Cathode material, cathode containing the same, and lithium secondary battery

Abstract

The present invention relates to a cathode material comprising a plurality of single-particle cathode active material particles, wherein the single-particle cathode active material particles comprise 1 to 30 primary particles, and the arithmetic mean of the curvature of the primary particles, measured from a segmentation image obtained by image processing of scanning electron microscope (SEM) images of the cathode material and partitioned by primary particle unit, is 0.92 or greater, and the curvature is a value defined by the following formula (1). Formula (1): Curvature = P c / P r In equation (1) above, P r P is the actual circumference of each primary particle measured from the segmentation image, c This is the perimeter of a virtual figure obtained by connecting the outermost points of each primary particle measured from the segmentation image.

Description

[Technical Field]

[0001] This application claims priority rights based on Korean Patent Applications No. 10-2023-0064596 and No. 10-2023-0064597 dated 18 May 2023, Korean Patent Applications No. 10-2023-0085631 and No. 10-2023-0085632 dated 3 July 2023, and Korean Patent Application No. 10-2024-0063764 dated 16 May 2024, and all content disclosed in the documents of said Korean Patent Applications is incorporated herein by reference.

[0002] The present invention relates to a cathode material, a cathode containing the same, and a lithium secondary battery, and more particularly to a cathode material comprising a single-particle cathode active material in which the surface morphology of primary particles is controlled to satisfy specific conditions, a cathode containing the same, and a lithium secondary battery. [Background technology]

[0003] Generally, a lithium secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and negative electrode contain an active material that allows for the insertion and deintercalation of lithium ions.

[0004] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or 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 advantage of a high operating voltage and excellent capacity characteristics, but the high price of cobalt, the raw material, and its unstable supply make it difficult to commercially apply to high-capacity batteries. Lithium nickel oxide has poor structural stability, making it difficult to achieve sufficient lifespan characteristics. On the other hand, lithium manganese oxide has excellent stability but poor capacity characteristics. Therefore, lithium composite transition metal oxides containing two or more transition metals have been developed to complement the problems of lithium transition metal oxides containing Ni, Co, or Mn alone, and among these, lithium nickel cobalt manganese oxide containing Ni, Co, and Mn is widely used in the field of electric vehicle batteries.

[0005] Conventional lithium nickel cobalt manganese oxides typically exist in a spherical secondary particle form, consisting of tens to hundreds of primary particles aggregated together. However, in the case of lithium nickel cobalt manganese oxides with this secondary particle form, particle cracking occurs easily during the rolling process in cathode manufacturing, causing primary particles to fall off, and cracks to develop inside the particles during the charge-discharge process. When particle cracking or cracking occurs in the cathode active material, the contact area with the electrolyte increases, leading to increased gas generation due to side reactions with the electrolyte and increased degradation of the active material, resulting in a decrease in lifespan characteristics.

[0006] Furthermore, in recent years, there has been an increasing demand for high-power, high-capacity batteries, such as those used in electric vehicles, which has led to a trend of gradually increasing nickel content in the positive electrode active material. While an increase in nickel content in the positive electrode active material improves initial capacity characteristics, repeated charging and discharging can cause structural breakdown of the positive electrode active material. This increases the degradation rate of the positive electrode active material, reduces its lifespan, and compromises the safety of the battery. [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to solve the above-mentioned problems and to provide a single-particle cathode material having superior lifetime characteristics, capacitance characteristics, and resistance characteristics compared to conventional materials, by controlling the shape of the primary particles of the cathode material powder to satisfy specific conditions. Furthermore, the present invention aims to provide a positive electrode containing the single-particle positive electrode material described above, and a lithium secondary battery containing the positive electrode. [Means for solving the problem]

[0008] According to one embodiment, the present invention provides a cathode material comprising a plurality of single-particle cathode active material particles, wherein the single-particle cathode active material particles comprise 1 to 30 primary particles, and the arithmetic mean of the convexity of the primary particles, measured from a segmentation image partitioned by primary particle units obtained by image processing of a scanning electron microscope (SEM) image of the cathode material, is 0.92 or more and 0.95 or less. In this case, the convexity is a value defined by the following formula (1). Formula (1): Curvature = P c / P r

[0009] In equation (1) above, P r P is the actual circumference of each primary particle measured from the segmentation image, c This is the perimeter of a virtual figure obtained by connecting the outermost points of each primary particle measured from the segmentation image.

[0010] The positive electrode material may have an arithmetic mean of the circularity (C) of primary particles measured from a segmentation image partitioned by primary particle unit obtained by image processing of scanning electron microscope (SEM) images of the positive electrode material, which is 0.65 or more and 0.98 or less, preferably 0.65 or more and 0.90 or less, and more preferably 0.65 or more and 0.85 or less. In this case, the circularity is a value defined by the following formula (2). Formula (2): Circularity (C) = 4πA / P 2

[0011] In the above formula (2), A is the area of each primary particle measured from the segmentation image, and P is the perimeter of each primary particle measured from the segmentation image.

[0012] The single-particle system cathode active material contains a lithium nickel-based oxide containing nickel and cobalt, and the nickel content in all metals excluding lithium in the lithium nickel-based oxide may be 50 mol% or more, 55 mol% or more, 60 mol% or more, 80 mol% or more, 85 mol% or more, or 88 mol% or more, and preferably less than 100 mol%, 99 mol% or less, or 95 mol% or less.

[0013] Specifically, the lithium nickel-based oxide may have a composition represented by the following [Chemical Formula 1].

[0014] [Chemical Formula 1] Li a [Ni x Co y M 1 z M 2 1-x-y-z O2

[0015] In the above Chemical Formula 1, M 1 includes Mn, Al, or a combination thereof, and M 2 includes one or more 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, and 0.9 ≦ a ≦ 1.3, 0.5 ≦ x < 1.0, 0 < y < 0.5, 0 < z < 0.5.

[0016] On the other hand, the single-particle positive electrode active material may include a lithium nickel-based oxide consisting of 1 to 30 primary particles and a coating layer formed on the lithium nickel-based oxide, and the coating layer may contain one or more coating elements 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.

[0017] The positive electrode material is D 50 The particle size may be 2 μm to 15 μm, preferably 3 μm to 10 μm, and more preferably 3 μm to 8 μm. Furthermore, the average particle size of the primary particles may be 1 μm to 6 μm, preferably 1 μm to 5 μm, more preferably 1 μm to 4 μm, and the average aspect ratio of the primary particles may be 1.2 to 4.0, preferably 1.2 to 3.0, more preferably 1.2 to 2.0.

[0018] According to another embodiment, the present invention provides a method for manufacturing a cathode material, comprising the steps of: mixing a transition metal precursor and a first lithium raw material, then performing a primary calcination to form a primary calcined product containing a single-particle cathode active material containing 1 to 30 primary particles; a first grinding step of grinding the primary calcined product; mixing the ground primary calcined product with a second lithium raw material, then performing a secondary calcination to form a secondary calcined product; and a second grinding step of grinding the secondary calcined product, wherein the grinding pressure in the second grinding step is smaller than the grinding pressure in the first grinding step.

[0019] Preferably, the grinding pressure in the first grinding step is 1.5 bar to 2.5 bar, and the grinding pressure in the second grinding step may be 0.4 bar to 1.4 bar.

[0020] On the other hand, the transition metal precursor may be a transition metal hydroxide represented by the following [Chemical Formula 2].

[0021] [Chemical formula 2] [Ni x1 Co y1 M 1z1 M 2 1-x1-y1-z1 ](OH)2

[0022] In the above chemical formula 2, M 1 This includes Mn, Al, or a combination thereof. 2 It includes one or more elements 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, and 0.5 ≤ x1 < 1.0, 0 <y1<0.5、0<z1<0.5である。

[0023] On the other hand, the first lithium raw material may be mixed such that the ratio of the number of moles of lithium to the total number of moles of transition metal contained in the transition metal precursor is 0.9 to 1.1, and the second lithium raw material may be mixed such that the ratio of the number of moles of lithium to the total number of moles of transition metal contained in the transition metal precursor is 0.005 to 0.1.

[0024] The primary firing may be carried out at a temperature of 800°C to 950°C, and the secondary firing may be carried out at a temperature 50°C to 100°C lower than the primary firing temperature. Preferably, the secondary firing temperature is 700°C to 850°C.

[0025] On the other hand, the method for producing a positive electrode material according to the present invention may further include, if necessary, a step after the second grinding step, in which the ground second calcined product and the coating raw material are mixed and then heat-treated to form a coating layer.

