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

Abstract

The present invention relates to a positive electrode active material that includes 30% to 80% of crystal grains A having high degrees of long axis orientation and c axis orientation in an outer region of the positive electrode active material, and can realize excellent capacity characteristics and life characteristics.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0036941, filed on March 22, 2021, and all of the contents disclosed in the Korean patent application document are incorporated herein by reference in their entirety.

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

Background Art

[0003] Recently, with the increasing development and demand for technologies related to mobile devices and electric vehicles, the demand for secondary batteries as an energy source has been rapidly increasing. Among such secondary batteries, lithium secondary batteries having a high energy density, a high voltage, a long cycle life, and a low self-discharge rate have been commercialized and widely used.

[0004] As positive electrode active materials for lithium secondary batteries, lithium cobalt oxides such as LiCoO 2 lithium nickel oxides such as LiNiO 2 etc., lithium manganese oxides such as LiMnO 2 or LiMn 2 O 4 etc., lithium iron phosphate oxides such as LiFePO 4 etc. have been developed, and recently, lithium composite transition metal oxides containing two or more transition metals such as Li[Ni a Co b Mn c O 2 Li[Ni a Co b Al c O 2 Li[Ni a Co b Mn c Al d O 2 have been developed and widely used.

[0005] Lithium composite transition metal oxides containing two or more types of transition metals developed so far are usually produced in the form of spherical secondary particles in which dozens to hundreds of primary particles are aggregated. However, physical properties such as lithium ion mobility and electrolyte impregnation properties change depending on the orientation form of the primary particles and the shape (aspect ratio) of the primary particles. Therefore, research has been attempted to control the particle structure of the cathode active material particles to improve the performance of the cathode active material.

[0006] Korean Registered Patent No. 10-1611784 (Patent Document 1) discloses a cathode active material in which the length of the a-axis of the primary particles is longer than the length of the c-axis and the a-axis of the primary particles is radially arranged. In Patent Document 1, the morphology and orientation of the primary particles of the cathode active material are analyzed using a Scanning Electron Microscope (SEM) and / or a Transmission Electron Microscope (TEM).

[0007] However, in the case of the TEM analysis used in Patent Document 1, there is a problem that it is only possible to obtain information about a partial region rather than the entire particle, and it is difficult to substitute for the characteristics of the entire cathode active material particles. In addition, the physical properties of the cathode active material change not only depending on the morphology and orientation of the primary particles but also depending on the morphology and orientation of the crystal grains (Crystalline). Therefore, even when the morphology and orientation of the primary particles are similar, they may exhibit different physical properties.

[0008] Therefore, in order to develop a cathode active material having more excellent characteristics, research on the crystal grain structure of the cathode active material is required.

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention is for solving the above-described problems, and aims to provide a cathode active material capable of realizing excellent capacity characteristics and life characteristics by including, at a specific ratio, crystal grains in which the long-axis and c-axis orientations of crystal grains in the outer region of the cathode active material particles satisfy specific conditions.

[0010] Further, the present invention aims to provide a cathode including the cathode active material according to the present invention and a lithium secondary battery.

Means for Solving the Problems

[0011] According to one embodiment, when the distance from the center to the surface of the cathode active material particles is R, the present invention includes an inner region which is the region from the center of the cathode active material particles to R / 2, and an outer region which is the region from R / 2 to the surface of the cathode active material particles. Among the total crystal grains in the outer region, the long-axis orientation degree DoA of the crystal grains represented by the following [Formula 1] is 0.5 to 1, and the ratio A1 of crystal grains A in which the c-axis orientation degree of the crystal lattice of the crystal grains obtained through Electron BackScatter Diffraction (EBSD) analysis, represented by the outer 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, is 0.5 to 1 is 30% to 80%, preferably 30% to 60%, more preferably 30% to 50%, and still more preferably 30% to 40%. The present invention provides a cathode active material.

[0012] [Formula 1]

Number

[0013] In the above [Formula 1], λ 1 is the magnitude of the long-axis vector E of the crystal grain measured from the image data obtained by scanning ion microscopy analysis of the cross-section of the cathode active material, I and λ 2 is the magnitude of the short-axis vector E of the crystal grain measured from the image data obtained by scanning ion microscopy analysis of the cross-section of the cathode active material. The above C II is the magnitude of the short-axis vector E of the crystal grain measured from the image data obtained by scanning ion microscopy analysis of the cross-section of the cathode active material. The above C Dis the inner product value of the position unit vector P’ of the crystal grain and the major axis unit vector E I ’.

[0014] Preferably, in the positive electrode active material according to the present invention, the ratio A1 of the crystal grain A in all the crystal grains in the external region is larger than the ratio A2 of the crystal grain A in all the crystal grains in the internal region. Specifically, the difference between the ratio A1 of the crystal grain A in all the crystal grains in the external region and the ratio A2 of the crystal grain A in all the crystal grains in the internal region can be 1% or more, 2% or more, preferably 5% or more, and can be 15% or less, preferably 10% or less.

[0015] On the other hand, the positive electrode active material may further include crystal grain B in which the major axis orientation degree DoA of the crystal grain is less than 0.5 and the c-axis orientation degree of the crystal grain is 0.5 to 1, crystal grain C in which the major axis orientation degree DoA of the crystal grain is 0.5 to 1 and the c-axis orientation degree of the crystal grain is less than 0.5, and crystal grain D in which the major axis orientation degree DoA of the crystal grain is less than 0.5 and the c-axis orientation degree of the crystal grain is less than 0.5.

[0016] At this time, in the external region, preferably, the ratio A1 of the crystal grain A in all the crystal grains is larger than the ratio B1 of the crystal grain B, the ratio C1 of the crystal grain C, and the ratio D1 of the crystal grain D.

[0017] Also, the ratio of the crystal grain A in all the crystal grains in the cross section of the positive electrode active material particles can be 20% to 80%, the ratio of the crystal grain B can be 5% to 40%, the ratio of the crystal grain C can be 5% to 40%, and the ratio of the crystal grain D can be 5% to 40%.

[0018] On the other hand, in the scanning ion microscope analysis, after irradiating a focused ion beam onto the cross section of the positive electrode active material to obtain a scanning ion microscope image, data segmented in units of crystal grains is acquired from the scanning ion microscope image using deep learning, and DoA represented by the [Formula 1] is calculated from the segmented data.

