Cathode material, manufacturing method therefor, and cathode and lithium secondary battery comprising same

Abstract

The present invention relates to a cathode material and a preparation method therefor, the cathode material comprising: a first cathode active material, which is in the form of a secondary particle obtained by aggregation of a plurality of primary particles, contains nickel, cobalt, and manganese, with 70 mol% or more of nickel among the total metals, and has a first average particle diameter (D50); and a second cathode active material having a second average particle diameter (D50) different from the first average particle diameter (D50), wherein the first cathode active material has an average aspect ratio of 0.86-0.94, which is the arithmetic average value of the aspect ratio defined by Equation 1 below, and an average compactness of 0.89-0.96, which is the arithmetic average value of the compactness defined by Equation 2 below. [Equation 1] Aspect ratio = ra / R; [Equation 2] Compactness) = rc / R. In Equations 1 and 2, R represents the length of the long axis passing through the center of the first cathode active material particle, ra represents is the length of the short axis passing through the center of the first cathode active material particle, and rc represents the diameter of a circle having the same area as the area of the first cathode active material.

Description

Cathode material, method for manufacturing same, cathode and lithium secondary battery containing same Cross-citation with related applications This application claims the benefit of priority to Korean Patent Application No. 10-2023-0169313, filed on November 29, 2023, and Korean Patent Application No. 10-2024-0166750, filed on November 20, 2024, the entire contents of which are incorporated herein by reference. Technical field The present invention relates to a cathode material, a method for manufacturing the same, a cathode comprising the same, and a lithium secondary battery, and more specifically, to a first cathode active material in which the average aspect ratio and average density of secondary particles are controlled to have specific values, and an average particle diameter (D) different from that of the first cathode active material. 50 ) and a second cathode active material, a method for manufacturing the same, a cathode including the cathode material, and a lithium secondary battery including the cathode. 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 (LiCoO) is used as a cathode material for lithium secondary batteries. 2 ), lithium nickel oxide (LiNiO 2 ), lithium manganese oxide (LiMnO 2 or LiMnO 4 etc.), lithium iron phosphate compound (LiFePO 4) have been used. 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 excellent stability but has the problem of 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 oxides containing Ni, Co, and Mn are widely used in the field of electric vehicle batteries. Meanwhile, the cathode material composed of lithium nickel cobalt manganese oxide continuously experiences side reactions at the interface with the electrolyte during the charge / discharge process, which generates oxidation gas. The gas thus generated causes problems such as swelling and gas traps in the battery, which reduces the high-temperature storage performance of the battery. Therefore, there is a need for the development of a cathode material capable of reducing the amount of gas generated by the lithium nickel cobalt manganese oxide. The present invention is to solve the above problems, and comprises a first cathode active material having a superior lifespan characteristic compared to the prior art by controlling the particle shape to reduce gas generation, and an average particle diameter (D) different from that of the first cathode active material. 50 ) and a second cathode active material, a method for manufacturing the same, a cathode including the cathode material, and a lithium secondary battery including the cathode. [1] The present invention is a secondary particle form in which a plurality of primary particles are aggregated, and comprises nickel, cobalt and manganese, and contains nickel in an amount of 70 mol% or more of the total metal, and has a first average particle diameter (D 50) and the first average particle diameter (D 50 ) and a second average particle diameter (D) different from 50 ) includes a second cathode active material, wherein the first cathode active material has an average aspect ratio, which is an arithmetic mean value of aspect ratio defined by Equation 1 below, of 0.86 to 0.94, and an average compactness, which is an arithmetic mean value of compactness defined by Equation 2 below, of 0.89 to 0.96. [Formula 1] Aspect ratio = r a / R [Formula 2] Compactness = r c / R In the above formulas 1 and 2, R is the length of the major axis passing through the center of the first positive electrode active material particle, and r a is the length of the short axis passing through the center of the first positive electrode active material particle, and r c is the diameter of a circle having an area equal to the area of ​​the first positive electrode active material. [2] The present invention provides a cathode material in the above [1], wherein the first cathode active material has an average roundness of 0.79 to 0.88, which is an arithmetic mean value of the roundness defined by the following Equation 3. [Formula 3] Roundness = [(4 × Area) / (π × R 2 )] In the above equation 3, R is the length of the major axis passing through the center of the first positive electrode active material particle, and Area is the actual area of ​​the first positive electrode active material particle. [3] The present invention provides a cathode material according to [1] or [2], wherein the first cathode active material has a composition represented by the following chemical formula 1. [Chemical Formula 1] Li x1Ni a1 Co b1 Mn c1 M 1 d1 O 2 In the above chemical formula 1, M 1 may be at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 1≤x1≤1.1, 0.6≤a1≤1.0, 0≤b1≤0.3, 0≤c1≤0.3, 0≤d1<0.15. [4] The present invention provides a cathode material in which, in at least one of the above [1] to [3], the average aspect ratio of the first cathode active material is 0.90 to 0.94. [5] The present invention provides a cathode material, wherein, in at least one of the above [1] to [4], the average density of the first cathode active material is 0.90 to 0.95. [6] The present invention provides a cathode material, wherein, in at least one of the above [1] to [5], the average circularity of the first cathode active material is 0.82 to 0.88. [7] The present invention, in at least one of the above [1] to [6], the first average particle diameter (D) of the first positive electrode active material 50 ) provides a cathode material having a diameter of 8 μm to 20 μm. [8] The present invention, in at least one of the above [1] to [7], the second average particle diameter (D) of the second positive electrode active material 50 ) provides a cathode material having a diameter of 2 μm to 8 μm. [9] The present invention, in at least one of the above [1] to [8], the first average particle diameter (D) of the first positive electrode active material 50 ) and the second average particle diameter (D) of the second positive electrode active material 50 ) provides a cathode material having a ratio of 2:1 to 8:1.

