Cathode material, secondary battery including same, and method for measuring particle strength of cathode material

Abstract

The present invention relates to a cathode material, a secondary battery including the same, and a method for measuring particle strength of the cathode material, and more particularly to a cathode material that is at least one selected from the group consisting of lithium cobalt oxide; lithium manganese oxide; lithium iron phosphate compound; lithium nickel cobalt aluminum oxide (NCA); lithium nickel oxide (LNO); a nickel manganese-based lithium composite metal oxide in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn); a lithium composite transition metal oxide (NCM) in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co); and a lithium composite transition metal oxide (NCMA) in which aluminum (Al) is added to the lithium composite transition metal oxide (NCM), and the cathode material is at least one selected from the group consisting of lithium cobalt oxide; lithium manganese oxide; lithium iron phosphate compound; lithium nickel cobalt aluminum oxide (NCA); [Formula 1] 1≦del_PD_absolute≦1.58 (Here, del_PD_absolute is the difference between the ideal value of rolling density and the absolute value of the measured value when the load is 9,000 kgf.) [Formula 2] 0.2≦del_PD≦0.3 (Here, del_PD is the difference between the ideal rolling density value and the measured relative value (normalized value) when the load is 9,000 kgf.) [Formula 3] 0.15≦del_inclination≦0.21 (Here, del_inclination is the difference in the inclination between the ideal value and the measured value of the rolling density when the load is between 0 and 9,000 kgf.) [Formula 4] 10.1≦(1-del_PD) / EMD (Here, del_PD is the difference between the ideal value of the rolling density at a load of 9,000 kgf and the relative value (normalized value) of the measured value, and EMD (Earth Mover's Distance) is the value calculated using the Wasserstein_distance function of SciPy (u_values ​​= particle distribution before rolling, v_values ​​= particle distribution after rolling, u_weights = none, v_weights = none).) The present invention relates to a cathode material that satisfies at least one of the following criteria, and a secondary battery that includes the same. According to the present invention, since particles are not broken during the electrode manufacturing process, deterioration of battery performance due to fine powder does not occur, and a cathode material having excellent life characteristics in a high voltage environment, high thermal stability, and low gas generation during charging and discharging, and a secondary battery including the same are provided. Furthermore, the present invention has the effect of providing a method for easily measuring the particle strength of a highly crystalline cathode material.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application Nos. 10-2023-0116895 and 10-2023-0116896, filed September 4, 2023, and Korean Patent Application Nos. 10-2024-0116537 and 10-2024-0116538, filed August 29, 2024, respectively, and all contents disclosed in the documents of these Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a cathode material, a secondary battery including the same, and a method for measuring particle strength of the cathode material. More specifically, the present invention provides a cathode material that does not cause particle cracking during the electrode manufacturing process, thereby preventing battery performance degradation due to fine powder, has excellent life characteristics in a high-voltage environment, has high thermal stability, and generates little gas during charging and discharging, and a secondary battery including the same. The present invention also relates to a method for easily measuring the particle strength of a highly crystalline cathode material. [Background technology]

[0003] Lithium secondary batteries are broadly composed of a positive electrode in which a positive electrode active material layer is coated on a metal foil such as aluminum, a negative electrode in which a negative electrode active material layer is coated on a metal foil such as copper, a separator that prevents the positive electrode and negative electrode from mixing, and an electrolyte that allows lithium ions to move between the positive electrode and negative electrode.

[0004] Positive electrode active materials (hereinafter also referred to as "positive electrode materials") used in the positive electrode active material layer include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2, etc.), lithium iron phosphate compound (LiFePO4), etc. Among them, lithium cobalt oxide (LiCoO2) is widely used as a positive electrode active material for high voltages due to its high operating voltage and excellent capacity characteristics. However, due to the rising price of cobalt (Co) and unstable supply, there are limitations to its application to large-capacity lithium secondary batteries used in electric vehicles, etc.

[0005] Therefore, lithium composite transition metal oxides (hereinafter referred to as "NCM positive electrode active materials") have been developed in which some of the cobalt (Co) in the lithium cobalt oxide is replaced with nickel (Ni) and manganese (Mn). However, because they are in the form of secondary particles formed by agglomeration of primary particles, they easily break down and generate fine powder during the electrode manufacturing process. In addition, because they have a large specific surface area and a high content of lithium by-products, they generate gas when the secondary battery is operated, reducing thermal stability and battery performance such as life characteristics in high-voltage environments.

[0006] In addition, a particle strength measuring device is generally used to easily measure the particle strength of the positive electrode active material. However, although it is possible to measure the particle strength of secondary particles of a positive electrode active material with low crystallinity, it is not possible to measure the strength of primary particles of a positive electrode active material with high crystallinity. Summary of the Invention [Problem to be solved by the invention]

[0007] In order to solve the above-mentioned problems of the conventional art, the present invention aims to provide a cathode material, which does not cause degradation of battery performance due to fine powder because particles are not broken during the electrode manufacturing process, has excellent life characteristics in high-voltage environments, has high thermal stability, and generates little gas during charging and discharging, and a secondary battery including the same.

[0008] Another object of the present invention is to provide a method for easily measuring the particle strength of a highly crystalline cathode material.

[0009] The above and other objects of the present invention can all be achieved by the present invention described below. [Means for solving the problem]

[0010] In order to achieve the above object, I) the present invention provides a cathode material comprising at least one selected from the group consisting of lithium cobalt oxide; lithium manganese oxide; lithium iron phosphate compound; lithium nickel cobalt aluminum oxide (NCA); lithium nickel oxide (LNO); nickel manganese-based lithium composite metal oxide in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn); lithium composite transition metal oxide (NCM) in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co); and lithium composite transition metal oxide (NCMA) in which aluminum (Al) is added to the lithium composite transition metal oxide (NCM), the cathode material having a monomodal particle size distribution and a crystal size of 216.2 nm or more as measured by XRD, and containing cobalt (Co) and manganese (Mn), and the molar ratio of cobalt to manganese is 1:0.5 to 2.5.

[0011] II) The present invention provides a lithium composite transition metal oxide (NCMA) comprising one or more selected from the group consisting of lithium cobalt oxide; lithium manganese oxide; lithium iron phosphate compound; lithium nickel cobalt aluminum oxide (NCA); lithium nickel oxide (LNO); nickel manganese-based lithium composite metal oxide in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn); lithium composite transition metal oxide (NCM) in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co); and lithium composite transition metal oxide (NCMA) in which aluminum (Al) is added to the lithium composite transition metal oxide (NCM), and the lithium composite transition metal oxide (NCMA) is represented by the following formulas 1 to 4: [Formula 1] 1≦del_PD_absolute≦1.58 (Here, del_PD_absolute is the difference between the ideal value of rolling density and the absolute value of the measured value when the load is 9,000 kgf.)

[0012] [Formula 2] 0.2≦del_PD≦0.3 (Here, del_PD is the difference between the ideal rolling density value and the measured relative value (normalized value) when the load is 9,000 kgf.)

[0013] [Formula 3] 0.15≦del_inclination≦0.21 (Here, del_inclination is the difference in the inclination between the ideal value and the measured value of the rolling density when the load is between 0 and 9,000 kgf.)

