Positive electrode material, positive electrode comprising same, and lithium secondary battery

Abstract

The present invention relates to a positive electrode material comprising a plurality of single-particle-type positive electrode active material particles, in which the single-particle-type positive electrode active material particles comprise 1 to 30 primary particles, the ratio of the arithmetic mean value of the convexity of the primary particles to the average aspect ratio of the primary particles being at least 0.63, the convexity of the primary particles is measured from a divided image divided for each primary particle unit obtained by image processing a scanning electron microscope (SEM) image of the positive electrode material, the convexity being defined by the following Equation 1, and the single particle type positive electrode active material contains a lithium nickel-based oxide represented by the following Equation 1: [Equation 1] convexity = Pc / Pr, where, in Equation 1 above, Pr is the actual circumference of each primary particle measured from a divided image, and Pc is the circumference of a virtual pattern obtained by connecting the outermost points of each primary particle measured from the divided image; [Formula 1] Lia [NixCoyM1zM21-x-y-z] O2 wherein, in the above Formula 1, M1 includes Mn, Al, or a combination thereof, M2 includes at least one selected from the group consisting of B, Ba, Ce, Cr, F, Mg, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, and Sr, 1.0 < = a < = 1.3, 0.5 < = xlt, 0 < = x < = 0.2, 0 < = y < = 0.2, 0 < = z < = 0.2, 0 < = z < = 0.2, 0 < = z < = 0.2, 0 < = z < = 0.2, and 0 < = z < = 0.2. 1.0, 0 lt; yt; Yt; 0.5, 0 lt; zlt, zlt; and 0.5.

Description

[0001] Cross-references to related applications

[0002] This invention claims the benefit of priority based on Korean Patent Application Nos. 10-2023-0064596 and 10-2023-0064597, filed May 18, 2023, and Korean Patent Application No. 10-2023-0076141, filed July 14, 2023, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] This invention relates to cathode materials, cathodes comprising the same, and lithium secondary batteries, and more particularly to cathode materials comprising a single-particle type cathode active material wherein the shape of primary particles is controlled to meet certain conditions, and cathodes comprising the cathode materials and lithium secondary batteries. Background Technology

[0004] Lithium-ion batteries typically include a positive electrode, a negative electrode, a separator, and an electrolyte, with the positive and negative electrodes comprising active materials capable of inserting and deintercalating lithium ions.

[0005] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2, LiMnO4, etc.), and lithium iron phosphate compounds (LiFePO4) have been used as positive electrode active materials for lithium secondary batteries. Among these, lithium cobalt oxide has the advantages of high operating voltage and excellent capacity characteristics; however, due to the high price and unstable supply of cobalt as a raw material, its commercial application in high-capacity batteries is difficult. Lithium nickel oxide has poor structural stability, making it difficult to achieve sufficient lifetime characteristics. Meanwhile, lithium manganese oxide has excellent stability but is limited by poor capacity characteristics. Therefore, lithium composite transition metal oxides including two or more transition metals have been developed to compensate for the limitations of lithium transition metal oxides that only include Ni, Co, or Mn. Among these, lithium nickel cobalt manganese-based oxides including Ni, Co, and Mn are widely used in electric vehicle batteries.

[0006] Conventional lithium metal oxides typically exist as spherical secondary particles containing tens to hundreds of primary particles aggregated therein. However, lithium metal oxides in the form of secondary particles, where many of the primary particles are aggregated as described above, have the following limitations: primary particles are prone to detachment during the rolling process in cathode fabrication, and cracks can appear within the particles during charging and discharging. When particle breakage or cracking occurs in the cathode active material, the increased contact area with the electrolyte solution leads to increased gas generation and degradation of the active material due to side reactions with the electrolyte solution, thus limiting its lifetime characteristics.

[0007] In addition, recently, demand for high-output and high-capacity batteries, such as electric vehicle batteries, has increased, and thus, the content of nickel in the positive active material has gradually increased. When the content of nickel in the positive active material increases, initial capacity characteristics improve, but repeated charging and discharging cause the structure of the positive active material to collapse, and thus, the degradation rate of the positive active material increases, thereby causing deterioration in life characteristics and battery safety.

[0008] To address the above limitations, a technique for preparing a positive active material in a single particle form rather than a secondary particle form by increasing the sintering temperature during the preparation of lithium nickel cobalt manganese oxide has been proposed. The positive active material in a single particle form has a smaller contact area with an electrolyte solution than the conventional positive active material in a secondary particle form, and thus, has less side reactions with the electrolyte, and has excellent particle strength, so that particle breakage is less during electrode manufacturing. Thus, when the positive active material in a single particle form is applied, there are advantages in that gas generation and life characteristics are excellent.

[0009] However, in the case of the conventional positive active material in a single particle form, the interface between primary particles, which are the movement paths of lithium ions, inside the particle is less, so that lithium transference is poor, and thus, the resistance is high and the output characteristics are deteriorated, and the roll-pressing property thereof is poorer than that of the positive active material in a secondary particle form, so that the roll-pressing density is deteriorated, resulting in a decrease in energy density. SUMMARY

[0010] TECHNICAL PROBLEM

[0011] To address the above limitations, one aspect of the present application provides a single particle type positive material having excellent capacity characteristics and resistance characteristics compared to the conventional single particle type positive active material by controlling the primary particle shape of the positive material powder to satisfy certain conditions.

[0012] In addition, another aspect of the present application provides a positive electrode including the above-described positive material and a lithium secondary battery having excellent life characteristics and output characteristics.

[0013] TECHNICAL SOLUTION

[0014] According to an embodiment of the present application, a positive material, a positive electrode including the same, and a lithium secondary battery including the same are provided.

[0015] (1) According to one embodiment of the present application, there is provided a positive electrode material including a plurality of single-particle-type positive electrode active material particles, wherein the single-particle-type positive electrode active material particles include 1 to 30 primary particles, a ratio of an arithmetic mean value of a convexity of the primary particles to an average aspect ratio of the primary particles is at least 0.63, the convexity of the primary particles is measured from a divided image for each primary particle unit division obtained by image processing on a scanning electron microscope (SEM) image of the positive electrode material, the convexity is defined by Equation 1 below, and the single-particle-type positive electrode active material includes a lithium nickel-based oxide having a composition represented by Formula 1 below:

[0016] [Equation 1] Convexity = P c / P r

[0017] wherein, in Equation 1 above, P r is an actual perimeter of each primary particle measured from the divided image, and P c is a perimeter of a virtual figure obtained by connecting outermost points of each primary particle measured from the divided image,

[0018] [Formula 1]

[0019] Li a [Ni x Co y M 1 z M 2 1-x-y-z ]O2

[0020] wherein, in Formula 1 above, M 1 includes Mn, Al, or a combination thereof, M 2 includes at least one selected from the group consisting of B, Ba, Ce, Cr, F, Mg, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, and Sr, 1.0 ≤ a ≤ 1.3, 0.5 ≤ x < 1.0, 0 < y < 0.5, and 0 < z < 0.5.

[0021] (2) In the above (1) of the present application, there is provided the positive electrode material, wherein the arithmetic mean value of the convexity of the primary particles is at least 0.92.

[0022] (3) In the above (1) or (2) of the present application, there is provided the positive electrode material, wherein the average aspect ratio of the primary particles is 1.2 to 4.0.

[0023] (4) In any one of the above (1) to (3) of the present application, the positive electrode material is provided, wherein a ratio of an arithmetic mean value of the convexity of the primary particles to a mean aspect ratio of the primary particles is 0.63 to 0.95.

[0024] (5) In any one of the above (1) to (4) of the present application, the positive electrode material is provided, wherein the single-particle type positive electrode active material includes a lithium nickel-based oxide composed of 1 to 30 primary particles; and a coating layer formed on the lithium nickel-based oxide.

[0025] (6) In the above (5) of the present application, the positive electrode material is provided, wherein the coating layer includes at least one coating element selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S.

[0026] (7) In any one of the above (1) to (6) of the present application, the positive electrode material is provided, wherein D50 of the positive electrode material is 2 μm to 15 μm. 50

[0027] (8) In any one of the above (1) to (7) of the present application, the positive electrode material is provided, wherein an average particle diameter of the primary particles is 1 μm to 6 μm.

[0028] (9) In any one of the above (1) to (8) of the present application, the positive electrode material is provided, wherein an arithmetic mean value of the roundness of the primary particles measured from a segmented image divided for each primary particle unit obtained by image processing on a scanning electron microscope (SEM) image of the positive electrode material is at least 0.65, and the roundness is defined by the following Equation 2:

[0029] [Equation 2] Roundness = 4πA / P 2

[0030] wherein, in Equation 2 above, A is an area of each primary particle measured from the segmented image, and P is a perimeter of each primary particle measured from the segmented image.