[0026] The cathode material manufactured by the method described above contains multiple single-particle cathode active material particles, and the arithmetic mean of the convexity of the primary particles, measured from segmentation images partitioned by primary particle units obtained by image processing of scanning electron microscope (SEM) images of the cathode material, is 0.92 or more and 0.95 or less. In this case, the convexity is the value defined by formula (1) above.

[0027] Furthermore, the positive electrode material may have an arithmetic mean of the circularity (C) of primary particles measured from a segmentation image partitioned by primary particle unit obtained by processing a scanning electron microscope (SEM) image of the positive electrode material, which is 0.65 or more and 0.98 or less, preferably 0.65 or more and 0.90 or less, and more preferably 0.65 or more and 0.85 or less. In this case, the circularity is the value defined by formula (2) above.

[0028] In another embodiment, the present invention provides a positive electrode containing the positive electrode material according to the present invention described above, and a lithium secondary battery containing the positive electrode. [Effects of the Invention]

[0029] The cathode material according to the present invention contains a single-particle cathode active material, and the arithmetic mean of the curvature of the primary particles in the cathode material is controlled to be between 0.92 and 0.95. As a result, cracking during the rolling process is reduced, the contact area with the electrolyte is small, and side reactions with the electrolyte are reduced. Therefore, when the cathode material according to the present invention is applied, the life characteristics of lithium secondary batteries can be improved.

[0030] Furthermore, the positive electrode material of the present invention exhibits excellent lithium mobility and rolling characteristics by controlling the arithmetic mean of the circularity of the primary particles in the positive electrode material to be between 0.65 and 0.98. Therefore, when the positive electrode material of the present invention is applied, a lithium secondary battery with excellent capacity characteristics and life characteristics can be realized. [Brief explanation of the drawing]

[0031] [Figure 1] This is a diagram illustrating the degree of curvature according to the present invention. [Figure 2] These are scanning electron microscope (SEM) images (A) of the cathode material manufactured according to Example 1 and segmentation images (B) obtained by image processing of the SEM images. [Figure 3] These are scanning electron microscope (SEM) images (A) of the cathode material manufactured according to Example 2 and segmentation images (B) obtained by image processing of the SEM images. [Figure 4] These are scanning electron microscope (SEM) images (A) of the cathode material manufactured according to Example 3 and segmentation images (B) obtained by image processing of the SEM images. [Figure 5] These are scanning electron microscope (SEM) images (A) of the cathode material manufactured according to Example 4 and segmentation images (B) obtained by image processing of the SEM images. [Figure 6] These are scanning electron microscope (SEM) images (A) of the cathode material manufactured according to Example 5 and segmentation images (B) obtained by image processing of the SEM images. [Figure 7] These are scanning electron microscope (SEM) images (A) of the cathode material manufactured according to Comparative Example 1 and segmentation images (B) obtained by image processing of the SEM images. [Figure 8] These are scanning electron microscope (SEM) images (A) of the cathode material manufactured according to Comparative Example 2 and segmentation images (B) obtained by image processing of the SEM images. [Figure 9] These are scanning electron microscope (SEM) images (A) of the cathode material manufactured according to Comparative Example 3 and segmentation images (B) obtained by image processing of the SEM images. [Figure 10] These are scanning electron microscope (SEM) images (A) of the cathode material manufactured according to Comparative Example 4 and a segmentation image (B) obtained by image processing of the SEM image. [Modes for carrying out the invention]

[0032] The terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0033] In this invention, "primary particle" refers to a particle unit in which no grain boundaries are visible when observed with a scanning electron microscope at a field of view of 5,000x to 20,000x.

[0034] In this invention, "secondary particles" are particles formed by the aggregation of multiple primary particles. In this invention, in order to distinguish them from conventional secondary particles formed by the aggregation of tens to hundreds of primary particles, secondary particles formed by the aggregation of 30 or fewer primary particles are referred to as single-particle positive electrode active materials.

[0035] In the present invention, "single-particle positive electrode active material" means a positive electrode active material in which the average particle size of the primary particles is 1 μm or more, preferably 1 μm to 5 μm, and which is composed of 1 to 30 primary particles.

[0036] In the present invention, "D 50 " refers to the particle size at the point where 50% of the volume cumulative distribution by particle size is reached. 50 This method involves dispersing the powder to be measured (e.g., cathode material powder) in a dispersion medium, then introducing it into a commercially available laser diffraction particle size analyzer (e.g., Microtrac's S3500), transmitting a laser beam through it, measuring the difference in diffraction patterns due to particle size to calculate the particle size distribution, and then calculating the particle diameter at the point where the cumulative volume distribution by particle size reaches 50%.

[0037] In the present invention, "flexibility" is an index indicating the surface roughness of the particle being measured, and is a value defined by the following formula (1). Formula (1): Curvature = P c / P r

[0038] In equation (1) above, P r This is the actual circumference of the particle being measured, and P c This is the perimeter of a virtual figure obtained by connecting the outermost points of the particles being measured.

[0039] In the present invention, "circularity (C)" is an index indicating the degree to which the cross-sectional shape of a particle is close to a circle, and is a value defined by the following formula (2). Equation (2): Circularity (C) = 4πA / P 2

[0040] In equation (2) above, A is the area of ​​each primary particle measured from the segmentation image, and P is the circumference of each primary particle measured from the segmentation image.

[0041] In this invention, "aspect ratio" means the ratio of the major axis to the minor axis of the particle being measured. In the present invention, the curvature, circularity, average particle size, and average aspect ratio of primary particles can be measured from a segmentation image partitioned by primary particle units, obtained by image processing of scanning electron microscope (SEM) images of the cathode material using an artificial intelligence model. Specifically, the segmentation image can be obtained by acquiring a scanning electron microscope (SEM) image of the cathode material powder to be measured, inputting the acquired scanning electron microscope image into a U-NET structure to generate a binary image, converting the binary image into a distance-transformed image based on a distance-transformed algorithm, filtering the binary image using a threshold set based on the distance-transformed image, identifying multiple objects included in the filtered binary image, and then segmenting the SEM image into primary particle units based on the multiple objects. The present invention will be described in more detail below.

[0042] Cathode material The cathode material according to the present invention comprises a plurality of single-particle cathode active material particles, and each single-particle cathode active material particle comprises 1 to 30 primary particles.

[0043] Single-particle cathode active materials have higher particle strength compared to conventional cathode active materials with a secondary particle structure where tens to hundreds of primary particles are aggregated, resulting in less particle cracking during rolling. Furthermore, because single-particle cathode active materials have fewer primary particles, the volume of the primary particles expands and contracts less during charging and discharging, which significantly reduces the occurrence of cracks inside the particles.

[0044] Therefore, when using the cathode material according to the present invention, which includes a single-particle cathode active material, the deterioration of electrochemical performance due to particle cracking and crack formation can be minimized.

[0045] On the other hand, the single-particle cathode active material includes a lithium nickel oxide containing nickel and cobalt. In this case, the lower limit of the nickel content among all metals excluding lithium in the lithium nickel oxide may be 50 mol% or more, 55 mol% or more, 60 mol% or more, 80 mol% or more, 85 mol% or more, or 88 mol% or more, and the upper limit of the nickel content among all metals excluding lithium may be less than 100 mol%, 99 mol% or less, or 95 mol% or less. When the nickel content in the lithium nickel oxide satisfies the above range, a high energy density can be achieved.

[0046] Specifically, the lithium nickel oxide may have a composition represented by the following [Chemical Formula 1].

[0047] [Chemical formula 1] Li a [Ni x Co y M 1 z M 2 1-x-y-z ]O2

[0048] In the above chemical formula 1, M 1 This includes Mn, Al, or a combination thereof. 2 This may include one or more 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 M 1 M may be Mn or a combination of Mn and Al, and the M 2 This may include Al, Zr, Y, Mg, Ti, Ba, Sr, Mo, or combinations thereof, and more preferably Zr, Y, or combinations thereof.2 While not essential, elements, when present in appropriate amounts, can promote grain growth during lithium nickel oxide calcination or improve the stability of the crystal structure.

[0049] The above 'a' represents the molar ratio of lithium in the lithium nickel oxide, and may be 0.9 ≤ a ≤ 1.3, 0.9 ≤ a ≤ 1.2, or 0.9 ≤ a ≤ 1.07. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium nickel oxide can be stably formed.

[0050] The aforementioned x represents the molar ratio of nickel among all metals excluding lithium in the lithium nickel oxide, and may be 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. A higher molar ratio of nickel is advantageous for achieving higher capacity.