[0014] [Formula 4] 10.1≦(1-del_PD) / EMD (Here, del_PD is the difference between the ideal rolling density value and the relative value (normalized value) of the measured value when the load is 9,000 kgf, and EMD (Earth Mover's Distance) is the value calculated using SciPy's Wasserstein_distance function (u_values ​​= particle distribution before rolling, v_values ​​= particle distribution after rolling, u_weights = none, v_weights = none).) We provide a cathode material that satisfies at least one of the following criteria.

[0015] III) In I) or II), the positive electrode material may have a monomodal particle size distribution.

[0016] IV) In the above I) to III), the positive electrode material may have a molar ratio of all transition metals to lithium of 1:1 to 1.05.

[0017] V) In the above I) - IV), the cathode material may have a crystal size of 216.2 nm or more as measured by XRD.

[0018] VI) In the above I) - V), the cathode material contains nickel (Ni) and may contain 65 mol% or more of nickel (Ni) based on 100 mol% of the total of the remaining metals excluding lithium (Li).

[0019] VII) In the above I) - VI), the cathode material contains cobalt (Co) and manganese (Mn), and the molar ratio of cobalt to manganese may be 1:0.5 - 2.5.

[0020] VIII) In the above I) - VII), the cathode material has the following chemical formula 1 (Chemical formula 1) Li Ni x Mn y Co z M w O 2+δ (In the above chemical formula 1, M contains one or more selected from the group consisting of B, W, Al, Ti, and Mg, and 1 < a ≤ 1.1, 0 < x < 0.95, 0 < y < 0.8, 0 < z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1.) It may be a compound represented thereby.

[0021] IX) In the above I) - VIII), the cathode material may have an EMD (Earth Mover’s Distance) value of 0.071 or less obtained using the Wasserstein_distance function of SciPy (u_values = particle distribution before rolling, v_values = particle distribution after rolling, u_weights = none, v_weights = none).

[0022] X) In the above I) - IX), the cathode material may be a single particle.

[0023] XI) In the above I) to X), the positive electrode material may have a surface coated with a coating agent containing metal or carbon.

[0024] Further, XII) The present invention provides a secondary battery including the positive electrode material according to the above I) to XI).

[0025] Further, XIII) The present invention includes: A) a step of measuring the rolling density of a positive electrode material using a powder resistance measuring instrument while the load is between 0 kgf and 2,000 kgf or less or less than; B) a step of measuring the rolling density of the positive electrode material using a hydraulic press when the load is more than or equal to 2,000 kgf; C) using the rolling density of the positive electrode material measured in the above steps A) and B), the absolute value difference (del_PD_absolute) between the ideal value and the measured value of the rolling density, the relative value difference (del_PD) between the ideal value and the measured value of the rolling density, the difference in the slope value (del_inclination) between the ideal value and the measured value of the rolling density, or the particle distribution degree before and after rolling is measured, and the Earth Mover's Distance (EMD) is obtained as a value obtained using the SciPy's Wasserstein_distance function (u_values = particle distribution before rolling, v_values = particle distribution after rolling, u_weights = none, v_weights = none). A method for measuring the particle strength of a positive electrode material is provided.

[0026] XIV) In the above XIII), the positive electrode material has the following Chemical Formula 1 (Chemical Formula 1) Li a Ni x Mn y Co z M w O 2+δ (In the above Chemical Formula 1, M includes one or more selected from the group consisting of B, W, Al, Ti, and Mg, 1 < a ≤ 1.1, 0 < x < 0.95, 0 < y < 0.8, 0 < z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1.) It may be a compound represented thereby.

[0027] XV) In XIII) or XIV) above, the particles may be single particles.

[0028] XVI) In XIII) to XV) above, the step B) may be a step of measuring the rolling density of the positive electrode material using a hydraulic press with a load exceeding 2,000 kgf or more to 9,000 kgf.

[0029] In addition, XVII) The present invention relates to the following Chemical Formula 1 (Chemical Formula 1) Li a Ni x Mn y Co z M w O 2+δ (In the above Chemical Formula 1, M contains one or more selected from the group consisting of B, W, Al, Ti, and Mg, 1 < a ≤ 1.1, 0 < x < 0.95, 0 < y < 0.8, 0 < z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1. It is a compound represented by, has a monomodal particle size distribution, the molar ratio of the total transition metal to lithium is 1:1 to 1.05, the crystal size measured by XRD is 216.2 nm or more, and based on 100 mol% of the total of the metals excluding lithium (Li), it contains 65 mol% or more of nickel (Ni), and the molar ratio of cobalt to manganese is 1:0.5 to 2.5. A positive electrode material is provided.)

[0030] XVIII) In XVII) above, the positive electrode material may be I) to XI), or may also be the positive electrode material of the secondary battery of XII).

Advantages of the Invention

[0031] According to the present invention, since the particles do not crack during the electrode manufacturing process, the performance degradation of the battery due to fine powder does not occur, it has excellent life characteristics in a high-voltage environment, high thermal stability, and a small amount of gas generation during charge and discharge. A positive electrode material and a secondary battery including the same are provided, and there is also an effect of providing a method capable of easily measuring the particle strength of the positive electrode material with high crystallinity. [Brief explanation of the drawings]

[0032] [Figure 1] 1 is a graph showing the rolling density of the cathode material prepared in Example 1 as an ideal value and a measured value depending on the load. [Figure 2] 1 is a graph showing the rolling density of the cathode material produced in Comparative Example 2 as ideal values ​​and measured values ​​depending on the load. [Figure 3] 1 is a graph showing the rolling density of the cathode material produced in Comparative Example 3 as ideal values ​​and measured values ​​depending on the load. [Figure 4] 2 is a graph showing the particle size distribution before and after rolling of the cathode material produced in Example 1. [Figure 5] 1 is a graph showing the particle size distribution before and after rolling of the cathode material produced in Comparative Example 2. [Figure 6] This is an SEM image of the positive electrode material published in Xiangbang Kong, Yige Zhang, Shiyun Peng, Jing Zeng, and Jinbao Zhao, “Superiority of Single-Crystal to Polycrystalline LiNixCoyMn1-x-yO2 Cathode Materials in Storage Behaviors for Lithium-Ion Batteries,” ACS Sustainable Chem.Eng.2020,8,14938-14948. DETAILED DESCRIPTION OF THE INVENTION

[0033] The inventors have confirmed that, when a cathode material is designed so that the difference between the absolute value of the ideal rolled density of the cathode material and the measured value (del_PD_absolute), the difference between the relative value of the ideal rolled density of the cathode material and the measured value (del_PD), the difference in slope between the ideal rolled density of the cathode material and the measured value (del_inclination), and / or the particle size distribution distance (EMD) before and after rolling of the cathode material fall within a predetermined range, such a cathode material does not suffer from particle cracking during the electrode manufacturing process, and therefore does not suffer from battery performance degradation due to fine powder, has excellent life characteristics in high-voltage environments, is highly thermally stable, and generates little gas during charging and discharging. Based on this, the inventors have conducted further research and have completed the present invention.

[0034] The presently described cathode material, a secondary battery containing the same, and a method for measuring the particle strength of the cathode material will be described in detail below.

