Cathode active material, and cathode and lithium secondary battery comprising same

Abstract

The present invention relates to a cathode active material comprising: a lithium composite transition metal oxide in the form of a single particle consisting of one nodule or a pseudo-single particle which is a composite of 30 or fewer nodules; and a coating layer including a first coating layer formed on the surface of the lithium composite transition metal oxide and a second coating layer formed on the surface of the first coating layer, wherein the lithium composite transition metal oxide has a roundness of 0.50-0.68 as defined by equation 1, and the second coating layer includes boron, wherein the boron is included in a weight of 300 ppm to 2400 ppm, based on the total weight of the cathode active material. [Equation 1] Roundness = (4×Area) / (π×R2) In equation 1, R indicates the length of a long axis passing through the center of the lithium composite transition metal oxide, and Area indicates the actual area of the lithium composite transition metal oxide.

Description

Cathode active material, cathode containing the same, and lithium secondary battery Cross-citation with related applications This application claims the benefit of priority to Korean Patent Application No. 10-2023-0188929, filed December 21, 2023, and Korean Patent Application No. 10-2024-0191934, filed December 19, 2024, the entire contents of which are incorporated herein by reference. Technical field The present invention relates to a cathode active material, a cathode comprising the same, and a lithium secondary battery, and more specifically, to a cathode active material that achieves kinetic balance with a silicon-based anode and improves side reactions with an electrolyte, a cathode comprising the same, and a lithium secondary battery. Lithium secondary batteries are generally composed of a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and negative electrode include an active material capable of insertion and deintercalation of lithium ions. Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (such as LiMnO2 or LiMnO4), and lithium iron phosphate compound (LiFePO4) have been used as cathode active materials for lithium secondary batteries. Among these, lithium cobalt oxide has the advantages of high operating voltage and excellent capacity characteristics, but the price of cobalt, which is the raw material, is high and its supply is unstable, making it difficult to commercially apply it to large-capacity batteries. Lithium nickel oxide has poor structural stability, making it difficult to implement sufficient life characteristics. On the other hand, lithium manganese oxide has the problem of 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 only Ni, Co, or Mn, and among these, lithium nickel cobalt manganese oxide containing Ni, Co, and Mn is widely used. Conventional lithium nickel cobalt manganese oxides are generally in the form of spherical secondary particles in which tens to hundreds of primary particles are aggregated. However, in the case of lithium nickel cobalt manganese oxides in the form of secondary particles in which many primary particles are aggregated, there is a problem in that the primary particles are easily broken during the rolling process during the manufacture of the positive electrode, and cracks occur inside the particles during the charge and discharge process. If the positive electrode active material is broken or cracked, the contact area with the electrolyte increases, which increases gas generation and active material degradation due to side reactions with the electrolyte, and this reduces the life characteristics. In addition, in order to achieve high capacity of lithium secondary batteries, it is necessary to apply silicon-based negative electrode active materials to the negative electrode. However, when using silicon-based negative electrode active materials, there is a problem of negative electrode deterioration due to an imbalance in the kinetic balance between the positive and negative electrodes. Meanwhile, techniques have been proposed to improve the life characteristics of lithium nickel cobalt manganese oxide by forming a coating layer on the surface of lithium nickel cobalt manganese oxide to prevent contact with the electrolyte. However, these methods have the problem that the life characteristics improvement effect is not sufficient, and the initial resistance characteristics deteriorate as the coating layer thickness increases. The present invention is intended to solve the above problems, and to provide a cathode active material having excellent life characteristics by controlling the shape of lithium composite transition metal oxide particles in the form of single particles or pseudo-single particles and additionally forming a boron coating layer, and a cathode and lithium secondary battery using the same. [1] The present invention provides a cathode active material comprising a lithium composite transition metal oxide in the form of a single particle consisting of one nodule or a pseudo-single particle consisting of 30 or fewer nodules; and a coating layer comprising a first coating layer formed on the surface of the lithium composite transition metal oxide and a second coating layer formed on the surface of the first coating layer; wherein the lithium composite transition metal oxide has a roundness of 0.50 to 0.68 defined by the following Equation 1, and the second coating layer contains boron, and the content of the boron is 300 ppm to 2400 ppm with respect to the total weight of the cathode active material. [Formula 1] Roundness = (4×Area) / (π×R 2 ) In the above equation 1, R is the length of the major axis passing through the center of the lithium composite transition metal oxide, and Area is the actual area of ​​the lithium composite transition metal oxide. [2] In the above [1], the lithium composite transition metal oxide may have a composition represented by the following chemical formula 1. [Chemical Formula 1] Li 1+x Ni a Co b Mn c Al d M 1 e O2 In the above chemical formula 1, M 1 is at least one selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, Mg, Ta and Nb, and 0≤x≤0.5, 0.8≤a<1.0, 0 <b≤0.1, 0<c<0.2, 0<d≤0.05, 0≤e≤0.05임. [3] In the above [1] or [2], the lithium composite transition metal compound may have a nickel content of 80 mol% or more among the total metals excluding lithium. [4] In at least one of the above [1] to [3], the lithium composite transition metal oxide has an average particle diameter (D 50 ) can be 1㎛ to 8㎛. [5] In at least one of the above [1] to [4], the lithium composite transition metal oxide may have a roundness of 0.58 to 0.65. [6] In at least one of the above [1] to [5], the first coating layer may include at least one selected from the group consisting of Ni, Co, and Al. [7] In at least one of the above [1] to [6], the second coating layer may have a boron content of 400 ppm to 1400 ppm with respect to the total weight of the positive electrode active material. [8] In at least one of the above [1] to [7], the positive electrode active material has a BET surface area of ​​0.4 m 2 / g to 1.0m 2 / g could be. [9] The present invention provides a positive electrode comprising a positive electrode active material according to at least one of [1] to [8].