[0010] The present invention provides a cathode material, wherein in at least one of the above [1] to [9], the weight ratio of the first cathode active material and the second cathode active material is 50:50 to 90:10.

[0011] The present invention provides a cathode material, wherein in at least one of the above [1] to

[0010] , the second cathode active material has a composition represented by the following chemical formula 2. [Chemical formula 2] Li x2 Ni a2 Co b2 Mn c2 M 2 d2 O 2 In the above chemical formula 2, M 2 may be at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 1≤x2≤1.1, 0.6≤a2≤1.0, 0≤b2≤0.3, 0≤c2≤0.3, 0≤d2<0.15.

[0012] The present invention comprises the steps of: introducing a transition metal aqueous solution, a basic compound, and an ammonium cation complex forming agent into a reactor, mixing the mixture at a stirring speed of 900 rpm to 1100 rpm while maintaining the pH in the reactor at 11 or higher; mixing the precursor for the first cathode active material and a lithium raw material; and heat-treating the mixture at a temperature of 850° C. to 1000° C. to obtain a first average particle diameter (D 50 ) and a step of preparing a first cathode active material having the first cathode active material and the first average particle diameter (D 50 ) and a second average particle diameter (D) different from 50) comprising a step of mixing a second cathode active material, wherein the first cathode active material is in the form of secondary particles in which a plurality of primary particles are aggregated, and includes nickel, cobalt, and manganese, and contains nickel in an amount of 70 mol% or more of the total metal, and the first cathode active material has an average aspect ratio, which is an arithmetic mean value of an aspect ratio defined by the following Equation 1, of 0.86 to 0.94, and an average compactness, which is an arithmetic mean value of a compactness defined by the following Equation 2, of 0.89 to 0.96. [Formula 1] Aspect ratio = r a / R [Formula 2] Compactness = r c / R In the above formulas 1 and 2, R is the length of the major axis passing through the center of the first positive electrode active material particle, and r a is the length of the short axis passing through the center of the first positive electrode active material particle, and r c is the diameter of a circle having an area equal to the area of ​​the first positive electrode active material.

[0013] The present invention provides a method for manufacturing a cathode material, wherein, in the above

[0012] , the first cathode active material has an average roundness of 0.79 to 0.88, which is an arithmetic mean value of the roundness defined by the following Equation 3. [Formula 3] Roundness = [(4 × Area) / (π × R 2 )] In the above equation 3, R is the length of the major axis passing through the center of the first positive electrode active material particle, and Area is the actual area of ​​the first positive electrode active material particle.

[0014] The present invention provides a cathode comprising at least one cathode material among [1] to

[0011] .

[0015] The present invention provides a lithium secondary battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte according to the above