[0051] The aforementioned y represents the molar ratio of cobalt among all metals excluding lithium in lithium nickel oxide, and 0 <y<0.5、0<y<0.45、0<y<0.4、0<y<0.2、0<y<0.15、または0<y<0.12であってよい。

[0052] The aforementioned z is M, which is the total metal in lithium nickel oxide excluding lithium. 1 This indicates the molar ratio of 0 <z<0.5、0<z<0.45、0<z<0.4、0<z<0.2、0<z<0.15、または0<z<0.12であってよい。

[0053] More specifically, the lithium nickel oxide may have the composition shown in [Chemical Formula 1-1] below.

[0054] [Chemical Formula 1-1] Li a [Ni x Co y Mn z-w Al w M 2 1-x-y-z O2 In the above Chemical Formula 1-1, M 2 , a, x, y, and z are the same as in Chemical Formula 1.

[0055] On the other hand, w represents the molar ratio of Al among the metals excluding lithium in the lithium nickel-based oxide, and 0 < w < 0.2, 0 < w ≤ 0.1, 0 < w ≤ 0.05, 0 < w ≤ 0.03, or 0 < w ≤ 0.02 may be satisfied. When the lithium nickel-based oxide has the composition of the above [Chemical Formula 1-1], the structural stability and capacity characteristics of the positive electrode active material are favorably exhibited.

[0056] On the other hand, the single-particle type positive electrode active material may further include a coating layer formed on the lithium nickel-based oxide as needed. At this time, the coating layer may include one or more coating elements 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 may include one or more coating elements selected from the group consisting of Co, Al, B, W, Ti, and Zr.

[0057] When a coating layer exists on the surface of the lithium nickel-based oxide, the contact between the electrolyte and the lithium nickel-based oxide is suppressed by the coating layer, and thereby, the effect of reducing the elution of transition metals and gas generation due to side reactions with the electrolyte can be obtained.

[0058] In particular, when the coating element includes Co, Al, or a combination thereof, the effect of suppressing side reactions with the electrolytic solution, improving the output, and reducing the resistance can be obtained.

[0059] On the other hand, the cathode material according to the present invention has an arithmetic mean of the convexity of primary particles measured from a segmentation image partitioned by primary particle unit obtained by image processing of scanning electron microscope (SEM) images, which is 0.92 or more and 0.95 or less. According to the inventors' research, it has become clear that when a cathode material is used in which the arithmetic mean of the convexity of primary particles satisfies the above range, the lifetime characteristics are significantly improved.

[0060] In this case, the curvature of the primary particle is a value defined by the following formula (1). Formula (1): Curvature = P c / P r

[0061] In equation (1) above, P r P is the actual circumference of each primary particle measured from the segmentation image, c This is the perimeter of a virtual figure obtained by connecting the outermost points of each primary particle measured from the segmentation image. Figure 1 is a diagram for explaining the meaning of curvature according to the present invention. As shown in Figure 1, P r This shows the actual circumference of the primary particle, P c This indicates the perimeter of the virtual figure obtained by connecting the outermost points of the primary particles. When the surface of the particles is smooth and without irregularities, P r and P c Because the values ​​are similar, the curvature approaches 1. In contrast, if the surface of the particles has many irregularities and is rough, P r As the value of increases, the degree of curvature decreases. In other words, the smaller the arithmetic mean of the degree of curvature of the primary particles constituting the single-particle cathode active material, the more irregularities there are on the surface of the primary particles. On the other hand, if the surface roughness of the particles increases, the contact area with the electrolyte increases, causing the irregular parts to crack during electrode rolling, increasing particle cracking, and thus reducing the lifetime characteristics. Therefore, in order to improve the lifetime characteristics of the cathode material, it is necessary to control the surface shape of the primary particles.

[0062] If the arithmetic mean of the curvature of the primary particles is greater than the range, an additional step to reduce surface roughness may be required to produce a single-particle cathode active material that satisfies this condition. In this case, the electrochemical performance of the cathode active material may be reduced as a result of the additional step. The additional step may be, for example, adding an excess of the second lithium raw material in the step of producing the secondary calcined product.

[0063] Furthermore, the positive electrode material according to the present invention may have an arithmetic mean of the circularity (C) of primary particles measured from a segmentation image partitioned by primary particle unit obtained by image processing of scanning electron microscope (SEM) images, which is 0.65 or more and 0.98 or less, preferably 0.65 or more and 0.90 or less, and more preferably 0.65 or more and 0.85 or less.

[0064] In this case, the circularity of the primary particle is a value defined by the following equation (2). Equation (2): Circularity (C) = 4πA / P 2

[0065] In equation (2) above, A is the area of ​​each primary particle measured from the segmentation image, and P is the circumference of each primary particle measured from the segmentation image.

[0066] When the arithmetic mean of the circularity of the primary particles constituting the single-particle positive electrode active material satisfies the aforementioned range, lithium ions can diffuse more smoothly into the interior of the particles, increasing the contact area between the single-particle positive electrode active material and the electrolyte, thereby improving electrochemical performance. Furthermore, the distance between particles within the electrode is maintained at a relatively constant level, current flow becomes smoother within the electrode, and particle arrangement becomes more uniform, resulting in increased mechanical stability and improved battery cycle life. Specifically, if the arithmetic mean of the circularity of the primary particles is less than 0.65, friction between single particles increases, and the distribution of the single-particle positive electrode active material within the electrode becomes non-uniform, potentially reducing the battery's capacity and / or life characteristics. To manufacture a single-particle positive electrode active material with an arithmetic mean of the circularity of primary particles exceeding 0.98, additional processes for excessive grinding or circularization are required, which can lead to particle damage or cracking, potentially reducing electrochemical performance.

[0067] The electrochemical performance of lithium secondary batteries, such as capacity characteristics and lifespan characteristics, is greatly influenced not only by the composition of the positive electrode active material used, but also by the primary shape of the positive electrode active material particles. This is because even positive electrode active materials with the same composition will have different physical properties, such as lithium mobility and rollability, depending on the shape of the primary particles of the positive electrode active material. Therefore, in order to manufacture lithium secondary batteries with desired performance, it is necessary to control the shape of the primary particles of the positive electrode active material.

[0068] Particle shape analysis of positive electrode active materials is performed using images of the positive electrode active material powder obtained by scanning electron microscope (SEM). However, in the case of SEM images of positive electrode material powder, it is difficult to visually distinguish aggregated primary particles due to image resolution, particle aggregation, and surface roughness. Therefore, conventionally, a method has been used in which a person selects individual active material particles and / or primary particles from the SEM image and manually measures the circumference, aspect ratio, particle size, etc. of the selected particles. However, in this case, quantitative analysis of a large number of positive electrode active material particles is difficult, and the measured values ​​may differ depending on the person performing the measurement, resulting in a decrease in analytical accuracy. Consequently, it has been difficult to accurately analyze the surface shape of primary particles of positive electrode active materials, and as a result, it has been difficult to derive a correlation between the surface shape of primary particles and battery performance.

[0069] Therefore, the inventors developed a method for quantitatively analyzing the surface shape of primary particles in cathode material powder using image analysis with an artificial intelligence model. They found that when the arithmetic mean of the curvature of the primary particles measured by this analysis method is 0.92 or more and 0.95 or less, the lifetime characteristics of the single-particle cathode material are significantly improved. They also found that when the arithmetic mean of the circularity of the primary particles measured by this analysis method is 0.65 or more and 0.98 or less, the electrochemical performance of the single-particle cathode material is significantly improved, thus completing the present invention.

[0070] The method for analyzing the shape of cathode material particles according to the present invention is as follows. First, a scanning electron microscope (SEM) image of the cathode material powder to be measured is acquired. Then, the acquired SEM image is input into an artificial intelligence (AI) model to generate a binary image. In this case, the AI ​​model may be a model trained to convert images of active materials into binary images. In this case, the training data uses the SEM image of the cathode material powder as the raw image and the binary image obtained by converting the SEM image into binary as the label image. The binary image is obtained by binaryizing the SEM image using computer vision techniques, or by drawing on the SEM image by hand. In addition, in order to train the model on various cases, additional images are generated by applying image enhancement algorithms (e.g., rotation, tilt, shear, brightness adjustment, contrast adjustment, enlargement, reduction, or combinations thereof) to the raw image and label image, and these are used as training data.

[0071] On the other hand, the sizes of the Raw image and the Label image may be the same. The size of an image can be defined as the number of horizontal pixels × the number of vertical pixels, and for example, the size of the Raw image and the Label image may be 256 × 256.