[0019] Further, the Electron BackScatter Diffraction (EBSD) analysis can obtain EBSD Euler map data including position information and Euler angle information of each crystal grain through Electron BackScatter Diffraction (EBSD) measurement of the cross-section of the positive electrode active material, and can obtain the c-axis rotation vector Rc(x, y, z) of the crystal lattice of the crystal grain through the following [Equation 2].

[0020] [Equation 2] [Number]

[0021] In the above [Equation 2], [X, Y, Z] is (0, 0, 1), and the Φ, θ, and Ψ are Euler angles obtained from the Euler map data.

[0022] The positive electrode active material according to the present invention can 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], the M 1 is one or more elements selected from the group consisting of Mn and Al, and the M 2is 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 the A is one or more elements selected from the group consisting of F, Cl, Br, I, At, and S, where 0.98 ≦ x ≦ 1.20, 0 < a < 1, 0 < b < 1, 0 < c < 1, 0 ≦ d ≦ 0.2, and 0 ≦ y ≦ 0.2.

[0023] 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.

Advantages of the Invention

[0024] As in the present invention, when the crystal grains A having a high long-axis orientation and c-axis orientation of crystal grains are included in a ratio of 30 to 80% in the external region of the positive electrode active material, the a-axis, which is the lithium ion movement path (Li path), and the grain boundary interface are arranged from the center to the surface direction of the positive electrode active material particles, minimizing the lithium ion movement distance, and the capacity characteristics can be improved. The external exposed area of the ab plane, which is the crystal plane where lithium ions are inserted and desorbed, is small, and the shrinkage and expansion energy of the particles during the charge and discharge process is dispersed, suppressing particle cracking, and minimizing the degradation of the crystal structure, and the life characteristics can be improved.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0026] The terms and words used in this specification and the claims should not be construed as being limited to their ordinary or dictionary meanings. The inventor must interpret them as meanings and concepts consistent with the technical idea of the present invention in accordance with the principle that the inventor can appropriately define the concept of the terms in order to explain his or her invention in the best way.

[0027] In the present invention, "crystal grain" means a single crystal particle unit having a regular atomic arrangement. The size of the crystal grain can be measured by analyzing the X-ray diffraction data of the cross-section of the positive electrode active material by the Rietveld refinement method. For example, the size of the crystal grain can be obtained by performing X-ray diffraction analysis under the following conditions using Empyreon XRD equipment of Malyer Panalyticla to obtain XRD data, and then processing the XRD data using the Highscore program of Malyer panalytical. At this time, the half-width was set to be measured using the Caglioti equation.

[0028] <Conditions for X-ray Diffraction Analysis> 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. Measurement time: About 30 minutes Measurement range: 2θ = 15° to 85°

[0029] 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 a single crystal grain or multiple crystal grains. In the present invention, the average particle size of the primary particles can be measured by measuring each particle size distinguished by the SEM data of the cross-section of the positive electrode active material particles and then obtaining the arithmetic mean value of these.

[0030] In the present invention, the "secondary particle" means a secondary structure formed by the aggregation of a plurality of 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.

[0031] In the present invention, the "particle size Dn" of the positive electrode active material precursor and the positive electrode active material means the particle size at the n% point of the cumulative distribution of the number of particles according to the particle size. That is, D50 is the particle size at the 50% point of the cumulative distribution of the number of particles according to the particle size, D90 is the particle size at the 90% point of the cumulative distribution of the number of particles according to the particle size, and D10 is the particle size at the 10% point of the cumulative distribution of the number of particles according to the particle size. The Dn can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac S3500), and the difference in the diffraction pattern due to the particle size when the particles pass through the laser beam is measured to calculate the particle size distribution. By calculating the diameters of the particles at the points where the cumulative distribution of the number of particles according to the particle size in the measuring device reaches 10%, 50%, and 90%, D10, D50, and D90 can be measured.

[0032] 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 region) × 100.

[0033] Hereinafter, the present invention will be specifically described.

[0034] As a result of repeated research to develop a positive electrode active material capable of realizing excellent life characteristics and resistance characteristics, the inventors of the present invention have found that when the external region of the positive electrode active material contains crystal grains having a high orientation of the major axis and the c-axis of the crystal grains at a specific ratio, the capacity characteristics and life characteristics of the secondary battery can be improved, and the present invention has been completed.

[0035] Positive electrode active material As shown in FIG. 1, the positive electrode active material according to the present invention includes an internal region 20, which is a region from the center to R / 2 of the positive electrode active material particles, where R is the distance from the center to the surface of the positive electrode active material particles, and an external region 10, which is a region from R / 2 to the surface of the positive electrode active material particles. Among all the crystal grains in the external region 10, the major axis orientation degree DoA of the crystal grains represented by the following [Formula 1] is 0.5 to 1, and the c-axis orientation degree of the crystal grains represented by the outer product value of the c-axis rotation vector Rc of the crystal lattice of the crystal grains obtained through Electron BackScatter Diffraction (EBSD) analysis and the position unit vector P' of the crystal grains is 0.5 to 1. The ratio A1 of the crystal grains (hereinafter referred to as "crystal grains A") is 30% to 80%, preferably 30% to 60%, more preferably 30% to 50%, and even more preferably 30% to 40%.

[0036] [Formula 1] [Number]

[0037] In the above [Formula 1], λ 1 is the magnitude of the major axis vector E of the crystal grain measured from the image data obtained by scanning ion microscopy analysis of the cross-section of the positive electrode active material, and λ I is the magnitude of the minor axis vector E of the crystal grain measured from the image data obtained by scanning ion microscopy analysis of the cross-section of the positive electrode active material. The C 2 is the inner product value of the position unit vector P' of the crystal grain and the major axis unit vector E II '. D is the inner product value of the position unit vector P' of the crystal grain and the major axis unit vector E I '.

[0038] First, the DoA represented by the above [Formula 1] will be described.

[0039] The DoA value represented by the above [Formula 1] is for indicating the orientation of the long axis of crystal grains, and can be obtained using the data obtained through scanning ion microscopy analysis.

[0040] Specifically, after irradiating the cross-section of the positive electrode active material with a focused ion beam to obtain a scanning ion microscope image, data segmented in crystal grain units is acquired from the scanning ion microscope image using deep learning, and the degree of orientation DoA of the long axis of the crystal grains represented by the above [Formula 1] can be calculated from the segmented data.