[0014] . The cathode active material according to the present invention has an average aspect ratio of 0.86 to 0.94 and an average density of 0.89 to 0.96, thereby minimizing the contact area with the electrolyte and reducing gas generation due to side reactions with the electrolyte. In addition, the cathode material according to the present invention has an average particle diameter (D) different from the cathode active material and the cathode active material. 50 ) can be mixed with other positive electrode active materials to improve the life characteristics. The effects according to the present invention are not limited to those exemplified above, and further diverse effects are included in the present specification. Hereinafter, the present invention will be described in 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 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. The terminology used herein is for the purpose of describing embodiments only and is not intended to limit the invention. In this specification, the singular also includes the plural unless specifically stated otherwise. The terms "comprises" and / or "comprising" as used herein do not exclude the presence or addition of one or more other components in addition to the components mentioned. In the present invention, a primary particle means a particle unit that has no apparent grain boundary when observed at a magnification of 5,000 to 20,000 times using a scanning electron microscope. In the present invention, a secondary particle means a particle formed by agglomeration of tens to hundreds of primary particles. More specifically, a secondary particle is an aggregate of 50 or more primary particles. In the present invention, the average aspect ratio is an arithmetic mean value of the aspect ratio, and the aspect ratio is the ratio of the length of the short axis passing through the center of the positive electrode active material particle to the length of the long axis passing through the center of the positive electrode active material particle. In the present invention, the average compactness is an arithmetic mean value of compactness, and compactness is the ratio of the diameter of a circle having the same area as the area of ​​the positive electrode active material to the length of the major axis passing through the center of the positive electrode active material particles. In the present invention, the average roundness is an arithmetic mean value of roundness, and the roundness is the ratio of the actual area of ​​the positive electrode active material to the area of ​​a circle whose diameter is the major axis passing through the center of the positive electrode active material particles. In the present invention, the average aspect ratio and average circularity can be measured by photographing the positive electrode active material by photographing the particles at 800x magnification using a scanning electron microscope (SEM, Hitachi S-4800), obtaining about 300 particle images, and then deriving the aspect ratio and circularity from the scanning electron microscope images using an image analysis program such as Image J and calculating the average. In the present invention, the average density can be measured by taking pictures of the positive electrode active material by photographing the particles at 2000x magnification using a scanning electron microscope (SEM, Hitachi S-4800), obtaining about 100 images, deriving the density from the scanning electron microscope images using an image analysis program such as Image J, and calculating the average. In the present invention, the average particle diameter (D 50 ) means the particle size at the 50% point of the volume cumulative distribution according to particle size. The average particle size (D50 ) can be measured by dispersing the target powder (e.g., positive electrode active material) in a dispersion medium, introducing it into a commercially available laser diffraction particle size measuring device (e.g., S3500 from Microtrac), transmitting a laser beam therethrough, measuring the difference in diffraction patterns according to particle size, calculating the particle size distribution, and calculating the particle diameter at the point where it becomes 50% of the volume cumulative distribution according to particle size. Bipolar material First, the cathode material according to the present invention will be described. The cathode material according to the present invention is in the form of secondary particles in which a plurality of primary particles are aggregated, contains nickel, cobalt and manganese, contains nickel in an amount of 70 mol% or more among the total metals, and has a first average particle diameter (D) in which the average aspect ratio, average density and average roundness satisfy specific value ranges. 50 ) and the first average particle diameter (D 50 ) and a second average particle diameter (D) different from 50 ) includes a second positive electrode active material. The above cathode material has an average particle diameter (D) of the first cathode active material 50 ) is the average particle diameter (D) of the second cathode active material. 50 ) can have a bimodal particle size distribution larger than that of the first cathode active material. When the cathode active material has a bimodal particle size distribution, a high electrode density can be realized, and thus, battery capacity characteristics can be improved. In the case of the second cathode active material, the average particle diameter (D 50 ) increases, the lithium diffusion path within the particle becomes longer, which may result in a decrease in resistance and output characteristics. Therefore, the average particle diameter (D) of the first cathode active material in the form of secondary particles 50 ) is the average particle diameter (D) of the second cathode active material. 50 ) is larger, it is desirable to implement high electrode density while minimizing the degradation of resistance and output characteristics. Specifically, the average particle diameter (D) of the first positive electrode active material 50) may be 8 ㎛ to 20 ㎛, preferably 8 ㎛ to 17 ㎛, more preferably 9 ㎛ to 15 ㎛, and the average particle diameter (D) of the second positive electrode active material 50 ) may be 2 μm to 8 μm, preferably 2 μm to 7 μm, more preferably 2 μm to 6 μm. The average particle diameter (D) of the first positive electrode active material and the second positive electrode active material 50 ) is too small, slurry agglomeration occurs, making electrode manufacturing difficult, electrolyte impregnation is poor, and electrochemical properties deteriorate, and the average particle diameter (D 50 ) is too large, there is a problem that the resistance increases and the output characteristics deteriorate. The average particle diameter (D) of the first positive electrode active material and the second positive electrode active material 50 ) when the above range is satisfied, the capacity characteristics, resistance characteristics and output characteristics are more excellent. In addition, the average particle diameter (D) of the first positive electrode active material and the second positive electrode active material 50 ) may be 2:1 to 8:1, more preferably 2:1 to 6:1, and even more preferably 2:1 to 4:1. The average particle diameter (D) of the first positive electrode active material and the second positive electrode active material 50 ) By satisfying the above range, the voids between the positive electrode active material particles can be more effectively reduced, the packing density can be increased, and the pressure applied according to the particle size can be optimized to reduce particle breakage during rolling, and the capacity per volume of the positive electrode can be effectively improved. Meanwhile, the first positive electrode active material and the second positive electrode active material may be mixed in a weight ratio of 50:50 to 90:10, preferably in a weight ratio of 60:40 to 90:10, more preferably in a weight ratio of 60:40 to 80:20. By mixing and using the