[0031] (10) In any one of the above (1) to (9) of the present application, the positive electrode material is provided, wherein an arithmetic mean value of the solidity of the primary particles measured from a segmented image divided for each primary particle unit obtained by image processing on a scanning electron microscope (SEM) image of the positive electrode material is 0.85 or more, and the solidity is defined by the following Equation 3:

[0032] ​[Equation 3] Solidity = A r / A c

[0033] wherein, in Equation 3 above, A r is an actual area of each primary particle measured from the segmented image, and A c is an area of a virtual figure obtained by connecting the outermost points of each primary particle measured from the segmented image.

[0034] (11) According to another embodiment of the present application, there is provided a positive electrode including the positive electrode material according to any one of (1) to (10) described above.

[0035] (12) According to still another embodiment of the present application, there is provided a lithium secondary battery including the positive electrode according to (11) described above.

[0036] Advantageous Effects

[0037] The positive electrode material of the present application includes a single-particle type positive electrode active material controlled so that the ratio of the arithmetic mean of the convexity of the primary particles to the average aspect ratio of the primary particles satisfies at least 0.63, and thus the lithium mobility and the roll-pressing property are superior to those of a conventional single-particle type positive electrode active material. Therefore, when the positive electrode material of the present application is applied, a lithium secondary battery having excellent capacity characteristics and life characteristics compared to the prior art can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is a view for explaining the convexity of the present application.

[0039] Figure 2 is a view for explaining the solidity of the present application.

[0040] Figure 3 (A) and a segmented image (B) obtained by image processing of the SEM image of the positive electrode material prepared in Example 1 are shown.

[0041] Figure 4 (A) and a segmented image (B) obtained by image processing of the SEM image of the positive electrode material prepared in Example 2 are shown.

[0042] Figure 5 (A) and a segmented image (B) obtained by image processing of the SEM image of the positive electrode material prepared in Example 3 are shown.

[0043] Figure 6A scanning electron microscope (SEM) image (A) and a segmented image (B) obtained by image processing of the SEM image of the positive electrode material prepared in Example 4 are shown.

[0044] Figure 7 A scanning electron microscope (SEM) image (A) and a segmented image (B) obtained by image processing of the SEM image of the positive electrode material prepared in Comparative Example 1 are shown.

[0045] Figure 8 A scanning electron microscope (SEM) image (A) and a segmented image (B) obtained by image processing of the SEM image of the positive electrode material prepared in Comparative Example 2 are shown.

[0046] Figure 9 A scanning electron microscope (SEM) image (A) and a segmented image (B) obtained by image processing of the SEM image of the positive electrode material prepared in Comparative Example 3 are shown. DETAILED DESCRIPTION

[0047] It should be understood that the terms or words used in the present specification and claims should not be interpreted as being limited to meanings defined in commonly used dictionaries, but should be interpreted based on the conceptual meanings of the terms that have been acquired by those skilled in the art as appropriate, given the technical concepts of the present application.

[0048] As used herein, the term "primary particle" refers to a particle unit in which no external grain boundary exists when observed in a view using a scanning electron microscope at a magnification of 5000 to 20000.

[0049] As used herein, the term "secondary particle" is a particle formed by aggregation of a plurality of primary particles. In the present application, in order to distinguish from the secondary particles formed by aggregation of tens to hundreds of primary particles in the past, the secondary particles formed by aggregation of at most 30 primary particles are referred to as "single particle type positive electrode active material".

[0050] In the present application, the term "single particle type positive electrode active material" refers to a positive electrode active material composed of 1 to 30 primary particles having an average particle diameter of at least 1 μm, preferably 1 μm to 5 μm.

[0051] As used herein, the term "D 50 " refers to a particle diameter at 50% in a volume cumulative distribution according to particle diameter. D 50It can be measured by dispersing a powder to be measured (for example, a positive electrode material powder) in a dispersion medium, and then introducing the powder into a commercially available laser diffraction particle size measuring device (for example, S3500 manufactured by Microtrac), measuring a diffraction pattern difference depending on particle size by a transmitted laser beam to calculate a particle size distribution, and calculating a particle size at a point corresponding to 50% of a volume cumulative distribution depending on particle diameter.

[0052] In the present application, "convexity" is an index indicating surface roughness of a particle to be measured, and is a value defined by the following Equation 1:

[0053] [Equation 1] Convexity = P c / P r

[0054] In the above Equation 1, P r is an actual circumference of a particle to be measured, and P c is a circumference of a virtual figure obtained by connecting the outermost points of the particle to be measured.

[0055] In the present application, "roundness" is an index indicating a degree to which a cross-sectional shape of a particle approaches a circular shape, and is a value defined by the following Equation 2:

[0056] [Equation 2] Roundness = 4πA / P 2

[0057] In the above Equation 2, A is an area of a cross-section of a particle to be measured, and P is a circumference of the cross-section of the particle to be measured.

[0058] In the present application, "solidity " is an index indicating surface roughness of a particle to be measured, and is a value defined by the following Equation 3:

[0059] [Equation 3] Solidity = A r / A c

[0060] In the above Equation 3, A r is an actual area of a particle to be measured, and A c is an area of a virtual figure obtained by connecting the outermost points of the particle to be measured.

[0061] Figure 1 is a figure for explaining the meaning of the convexity of the present application. As Figure 1 shown, P r represents an actual circumference of a primary particle, and P c represents a circumference of a virtual figure obtained by connecting the outermost points of the primary particle. If the particle surface is formed smoothly without irregularities, P r and P cThe values of A and A are similar, and thus the convexity is close to 1. On the other hand, when the roughness is high due to many irregularities on the surface of the particle, A r increases, and thus the convexity decreases. That is, the lower the arithmetic mean value of the convexity of the primary particles constituting the single-particle type positive electrode active material, the more irregularities there are on the surface of the primary particles.

[0062] Figure 2 is a view for explaining the meaning of the solidity according to the present application. As shown in Figure 2 , A r represents the actual area of the primary particle, A c represents the area of a virtual figure obtained by connecting the outermost points of the primary particle. If the surface of the particle is formed smoothly without irregularities, A r and A c are similar in value, and thus the solidity is close to 1. On the other hand, when the roughness is high due to many irregularities on the surface of the particle, A r decreases, and thus the solidity decreases. That is, the lower the arithmetic mean value of the solidity of the primary particles constituting the single-particle type positive electrode active material, the more irregularities there are on the surface of the primary particles.

[0063] Meanwhile, when the surface roughness of the particle increases, the contact area with the electrolyte increases, and when the electrode is wound, the irregular portions are broken, thereby increasing the particle breakage, which leads to a decrease in the life characteristics. Therefore, in order to improve the life characteristics of the positive electrode material, it is necessary to control the surface shape of the primary particles.

[0064] In the present application, the "aspect ratio" refers to the ratio of the long diameter to the short diameter of the particle of the measurement object.

[0065] In the present application, the roundness, convexity, concavo-convexity, average particle diameter, and average aspect ratio of the primary particles can be measured from a segmented image divided for each primary particle unit obtained by image processing of a scanning electron microscope (SEM) image of the positive electrode material using an artificial intelligence model. Specifically, the segmented image can be obtained by obtaining a scanning electron microscope (SEM) image of the positive electrode material powder to be measured, inputting the obtained scanning electron microscope image into a U-NET structure to generate a binary image, converting the binary image into a distance conversion image based on a distance conversion algorithm, filtering the binary image using a threshold value set based on the distance conversion image, identifying a plurality of objects contained in the filtered binary image, and then segmenting the SEM image in units of primary particles based on the plurality of objects.

[0066] Hereinafter, the present application will be described in more detail.

[0067] Positive electrode material

[0068] The positive electrode material according to the present application includes a plurality of single-particle type positive electrode active material particles, and the single-particle type positive electrode active material particles include 1 to 30 primary particles.

[0069] The single-particle type positive electrode active material has higher particle strength than the existing positive electrode active material in the form of secondary particles in which tens to hundreds of primary particles are aggregated, and thus, particle breakage is less during calendering. In addition, in the case of the single-particle type positive electrode active material, the number of primary particles constituting the particle is small, so that changes due to volume expansion and shrinkage of the primary particles during charging and discharging are small, and thus, the occurrence of internal cracks of the particle can be significantly reduced.

[0070] Therefore, when the positive electrode material according to the present application including the single-particle type positive electrode active material is used, the deterioration of electrochemical properties due to particle breakage and crack occurrence can be minimized.

[0071] Meanwhile, the single-particle-based positive electrode active material includes a lithium nickel-based oxide containing nickel and cobalt.

[0072] In this case, the lower limit of the content of nickel among all the metals except lithium in the lithium nickel-based oxide can be at least 50 mol%, at least 55 mol%, at least 60 mol%, at least 80 mol%, at least 85 mol%, or at least 88 mol%, and the upper limit of the content of nickel among all the metals except lithium can be less than 100 mol%, at most 99 mol%, or at most 95 mol%. When the content of nickel in the lithium nickel-based oxide satisfies the above range, a high energy density can be achieved.