[0041] Hereinafter, a method for obtaining the DoA value through scanning ion microscopy analysis will be described more specifically.

[0042] A scanning ion microscope is a device that measures the surface structure of a sample through a signal ion image emitted at this time while irradiating the surface of the sample with an ion beam. At this time, since the reflectivity of the ion beam changes on different crystal planes, a cross-sectional image of the positive electrode active material particles distinguished in crystal grain units having the same atomic arrangement structure can be obtained using a scanning ion microscope. A scanning ion microscope image of the cross-section of the positive electrode active material particles is shown in FIG. 1. It can be confirmed from FIG. 1 that the cross-sectional image of the positive electrode active material particles is distinguished in crystal grain units.

[0043] Next, the scanning ion microscope image obtained as described above is analyzed to acquire data segmented in crystal grain units. At this time, the image analysis can be performed using deep learning.

[0044] FIG. 2 shows the process of obtaining segmented data information by analyzing a scanning ion microscope image. As shown in FIG. 2, the image analysis can be performed, for example, by detecting a boundary line from a scanning ion microscope image through deep learning and then obtaining image data segmented in units of crystal grains using the boundary line.

[0045] At this time, the boundary line detection can be performed using an AutoEncoder neural network (U-NET) algorithm, and the segmentation can be performed using a Watershed segmentation algorithm or the like.

[0046] Since the scanning ion microscope image itself does not contain digitized information, in the present invention, data information segmented in units of each crystal grain is obtained through deep learning, and information such as the shape and position of the crystal grain can be digitized through this.

[0047] If data segmented through the above-described scanning ion microscope image analysis is obtained, the position vector, major axis vector, and minor axis vector of the crystal grain to be measured can be obtained from the data, and the DoA value of Equation 1 can be calculated using this.

[0048] [Equation 1] [Number]

[0049] In the above [Equation 1], λ 1 is the magnitude of the major axis vector E of the crystal grain measured from the image data obtained by scanning ion microscope analysis of the cross-section of the positive electrode active material. At this time, the major axis vector E I IIt means the vector among the vectors passing through the center of gravity of the crystal grain for which the sum of the distances from the vector to each pixel within the crystal grain is the smallest.

[0050] λ 2 is the minor axis vector E of the crystal grain measured from the image data obtained by scanning ion microscopy of the cross-section of the positive electrode active material. II is the magnitude of, and at this time, the minor axis vector E II It means the vector among the vectors passing through the center of gravity of the crystal grain for which the sum of the distances from the vector to each pixel within the crystal grain is the largest.

[0051] On the other hand, the C D is the inner product value of 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 the position vector connecting the center of the cross-section of the positive electrode active material particle to the center of gravity point of the crystal grain so that the magnitude becomes 1. The major axis unit vector E I ' is a vector obtained by converting the major axis vector E I so that the magnitude becomes 1.

[0052] The DoA value calculated through the [Equation 1] is a value indicating how much the major axis of the crystal grain is inclined with respect to the shortest line segment connecting the center and the surface of the positive electrode active material while passing through the crystal grain. The closer the DoA value is to 1, the smaller the angle between the major axis of the crystal grain and the shortest line segment, and the closer it is to 0, the larger the angle between the major axis of the crystal grain and the shortest line segment. That is, it can be said that the higher the major axis orientation of the crystal grain, the closer the DoA is to 1.

[0053] FIG. 3 shows a drawing representing the DoA value obtained through the above method and the major axis of the crystal grain. As shown in FIG. 3, in the case of crystal grain 1 where the angle between the shortest line segment connecting the center and the surface of the positive electrode active material particle and the major axis of the crystal grain is small, the DoA appears close to 0.965 and 1. On the contrary, it can be seen that for crystal grain 2 where the angle between the shortest line segment connecting the center and the surface of the positive electrode active material particle and the major axis of the crystal grain is large, the DoA appears small at 0.352.

[0054] On the other hand, by mapping the long-axis orientation degree information of each crystal grain as described above, it is possible to measure the ratio of crystal grains having specific long-axis orientation degree values in the external region and the internal region in the cross-section of the positive electrode active material particles.

[0055] Next, the c-axis orientation degree of the crystal grains will be described.

[0056] The c-axis orientation degree of the crystal grains is for indicating the orientation of the c-axis of the crystal lattice of the crystal grains, and is the outer product value of the c-axis rotation vector Rc of the crystal lattice of the crystal grains obtained through Electron BackScatter Diffraction (EBSD) analysis and the position unit vector P' of the crystal grains.

[0057] Specifically, the c-axis orientation degree of the crystal grains is obtained by acquiring EBSD Euler map data including the position information and Euler angle information of each crystal grain through Electron BackScatter Diffraction (EBSD) measurement of the cross-section of the positive electrode active material, obtaining the c-axis rotation vector Rc of the crystal lattice using the EBSD Euler map data, and taking the outer product of the c-axis rotation vector Rc of the crystal lattice and the position unit vector P' of the crystal grain.

[0058] Hereinafter, the method for obtaining the c-axis orientation degree of the crystal grains according to the present invention will be specifically described.

[0059] Electron backscatter diffraction analysis is a method of measuring the crystallographic phase and crystallographic orientation using the diffraction pattern of a sample, and analyzing the crystallographic information of the sample based on this. When a sample (i.e., the cross-section of the positive electrode active material) is tilted at a large angle with respect to the incident direction of the electron beam in a scanning electron microscope, the incident electron beam scatters within the sample and a diffraction pattern appears in the surface direction of the sample, which is called an electron backscattered diffraction pattern (EBSP). Since the electron backscattered diffraction pattern responds to the crystallographic orientation of the region irradiated with the electron beam, the crystallographic orientation of the sample can be accurately measured using this, and Euler map data including various information related to the crystallographic orientation of the entire sample can be obtained via EBSD software. Figure 4 shows an Euler map obtained by analyzing the cross-section of positive electrode active material particles by electron backscatter diffraction (EBSD).

[0060] The EBSD Euler map data includes position vector information and Euler angle information of each crystal grain. On the other hand, by using the Euler angle information, the c-axis rotation vector Rc of the crystal lattice in each crystal grain can be obtained.