[0072] On the other hand, the artificial intelligence model used a U-NET structure in which skip connections are added during the encoding and decoding processes to reflect the input image. The artificial intelligence model has a structure in which multiple layers are sequentially connected, and the input of a sequentially connected layer may be the output of the immediately preceding connected layer, and the output of a sequentially connected layer may be the input of the immediately following connected layer. The layers included in the encoding region have a structure in which a 2D convolutional layer, a batch normalization layer, an activation layer, and a maximum pooling layer are sequentially connected, and the layers included in the decoding region have a structure in which a 2D convolutional layer, a batch normalization layer, an activation layer, and an upsampling layer are sequentially connected.

[0073] The artificial intelligence model was trained using a deep learning backpropagation algorithm, with a binary cross-entropy loss function used as the loss function. Where necessary, the binary cross-entropy loss function was a function in which weights between 1 and 1000 were applied to one of two colors (or classes), for example, white out of black and white.

[0074] Next, the binary images generated from the artificial intelligence model were converted into distance-transformed images based on a distance-transformation algorithm. In this case, the distance-transformation algorithm may be a maximum-minimum normalization, Z-score normalization, L1 normalization, or L2 normalization algorithm.

[0075] Next, the binary image is filtered using a threshold set based on the distance-transformed image to obtain a filtered binary image. In this case, the threshold may be a value obtained by multiplying the normalized maximum distance of the distance-transformed image by a specified ratio (for example, 0 to 0.1). The filtering may be performed by selecting pixels in the distance-transformed image that have a distance value less than or equal to the specified threshold, and setting the color value of the pixels in the binary image that correspond to the pixels selected from the distance-transformed image to the specified color value. A filtered image containing multiple objects is obtained by this method.

[0076] Next, after identifying multiple objects contained in the filtered image, the SEM image is segmented based on these multiple objects to obtain segmented images divided into primary particle units. In this case, the segmentation is performed using the Watershed algorithm.

[0077] The segmentation image obtained by the method described above divides the positive electrode active material particles in the positive electrode material into primary particle units. Therefore, when using this image, various shape information related to the primary particles of the positive electrode active material (for example, the degree of curvature of the primary particle, the circumference of the primary particle, the area of ​​the primary particle, the aspect ratio of the primary particle, the circularity of the primary particle, etc.) can be obtained quantitatively.

[0078] Furthermore, the aforementioned analysis method utilizes an artificial intelligence model that minimizes user input, thus minimizing the problem of differing measurement values ​​depending on the user, resulting in superior accuracy and reproducibility.

[0079] In the cathode material according to the present invention, the single-particle cathode active material is D 50 The diameter may be 2 μm to 15 μm, preferably 3 μm to 10 μm, more preferably 3 μm to 8 μm. D of the positive electrode active material 50 If the value is excessively small, it becomes difficult to form the active material layer during electrode manufacturing, reducing electrolyte impregnation and lowering electrochemical properties. 50 If this value is excessively large, it can lead to increased resistance and a decrease in output characteristics.

[0080] Furthermore, in the cathode material according to the present invention, the average particle size of the primary particles may be 1 μm to 6 μm, preferably 1 μm to 5 μm, and more preferably 1 μm to 4 μm. When the average particle size of the primary particles satisfies the above range, a single-particle cathode active material with excellent electrochemical properties can be formed. If the average particle size of the primary particles is excessively small, the number of aggregates of primary particles forming lithium nickel oxide particles increases, reducing the effect of suppressing particle cracking during rolling. If the average particle size of the primary particles is excessively large, the lithium diffusion path inside the primary particles becomes longer, increasing resistance and potentially degrading output characteristics.

[0081] Furthermore, in the positive electrode material according to the present invention, the average aspect ratio of the primary particles may be 1.2 to 4.0, preferably 1.2 to 3.0. In this case, the aspect ratio refers to the ratio of the length of the major axis to the length of the minor axis of the primary particles. If the average aspect ratio of the primary particles is excessively small, contact between particles may be poor and lithium mobility may decrease. If it is excessively large, the diffusion distance of lithium ions within the particles increases, electrochemical performance decreases, the distance between particles increases, and lithium ion diffusion within the electrode may be hindered.

[0082] Manufacturing method for positive electrode material Next, a method for producing a positive electrode material according to the present invention will be described. The method for producing a positive electrode material according to the present invention includes the steps of: (1) mixing a transition metal precursor with a first lithium raw material and then performing primary calcination to form a primary calcined product containing a single-particle lithium nickel oxide containing 1 to 30 primary particles; (2) a first grinding step of grinding the primary calcined product; (3) mixing the ground primary calcined product with a second lithium raw material and then performing secondary calcination to form a secondary calcined product; and (4) a second grinding step of grinding the secondary calcined product.

[0083] (1) Step of forming the primary fired product First, the transition metal precursor and the primary lithium raw material are mixed and then subjected to primary calcination to form the primary calcined product.

[0084] In this case, the transition metal precursor may be purchased from a commercially available nickel-cobalt-manganese hydroxide or other precursor, or it may be produced by a precursor manufacturing method well known in the art.

[0085] Preferably, the transition metal precursor may be a transition metal hydroxide represented by the following [Chemical Formula 2].

[0086] [Chemical formula 2] [Ni x1 Co y1 M 1 z1 M 21-x1-y1-z1 ](OH)2

[0087] In the above chemical formula 2, M 1 and M 2 This is the same as the definition in chemical formula 1. That is, M 1 This includes Mn, Al, or a combination thereof. 2 It includes one or more elements 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.

[0088] On the other hand, x1 represents the molar ratio of nickel among all metal elements in the transition metal precursor, where 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, The following conditions may be met: 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.

[0089] The aforementioned y1 represents the molar ratio of cobalt among all metals in the transition metal precursor, and 0 <y1<0.5、0<y1<0.45、0<y1<0.4、0<y1<0.2、0<y1<0.15、または0<y1<0.12であってよい。

[0090] The aforementioned z1 is M of all metals in the transition metal precursor. 1 This indicates the molar ratio of 0 <z1<0.5、0<z1<0.45、0<z1<0.4、0<z1<0.2、0<z1<0.15、または0<z1<0.12であってよい。

[0091] The transition metal precursor can be produced, for example, by adding an aqueous transition metal solution, an ammonium cation complex-forming agent, and a basic compound to a reactor and carrying out a coprecipitation reaction while stirring.

[0092] The transition metal aqueous solution may be produced by dissolving a transition metal-containing raw material in a solvent such as water. For example, it may be produced by dissolving a nickel-containing raw material or a cobalt-containing raw material in water. Furthermore, if necessary, the transition metal aqueous solution may be M 1 Raw materials and / or M 2 It may further contain metal-containing raw materials.

[0093] On the other hand, the transition metal-containing raw material may be an acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide of the transition metal. Specifically, the nickel-containing raw material may be, for example, NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, nickel halides, or combinations thereof.

[0094] The cobalt-containing raw material may be, for example, CoSO4, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4·7H2O, or a combination thereof.

[0095] Said M 1 The included raw materials may be manganese-containing raw materials and / or aluminum-containing raw materials. The manganese-containing raw materials may be, for example, Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halides, or combinations thereof, and the aluminum-containing raw materials may be, for example, Al2O3, Al(OH)3, Al(NO3)3, Al2(SO4)3, (HO)2AlCH3CO2, HOAl(CH3CO2)2, Al(CH3CO2)3 aluminum halides, or combinations thereof. However, in the case of Al, it may not be added to the transition metal aqueous solution but added together with the lithium raw material in the calcination step described later.

[0096] M 2 The raw materials contained are M 2This may be a metal acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide. The amount of each transition metal-containing raw material to be added may be determined considering the molar ratio of the transition metal in the cathode active material to be ultimately produced.

[0097] On the other hand, the ammonium cation complex-forming agent may contain at least one compound selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and NH4CO3, and may be introduced into the reactor in the form of a solution in which the compound is dissolved in a solvent. In this case, the solvent may be water, or a mixture of water and an organic solvent that can be homogeneously mixed with water (specifically, an alcohol, etc.).

[0098] The basic compound may be at least one compound selected from the group consisting of NaOH, KOH, and Ca(OH)2, and may 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 that can be homogeneously mixed with water (specifically, alcohol, etc.) may be used as the solvent.

[0099] As described above, when an aqueous transition metal solution, an ammonium cation complex-forming agent, and a basic compound are added to the reactor and stirred, the transition metal in the aqueous transition metal solution co-precipitates, generating precursor particles in the form of transition metal hydroxides. In this case, the transition metal aqueous solution, ammonium cation complex forming agent, and basic compound may be added in amounts such that the pH of the reaction solution falls within the desired range.