[0073] Specifically, the lithium nickel-based oxide can have a composition represented by the following Formula 1:

[0074] [Formula 1]

[0075] Li a [Ni x Co y M 1 z M 2 1-x-y-z ]O2

[0076] In the above Formula 1, M 1 may include Mn, Al, or a combination thereof, M 2 may include at least one selected from the group consisting of B, Ba, Ce, Cr, F, Mg, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, and Sr. Preferably, the above M 1 may be Mn or a combination of Mn and Al, the above M 2may include Al, Zr, Y, Mg, Ti, Ba, Sr, Mo, or a combination thereof, more preferably Zr, Y, or a combination thereof. M 2 The element is not necessarily included, but if included in an appropriate amount, M 2 The element can be used to promote particle growth or improve crystal structure stability during firing of the lithium nickel-based oxide.

[0077] The above a represents the molar ratio of lithium in the lithium nickel-based oxide, and can satisfy 1.0 ≤ a ≤ 1.3, 1.0 ≤ a ≤ 1.2, or 1.0 ≤ a ≤ 1.07. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium nickel-based oxide can be stably formed.

[0078] The above x represents the molar ratio of nickel among all metals other than lithium in the lithium nickel-based oxide, and can satisfy 0.5 ≤ x < 1.0, 0.55 ≤ x < 1.0, 0.60 ≤ x < 1.0, 0.80 ≤ x < 1.0, 0.85 ≤ x < 1.0, 0.88 ≤ x < 1.0, 0.5 ≤ x ≤ 0.99, 0.55 ≤ x ≤ 0.99, 0.60 ≤ x ≤ 0.99, 0.80 ≤ x ≤ 0.99, 0.85 ≤ x ≤ 0.99, 0.88 ≤ x ≤ 0.99, 0.5 ≤ x ≤ 0.95, 0.55 ≤ x ≤ 0.95, 0.60 ≤ x ≤ 0.95, 0.80 ≤ x ≤ 0.95, 0.85 ≤ x ≤ 0.95, or 0.88 ≤ x ≤ 0.95. The higher the molar ratio of nickel, the more advantageous it is to achieve high capacity.

[0079] The above y represents the molar ratio of cobalt among all metals other than lithium in the lithium nickel-based oxide, and can satisfy 0 < y < 0.5, 0 < y < 0.45, 0 < y < 0.4, 0 < y < 0.2, 0 < y < 0.15, or 0 < y < 0.12.

[0080] The above z represents the molar ratio of M 1 among all metals other than lithium in the lithium nickel-based oxide, and can satisfy 0 < z < 0.5, 0 < z < 0.45, 0 < z < 0.4, 0 < z < 0.2, 0 < z < 0.15, or 0 < z < 0.12.

[0081] More specifically, the lithium nickel-based oxide can have a composition represented by the following formula 1-1:

[0082] [Formula 1-1]

[0083] Li a [Ni x Co y Mn z-w Al w M 2 1-x-y-z ]O2

[0084] In the above formula 1-1, M 2 , A, x, y, and z are the same as in formula 1.

[0085] Meanwhile, w represents the molar ratio of Al among the metals other than lithium in the lithium-nickel-based oxide, and can satisfy 0 < w < 0.2, 0 < w ≤ 0.1, 0 < w ≤ 0.05, 0 < w ≤ 0.03, or 0 < w ≤ 0.02. When the lithium-nickel-based oxide has the composition of the above formula 1-1, the structural stability and capacity characteristics of the positive electrode active material are excellent.

[0086] Meanwhile, as needed, the single particle-based positive electrode active material can further include a coating layer formed on the lithium-nickel-based oxide.

[0087] In this case, the coating layer can include at least one coating element selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S, and preferably, can include at least one coating element selected from the group consisting of Co, Al, B, W, Ti, and Zr.

[0088] If the coating layer exists on the surface of the lithium-nickel-based oxide, contact between the electrolyte and the lithium-nickel-based oxide is inhibited by the coating layer, and thus an effect of reducing elution of transition metals or generation of gas due to a side reaction with the electrolyte can be obtained.

[0089] In particular, if Co, Al, or a combination thereof is included as a coating element, an output improvement and resistance reduction effect and an effect of inhibiting a side reaction with an electrolyte solution can be obtained.

[0090] In the positive electrode material according to the present application, the ratio of the arithmetic mean value of the convexity of the primary particles measured from a divided image divided for each primary particle unit obtained by image processing of a scanning electron microscope (SEM) image to the average length-diameter ratio of the primary particles is at least 0.63, specifically 0.63 to 0.95, and more specifically 0.64 to 0.90. According to the research of the present inventors, it was found that the life characteristics are significantly improved by using a positive electrode material in which the ratio of the arithmetic mean value of the convexity of the primary particles to the average length-diameter ratio of the primary particles satisfies the above range.

[0091] In this case, the convexity of the primary particles is a value defined by the following Equation 1:

[0092] [Equation 1] Convexity = P c / P r

[0093] wherein, in the above Equation 1, P r is the actual circumference of each primary particle measured from the divided image, P cis a length of a virtual figure obtained by connecting the outermost points of each primary particle measured from the segmented image.

[0094] Particle shape analysis of the positive active material is performed using an image of the positive active material powder obtained by a scanning electron microscope (SEM), and in the case of the SEM image of the positive material powder, it is difficult to distinguish the aggregated primary particles on the image due to the image resolution, particle agglomeration, surface roughness, etc. Therefore, conventionally, a method in which a person selects each active material particle and / or primary particle from the SEM image and manually measures the length, aspect ratio, particle size, etc. of the selected particle is used. However, in this case, there is a limitation in that it is difficult to quantitatively analyze a large number of positive active material particles, and the measurement value can vary depending on the measurer, so the analysis accuracy deteriorates. Therefore, conventionally, it is difficult to accurately analyze the surface shape of the primary particles of the positive active material, and thus it is difficult to derive the correlation between the surface shape of the primary particles and the battery performance.

[0095] Therefore, the present inventors developed a method capable of quantitatively analyzing the surface shape of the primary particles in the positive material powder by using image analysis of an artificial intelligence model, and found that when the ratio of the arithmetic mean of the convexity of the primary particles measured according to the analysis method to the average aspect ratio of the primary particles is at least 0.63, the life characteristics of the single particle type positive material are significantly improved, thereby completing the present invention.

[0096] The shape analysis method of the positive material particles according to the present invention is as follows.

[0097] First, a scanning electron microscope image of the positive material powder to be measured is obtained, and then the obtained scanning electron microscope image is input to an artificial intelligence model to generate a binary image. In this case, the artificial intelligence model can be a model trained to convert an active material image into a binary image, and in this case, the training data uses the SEM image of the positive material powder as a raw image, and uses a binary image obtained by binarizing the SEM image as a label image. The binary image is an image obtained by binarizing the SEM image through computer vision technology or an image obtained by manually drawing the SEM image. Furthermore, in order to learn various cases, an image enhancement algorithm (for example, rotation, tilt, shear, brightness adjustment, contrast adjustment, enlargement, reduction, or a combination thereof) is applied to the raw image and the label image to generate additional images, and this is used as training data.

[0098] Meanwhile, the size of the original image and the label image can be the same. The image size can be defined as the number of horizontal pixels x the number of vertical pixels, and for example, the size of the original image and the label image can be 256 x 256.

[0099] Meanwhile, as the artificial intelligence model, a U-NET structure capable of reflecting an input image by adding a skip connection in an encoding and decoding process is used. The artificial intelligence model can have a structure in which a plurality of layers are sequentially connected, the input of a sequentially connected layer can be the output of a layer connected immediately before the input, and the output of a sequentially connected layer can be the input of a layer connected immediately after the output. The layers included in the encoding region have a structure in which a 2D convolution layer, a batch normalization layer, an activation layer, and a max pooling layer are sequentially connected, and the layers included in the decoding region have a structure in which a 2D convolution layer, a batch normalization layer, an activation layer, and an up-sampling layer are sequentially connected.

[0100] The training of the artificial intelligence model is performed using a deep learning backpropagation algorithm, a binary cross entropy loss function is used as a loss function, and when the binary cross entropy loss function is used as a function, a weight between 1 and 1000 is applied to one of the two colors (or categories) as needed (for example, white in black and white).

[0101] Next, a binary image generated from the artificial intelligence model is converted into a distance conversion image based on a distance conversion algorithm. In this case, the distance conversion algorithm can be a max-min normalization, a Z-score normalization, an L1 normalization, or an L2 normalization algorithm.

[0102] Next, a filtered binary image is obtained by filtering the binary image using a threshold value set based on the distance conversion image. In this case, the threshold value can be a value obtained by multiplying a normalized maximum distance of the distance conversion image by a designated ratio (for example, 0 to 0.1). The filtering can be performed by selecting a pixel having a distance value less than or equal to a designated threshold value among pixels included in the distance conversion image, and setting a color value of a pixel corresponding to the pixel selected from the distance conversion image in a pixel included in the binary image with a designated color value. Through this method, a filtered image including a plurality of objects is obtained.