[0061] The c-axis rotation vector Rc of the crystal lattice indicates in which direction the c-axis of the crystal grain rotates with respect to the shortest line segment connecting the center and the surface of the positive electrode active material while passing through the crystal grain.

[0062] Specifically, the c-axis rotation vector Rc of the crystal lattice can be expressed as (x, y, z) calculated by the following [Equation 2].[[]END]]

[0063] [Equation 2] [Number]

[0064] In the above [Equation 2], [X, Y, Z] is (0, 0, 1), and the Φ, θ, and Ψ are the Euler angles of each crystal grain obtained from the Euler map data.

[0065] Using the c-axis rotation vector Rc of the crystal lattice obtained as described above and the position vector information of each crystal grain included in the Euler map data, the orientation degree of the crystal grain can be obtained. Specifically, the orientation degree of the crystal grain can be quantified as the value obtained by taking the outer product of the c-axis rotation vector Rc of the crystal lattice and the position unit vector P' of the crystal grain.

[0066] At this time, the position unit vector P' means the one obtained by converting the position vector of the crystal grain so that its magnitude becomes 1. For example, if the position vector of the crystal grain is (a, b, o), the position unit vector is

[0067]

Number

[0068] as follows.

[0069] The outer product value of the position unit vector P' and the c-axis rotation vector Rc of the crystal lattice is a numerical value indicating the c-axis orientation degree of the crystal grain within the positive electrode active material particle. Specifically, when the outer product value of the position unit vector P' and the c-axis rotation vector Rc of the crystal lattice is 1, it means that the c-axis of the crystal grain is arranged perpendicular to the shortest line segment connecting the center and the surface of the positive electrode active material particle, and when the outer product value is 0, it means that the c-axis of the crystal grain is arranged horizontally with the shortest line segment.

[0070] In the positive electrode active material, the mobility of lithium ions when moving along a direction perpendicular to the c-axis is more than 10 times faster than when moving in the c-axis direction. Therefore, a lithium migration path is formed along a direction perpendicular to the c-axis. Further, when the lithium migration path is formed parallel to the shortest line segment connecting the center and the surface of the positive electrode active material particles, the lithium migration distance is minimized, so the conductivity of lithium is improved. Therefore, it can be determined that the closer the cross product value of the position unit vector P’ and the c-axis rotation vector Rc of the crystal lattice is to 1, the better the orientation of the crystal grains.

[0071] On the other hand, by integrating the c-axis orientation degrees of the respective crystal grains obtained as described above, the c-axis orientation degree of the entire crystal grains in the cross section of the positive electrode active material particles can be obtained. FIG. 5 shows a c-axis orientation map of the crystal grains of the positive electrode active material obtained by integrating the c-axis orientation degrees of the respective crystal grains. In FIG. 5, it means that the c-axis orientation is better as it goes to red, and the c-axis orientation deteriorates as it goes to blue. By using the c-axis orientation map as described above, the ratio of crystal grains satisfying the c-axis orientation conditions in the external region and the internal region can be obtained in the cross section of the positive electrode active material particles.

[0072] According to the research of the present inventors, in the external region of the positive electrode active material particles, the long-axis orientation degree DoA of the crystal grains represented by [Equation 1] among the entire crystal grains is 0.5 to 1, and the c-axis orientation degree of the crystal grains is 0.5 to 1. It has been clarified that excellent life characteristics and capacity characteristics can be realized when the ratio (hereinafter referred to as A1) of the crystal grains (hereinafter referred to as crystal grains A) is in the range of 30% to 80%, preferably 30% to 60%, more preferably 30% to 50%, and even more preferably 30% to 40%. When the ratio of the crystal grains A in the external region is less than 30% or exceeds 80%, the length of the lithium migration path inside the positive electrode active material becomes long, the lithium ion mobility decreases, and the contact area between the ab plane where structural degradation occurs during charge and discharge and the electrolyte increases, so that the capacity characteristics and life characteristics cannot obtain an improvement effect, and side effects such as gas generation may increase.

[0073] Further, in the positive electrode active material of the present invention, it is preferable that the ratio A1 of the crystal grains A in the external region is larger than the ratio A2 of the crystal grains A in the internal region. When the ratio of the crystal grains A in the external region of the positive electrode active material is larger than the ratio of the crystal grains A in the internal region, the improvement effects on the life characteristics and the capacity characteristics can be maximized while maintaining the balance with other physical properties such as the output characteristics and the high-temperature storage characteristics.

[0074] Specifically, the difference between the ratio A1 of the crystal grains A in all the crystal grains in the external region and the ratio A2 of the crystal grains A in all the crystal grains in the internal region can be 2% or more, or 5% or more, and can be 15% or less, or 10% or less. When the difference in the ratio of the crystal grains A between the external region and the internal region satisfies the above range, the improvement effects on the life characteristics and the capacity characteristics are excellently manifested, and further improved effects can be obtained when the ratio difference of the crystal grains A is high.

[0075] On the other hand, in the positive electrode active material according to the present invention, in the external region and the internal region, in addition to the crystal grains A, crystal grains (hereinafter referred to as crystal grains B) having a c-axis orientation degree of 0.5 to 1 and a major axis DoA of less than 0.5, crystal grains having a c-axis orientation degree of less than 0.5 and a major axis orientation degree DoA of 0.5 to 1 (hereinafter referred to as crystal grains C), and crystal grains having a c-axis orientation degree of less than 0.5 and a major axis orientation degree DoA of less than 0.5 (hereinafter referred to as crystal grains D) may be further included.

[0076] On the other hand, in the positive electrode active material of the present invention, it is preferable that the ratio A1 of the crystal grains A in all the crystal grains in the external region is larger than the ratios of the other crystal grains, that is, the ratio B1 of the crystal grains B, the ratio C1 of the crystal grains C, and the ratio D1 of the crystal grains D. That is, it is preferable to satisfy A1 > B1, A1 > C1, and A1 > D1. This is because when the ratio of the crystal grains A in the external region is higher than that of the other crystal grains, the effects of improving the life characteristics and the capacity characteristics can be obtained.