large-particle first positive electrode active material and the small-particle second positive electrode active material within the above range, the energy density of the positive electrode can be increased, the pressure applied according to the particle size can be optimized to reduce particle breakage during rolling, and high capacity and excellent thermal stability can be secured, and side reactions with the electrolyte can be suppressed. Next, the first cathode active material and the second cathode active material constituting the cathode material of the present invention will be described in more detail. (1) First positive electrode active material The above first cathode active material is a lithium composite transition metal oxide containing nickel, cobalt, and manganese, i.e., an NCM-based lithium composite transition metal oxide. The lithium composite transition metal oxide may have a nickel content of 70 mol% or more among the total metals, and more preferably, may have a nickel content of 80 mol% or more among the total transition metals of the lithium composite transition metal oxide. By satisfying a nickel content of 70 mol% or more among the total transition metals of the lithium composite transition metal oxide, it is possible to secure a high capacity. Specifically, the first positive electrode active material may include lithium composite transition metal oxide particles represented by the following chemical formula 1. [Chemical Formula 1] Li x1 Ni a1 Co b1 Mn c1 M 1 d1 O 2 In the above chemical formula 1, M 1 M may be at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr and Zr. 1Although it is not essential, if included in an appropriate amount, it can play a role in improving the stability of the crystal structure during sintering. Meanwhile, the above x1 represents a lithium molar ratio in the lithium composite transition metal oxide particles, and may be 1.0≤x1≤1.1, preferably 1.00≤x1≤1.09, and more preferably 1.00≤x1≤1.07. When the lithium molar ratio satisfies the above range, the crystal structure of the lithium composite transition metal oxide particles 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 particles, and may be 0.6≤a1≤1.0, preferably 0.65≤a1≤1.0, more preferably 0.7≤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 the total metals excluding lithium in the lithium composite transition metal oxide particles, and may be 0≤b1≤0.3, preferably 0≤b1≤0.25, and more preferably 0≤b1≤0.2. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be implemented. The above c1 represents the molar ratio of manganese among the total metals excluding lithium in the lithium composite transition metal oxide particles, and may be 0≤c1≤0.3, preferably 0≤c1≤0.25, and more preferably 0≤c1≤0.2. When the molar ratio of manganese satisfies the above range, the structural stability of the positive electrode active material may be excellent. The above d1 is M among all metals except lithium in the lithium composite transition metal oxide particles. 1 It represents the molar ratio of M, and may be 0≤d1≤0.15, preferably 0≤d1≤0.1, more preferably 0≤d1≤0.07. 1When the molar ratio satisfies the above range, the structural stability of the positive electrode active material can be excellent. The average aspect ratio of the first positive electrode active material may be 0.86 to 0.94, preferably 0.90 to 0.94, and more preferably 0.93 to 0.94. When the average aspect ratio of the first positive electrode active material is less than 0.86, the contact between particles is not good, which may result in reduced lithium mobility, and when the average aspect ratio is greater than 0.94, the diffusion distance of lithium ions within the particles may increase, which may result in reduced electrochemical performance, and the distance between particles may become longer, which may hinder lithium ion diffusion within the electrode. The average density of the first positive electrode active material may be 0.89 to 0.96, preferably 0.90 to 0.95, and more preferably 0.91 to 0.94. When the average density of the first positive electrode active material is less than 0.89, the contact between particles is not good, so that lithium mobility is reduced and particle breakage increases during the rolling process, and when it exceeds 0.96, the contact between particles may be favorable, but the size of fine particles generated when particle breakage occurs is small, which may ultimately aggravate particle breakage. Specifically, the first positive electrode active material according to the present invention is characterized by satisfying both the range of the above average aspect ratio and the range of the above average density. Even if the average aspect ratio of the first positive electrode active material satisfies a value of 0.86 to 0.94, if the average density is less than 0.89, the shape of the first positive electrode active material becomes irregular and structurally loose, so that fine particles are separated and fallen off under external pressure or during the charge / discharge process, which may generate fine dust and deteriorate the performance of the electrode. In addition, since the electrolyte excessively penetrates into the empty space between the positive electrode materials and promotes side reactions, the amount of gas generation may increase. In addition, even if the average aspect ratio of the first positive electrode active material satisfies a value of 0.86 to 0.94, if the average density exceeds 0.96, the bonding between the primary particles may be too dense and may easily break due to friction between them during the charge / discharge process, which may generate fine dust. In addition, since the average density is too high, the electrolyte may not penetrate uniformly, so that some particles may excessively react with the electrolyte, which may increase the amount of gas generation inside the electrode. In addition, even if the average density of the first positive electrode active material satisfies a value of 0.89 to 0.96, if the average aspect ratio is less than 0.86, it means that the first positive electrode active material is flat or irregularly shaped, and in this case, there is a problem that the first positive electrode active material is sensitive to pressure and is likely to break during the charge / discharge cycle, resulting in fine particles. In addition, even if the average density of the first positive electrode active material satisfies a value of 0.89 to 0.96, if the average aspect ratio is greater than 0.94, it means that the first positive electrode active material is excessively spherical, and in this case, the empty space between the first positive electrode active materials becomes relatively large, so that the density within the electrode decreases, and electrolyte decomposition may be promoted only in some areas during charge / discharge. Therefore, this increases the amount of internal gas generated, which causes a problem of shortening the life of the battery. The average circularity of the first positive electrode active material may be 0.79 to 0.88, preferably 0.82 to 0.88, and more preferably 0.86 to 0.88. When the average circularity of the first positive electrode active material satisfies the above range, lithium ions can diffuse more smoothly into the interior of the particles, and the contact area between the first positive electrode 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 is improved. When the average circularity of the first positive electrode active material is less than 0.79, the friction between single particles increases, and at the same time, the distribution of the first positive electrode active material within the electrode becomes uneven, so that the capacity and life characteristics of the battery may be deteriorated, and when the average circularity exceeds 0.88, there is a problem that the amount of fine powder generated during rolling may increase. (2) Second positive electrode active material The second positive electrode active material may have the same composition as or different from the first positive electrode active