[0010] The present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte according to the above [9].

[0011] In the above

[0010] , the negative electrode may include a negative electrode active material layer including a silicon-based negative electrode active material.

[0012] In the above

[0011] , the negative electrode may further include a carbon-based negative electrode active material. The cathode active material according to the present invention can reduce its own resistance by controlling the shape of a lithium composite transition metal oxide in the form of a single particle, and achieve excellent lifespan by aligning the kinetic balance with the silicon-based anode. In addition, the cathode active material according to the present invention forms a boron coating layer by forming a lithium composite transition metal oxide in the form of a single particle consisting of one nodule or a pseudo-single particle which is a complex of 30 or fewer nodules, and then firing at high temperature. When high-temperature firing is performed as in the present invention and a boron coating layer is formed, the surface structure of the lithium composite transition metal oxide is improved by high-temperature firing, so that an increase in resistance after the formation of the coating layer can be suppressed, and the side reaction with the electrolyte on the cathode surface can be improved, so that gas generation can be reduced. Figure 1 is a photograph showing the results of SEM-IAM (Scanning Electron Microscope-Image Analysis Management) analysis of the surface and interior of a positive electrode active material manufactured by Example 1. Figure 2 is a photograph showing the results of SEM-IAM (Scanning Electron Microscope-Image Analysis Management) analysis of the surface and interior of the positive electrode active material manufactured by Comparative Example 1. Hereinafter, the present invention will be described in more detail. The terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as having meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to explain his or her own invention in the best manner. In the present invention, “single particle” means a particle composed of one nodule. The above “nodule” refers to a sub-particle unit constituting a single particle or a quasi-single particle, and may be a single crystal without grain boundaries, or a polycrystal with no grain boundaries in appearance when observed under a field of view of 5,000 to 20,000 times using a scanning electron microscope. The above “quasi-single particle” means a complex formed by the aggregation of 30 or fewer, preferably 2 to 30 nodules. In the present invention, “roundness” is the ratio of the actual area of ​​a lithium composite transition metal oxide to the area of ​​a circle whose diameter is the major axis passing through the center of the lithium composite transition metal oxide. The above "roundness" can be measured by extracting an image of a target powder (e.g., lithium composite transition metal oxide) through a Scanning Electron Microscope (SEM) and then identifying the particles through Image Analysis Management (IAM) analysis to measure the roundness of the lithium composite transition metal oxide. In the present invention, "average particle diameter D 50 " means the particle size based on 50% of the volume cumulative particle size distribution of the target powder (e.g., lithium composite transition metal oxide). The average particle diameter D 50 can be measured using a laser diffraction method. For example, after dispersing the target powder in a dispersion medium, it can be measured by introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating it with ultrasonic waves of about 28 kHz with an output of 60 W, obtaining a volume-cumulative particle size distribution graph, and then calculating the particle size corresponding to 50% of the volume-cumulative amount. In the present invention, the “specific surface area” is measured by the BET method, and specifically, can be calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II of BEL Japan. Bipolar active material Hereinafter, the positive electrode active material according to the present invention will be described. The cathode active material according to the present invention comprises (1) a lithium composite transition metal oxide in the form of a single particle or a pseudo-single particle having a circularity of a specific value, and (2) a boron coating layer including a first coating layer formed on the surface of the lithium composite transition metal oxide and a second coating layer formed on the surface of the first coating layer, wherein the boron is contained in an amount of 300 ppm to 2400 ppm based on the total weight of the cathode active material. (1) Lithium complex transition metal oxide The above lithium composite transition metal oxide is a single particle consisting of one nodule or a pseudo-single particle which is a complex of 30 or less, preferably 2 to 30, more preferably 2 to 20 nodules. The lithium composite transition metal oxide particles in the form of single particles or pseudo-single particles have higher particle strength than the existing lithium composite transition metal oxide particles in the form of secondary particles in which tens to hundreds of primary particles are aggregated, and thus particle breakage is less likely to occur during rolling. In addition, in the case of the lithium composite transition metal oxide in the form of single particles or pseudo-single particles according to the present invention, since the number of nodules constituting the particles is small, the change due to volume expansion and contraction of the nodules during charge and discharge is small, and accordingly, the occurrence of cracks inside the particles is also significantly reduced. The above lithium composite transition metal oxide may be, for example, a lithium nickel-based oxide, and specifically, may be a lithium nickel-based oxide containing nickel, cobalt, and manganese, and having a molar ratio of nickel of 50 mol% or more among metals other than lithium. Preferably, the lithium composite transition metal oxide may have a composition represented by the following [chemical formula 1]. [Chemical Formula 1] Li 1+x Ni a Co b Mn c Al d M 1 e O2 In the above chemical formula 1, M 1 M may be at least one selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, Mg, Ta and Nb. 1 Although the element is not essential, when included in an appropriate amount, it can play a role in improving the stability of the crystal structure during sintering. The above 1+x represents the molar ratio of lithium in the lithium composite transition metal oxide, and may be 0≤x≤0.5, preferably 0.05≤x≤0.45, and more preferably 0.1≤x≤0.4. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium composite transition metal oxide particle can be stably formed. The above a represents the molar ratio of nickel among the total metals excluding lithium in the lithium composite transition metal oxide, and may be 0.8≤a<1.0, preferably 0.85≤a<1.0, more preferably 0.9≤a<1.0. When the molar ratio of nickel satisfies the above range, high energy density is exhibited, enabling high capacity implementation. The above b represents the molar ratio of cobalt among all metals excluding lithium in the lithium composite transition metal oxide, and is 0. <b≤0.1, 바람직하게는 0<b≤0.09, 더 바람직하게는 0.01≤b≤0.08일 수 있다. 