[0035] However, the terms and words used in this specification and claims should not be interpreted limitedly to their ordinary or dictionary meanings, but should be interpreted in terms and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of terms to best describe his or her invention. Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely one embodiment of the present invention and do not represent the entire technical idea of ​​the present invention, and that various equivalents and modifications may be available to replace them, and that they may be arranged, substituted, combined, separated, or designed in various other configurations.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0037] The positive electrode material of the present invention is at least one selected from the group consisting of lithium cobalt oxide; lithium manganese oxide; lithium iron phosphate compound; lithium nickel cobalt aluminum oxide (NCA); lithium nickel oxide (LNO); nickel manganese-based lithium composite metal oxide in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn); lithium composite transition metal oxide (NCM) in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co); and lithium composite transition metal oxide (NCMA) in which aluminum (Al) is added to the lithium composite transition metal oxide (NCM), and is characterized by having a monomodal particle size distribution and a crystal size of 216.2 nm or more as measured by XRD, and containing the cobalt (Co) and manganese (Mn), with a cobalt to manganese molar ratio of 1:0.5 to 2.5. In this case, the particles do not break during the electrode manufacturing process, so there is no degradation of battery performance due to fine powder, and there is an effect of providing a cathode material that has excellent life characteristics in high-voltage environments, high thermal stability, and generates little gas during charging and discharging.

[0038] The positive electrode material of the present invention is at least one selected from the group consisting of lithium cobalt oxide; lithium manganese oxide; lithium iron phosphate compound; lithium nickel cobalt aluminum oxide (NCA); lithium nickel oxide (LNO); nickel manganese-based lithium composite metal oxide in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn); lithium composite transition metal oxide (NCM) in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co); and lithium composite transition metal oxide (NCMA) in which aluminum (Al) is added to the lithium composite transition metal oxide (NCM), and the positive electrode material is at least one selected from the group consisting of lithium cobalt oxide; lithium manganese oxide; lithium iron phosphate compound; lithium nickel cobalt aluminum oxide (NCA); [Formula 1] 1≦del_PD_absolute≦1.58 (Here, del_PD_absolute is the difference between the ideal value of rolling density and the absolute value of the measured value when the load is 9,000 kgf.) [Formula 2] 0.2≦del_PD≦0.3 (Here, del_PD is the difference between the ideal rolling density value and the measured relative value (normalized value) when the load is 9,000 kgf.) [Formula 3] 0.15≦del_inclination≦0.21 (Here, del_inclination is the difference in the gradient between the ideal value of rolling density and the measured value when the load is between 0 kgf and 9,000 kgf.) [Formula 4] 10.1≦(1-del_PD) / EMD (Here, del_PD is the difference between the ideal rolling density value at a load of 9,000 kgf and the relative value (normalized value) of the measured value, and EMD (Earth Mover's Distance) is the value calculated using SciPy's Wasserstein_distance function (u_values ​​= particle distribution before rolling, v_values ​​= particle distribution after rolling, u_weights = none, v_weights = none).) In this case, the particles do not break during the electrode manufacturing process, so there is no degradation of battery performance due to fine powder, and it has the effect of providing a cathode material with excellent life characteristics in high-voltage environments, high thermal stability, and low gas generation during charging and discharging.

[0039] The formula 1 is preferably expressed by the following formula 1-1: [Formula 1-1] 1≦del_PD_absolute≦1.4 (where del_PD_absolute is the difference between the ideal value of the rolling density and the absolute value of the measured value when the load is 9,000 kgf), or more preferably, the following formula 1-2: [Formula 1-2] 1.1≦del_PD_absolute≦1.35 (Here, del_PD_absolute is the difference between the ideal value of the rolling density at a load of 9,000 kgf and the absolute value of the measured value.) Within this range, particles will not crack during the electrode manufacturing process, so there is no degradation of battery performance due to fine powder, and there are advantages in providing a cathode material with excellent life characteristics in a high-voltage environment, high thermal stability, and little gas generation during charging and discharging.

[0040] The formula 2 is preferably expressed by the following formula 2-1: [Formula 2-1] 0.2≦del_PD≦0.29 (where del_PD is the difference between the ideal value of the rolling density and the relative value (normalized value) of the measured value when the load is 9,000 kgf), or more preferably, the following formula 2-2 [Formula 2-2] 0.21≦del_PD≦0.29 (where del_PD is the difference between the ideal value of the rolling density and the relative value (normalized value) of the measured value when the load is 9,000 kgf), and more preferably satisfies the following formula 2-3 [Formula 2-3] 0.22≦del_PD≦0.28 (where del_PD is the difference between the ideal value of the rolling density and the relative value (normalized value) of the measured value when the load is 9,000 kgf), and more preferably satisfies the following formula 2-4: [Formula 2-4] 0.23≦del_PD≦0.28 (Here, del_PD is the difference between the ideal rolling density value at a load of 9,000 kgf and the relative value (normalized value) of the measured value.) Within this range, particles do not break during the electrode manufacturing process, so there is no degradation of battery performance due to fine powder, and there are advantages in providing a cathode material with excellent life characteristics in high-voltage environments, high thermal stability, and low gas generation during charging and discharging.

[0041] The formula 3 is preferably expressed by the following formula 3-1: [Formula 3-1] 0.15≦del_inclination≦0.20 (where del_inclination is the difference in the gradient between the ideal value of the rolling density and the measured value when the load is between 0 kgf and 9,000 kgf), and more preferably, the following formula 3-2: [Formula 3-2] 0.15≦del_inclination≦0.19 (Here, del_inclination is the difference in the gradient between the ideal value of the rolling density when the load is between 0 kgf and 9,000 kgf and the measured value.) Within this range, particles do not crack during the electrode manufacturing process, so there is no degradation of battery performance due to fine powder, and there are advantages in providing a cathode material with excellent life characteristics in high voltage environments, high thermal stability, and little gas generation during charging and discharging.

[0042] The formula 4 is preferably expressed by the following formula 4-1: [Formula 4-1] 11≦(1-del_PD) / EMD (Here, del_PD is the difference between the ideal value of the rolling density when the load is 9,000 kgf and the relative value (normalized value) of the measured value, and EMD (Earth Mover's Distance) is a value calculated using the Wasserstein_distance function of SciPy (u_values ​​= particle distribution before rolling, v_values ​​= particle distribution after rolling, u_weights = none, v_weights = none).) [Formula 4-2] 15≦(1-del_PD) / EMD (Here, del_PD is the difference between the ideal value of the rolling density when the load is 9,000 kgf and the relative value (normalized value) of the measured value, and EMD (Earth Mover's Distance) is a value calculated using the Wasserstein_distance function of SciPy (u_values ​​= particle distribution before rolling, v_values ​​= particle distribution after rolling, u_weights = none, v_weights = none).) [Formula 4-3] 20≦(1-del_PD) / EMD (Here, del_PD is the difference between the ideal value of the rolling density when the load is 9,000 kgf and the relative value (normalized value) of the measured value, and EMD (Earth Mover's Distance) is a value calculated using the Wasserstein_distance function of SciPy (u_values ​​= particle distribution before rolling, v_values ​​= particle distribution after rolling, u_weights = none, v_weights = none).) [Formula 4-4] 25≦(1-del_PD) / EMD (Here, del_PD is the difference between the ideal value of the rolling density when the load is 9,000 kgf and the relative value (normalized value) of the measured value, and EMD (Earth Mover's Distance) is a value calculated using the Wasserstein_distance function of SciPy (u_values ​​= particle distribution before rolling, v_values ​​= particle distribution after rolling, u_weights = none, v_weights = none).) [Formula 4-5] 30≦(1-del_PD) / EMD (Here, del_PD is the difference between the ideal value of the rolling density when the load is 9,000 kgf and the relative value (normalized value) of the measured value, and EMD (Earth Mover's Distance) is a value calculated using the Wasserstein_distance function of SciPy (u_values ​​= particle distribution before rolling, v_values ​​= particle distribution after rolling, u_weights = none, v_weights = none).) [Formula 4-6] 35≦(1-del_PD) / EMD (Here, del_PD is the difference between the ideal value of the rolling density at a load of 9,000 kgf and the relative value (normalized value) of the measured value, and EMD (Earth Mover's Distance) is the value calculated using SciPy's Wasserstein_distance function (u_values ​​= particle distribution before rolling, v_values ​​= particle distribution after rolling, u_weights = none, v_weights = none).) Within this range, particles will not break during the electrode manufacturing process, so there is no degradation of battery performance due to fine powder, and there are advantages in providing a cathode material with excellent life characteristics in high-voltage environments, high thermal stability, and little gas generation during charging and discharging.