[0100] Once the precursor particles are formed using the method described above, the particles are separated from the reaction solution to obtain the transition metal precursor. For example, the reaction solution can be filtered to separate the transition metal precursor, and then the separated transition metal precursor can be washed with water and dried to obtain the transition metal precursor. In this process, steps such as grinding and / or classification may be performed as needed.

[0101] Next, the transition metal precursor and the first lithium raw material are mixed and then subjected to primary calcination to form a primary calcined product containing single-particle lithium nickel oxide containing 1 to 30 primary particles. At this time, if necessary, aluminum-containing raw material and / or M 2 Metal-containing raw materials may be mixed together and fired.

[0102] As the first lithium raw material, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides may be used. For example, Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, Li3C6H5O7, or mixtures thereof may be used.

[0103] On the other hand, the first lithium raw material may be mixed such that the ratio of the number of moles of lithium to the total number of moles of transition metal contained in the transition metal precursor is 0.9 to 1.1, preferably 0.95 to 1.07, and more preferably 1 to 1.06. When the ratio of the number of moles of the transition metal precursor to the first lithium raw material satisfies the above range, the layered crystal structure of the positive electrode active material develops well, and a positive electrode material with excellent electrochemical performance can be manufactured.

[0104] On the other hand, the primary calcination is carried out under conditions that allow the primary particles to grow to 1 μm or larger and form single-particle lithium nickel oxide. The preferred primary firing temperature varies depending on the metal composition in the precursor. For example, if the nickel (Ni) content is 80 mol% or more, the primary firing may be performed at a temperature of 800°C to 950°C, preferably 820°C to 950°C, and more preferably 850°C to 950°C.

[0105] Furthermore, the primary firing time may be 5 to 35 hours, preferably 5 to 20 hours, and more preferably 5 to 15 hours. Furthermore, the primary firing may be carried out in an oxygen atmosphere. In this specification, an oxygen atmosphere means an atmosphere containing a sufficient amount of oxygen for firing, including an atmospheric atmosphere. In particular, it is preferable to carry out the firing in an atmosphere in which the partial pressure of oxygen is higher than that of the atmospheric atmosphere.

[0106] When primary firing is performed under the conditions described above, single-particle lithium nickel oxide with excellent electrochemical properties can be formed. If the primary firing temperature and time are excessively low, the primary particles will not grow sufficiently, and a positive electrode active material in the form of secondary particles will be produced. If they are excessively high, an excessive amount of electrically inert rock-salt phase will be formed during the firing process, resulting in a structurally unstable fired product with low crystallinity, which may lead to a decrease in electrochemical properties.

[0107] (2) First grinding step Once a primary calcined product is formed by the primary calcination process described above, a first grinding step is performed to grind the primary calcined product.

[0108] The first grinding step is for breaking up the aggregated positive electrode active material and appropriately adjusting the particle size and shape of the particles in the positive electrode material, and may be carried out using a grinding device well known in the art, such as a jet mill or a ball mill.

[0109] In the first grinding step, by appropriately adjusting the grinding conditions such as grinding pressure and classification speed, the particle size distribution (D) of lithium nickel oxide particles can be improved. 50 ) and the shape and aspect ratio of the primary particles can be adjusted.

[0110] For example, the first grinding step may be carried out under grinding pressure conditions of 1.5 bar to 2.5 bar, preferably 1.5 bar to 2.4 bar, and more preferably 1.5 bar to 2.3 bar. When the grinding pressure of the first grinding step satisfies the above range, it becomes easier to manufacture a cathode material having the arithmetic mean of the curvature of the target primary particles.

[0111] Furthermore, the first grinding step may be performed at a classification speed of 800 rpm to 1800 rpm, preferably 900 rpm to 1800 rpm, and more preferably 900 rpm to 1700 rpm. When the classification speed of the first grinding step satisfies the above range, the D of the positive electrode material 50 And / or it becomes easier to adjust the average particle size of the primary particles to a desired range.

[0112] (3) Step of forming a secondary fired product Next, the primary calcined product, which was pulverized in the first pulverization step, is mixed with the second lithium raw material and then subjected to secondary calcination.

[0113] In this case, the second lithium raw material may be a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, for example, Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, Li3C6H5O7, or a mixture thereof. The second lithium raw material may be the same as or different from the first lithium raw material.

[0114] On the other hand, the second lithium raw material may be mixed such that the ratio of the number of moles of lithium to the total number of moles of transition metal contained in the transition metal precursor is 0.005 to 0.1, preferably 0.005 to 0.05, and more preferably 0.005 to 0.04. When the amount of the second lithium raw material added satisfies the above range, it becomes easier to manufacture a cathode material having primary particles of a desired shape without degrading the physical properties of the cathode material. When secondary calcination is performed without adding the second lithium raw material, there are problems such as a slow reaction rate and the need for high temperature and long calcination time. Even when the second lithium raw material is added, if the amount added is excessively small, the effect of reducing the rock salt structure on the surface of the single-particle lithium nickel oxide is negligible, and if the amount added is excessively large, lithium by-products increase, and electrochemical performance may decrease.

[0115] As described above, when a second lithium raw material is added and secondary calcination is performed, lithium is inserted into the rock salt structure that may form on the surface of the single-particle lithium nickel oxide, restoring it to a layered structure and improving its crystallinity. During the secondary calcination process, the surface of the primary particles becomes smoother, increasing its circularity and making it easier to manufacture cathode materials with the desired curvature and circularity.

[0116] On the other hand, the secondary firing may be performed at a temperature 50°C to 100°C lower than the primary firing temperature. If the secondary firing temperature is higher than the primary firing temperature, an excessive amount of rock salt phase may be generated on the surface of the lithium nickel oxide, the surface may deteriorate, lithium by-products may remain, and the electrochemical properties may decrease. If the secondary firing is performed at a temperature 100°C or more lower than the primary firing temperature, the lithium insertion rate will be slower, the electrochemical performance will decrease, and the effect of improving the curvature or circularity of the primary particles will be minimal. For example, the secondary firing temperature may be 700°C to 850°C, preferably 750°C to 850°C, and more preferably 750°C to 840°C.

[0117] On the other hand, the secondary firing time may be, for example, 3 to 20 hours, preferably 3 to 15 hours, and more preferably 5 to 15 hours, from the viewpoint of increasing the degree of crystallinity of the crystal structure inside the positive electrode active material.

[0118] Furthermore, the secondary firing may be carried out in an oxygen atmosphere. When secondary firing is performed under the conditions described above, a cathode material with excellent electrochemical properties and the desired surface shape of primary particles can be easily formed.

[0119] (4) Second grinding step Next, a second grinding step is performed to grind the secondary calcined product obtained by the secondary calcination. In this step, it is preferable that the grinding pressure in the second grinding step is lower than the grinding pressure in the first grinding step. If the grinding pressure in the second grinding step is higher than the grinding pressure in the first grinding step, excessive grinding occurs, making it difficult to form the surface shape and circularity of the primary particles within the desired range, and in severe cases, fracture surfaces may occur in the single-particle lithium nickel oxide particles.

[0120] For example, the second grinding step may be carried out under grinding pressure conditions of 0.4 bar to 1.4 bar, 0.5 bar to 1.4 bar, or 0.6 bar to 1.3 bar.

[0121] Furthermore, the second grinding step may be performed at a classification speed of 800 rpm to 1800 rpm, preferably 900 rpm to 1800 rpm, and more preferably 900 rpm to 1700 rpm. If the classification speed of the second grinding step satisfies the above range, D 50 And / or it becomes easier to adjust the average particle size of the primary particles to a desired range.

[0122] (5) Coating step On the other hand, the method for producing a positive electrode material according to the present invention may further include, if necessary, a step after the second grinding step, in which the ground second calcined product and the coating raw material are mixed and then heat-treated to form a coating layer. The coating raw material may be an acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide containing a coating element.

[0123] On the other hand, the mixing may be carried out by solid-phase mixing or liquid-phase mixing, and the heat treatment may be carried out at a temperature suitable for the type of element to be coated. For example, the heat treatment may be carried out at a temperature of 200°C to 800°C, preferably 300°C to 750°C. Also, the heat treatment may be carried out in two or more stages at different temperatures. On the other hand, the heat treatment may be carried out for 1 to 10 hours, specifically 2 to 8 hours, and more specifically 3 to 6 hours, in order to increase the degree of crystallinity of the coated portion.