material. For example, the second positive electrode active material may include a lithium transition metal oxide represented by the following chemical formula 2. [Chemical formula 2] Li x2 Ni a2 Co b2 Mn c2 M 2 d2 O 2 In the above chemical formula 2, M 2 M may be at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr and Zr. 2 Although not essential, if included in an appropriate amount, it can play a role in improving the stability of the crystal structure during sintering. Meanwhile, the above x2 represents a lithium molar ratio in the lithium composite transition metal oxide particles, and may be 1.0≤x2≤1.1, preferably 1.00≤x2≤1.09, and more preferably 1.00≤x2≤1.07. When the lithium molar ratio satisfies the above range, the crystal structure of the lithium composite transition metal oxide particles can be stably formed. The above a2 represents the molar ratio of nickel among the total metals excluding lithium in the lithium composite transition metal oxide particles, and may be 0.6≤a2≤1.0, preferably 0.65≤a2≤1.0, more preferably 0.7≤a2≤1.0. When the molar ratio of nickel satisfies the above range, high energy density is exhibited, enabling high capacity implementation. The above b2 represents the molar ratio of cobalt among the total metals excluding lithium in the lithium composite transition metal oxide particles, and may be 0≤b2≤0.3, preferably 0≤b2≤0.25, and more preferably 0≤b2≤0.2. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be implemented. The above c2 represents the molar ratio of manganese among the total metals excluding lithium in the lithium composite transition metal oxide particles, and may be 0≤c2≤0.3, preferably 0≤c2≤0.25, and more preferably 0≤c2≤0.2. When the molar ratio of manganese satisfies the above range, the structural stability of the positive electrode active material may be excellent. The above d2 is M among all metals except lithium in the lithium composite transition metal oxide particles. 2 It represents the molar ratio of M, and may be 0≤d2≤0.15, preferably 0≤d2≤0.1, more preferably 0≤d2≤0.07. 2 When the molar ratio satisfies the above range, the structural stability of the positive electrode active material can be excellent. Method for manufacturing cathode material Next, a method for manufacturing a cathode material according to the present invention is described. The cathode material according to the present invention comprises the first cathode active material and the first average particle diameter (D 50 ) and a second average particle diameter (D) different from 50 ) is manufactured by mixing a second positive electrode active material having a first electrode active material and a second positive electrode active material having a second electrode active material. Specifically, the first cathode active material is manufactured by a step of manufacturing a precursor for the first cathode active material by introducing a transition metal aqueous solution, a basic compound, and an ammonium cation complex forming agent into a reactor, mixing the mixture at a stirring speed of 900 rpm to 1100 rpm while maintaining the pH within the reactor at 11 or higher, and then a step of mixing the precursor for the first cathode active material and a lithium raw material and performing a heat treatment at a temperature of 850° C. to 1000° C. The above transition metal aqueous solution can be prepared by dissolving a transition metal raw material in a solvent such as water, and for example, can be prepared by dissolving a nickel raw material, a cobalt raw material, and a manganese raw material in water. Meanwhile, the above transition metal raw material may be an acetate, carbonate, nitrate, sulfate, halite, sulfide or oxide of the transition metal. Specifically, the nickel raw material is, for example, NiO, NiCO. 3 ·2Ni(OH) 2 ·4H 2 O, NiC 2 O 2 ·2H 2 O, Ni(NO 3 ) 2 ·6H 2 O, NiSO 4 , NiSO 4 ·6H 2 O, nickel halides or combinations thereof, but are not limited thereto. The above cobalt raw material is, for example, CoSO 4,　 Co(OCOCH 3 ) 2 ㆍ4H2 O, Co(NO 3 ) 2 ㆍ6H 2 O, CoSO 4 ㆍ7H 2 O or a combination thereof, but is not limited thereto. The above manganese raw material is, for example, Mn 2 O 3 , MnO 2 , Mn 3 O 4 MnCO 3 , Mn(NO 3 ) 2 , MnSO 4　 ㆍH 2 O, manganese acetate, manganese halide, or a combination thereof, but is not limited thereto. The above basic compounds are NaOH, KOH, and Ca(OH). 2 It may be at least one compound selected from the group consisting of, 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 ammonium cation complex forming agent is NH 4 OH, (NH 4 ) 2 SO 4 , NH 4 NO 3 , NH 4 Cl, CH 3 COONH 4 , and NH 4 CO 3 It may include at least one compound selected from the group consisting of, 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. In addition, the concentration of the ammonium cation complex is preferably 9000 ppm or more based on the total weight of the precursor for the first positive electrode active material. As the amount of ammonium cation complex added increases, the BET specific surface area of ​​the precursor increases, and as a result, the primary particles of the positive electrode material may become smaller during sintering, and as the primary particles become smaller, the density tends to increase. At this time, the above transition metal aqueous solution, the basic compound, and the ammonium cation complex forming agent are added in an amount such that the pH of the reaction solution becomes within the desired range. In the present invention, the pH within the reactor is maintained at 11 or higher. When the pH range is satisfied, the particle size decreases during precursor synthesis, and when grown to the same size, the aspect ratio and circularity tend to improve. In addition, the reactor is mixed at a stirring speed of 900 rpm to 1100 rpm. If mixed at a stirring speed of less than 900 rpm, the mixture is not uniformly mixed, so that the average aspect ratio and average density of the final first positive electrode active material are low, and there is a problem that the mixture is easily broken during the charge / discharge cycle and fine powder is generated. If mixed at a stirring speed exceeding 1100 rpm, the empty space between the final first positive electrode active materials becomes large, so that the electrolyte does not react uniformly, which may increase the amount of internal gas generation. As described above, when a transition metal aqueous solution, a basic compound, and an ammonium cation complex forming agent are added to a reactor and stirred, the transition metals in the transition metal aqueous solution coprecipitate, thereby generating a precursor for a first cathode active material in the form of a transition metal hydroxide. The precursor for the first positive electrode active material and the lithium raw material manufactured above are mixed by heat-treating at a temperature of 850°C to 1000°C, preferably 850°C to 950°C, and more preferably 870°C to 930°C. Since the first positive electrode active material according to the present invention has a nickel (Ni) content of 70 mol% or more, if it is heat-treated at a temperature lower than 850°C, there is a problem that the crystal structure of the active material is not sufficiently stabilized, so that oxygen vacancies inside increase, causing oxygen to be desorbed and reacting with the electrolyte to generate gas, and if it is heat-treated at a temperature higher than 1000°C, the particles grow excessively, causing a decrease in the specific surface area, which leads to a decrease in the reaction area with the electrolyte, resulting in a problem that the life characteristics are deteriorated. Additionally, the heat treatment can be performed for 10 to 24 hours, preferably 12 to 20 hours, more preferably 15 to 20 hours. In addition, the heat treatment can be performed in an oxygen atmosphere. In the present specification, an oxygen atmosphere means an atmosphere including an atmospheric atmosphere and containing oxygen sufficient for sintering. In particular, it is preferable to perform the heat treatment in an atmosphere having a higher oxygen partial