[0043] The cathode material may preferably have a monomodal particle size distribution, more preferably a monomodal particle size distribution with a peak existing between particle sizes of 1 μm and 8 μm, and even more preferably a monomodal particle size distribution with a peak existing between particle sizes of 2 μm and 7 μm. Within this range, particles do not break during the electrode manufacturing process, and there is no deterioration in battery performance due to fine powder. This has the effect of providing a cathode material with excellent life characteristics in high-voltage environments, high thermal stability, and little gas generation during charging and discharging.

[0044] The cathode material may preferably have a monomodal particle size distribution even after rolling under a load of 9 tons, more preferably a monomodal particle size distribution in which the difference in particle size between the peaks before and after rolling is 2 μm or less, even more preferably a monomodal particle size distribution in which the difference in particle size between the peaks before and after rolling is 1.5 μm or less, and even more preferably a monomodal particle size distribution in which the difference in particle size between the peaks before and after rolling is 1 μm or less. Within this range, particles do not break during the electrode manufacturing process, preventing battery performance degradation due to fine powder. This provides a cathode material with excellent life characteristics in high-voltage environments, high thermal stability, and low gas generation during charging and discharging. Here, rolling can be performed using a hydraulic press.

[0045] In this description, the particle size distribution is a PSD (Particle Size Distribution) graph that can be measured using a laser diffraction particle size analyzer. As an example, the positive electrode active material powder is dispersed in a dispersion medium, and then the dispersion medium is introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000, etc.) for measurement. As a specific example, the mixture of the positive electrode active material powder and dispersion medium is dispersed using an ultrasonic disperser with ultrasonic waves at an output of about 40 kHz and 40 W, and then the mixture is irradiated with a laser at an output of about 3 mW to 4 mW for measurement.

[0046] The positive electrode material may preferably have a molar ratio of all transition metals to lithium of 1:1 to 1.05, more preferably 1:1.01 to 1.05, even more preferably 1:1.02 to 1.05, and even more preferably 1:1.03 to 1.05, and within this range, there is an advantage in that the life characteristics are excellent.

[0047] The positive electrode material may preferably have a crystal size measured by XRD of 216.2 nm or more, more preferably 217 nm or more, even more preferably 260 nm or less, and even more preferably 257 nm or less. Within this range, there is an advantage in that the battery life characteristics are excellent in a high-voltage environment.

[0048] In this description, the crystal size can be measured by XRD crystal analysis, and there is no deviation depending on the measurement device or method. Specifically, the crystal size can be determined by placing about 5 g to 10 g of the positive electrode material in a holder, irradiating the particles with X-rays, and analyzing the resulting diffraction grating.

[0049] The positive electrode material preferably contains nickel (Ni), and can contain 65 mol% or more of nickel (Ni) based on a total of 100 mol% of the remaining metals excluding lithium (Li), more preferably 70 mol% or more, even more preferably 75 mol% or more, even more preferably 80 mol% or more, still more preferably 85 mol% or more, specifically 95 mol% or less, and preferably 90 mol% or less, and within this range, there is an advantage in that the life characteristics are excellent.

[0050] The positive electrode material preferably contains cobalt (Co) and manganese (Mn), and the molar ratio of cobalt to manganese may be 1:0.5 to 2.5, more preferably 1:0.7 to 2.3, even more preferably 1:0.7 to 2.0, still more preferably 1:1.6 to 2.0, and particularly preferably 1:1.6 to 1.9. Within this range, there is an advantage in that the life characteristics are excellent.

[0051] In the present description, the content of metal components such as nickel (Ni), cobalt (Co), and manganese (Mn) is not particularly limited as long as it is measured by a method using IC (Ion Chromatography) or the like, which is commonly used in the technical field to which the present invention pertains. For example, it may be measured using an IC-ICP (Inductively Coupled Plasma) analyzer, an IC-ICP-MS analyzer, or an IC-ICP-AES analyzer.

[0052] The positive electrode material preferably has the following chemical formula 1 (Chemical formula 1) Li a Ni x Mn y Co z M w O 2+δ (In the above chemical formula 1, M contains one or more selected from the group consisting of B, W, Al, Ti, and Mg, 1 < a ≤ 1.1, 0 < x < 0.95, 0 < y < 0.8, 0 < z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1). It may be a compound represented by this, and within this range, since the particles do not crack during the manufacturing process of the electrode, there is no reduction in the performance of the battery due to fine powder, and it has excellent life characteristics in a high-voltage environment, high thermal stability, and a small amount of gas generation during charge and discharge.

[0053] The positive electrode material preferably has an EMD (Earth Mover’s Distance) value of 0.071 or less, preferably 0.069 or less, and more preferably 0.65 or less, obtained using the Wasserstein_distance function of SciPy (u_values = particle distribution before rolling, v_values = particle distribution after rolling, u_weights = none, v_weights = none). Within this range, since the particles do not crack during the manufacturing process of the electrode, there is no reduction in the performance of the battery due to fine powder, and it has the advantage of providing a positive electrode material with excellent life characteristics in a high-voltage environment, high thermal stability, and a small amount of gas generation during charge and discharge. Here, "u_values" and "v_values" are vol% with respect to the particle size, and the values of the respective vol% before and after rolling at the same particle size (μm) can be input into u_values and v_values. Also, "u_weights" and "v_weights" are weights, and "none" means that no value is input, so the weights are equal.

[0054] For the particle distribution before rolling and the particle distribution after rolling, preferably, the entire particle size distribution graph value (vector value) is input. As a specific example, 100 to 150 values ​​can be input, and in the embodiment of the present invention, 131 values ​​are input.

[0055] The rolling can be carried out under a load of, for example, 9,000 kgf.