[0103] Next, after identifying a plurality of objects included in the filtered image, a segmented image divided for each primary particle unit is obtained by segmenting the SEM image based on the plurality of objects. In this case, segmentation is performed using a Watershed algorithm.

[0104] Since the segmented image obtained by the above-described method shows the positive active material particles in the positive electrode material by segmenting into primary particle units, various shape information related to the primary particles of the positive active material particles (e.g., the roundness, the circumference, the area, the aspect ratio, the convexity, the concavity, etc. of the primary particles) can be quantitatively obtained by using the segmented image.

[0105] In addition, in the case of the above-described analysis method, since an artificial intelligence model in which user input is minimized is utilized, a problem in which a measured value varies depending on a user is minimized, and thus accuracy and reproducibility are excellent.

[0106] In the positive electrode material according to the present application, the arithmetic mean value of the convexity of the primary particles can be at least 0.92, specifically 0.92 to 1.0, and more specifically 0.92 to 0.98.

[0107] In addition, in the positive electrode material according to the present application, the arithmetic mean value of the primary particle solidity of the primary particles measured from a segmented image divided by each primary particle unit obtained by image processing of a scanning electron microscope (SEM) image can be at least 0.85, specifically 0.85 to 1.0, and more specifically 0.86 to 0.98.

[0108] When the arithmetic mean value of the convexity of the primary particles and / or the arithmetic mean value of the solidity of the primary particles are within the above-described ranges, the surface roughness of the particles increases, so that the contact area with the electrolyte solution increases, and uneven portions are prevented from being broken during the rolling of the electrode, thereby preventing an increase in particle breakage, thus improving the life characteristics of the battery.

[0109] In this case, the solidity of the primary particles is a value defined by Equation 3 below:

[0110] [Equation 3] Solidity = A r / A c

[0111] where, in the above Equation 1, A r is the actual area of each primary particle measured from the segmented image, A c is the area of a virtual figure obtained by connecting the outermost points of each primary particle measured from the segmented image.

[0112] In the positive electrode material according to the present application, the average aspect ratio of the primary particles can be 1.2 to 4.0, and preferably 1.2 to 3.0. In this case, the aspect ratio refers to the ratio of the length of the long diameter to the length of the short diameter of the primary particles. If the average aspect ratio of the primary particles is too small, the lithium ion mobility can be deteriorated due to poor contact between the particles, and if the average aspect ratio is too large, the electrochemical performance can be deteriorated due to an increase in the diffusion distance of the lithium ions inside the particles, and the lithium ion diffusion in the electrode can be hindered due to a long distance between the particles.

[0113] In the positive electrode material according to the present application, the arithmetic mean of the roundness of the primary particles measured from the segmented image divided for each primary particle unit obtained by image processing of a scanning electron microscope image can be at least 0.65, specifically 0.65 to 0.98, and more specifically 0.65 to 0.90, or 0.65 to 0.85.

[0114] When the arithmetic mean of the roundness of the primary particles is within the above range, the lithium ions can more smoothly diffuse into the particles, and the contact area between the single particle type positive electrode active material and the electrolyte can increase, so that the electrochemical performance can be improved. In addition, since the distance between the particles in the electrode remains relatively constant, the current flows smoothly in the electrode, and the arrangement of the particles is uniform, so that the mechanical stability increases, thereby improving the cycle life of the battery. In addition, within the above range, deterioration in the capacity and / or life characteristics of the battery due to an increase in friction between the single particles and uneven distribution of the single particle type positive electrode active material can be prevented, while the need for an additional process for excessive pulverization or rounding, or particle damage or particle breakage can be suppressed.

[0115] In this case, the roundness of the primary particles is a value defined by Equation 2 below:

[0116] [Equation 2] Roundness = 4πA / P 2

[0117] wherein, in the above Equation 2, A is the area of each primary particle measured from the segmented image, and P is the perimeter of each primary particle measured from the segmented image.

[0118] The positive electrode active material according to the present application can have a D 50 of 2 μm to 15 μm, preferably 3 μm to 10 μm, and more preferably 3 μm to 8 μm. 50 There is a limitation in that if the D 50 of the positive electrode active material is too small, it is difficult to form an active material layer when manufacturing an electrode, the electrochemical performance is deteriorated due to poor electrolyte wettability, and if the D

[0119] Meanwhile, in the positive electrode material according to the present application, the average particle diameter of the primary particles can be 1 to 6 μm, preferably 1 to 5 μm, and more preferably 1 to 4 μm. When the average particle diameter of the primary particles satisfies the above range, a single particle type positive electrode active material having excellent electrochemical properties can be formed. If the average particle diameter of the primary particles is too small, the number of agglomerations of the primary particles forming the lithium nickel-based oxide particles increases, thereby reducing the effect of suppressing the generation of particle breakage during rolling, and if the average particle diameter of the primary particles is too large, the lithium diffusion path inside the primary particles becomes long, thereby increasing the electric resistance and reducing the output characteristics.

[0120] Method of preparing positive electrode material

[0121] Next, a method of preparing a positive electrode material according to the present application will be described.

[0122] The method of preparing a positive electrode material of the present application includes: (1) a step of mixing a transition metal precursor and a first lithium raw material, and then performing primary sintering to form a primary sintered product including a single particle type lithium nickel-based oxide having 1 to 30 primary particles; (2) a first pulverization step of pulverizing the primary sintered product; (3) a step of mixing the pulverized primary sintered product and a second lithium raw material, and then performing secondary sintering to form a secondary sintered product; and (4) a second pulverization step of pulverizing the secondary sintered product.

[0123] (1) Step of forming primary sintered product

[0124] First, a transition metal precursor and a first lithium raw material are mixed, and then primary sintering is performed to form a primary sintered product.

[0125] In this case, the transition metal precursor can be used by purchasing a precursor such as a commercially available nickel-cobalt-manganese-based hydroxide, or can be prepared by a precursor preparation method known in the art.

[0126] Preferably, the transition metal precursor can be a transition metal hydroxide represented by the following Formula 2:

[0127] [Formula 2]

[0128] [Ni x1 Co y1 M 1 z1 M 2 1-x1-y1-z1 ](OH)2

[0129] In the above Formula 2, M 1 and M 2 are the same as defined in Formula 1. In other words, M 1 includes Mn, Al, or a combination thereof, and M 2comprises at least one selected from the group consisting of B, Ba, Ce, Cr, F, Mg, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, and Sr.

[0130] Meanwhile, x1 denotes the molar ratio of nickel among all the metal elements in the transition metal precursor, and can satisfy 0.5 ≤ x1 < 1.0, 0.55 ≤ x1 < 1.0, 0.60 ≤ x1 < 1.0, 0.80 ≤ x1 < 1.0, 0.85 ≤ x1 < 1.0, 0.88 ≤ x1 < 1.0, 0.5 ≤ x1 ≤ 0.99, 0.55 ≤ x1 ≤ 0.99, 0.60 ≤ x1 ≤ 0.99, 0.80 ≤ x1 ≤ 0.99, 0.85 ≤ x1 ≤ 0.99, 0.88 ≤ x1 ≤ 0.99, 0.5 ≤ x1 ≤ 0.95, 0.55 ≤ x1 ≤ 0.95, 0.60 ≤ x1 ≤ 0.95, 0.80 ≤ x1 ≤ 0.95, 0.85 ≤ x1 ≤ 0.95, or 0.88 ≤ x1 ≤ 0.95.

[0131] The above-described y1 denotes the molar ratio of cobalt among all the metals in the transition metal precursor, and can satisfy 0 < y1 < 0.5, 0 < y1 < 0.45, 0 < y1 < 0.4, 0 < y1 < 0.2, 0 < y1 < 0.15, or 0 < y1 < 0.12.

[0132] The above-described z1 denotes the molar ratio of M 1 among all the metals in the transition metal precursor, and can satisfy 0 < z1 < 0.5, 0 < z1 < 0.45, 0 < z1 < 0.4, 0 < z1 < 0.2, 0 < z1 < 0.15, or 0 < z1 < 0.12.

[0133] For example, the transition metal precursor can be prepared by forming a transition metal aqueous solution and an ammonium cation complex, injecting a basic compound into a reactor, stirring the mixture, and performing a co-precipitation reaction.

[0134] The transition metal aqueous solution can be prepared by dissolving a raw material containing a transition metal in a solvent (e.g., water), for example, dissolving a nickel-containing raw material or a cobalt-containing raw material in water. In addition, as necessary, the transition metal aqueous solution can further include a raw material of M 1 and / or a raw material containing a metal of M 2 .

[0135] Meanwhile, the raw material containing a transition metal can be an acetate, a carbonate, a nitrate, a sulfate, a halide, a sulfide, or an oxide of the transition metal.

[0136] Specifically, the nickel-containing raw material can be, for example, NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, a nickel halide, or a combination thereof.

[0137] The cobalt-containing raw material can be, for example, CoSO4, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4·7H2O, or a combination thereof.