[0077] On the one hand, in the positive electrode active material according to the present invention, the ratio of crystal grains A in the total crystal grains of the cross-section of the positive electrode active material particles including the external region and the internal region can be 20% to 80%, 25% to 70%, 25 to 60%, 25 to 50%, or 25% to 40%. The ratio of the crystal grains B can be 5% to 40%, 5% to 30%, or 10 to 30%. The ratio of the crystal grains C can be 5% to 40%, 5% to 30%, or 10 to 30%. The ratio of the crystal grains D can be 5% to 40%, 5% to 30%, or 10 to 30%. When the ratio of the crystal grains in the entire positive electrode active material satisfies the above range, it is possible to minimize the deterioration of physical properties such as output characteristics and high-temperature storage characteristics and obtain the improvement effects of life characteristics and capacity characteristics.

[0078] On the other hand, the ratio of the crystal grains in the positive electrode active material is determined by the combined action of the coprecipitation reaction conditions during the production of the positive electrode active material precursor, the type of doping element, the firing conditions, etc. Therefore, by appropriately adjusting the coprecipitation conditions, doping elements, firing temperature, mixing ratio of lithium raw materials during firing, etc. during the production of the precursor, it is possible to produce a positive electrode active material that satisfies the ratio of the crystal grains of the present invention.

[0079] 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. For example, it can be a lithium composite transition metal oxide represented by the following [Chemical Formula 1].

[0080] [Chemical Formula 1] Li x [Ni a Co b M 1 c M 2 d O 2-y A y

[0081] In the above [Chemical Formula 1], the M 1 can be one or more elements selected from the group consisting of Mn and Al.

[0082] The M 2It may 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.

[0083] Also, the A may be one or more elements selected from the group consisting of F, Cl, Br, I, At, and S.

[0084] The x represents the molar ratio of Li to the total number of moles of transition metals, and 0.98 ≦ x ≦ 1.20, preferably 0.99 ≦ x ≦ 1.10, more preferably 1.0 ≦ x ≦ 1.10.

[0085] The a represents the molar ratio of Ni to the total number of moles of transition metals, and 0 < a < 1, preferably 0.3 ≦ a < 1, more preferably 0.6 ≦ a < 1, still more preferably 0.8 ≦ a < 1, even more preferably 0.85 ≦ a < 1.

[0086] The b represents the molar ratio of Co to the total number of moles of transition metals, and 0 < b < 1, preferably 0 < b < 0.7, more preferably 0 < b < 0.4, still more preferably 0 < b < 0.2, even more preferably 0 < b ≦ 0.1.

[0087] The c represents the molar ratio of M 1 to the total number of moles of transition metals, and 0 < c < 1, preferably 0 < c < 0.7, more preferably 0 < c < 0.4, still more preferably 0 < c < 0.2, even more preferably 0 < c ≦ 0.1.

[0088] The d represents the molar ratio of M 2 to the total number of moles of transition metals, and 0 ≦ d ≦ 0.2, preferably 0 ≦ d ≦ 0.15, more preferably 0 ≦ d ≦ 0.10.

[0089] The y represents the molar ratio of the A element substituted at the oxygen position, and 0 ≦ y ≦ 0.2, preferably 0 ≦ y ≦ 0.15, more preferably 0 ≦ y ≦ 0.10.

[0090] On the one hand, the positive electrode active material may have a crystal grain size of 100 nm to 200 nm, preferably 100 nm to 180 nm, 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.

[0091] In addition, 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 diameter of 2 μm to 25 μm, preferably 5 μm to 18 μm. When the average secondary particle diameter satisfies the above range, it is possible to prevent the positive electrode active material particles from cracking in the rolling process and the processability from decreasing during slurry production.

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

[0094] The positive electrode includes the 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, and the positive electrode active material layer includes the positive electrode active material according to the present invention.

[0095] At this time, since the positive electrode active material is the same as that described above, specific description is omitted, and only the remaining configuration will be specifically described below.

[0096] The positive electrode current collector can contain a metal with high conductivity, and is not particularly limited as long as the positive electrode active material layer can easily adhere thereto and it has no reactivity within the voltage range of the battery. The positive electrode current collector can be, for example, stainless steel, aluminum, nickel, titanium, fired carbon, or a material obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. Further, the positive electrode current collector can usually have a thickness of 3 to 500 μm, and fine irregularities can also be formed on the surface of the current collector to enhance the adhesive force of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0097] The positive electrode active material layer can further contain a conductive material and / or a binder, optionally and selectively, together with the positive electrode active material.

[0098] At this time, the positive electrode active material can be contained in a content of 80 to 99% by weight, more specifically 85 to 98.5% by weight, based on the total weight of the positive electrode active material layer. When contained within the above content range, excellent capacity characteristics can be exhibited.

[0099] The conductive material is used to impart conductivity to the electrode, and can be used without particular limitation as long as it has electronic conductivity without causing chemical changes in the configured battery. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Among these, one kind alone or a mixture of two or more kinds can be used. The conductive material can be contained in an amount of 0.1 to 15% by weight based on the total weight of the positive electrode active material layer.

[0100] The binder serves to improve the adhesion between the particles of the positive electrode active material and the adhesive force between the positive electrode active material and the current collector. Specific examples 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, and polymers in which hydrogen thereof is substituted with Li, Na, or Ca, or various copolymers thereof, etc. One of these alone or a mixture of two or more thereof can be used. The binder can be contained in an amount of 0.1 to 15% by weight based on the total weight of the positive electrode active material layer.

[0101] The positive electrode can be manufactured by a normal positive electrode manufacturing method except that the above-described positive electrode active material is used. Specifically, it can be manufactured by applying a positive electrode slurry composition prepared by dissolving or dispersing the above-described positive electrode active material, and optionally a binder and a conductive material, in a solvent onto a positive electrode current collector, followed by drying and rolling.

[0102] The solvent can be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethyl formamide (DMF), acetone, or water, etc. Among these, one kind alone or a mixture of two or more kinds can be used. The amount of the solvent used is such that, considering the coating thickness of the slurry and the production yield, it can dissolve or disperse the positive electrode active material, conductive material, and binder, and has a viscosity that can exhibit excellent thickness uniformity during coating for subsequent positive electrode production.

[0103] Also, as another method, the positive electrode can be manufactured by casting the positive electrode slurry composition on a separate support, and then laminating the film obtained by peeling it from this support on the positive electrode current collector.

[0104] Secondary battery Moreover, the present invention can manufacture an electrochemical element including the positive electrode. Specifically, the electrochemical element can be a battery, a capacitor, etc., and more specifically, it can be a lithium secondary battery.

