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

Abstract

The present invention relates to a positive electrode active material comprising a lithium transition metal oxide in single-particle form, and a positive electrode and a lithium secondary battery comprising the same, wherein the lithium transition metal oxide in single-particle form comprises an external interface forming the outer edge of the particle and an internal interface formed within the particle, and the length of the internal interface / the length of the external interface ≥ 0.4.

Description

【Technical Field】 【0001】 This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0071876 filed on June 2, 2023, and all the contents disclosed in the literature of the Korean patent application are incorporated herein by reference in their entirety. 【0002】 The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode including the same, and a lithium secondary battery. 【Background Art】 【0003】 Recently, with the development of technologies such as electric vehicles, the need for high-capacity secondary batteries has been increasing, and thus, research on positive electrodes using high-nickel (High Ni) positive electrode active materials with excellent capacity characteristics has been actively conducted. 【0004】 In order to manufacture a high-nickel positive electrode active material, a co-precipitation method is used, and thus, the manufactured high-nickel positive electrode active material has a form of secondary particles in which primary particles are aggregated. However, an active material having a form of secondary particles has fine cracks generated in the secondary particles during a long-term charge and discharge process, causing side reactions. Also, when the secondary particles increase the density of the electrode to improve the energy density, the structure of the secondary particles collapses, resulting in disadvantages such as a decrease in energy density and a decrease in life characteristics due to a decrease in the active material and the electrolyte. 【0005】 To address the problems associated with secondary particle-type high-nickel cathode active materials, the development of single-particle nickel-based cathode active materials has recently progressed. Single-particle nickel-based cathode active materials have the advantage of not causing particle breakdown even when increasing electrode density due to their high energy density. However, because single-particle nickel-based cathode active materials require relatively high firing temperatures to manufacture, the R-3m layered structure cannot be properly maintained, lithium detaches from the crystalline structure, and a phase change occurs to an Fm-3m rock-salt structure such as NiO. As the crystallinity of the cathode active material decreases, the proportion of NiO on the surface of the manufactured single particles increases, and with the increase in NiO, resistance increases, leading to problems of decreased energy density and output. Furthermore, at lower firing temperatures, they exist in the form of overfired secondary particles, resulting in problems where the improvement in lifetime and gas generation does not reach the level expected from single-particle materials. 【0006】 Therefore, there is still a need for the development of positive electrode active materials that have high electrode density and exhibit excellent properties. [Prior art documents] [Patent Documents] 【0007】 [Patent Document 1] KR2019-0094529 A1 [Overview of the Initiative] [Problems that the invention aims to solve] 【0008】 The problem that this invention aims to solve is to provide a positive electrode active material having excellent capacitance characteristics. [Means for solving the problem] 【0009】 To solve the above problems, the present invention provides a positive electrode active material, a positive electrode, and a lithium secondary battery. 【0010】 (1) The present invention relates to a positive electrode active material comprising a lithium transition metal oxide in single-particle form, wherein the lithium transition metal oxide in single-particle form includes an external interface forming the outer edge of the particle and an internal interface formed within the particle, and the external interface and the internal interface satisfy the following formula 1. [Equation 1] Length of internal boundary / Length of external boundary ≥ 0.4 The present invention provides a positive electrode active material in which the length of the internal interface is the length obtained by subtracting the length of the interface measured from the EBSD band contrast map from the length of the interface measured from the electron backscatter diffraction (EBSD)-IPF map for the lithium transition metal oxide particles, and the length of the external interface is the length of the external interface of the transition metal oxide particles measured by SEM image resolution. 【0011】 (2) The present invention further provides a positive electrode active material that satisfies the following formula 2, wherein the lithium transition metal oxide in single-particle form in (1) above. [Equation 2] Interface length measured from EBSD IPF map / Interface length measured from EBSD band contrast map ≥ 1.3 【0012】 (3) The present invention provides a positive electrode active material in which, in either (1) or (2) above, the length of the interface measured from the electron backscatter diffraction (EBSD)-IPF map includes the length of a weak interface contained in the single-particle lithium transition metal oxide particle that differs only in atomic arrangement and has not undergone crystallinity collapse, and the length of a strong interface formed by the collapse of the layered structure. 【0013】 (4) The present invention provides a positive electrode active material in any one of (1) to (3) above, wherein the length of the interface measured from the EBSD band contrast map includes the length of the strong interface formed by the collapse of the layered structure contained in the single-particle lithium transition metal oxide particles. 【0014】 (5) In any one of the above (1) to (4), the present invention provides a cathode active material in which the single-particle form lithium transition metal oxide contains 2 to 50 particles. 【0015】 (6) In any one of the above (1) to (5), the present invention provides a cathode active material in which the lithium transition metal oxide is a lithium composite transition metal oxide containing nickel, cobalt, and manganese. 【0016】 (7) In any one of the above (1) to (6), the present invention provides a cathode active material in which the lithium transition metal oxide is a lithium composite transition metal oxide represented by the following Chemical Formula 1. [Chemical Formula 1] Li Ni b Co c Mn d M 1 e O2 In Chemical Formula 1 above, M 1 is one or more selected from the group consisting of Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P, and S, and 0.9 ≦ a ≦ 1.1, 0.6 ≦ b < 1, 0 < c < 0.4, 0 < d < 0.4, 0 ≦ e < 0.1, and b + c + d + e = 1. 【0017】 (8) In any one of the above (1) to (7), the present invention provides a cathode active material in which the lithium transition metal oxide is a lithium composite transition metal oxide represented by the following Chemical Formula 2. [Chemical Formula 2] Li a Ni b Co c Mn d O2 In Chemical Formula 2 above, 0.9 ≦ a ≦ 1.1, 0.6 ≦ b < 1, 0 < c < 0.4, 0 < d < 0.4, and b + c + d = 1. 【0018】 (9) In any one of the above (1) to (8), the average particle size (D 50The present invention provides a cathode active material having a bimodal particle size distribution, further comprising a second lithium transition metal oxide in the form of small single particles. 