[0138] The M 1 -containing raw material can be a manganese-containing raw material and / or an aluminum-containing raw material. The manganese-containing raw material can be, for example, Mn2O3, MnO2, Mn3O4 MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, a manganese halide, or a combination thereof, and the aluminum-containing raw material can be, for example, Al2O3, Al(OH)3, Al(NO3)3, Al2(SO4)3, (HO)2AlCH3CO2, HOAl(CH3CO2)2, Al(CH3CO2)3, an aluminum halide, or a combination thereof. However, Al can not be added to the transition metal aqueous solution, but can be added with the lithium raw material in a firing step to be described later.

[0139] The M 2 -containing raw material can be an acetate, a carbonate, a nitrate, a sulfate, a halide, a sulfide, or an oxide of the M 2 metal.

[0140] The input amount of each transition metal-containing raw material can be determined in consideration of the molar ratio of the transition metal in the final produced positive electrode active material.

[0141] Meanwhile, the ammonium cation complexing agent can include at least one compound selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and NH4CO3, and can be introduced into the reactor in the form of a solution in which the compound is dissolved in a solvent. In this case, water or a mixture of water and an organic solvent (specifically, an alcohol or the like) that can be uniformly mixed with water can be used as the solvent.

[0142] The basic compound can be at least one compound selected from the group consisting of NaOH, KOH, and Ca(OH)2, and can be introduced into the reactor in the form of a solution in which the compound is dissolved in a solvent. In this case, water or a mixture of water and an organic solvent (specifically, an alcohol or the like) that can be uniformly mixed with water can be used as the solvent.

[0143] As described above, when the aqueous transition metal solution, the ammonium cation complex forming agent, and the basic compound are introduced into the reactor and stirred, the transition metal in the aqueous transition metal solution co-precipitates to produce precursor particles in the form of transition metal hydroxide.

[0144] In this case, the aqueous transition metal solution, the ammonium cation complex forming agent, and the basic compound are added in amounts such that the pH of the reaction solution is within the desired range.

[0145] When the precursor particles are formed by the above-described method, the particles are separated from the reaction solution to obtain a transition metal precursor. For example, the transition metal precursor can be separated from the reaction solution by filtering the reaction solution, and then the separated transition metal precursor can be washed with water and dried to obtain the transition metal precursor. In this case, processes such as pulverization and / or classification can be performed as needed.

[0146] Next, the transition metal precursor and the first lithium raw material are mixed, and then primary firing is performed to form a primary firing product including single-particle type lithium nickel-based oxides including 1 to 30 primary particles. In this case, if necessary, an aluminum-containing raw material and / or an M 2 The metal-containing raw material can be mixed together and fired.

[0147] As the first lithium raw material, a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, oxyhydroxide, or the like can be used, and for example, Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or a mixture thereof can be used.

[0148] Meanwhile, the first lithium raw material can be mixed such that the ratio of the number of moles of lithium to the total number of moles of transition metals contained in the transition metal precursor is 0.9 to 1.1, preferably 0.95 to 1.07, and more preferably 1 to 1.05. When the ratio of the number of moles of the transition metal precursor and the first lithium raw material satisfies the above-described range, the layered crystal structure of the positive electrode active material is well developed, and thus a positive electrode material having excellent electrochemical properties can be prepared.

[0149] Meanwhile, the primary firing is performed under conditions in which the primary particles grow to at least 1 µm to form single-particle type lithium nickel-based oxides.

[0150] The appropriate primary firing temperature can vary depending on the metal composition in the precursor, and for example, when the content of nickel (Ni) is at least 80 mol%, the primary firing can be performed at a temperature of 800°C to 950°C, preferably 820°C to 950°C, more preferably 850°C to 950°C.

[0151] Further, the primary firing can be performed in an oxygen atmosphere for 5 hours to 35 hours, preferably 5 hours to 20 hours, more preferably 5 hours to 15 hours.

[0152] Further, the primary firing can be performed in an oxygen atmosphere. In the present specification, the oxygen atmosphere refers to an atmosphere containing a sufficient amount of oxygen for firing, and the atmosphere includes an air atmosphere. In particular, it is preferable to perform the firing in an atmosphere having a higher oxygen partial pressure than the air atmosphere.

[0153] When the primary firing is performed under the above conditions, a single particle type lithium nickel-based oxide having excellent electrochemical properties can be formed. When the primary firing temperature is too low and the time is too short, the primary particles do not sufficiently grow, so that a positive electrode active material in the form of secondary particles is prepared; whereas when the primary firing temperature is too high and the time is too long, an electrically inert rock salt phase is excessively formed during the firing, so that a fired product having a structure that is unstable and having low crystallinity is prepared, resulting in deterioration of the electrochemical properties.

[0154] (2) First pulverization step

[0155] When the primary fired product is formed by the primary firing as described above, a first pulverization step of pulverizing the primary fired product is performed.

[0156] The first pulverization step is used to disintegrate the aggregated positive electrode active material and to appropriately adjust the particle size and shape of the particles in the positive electrode material, and can be performed using a pulverization device well known in the art, such as a jet mill pulverizer or a ball mill pulverizer.

[0157] In the first pulverization step, by appropriately adjusting the pulverization conditions such as the pulverization pressure and the classification speed, the particle size distribution (D 50 ) of the lithium nickel-based oxide particles and the shape and aspect ratio of the primary particles can be adjusted.

[0158] For example, the first pulverization step can be performed under a pulverization pressure condition of 1.5 bar to 2.5 bar, preferably 1.5 bar to 2.4 bar, more preferably 1.5 bar to 2.3 bar. When the pulverization pressure of the first pulverization step satisfies the above range, it is easy to prepare a positive electrode material having a desired convexity of the arithmetic mean value of the primary particles.

[0159] Further, the first pulverization step can be performed at a classification speed of 800 rpm to 1800 rpm, preferably 900 rpm to 1800 rpm, more preferably 900 rpm to 1700 rpm. When the classification speed of the first pulverization step satisfies the above range, it is easy to adjust the D90 of the positive electrode material to the desired range. 50 and / or the average particle diameter of the primary particles is adjusted to the desired range.

[0160] (3) a step of forming a secondary sintered product

[0161] Next, the primary sintered product pulverized by the first pulverization step and a second lithium raw material are mixed, and then secondary sintering is performed.

[0162] In this case, as the second lithium raw material, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, oxyhydroxides, etc. can be used, and for example, Li2CO3, LiNO3, LiNO2, LiOH, LiOH, H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or a mixture thereof can be used. The second lithium raw material can be the same as or different from the first lithium raw material.

[0163] Meanwhile, the second lithium raw material can be mixed such that the ratio of the number of moles of lithium to the total number of moles of transition metals contained in the transition metal precursor is 0.005 to 0.1, preferably 0.005 to 0.05, more preferably 0.005 to 0.04. When the input amount of the second lithium raw material satisfies the above range, it is easy to prepare a positive electrode material having primary particles of a desired shape without deteriorating the physical properties of the positive electrode material. When secondary sintering is performed without injecting the second lithium raw material, there is a limitation that high-temperature and long-term sintering is required due to a slow reaction rate, and even if the second lithium raw material is injected, if the input amount is too small, the effect of reducing the rock salt structure on the surface of the single particle type lithium nickel-based oxide is not significant, and if the input amount is too large, lithium by-products can increase, thereby reducing the electrochemical performance.

[0164] When secondary sintering is performed by additionally injecting the second lithium raw material as described above, lithium is inserted into the rock salt structure that can be formed on the surface of the single particle type lithium nickel-based oxide and restored to a layered structure, thereby improving the crystallinity, and the surface of the primary particles is smoothly formed during the secondary sintering process, thereby making it easy to prepare a positive electrode material having a desired convexity.

[0165] Meanwhile, the secondary firing can be performed at a temperature 50°C to 100°C lower than the primary firing temperature. When the secondary firing temperature is higher than the primary firing temperature, the surface of the lithium nickel-based oxide deteriorates due to excessive appearance of the rock salt phase on the surface thereof, and lithium by-products remain, thereby deteriorating the electrochemical properties. When the secondary firing is performed at a temperature at least 100°C lower than the primary firing temperature, the lithium intercalation rate decreases, thereby deteriorating the electrochemical properties, and the effect of improving the convexity of the primary particles is not significant. For example, the secondary firing temperature can be 700°C to 850°C, preferably 750°C to 850°C, more preferably 750°C to 840°C.

[0166] Meanwhile, in terms of improving the crystallinity of the internal crystal structure of the positive active material, the secondary firing time can be, for example, 5 hours to 35 hours, preferably 5 hours to 20 hours, more preferably 5 hours to 15 hours.

[0167] Further, the secondary firing can be performed in an oxygen atmosphere.

[0168] When the secondary firing is performed under the above conditions, a positive electrode material having excellent electrochemical properties and having a desired primary particle shape can be easily formed.