[0056] In this description, EMD (Earth Mover's Distance) is a measure of the similarity between two distributions and is also called the 1st Wasserstein metric. EMD is a measure of the distance that indicates the minimum amount of work required to move a u distribution to a v distribution. The work can be calculated by summing the product of the weight moved for each section of a histogram (discrete distribution) and the distance moved. In this invention, the weight moved for each section corresponds to vol% of the particle size.

[0057] The cathode material may preferably be a single particle, more preferably containing no secondary particles, which prevents the particles from cracking during the electrode manufacturing process, thereby preventing deterioration of battery performance due to fine powder, and providing a cathode material with excellent life characteristics in a high-voltage environment, high thermal stability, and low gas generation during charging and discharging.

[0058] For example, the single particle may be a particle consisting of 30 or less nodules, preferably a particle consisting of 1 to 20 nodules, more preferably a particle consisting of 1 to 10 nodules, even more preferably a particle consisting of 1 to 5 nodules, and most preferably a particle consisting of 1 nodule. In this case, the particles do not break during the electrode manufacturing process, so there is no deterioration in battery performance due to fine powder, and there is an effect of providing a cathode material that has excellent life characteristics in a high-voltage environment, high thermal stability, and generates little gas during charging and discharging.

[0059] In this description, the term "nodule" refers to a particle unit body constituting a single particle, and may refer to a single crystal lacking a crystalline grain boundary, or a polycrystal that does not appear to have a grain boundary when observed at a magnification of 5,000 to 20,000 times using a scanning electron microscope (SEM) or an electron backscatter diffraction pattern analyzer (EBSD).

[0060] In this description, the number of nodules refers to the average number of nodules in cathode material particles, and can be determined by cutting a cathode containing a cathode active material by ion milling, obtaining a cross-sectional image of the cut cathode in the thickness direction using a scanning electron microscope (SEM), selecting at least 30 particles from each of the large-diameter cathode active material particles and the small-diameter cathode active material particles in the cross-sectional image, and then measuring the number of nodules in the cross section of each cathode active material particle through SEM image analysis, and then arithmetically averaging the numbers.

[0061] In this description, secondary particles refer to particles that are aggregates formed by the aggregation of several single particles and contain more than 30 nodules.

[0062] Figure 6 below is from Xiangbang Kong, Yige Zhang, Shiyun Peng, Jing Zeng, and Jinbao Zhao, "Superiority of Single-Crystal to Polycrystalline LiNi x Co y Mn 1-x-y This is an SEM image of the cathode material published in “O2Cathode Materials in Storage Behaviors for Lithium-Ion Batteries”, ACS Sustainable Chem.Eng.2020,8,14938-14948.

[0063] 6, image a shows a single particle of NCM622 cathode active material, which is a smooth particle without nodules on its surface, images b and b1 show secondary particles of NCM622 cathode active material, which are particles with numerous nodules formed on their surface, image c shows a single particle of NCM811 cathode active material, which is a smooth particle without nodules on its surface, and images d and d1 show secondary particles of NCM811 cathode active material, which are particles with numerous nodules formed on their surface. As such, single particles and secondary particles can be easily distinguished through SEM image analysis.

[0064] The method for producing the cathode material according to the present invention is not particularly limited, and may be one of the methods for producing cathode materials commonly used in the technical field to which the present invention pertains, as long as it satisfies the definition of the cathode material according to the present invention.

[0065] The method for producing the positive electrode material preferably includes a step of calcining a transition metal hydroxide and lithium hydroxide at 750°C to 950°C, preferably 800°C to 900°C, for 5 to 15 hours, preferably 10 to 15 hours, in an air or oxygen atmosphere.

[0066] The transition metal hydroxide is a transition metal source for the positive electrode active material and can be referred to as a transition metal precursor, and the lithium hydroxide is a lithium source for the positive electrode active material and can be referred to as a lithium precursor.

[0067] The surface of the cathode material may preferably be coated with a coating agent containing metal or carbon. In this case, the structural stability of the cathode active material is improved without chemical or physical changes to the cathode active material itself, thereby improving electrochemical properties such as output performance, life characteristics, and capacity. Furthermore, the surface of the cathode active material is substituted with a different element, which adjusts the amount of residual lithium and reduces the pH, thereby improving physicochemical properties.

[0068] The metal is preferably at least one selected from the group consisting of B, W, Al, Ti, Mg, Ni, Co, Mn, Si, Zr, Ge, Sn, Cr, Fe, V, and Y, more preferably at least one selected from the group consisting of B, W, Al, Ti, and Mg, even more preferably boron (B), tungsten (W), or a mixture thereof, and even more preferably tungsten (W) and boron (B). A specific example is tungsten boride (WB), in which case there is an effect of improving resistance characteristics and life characteristics.

[0069] The coating agent containing the metal may be, for example, an oxide or acid containing the metal as an element in its molecule.

[0070] The coating agent containing the organometallic is not particularly limited as long as it is a coating agent that is commonly used in the technical field to which the present invention pertains and contains an organometallic compound containing the metal, and a specific example thereof may be a metal alkoxide.

[0071] The coating agent containing a carbon component is not particularly limited as long as it is a coating agent containing a carbon component that is commonly used in the technical field to which the present invention pertains, and a specific example thereof may be a sugar such as sucrose.

[0072] For example, the coating agent may be contained in an amount of 0.001 mol % to 0.3 mol % relative to 1 mol % of the metal in the positive electrode active material before the coating treatment, preferably 0.01 mol % to 0.3 mol %, more preferably 0.01 mol % to 0.15 mol %, even more preferably 0.01 mol % to 0.1 mol %, and still more preferably 0.01 mol % to 0.05 mol %. Within this range, the properties of the positive electrode active material itself are maintained as they are, while the structural stability and electrochemical performance are improved.

[0073] The surface coating is preferably carried out by coating the surface with a coating agent containing at least one of a metal, an organic metal, and a carbon component using a solid phase or liquid phase method, followed by heat treatment at 100°C to 1200°C, more preferably 200°C to 1000°C, and even more preferably 250°C to 800°C. In this case, the structural stability and electrochemical performance are improved while the properties of the positive electrode active material itself are maintained.

[0074] The heat treatment time is preferably 1 hour to 16 hours, more preferably 3 hours to 7 hours. Within this range, the properties of the positive electrode active material itself are maintained as they are, while the structural stability and electrochemical performance are improved.

[0075] The coating method is not particularly limited as long as it is a coating method commonly used in the technical field to which the present invention pertains, and examples thereof include a liquid phase method in which a liquid coating agent is prepared and mixed with a positive electrode active material, a mechanochemical method using high mechanical energy such as ball milling, a fluidized bed coating method, a spray drying method, a precipitation method in which a coating agent in an aqueous solution state is precipitated on the surface of a positive electrode active material, a method utilizing a reaction between a gaseous coating agent and a positive electrode active material, and a sputtering method.

[0076] The metal, organometallic, and carbon components may be, for example, spherical, plate-like, angular, or needle-like, and such shapes can be adjusted by changing process conditions during the manufacturing process. The definition of each shape is not particularly limited as long as it follows the definition generally accepted in the technical field to which the present invention belongs.