【0019】 (10) The present invention provides a positive electrode active material in which the second lithium transition metal oxide is a lithium composite transition metal oxide represented by the following chemical formula 3, as described in (9) above. [Chemical formula 3] Li a3 Ni b3 Co c3 Mn d3 M 3 e3 O2 In the above chemical formula 3, M 3 is one or more elements selected from the group consisting of Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P, and S, and 0.9 ≤ a3 ≤ 1.1, 0.6 ≤ b3 < 1, 0 <c3<0.4、0<d3<0.4、0≦e3<0.1、b3+c3+d3+e3=1である。 【0020】 (11) The present invention provides a positive electrode active material in which, in (9) or (10) above, the weight ratio of the lithium transition metal oxide to the second lithium transition metal oxide is 1 to 9:1. 【0021】 (12) The present invention relates to any one of the above (9) to (11), wherein the press density is 3.50 g / cm³. 2 ~3.90g / cm 2 The present invention provides a positive electrode active material. 【0022】 (13) The present invention provides a positive electrode comprising a positive electrode active material according to any one of (1) to (12) above. 【0023】 (14) The present invention provides a lithium secondary battery including a positive electrode according to (13) above. [Effects of the Invention] 【0024】 The positive electrode active material of the present invention is a positive electrode active material comprising a lithium transition metal oxide in single-particle form, wherein the length of the internal interface of the particle, obtained by subtracting the length of the strong interface measured from the EBSD band contrast map from the length of the weak interface measured from the EBSD IPF map relative to the length of the external interface of the particle, satisfies a predetermined value, thereby facilitating lithium ion exchange between charge and discharge and enabling the material to exhibit excellent capacity characteristics. [Brief explanation of the drawing] 【0025】 [Figure 1] The images show the SEM image, EBSD band contrast map, EBSD IPF map, and IPF interface of the positive electrode active material of Example 1. [Figure 2] The images show the SEM image, EBSD band contrast map, BC interface, EBSD IPF map, and IPF interface of the cathode active material of Example 4. [Figure 3] The images show the SEM image, EBSD band contrast map, EBSD IPF map, and IPF interface of the positive electrode active material of Comparative Example 3. [Modes for carrying out the invention] 【0026】 The present invention will be described in more detail below to facilitate understanding of it. 【0027】 The terms and words used in the description and claims of this invention 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 ​​this invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention. 【0028】 In the present invention, the term "primary particle" refers to the smallest particle unit that can be distinguished as a single mass when a cross-section of the positive electrode active material is observed via a scanning electron microscope (SEM), and can consist of one crystal grain or multiple crystal grains. 【0029】 In this invention, the term "secondary particle" refers to a secondary structure formed by the aggregation of multiple primary particles. The average particle size of the secondary particle can be measured using a particle size analyzer. 【0030】 In the present invention, the term "single-particle form" can be used interchangeably with the term "single-particle type," and refers to a form that is contrasted with the form of secondary particles formed by the aggregation of several hundred primary particles manufactured by conventional methods. Furthermore, in the present invention, the terms "single-particle type positive electrode active material" or "single-particle form lithium transition metal oxide" are concepts that are contrasted with positive electrode active materials in the form of secondary particles formed by the aggregation of several hundred primary particles manufactured by conventional methods, and refer to positive electrode active materials or lithium transition metal active materials consisting of 1 to 50 particles, 1 to 40 particles, 1 to 30 particles, 1 to 20 particles, 1 to 15 particles, 1 to 10 particles, or 1 to 5 particles. 【0031】 In this invention, the term "single crystal" can be used interchangeably with the term "single-crystal properties," and refers to a cathode active material or lithium transition metal oxide containing 2 to 50, specifically 2 to 30, crystal grains. Typically, single-crystal particles represent particles in which the entire sample consists of only one crystal grain or grain region. In this invention, single-particle cathode active materials or lithium transition metal oxides in single-particle form can exhibit properties similar to those of a single-crystal particle by containing a small number of crystal grains. 【0032】 The term "single particle" refers to the smallest unit of particle recognized when observing the positive electrode active material with a scanning electron microscope, and the term "grain" or "grain region" refers to a region in the sample where atoms are arranged continuously and periodically in one direction. The grain can be analyzed using an electron backscatter diffraction (ESBD) analyzer. 【0033】 In this invention, the term "average particle size (D 50 )" refers to the particle size at the 50% point of the cumulative volume distribution by particle size. The average particle size is calculated by dispersing the powder to be measured in a dispersion medium, introducing it into a commercially available laser diffraction particle size analyzer (for example, Microtrac's S3500), measuring the difference in diffraction patterns due to particle size as the particles pass through the laser beam to calculate the particle size distribution, and then calculating the particle diameter at the point where the cumulative volume distribution by particle size in the measuring device reaches 50%. 50 It can be measured. 【0034】 In the present invention, the term "segmentation image" refers to an image segmented into individual positive electrode active material particle units, and can be obtained by a method comprising: a first step of obtaining an SEM image by analyzing the positive electrode active material powder with a scanning electron microscope; and a second step of using computer image processing techniques to remove the boundaries (edges) of individual positive electrode active material particles from the SEM image, then detecting the seeds or contours of individual positive electrode active material particles, and using these to obtain an image segmented into individual positive electrode active material particle units. Specifically, the segmentation image can be obtained by the method described in KR10-2022-0048191 A and KR10-2022-0048192 A. 【0035】 positive electrode active material The positive electrode active material of the present invention is a positive electrode active material comprising a lithium transition metal oxide in single-particle form, wherein the lithium transition metal oxide in single-particle form includes an external interface forming the outer edge of the particle and an internal interface formed within the particle, and the external interface and the internal interface satisfy the following formula 1. 