[0169] (4) Second pulverization step

[0170] Next, a second pulverization step of pulverizing the secondary firing product obtained by the secondary firing is performed. In this case, it is preferable that the pulverization pressure of the second pulverization step be less than the pulverization pressure of the first pulverization step. When the pulverization pressure of the second pulverization step is greater than the pulverization pressure of the first pulverization step, the pulverization is excessively performed, and thus it is difficult to form the surface shape of the primary particles within a desired range, and in a severe case, a broken surface can appear in the single particle type lithium nickel-based oxide particles.

[0171] For example, the second pulverization step can be performed under a pulverization pressure condition of 0.4 bar to 1.4 bar, 0.5 bar to 1.4 bar, or 0.6 bar to 1.3 bar.

[0172] Further, the second pulverization step can be performed at a classification speed of 800 rpm to 1800 rpm, preferably 900 rpm to 1800 rpm, more preferably 900 rpm to 1700 rpm. When the classification speed of the second pulverization step satisfies the above range, the D 50 and / or the average particle diameter is adjusted to a desired range.

[0173] (5) Coating step

[0174] Meanwhile, the method of producing the positive electrode material of the present application can further include a step of mixing the pulverized secondary calcination product with a coating raw material after the second pulverization step, and then performing heat treatment to form a coating layer, as needed.

[0175] The coating raw material can be an acetate, a carbonate, a nitrate, a sulfate, a halide, a sulfide, an oxide, or the like, containing a coating element.

[0176] Meanwhile, the mixing can be performed by solid-phase mixing or liquid-phase mixing, and heat treatment can be performed at an appropriate temperature according to the type of element to be coated. For example, the heat treatment can be performed at a temperature of 200°C to 800°C, preferably 400°C to 750°C. In addition, the heat treatment can be performed in two or more steps at different temperatures.

[0177] The heat treatment can be performed for 1 hour to 10 hours, particularly 2 hours to 8 hours, and more particularly 3 hours to 6 hours, thereby increasing the crystallinity of the coating portion.

[0178] The positive electrode material produced according to the above-described method includes a plurality of single-particle type positive electrode active materials. In addition, when measured from a divided image divided for each primary particle unit obtained by image processing of a scanning electron microscope (SEM) image of the positive electrode material, the ratio of the arithmetic mean value of the convexity of the primary particles to the average aspect ratio of the primary particles can be at least 0.63. In addition, other physical properties of the positive electrode material according to the present application can be satisfied.

[0179] Positive electrode

[0180] Next, the positive electrode of the present application will be described.

[0181] The positive electrode of the present application includes a positive electrode active material layer containing the positive electrode active material of the present application. 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 containing the positive electrode material.

[0182] In the positive electrode, the positive electrode current collector is not particularly limited as long as it has electrical conductivity without causing adverse chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, or silver, or the like can be used. Also, the positive electrode current collector can generally have a thickness of 3 μm to 500 μm, and micro-irregularities can be formed on the surface of the current collector to improve adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various shapes, such as a film, a sheet, a foil, a mesh, a porous body, a foam body, and a non-woven fabric body.

[0183] In addition, the positive electrode active material layer can include a conductive agent and a binder, as well as the above-described positive electrode material.

[0184] The conductive agent serves to provide conductivity to the electrode, and any conductive agent can be used without particular limitation as long as it has suitable electron conductivity without causing adverse chemical changes in the battery. Specific examples of the conductive agent can include: graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal crack carbon black, carbon fibers, and carbon nanotubes; powders or fibers of metals such as copper, nickel, aluminum, and silver; 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 of these alone or a mixture of two or more of these can be used. The content of the conductive agent can generally be 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight, relative to the total weight of the positive electrode active material layer.

[0185] The binder serves to improve the binding between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples of the binder can include: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluoro rubber, or various copolymers thereof, and any one of these alone or a mixture of two or more of these can be used. The content of the binder can be 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight, relative to the total weight of the positive electrode active material layer.

[0186] The positive electrode can be prepared according to a conventional method for preparing a positive electrode. For example, the positive electrode can be prepared by mixing a positive electrode material, a binder, and / or a conductive agent in a solvent to prepare a positive electrode slurry, and coating the positive electrode slurry onto a positive electrode current collector, followed by drying and roll-pressing the positive electrode current collector.

[0187] The solvent can be a solvent generally used in the art. The solvent can include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methyl pyrrolidone (NMP), acetone, or water, and any one of these alone or a mixture of two or more of these can be used. The amount of the solvent used can be sufficient in that the solvent can dissolve or disperse the positive electrode material, the conductive agent, and the binder, taking into account the application thickness of the slurry and the production yield, and can allow a viscosity that can provide excellent thickness uniformity during the subsequent application for preparing the positive electrode.

[0188] Alternatively, the positive electrode can be prepared by casting the positive electrode slurry on a separate support, and then laminating the film separated from the support on the positive electrode current collector.

[0189] Lithium secondary battery

[0190] Next, a lithium secondary battery of the present application will be described.

[0191] The lithium secondary battery of the present application includes the positive electrode of the present application. Specifically, the lithium secondary battery includes a positive electrode, a negative electrode disposed to face the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is as described above. Further, the lithium secondary battery can also optionally include a battery container that houses an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

[0192] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0193] The negative electrode current collector is not particularly limited as long as it has high electrical conductivity without causing adverse chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper, or copper or stainless steel surface-treated with one of carbon, nickel, titanium, or silver, and an aluminum cadmium alloy can be used. Also, the negative electrode current collector can generally have a thickness of 3 μm to 500 μm, and similar to the positive electrode current collector, micro-irregularities can be formed on the surface of the current collector to improve adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various shapes, such as a film, a sheet, a foil, a mesh, a porous body, a foam body, and a non-woven fabric body.

[0194] The negative electrode active material layer optionally contains a binder and a conductive agent in addition to the negative electrode active material.

[0195] A compound capable of reversibly intercalating and deintercalating lithium can be used as the negative electrode active material. Specific examples of the negative electrode active material can be carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal compounds that can alloy with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides that can be doped with and without lithium, such as SiO β (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composite materials containing a metal compound and a carbonaceous material, such as Si-C composite materials or Sn-C composite materials, and any one thereof or a mixture of two or more thereof can be used.

[0196] In addition, a metal lithium thin film can be used as the negative electrode active material. Furthermore, both low-crystalline carbon and high-crystalline carbon can be used as the carbon material. Typical examples of the low-crystalline carbon can be soft carbon and hard carbon, and typical examples of the high-crystalline carbon can be irregular, planar, flaky, spherical, or fibrous natural graphite or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbead, mesophase pitch, and high-temperature sintered carbon such as petroleum or coal tar pitch-derived coke.

[0197] The conductive agent is used to provide conductivity to the electrode, and any conductive agent can be used without particular limitation as long as it has suitable electron conductivity without causing adverse chemical changes in the battery. Specific examples of the conductive agent can include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotube; a powder or fiber of a metal such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide whisker and potassium titanate whisker; a conductive metal oxide such as titanium oxide; or a conductive polymer such as a polyphenylene derivative, and any one of these alone or a mixture of two or more of these can be used. The content of the conductive agent can generally be 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight, relative to the total weight of the negative electrode active material layer.

[0198] The binder is used to improve the binding between the negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Specific examples of the binder can include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of these alone or a mixture of two or more of these can be used. The content of the binder can be 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight, relative to the total weight of the negative electrode active material layer.

[0199] The negative electrode active material layer can be prepared, for example, by coating a negative electrode slurry containing a negative electrode active material and, optionally, a binder and a conductive agent on a negative electrode current collector and drying the coated negative electrode current collector, or by casting a negative electrode slurry on a separate carrier and then laminating the film separated from the carrier on a negative electrode current collector.

[0200] In the lithium secondary battery, a separator separates the negative electrode and the positive electrode and provides a path for movement of lithium ions, wherein any separator can be used as the separator without particular limitation as long as it is generally used for lithium secondary batteries, and particularly, a separator having a high moisture retaining ability with respect to an electrolyte and a low electric resistance with respect to ion transfer of the electrolyte can be used. Specifically, a porous polymer film, for example, a porous polymer film prepared from a polyolefin type polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure having two or more layers can be used. In addition, a typical porous nonwoven fabric, for example, a nonwoven fabric formed of high-melting point glass fibers or polyethylene terephthalate fibers can be used. In addition, a coated separator including a ceramic component or a polymer material can be used to secure heat resistance or mechanical strength, and a separator having a single layer or a multi-layer structure can be optionally used.

[0201] In addition, the electrolyte used in the present application can include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten-type inorganic electrolyte, which can be used to prepare a lithium secondary battery, but the present application is not limited thereto.

[0202] Specifically, the electrolyte can include an organic solvent and a lithium salt.