코발트의 몰비가 상기 범위를 만족할 때, 양호한 저항 특성 및 출력 특성을 구현할 수 있다. The above c represents the molar ratio of manganese among all metals excluding lithium in the lithium composite transition metal oxide, and is 0. <c<0.2, 바람직하게는 0<c≤0.18, 더 바람직하게는 0.02≤c≤0.17일 수 있다. 망간의 몰비가 상기 범위를 만족할 때, 양극 활물질의 구조 안정성이 우수하게 나타날 수 있다. The above d represents the molar ratio of aluminum among the total metals excluding lithium in the lithium composite transition metal oxide, and is 0. <d≤0.05, 바람직하게는 0<d≤0.04, 더 바람직하게는 0<d≤0.03일 수 있다. 알루미늄의 몰비가 상기 범위를 만족할 때, 안정성 및 우수한 출력 특성을 구현할 수 있다. The above e is M of all metals except lithium in the lithium complex transition metal oxide. 1 It represents the molar ratio of elements, and can be 0≤e≤0.05, preferably 0≤e≤0.04, more preferably 0≤e≤0.03. M 1 When the molar ratio of the elements satisfies the above range, the structural stability of the positive electrode active material can be excellent. The above lithium composite transition metal oxide may have a composition in which the nickel content is 80 mol% or more, preferably 82 mol% or more, and more preferably 85 mol% or more, of the total metal excluding lithium. When the nickel content in the lithium composite transition metal oxide satisfies the above range, a high energy density can be realized. The average particle diameter (D) of the above lithium composite transition metal oxide 50 ) may be 1 ㎛ to 8 ㎛, preferably 2 ㎛ to 6 ㎛, more preferably 3 ㎛ to 4 ㎛. The average particle diameter (D 50 ) is too small, the processability of electrode manufacturing is poor, the electrolyte impregnation is poor, and the electrochemical properties may increase, and the average particle diameter (D 50 ) is too large, there is a problem that resistance increases and output characteristics deteriorate. The roundness of the above lithium composite transition metal oxide may be 0.50 to 0.68, preferably 0.55 to 0.66, and more preferably 0.58 to 0.65. When the roundness satisfies the above range, lithium ions can diffuse more smoothly into the interior of the particles, and the contact area between the positive active material and the electrolyte increases, so that the battery chemical performance can be improved. In addition, since the distance between the particles within the electrode is maintained relatively constant, the flow of current within the electrode is smooth, and the particle arrangement is uniform, the mechanical stability is increased, so that the cycle life of the battery can be improved. The average particle diameter above (D 50 ) and a lithium composite transition metal oxide having the above roundness can be manufactured by the following method. The method for manufacturing a cathode active material according to the present invention comprises: 1) a step of mixing a transition metal precursor and a first lithium raw material and then performing a first firing to form a first fired product including a single-particle lithium composite transition metal oxide having single particles composed of 1 to 30 nodules; and 2) a step of performing a second firing on the first fired product to form a second fired product. 1) Step of forming the first plastic product First, the transition metal precursor and the first lithium raw material are mixed and then calcined for the first time to form the first calcined product. At this time, the transition metal precursor may be purchased and used as a commercially available precursor such as nickel-cobalt-manganese hydroxide, or may be manufactured according to a precursor manufacturing method known in the art. Preferably, the transition metal precursor may be a transition metal hydroxide represented by the following chemical formula 2. [Chemical formula 2] Li 1+x1 Ni a1 Co b1 Mn c1 Ald1 M 2 e1 O2 In the above chemical formula 2, M 2 is the same as defined in chemical formula 1. That is, M 2 is at least one selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, Mg, Ta, and Nb. The above 1+x1 represents the molar ratio of lithium in the lithium composite transition metal oxide, and may be 0≤x1≤0.5, preferably 0.05≤x1≤0.45, and more preferably 0.1≤x1≤0.4. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium composite transition metal oxide can be stably formed. The above a1 represents the molar ratio of nickel among the total metals excluding lithium in the lithium composite transition metal oxide, and may be 0.8≤a1<1.0, preferably 0.85≤a1<1.0, more preferably 0.9≤a1<1.0. When the molar ratio of nickel satisfies the above range, high energy density is exhibited, enabling high capacity implementation. The above b1 represents the molar ratio of cobalt among all metals excluding lithium in the lithium composite transition metal oxide, and is 0. <b1≤0.1, 바람직하게는 0<b1≤0.09, 더 바람직하게는 0.01≤b1≤0.08일 수 있다. 코발트의 몰비가 상기 범위를 만족할 때, 양호한 저항 특성 및 출력 특성을 구현할 수 있다. The above c1 represents the molar ratio of manganese among all metals excluding lithium in the lithium composite transition metal oxide, and is 0. <c1<0.2, 바람직하게는 0<c1≤0.18, 더 바람직하게는 0.02≤c1≤0.17일 수 있다. 망간의 몰비가 상기 범위를 만족할 때, 양극 활물질의 구조 안정성이 우수하게 나타날 수 있다. The above d1 represents the molar ratio of aluminum among the total metals excluding lithium in the lithium composite transition metal oxide, and is 0. <d1≤0.05, 바람직하게는 0<d1≤0.04, 더 바람직하게는 0<d1≤0.03일 수 있다. 알루미늄의 몰비가 상기 범위를 만족할 때, 안정성 및 우수한 출력 특성을 구현할 수 있다. The above e1 is M among all metals except lithium in the lithium complex transition metal oxide. 2 It represents the molar ratio of elements, and may be 0≤e1≤0.05, preferably 0≤e1≤0.04, more preferably 0≤e1≤0.03. M 2 When the molar ratio of the elements satisfies the above range, the structural stability of the positive electrode active material can be excellent. The above transition metal precursor can be prepared, for example, by introducing a transition metal aqueous solution and an ammonium cation complex forming and basic compound into a reactor and performing a co-precipitation reaction while stirring. The above transition metal aqueous solution can be prepared by dissolving a transition metal-containing raw material in a solvent such as water, and for example, it can be prepared by dissolving a nickel-containing raw material, a cobalt-containing raw material, or an aluminum raw material in water. In addition, if necessary, the above transition metal aqueous solution can be prepared by dissolving M 2 It may further contain element-containing raw materials. Meanwhile, the above transition metal-containing raw material may be an acetate, carbonate, nitrate, sulfate, halite, sulfide or oxide of the transition metal. M 2 Contains raw materials M 2 It may be an acetate, carbonate, nitrate, sulfate, halite, sulfide or oxide of the element. The input amount of each of the above transition metal-containing raw materials can be determined by considering the molar ratio of the transition metal in the cathode active material to be ultimately produced. Meanwhile, the ammonium cation complex forming agent may include 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. At this time, as the solvent, water or a mixture of water and an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water may be used. The above 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. At this time, as the solvent, water or a mixture of water and an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water may be used. As described above, when a transition metal aqueous solution, an ammonium cation complex forming agent, and a basic compound are placed in a reactor and stirred, the transition metals in the transition metal aqueous solution coprecipitate, generating precursor particles in the form of transition metal hydroxide. At this time, the above transition metal aqueous solution, ammonium cation complex forming agent, and basic compound are added in an amount such that the pH of the reaction solution becomes within the desired range. When the precursor particles are formed in the above manner, the particles are separated from the reaction solution to obtain a transition metal precursor. For example, the reaction solution may be filtered to separate the transition metal precursor from the reaction solution, and then the separated transition metal precursor may be washed and dried to obtain a transition metal precursor. Next, the transition metal precursor and the first lithium raw material are mixed and then first calcined to form a first calcined product including a single particle lithium composite transition metal oxide including 1 to 30 primary particles. At this time, M is added as needed. 