[0077] The coating agent preferably has an average diameter of 1 nm to 1000 nm and a specific surface area of ​​10 m 2 / g~100m 2 / g, and more preferably, the average diameter is 10 nm to 100 nm and the specific surface area is 20 m 2 / g~100m 2 / g, and within this range, the particles are uniformly attached to the surface of the positive electrode active material, imparting structural stability to the positive electrode active material, thereby improving the problems of deterioration in life characteristics and electrochemical performance due to lattice deformation and collapse of the crystal structure of the positive electrode active material.

[0078] In this description, the average diameter can be measured by a measurement method commonly used in the technical field to which the present invention pertains, for example, by using a laser diffraction method. Specifically, after dispersing particles of a positive electrode active material in a dispersion medium, the particles are introduced into a commercially available laser diffraction particle size measuring device such as Microtrac MT 3000, and ultrasonic waves of about 28 kHz are irradiated at an output of 60 W to measure the average particle diameter (D ) at 50% of the particle size distribution in the measuring device. 50 ) can be calculated.

[0079] In this description, the specific surface area can be measured by a measurement method commonly used in the technical field to which the present invention pertains, for example, by the BET (Brunauer-Emmett-Teller) method, and specifically, can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77 K) using a BELSORP-mino II from BEL Japan.

[0080] Furthermore, the secondary battery of the present invention includes the above-described cathode material. In this case, the cathode material does not crack during the electrode manufacturing process, and therefore, there is no degradation of battery performance due to fine powder. The secondary battery has the following advantages: excellent life characteristics in a high-voltage environment, high thermal stability, and little gas generation during charging and discharging.

[0081] The secondary battery of the present invention can include all of the above-mentioned positive electrode materials, and therefore, redundant description thereof will be omitted here.

[0082] The method for manufacturing the secondary battery according to the present invention is not particularly limited as long as it is a method for manufacturing a lithium secondary battery that is commonly used in the technical field to which the present invention pertains.

[0083] Also, the method for measuring the particle strength of the positive electrode material of the present invention includes: A) measuring the rolling density of the positive electrode material using a powder resistance measuring instrument while the load is between 0 kgf and 2,000 kgf or less; B) measuring the rolling density of the positive electrode material using a hydraulic press when the load is more than 2,000 kgf; and C) using the rolling densities of the positive electrode material measured in steps A) and B), measuring the absolute value difference (del_PD_absolute), relative value difference (del_PD), difference in slope value (del_inclination) between the ideal value and the measured value of the rolling density, or the particle distribution degree before and after rolling, and obtaining the EMD as the value obtained using the SciPy's Wasserstein_distance function (u_values = particle distribution before rolling, v_values = particle distribution after rolling, u_weights = none, v_weights = none). In such a case, there is an advantage that the particle strength of a positive electrode material with high crystallinity can be easily measured.

[0084] The positive electrode material is preferably represented by the following Chemical Formula 1 (Chemical Formula 1) Li a Ni x Mn y Co z M w O 2+δ (In Chemical Formula ①, M includes one or more selected from the group consisting of B, W, Al, Ti, and Mg, 1 < a ≤ 1.1, 0 < x < 0.95, 0 < y < 0.8, 0 < z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1.) It may be a compound represented thereby.

[0085] The particles may preferably be single particles.

[0086] In the step A), preferably, the rolling density is measured using a powder resistivity meter when the load is 0 kgf to 2,000 kgf or less, and two or more measured rolling densities are extended to calculate the rolling density value at a point where the load is 9,000 kgf as the ideal value of the rolling density (PD) under a load of 9,000 kgf. i ) can be included.

[0087] Specifically, the rolling density according to the load has an ideal linear causal relationship, and by extending two or more rolling densities measured under a load of 2,000 kgf or less, the rolling density at a load of more than 2,000 kgf, preferably 9,000 kgf, can be obtained. This is called the ideal value of the rolling density (PD i ) is called.

[0088] Step B) may preferably be a step of measuring the rolling density of the cathode material using a hydraulic press under a load of more than 2,000 kgf or between 2,000 kgf and 9,000 kgf. In this case, there is an advantage that the particle strength of a highly crystalline cathode material can be easily measured.

[0089] Specifically, the rolling density of the cathode material does not actually have a linear causal relationship, but increases linearly when the load is less than or equal to 2,000 kgf, and gradually stabilizes when the load is greater than or equal to 2,000 kgf or between 2,000 kgf and 9,000 kgf, showing the behavior of a logarithmic function. This is called the measured rolling density (PD r ) is called.

[0090] The difference between the ideal and measured rolling density values ​​(del_PD), as well as the particle distribution before and after rolling, are measured, and the EMD is calculated using the Wasserstein_distance function in SciPy. These values ​​are proportional to or correspond to the particle strength of the cathode material within the range of particle strength (absolute value) generally required for cathode materials, and therefore have the advantage of being able to indirectly confirm the particle strength of the cathode material (relative value).

[0091] The difference between the ideal and measured absolute values ​​of the rolling density (del_PD_absolute), the difference between the ideal and measured relative values ​​of the rolling density (del_PD), and the difference between the ideal and measured slopes of the rolling density (del_inclination) are generally proportional to or correspond to the particle strength of the cathode material within the range of particle strength (absolute value) required for the cathode material, and therefore have the advantage of being able to indirectly check the particle strength of the cathode material (relative value).

[0092] The particle strength (absolute value) required for the cathode material may be, for example, in the range of 10 MPa to 1000 MPa, preferably 50 MPa to 500 MPa, more preferably 100 MPa to 400 MPa, and even more preferably 100 MPa to 350 MPa, and within this range, excellent accuracy is obtained. Here, the particle strength (absolute value) is a value obtained by measuring the time when cracks occur in the particles while gradually increasing pressure on the cathode material particles, and converting the value into pressure units (MPa).

[0093] In step C), the EMD can be calculated, for example, by measuring the particle distribution before and after rolling and using this to determine the distance between particle distributions using the Wasserstein_distance function of SciPy.

[0094] The method for measuring particle strength of a cathode material according to the present invention may include all of the above-described cathode materials and secondary batteries containing the same, and therefore, a redundant description thereof will be omitted here.

[0095] In addition, in order to easily convey the method for measuring particle strength of the cathode material of the present invention to those skilled in the art, only the essential conditions and devices are described, and other obvious additional conditions and devices are omitted.

[0096] Preferred examples are presented below to aid in understanding the present invention. However, the following examples are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the scope and technical idea of ​​the present invention. Naturally, such changes and modifications also fall within the scope of the appended claims.

[0097] [Example] Example 1 Ni x Mn y Co z (OH)2 and LiOH were mixed so that the molar ratio of transition metals (Ni + Mn + Co):Li was 1:1.05, the molar ratio of transition metals (Ni + Mn + Co):Ni was 0.700, and the molar ratio of Mn / Co was 1.9, and the mixture was fired at 850°C for 12 hours to produce a positive electrode active material LiNi with a particle size of 227.6 nm. 0.700 Mn y Co z O2 was produced, and a scanning electron microscope (SEM) was used to confirm that the produced positive electrode active material was a single particle.

[0098] Examples 2 to 18 Ni in Example 1 x Mn y Co z Cathode active materials having particle sizes shown in Table 1 were prepared in the same manner as in Example 1, except that the molar ratio of transition metals (Ni + Mn + Co):Li, the molar ratio of transition metals (Ni + Mn + Co):Ni, and the molar ratio of Mn / Co in (OH)2 and LiOH were changed as shown in Table 1. The particle types of the prepared cathode active materials were confirmed using a scanning electron microscope (SEM), and the results are shown in Table 1.