pressure than an atmospheric atmosphere. When sintering is performed under the conditions described above, a first cathode active material having excellent electrochemical properties can be formed. As the above lithium raw material, lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide can be used, for example, LiOH, Li 2 CO 3 , LiNO 3 , LiNO 2 , LiOHㆍH 2 O, LiH, LiF, LiCl, LiBr, LiI, CH 3 COOLi, Li 2 O, Li 2 SO 4 , Li 3C 6 H 5 O 7 Or mixtures of these may be used. The precursor for the first positive electrode active material and the lithium raw material can be mixed so that the molar ratio of Li: (Ni+Co+Mn) is 1:1 to 1.1:1, preferably 1.01:1 to 1.09:1, more preferably 1.03:1 to 1.07:1. When the above range is satisfied, the layered crystal structure of the positive electrode active material is well developed, so that a positive electrode active material having excellent electrochemical performance can be manufactured. The above first positive electrode active material and the above second positive electrode active material can be mixed in a weight ratio of 50:50 to 90:10. By mixing and using the first positive electrode active material, which is a large particle, and the second positive electrode active material, which is a small particle, within the above range, the energy density of the positive electrode can be increased, the pressure applied according to the particle size can be optimized to reduce particle breakage during rolling, high capacity and excellent thermal stability can be secured, and side reactions with the electrolyte can be suppressed. anode Next, the anode according to the present invention will be described. The positive electrode according to the present invention includes the positive electrode material. The above positive electrode includes a positive electrode current collector, and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, and the positive electrode active material layer includes the positive electrode material. Since the positive electrode material is the same as described above, a detailed description is omitted, and only the remaining components are specifically described below. The positive electrode current 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 current collector may typically have a thickness of 3 ㎛ to 500 ㎛, and fine unevenness may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector 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. The above-described positive electrode active material layer may include a conductive material and a binder together with the positive electrode material according to the present invention described above. The above cathode material may be included in an amount of 80 wt% to 99 wt%, more specifically 85 wt% to 99 wt%, based on the total weight of the cathode active material layer. When included in the above content range, excellent capacity characteristics may be exhibited. The conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without special restrictions. 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, summer black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one of these may be used alone or a mixture of two or more may be used. The conductive material may be included in an amount of 1 to 30 wt% with respect to the total weight of the positive electrode active material layer. The above binder serves to improve the adhesion between the positive electrode particles and the adhesive strength between the positive electrode and the 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, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), 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 binder may be included in an amount of 1 to 30 wt% with respect to 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, except that the positive electrode material according to the present invention is used. Specifically, the positive electrode material and, optionally, a binder and a conductive material are dissolved or dispersed in a solvent to manufacture a positive electrode composite, which is then applied onto a positive electrode current collector, followed by drying and rolling, or the positive electrode composite is cast onto a separate support, and then a film obtained by peeling off the support is laminated onto a positive electrode current collector. 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 or the positive electrode 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. 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. In addition, the lithium secondary battery may optionally further include a battery container that accommodates the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container. (1) Cathode In the above lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector. The above negative electrode current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 ㎛ to 500 ㎛, and, like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric. The above negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material. As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium 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 alloy, Sn alloy, or Al alloy; SiO β (0<β<2), SnO 2, a metal oxide capable of doping and dedoping lithium, such as vanadium oxide, lithium vanadium oxide; or a composite including the above-mentioned metallic compound and a carbonaceous material, such as a Si-C composite or a Sn-C composite, and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbon material. Representative examples of low-crystallization carbon include soft carbon and hard carbon, and representative examples of high-crystallization carbon include amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase pitches, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes. 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. The above binder is a component that assists in bonding between the conductive agent, the active material, and the current collector, and is typically added in an amount of 0.1 to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, various copolymers thereof, and the like. The conductive agent is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer. The conductive agent is not particularly limited as long as it has conductivity and does not induce a chemical change in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers such as carbon fiber or metal fiber; fluorinated carbon; metal powder such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. may be used. The above negative electrode may be manufactured, for example, by applying a negative electrode composite prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material in a solvent, onto a negative electrode current collector and drying it, or by casting the negative electrode composite onto a separate support and then laminating the resulting film onto a negative electrode current collector by peeling it off from the support. (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 fiber, polyethylene terephthalate fiber, 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 The electrolyte used in the present invention 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. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable. 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 above lithium salt is LiPF 6 , LiClO 4 , LiAsF 6 , LiBF 4 , LiSbF 6 , LiAl0 4 , LiAlCl 4 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN(C 2 F 5 SO 3 ) 2 , LiN(C 2 F 5 SO 2 ) 2 , LiN(CF 3 SO 2 ) 2. LiCl, LiI, or LiB(C 2 O 4 ) 2 The above lithium salt concentration is preferably used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so that it can exhibit excellent electrolyte performance, 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. Manufacturing example 1 NiSO 4 , CoSO 4 and MnSO 4 A transition metal aqueous solution was prepared by mixing Ni:Co:Mn in distilled water in an amount such that the molar ratio was 7:1:2. Next, deionized water was added to the reactor, nitrogen gas was purged into the reactor to remove dissolved oxygen in the water, and NaOH was added to maintain the pH inside the reactor at 11.5. Afterwards, a transition metal aqueous solution, a NaOH aqueous solution and NH were added to the reactor. 