2 Element-containing raw materials can be mixed and fired together. As the first lithium raw material, lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide can be used, and for example, Li2CO3, LiNO3, LiNO2, LiOH, LiOHㆍH2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, Li3C6H5O7 or a mixture thereof can be used. Meanwhile, the first sintering is performed under conditions where the primary particles grow to 1 ㎛ or more to form a single-particle lithium composite transition metal oxide. The appropriate first calcination temperature may vary depending on the metal composition in the precursor, and for example, when the nickel content is 80 mol% or more, the first calcination may be performed at a temperature of 750°C to 1000°C, preferably 800°C to 950°C, and more preferably 825°C to 950°C. Additionally, the first firing time may be 6 hours to 30 hours, preferably 8 hours to 25 hours, and more preferably 8 hours to 20 hours. In addition, the first firing can be performed in an oxygen atmosphere. In the present specification, the oxygen atmosphere means an atmosphere including an atmospheric atmosphere and containing oxygen sufficient for firing. In particular, it is preferable to perform the firing in an atmosphere having a higher oxygen partial pressure than an atmospheric atmosphere. When the first sintering is performed under the conditions described above, a single-particle lithium composite transition metal oxide having excellent electrochemical properties can be formed. If the first sintering temperature and time are too small, the primary particles do not grow sufficiently, and a cathode active material in the form of secondary particles is manufactured. If the temperature and time are too large, too much electrically inactive rock-salt phase is formed during the sintering process, and a structurally unstable sintered product with low crystallinity is manufactured, which may result in deterioration of the electrochemical properties. 2) Secondary firing stage The secondary sintering can be performed at a temperature 50°C to 200°C lower than the primary sintering temperature. If the secondary sintering temperature is higher than the primary sintering temperature, an excessive amount of rock salt phase may occur on the surface of the lithium composite transition metal oxide, causing the surface to deteriorate and lithium byproducts to remain, which may deteriorate the electrochemical properties. In addition, if the secondary sintering is performed at a temperature 200°C or lower than the primary sintering temperature, the lithium insertion speed is slowed down, deteriorating the electrochemical performance and having a minimal effect on improving the circularity of the primary particles. For example, the secondary sintering temperature may be 700°C to 900°C, preferably 700°C to 875°C, and more preferably 680°C to 850°C. The above secondary firing time may be, for example, 6 hours to 15 hours, preferably 8 hours to 15 hours, and more preferably 8 hours to 14 hours, in order to increase the crystallinity of the internal crystal structure of the positive electrode active material. Additionally, the secondary firing can be performed in an oxygen atmosphere. When secondary sintering is performed under the conditions described above, a cathode active material having excellent electrochemical properties and the desired primary particle surface shape can be easily formed. (2) Coating layer The cathode active material according to the present invention includes a first coating layer formed on the surface of the lithium composite transition metal oxide and a second coating layer formed on the surface of the first coating layer. The first coating layer may include at least one selected from the group consisting of Ni, Co, and Al, preferably at least one selected from Co and Al, and more preferably Co and Al. By including this, the structural stability and particle strength of the active material can be improved, and the effects of improving high-temperature life characteristics and resistance increase rate can be obtained. Preferably, the first coating layer may include Al2O3 and / or Co3O4 components. Next, the second coating layer contains boron. When the second coating layer contains boron, lithium movement on the surface of the lithium composite transition metal oxide is facilitated, thereby obtaining an effect of improving the initial capacity compared to when the coating layer is not formed. At this time, the boron may be included in a weight of 300 ppm to 2400 ppm, preferably 350 ppm to 2000 ppm, and more preferably 400 ppm to 1400 ppm based on the total weight of the positive electrode active material. If the content of the boron is less than 300 ppm based on the total weight of the positive electrode active material, there is a problem that the amount of gas generated increases and the life characteristics deteriorate, and if it exceeds 2400 ppm, there is a problem that the initial resistance increases and the capacity retention rate decreases. The boron may be included in an amount of 300 ppm to 2400 ppm, preferably 400 ppm to 1400 ppm, and more preferably 1000 ppm to 1400 ppm based on the total weight of the positive electrode active material. When the above range is satisfied, boron reacts with oxygen to form a surface-protective oxide such as B2O3, thereby suppressing side reactions with the electrolyte and reducing the amount of gas generated, and thus the high-temperature life characteristics may be improved. The BET surface area of ​​the above positive electrode active material is 0.4 m 2 / g to 1.0m 2 / g, preferably 0.45m 2 / g to 0.95m 2 / g, more preferably 0.45m 2 / g to 0.9m 2 / g. When the BET surface area satisfies the above range, appropriate electrochemical characteristics can be secured. If the surface area is too small, the electrochemical characteristics may deteriorate as the reaction site decreases, and if it is too large, the reaction area with the electrolyte increases, which may further activate side reactions at high voltage. anode Next, the anode according to the present invention will be described. The positive electrode according to the present invention includes a positive electrode active material layer including the positive electrode active material. Specifically, the positive electrode is formed on a positive electrode current collector and a positive electrode active material layer including the positive electrode active material. In the above positive electrode, the positive electrode collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode collector may typically have a thickness of 3 ㎛ to 500 ㎛, and fine unevenness may be formed on the surface of the positive electrode collector to increase the adhesion of the positive electrode active material. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc. In addition, the positive electrode active material layer may include a conductive material and a binder together with the positive electrode active material described above. The conductive material is used to provide conductivity to the electrode, and can be used without special restrictions as long as it does not cause a chemical change in the battery to be formed and has electronic conductivity. Specific examples thereof 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, summer black, carbon fiber, and carbon nanotube; metal powder or metal fiber 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, and the like. One of these may be used alone or a mixture of two or more may be used. The conductive material may be typically included in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt%, relative to the total weight of the positive electrode active material layer. The above binder serves to improve the adhesion between the positive electrode active material particles and the adhesiveness between the positive electrode active material and the positive electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, 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 may be used alone or a mixture of two or more thereof may be used. The above binder may be included in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt%, based on the total weight of the positive electrode active material layer. The above positive electrode can be manufactured according to a conventional positive electrode manufacturing method. For example, the positive electrode can be manufactured by mixing a positive electrode active material, a binder, and / or a conductive agent in a solvent to manufacture a positive electrode slurry, applying the positive electrode slurry onto a positive electrode current collector, and then drying and rolling. The solvent may be a solvent generally used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity during subsequent coating for manufacturing the positive electrode. Alternatively, the positive electrode may be manufactured by casting the positive electrode slurry onto a separate support, peeling the resulting film from the support, and laminating the resulting film onto a positive electrode current collector. Lithium secondary battery Next, a lithium secondary battery according to the present invention will be described. The lithium secondary battery specifically includes the positive electrode, the negative electrode positioned opposite the positive electrode, and the separator and electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is the same as described above, a detailed description is omitted, and only the remaining components are specifically described below. (1) Cathode The negative electrode according to the present invention includes a negative electrode active material layer including a negative electrode active material, and the negative electrode active material layer may further include a conductive material and / or a binder, if necessary. As the above negative electrode active material, various negative electrode active materials used in the art can be used, for example, silicon-based negative electrode active materials, carbon-based negative electrode active materials, metal alloys, etc. The above negative electrode active material may include a silicon-based negative electrode active material. Since a silicon-based negative electrode active material has a higher theoretical capacity than a carbon-based negative electrode active material and a faster reaction rate with lithium, when a silicon-based negative electrode active material is included in the negative electrode, the energy density and rapid charging performance are improved. However, a silicon-based negative electrode active material has a large irreversible capacity and a large volume expansion during charge and discharge, so it is inferior in terms of life characteristics. In particular, when used in combination with a lithium composite transition metal oxide that generates a lot of gas, there is a problem that the deterioration of life characteristics is further aggravated. However, when a lithium composite transition metal oxide in the form of a single particle or a pseudo-single particle as in the present invention is applied, the gas generation is less than that of a conventional lithium composite transition metal oxide in the form of a secondary particle, so the deterioration of life characteristics can be minimized, and an excess of lithium generated from a rock salt phase during the activation process of the lithium composite transition metal oxide can compensate for the irreversible capacity of the silicon-based negative electrode active material. The above silicon-based negative electrode active material is, for example, Si, SiOw (wherein, 0 <w≤2), Si-C 복합체, Si-M a Alloy(M a It may be at least one selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, Ni) or a combination thereof. Meanwhile, the silicon-based negative electrode active material may be, as needed, M b It can be doped with a metal, and in this case, the M b The metal may be a Group 1 alkali metal element and / or a Group 2 alkaline earth metal element, for example, Li, Mg, etc. Specifically, the silicon negative electrode active material may be M bMetal-doped Si, SiOw (where, 0 <w≤2), Si-C 복합체 등일 수 있다. 금속 도핑된 실리콘계 음극 활물질의 경우, 도핑 원소로 인해 활물질 용량은 저하되나 높은 효율을 갖기 때문에, 높은 에너지 밀도를 구현할 수 있다. In addition, the silicon-based negative electrode active material may further include a carbon coating layer on the particle surface, if necessary. At this time, the amount of carbon coating may be 20 wt% or less, preferably 0.1 wt% to 20 wt%, based on the total weight of the silicon-based negative electrode active material. When the carbon coating is applied, the electrical conductivity of the silicon surface is improved, thereby improving the uniformity of the SEI layer and improving the initial efficiency and life characteristics. The above carbon coating layer can be formed through methods such as dry coating, wet coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD). It is preferable that the above silicon-based negative electrode active material has a capacity of 1000 mAh / g to 4000 mAh / g, preferably 1000 mAh / g to 3800 mAh / g, more preferably 1200 mAh / g to 3800 mAh / g. By using a silicon-based negative electrode active material satisfying the above capacity range, high-capacity characteristics can be realized. The above silicon-based negative electrode active material may have an initial efficiency of 60% to 95%, preferably 70% to 95%, and more preferably 75% to 95%. The initial efficiency of the silicon-based negative electrode active material refers to the percentage of discharge capacity to charge capacity measured by charging and discharging between 0.01 V and 1.5 V at 0.1 C-rate after manufacturing a half-cell using a negative electrode using 100% of the silicon-based negative electrode active material as the negative electrode active material and a lithium counter electrode. When the initial efficiency of the silicon-based negative electrode active material satisfies the above range, lithium provided from the positive electrode can be reversibly used, and excellent rapid charge performance can be implemented. The