[0203] As the organic solvent, any organic solvent can be used without particular limitation as long as it can be used as a medium through which ions participating in an electrochemical reaction of a battery can move. Specifically, as the organic solvent, an ester-based solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; an ether-based solvent such as dibutyl ether or tetrahydrofuran; a ketone-based solvent such as cyclohexanone; an aromatic hydrocarbon-based solvent such as benzene and fluorobenzene; a carbonate-based solvent such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); an alcohol-based solvent such as ethanol and isopropyl alcohol; a nitrile such as R-CN (wherein R is a linear, branched, or cyclic C2-C20 hydrocarbon group, and can include a double-bonded aromatic ring or an ether bond); an amide such as dimethylformamide; a dioxolane such as 1,3-dioxolane; or a sulfolane can be used. Among these solvents, a carbonate-based solvent such as a mixture of a cyclic carbonate having a high ionic conductivity and a high dielectric constant (for example, ethylene carbonate or propylene carbonate) which can improve the charge / discharge performance of a battery and a linear carbonate compound having a low viscosity (for example, ethylmethyl carbonate, dimethyl carbonate, or diethyl carbonate) can be used.

[0204] The lithium salt can be used without particular limitation, as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, as the lithium salt, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, and the like can be used. It is preferable to use a lithium salt having a concentration ranging from 0.1 M to 5.0 M, preferably from 0.1 M to 3.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can have a suitable conductivity and viscosity, thereby exhibiting excellent performance, and lithium ions can move effectively.

[0205] To improve the life characteristics of the battery, suppress the decrease in the capacity of the battery, and improve the discharge capacity of the battery, an additive can be additionally included in the electrolyte in addition to the above electrolyte components. For example, as the additive, any one or a mixture of halogenated alkylene carbonate compounds (e.g., difluoroethylene carbonate, etc.), pyridine, triethyl phosphite, triethanolamine, a cyclic ether, ethylenediamine, n-glyme, hexamethylphosphoric triamide, a nitrobenzene derivative, sulfur, a quinonimine dye, an N-substituted oxazolidinone, an N,N-substituted imidazolidine, an ethylene glycol dialkyl ether, an ammonium salt, a pyrrole, 2-methoxyethanol, or aluminum trichloride can be used, but embodiments of the present application are not limited thereto. The content of the additive can be 0.1 to 10% by weight, preferably 0.1 to 5% by weight, with respect to the total weight of the electrolyte.

[0206] Hereinafter, embodiments of the present application will be described in detail so that those of ordinary skill in the art to which the present application pertains can easily practice the present application. However, the present application can be implemented in many different forms and should not be construed as limited to the embodiments set forth herein.

[0207] Example 1

[0208] D 50 Ni 0.885 Co 0.035 Mn 0.08 (OH)2 and LiOH were mixed so that the ratio of the number of moles of Ni+Co+Mn:Li was 1:1.03, and Al(OH)3, Y2O3, and ZrO2 were added thereto in amounts of 1470 ppm, 1000 ppm, and 1500 ppm, respectively, with respect to the total weight of the transition metal precursor, thereby preparing a mixture. Then, the mixture was once fired at 890 to 900°C for 6 hours to obtain a once-fired product.

[0209] Then, the primary sintered product was finely pulverized at room temperature using a jet mill pulverizer at a pulverization pressure of 2.1 bar and a classifying speed of 1600 rpm (first pulverization step).

[0210] Next, the pulverized primary sintered product and LiOH were mixed so that the ratio of the number of moles of Ni+Co+Mn : Li was 1 : 0.01, and the mixture was secondary sintered at 820°C for 9 hours to obtain a secondary sintered product.

[0211] Then, the secondary sintered product was finely pulverized at room temperature using a jet mill pulverizer at a pulverization pressure of 0.9 bar and a classifying speed of 1600 rpm to obtain a single particle type lithium nickel-based oxide LiNi 0.8784 Co 0.0347 Mn 0.0794 Al 0.005 Zr 0.0015 Y 0.001 O2 (second pulverization step).

[0212] Next, the single particle type lithium nickel-based oxide obtained above was uniformly mixed with Co(OH)2and Al(OH)3, and then heat-treated at 700°C for 5 hours and at 500°C for 3 hours in an oxygen atmosphere to prepare a positive electrode material on which a coating layer was formed. In this case, the amount of mixed Co(OH)2was such that the ratio (B / A) of the number of moles (B) of Co in Co(OH)2to the total number of moles (A) of the remaining metals other than lithium in the lithium nickel-based oxide was 0.02, and the amount of mixed Al(OH)3was 0.05 parts by weight with respect to 100 parts by weight of the lithium nickel-based oxide.

[0213] Example 2

[0214] A positive electrode material was prepared in the same manner as in Example 1, except that the first pulverization step was performed at a pulverization pressure of 1.6 bar.

[0215] Example 3

[0216] D 50 Ni 0.885 Co 0.035 Mn 0.08 (OH)2and LiOH were mixed so that the ratio of the number of moles of Ni+Co+Mn : Li was 1 : 1, and Al(OH)3, Y2O3, and ZrO2were added thereto in amounts of 1470 ppm, 1000 ppm, and 1500 ppm, respectively, with respect to the total weight of the transition metal precursors, thereby preparing a mixture. Then, the mixture was primary sintered at 850°C for 12 hours to obtain a primary sintered product.

[0217] Then, the primary sintered product was finely pulverized at room temperature using a jet mill pulverizer at a pulverization pressure of 2.1 bar and a classifying speed of 1600 rpm (first pulverization step).

[0218] Next, the pulverized primary sintered product and LiOH were mixed so that the ratio of the number of moles of Ni+Co+Mn : Li was 1 : 0.05, and the mixture was secondary sintered at 800°C for 12 hours to obtain a secondary sintered product.

[0219] Then, the secondary sintered product was finely pulverized at room temperature using a jet mill pulverizer at a pulverization pressure of 0.9 bar and a classifying speed of 1600 rpm to obtain a single particle type lithium nickel-based oxide LiNi 0.8784 Co 0.0347 Mn 0.0794 Al 0.005 Zr 0.0015 Y 0.001 O2 (second pulverization step).

[0220] Next, the single particle type lithium nickel-based oxide obtained above was uniformly mixed with Co(OH)2, and then heat-treated at 700°C for 5 hours in an oxygen atmosphere to form a Co coating layer on the surface of the single particle type lithium nickel-based oxide. Then, the Co-coated single particle type lithium nickel-based oxide and Al(OH)3 were uniformly mixed, and then heat-treated at 500°C for 5 hours in an oxygen atmosphere to form a Co and Al-coated single particle type lithium nickel-based oxide. In this case, the amount of mixed Co(OH)2 was such that the ratio (B / A) of the number of moles (B) of Co in Co(OH)2 to the total number of moles (A) of the remaining metals other than lithium in the lithium nickel-based oxide was 0.02, and the amount of mixed Al(OH)3 was 0.05 parts by weight with respect to 100 parts by weight of the lithium nickel-based oxide.

[0221] Example 4

[0222] D 50 Ni 0.905 Co 0.085 Mn 0.01 (OH)2 and LiOH were mixed so that the ratio of the number of moles of Ni+Co+Mn : Li was 1 : 1, and Al(OH)3, Y2O3, and ZrO2 were added thereto in amounts of 1470 ppm, 1000 ppm, and 1500 ppm, respectively, with respect to the total weight of the transition metal precursor, thereby preparing a mixture. Then, the mixture was primary sintered at 820°C for 12 hours to obtain a primary sintered product.

[0223] Then, the primary sintered product was finely pulverized at room temperature using a jet mill pulverizer at a pulverization pressure of 1.5 bar and a classifying speed of 1250 rpm (first pulverization step).

[0224] Next, the pulverized primary sintered product and LiOH were mixed so that the ratio of the number of moles of Ni+Co+Mn : Li was 1 : 0.03, and the mixture was sintered at 770°C for 12 hours to obtain a secondary sintered product.

[0225] Then, the secondary sintered product was finely pulverized at room temperature using a jet mill pulverizer at a pulverization pressure of 0.6 bar and a classifying speed of 1250 rpm to obtain a single particle type lithium nickel-based oxide LiNi 0.8982 Co 0.0844 Mn 0.0099 Al 0.005 Zr 0.0015 Y 0.001 O2 (second pulverization step).

[0226] Next, the single particle type lithium nickel-based oxide obtained above was uniformly mixed with Co(OH)2and Al(OH)3, and then heat-treated at 700°C for 5 hours and at 500°C for 3 hours in an oxygen atmosphere to prepare a positive electrode material on which a coating layer was formed. In this case, the amount of mixed Co(OH)2was such that the ratio (B / A) of the number of moles (B) of Co in Co(OH)2to the total number of moles (A) of the remaining metals other than lithium in the lithium nickel-based oxide was 0.02, and the amount of mixed Al(OH)3was 0.05 parts by weight with respect to 100 parts by weight of the lithium nickel-based oxide.