[0124] The cathode material manufactured by the method described above may contain multiple single-particle cathode active material particles, and the arithmetic mean of the convexity of the primary particles measured from a segmentation image partitioned by primary particle units obtained by image processing of scanning electron microscope (SEM) images of the cathode material may be 0.92 or more and 0.95 or less.

[0125] Furthermore, the positive electrode material manufactured by the method described above may have an arithmetic mean of the circularity (C) of primary particles measured from a segmentation image partitioned by primary particle unit obtained by image processing of a scanning electron microscope (SEM) image of the positive electrode material, which is 0.65 or more and 0.98 or less, preferably 0.65 or more and 0.90 or less, and more preferably 0.65 or more and 0.85 or less.

[0126] positive electrode Next, the positive electrode according to the present invention will be described. The positive electrode according to the present invention includes a positive electrode active material layer containing the positive electrode material according to the present invention. Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode material.

[0127] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the positive electrode current collector to increase the adhesion strength of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0128] Furthermore, the positive electrode active material layer may include a conductive material and a binder, along with the positive electrode material described above. The conductive material is used to impart conductivity to the electrodes and can be used in any battery without particular limitations as long as it has electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more may be used. The conductive material is usually included in an amount of 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 positive electrode active material layer.

[0129] The binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The binder may be present in an amount of 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 positive electrode active material layer.

[0130] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode. For example, the positive electrode can be manufactured by mixing a positive electrode material, a binder, and / or a conductive material in a solvent to produce a positive electrode slurry, applying the positive electrode slurry onto a positive electrode current collector, and then drying and rolling it.

[0131] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or more of these may be used individually or in mixtures of two or more. The amount of solvent used should be sufficient to dissolve or disperse the cathode material, conductive material, and binder, and to have a viscosity that allows for excellent thickness uniformity when applied for cathode manufacturing, taking into consideration the coating thickness and production yield of the slurry.

[0132] Alternatively, the positive electrode can be manufactured by casting the positive electrode slurry onto another support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0133] Lithium-ion battery Next, the lithium secondary battery according to the present invention will be described. The lithium secondary battery of the present invention includes the positive electrode according to the present invention. Specifically, the lithium secondary battery includes a positive electrode, a negative electrode positioned opposite the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is the same as described above. The lithium secondary battery may further optionally include a battery container for housing the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0134] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector. The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The negative electrode current collector may also have a thickness of 3 to 500 μm, and, similar to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0135] The negative electrode active material layer selectively includes a binder and a conductive material together with the negative electrode active material. As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. β Examples include lithium-doped and dedoped metal oxides such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites, and one or more of these mixtures may be used.

[0136] Furthermore, a metallic lithium thin film may be used as the negative electrode active material. In addition, either low-crystalline carbon or high-crystalline carbon may be used as the carbon material. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0137] The conductive material is used to impart conductivity to the electrodes and can be used in any battery without particular limitations as long as it has electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these may be used alone or in mixtures of two or more. The conductive material is usually included in an amount of 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.

[0138] The binder plays a role in improving adhesion between negative electrode active material particles and adhesion between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The binder may be present in an amount of 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.

[0139] The negative electrode active material layer can be manufactured, for example, by applying a negative electrode slurry containing a negative electrode active material and selectively a binder and conductive material onto a negative electrode current collector and drying it, or by casting the negative electrode slurry onto another support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0140] On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Generally, any separator commonly used in lithium secondary batteries can be used without particular limitations, and it is especially preferable that the separator has low resistance to ion movement of the electrolyte and excellent electrolyte impregnation ability. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separators containing ceramic components or polymeric substances may be used, and they may be selectively used as single-layer or multi-layer structures.

[0141] Furthermore, the electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0142] Specifically, the electrolyte may include an organic solvent and a lithium salt. The organic solvent can be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move, without any particular limitations. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group of C2-C20, which may include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery (e.g., ethylene carbonate or propylene carbonate) and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred.

[0143] The lithium salt can be any compound capable of providing lithium ions for use in lithium secondary batteries, without any particular limitations. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within the range of 0.1 to 5.0 M, more preferably 0.1 to 3.0 M. When the concentration of the lithium salt falls within this range, the electrolyte has suitable conductivity and viscosity, exhibiting excellent electrolyte performance and allowing lithium ions to move effectively.

[0144] The electrolyte may further contain additives in addition to the electrolyte components to improve battery life characteristics, suppress the decrease in battery capacity, and improve battery discharge capacity. For example, the additives may be, but are not limited to, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethyl phosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, either alone or in combination. The additives may be present in an amount of 0.1 to 10% by weight, preferably 0.1 to 5% by weight, relative to the total weight of the electrolyte.

[0145] The following describes in detail embodiments of the present invention so that those with ordinary skill in the art to which the present invention pertains can easily implement it. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0146] Example 1 D 50The transition metal precursor Ni with a diameter of 4.20 μm 0.885 Co 0.035 Mn 0.08 (OH)2 and LiOH were mixed so that the molar ratio of Ni+Co+Mn:Li was 1:1.03, and Al(OH)3, Y2O3, and ZrO2 were mixed in amounts of 1470 ppm, 1000 ppm, and 1500 ppm, respectively, based on the total weight of the transition metal precursor to produce a mixture. Next, the mixture was calcined at 890 °C to 900 °C for 6 hours to obtain a primary calcined product.

[0147] Next, the primary calcined product was pulverized at room temperature using a jet mill under conditions of a pulverization pressure of 2.1 bar and a classification speed of 1600 rpm (first pulverization step).

[0148] Next, the pulverized primary calcined product and LiOH were mixed so that the molar ratio of Ni+Co+Mn:Li was 1:0.01, and calcined at 820 °C for 9 hours to obtain a secondary calcined product.

[0149] Next, the secondary calcined product was pulverized at room temperature using a jet mill under conditions of a pulverization pressure of 0.9 bar and a classification speed of 1600 rpm to obtain single-particle lithium nickel oxide LiNi 0.8784 Co 0.0347 Mn 0.0794 Al 0.005 Zr 0.0015 Y 0.001 O2 (second pulverization step).

[0150] Next, the single-particle lithium nickel oxide obtained above was uniformly mixed with Co(OH)2 and Al(OH)3, heat-treated in an oxygen atmosphere at 700 °C for 5 hours, and then heat-treated at 500 °C for 3 hours to produce a cathode material with a coating layer formed. At this time, the Co(OH)2 was mixed in an amount such that the ratio (B / A) of the molar number of Co in Co(OH)2 to the total molar number (A) of the metals other than lithium in the lithium nickel oxide was 0.02, and the Al(OH)3 was mixed in an amount of 0.05 parts by weight based on 100 parts by weight of the lithium nickel oxide.

[0151] Example 2 The positive electrode material was produced in the same manner as in Example 1, except that the first pulverization step was performed at a pulverization pressure of 1.6 bar.

[0152] Example 3 D 50 The transition metal precursor Ni 0.885 Co 0.035 Mn 0.08 (OH)2 and LiOH were mixed so that the molar ratio of Ni + Co + Mn:Li was 1:1, and Al(OH)3, Y2O3, and ZrO2 were mixed in amounts of 1470 ppm, 1000 ppm, and 1500 ppm, respectively, based on the total weight of the transition metal precursor to produce a mixture. Next, the mixture was primary fired at 850 °C for 12 hours to obtain a primary fired product.

[0153] Next, the primary fired product was pulverized at room temperature using a jet mill pulverizer under conditions of a pulverization pressure of 2.1 bar and a classification speed of 1600 rpm (first pulverization step).

[0154] Next, the pulverized primary fired product and LiOH were mixed so that the molar ratio of Ni + Co + Mn:Li was 1:0.05, and secondary fired at 800 °C for 12 hours to obtain a secondary fired product.

[0155] Next, the secondary fired product was pulverized at room temperature using a jet mill pulverizer under conditions of a pulverization pressure of 0.9 bar and a classification speed of 1600 rpm to obtain single-particle 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).

[0156] Next, the single-particle lithium nickel 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 lithium nickel oxide. Next, the Co-coated single-particle lithium nickel oxide was uniformly mixed with Al(OH)3, and then heat-treated at 500°C for 5 hours in an oxygen atmosphere to form a single-particle lithium nickel oxide coated with Co and Al. In this case, the Co(OH)2 was mixed in an amount such that the ratio (B / A) of the number of moles of Co in Co(OH)2 to the total number of moles of the remaining metals (A) in the lithium nickel oxide was 0.02, and the Al(OH)3 was mixed in an amount of 0.05 parts by weight per 100 parts by weight of the lithium nickel oxide.