above negative electrode may further include a carbon-based negative electrode active material as a negative electrode active material. The carbon-based negative electrode active material may be, for example, artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, soft carbon, hard carbon, etc., but is not limited thereto. The above silicon-based negative electrode active material may be included in an amount of 1 wt% to 100 wt%, 1 wt% to 50 wt%, 1 wt% to 30 wt%, 1 wt% to 15 wt%, 10 wt% to 70 wt%, or 10 wt% to 50 wt% based on the total weight of the negative electrode active material. The above carbon-based negative electrode active material may be included in an amount of 0 wt% to 99 wt%, 50 wt% to 99 wt%, 70 wt% to 99 wt%, 85 wt% to 99 wt%, 30 wt% to 90 wt%, or 50 wt% to 90 wt% based on the total weight of the negative electrode active material. The above negative electrode active material may be a mixture of a silicon-based negative electrode active material and a carbon-based negative electrode active material, and at this time, the mixing ratio of the silicon-based negative electrode active material: the carbon-based negative electrode active material may be 1:99 to 50:50 by weight, preferably 3:97 to 30:70. When the mixing ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material satisfies the above range, the capacity characteristics can be improved while the volume expansion of the silicon-based negative electrode active material is suppressed, thereby ensuring excellent cycle performance. The above negative active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the negative active material layer. When the content of the negative active material satisfies the above range, excellent capacity characteristics and electrochemical characteristics can be obtained. Examples of the conductive material include: spherical or flake graphite; carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fibers, single-walled carbon nanotubes, multi-walled carbon nanotubes, and the like; 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, and these may be used alone or in combination of two or more. The conductive material may be included in an amount of 0.1 wt% to 30 wt%, 1 wt% to 20 wt%, or 1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. Preferably, single-walled carbon nanotubes can be used as the conductive material. When single-walled carbon nanotubes are used as the conductive material, a conductive path is evenly formed on the surface of the negative electrode active material, thereby improving the cycle characteristics. Examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylic acid, polyacrylamide, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, 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 may be used alone or a mixture of two or more thereof may be used. The above binder may be included in an amount of 1 wt% to 20 wt%, 2 wt% to 20 wt%, or 2 wt% to 10 wt% based on the total weight of the negative electrode active material layer. The above negative electrode may have a multilayer structure in which the negative electrode active material layer is composed of a single layer or two or more layers. When the negative electrode active material layer is a multilayer structure composed of two or more layers, each layer may have different types and / or contents of the negative electrode active material, binder, and / or conductive material. For example, the negative electrode according to the present invention may have a lower layer formed with a higher content of carbon-based negative electrode active material than the upper layer, and may have a higher content of silicon-based negative electrode active material in the upper layer. In this case, the effect of improving rapid charging performance may be obtained compared to a case in which the negative electrode active material layer is formed with a single layer. (2) Membrane In the above lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. If it is a separator that is usually used in lithium secondary batteries, it can be used without any special restrictions, and in particular, it is preferable that it has low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, can be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. can be used. In addition, a coated separator containing a ceramic component or a polymer material can be used to secure heat resistance or mechanical strength, and can be selectively used in a single-layer or multi-layer structure. (3) Electrolyte In the above lithium secondary battery, the electrolyte may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. that can be used in the manufacture of a lithium secondary battery. Specifically, the electrolyte may include an organic solvent and a lithium salt. As the organic solvent, any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move may be used without particular limitation. Specifically, the organic solvent may 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; Examples of solvents that can be used include carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (wherein R represents a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; and sulfolanes. The above lithium salt can be used without any special limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the anion of the above lithium salt is F - , Cl - , Br - , I -, NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - At least one selected from the group consisting of LiPF6, LiN(FSO2)2, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2 can be used. It is recommended that the concentration of the lithium salt be within the range of 0.1 to 5.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively. In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as, for example, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxy ethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. In this case, the additive may be contained in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the total weight of the electrolyte. Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are intended to illustrate the present invention and the scope of the present invention is not limited to these examples. Examples and Comparative Examples Manufacturing example 1 Average particle diameter (D 50 ) is a transition metal precursor Ni with a thickness of 3.7 μm 0.8 Co 0.09 Mn 0.1 Al 0.01 (OH)2 and LiOH were mixed so that the molar ratio of Ni+Co+Mn+Al:Li was 1:1.03, and Zr(SO4)·4H2O was mixed thereto in an amount of 1000 ppm based on the total weight of the transition metal precursor to prepare a mixture. Then, the mixture was first calcined at 850°C for 18 hours to obtain a first calcined product. Next, a lithium composite transition metal oxide having a circularity as shown in Table 1 was manufactured by secondary firing at 780°C for 10 hours. Manufacturing example 2 Average particle diameter (D 50) was manufactured using the same method as Manufacturing Example 1, except that a transition metal precursor having a diameter of 3.8 μm was used, thereby manufacturing a lithium composite transition metal oxide having a circularity as shown in Table 1 below. Manufacturing example 3 A lithium composite transition metal oxide having the circularity described in Table 1 below was manufactured using the same method as Manufacturing Example 1, except that the first calcination was performed at 900°C for 12 hours and the second calcination was performed at 800°C for 10 hours. Manufacturing example 4 A lithium composite transition