[0227] Comparative Example 1 - Preparation of OS instead of TS

[0228] D 50 Ni 0.885 Co 0.035 Mn 0.08 (OH)2and LiOH were mixed so that the ratio of the number of moles of Ni+Co+Mn : Li was 1 : 1.05, and Al(OH)3, Y2O3, and ZrO2were added thereto in amounts of 1470 ppm, 1000 ppm, and 1500 ppm, respectively, with respect to the total weight of the transition metal precursor, thereby preparing a mixture.

[0229] Then, the mixture was sintered at 880°C for 3 hours and then again at 800°C for 9 hours, and then finely pulverized at room temperature using a jet mill pulverizer at a pulverization pressure of 2.1 bar and a classifying speed of 1600 rpm to have a D 50thereby obtaining single-particle type lithium nickel oxide LiNi 0.8784 Co 0.0347 Mn 0.0794 Al 0.005 Zr 0.0015 Y 0.001 O2.

[0230] Next, the single-particle type lithium nickel-based oxide obtained above was uniformly mixed with Co(OH)2and Al(OH)3, and then heat-treated at 700°C for 5 hours in an oxygen atmosphere, and then heat-treated at 500°C for 3 hours, to prepare a positive electrode material on which a coating layer was formed. In this case, the amount of mixed Co(OH)2was such that the ratio (B / A) of the number of moles of Co in Co(OH)2(B) to the total number of moles of the remaining metals other than lithium in the lithium nickel-based oxide (A) was 0.02, and the amount of mixed Al(OH)3was 0.05 parts by weight with respect to 100 parts by weight of the lithium nickel-based oxide.

[0231] Comparative Example 2 - Second pulverization at a higher pulverization pressure than the first pulverization

[0232] A positive electrode material was prepared in the same manner as in Example 1, except that the first pulverization step was performed at a pulverization pressure of 1.6 bar, and the second pulverization step was performed at a pulverization pressure of 2.1 bar.

[0233] Comparative Example 3 - Only second pulverization was performed without first pulverization

[0234] A positive electrode material was prepared in the same manner as in Example 1, except that the primary sintered product was not pulverized, secondary sintering was performed, and the secondary sintered product was pulverized at a pulverization pressure of 2.1 bar.

[0235] [Table 1]

[0236]

[0237] Experimental Example 1. Measurement of sphericity and convexity

[0238] Scanning electron microscope images of the positive electrode materials prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were obtained by a scanning electron microscope, and each image was subjected to image processing by the above-described particle shape analysis method to obtain a divided image for each primary particle unit division. The SEM images and the divided images of each of the positive electrode materials prepared in Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Figures 3 to 9 In Figures 3 to 9 (A) is an SEM image, and (B) is a divided image obtained by image processing of the SEM image.

[0239] The arithmetic mean of the roundness of the primary particles, the arithmetic mean of the convexity of the primary particles, the average particle size of the primary particles, and the average aspect ratio of the primary particles were measured from the segmented images.

[0240] In addition, 0.01 g of the positive electrode material powder prepared in Examples 1 to 4 and Comparative Examples 1 to 3 was collected, placed in a vial containing 30 mL of ultrapure water and 500 μL of a dispersant, dispersed for 1 minute using an ultrasonic device, and then placed in a particle size analyzer (PSA) (S3500, manufactured by Microtrac, Inc.) to measure the D50 of each positive electrode material powder. 50 .

[0241] The measurement results are listed in Table 2 below.

[0242] [Table 2]

[0243]

[0244] Experimental Example 2

[0245] The positive electrode materials prepared in Examples 1 to 4 and Comparative Examples 1 to 3, a conductive agent (FX35), and a binder (a mixture of KF9700 and BM730H at a weight ratio of 2.8:0.2) were mixed in an N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was applied to one surface of an aluminum current collector, dried at 130°C, and then roll-pressed to prepare a positive electrode.

[0246] An electrode assembly was prepared by interposing a porous polyethylene separator between each of the prepared positive electrodes and a Li metal disc, then placed in a battery case, and an electrolyte solution was injected to prepare a half-cell. The electrolyte solution was prepared by dissolving LiPF6 at a concentration of 1 M in a mixed organic solvent in which ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed at a volume ratio of 3:3:4.

[0247] (1) Initial capacity

[0248] Each of the lithium secondary batteries prepared above was charged at 25°C in a CC / CV mode until 4.25 V under 0.1 C and 0.5 C cutoff conditions, and then discharged to 2.5 V in a CC mode to measure the initial discharge capacity.

[0249] (2) Life characteristics

[0250] For each of the above-prepared lithium secondary batteries, 50 repeated charge and discharge cycles were performed at 45℃ in a voltage range of 2.5 V to 4.25 V, and the capacity retention rate and the resistance increase rate at the 50th cycle were measured. At this time, charging was performed to 4.25 V in the CC / CV mode, and when 0.05 C was reached, cutoff was performed, and discharging was performed to 2.5 V in the CC mode.

[0251] The capacity retention rate was measured as the percentage of the discharge capacity after 50 cycles to the discharge capacity after 1 cycle ((discharge capacity after 50 cycles / discharge capacity after 1 cycle) x 100), and the resistance increase rate was measured as the percentage of the resistance increased after 50 cycles to the resistance after 1 cycle ({(resistance after 50 cycles - resistance after 1 cycle) / resistance after 1 cycle)} x 100).

[0252] The measurement results are shown in Table 3 below.

[0253] [Table 3]

[0254]

[0255] Referring to Table 3 above, it can be confirmed that the battery applying the cathode material of Examples 1 to 4, in which the ratio of the arithmetic mean of the convexity of primary particles to the average aspect ratio of primary particles is at least 0.63, has an excellent capacity retention rate and has a low resistance increase after 50 cycles, compared to the batteries applying the cathode materials of Comparative Examples 1 to 3.

Claims

1. A positive electrode material comprising a plurality of single-particle-type positive electrode active material particles, wherein the single-particle-type positive electrode active material particles comprising 1 to 30 primary particles, a ratio of an arithmetic mean value of a convexity of the primary particles to an average aspect ratio of the primary particles is at least 0.63, the convexity and the average aspect ratio of the primary particles being measured from a segmented image divided for each primary particle unit obtained by image processing of a scanning electron microscope (SEM) image of the positive electrode material, the convexity is defined by the following Equation 1, and the single-particle-type positive electrode active material includes a lithium nickel-based oxide having a composition represented by the following Formula 1, [Equation 1] Convexity = P c / P r wherein, in the above equation 1, P r is an actual perimeter of each primary particle measured from the segmented image, and P c is a perimeter of a virtual figure obtained by connecting the outermost points of each primary particle measured from the segmented image, [Formula 1] Li a [Ni x Co y M 1 z M 2 1-x-y-z ]O2 wherein, in the above Formula 1, M 1 comprising Mn, Al, or a combination thereof, M 2 comprising at least one selected from the group consisting of B, Ba, Ce, Cr, F, Mg, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, and Sr, 1.0≤a≤1.3, 0.5≤x<1.0, 0<y<0.5, and 0<z<0.

5.

2. The positive electrode material of claim 1, wherein, the arithmetic mean value of the convexity of the primary particles is at least 0.

92.

3. The cathode material of claim 1, wherein, the average aspect ratio of the primary particles is 1.2 to 4.

0.

4. The cathode material of claim 1, wherein, the ratio of the arithmetic mean value of the convexity of the primary particles to the average aspect ratio of the primary particles is 0.63 to 0.

95.

5. The cathode material of claim 1, wherein, the single-particle-type positive electrode active material includes: a lithium nickel-based oxide composed of 1 to 30 primary particles; and a coating layer formed on the lithium nickel-based oxide.

6. The cathode material of claim 5, wherein, the coating layer includes at least one coating element selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S.

7. The cathode material of claim 1, wherein, D50 of the positive electrode material is 2 μm to 15 μm. 50 2 μm to 15 μm.

8. The cathode material of claim 1, wherein, the average particle diameter of the primary particles is 1 μm to 6 μm.

9. The cathode material of claim 1, wherein, an arithmetic mean value of a roundness of the primary particles is at least 0.65, the roundness being measured from a segmented image divided for each primary particle unit obtained by image processing of a scanning electron microscope (SEM) image of the positive electrode material, and the roundness being defined by the following Equation 2: [Equation 2] Circularity = 4πA / P 2 where, in the above Equation 2, A is an area of each primary particle measured from the segmented image, and P is a perimeter of each primary particle measured from the segmented image.

10. The cathode material of claim 1, wherein, an arithmetic mean value of a solidity of the primary particles is at least 0.85, the solidity being measured from a segmented image divided for each primary particle unit obtained by image processing of a scanning electron microscope (SEM) image of the positive electrode material, and the solidity being defined by the following Equation 3: [Equation 3] Firmness = A r / A c wherein, in equation 3 above, A r is the actual area of each primary particle measured from the segmented image, and A c is the area of a virtual figure obtained by connecting the outermost points of each primary particle measured from the segmented image.

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

12. A lithium secondary battery including the positive electrode of claim 11.

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