[0157] Example 4 D 50 This is a 5.50 μm transition metal precursor Ni 0.905 Co 0.085 Mn 0.01 (OH)2 and LiOH were mixed in a ratio of Ni+Co+Mn:Li moles of 1:1. Al(OH)3, Y2O3, and ZrO2 were then added to this mixture in amounts of 1470 ppm, 1000 ppm, and 1500 ppm, respectively, relative to the total weight of the transition metal precursor, to produce a mixture. Next, the mixture was subjected to primary calcination at 820°C for 12 hours to obtain a primary calcined product.

[0158] Next, the first-fired product was finely ground at room temperature using a jet mill pulverizer under the conditions of a grinding pressure of 1.5 bar and a classification speed of 1250 rpm (first grinding step).

[0159] Next, the pulverized primary calcined product and LiOH were mixed so that the ratio of Ni+Co+Mn:Li moles was 1:0.03, and the mixture was then subjected to secondary calcination at 770°C for 12 hours to obtain the secondary calcined product.

[0160] Next, the secondary calcined product is finely ground at room temperature using a jet mill pulverizer under the conditions of a grinding pressure of 0.6 bar and a classification speed of 1250 rpm, resulting in single-particle lithium nickel oxide LiNi 0.8982Co 0.0844 Mn 0.0099 Al 0.005 Zr 0.0015 Y 0.001 O2 was obtained (second grinding step).

[0161] Next, the single-particle lithium nickel oxide obtained above was uniformly mixed with Co(OH)2 and Al(OH)3, and the mixture was heat-treated in an oxygen atmosphere at 700°C for 5 hours, followed by heat-treatment at 500°C for 3 hours to produce a cathode material with a coating layer formed on top. In this process, the Co(OH)2 was mixed in an amount such that the ratio (B / A) of the number of moles of Co in Co(OH)2 to the total number of moles of the remaining metals (A) in the lithium nickel oxide was 0.02, and the Al(OH)3 was mixed in an amount of 0.05 parts by weight per 100 parts by weight of the lithium nickel oxide.

[0162] Example 5 D 50 This is a 4.00 μm transition metal precursor Ni 0.605 Co 0.198 Mn 0.197 (OH)2 and LiOH were mixed in such a ratio of Ni+Co+Mn:Li moles of 1:1.06. Al(OH)3, Y2O3, and ZrO2 were then added to this mixture in amounts of 800 ppm, 1000 ppm, and 2100 ppm, respectively, relative to the total weight of the transition metal precursor, to produce a mixture. Next, the mixture was subjected to primary calcination at 890°C to 950°C for 8 hours to obtain a primary calcined product.

[0163] Next, the first-fired product was finely ground at room temperature using a jet mill pulverizer under the conditions of a grinding pressure of 2.1 bar and a classification speed of 1600 rpm (first grinding step).

[0164] Next, the pulverized primary calcined product and LiOH were mixed so that the ratio of Ni+Co+Mn:Li moles was 1:0.01, and the mixture was then subjected to secondary calcination at 800°C for 6 hours to obtain the secondary calcined product.

[0165] Next, the secondary calcined product is finely ground at room temperature using a jet mill pulverizer under the conditions of a grinding pressure of 0.9 bar and a classification speed of 1600 rpm, resulting in single-particle lithium nickel oxide LiNi 0.6026 Co 0.1972 Mn 0.1962 Al 0.0008 Zr 0.0021 Y 0.001 O2 was obtained (second grinding step).

[0166] Next, the single-particle lithium nickel oxide obtained above and H3BO3 were uniformly mixed, and then heat-treated at 340°C for 5 hours in an oxygen atmosphere to produce a cathode material with a coating layer formed on it. In this case, the H3BO3 was mixed in an amount of 0.05 parts by weight per 100 parts by weight of lithium nickel oxide.

[0167] Comparative Example 1 D 50 This is a 4.20 μm transition metal precursor Ni 0.885 Co 0.035 Mn 0.08 (OH)2 and LiOH were mixed so that the ratio of Ni+Co+Mn:Li moles was 1:1.05. Al(OH)3, Y2O3, and ZrO2 were then added to this mixture in amounts of 1470 ppm, 1000 ppm, and 1500 ppm, respectively, relative to the total weight of the transition metal precursor, to prepare the mixture.

[0168] Next, the mixture is calcined at 880°C for 3 hours, then again at 800°C for 9 hours, and then at room temperature, it is processed using a jet mill fine grinder under the conditions of a grinding pressure of 2.1 bar and a classification speed of 1600 rpm. 50 The material is finely ground to a size of 3.8 μm, and single-particle lithium nickel oxide (LiNi) is used. 0.8784 Co 0.0347 Mn 0.0794 Al 0.005 Zr 0.0015 Y 0.001 O2 was obtained.

[0169] Next, the single-particle lithium nickel oxide obtained above was uniformly mixed with Co(OH)2 and Al(OH)3, and the mixture was heat-treated in an oxygen atmosphere at 700°C for 5 hours, followed by heat-treatment at 500°C for 3 hours to produce a cathode material with a coating layer formed on top. In this process, the Co(OH)2 was mixed in an amount such that the ratio (B / A) of the number of moles of Co in Co(OH)2 to the total number of moles of the remaining metals (A) in the lithium nickel oxide was 0.02, and the Al(OH)3 was mixed in an amount of 0.05 parts by weight per 100 parts by weight of the lithium nickel oxide.

[0170] Comparative Example 2 The cathode material was manufactured in the same manner as in Example 1, except that the first grinding step was performed at a grinding pressure of 1.6 bar and the second grinding step at a grinding pressure of 2.1 bar.

[0171] Comparative Example 3 The cathode material was manufactured in the same manner as in Example 1, except that the primary calcined product was not crushed, a secondary calcination was performed, and the secondary calcined product was crushed at a crushing pressure of 2.1 bar.

[0172] Comparative Example 4 The cathode material was manufactured in the same manner as in Example 5, except that the crushed primary calcined product and LiOH were mixed so that the molar ratio of Ni+Co+Mn:Li was 1:0.11, and secondary calcination was performed at 800°C for 6 hours.

[0173] [Table 1]

[0174] Experimental Example 1 - Measurement of Curvature and Circumference Scanning electron microscope (SEM) images of the cathode materials manufactured according to Examples 1-5 and Comparative Examples 1-4 were obtained using a scanning electron microscope. Each image was then processed using the particle shape analysis method described above to obtain segmentation images partitioned by primary particle units. Figures 2-10 show the SEM images and segmentation images of the cathode materials manufactured according to Examples 1-5 and Comparative Examples 1-4. In Figures 2-10, (A) is the SEM image, and (B) is the segmentation image obtained by processing the SEM image.

[0175] From the segmentation images, the arithmetic mean of the curvature of the primary particles, the arithmetic mean of the circularity of the primary particles, the average particle size of the primary particles, and the average aspect ratio of the primary particles were measured.

[0176] Furthermore, 0.01 g each of the cathode material powder produced in Examples 1-5 and Comparative Examples 1-4 was taken, placed in a vial containing 30 ml of ultrapure water and 500 μl of dispersant, dispersed in a sonicator for 1 minute, and then placed in a particle size analyzer (PSA) (Microtrac S3500) to determine the D content of the cathode material powder. 50 We measured it. The measurement results are shown in [Table 2] below.

[0177] [Table 2]

[0178] Experimental Example 2 - Cell Performance Data The respective positive electrode materials, conductive material (FX35), and binder (a mixture of KF9700 and BM730H in a weight ratio of 2.8:0.2) produced in Examples 1-5 and Comparative Examples 1-4 were mixed in N-methylpyrrolidone in a weight ratio of 95:2:3 to produce a positive electrode slurry. The positive electrode slurry was applied to one side of an aluminum current collector, dried at 130°C, and then rolled to produce a positive electrode.

[0179] An electrode assembly was manufactured by interposing a porous polyethylene separator between each manufactured positive electrode and a lithium metal disk. After positioning this assembly inside a battery case, an electrolyte was injected to produce a half-cell. The electrolyte was prepared by dissolving LiPF6 at a concentration of 1M in a mixed organic solvent consisting of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a volume ratio of 3:3:4.

[0180] (1)Initial capacity Each of the lithium secondary batteries manufactured as described above was charged to 4.25V in CC / CV mode at 25°C under 0.1C and 0.5C cutoff conditions, and then discharged to 2.5V in CC mode to measure its initial discharge capacity.