metal oxide having the circularity described in Table 1 below was manufactured using the same method as Manufacturing Example 1, except that the first calcination was performed at 800°C for 12 hours and the second calcination was performed at 750°C for 10 hours. Manufacturing Example 1 Manufacturing Example 2 Manufacturing Example 3 Manufacturing Example 4 Circularity 0.60 0.64 0.69 0.49 The above circularity was measured by photographing lithium composite transition metal oxides at 2000x magnification using a scanning electron microscope (SEM), and then obtaining approximately 300 particle images using the Image Analysis Management (IAM) program. Example 1 The lithium composite transition metal oxide of the above Manufacturing Example 1 and Co(OH)2 were mixed at a weight ratio of 100:2 and heat-treated at 700°C for 6 hours to manufacture an intermediate in which a cobalt coating layer was formed as the first coating layer. The above intermediate and H3BO3 were mixed in a weight ratio of 100:0.2 and heat-treated at 400°C for 6 hours to produce a cathode active material having a boron coating layer formed as a second coating layer. The boron content in the positive electrode active material is shown in Table 2 below. Example 2 A cathode active material was manufactured in the same manner as in Example 1, except that the lithium composite transition metal oxide of Manufacturing Example 2 was used and the intermediate and H3BO3 were mixed in a weight ratio of 100:0.1. The boron content in the positive electrode active material is shown in Table 2 below. Comparative Example 1 A positive electrode active material was manufactured in the same manner as in Example 1, except that the process of forming a boron coating layer as the second coating layer was omitted. The boron content in the positive electrode active material is shown in Table 2 below. Comparative Example 2 A cathode active material was prepared in the same manner as in Example 1, except that the above intermediate and H3BO3 were mixed in a weight ratio of 100:0.2. The boron content in the positive electrode active material is shown in Table 2 below. Comparative Example 3 A cathode active material was manufactured in the same manner as in Example 1, except that the lithium composite transition metal oxide of Manufacturing Example 3 was used. The boron content in the positive electrode active material is shown in Table 2 below. Comparative Example 4 A cathode active material was manufactured in the same manner as in Example 1, except that the lithium composite transition metal oxide of Manufacturing Example 4 was used. The boron content in the positive electrode active material is shown in Table 2 below. Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Boron content [ppm] 1300 5000 2500 1300 1300 The content of boron in the positive electrode active materials manufactured according to Examples 1 to 2 and Comparative Examples 1 to 4 was measured by the inductively coupled plasma (ICP) method using an ICP-OES (PerkinElmer, Optima7300DV) device. Experimental Example 1 The positive electrode active materials manufactured in Example 1 and Comparative Example 1 were analyzed using a scanning electron microscope (SEM) to confirm the surface and internal structure of the positive electrode active materials. The measurement results are shown in Figs. 1 and 2. Referring to FIGS. 1 and 2, it can be seen that the cathode active materials manufactured by Example 1 and Comparative Example 1 are made of lithium composite transition metal compound particles in the form of single particles consisting of one nodule or pseudo-single particles consisting of 30 or fewer nodules. Experimental Example 2: Measurement of Gas Emission <Lithium secondary battery manufacturing> The cathode active materials manufactured in Examples 1 to 2 and Comparative Examples 1 to 4: carbon nanotubes: PVDF were mixed in a weight ratio of 95:2:3 in N-methylpyrrolidone to manufacture a cathode slurry. The cathode slurry was applied onto an aluminum current collector sheet, dried, and then rolled to manufacture a cathode. A negative electrode slurry was prepared by mixing a negative electrode active material (SiO2 and graphite) in a weight ratio of 5:95: carbon nanotubes: styrene-butadiene rubber (SBR) in a weight ratio of 95.5:1:3.5 in water. The negative electrode slurry was applied onto a copper current collector sheet, dried, and then rolled to prepare a negative electrode. An electrode assembly was manufactured by interposing a separator between the positive and negative electrodes manufactured as described above, and the electrode assembly was positioned inside a case, and an electrolyte was injected into the case to manufacture a lithium secondary battery. At this time, the electrolyte was prepared by dissolving 1.0 M lithium hexafluorophosphate (LiPF6) in an organic solvent containing ethylene carbonate / ethyl methyl carbonate / diethyl carbonate in a volume ratio of 3:4:4. <Gas Emission Measurement> Each of the lithium secondary batteries manufactured above was charged to SOC 100, and then the lithium secondary batteries were disassembled to separate the positive electrodes. Then, the positive electrode and 400 ㎕ of the electrolyte were placed in a pouch-type battery case and sealed to manufacture a cell, and the cell was stored at 60℃ for 8 weeks, and the cell volume change (△Cell volume, unit: ㎖) before and after high-temperature storage was measured. The cell volume change was measured by placing the cell in water and measuring the change in the volume of water. The measurement results are shown in Table 3 below. Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Gas generation amount [㎕] 0.110.210.350.280.230.35 As shown in Table 3 above, it can be seen that the amount of gas generated by lithium secondary batteries using the positive electrode active materials manufactured according to Examples 1 to 2 of the present invention is less than that by lithium secondary batteries using the positive electrode active materials manufactured according to Comparative Examples 1 to 4. Experimental Example 3: Evaluation of High Temperature Life Characteristics Each lithium secondary battery manufactured above was charged to 4.25 V at 0.5 C and then discharged to 2.5 V at 1 C, which is considered one cycle. After performing 100 charge / discharge cycles, the capacity retention rate and resistance increase rate were measured to evaluate the life characteristics. The measurement results are shown in Table 4 below. At this time, the capacity retention rate and resistance increase rate were calculated using Equations 2 and 3 below. Equation 2: Capacity retention rate (%) = (discharge capacity after 100 cycles / discharge capacity after 1 cycle) × 100 Equation 3: Resistance increase rate (%) = {(resistance after 100 cycles / resistance after 1 cycle) × 100} - 100 Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Capacity retention rate [%] 96.195.087.690.890.091.8 Resistance increase rate [%] 14.818.835.730.328.727.8 As shown in Table 4 above, in the case of lithium secondary batteries using the positive electrode active materials manufactured according to Examples 1 to 2 of the present invention, it can be seen that the capacity retention rate is higher and the resistance increase rate is lower than in the case of lithium secondary batteries using the positive electrode active materials manufactured according to Comparative Examples 1 to 4, and thus the high temperature life characteristics are excellent.