4 A precursor for the first cathode active material was manufactured by conducting a co-precipitation reaction for 48 hours under the conditions of a reaction temperature of 50°C, pH 11.5, and a stirring speed of 1000 rpm while adding an OH aqueous solution. The precursor for the first cathode active material and LiOH were mixed so that the molar ratio of Li: (Ni+Co+Mn) was 1.05:1, calcined at 900°C for 16 hours, and then washed and dried to obtain Li[Ni 0.7 Co 0.1 Mn 0.2 ]O 2 It has a composition of , and an average particle size (D 50 ) was manufactured as a first positive electrode active material A in the form of secondary particles having a size of 11 μm. Manufacturing example 2 A first cathode active material B was manufactured using the same method as Manufacturing Example 1, except that the precursor for the cathode active material and LiOH were mixed and then calcined at 850°C for 15 hours. Manufacturing example 3 A first cathode active material C was manufactured using the same method as Manufacturing Example 1, except that a co-precipitation reaction was performed for 36 hours under conditions of pH 10.2 and a stirring speed of 800 rpm when manufacturing a precursor for the cathode active material. Manufacturing example 4 A first cathode active material D was manufactured using the same method as Manufacturing Example 1, except that the precursor for the cathode active material and LiOH were mixed and then calcined at 800°C for 12 hours. Manufacturing example 5 A first cathode active material E was manufactured in the same manner as in Manufacturing Example 1, except that a co-precipitation reaction was performed for 36 hours under conditions of pH 10.2 and a stirring speed of 800 rpm when manufacturing a precursor for a cathode active material, and that the precursor for the cathode active material was mixed with LiOH and then calcined at 850°C for 12 hours. Cross sections of the first positive electrode active materials A to E manufactured by Manufacturing Examples 1 to 5 were photographed at 800x magnification using a scanning electron microscope (SEM), and then approximately 300 particle images were obtained using the Image J program to obtain the aspect ratio and circularity, and then the average aspect ratio and average circularity were measured by calculating the average values ​​of these. The cross-sections of the first positive electrode active materials A to E manufactured by Manufacturing Examples 1 to 5 were photographed at 2000x magnification using a scanning electron microscope (SEM), and then about 100 particle images were obtained using the Image J program to obtain the density, and the average density was measured by calculating the average value of these. After dispersing 0.1 g of the first cathode active materials A to E manufactured by Manufacturing Examples 1 to 5 in a dispersion medium, the particles were introduced into a laser diffraction particle size measuring device (S3500 from Microtrac) and a laser beam was transmitted to calculate the particle size distribution, and the diameter of each particle at the point where it becomes 50% of the volume cumulative distribution according to particle diameter was calculated to obtain the average particle diameter (D 50 ) was measured. The average aspect ratio, average roundness, average density and average particle diameter (D) measured above 50 ) are shown in Table 1 below. Manufacturing Example 1 Manufacturing Example 2 Manufacturing Example 3 Manufacturing Example 4 Manufacturing Example 5 Sphericity Average aspect ratio 0.935 0.930 0.810 0.942 0.851 Average circularity 0.861 0.876 0.75 10.888 0.785 Average density 0.919 0.936 0.865 0.96 10.886 Average particle size (D 50 )[㎛]9.910.19.710.19.9 Example 1 The first positive electrode active material A manufactured by the above manufacturing example 1 and the average particle diameter (D 50 ) is a second cathode active material Li[Ni having a thickness of 4㎛ 0.7 Co 0.1 Mn 0.2 ]O 2 The cathode material was manufactured by mixing the two in a weight ratio of 7:3. Example 2 The first positive electrode active material B manufactured by the above manufacturing example 2 and the average particle diameter (D 50 ) is a second cathode active material Li[Ni having a thickness of 4㎛ 0.7 Co 0.1 Mn 0.2 ]O 2 The cathode material was manufactured by mixing the two in a weight ratio of 7:3. Comparative Example 1 The first positive electrode active material C manufactured by the above manufacturing example 3 and the average particle diameter (D 50 ) is a second cathode active material Li[Ni having a thickness of 4㎛ 0.7 Co 0.1 Mn 0.2 ]O 2 The cathode material was manufactured by mixing the two in a weight ratio of 7:3. Comparative Example 2 The first positive electrode active material D manufactured by the above manufacturing example 4 and the average particle diameter (D 50 ) is a second cathode active material Li[Ni having a thickness of 4㎛ 0.7 Co 0.1 Mn 0.2 ]O 2 The cathode material was manufactured by mixing the two in a weight ratio of 7:3. Comparative Example 3 The first positive electrode active material E manufactured by the above manufacturing example 5 and the average particle diameter (D 50 ) is a second cathode active material Li[Ni having a thickness of 4㎛ 0.7 Co 0.1 Mn 0.2 ]O 2 The cathode material was manufactured by mixing the two in a weight ratio of 7:3. Experimental Example 1: Measurement of Differential Generation Rate After pressing 3 g of the cathode materials manufactured by Examples 1 to 2 and Comparative Examples 1 to 3 at a pressure of 9 tons, the volume cumulative particle size distribution (PSD) was measured to determine the rate of occurrence of fine particles less than 1 μm. The particle size distribution was measured using S-3500 from Microtrac, and the rate of occurrence of fine particles less than 1 μm in particle size was converted into weight% with respect to the total weight of the cathode materials. The measurement results are shown in Table 2 below. Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Differentiation occurrence rate [%] 810151719 Through the above Table 2, it can be confirmed that the cathode materials of Examples 1 and 2 have a lower rate of fine particle generation than the cathode materials of Comparative Examples 1 to 3. Experimental Example 2: Measuring Gas Increase Rate Each of the cathode materials manufactured in Examples 1 to 2 and Comparative Examples 1 to 3 was mixed with carbon black, PVDF, and N-methylpyrrolidone at a weight ratio of 96:2:2 to manufacture a cathode composite, which was then applied to one surface of an aluminum current collector, dried at 130°C, and rolled to manufacture a cathode. Lithium metal was used as the cathode. An electrode assembly was manufactured by interposing a porous polyethylene separator between the positive and negative electrodes manufactured as described above, and the electrode assembly was placed inside a case, and an electrolyte was injected into the case to manufacture a lithium secondary battery. At this time, the electrolyte was lithium hexafluorophosphate (LiPF) having a concentration of 1.0 M in an organic solvent composed of ethylene carbonate / ethyl methyl carbonate / diethyl carbonate / (mixed volume ratio = 3:4:3). 6 ) was prepared by dissolving it. Each of the lithium secondary batteries manufactured above was charged to SOC 100, stored at 60℃ for 8 weeks, and then perforated in a vacuum chamber to discharge the gas inside the battery and capture it inside the vacuum chamber. The gas in the chamber was analyzed for gas generation using a gas chromatography-flame ionization detector (GC-FID) to calculate the gas increase rate. The calculation results are shown in Table 3 below. Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Gas Increase Rate [%] 1013242337 Through the above Table 3, it can be confirmed that the gas increase rate of the cathode materials of Examples 1 to 2 is lower than that of the cathode materials of Comparative Examples 1 to 3.