【0036】 [Formula 1] Length of internal interface / Length of external interface ≥ 0.4 【0037】 The length of the internal interface is the length obtained by subtracting the length of the interface measured from the EBSD band contrast (BC) map from the length of the interface measured from the electron backscatter diffraction (EBSD) IPF map for the lithium transition metal oxide particles, and the length of the external interface is the length of the external interface of the transition metal oxide particles measured by SEM image resolution. 【0038】 In the present invention, the internal interface can mean an interface formed by grains contained in the single-particle lithium transition metal oxide particles while they are in contact with each other. Since lithium ions can easily move at the internal interface formed by the grains in contact with each other, single-particle lithium transition metal oxide particles containing a large amount of the internal interface exhibit an excellent capacity-generating effect. The content of the internal interface can be quantitatively determined by the length of the internal interface contained in the single-particle lithium transition metal oxide particles. 【0039】 By obtaining an EBSD IPF map using the EBSD IPF measurement method for the single-particle lithium transition metal oxide particles, it is possible to distinguish the grains contained in the single-particle lithium transition metal oxide particles. Therefore, from the EBSD IPF map, it is possible to identify the interface formed when any one grain contained in the single-particle lithium transition metal oxide particle comes into contact with other grains. 【0040】 However, the interfaces identified by the EBSD IPF map include not only interfaces between grains where the orientation of atoms simply changes relative to the interface (weak interfaces), but also interfaces where the layered structure of the transition metal oxide layer collapses, particularly the layered structure of the NiO layer, along with the change in the orientation of atoms (strong interfaces). Therefore, in order to obtain only the interfaces between grains, it is necessary to exclude interfaces where the layered structure of the transition metal oxide layer collapses. 【0041】 When a BC map is obtained by EBSD for the single-particle lithium transition metal oxide particles, weak interfaces containing the single-particle lithium transition metal oxide particles that simply differ only in atomic arrangement and do not exhibit crystallinity collapse are not distinguishable, but strong interfaces where the layered structure of the transition metal oxide collapses can be distinguished. The interfaces where the layered structure of the transition metal oxide collapses may be interfaces formed between any one single crystal particle contained in the single-particle lithium transition metal oxide particles and other single crystal particles. 【0042】 The interface lengths measured from the EBSD IPF map may include the interfaces between grains contained in the single-particle lithium transition metal oxide particles, interfaces formed by the collapse of the layered structure, and the external interfaces of the particles. 【0043】 Furthermore, the interface length measured from the EBSD BC map may include the lengths of the interface formed by the collapse of the layered structure contained in the single-particle lithium transition metal oxide particles and the external interface. 【0044】 Therefore, the length of the internal interface is the length obtained by subtracting the length of the interface measured from the EBSD BC map from the length of the interface measured from the EBSD IPF map for the lithium transition metal oxide particles. Since the length of the outer edge (external interface) of the single-particle transition metal oxide particles is measured similarly in the EBSD IPF map and the EBSD BC map, if this is excluded, it can be expressed as follows. 【0045】 Length of the internal interface =[Boundary surface length measured from EBSD IPF map]-[Boundary surface length measured from EBSD BC map] =[Length of strong boundary + Length of weak boundary] - [Length of strong boundary] = Length of the weak boundary 【0046】 Furthermore, the length of the external interface of the single-particle transition metal oxide particle can be obtained by acquiring an SEM image of the single-particle lithium transition metal oxide particle and performing SEM image segmentation to obtain the length of the external interface that forms the outer surface of the transition metal oxide particle. 【0047】 Equation 1 above is a numerical representation of the extent to which the internal interface of the single-particle transition metal oxide particle is included, obtained by dividing the length of the internal interface by the length of the external interface. 【0048】 The fact that the value obtained by dividing the length of lines formed inside circular or similarly shaped objects by the length of the outer edge of the object, calculated from two-dimensional images obtained using EBSD and SEM, is 1.0 or greater suggests that the interface between grains contained in the single-particle lithium transition metal oxide particles may be wider than the outer surface of the single-particle lithium transition metal oxide particles. At the interface between grains, the lithium ion migration rate is much faster than inside the lattice (inside the single-grain region) due to lattice symmetry collapse, allowing for easy lithium ion migration and thus demonstrating an excellent capacity expression effect. 【0049】 The positive electrode active material of the present invention can satisfy the ratio of the length of the internal interface to the length of the external interface in formula 1 to a value of 0.5 to 1.5, more specifically 0.5 to 1.3. When formula 1 satisfies the above range, excellent capacitance characteristics can be exhibited. If formula 1 is too small compared to the above range, the capacitance characteristics may be insufficient, and if the value of formula 1 is too large, the lifetime characteristics of the positive electrode active material may deteriorate. 【0050】 The value of Equation 1 allows us to determine the degree of single crystallinity of the single-particle transition metal oxide particles. For example, if the single-particle transition metal oxide particles are single crystals, the value of Equation 1 becomes 0. If the single-particle transition metal oxide particles contain a large amount of crystals and have a low degree of single crystallinity, the value of Equation 1 increases. 【0051】 Furthermore, the lithium transition metal oxide in single-particle form can also satisfy the following equation 2. 【0052】 [Formula 2] The boundary length measured from the EBSD IPF map / the boundary length measured from the EBSD band contrast map ≥ 1.3 【0053】 Equation 2 is the value obtained by dividing the sum of the lengths of strong and weak boundaries measured from the EBSD IPF map by the length of strong boundaries measured from the EBSD BC map. The value of Equation 2 increases as the ratio of the length of weak boundaries, which differ only in atomic arrangement and whose crystallinity has not collapsed, among the interfaces of single-particle transition metal oxides increases. 【0054】 The positive electrode active material of the present invention can satisfy the ratio of the interface length measured from the EBSD IPF map of formula 2 to the interface length measured from the EBSD band contrast map, specifically between 1.3 and 2.5, and more specifically between 1.4 and 2.3. 【0055】 When the value of Equation 2 satisfies the range, excellent capacity and output characteristics can be achieved, and the lifetime characteristics can be appropriately maintained. If the value of Equation 2 is too small, the lifetime characteristics of the positive electrode active material may deteriorate, and if the value of Equation 2 is too large, problems such as increased resistance, decreased capacity, and decreased output of the positive electrode active material may occur. 