[0181] (2) Life characteristics Each of the lithium secondary batteries manufactured as described above was subjected to 50 charge-discharge cycles at 45°C and a voltage range of 2.5 to 4.25V, and the capacity retention rate and resistance increase rate over the 50 cycles were measured. During this process, charging was performed in CCCV mode until the voltage reached 4.25V, then cut-off was performed when the voltage reached 0.05C, and discharging was performed in CC mode until the voltage reached 2.5V.

[0182] The capacity retention rate was measured as the percentage of the discharge capacity after 50 cycles relative to the discharge capacity after 1 cycle ((discharge capacity after 50 cycles / discharge capacity after 1 cycle) × 100), and the resistance increase rate was measured as the percentage of the resistance after 50 cycles relative to the resistance after 1 cycle ({(resistance after 50 cycles - resistance after 1 cycle) / resistance after 1 cycle)} × 100). The measurement results are shown in [Table 3] below.

[0183] [Table 3]

[0184] From [Table 3] above, it can be confirmed that batteries using the cathode materials of Examples 1 to 5, in which the arithmetic mean of the curvature of the primary particles is 0.92 or more and 0.95 or less, exhibit superior capacity retention after 50 cycles and less resistance increase compared to batteries using the cathode materials of Comparative Examples 1 to 3, in which the arithmetic mean of the curvature of the primary particles is less than 0.92. Furthermore, it can be confirmed that batteries using the cathode material of Example 5, in which the arithmetic mean of the curvature of the primary particles is 0.92 or more and 0.95 or less, exhibit superior charge / discharge capacity and efficiency and less resistance increase compared to batteries using the cathode material of Comparative Example 4, in which the arithmetic mean of the curvature of the primary particles is greater than 0.95.

[0185] Furthermore, it can be confirmed that batteries using the cathode materials of Examples 1 to 5, in which the arithmetic mean of the circularity of the primary particles is 0.65 to 0.98, exhibit superior initial capacity and lifespan characteristics after 50 cycles compared to batteries using the cathode materials of Comparative Examples 1 to 3, in which the arithmetic mean of the circularity of the primary particles is less than 0.65.

Claims

1. A cathode material comprising multiple single-particle cathode active material particles, The aforementioned single-particle positive electrode active material particles contain 1 to 30 primary particles. The arithmetic mean of the convexity of the primary particles, measured from segmentation images partitioned by primary particle units and obtained by image processing of scanning electron microscope (SEM) images of the positive electrode material, is 0.92 or more and 0.95 or less. The degree of flexibility is defined by the following formula (1) for the positive electrode material. Equation (1): Buckling degree = P ｃ / P ｒ In the above formula (1), P ｒ P is the actual circumference of each primary particle measured from the segmentation image. ｃ This is the perimeter of a virtual figure obtained by connecting the outermost points of each primary particle measured from the segmentation image.

2. The arithmetic mean of the circularity (C) of the primary particles, measured from the segmentation image obtained by image processing of scanning electron microscope (SEM) images of the positive electrode material, is 0.65 or more and 0.98 or less. The positive electrode material according to claim 1, wherein the circularity (C) is defined by the following formula (2). Equation (2): Circularity (C) = 4πA / P ２ In equation (2) above, A is the area of ​​each primary particle measured from the segmentation image, and P is the circumference of each primary particle measured from the segmentation image.

3. The positive electrode material according to claim 2, wherein the arithmetic mean of the circularity (C) of the primary particles is 0.65 or more and 0.90 or less.

4. The positive electrode material according to claim 2, wherein the arithmetic mean of the circularity (C) of the primary particles is 0.65 or more and 0.85 or less.

5. The aforementioned single-particle positive electrode active material includes a lithium nickel-based oxide containing nickel and cobalt. The cathode material according to claim 1, wherein the lithium nickel oxide has a nickel content of 50 mol% or more of all metals excluding lithium.

6. The positive electrode material according to claim 5, wherein the lithium nickel oxide has a composition represented by the following [Chemical Formula 1]. [Chemical formula 1] Li ａ [Ni ｘ Co ｙ M １ ｚ M ２ １－ｘ－ｙ－ｚ ]O ２ In the above chemical formula 1, M １ This includes Mn, Al, or combinations thereof, M ２ It contains one or more elements 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, and satisfies 0.9 ≤ a ≤ 1.3, 0.5 ≤ x < 1.0, 0 < y < 0.5, and 0 < z < 0.

5.

7. The cathode material according to claim 1, wherein the single-particle cathode active material comprises a lithium nickel-based oxide consisting of 1 to 30 primary particles and a coating layer formed on the lithium nickel-based oxide.

8. The positive electrode material according to claim 7, wherein the coating layer comprises one or more coating elements 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.

9. The positive electrode material is D ５０ The positive electrode material according to claim 1, wherein the thickness is 2 μm to 15 μm.

10. The positive electrode material according to claim 1, wherein the average particle size of the primary particles is 1 μm to 6 μm.

11. The positive electrode material according to claim 1, wherein the average aspect ratio of the primary particles is 1.2 to 4.

0.

12. The process involves mixing a transition metal precursor with a first lithium raw material, followed by primary calcination to form a primary calcined product containing a single-particle cathode active material comprising 1 to 30 primary particles, and A first grinding step in which the aforementioned primary calcined product is ground, The steps include mixing the pulverized primary calcined product with a second lithium raw material, followed by secondary calcination to form a secondary calcined product, A second grinding step in which the aforementioned secondary calcined product is ground, Includes, A method for manufacturing a cathode material, wherein the grinding pressure in the second grinding step is smaller than the grinding pressure in the first grinding step.

13. The grinding pressure in the first grinding step is 1.5 bar to 2.5 bar. The method for manufacturing a positive electrode material according to claim 12, wherein the grinding pressure in the second grinding step is 0.4 bar to 1.4 bar.

14. The method for producing a cathode material according to claim 12, wherein the transition metal precursor is a transition metal hydroxide represented by the following [Chemical Formula 2]. [Chemical formula 2] [Ni ｘ１ Co ｙ１ M １ ｚ１ M ２ １－ｘ１－ｙ１－ｚ１ ](O+) ２ In the above chemical formula 2, M １ This includes Mn, Al, or combinations thereof, M ２ It contains one or more elements 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, and satisfies 0.5 ≤ x1 < 1.0, 0 < y1 < 0.5, and 0 < z1 < 0.

5.

15. The method for producing a cathode material according to claim 12, wherein the first lithium raw material is mixed such that the ratio of the number of moles of lithium to the total number of moles of transition metal contained in the transition metal precursor is 0.9 to 1.

1.

16. The method for manufacturing a cathode material according to claim 12, wherein the primary firing is performed at a temperature of 800°C to 950°C.

17. The method for producing a cathode material according to claim 12, wherein the second lithium raw material is mixed such that the ratio of the number of moles of lithium to the total number of moles of transition metal contained in the transition metal precursor is 0.005 to 0.

1.

18. The method for manufacturing a cathode material according to claim 12, wherein the secondary firing is performed at a temperature 50°C to 100°C lower than the primary firing temperature.

19. The method for producing a cathode material according to claim 12, further comprising the step of mixing the pulverized second calcined product with a coating raw material after the second pulverization step and then heat-treating it to form a coating layer.

20. The aforementioned cathode material includes a plurality of single-particle cathode active material particles, A method for manufacturing a cathode material according to any one of claims 12 to 19, wherein the arithmetic mean of the curvature of primary particles measured from a segmentation image partitioned by primary particle units obtained by image processing of a scanning electron microscope (SEM) image of the cathode material is 0.92 or more and 0.95 or less, and the curvature is defined by the following formula (1). Equation (1): Buckling degree = P ｃ / P ｒ In the above formula (1), P ｒ P is the actual circumference of each primary particle measured from the segmentation image. ｃ This is the perimeter of a virtual figure obtained by connecting the outermost points of each primary particle measured from the segmentation image.

21. The method for manufacturing a cathode material according to claim 20, wherein the arithmetic mean of the circularity (C) of primary particles measured from a segmentation image partitioned by primary particle units obtained by processing a scanning electron microscope (SEM) image of the cathode material is 0.65 or more and 0.98 or less, and the circularity (C) is defined by the following formula (2). Equation (2): Circularity (C) = 4πA / P ２ In equation (2) above, A is the area of ​​each primary particle measured from the segmentation image, and P is the circumference of each primary particle measured from the segmentation image.

22. A positive electrode comprising the positive electrode material described in any one of claims 1 to 11.

23. A lithium secondary battery comprising the positive electrode described in claim 22.

Images