[0105] Specifically, the lithium secondary battery can include a positive electrode, a negative electrode positioned opposite to 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, a specific description is omitted, and hereinafter, only the remaining configuration will be specifically described.

[0106] Also, the lithium secondary battery can selectively further include a battery container for housing the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0107] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0108] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those obtained by surface treatment of the surface of copper or stainless steel with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. Further, the negative electrode current collector can usually have a thickness of 3 μm to 500 μm. Similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the binding force of the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabric bodies, etc.

[0109] The negative electrode active material layer selectively contains a binder and a conductive material together with the negative electrode active material.

[0110] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; SiOβ(0 < β < 2), SnO 2, metal oxides such as vanadium oxide and lithium vanadium oxide that can be doped and undoped with lithium; or composites containing the metallic compound and the carbonaceous material such as Si-C composites or Sn-C composites, etc. can be mentioned, and any one or a mixture of two or more of these can be used. Further, a thin film of metallic lithium can also be used as the negative electrode active material. Further, as the carbon material, all of low-crystalline carbon and high-crystalline carbon, etc. can be used. Representative examples of low-crystalline carbon are soft carbon and hard carbon, and representative examples of high-crystalline carbon are amorphous, plate-like, scaly, spherical or fibrous natural graphite or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes, etc.

[0111] The negative electrode active material can be contained in an amount of 80% by weight to 99% by weight based on the total weight of the negative electrode active material layer.

[0112] The binder is a component that helps bond the conductive material, the active material, and the current collector, and is usually added in an amount of 0.1% by weight to 10% by weight 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, various copolymers thereof, etc.

[0113] The conductive material is a component for further improving the conductivity of the negative electrode active material, and can be added in an amount of 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, 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 fibers and metal fibers; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives can be used.

[0114] As an example, the negative electrode active material layer can be manufactured by applying and drying 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, or by casting the negative electrode slurry composition on a separate support and then laminating the film obtained by peeling the support from the support on the negative electrode current collector.

[0115] On one hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Generally, any separator that can be used in a lithium secondary battery can be used without special restrictions. In particular, a separator that has a low resistance to the ion migration of the electrolyte and excellent electrolyte moisture retention ability is preferred. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as a homopolymer of ethylene, a homopolymer of propylene, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof can be used. Also, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. can be used. Further, a coated separator containing a ceramic component or a polymer substance for ensuring heat resistance or mechanical strength can be used, and it can be selectively used in a single-layer or multilayer structure.

[0116] In addition, examples of the electrolyte used in the present invention include, but are not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used during the manufacture of a lithium secondary battery.

[0117] Specifically, the electrolyte can contain an organic solvent and a lithium salt.

[0118] As the organic solvent, any solvent can be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, 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 or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double bond, aromatic ring, or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, which can enhance the charge-discharge performance of the battery, and a linear carbonate compound having low viscosity (e.g., ethylmethylcarbonate, dimethylcarbonate, or diethylcarbonate) is more preferred.

[0119] The lithium salt can be used without special restrictions as long as it is a compound that can provide lithium ions used in lithium secondary batteries. Specifically, as the anion of the lithium salt, F - , Cl - , Br - , I - , NO 3 - , N(CN) 2 - , BF 4 - , CF 3 CF 2 , SO 3 - , (CF 3 , SO 2 ) 2 , N - , (FSO 2 ) 2 , N - , CF 3 CF 2 (CF 3 ) 2 , CO - , (CF 3 , SO 2 ) 2 , CH - , (SF 5 ) 3 , C - , (CF 3 , SO 2 ) 3 , C - , CF 3 (CF 2 ) 7 , SO 3 - , CF 3 , CO 2 - , CH 3 , CO 2 - , SCN - and (CF 3 CF 2 , SO 2 ) 2 , N - can be at least one or more selected from the group consisting of, and the lithium salt is LiPF 6 , LiClO 4 , LiAsF 6 , LiBF4 , LiSbF 6 , LiAlO 4 , LiAlCl 4 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN(C 2 F 5 SO 3 ) 2 , LiN(C 2 F 5 SO 2 ) 2 , LiN(CF 3 SO 2 ) 2 , LiCl, LiI, or LiB(C 2 O 4 ) 2 etc. can be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0 M. If the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0120] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent capacity characteristics and life characteristics, and can be usefully used in various fields such as portable devices such as mobile phones, notebook computers, digital cameras, and electric vehicles.

[0121] Hereinafter, examples will be given to specifically explain the present invention in detail. However, the examples according to the present invention can be deformed into various forms, 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 fully explain the present invention to those having average knowledge in the industry.

Examples

[0122] Production Example 1 - Production of Positive Electrode Active Material Precursor A NiSO 4 , CoSO 4 , and MnSO 4They were mixed in distilled water in an amount such that the molar ratio of nickel:cobalt:manganese was 92:4:4 to prepare an aqueous transition metal solution with a concentration of 2.4 M.

[0123] Subsequently, after deionized water was put into the reactor, nitrogen gas was purged into the reactor to remove dissolved oxygen in the water, and the inside of the reactor was adjusted to a non-oxidizing atmosphere. Then, 7.96 M of NaOH was added so that the pH inside the reactor was maintained at 11.9.

[0124] Thereafter, the aqueous transition metal solution was introduced into the reactor at a rate of 850 mL / hr, and an aqueous NaOH solution was introduced at 510 mL / hr and an aqueous NH 4 OH solution was introduced at 160 mL / hr while a coprecipitation reaction was allowed to proceed for 40 hours under the conditions of a reaction temperature of 50 °C, pH 11.4, and a stirring speed of 600 rpm to produce a cathode active material precursor A represented by an average particle diameter D 50 of 15 μm and Ni 0.92 Co 0.04 Mn 0.04 (OH) 2 .

[0125] Production Example 2 - Production of Cathode Active Material Precursor B An average particle diameter D 50 of 4 μm and Ni 0.92 Co 0.04 Mn 0.04 (OH) 2 were produced in the same manner as in Production Example 1, except that the coprecipitation reaction was allowed to proceed for 12 hours.

[0126] Example 1 The cathode active material precursor A produced in Production Example 1 and LiOH were mixed so that the molar ratio of Li:transition metal (Ni + Co + Mn) was 1.05:1, and Ta 2 O 5 was additionally mixed so that the molar ratio of transition metal (Ni + Co + Mn):Ta was 99.75:0.25, and then fired at 770 °C for 13 hours to obtain Li[Ni 0.92 Co 0.04 Mn 0.04 0.9975 Ta 0.0025 ​O 2 was manufactured.