【0056】 Therefore, when the single-particle lithium transition metal oxide of the present invention satisfies the value of formula 1 and the value of formula 2 satisfies the range, it can exhibit superior capacity and power characteristics. 【0057】 In a positive electrode active material according to an example of the present invention, the particles contained in the positive electrode active material have an average particle size (D 50 The particle size may be 0.1 μm to 10 μm. When the average particle size of the particles contained in the positive electrode active material satisfies the above range, they aggregate to form a single-particle positive electrode active material or a lithium transition metal oxide in single-particle form, which can have advantages in terms of rolling ratio, electrode void, etc. If the average particle size is too small or too large compared to the above range, performance in terms of electrode capacity, lifetime characteristics, resistance, etc. may deteriorate. 【0058】 In a positive electrode active material according to an example of the present invention, the single-particle lithium transition metal oxide may be a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co), and manganese (Mn). 【0059】 Specifically, the lithium transition metal oxide in single-particle form may be a lithium composite transition metal oxide represented by the following chemical formula 1. 【0060】 [Chemical formula 1] Li a Ni b Co c Mn d M 1 e O2 【0061】 In the above chemical formula 1, M 1 is one or more elements selected from the group consisting of Al, B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf, with 0.9 ≤ a ≤ 1.1, 0.6 ≤ b < 1, 0 <c<0.4、0<d<0.4、0≦e<0.1、b+c+d+e=1である。 【0062】 Furthermore, the lithium transition metal oxide may be a lithium composite transition metal oxide represented by the following chemical formula 2 as the positive electrode active material. 【0063】 [Chemical formula 2] Li a Ni b Co c Mn d O2 【0064】 In the above chemical formula 2, 0.9 ≤ a ≤ 1.1, 0.6 ≤ b < 1, 0 <c<0.4、0<d<0.4、b+c+d=1である。 【0065】 The positive electrode active material has an average particle size (D) of 1 to 50 μm, taking into consideration the specific surface area and the density of the positive electrode mixture. 50 ) may have, specifically, an average particle size (D) of 2 to 20 μm. 50 ) may have the above. If the average particle size of the positive electrode active material satisfies the above range, it may have advantages in terms of rolling ratio, electrode void, etc. If the average particle size is too small or too large compared to the above range, performance may deteriorate in terms of electrode capacity, life characteristics, resistance, etc. 【0066】 In one embodiment of the present invention, the positive electrode active material may consist of 2 to 50 particles, 2 to 40 particles, 2 to 30 particles, 2 to 20 particles, 2 to 15 particles, 2 to 10 particles, or 2 to 5 particles. 【0067】 In one example of the present invention, the lithium transition metal oxide particles in single-particle form may be produced by mixing a transition metal oxide precursor with a lithium raw material and performing primary calcination, crushing the calcined product produced by the primary calcination, and then performing secondary calcination. 【0068】 Specifically, the lithium transition metal oxide particles in single-particle form can be produced by a method comprising: (A) mixing a positive electrode active material precursor containing Ni, Co, and Mn with a first lithium-containing raw material to produce a mixture; (B) primary calcining the mixture at a temperature of 800°C to 950°C to produce a primary calcined product; and (C) mixing a second lithium-containing raw material with the primary calcined product and then secondary calcining at a temperature of 680°C to 850°C to produce a secondary calcined product. 【0069】 When the mixture is subjected to primary calcination at a temperature of 800°C to 950°C, the primary particles of the positive electrode active material precursor aggregate to produce a primary calcined product in the form of single particles. Specifically, the primary calcination temperature may be 800°C or higher, 810°C or higher, 820°C or higher, 830°C or higher, 840°C or higher, 850°C or higher, 900°C or lower, 910°C or lower, 920°C or lower, 930°C or lower, 940°C or lower, or 950°C or lower. When the primary calcination temperature is within the above range, the primary particles of the positive electrode active material precursor aggregate to form a primary calcined product in the form of a structurally stable single particle. When the primary calcination temperature is below 800°C, there is a problem that the primary particles do not aggregate sufficiently, and when it is above 950°C, there is a problem that a calcined product is produced that is structurally unstable and has a low degree of crystallinity. 【0070】 The aforementioned primary calcination may be carried out under an oxygen atmosphere in order to prevent the lithium transition metal oxide from degenerating into a rock salt structure. 【0071】 The aforementioned primary firing may be carried out for 3 to 12 hours, specifically for 3 hours or more, 4 hours or more, 5 hours or more, 6 hours or more and 9 hours or less, 10 hours or less, 11 hours or less, or 12 hours or less, in order to aggregate the primary particles and improve the crystallinity of the primary fired product. 【0072】 When the primary-fired product is subjected to secondary firing at a temperature of 680°C to 850°C, lithium is inserted into the primary-fired product to produce a secondary-fired product. Here, the secondary-fired product is a lithium composite transition metal oxide in single-particle form. Specifically, the secondary firing temperature may be 680°C or higher, 700°C or higher, 720°C or higher, 740°C or higher, 760°C or higher, 780°C or higher, 800°C or higher, 840°C or lower, or 850°C or lower. When the secondary firing temperature is within the above range, lithium is inserted into the rock salt structure formed on the surface of the primary-fired product by the high temperature during primary firing, restoring it to a layered structure and reducing lithium byproducts. On the other hand, when the secondary firing temperature is below 680°C, there is a problem that the lithium insertion rate is slow due to the low temperature, and when it is above 850°C, there is a problem that the surface of the primary-fired product degenerates to a rock salt structure due to the high temperature, and lithium byproducts remain. 【0073】 The aforementioned secondary calcination may be carried out under an oxygen atmosphere in order to prevent the lithium transition metal oxide from degenerating into a rock salt structure. 【0074】 The aforementioned secondary firing may be performed for 3 to 12 hours, specifically for 3 hours or more, 4 hours or more, 5 hours or more, 6 hours or more, 9 hours or more but 9 hours or less, 10 hours or less, 11 hours or less, or 12 hours or less, in order to increase the degree of crystallinity of the crystal structure inside the positive electrode active material. 【0075】 Furthermore, the method for producing a positive electrode active material according to the present invention may further include, before step (C), step (B') of crushing the primary calcined product. Step (B') is used to prevent the initial resistance from becoming high by crushing the primary calcined product to an average particle size (D 50 The particles may be ground to a size of 3 μm to 20 μm. 