deep learning, and Calculate the DoA expressed by [Formula 1] from the segmented data.

3. The positive electrode active material according to claim 1, wherein the electron backscatter diffraction (EBSD) analysis is performed in the following manner, Electron backscatter diffraction (EBSD) measurements of the cross-section of the positive electrode active material are used to obtain EBSD Euler diagram data, including the positional information and Euler angle information of each grain. The c-axis rotation vector Rc(x, y, z) of the grain's lattice is obtained using [Formula 2]. [Formula 2] in, In [Formula 2], [X, Y, Z] is (0, 0, 1). ψ, θ, and ф are Euler angles obtained from the Euler plot data.

4. The positive electrode active material according to claim 1, wherein the positive electrode active material further comprises: Grain A, wherein grain A has a DoA of 0.5 to 1 and a c-axis orientation of 0.5 to 1; Grain B, wherein grain B has a DoA of less than 0.5 and a c-axis orientation of 0.5 to 1; and Grain D, wherein grain D has a DoA of less than 0.5 and a c-axis orientation of less than 0.

5. in, In all the grains in the cross-section of the positive electrode active material particles, The proportion of grain A is in the range of 20% or more and less than 25%. The proportion of B grains is in the range of 5% to 30%. The proportion of C in the grains is in the range of 25% to 70%. The ratio of the grain D is in the range of 5% to 30%.

5. The positive electrode active material according to claim 4, wherein the sum of the ratio of grain A and the ratio of grain C in all the grains in the cross-section of the positive electrode active material particles is in the range of 50% to 90%.

6. The positive electrode active material according to claim 1, wherein the positive electrode active material has a grain size of 70 nm to 200 nm.

7. The positive electrode active material according to claim 1, wherein the positive electrode active material has a micro-strain of 0.04% to 0.25%.

8. The positive electrode active material according to claim 1, wherein the positive electrode active material has an average particle size of primary particles of 0.05 μm to 8 μm.

9. The positive electrode active material according to claim 1, wherein the positive electrode active material has an average particle size of secondary particles of 2 μm to 25 μm.

10. A positive electrode, said positive electrode comprising the positive electrode active material according to any one of claims 1 to 9.

11. A lithium secondary battery, the lithium secondary battery comprising the positive electrode as described in claim 10.

Images