[0127] Next, the Li[Ni 0.92 Co 0.04 Mn 0.04 0.9975 Ta 0.0025 O 2 was washed with water, dried, and then mixed with 500 ppm of boric acid and heat-treated at 300 °C to produce a B-coated positive electrode active material.

[0128] Example 2 A positive electrode active material was manufactured in the same manner as in Example 1, except that the firing was performed at 790 °C.

[0129] Example 3 The positive electrode active material precursor A produced according to Production Example 1 and LiOH were mixed so that the molar ratio of Li: transition metal (Ni + Co + Mn) was 1.05:1, and WO 3 was additionally mixed so that the molar ratio of transition metal (Ni + Co + Mn):W was 99.75:0.25, and then fired at 770 °C for 13 hours to produce Li[Ni 0.92 Co 0.04 Mn 0.04 0.9975 W 0.0025 O 2 was manufactured.

[0130] Next, the Li[Ni 0.92 Co 0.04 Mn 0.04 0.9975 W 0.0025 O 2 was washed with water, dried, and then mixed with 500 ppm of boric acid and heat-treated at 300 °C to produce a B-coated positive electrode active material.

[0131] Example 4 The positive electrode active material precursor A produced according to Production Example 1 and LiOH were mixed so that the molar ratio of Li: transition metal (Ni + Co + Mn) was 1.05:1, and B(OH) 3 ​​​After additional mixing so that the molar ratio of transition metal (Ni + Co + Mn): B becomes 99.75:0.25, it was calcined at 770 °C for 13 hours to produce Li[Ni 0.92 Co 0.04 Mn 0.04 0.9975 B 0.0025 O 2 .

[0132] Next, the Li[Ni 0.92 Co 0.04 Mn 0.04 0.9975 B 0.0025 O 2 was washed with water and dried, and then 500 ppm of boric acid was mixed and heat-treated at 300 °C to produce a B-coated positive electrode active material.

[0133] Example 5 The positive electrode active material precursor A produced according to Production Example 1 and LiOH were mixed so that the molar ratio of Li: transition metal (Ni + Co + Mn) became 1.05:1, and Mo 2 O 5 was additionally mixed so that the molar ratio of transition metal (Ni + Co + Mn): Mo became 99.75:0.25, and then calcined at 770 °C for 13 hours to produce Li[Ni 0.92 Co 0.04 Mn 0.04 0.9975 Mo 0.0025 O 2 .

[0134] Next, the Li[Ni 0.92 Co 0.04 Mn 0.04 0.9975 Mo 0.0025 O 2 was washed with water and dried, and then 500 ppm of boric acid was mixed and heat-treated at 300 °C to produce a B-coated positive electrode active material.

[0135] Example 6 ​​​​The cathode active material precursor A produced according to Production Example 1 and LiOH were mixed so that the molar ratio of Li: transition metal (Ni + Co + Mn) was 1.03:1, and then fired at 740 °C for 13 hours to obtain Li[Ni 0.92 Co 0.04 Mn 0.04 O 2 was produced.

[0136] Next, the Li[Ni 0.92 Co 0.04 Mn 0.04 O 2 was washed with water and dried, and then 500 ppm of boric acid was mixed and heat-treated at 300 °C to produce a B-coated cathode active material.

[0137] Comparative Example 1 The cathode active material precursor A produced according to Production Example 1 and LiOH were mixed so that the molar ratio of Li: transition metal (Ni + Co + Mn) was 1.07:1, and then fired at 790 °C for 13 hours to obtain Li[Ni 0.92 Co 0.04 Mn 0.04 O 2 was produced.

[0138] Next, the Li[Ni 0.92 Co 0.04 Mn 0.04 O 2 was washed with water and dried, and then 500 ppm of boric acid was mixed and heat-treated at 300 °C to produce a B-coated cathode active material.

[0139] Comparative Example 2 The cathode active material precursor B produced according to Production Example 2 and LiOH were mixed so that the molar ratio of Li: transition metal (Ni + Co + Mn) was 1.05:1, and then fired at 780 °C for 13 hours to obtain Li[Ni 0.92 Co 0.04 Mn 0.04 O 2 was produced.

[0140] Next, the Li[Ni 0.92 Co 0.04 Mn 0.04 O2 It was washed with water and dried, and then 500 ppm of boric acid was mixed and heat-treated at 300 °C to produce a cathode active material coated with B.

[0141] Comparative Example 3 The cathode active material precursor A produced according to Production Example 1 and LiOH were mixed so that the molar ratio of Li: transition metal (Ni + Co + Mn) was 1.05:1, and Nb 2 O 3 was additionally mixed so that the molar ratio of transition metal (Ni + Co + Mn): Nb was 99.75:0.25, and then calcined at 770 °C for 13 hours to obtain Li[Ni 0.92 Co 0.04 Mn 0.04 0.9975 Nb 0.0025 O 2 was produced.

[0142] Next, the Li[Ni 0.92 Co 0.04 Mn 0.04 0.9975 Nb 0.0025 O 2 was washed with water and dried, and then 500 ppm of boric acid was mixed and heat-treated at 300 °C to produce a cathode active material coated with B.

[0143] Experimental Example 1: Analysis of Cathode Active Material Using an ion milling system (Hitachi, IM4000), each of the cathode active materials produced in Examples 1 to 6 and Comparative Examples 1 to 3 was cut cross-sectionally, and then the above-described scanning ion microscope analysis and electron backscatter diffraction (EBSD) analysis were performed to measure the ratios of crystal grains A, B, C, and D in the external region and the internal region.

[0144] The measurement results are shown in Table 1 below.

[0145] [Table 1]

Table 1

[0146] Experimental Example 2: Evaluation of Battery Characteristics The positive electrode active materials manufactured in Examples 1 to 6 and Comparative Examples 1 to 3, a conductive material (Denka black), and a binder (PVDF) were mixed in an N-methyl-2-pyrrolidone (NMP) solvent at a weight ratio of 97.5:1:1.5 to produce a positive electrode slurry. The positive electrode slurry was applied to one surface of an aluminum current collector, dried, and then rolled to produce a positive electrode.