【0076】 Furthermore, the method for producing a positive electrode active material according to the present invention may further include (C') a step of crushing the secondary calcined product. The (C') step may also be used to prevent the initial resistance from becoming high by crushing the secondary calcined product to an average particle size (D 50 The particles may be ground to a size of 3 μm to 20 μm. 【0077】 The grinding in steps (B') and (C') above can be carried out using a pin mill, ACM, jet mill, etc. On the other hand, the pin mill can be used at 18,000 rpm, the ACM can be used with Hosokawa equipment at 6,000 rpm for classification and 12,000 rpm for grinding, and the jet mill can be used with ZM Solution equipment at a grinding pressure of 6 bar and 3,500 rpm for classification. In this case, the desired average particle size (D 50 A positive electrode active material having ) can be easily obtained. 【0078】 The cathode active material according to the present invention is manufactured by a process in which lithium-containing raw material is added in two stages. That is, the lithium-containing raw material is added before the primary calcination and before the secondary calcination, respectively. In this case, lithium is inserted into the rock salt structure formed on the surface, which has the advantage of favoring the recovery to a layered structure. On the other hand, if the lithium-containing raw material is added in one stage before the primary calcination, there is a problem of decreased electrochemical performance due to an increase in lithium byproducts, and if the lithium-containing raw material is not added in the secondary calcination step, a problem arises in which a slow reaction rate, high temperature and long time are required. 【0079】 When the lithium-containing raw material is added in two separate steps, in step (A), the first lithium-containing raw material can be mixed such that the ratio (M:Li) of the total number of moles of transition metal (M) contained in the positive electrode active material precursor to the number of moles of lithium (Li) contained in the first lithium-containing raw material is 1:0.98 or higher, 1:0.99 or higher, 1:1.00 or higher, 1:1.01 or higher, 1:1.02 or higher, 1:1.04 or lower, or 1:1.05 or lower. In step (C), the second lithium-containing raw material can be mixed such that the ratio (M:Li) of the total number of moles of transition metal (M) contained in the positive electrode active material precursor in step (A) to the number of moles of lithium (Li) contained in the second lithium-containing raw material is 1:0.01 or higher, 1:0.05 or lower, 1:0.06 or lower, 1:0.07 or lower, 1:0.08 or lower, 1:0.09 or lower, or 1:0.10 or lower. 【0080】 Furthermore, the present invention provides a lithium transition metal oxide in single-particle form (hereinafter referred to as the first lithium transition metal oxide) with an average particle size (D 50 The present invention provides a cathode active material having a bimodal particle size distribution, further comprising a second lithium transition metal oxide in the form of small single particles. 【0081】 The positive electrode active material having a bimodal particle size distribution contains two lithium transition metal oxides of different sizes, and the second lithium transition metal oxide fills the spaces between the first lithium transition metal oxides. As a result, it has a high rolling density, and the desired electrode thickness can be achieved without applying high pressure. Furthermore, the stress applied to the first lithium transition metal oxide during rolling for electrode manufacturing is dispersed, preventing particle cracking. 【0082】 When the positive electrode active material according to the present invention has a bimodal particle size distribution, the first lithium transition metal oxide has an average particle size (D 50 The average particle size (D) of the first lithium transition metal oxide may be 5 μm to 9 μm. Specifically, the average particle size (D) of the first lithium transition metal oxide may be 5 μm to 9 μm. 50 The particle size may be 5 μm or larger, 5.5 μm or larger, 6 μm or larger, 6.5 μm or larger, 7.5 μm or smaller, 8 μm or smaller, 8.5 μm or smaller, or 9 μm or smaller. Furthermore, the second lithium transition metal oxide may have an average particle size (D 50 The average particle size (D) of the second lithium transition metal oxide may be 1 μm to 4 μm. Specifically, the average particle size (D) of the second lithium transition metal oxide may be 1 μm to 4 μm. 50 ) may be 1 μm or larger, 1.5 μm or larger, 2 μm or larger, 2.5 μm or larger, 2.5 μm or smaller, 3 μm or smaller, 3.5 μm or smaller, or 4 μm or smaller. 【0083】 The average particle size (D) of the first lithium transition metal oxide and the second lithium transition metal oxide. 50 When the range is within the above range, the second lithium transition metal oxide is appropriately distributed among the first lithium transition metal oxides, and excellent packing efficiency can be achieved. 【0084】 The ratio of the average particle size of the first lithium transition metal oxide to the average particle size of the second lithium transition metal oxide may be 2 to 5:1. When the ratio of the average particle size of the first lithium transition metal oxide to the average particle size of the second lithium transition metal oxide is within the above range, there is the advantage of not only excellent packing efficiency but also improved rolling density. 【0085】 According to the present invention, the second lithium transition metal oxide may be a lithium composite transition metal oxide represented by the following chemical formula 3. 【0086】 [Chemical formula 3] Li a3 Ni b3 Co c3 Mn d3 M 3 e3 O2 【0087】 In the above chemical formula 3, M 3 is one or more elements selected from the group consisting of Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P, and S, and 0.9 ≤ a3 ≤ 1.1, 0.6 ≤ b3 < 1, 0 <c3<0.4、0<d3<0.4、0≦e3<0.1、b3+c3+d3+e3=1である。 【0088】 According to the present invention, the weight ratio of the first lithium transition metal oxide to the second lithium transition metal oxide may be 1 to 9:1. When the weight ratio of the first lithium transition metal oxide to the second lithium transition metal oxide is within the above range, the particle packing density can be increased, and as a result, the battery capacity can be increased when applied to a battery. 【0089】 When the positive electrode active material according to the present invention has a bimodal particle size distribution, the positive electrode active material has a press density of 3.50 g / cm³. 2 ~3.90g / cm 2 This may also be the case. Specifically, the rolling density of the positive electrode active material is 3.50 g / cm³. 2 More than 3.55g / cm 2 More than 3.60g / cm 2 More than 3.80g / cm 2 Below, 3.85g / cm 2 Below, 3.90g / cm 2 The following may also apply: If the rolling density of the positive electrode active material is within the above range, the energy density per unit volume may increase. 【0090】 positive electrode According to yet another embodiment of the present invention, a positive electrode containing the above-described positive electrode active material is provided. 【0091】 Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, which contains the positive electrode active material described above. 【0092】 The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., can be used. The positive electrode current collector can usually have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric. 