Claims

1. A secondary particle in the form of a plurality of primary particles aggregated together, containing nickel, cobalt and manganese, containing nickel in an amount of 70 mol% or more of the total metal, and having a first average particle diameter (D 50 ) having a first positive electrode active material; and The above first average particle diameter (D 50 ) and a second average particle diameter (D) different from 50 ) comprising a second positive electrode active material; The above first cathode active material is a cathode material having an average aspect ratio, which is an arithmetic mean value of the aspect ratio defined by the following Equation 1, of 0.86 to 0.94, and an average compactness, which is an arithmetic mean value of the compactness defined by the following Equation 2, of 0.89 to 0.96: [Formula 1] Aspect ratio = r a / R [Formula 2] Compactness = r c / R In the above formulas 1 and 2, R is the length of the major axis passing through the center of the first positive electrode active material particle, and r a is the length of the short axis passing through the center of the first positive electrode active material particle, and r c is the diameter of a circle having an area equal to the area of ​​the first positive electrode active material.

2. In claim 1, The above first cathode active material is a cathode material having an average roundness of 0.79 to 0.88, which is an arithmetic mean value of roundness defined by the following Equation 3: [Formula 3] Roundness = [(4 × Area) / (π × R 2 )] In the above equation 3, R is the length of the major axis passing through the center of the first positive electrode active material particle, and Area is the actual area of ​​the first positive electrode active material particle.

3. In claim 1, The above first positive electrode active material is a positive electrode material having a composition represented by the following chemical formula 1: [Chemical Formula 1] Li x1 Ni a1 Co b1 Mr c1 M 1 d1 O 2 In the above chemical formula 1, M 1 may be at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 1≤x1≤1.1, 0.6≤a1≤1.0, 0≤b1≤0.3, 0≤c1≤0.3, 0≤d1<0.

15.

4. In claim 1, A cathode material, wherein the average aspect ratio of the first cathode active material is 0.90 to 0.

94.

5. In claim 1, A cathode material wherein the average density of the first cathode active material is 0.90 to 0.

95.

6. In claim 2, A cathode material, wherein the average circularity of the first cathode active material is 0.82 to 0.

88.

7. In claim 1, The first average particle diameter (D) of the first positive electrode active material 50 ) is a cathode material having a diameter of 8㎛ to 20㎛.

8. In claim 1, The second average particle diameter (D) of the second positive electrode active material 50 ) is a cathode material having a diameter of 2㎛ to 8㎛.

9. In claim 1, The first average particle diameter (D) of the first positive electrode active material 50 ) and the second average particle diameter (D) of the second positive electrode active material 50 ) A cathode material having a ratio of 2:1 to 8:

1.

10. In claim 1, A cathode material wherein the weight ratio of the first cathode active material and the second cathode active material is 50:50 to 90:

10.

11. In claim 1, The above second positive electrode active material is a positive electrode material having a composition represented by the following chemical formula 2: [Chemical formula 2] Li x2 Ni a2 Co b2 Mr c2 M 2 d2 O 2 In the above chemical formula 2, M 2 may be at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 1≤x2≤1.1, 0.6≤a2≤1.0, 0≤b2≤0.3, 0≤c2≤0.3, 0≤d2<0.

15.

12. A step of preparing a precursor for a first cathode active material by introducing a transition metal aqueous solution, a basic compound, and an ammonium cation complex forming agent into a reactor and mixing them at a stirring speed of 900 rpm to 1100 rpm while maintaining the pH within the reactor at 11 or higher; The precursor for the first positive electrode active material and the lithium raw material are mixed and heat-treated at a temperature of 850°C to 1000°C to obtain a first average particle diameter (D 50 ) preparing a first positive electrode active material; and The above first positive electrode active material and the above first average particle diameter (D 50 ) and a second average particle diameter (D) different from 50 ) comprising a step of mixing a second positive electrode active material; The above first cathode active material is in the form of secondary particles in which a plurality of primary particles are aggregated, and contains nickel, cobalt and manganese, and contains nickel at 70 mol% or more of the total metal. A method for manufacturing a cathode material, wherein the first cathode active material has an average aspect ratio, which is an arithmetic mean value of the aspect ratio defined by Equation 1 below, of 0.86 to 0.94, and an average compactness, which is an arithmetic mean value of the compactness defined by Equation 2 below, of 0.89 to 0.

96. [Formula 1] Aspect ratio = r a / R [Formula 2] Compactness = r c / R In the above formulas 1 and 2, R is the length of the major axis passing through the center of the first positive electrode active material particle, and r a is the length of the short axis passing through the center of the first positive electrode active material particle, and r c is the diameter of a circle having an area equal to the area of ​​the first positive electrode active material.

13. In claim 12, A method for manufacturing a cathode material, wherein the first cathode active material has an average roundness of 0.79 to 0.88, which is an arithmetic mean value of the roundness defined by Equation 3 below. [Formula 3] Roundness = [(4 × Area) / (π × R 2 )] In the above equation 3, R is the length of the major axis passing through the center of the first positive electrode active material particle, and Area is the actual area of ​​the first positive electrode active material particle.

14. A cathode comprising the cathode material of claim 1.

15. A lithium secondary battery comprising a cathode, an anode, a separator interposed between the cathode and the anode, and an electrolyte according to claim 14.