[0099] Comparative Example 1 Ni x Mn y Co z (OH)2 and LiOH were mixed so that the molar ratio of transition metals (Ni + Co + Mn):Li was 1:1.06, the molar ratio of transition metals (Ni + Mn + Co):Ni was 0.87, and the molar ratio of Mn / Co was 1.4, and the mixture was fired at 850°C for 12 hours to produce a positive electrode active material LiNi with a particle size of 109.5 nm. 0.87 Mn y Co z O2 was produced, and a scanning electron microscope (SEM) was used to confirm that the produced positive electrode active material was a secondary particle.

[0100] Comparative Examples 2 to 18 The Ni of Comparative Example 1 x Mn y Co z Cathode active materials having particle sizes shown in Table 2 were prepared in the same manner as in Comparative Example 1, except that the molar ratio of transition metals (Ni + Mn + Co):Li, the molar ratio of transition metals (Ni + Mn + Co):Ni, and the molar ratio of Mn / Co in (OH)2 and LiOH were changed as shown in Table 2. The particle types of the prepared cathode active materials were confirmed using a scanning electron microscope (SEM), and the results are shown in Table 2.

[0101] [Test Example I] The properties of the positive electrode active materials prepared in Examples 1 to 18 and Comparative Examples 1 to 18 were measured by the following methods, and the results are shown in Tables 1 and 2 below.

[0102] *ICP analysis: Using an ICP analyzer, the ratio of lithium (Li) to transition metals (Me), the ratio of nickel to transition metals, the ratio of Mn / Co, and the content of specific elements (mg / kg) in the positive electrode active material were measured. This can be measured using a general ICP analyzer commonly used in laboratories, and there is no deviation due to the measurement device or method.

[0103] *Particle size (crystal size): Measured by XRD crystal analysis. Specifically, approximately 5g to 10g of positive electrode active material particles are placed in a holder, and X-rays are irradiated onto the particles to analyze the resulting diffraction grating. This can be measured using a general X-ray diffraction analyzer, and there is no deviation due to the measurement device or method.

[0104] [Table 1]

[0105] [Table 2]

[0106] As shown in Tables 1 and 2, the positive electrode active materials (Examples 1 to 18) according to the present invention were found to satisfy, compared to the positive electrode active materials of Comparative Examples 1 to 18, a monomodal particle size distribution, a molar ratio of all transition metals to lithium of 1:1 to 1.05, a crystal size of 216.2 nm or more as measured by XRD, a nickel (Ni) content of 65 mol % or more based on 100 mol % of the total of the remaining metals excluding Li, and a cobalt to manganese molar ratio of 1:0.5 to 2.5.

[0107] [Test Example II] The properties of the positive electrode active materials prepared in Examples 1 to 18 and Comparative Examples 1 to 18 were measured by the following methods, and the results are shown in Tables 3 and 4 below.

[0108] *del_PD_absolute, del_PD, and del_inclination: 5 g of the prepared positive electrode active material powder was placed in a Φ1 cm mold of a powder resistance measuring device, and the roll density was measured under loads of 400 kgf, 800 kgf, 1200 kgf, 1600 kgf, and 2000 kgf. Then, 3 g of the prepared positive electrode active material powder, which was separately prepared, was placed in a Φ12.9 mm mold of a hydraulic press, and the roll density was measured under a load of 9000 kgf.

[0109] As shown in Figures 1 to 3 below, the rolled density values ​​(measured values; blue or dark dots) under loads of 400 kgf, 800 kgf, 1200 kgf, 1600 kgf, 2000 kgf, and 9000 kgf were plotted in a graph, and lines were drawn between them to obtain a measurement graph (blue or dark line). Next, a line (linear function, brown or light line) was drawn through the measured values ​​of rolled density under loads of 400 kgf and 2000 kgf, and the rolled density value at the point on that line where the load was 9000 kgf was determined as the ideal value of rolled density under a load of 9000 kgf (brown or light dot).

[0110] The values ​​written on the completed graph were substituted into the following formulas 5 to 9 to obtain del_PD_absolute, del_PD, and del_inclination values.

[0111] [Formula 5] del_PD_absolute=PD i -PD r (where PD i is the ideal value of rolling density under a load of x kgf, and PD r is the measured rolling density under a load of x kgf, where x is 9000.

[0112] [Formula 6] del_PD=(PD i -PD r ) / PD i (where PD i is the ideal value of rolling density under a load of x kgf, and PD r is the measured rolling density under a load of x kgf, where x is 9000.

[0113] [Formula 7] del_inclination=inclination(i)-inclination(r) (where inclination(i) is the slope of the ideal value and inclination(r) is the slope of the measured value.)

[0114] [Formula 8] inclination(i)=(PD i (x)-PD i (y) / (xy) (where PD i (x) is the ideal value of rolling density under a load of x kgf, and PD i (y) is the ideal value of rolling density under a load of y kgf, where x>y, x is 9000, and y is 400 or 2000.

[0115] [Formula 9] inclination(r)=(PD r (x)-PD r (y) / (xy) (where PD r (x) is the measured rolling density under a load of x kgf, and PD r (y) is the measured value of rolling density under a load of y kgf, where x>y, x is 9000, and y is 2000.

[0116] *EMD: The prepared cathode active material powder was measured using a particle size analyzer before and after rolling under a load of 9000 kgf. Particle Size Distribution (PSD) graphs for each were obtained as shown in Figures 4 and 5 below, and the values ​​shown in the graphs were then substituted into the Wasserstein_distance function of SciPy (u_values ​​= particle distribution before rolling, v_values ​​= particle distribution after rolling, u_weights = none, v_weights = none).

[0117] [Table 3]

[0118] [Table 4]

[0119] As shown in Tables 3 and 4, it was confirmed that the positive electrode active materials (Examples 1 to 18) according to the present invention, unlike the positive electrode active materials of Comparative Examples 1 to 18, all satisfy the ranges of Formulas 1 to 4 and EMD according to the present invention.

[0120] In particular, the positive electrode active materials of Comparative Examples 3 and 14 to 18, although being single particles, do not satisfy the formulas 1 to 4 according to the present invention. Therefore, it was confirmed that even if a particle is a single particle, if the formulas 1 to 4 according to the present invention are not satisfied, the life characteristics will be poor.

[0121] 1 to 3 are graphs showing the rolling densities of the cathode active materials produced in Example 1 and Comparative Examples 1 and 2, respectively, as ideal values ​​and measured values ​​depending on the load. The ideal values ​​are represented by brown dots and lines or light-colored dots and lines, and the measured values ​​are represented by blue dots and lines or dark-colored dots and lines. From these values, it was confirmed that the cathode active material of Example 1 satisfies Formulas 1 to 4 according to the present invention, whereas the cathode active materials of Comparative Examples 1 and 2 do not satisfy any of Formulas 1 to 4 according to the present invention.