【0093】 The positive electrode active material layer may include a conductive material and a binder, along with the positive electrode active material described above. 【0094】 Here, the conductive material is used to impart conductivity to the electrodes and can be used without particular limitations as long as it does not cause chemical changes in the battery and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or 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. Of these, one or more can be used. The conductive material can usually be included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer. 【0095】 The binder plays a role in improving adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the 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, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one or more can be used. The binder can be contained in an amount of 1% to 30% by weight relative to the total weight of the positive electrode active material layer. 【0096】 The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material described above. Specifically, it can be manufactured by coating the entire positive electrode assembly with a composition for forming a positive electrode active material layer, which is prepared by dissolving or dispersing the positive electrode active material, a binder, and a conductive material selectively in a solvent, followed by drying and rolling. In this case, the types and contents of the positive electrode active material, binder, and conductive material are as described above. 【0097】 The solvent can 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 can be used individually or in mixtures of two or more. The amount of solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into consideration the coating thickness of the slurry and the manufacturing yield, and to have a viscosity that allows for excellent thickness uniformity when applied for the manufacture of the positive electrode. 【0098】 Alternatively, the positive electrode can also be manufactured by casting the positive electrode active material layer forming composition onto another support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector. 【0099】 Lithium-ion battery According to yet another example of the present invention, an electrochemical element including the positive electrode is provided. Specifically, the electrochemical element may be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery. 【0100】 The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and electrolyte interposed between the positive and negative electrodes, wherein the positive electrode is as described above. The lithium secondary battery may also selectively further include a battery container for housing the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container. 【0101】 In the lithium secondary battery described above, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector. 【0102】 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 with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. The negative electrode current collector can usually have a thickness of 3 to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric. 【0103】 The negative electrode active material layer selectively includes a binder and a conductive material together with the negative electrode active material. 【0104】 As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon 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; SiO x (0 < x < 2), metal oxides such as SnO2, vanadium oxides, and lithium vanadium oxides that can be doped and undoped with lithium; or composites containing the metallic compound and the carbonaceous material, such as Si-C composites or Sn-C composites, etc. Any one or a mixture of two or more of these can be used. Also, a thin film of metallic lithium can be used as the negative electrode active material. Further, as the carbon material, both low-crystalline carbon and high-crystalline carbon can be used. Representative examples of low-crystalline carbon are soft carbon and hard carbon, and representative examples of high-crystalline carbon are amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbons such as petroleum or coal tar pitch derived cokes. 【0105】 Also, the binder and the conductive material can be as described for the above positive electrode. 【0106】 The negative electrode active material layer may be manufactured, for example, by coating a negative electrode forming composition, which is prepared by dispersing a negative electrode active material and selectively a binder and a conductive material in a solvent, onto a negative electrode current collector and drying it, or by casting the negative electrode forming composition onto another support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector. 【0107】 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 used in lithium secondary batteries can be used without particular limitations, but those with low resistance to ion movement of the electrolyte and excellent electrolyte impregnation ability are particularly preferred. 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, can be used. Ordinary porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separators containing ceramic components or polymeric substances can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures. 【0108】 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. 【0109】 Specifically, the electrolyte may include an organic solvent and a lithium salt. 【0110】 The organic solvent can be used without particular limitations as long as it serves as a medium through which ions involved in the electrochemical reaction of the battery can move. 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), 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 C2-C20 linear, branched, or cyclic hydrocarbon group, which can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the electrolyte can exhibit excellent performance by mixing the cyclic carbonate and the linear carbonate in a volume ratio of about 1:1 to about 1:9. 【0111】 The lithium salt can be used without particular limitations as long as it is a compound that can provide lithium ions for use in lithium secondary batteries. 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 lithium salt is preferably used within a concentration range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, exhibiting excellent electrolyte performance and allowing lithium ions to move effectively. 【0112】 In addition to the components of the electrolyte, the electrolyte may also contain one or more additives, such as haloalkylene carbonate compounds including difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate 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, for purposes such as improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. In this case, the additive may be present in an amount of 0.1 to 5% by weight relative to the total weight of the electrolyte. 【0113】 As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent discharge capacity, output characteristics, and capacity retention rate stably, making it useful in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs). 【0114】 Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided. 【0115】 The aforementioned battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems. 【0116】 The external shape of the lithium secondary battery of the present invention is not particularly limited, but it can be cylindrical, rectangular, pouch-type, or coin-type, using a can. 【0117】 The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also preferably as a unit battery in medium- and large-sized battery modules containing a large number of battery cells. 