Claims

1. 1 Lithium complex transition metal oxide in the form of single particles or pseudo-single particles consisting of nodules of 30 or less; and A positive electrode active material comprising a coating layer including a first coating layer formed on the surface of the lithium composite transition metal oxide and a second coating layer formed on the surface of the first coating layer; The above lithium composite transition metal oxide has a roundness of 0.50 to 0.68, as defined by the following formula 1: The second coating layer comprises boron, and the boron is contained in a weight of 300 ppm to 2400 ppm based on the total weight of the positive electrode active material: [Formula 1] Roundness = (4×Area) / (π×R 2 ) In the above equation 1, R is the length of the major axis passing through the center of the lithium composite transition metal oxide, and Area is the actual area of ​​the lithium composite transition metal oxide.

2. In claim 1, The above lithium composite transition metal oxide is a cathode active material having a composition represented by the following chemical formula 1. [Chemical Formula 1] Li 1+x Ni a Co b Mr c Al d M 1 e O2 In the above chemical formula 1, M 1 is at least one selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, Mg, Ta and Nb, and 0≤x≤0.5, 0.8≤a<1.0, 0 <b≤0.1, 0<c<0.2, 0<d≤0.05, 0≤e≤0.05임.

3. In claim 1, The above lithium composite transition metal compound is a cathode active material having a nickel content of 80 mol% or more among all metals excluding lithium.

4. In claim 1, The above lithium composite transition metal oxide has an average particle diameter (D 50 ) is a positive electrode active material having a diameter of 1㎛ to 8㎛.

5. In claim 1, The above lithium composite transition metal oxide is a cathode active material having a roundness of 0.58 to 0.

65.

6. In claim 1, A cathode active material, wherein the first coating layer comprises at least one selected from the group consisting of Ni, Co, and Al.

7. In claim 1, The above-mentioned positive electrode active material comprises boron in an amount of 400 ppm to 1400 ppm based on the total weight of the positive electrode active material.

8. In claim 1, The above cathode active material has a BET surface area of ​​0.4 m 2 / g to 1.0m 2 / g is a positive electrode active material.

9. A positive electrode comprising the positive electrode active material of claim 1.

10. A lithium secondary battery comprising a cathode, an anode, a separator interposed between the cathode and the anode, and an electrolyte according to claim 9.

11. In claim 10, A lithium secondary battery, wherein the negative electrode includes a negative electrode active material layer including a silicon-based negative electrode active material.

12. In claim 11, A lithium secondary battery wherein the negative electrode further includes a carbon-based negative electrode active material.

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