[0122] As shown in FIGS. 4 and 5 below, FIGS. 4 and 5 are graphs showing the particle size distributions before and after rolling of the cathode active materials prepared in Example 1 and Comparative Example 2, respectively. It was confirmed that the shape of the particle size distribution of the cathode active material of Example 1 did not change before and after rolling, and the peak shifted only slightly, whereas the shape of the particle size distribution of the cathode active material of Comparative Example 2 changed from a monomodal to a bimodal shape before and after rolling, and a significant peak shift occurred.

[0123] [Test Example III: Evaluation of Coin Half Cell (CHC)] The electrochemical performance of the positive electrode active materials prepared in Examples 1 to 18 and Comparative Examples 1 to 18 was measured through the CHC cell evaluation as follows, and the results are shown in Tables 5 and 6 below.

[0124] * Coin half cell (CHC) fabrication: 96.5 wt% of the positive electrode active material, 1.5 wt% of carbon black, and 2 wt% of PVdF were weighed and mixed with NMP to prepare a slurry. This was applied to a 20 μm thick aluminum foil, dried at 130°C for 1 hour, and then punched out to prepare a positive electrode, followed by the fabrication of a coin half cell (CHC).

[0125] *High temperature (45℃) life capacity retention rate: Each manufactured coin half cell was subjected to formation at a 0.1C rate, and then charged and discharged 50 times at a high temperature (45℃) with a voltage of 2.5V to 4.25V at 0.33C / 0.33C. The discharge capacity after the first cycle and after 50 cycles were measured using a PNE-0506 charger / discharger (manufacturer: PNE Solution Co., Ltd., 5V, 6A), and the discharge capacity after the first cycle was set as the initial capacity.

[0126] Thereafter, the 50th discharge capacity was compared with the initial discharge capacity, and the high temperature capacity retention rate was calculated as the high temperature life characteristics using the following equation 10. The results are shown in Tables 5 and 6 below.

[0127] [Formula 10] High-temperature capacity retention rate (%) = (discharge capacity after high-temperature cycle / initial discharge capacity) x 100

[0128] [Table 5]

[0129] [Table 6]

[0130] As shown in Tables 5 and 6, the secondary batteries including the cathode materials according to the present invention (Examples 1 to 18) had high-temperature capacity retention rates of 94.8% or more, more precisely, in the range of 94.8% to 97% relative to CHC, and were excellent in high-temperature life characteristics. However, it was confirmed that the CHCs including the cathode materials of Comparative Examples 1 to 18 had poor high-temperature life capacity retention rates of 93.9% or less.

Claims

1. lithium iron phosphate compound; lithium nickel cobalt aluminum oxide (NCA); lithium nickel oxide (LNO); nickel manganese-based lithium composite metal oxide in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn); lithium composite transition metal oxide (NCM) in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co); and lithium composite transition metal oxide (NCMA) in which aluminum (Al) is added to the lithium composite transition metal oxide (NCM), It is characterized by satisfying at least one of the following formulas 1 to 4: [Formula 1] 1≦del_PD_absolute≦1.58 del_PD_absolute is the difference between the ideal rolling density value and the absolute value of the measured value when the load is 9,000 kgf, [Formula 2] 0.2≦del_PD≦0.3 del_PD is the difference between the ideal rolling density value and the relative value (normalized value) of the measured value when the load is 9,000 kgf, [Formula 3] 0.15≦del_inclination≦0.21 del_inclination is the difference in the inclination between the ideal value and the measured value of the rolling density when the load is between 0 and 9,000 kgf, [Formula 4] 10.1≦(1-del_PD) / EMD del_PD is the difference between the ideal rolling density value and the relative value (normalized value) of the measured value when the load is 9,000 kgf, and EMD (Earth Mover's Distance) is a value calculated using the Wasserstein_distance function of SciPy (u_values ​​= particle distribution before rolling, v_values ​​= particle distribution after rolling, u_weights = none, v_weights = none).

2. The cathode material according to claim 1 , wherein the cathode material has a monomodal particle size distribution.

3. The cathode material according to claim 1, wherein the molar ratio of the total transition metals to lithium is 1:1 to 1.

05.

4. The cathode material according to claim 1 , wherein the crystal size measured by XRD is 216.2 nm or more.

5. The cathode material according to claim 1, characterized in that the cathode material contains nickel (Ni) and contains 65 mol% or more of nickel (Ni) based on a total of 100 mol% of the remaining metals excluding lithium (Li).

6. The cathode material according to claim 1, wherein the cathode material contains cobalt (Co) and manganese (Mn), and the molar ratio of cobalt to manganese is 1:0.5 to 2.

5.

7. The cathode material is characterized by being a compound represented by the following chemical formula 1: (Chemical formula 1) Li ａ Ni ｘ Mn ｙ Co ｚ M ｗ O ２＋δ 2. The cathode material of claim 1, wherein, in Chemical Formula 1, M comprises one or more selected from the group consisting of B, W, Al, Ti, and Mg, and 1<a≦1.1, 0<x<0.95, 0<y<0.8, 0<z<1.0, 0≦w≦0.1, −0.02≦δ≦0.02, and x+y+z+w=1.

8. The cathode material according to claim 1, characterized in that the cathode material has an Earth Mover's Distance (EMD) value calculated using SciPy's Wasserstein_distance function (u_values ​​= particle distribution before rolling, v_values ​​= particle distribution after rolling, u_weights = none, v_weights = none) of 0.071 or less.

9. The cathode material according to claim 1 , wherein the cathode material is a single particle.

10. The cathode material according to claim 1 , wherein the surface of the cathode material is coated with a coating agent containing metal or carbon.

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

12. A) measuring the rolling density of the cathode material using a powder resistivity meter when the load is 0 kgf to 2,000 kgf or less; B) measuring the rolling density of the cathode material using a hydraulic press when the load is 2,000 kgf or more; and C) calculating the difference between the ideal rolling density and the absolute value of the measured rolling density (del_PD_absolute), the difference between the ideal rolling density and the relative value of the measured rolling density (del_PD_absolute), and the difference between the ideal rolling density and the relative value of the measured rolling density (del_PD_absolute). and measuring the difference in inclination between the ideal value of the rolling density and the measured value (del_inclination), or the particle distribution before and after rolling, and acquiring the EMD as a value calculated using SciPy's Wasserstein_distance function (u_values ​​= particle distribution before rolling, v_values ​​= particle distribution after rolling, u_weights = none, v_weights = none).

13. The cathode material is characterized by being a compound represented by the following chemical formula 1: (Chemical formula 1) Li ａ Ni ｘ Mn ｙ Co ｚ M ｗ O ２＋δ 13. The method for measuring particle strength of a cathode material according to claim 12, wherein, in Chemical Formula 1, M comprises one or more selected from the group consisting of B, W, Al, Ti, and Mg, and 1<a≦1.1, 0<x<0.95, 0<y<0.8, 0<z<1.0, 0≦w≦0.1, −0.02≦δ≦0.02, and x+y+z+w=1.

14. The method for measuring particle strength of a positive electrode material according to claim 12 or 13, wherein the particle is a single particle.

15. 14. The method for measuring particle strength of a cathode material according to claim 12 or 13, wherein step B) is a step of measuring the rolling density of the cathode material using a hydraulic press under a load of more than 2,000 kgf or between 2,000 kgf and 9,000 kgf.

Images