【0118】 Examples Hereinafter, embodiments of the present invention will be described in detail so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein. 【0119】 Example 1 Cathode active material precursor [Composition: Ni 0.95 Co 0.03 Mn 0.02 (OH)2, average particle size (D 50 A calcined product is produced by mixing [5.0 μm] with LiOH as a lithium raw material in a molar ratio of 1:1.07, and then performing primary calcination at a temperature of 850°C for 6 hours under an oxygen atmosphere, after which the calcined product is subjected to an average particle size (D 50After grinding to a size of 5.0 μm, the cathode active material was produced in single-particle form by secondary calcination at 750°C for 9 hours under an oxygen atmosphere. 【0120】 Example 2 A single-particle positive electrode active material was produced in the same manner as in Example 1, except that the molar ratio of the positive electrode active material precursor to LiOH was changed to 1:1.05. 【0121】 Example 3 In this example, a single-particle positive electrode active material was produced using the same method as in Example 1, except that the molar ratio of the positive electrode active material precursor to LiOH was changed to 1:1.05 and the temperature during primary calcination was changed to 830°C. 【0122】 Example 4 In the above Example 1, the positive electrode active material precursor was given an average particle size (D 50 A single-particle cathode active material was produced using the same method as in Example 1, except that a 10.0 μm particle was used and the primary calcination time was changed to 9 hours. 【0123】 Example 5 Cathode active material precursor [Composition: Ni 0.60 Co 0.10 Mn 0.30 (OH)2, average particle size (D 50 A calcined product is produced by mixing [4μm] and LiOH as a lithium raw material in a molar ratio of 1:1.05, and then performing primary calcination at a temperature of 950°C for 9 hours in an air atmosphere, after which the calcined product is subjected to an average particle size (D 50 After grinding to a size of 4 μm, the cathode active material was produced in single-particle form by secondary calcination at a temperature of 850°C for 9 hours under an atmospheric environment. 【0124】 Comparative Example 1 In the above Example 1, the positive electrode active material precursor was given an average particle size (D 50 Using 10.0 μm particles, a single-particle form of the positive electrode active material was produced in the same manner as in Example 1, except that the molar ratio of the positive electrode active material precursor to LiOH was changed to 1:1.05 and the primary calcination time was changed to 9 hours. 【0125】 Comparative Example 2 In the above Example 1, the positive electrode active material precursor was given an average particle size (D 50 Using 10.0 μm particles, a single-particle form of the positive electrode active material was produced in the same manner as in Example 1, except that the molar ratio of the positive electrode active material precursor to LiOH was changed to 1:1.03, the temperature during primary calcination was changed to 830°C, and the calcination time was changed to 9 hours. 【0126】 Comparative Example 3 A single-particle positive electrode active material was produced in the same manner as in Example 1, except that the molar ratio of the positive electrode active material precursor to LiOH was changed to 1:1.03. 【0127】 Comparative Example 4 Cathode active material precursor [Composition: Ni 0.60 Co 0.10 Mn 0.30 (OH)2, average particle size (D 50 A calcined product is produced by mixing [4μm] and LiOH as a lithium raw material in a molar ratio of 1:1.07, and then performing primary calcination at a temperature of 980°C for 9 hours under an atmospheric atmosphere, after which the calcined product is given an average particle size (D 50 After grinding to a size of 4 μm, the cathode active material was produced in single-particle form by secondary calcination at a temperature of 880°C for 9 hours under an atmospheric environment. 【0128】 [Table 1] 【0129】 Experimental Example 1: Analysis of Cathode Active Material Cross-sectional samples were prepared by performing Ar ion milling for 2 hours on each of the single-particle positive electrode active materials produced in Examples 1-5 and Comparative Examples 1-4 using an ion milling system (JBOL, IB19520CCP) (acceleration voltage: 6kV). 【0130】 1) For each cross-sectional sample of powdered single-particle cathode active material, an EBSD band contrast map was created using a field emission scanning microscope (SEM, JEOL JSM-7900F w / Oxford symmetry EBSD detector) (acceleration voltage: 20kV). AztecCrystal from OXFORD Instruments was used as the image processing-EBSD quantification analysis software. 【0131】 2) For each cross-sectional sample of the powder-type single-particle cathode active material, the cross-section of the cathode was measured and analyzed using a field emission scanning microscope (SEM, JEOL JSM-7900F w / Oxford symmetry EBSD detector) (acceleration voltage: 20kV). For image processing-EBSD quantification analysis, AztecCrystal from OXFORD Instruments was used to create EBSD IPF maps. 【0132】 3) Using a scanning microscope (SEM, JEOL JSM-7900F), SEM images were taken of the surface of a cross-sectional sample of powdered single-particle cathode active material. 【0133】 Experimental Example 2: Measurement of Interface Length (1) Calculation of interface length using EBSD IPF map Using an EBSD IPF map, we utilized the imageJ program to detect boundaries and obtain boundary images, and then calculated the length of the boundary surface measured from the EBSD IPF map. 【0134】 (2) Calculation of interface length using EBSD band contrast map The interface length was calculated using the same method as in (1) above, with an EBSD band contrast map. 【0135】 (3) Using the SEM image, the interior and exterior of the particle were differentiated and boundary images were obtained using the same method as in (1) above, and the length of the SEM exterior boundary surface was calculated. 【0136】 Experimental Example 3: Evaluation of Electrochemical Properties Manufacturing of positive electrodes and half-cells Using the positive electrode active material produced in Example 1, carbon black (Denka Black, manufactured by Denka) as a conductive material and PVdF (Kureha KF1300, manufactured by Kureha) as a binder were added to a solvent (N-methylpyrrolidone (NMP), manufactured by Oi Chemical Co., Ltd.) in a weight ratio of 97.5:1:1.5 (positive electrode active material: conductive material: binder) to produce a composition for forming a positive electrode active material layer. 【0137】 The manufactured positive electrode active material layer forming composition was coated onto one surface of a 12 μm thick aluminum foil current collector and dried at 135°C for 3 hours to form a positive electrode active material layer. Next, the positive electrode active material layer was rolled using a roll persing method, and after rolling, a positive electrode was manufactured with a porosity of 24% in the positive electrode active material layer. 【0138】 Instead of the positive electrode active material produced in Example 1, positive electrodes were produced in the same manner as described above, using the positive electrode active materials of Examples 2-5 and Comparative Examples 1-4, respectively. 【0139】 A half-cell was manufactured using lithium metal as the negative electrode along with the positive electrode produced as described above. 