[0147] A lithium metal electrode was used as the negative electrode.

[0148] After manufacturing an electrode assembly with a separator interposed between the positive electrode and the negative electrode, and placing it inside a battery case, an electrolytic solution was injected to manufacture a lithium secondary battery. At this time, as the electrolytic solution, an electrolytic solution in which 1 M of LiPF 6 was dissolved in an organic solvent in which ethylene carbonate:ethyl methyl carbonate:diethyl carbonate were mixed at a volume ratio of 3:3:4 was used.

[0149] Next, each of the secondary batteries was charged at 25°C at a constant current of 0.1C up to 4.2V. Then, discharge was performed at a constant current of 0.1C up to 3V to measure the initial charge capacity and the initial discharge capacity.

[0150] Also, each of the secondary batteries was charged at 45°C at a constant current of 0.33C up to 4.2V, and then the charge-discharge behavior of discharging at a constant current of 0.33C up to 3V was defined as one cycle. After repeating such cycles 30 times, the capacity retention rate and the resistance increase rate were measured.

[0151] The capacity retention rate and the resistance increase rate were calculated by the following [Equation 3] and [Equation 4].

[0152] [Equation 3] Capacity retention rate (%) = {Discharge capacity after 30 cycles / Discharge capacity after 1 cycle} × 100

[0153] [Equation 4] Rate of increase in resistance (%) = { (Resistance after 30 cycles - Resistance after 1 cycle) / Resistance after 1 cycle} × 100

[0154] The measurement results are shown in Table 2 below.

[0155] [Table 2]

Table 2

[0156] As shown in the above [Table 2], the capacity characteristics and life characteristics of the secondary batteries using the positive electrode active materials of Examples 1 to 6 in which the ratio of crystal grains A in the external region of the positive electrode active material particles satisfies the scope of the present invention were shown to be superior to those of the secondary batteries using the positive electrode active materials of Comparative Examples 1 to 3. Further, it can be confirmed that when using the positive electrode active materials of Example 1 and Example 4 in which the difference in the ratio of crystal grains A between the external region and the internal region is as large as 5% or more, the improvement effect of the life characteristics is further excellent.

Claims

1. When the distance from the center to the surface of the positive electrode active material particles is R, it includes an internal region which is the region from the center of the positive electrode active material particles to R / 2, and an external region which is the region from R / 2 to the surface of the positive electrode active material particles. Among the total crystal grains in the external region, the major axis orientation degree DoA of the crystal grains represented by the following [Formula 1] is 0.5 to 1, and the c-axis orientation degree of the crystal grains represented by the outer product value of the c-axis rotation vector Rc of the crystal lattice of the crystal grains obtained through Electron Backscatter Diffraction (EBSD) analysis and the position unit vector P' of the crystal grains is 0.5 to 1. The ratio (A1) of crystal grains A is 30% to 80%. Positive electrode active material: [Formula 1] 【Number 1】 In the above [Formula 1], λ １ is the length of the major axis vector E of the crystal grain measured from the image data obtained by scanning ion microscopy of the cross-section of the positive electrode active material Ｉ and is the magnitude of λ ２ is the size of the short-axis vector E of the crystal grain measured from the image data obtained by scanning ion microscopy analysis of the cross-section of the positive electrode active material ＩＩ and is The above-mentioned C Ｄ is the inner product value of the position unit vector P' of the crystal grain and the major axis unit vector E Ｉ '.

2. The ratio (A1) of crystal grains A in the total crystal grains in the external region is 30% to 60%. The positive electrode active material according to Claim 1.

3. The ratio (A1) of the crystal grains A in the total crystal grains in the external region is greater than the ratio (A2) of the crystal grains A in the total crystal grains in the internal region. The positive electrode active material according to Claim 1 or 2.

4. The difference between the ratio (A1) of the crystal grains A in the total crystal grains in the external region and the ratio (A2) of the crystal grains A in the total crystal grains in the internal region is 5% or more. The positive electrode active material according to Claim 3.

5. The positive electrode active material includes crystal grains B in which the major axis orientation degree DoA of the crystal grains is less than 0.5 and the c-axis orientation degree of the crystal grains is 0.5 to 1. crystal grains C in which the major axis orientation degree DoA of the crystal grains is 0.5 to 1 and the c-axis orientation degree of the crystal grains is less than 0.5, and further includes crystal grains D in which the major axis orientation degree DoA of the crystal grains is less than 0.5 and the c-axis orientation degree of the crystal grains is less than 0.

5. The positive electrode active material according to any one of Claims 1 to 4.

6. In the external region, the ratio (A1) of crystal grains A in the total crystal grains is greater than the ratio (B1) of crystal grains B, the ratio (C1) of crystal grains C, and the ratio (D1) of crystal grains D. The positive electrode active material according to Claim 5.

7. The ratio of crystal grains A in the total crystal grains of the cross-section of the positive electrode active material particles is 20% to 80%, the ratio of crystal grains B is 5% to 40%, the ratio of crystal grains C is 5% to 40%, and the ratio of crystal grains D is 5% to 40%. The positive electrode active material according to Claim 5 or 6.

8. The scanning ion microscope analysis irradiates a focused ion beam on a cross-section of the positive electrode active material to obtain a scanning ion microscope image, and then uses deep learning to acquire data segmented in crystal grain units from the scanning ion microscope image, and calculates the DoA represented by the [Formula 1] from the segmented data. The positive electrode active material according to any one of claims 1 to 7.

9. The electron backscatter diffraction (EBSD) analysis obtains 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, and obtains the c-axis rotation vector Rc(x, y, z) of the crystal lattice of the crystal grain through the following [Formula 2]. The positive electrode active material according to any one of claims 1 to 8: [Formula 2] 【Number 2】 In the [Formula 2], [X, Y, Z] is (0, 0, 1), and the Φ, θ, and Ψ are Euler angles obtained from the Euler map data.

10. The positive electrode active material is a lithium composite transition metal oxide represented by the following [Chemical Formula 1]. The positive electrode active material according to any one of claims 1 to 9: [Chemical Formula 1] Li ｘ [Ni ａ Co ｂ M １ ｃ M ２ ｄ O ２－ｙ A ｙ In the [Chemical Formula 1], Said M １ is one or more elements selected from the group consisting of Mn and Al, Said M 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, 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.

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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