【0140】 Methods for evaluating electrochemical properties The coin half-cell manufactured as described above was charged at 25°C with a constant current (CC) of 0.2C until it reached 4.25V, then charged with a constant voltage (CV) until the charging current reached 0.05C (cut-off current), and the charging capacity was measured. Next, after being left for 20 minutes, it was discharged with a constant current (CC) of 0.2C until it reached 2.5V, and the discharge capacity of the first cycle was measured. 【0141】 After completing the first cycle, the cell was transferred to a 45°C chamber, and charging and discharging were repeated at 0.33C until the 50th cycle. The discharge capacity at the 50th cycle was measured, and the discharge capacity at the 50th cycle was calculated relative to the discharge capacity at the first cycle to evaluate the capacity retention rate. 【0142】 [Table 2] 【0143】 Figure 1 shows the SEM image, EBSD band contrast map, EBSD IPF map, and IPF interface for Example 1, Figure 2 shows Example 4, and Figure 3 shows the SEM image, EBSD band contrast map, EBSD IPF map, and IPF interface for Comparative Example 3. Referring to Figure 1, in the positive electrode active material of Example 1, the EBSD BC map does not show any interfaces formed inside the positive electrode active material particles, similar to the SEM image, but the EBSD IPF map shows numerous interfaces formed inside the positive electrode active material particles. On the other hand, referring to Figure 2, in contrast to this, in the positive electrode active material of Example 4, interfaces formed inside the positive electrode active material particles that were not observed in the SEM image are observed in the EBSD BC map, and further interfaces not observed in the EBSD BC map are observed in the EBSD IPF map. The interfaces that are not observed in SEM but are observed in the EBSD BC map correspond to strong interfaces formed by the collapse of the layered structure of the NiO layer. The EBSD IPF maps in Figures 1 and 2 reveal additional interfaces that were not observed in the EBSD BC maps. Thus, the interfaces observed only in the EBSD IPF maps correspond to weak interfaces where only the atomic arrangement differs and the crystallinity has not collapsed. 【0144】 On the other hand, referring to Figure 3, in Comparative Example 3, no internal boundary surfaces were observed in the SEM image, EBSD BC map, or EBSD IPF map of the positive electrode active material. This confirmed that neither strong nor weak boundaries were formed inside the particles of the positive electrode active material of Comparative Example 1. 【0145】 Referring to Table 2 above, it can be confirmed that Examples 1 to 4 maintain an appropriate level of 50-cycle life and exhibit superior capacity characteristics compared to Comparative Examples 1 to 3. Furthermore, it can be confirmed that Example 5 also maintains an appropriate level of 50-cycle life and exhibits superior capacity characteristics compared to Comparative Example 4.

Claims

[Claim 1] A positive electrode active material containing a lithium transition metal oxide in single-particle form, The aforementioned single-particle lithium transition metal oxide includes an external interface forming the outer edge of the particle and an internal interface formed within the particle, wherein the external interface and the internal interface satisfy the following formula 1. [Equation 1] Length of internal boundary surface / Length of external boundary surface ≥ 0.4 The length of the internal interface is the length obtained by subtracting the length of the interface measured from the EBSD band contrast map from the length of the interface measured from the electron backscatter diffraction (EBSD)-IPF map for the lithium transition metal oxide particles. The length of the external interface is the length of the external interface of the transition metal oxide particles measured by SEM image segmentation, wherein the positive electrode active material. [Claim 2] The lithium transition metal oxide in single-particle form further satisfies the following formula 2, wherein the positive electrode active material is as described in claim 1. [Equation 2] Interface length measured from EBSD IPF map / Interface length measured from EBSD band contrast map ≥ 1.3 [Claim 3] The cathode active material according to claim 1, wherein the length of the interface measured from the electron backscatter diffraction (EBSD)-IPF map includes the length of a weak interface contained in the single-particle lithium transition metal oxide particle, which differs only in atomic arrangement and has not undergone crystallinity collapse, and the length of a strong interface formed by the collapse of the layered structure. [Claim 4] The cathode active material according to claim 1, wherein the length of the interface measured from the EBSD band contrast map includes the length of the strong interface formed by the collapse of the layered structure contained in the single-particle lithium transition metal oxide particles. [Claim 5] The lithium transition metal oxide in single-particle form comprises 2 to 50 particles, as described in claim 1, for the positive electrode active material. [Claim 6] The positive electrode active material according to claim 1, wherein the lithium transition metal oxide is a lithium composite transition metal oxide containing nickel, cobalt, and manganese. [Claim 7] The positive electrode active material according to claim 1, wherein the lithium transition metal oxide is a lithium composite transition metal oxide represented by the following chemical formula 1. [Chemical formula 1] Li ａ Ni ｂ Co ｃ Mn ｄ M １ ｅ O ２ In the above chemical formula 1, M １ is one or more elements selected from the group consisting of Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P, and S, and satisfies 0.9 ≤ a ≤ 1.1, 0.6 ≤ b < 1, 0 < c < 0.4, 0 < d < 0.4, 0 ≤ e < 0.1, and b + c + d + e = 1. [Claim 8] The positive electrode active material according to claim 1, wherein the lithium transition metal oxide is a lithium composite transition metal oxide represented by the following chemical formula 2. [Chemical formula 2] Li ａ Ni ｂ Co ｃ Mn ｄ O ２ In the above chemical formula 2, 0.9 ≤ a ≤ 1.1, 0.6 ≤ b < 1, 0 < c < 0.4, 0 < d < 0.4, and b + c + d = 1. [Claim 9] From the aforementioned single-particle form of lithium transition metal oxide, the average particle size (D ５０ ) further contains a small single-particle form of a second lithium transition metal oxide, The positive electrode active material according to claim 1, having a bimodal particle size distribution. [Claim 10] The positive electrode active material according to claim 9, wherein the second lithium transition metal oxide is a lithium composite transition metal oxide represented by the following chemical formula 3. [Chemical formula 3] Li ａ３ Ni ｂ３ Co ｃ３ Mn ｄ３ M ３ ｅ３ O ２ In the above chemical formula 3, M ３ is one or more elements selected from the group consisting of Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P, and S, and satisfies 0.9 ≤ a3 ≤ 1.1, 0.6 ≤ b3 < 1, 0 < c3 < 0.4, 0 < d3 < 0.4, 0 ≤ e3 < 0.1, and b3 + c3 + d3 + e3 = 1. [Claim 11] The positive electrode active material according to claim 9, wherein the weight ratio of the lithium transition metal oxide to the second lithium transition metal oxide is 1 to 9:

1. [Claim 12] The rolled density is 3.50 g / cm³. ２ ~3.90 g / cm ２ The positive electrode active material according to claim 9. [Claim 13] A positive electrode comprising the positive electrode active material according to any one of claims 1 to 12. [Claim 14] A lithium secondary battery comprising the positive electrode described in claim 13.

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