Positive electrode active material for lithium secondary battery and method for preparing same

Abstract

The present invention relates to a positive electrode active material, a method for preparing the same, and a lithium secondary battery including the positive electrode active material. The positive electrode active material is of the formula Li 1+a1 Ni x1 Co y1 M z1 M’ 1-x1-y1-z1 O2 and agglomerated particles represented by the formula Li 1+a2 Ni x2 Co y2 M z2 M’ 1-x2-y2-z2 O2 and single crystal particles, where M is one or two elements selected from Mn and Al, M’ is one or more elements selected from B, F, Mg, Si, P, Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce, and W, -0.03 ≦ a1 ≦ 0.20, 0.30 ≦ x1 ≦ 0.99, 0 ≦ y1 ≦ 0.30, 0 ≦ z1 ≦ 0.30, 0 ≦ 1 - x1 - y1 - z1 ≦ 0.10, -0.03 ≦ a2 ≦ 0.20, 0.31 ≦ x2 ≦ 1.00, 0 ≦ y2 ≦ 0.30, 0 ≦ z2 ≦ 0.30, 0 ≦ 1 - x2 - y2 - z2 ≦ 0.10, provided that 0

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material, a method for preparing the same, and a lithium secondary battery containing the positive electrode active material. [Background technology]

[0002] In recent years, with the worsening energy and environmental crisis, natural energy sources such as wind and solar power have been actively developed. However, these energy sources have low efficiency and cannot compensate for the lack of large-scale energy resource utilization. Lithium-ion batteries, a green secondary battery with significant advantages such as high operating voltage, high energy density, good cycle life, low self-discharge, and no memory effect, have been rapidly developed.

[0003] In the field of lithium-ion batteries, ternary layer materials (nickel-cobalt-manganese, NCM) have great potential for development due to their high specific capacity and stability. However, as the nickel content in NCM increases, the stability of the material gradually decreases. Highly active Ni, which is generated during the charging process, 4+ The reaction of NiO with the electrolyte results in the formation of a NiO-like rock salt phase, which severely damages the structure of the layered material, leading to the collapse of the cathode structure and further inducing the dissolution of transition metal ions, phase transitions, and lattice oxygen precipitation. Currently, the "secondary particles" of conventional agglomerated NCMs typically consist of numerous nanoscale "primary particles." During the charge and discharge process, changes in lattice parameters lead to the formation of microcracks in the secondary particles. These microcracks expose new interfaces within the secondary particles, further accelerating performance degradation. It is known that the destructive effects of cracks become more pronounced with higher nickel content. Therefore, microcracks are the primary cause of the deterioration of the cycle life of NCMs, especially high-nickel NCMs, which simultaneously reduces the thermal, structural, and cycling stability of the cathode material.

[0004] Currently, to minimize the occurrence of microcracks in high-nickel agglomerate materials, most research has applied techniques such as coating and doping to improve the strength of large particles. However, it is very difficult to increase the packed density during battery manufacturing. For the same nickel content, small agglomerate particles have a higher capacity than large particles, but properties such as cycle life and gas generation are reduced. The morphology of small single-crystal particles is different from that of small agglomerate particles, and their particle strength is relatively high. However, properties such as capacity and gas generation hardly reach the desired levels, and there are also significant problems with sorting and pulping.

[0005] Chinese Patent No. 109962221 uses an aggregate-doped monocrystalline material, whose main components are a monocrystalline lithium manganese iron phosphate material and an aggregated multi-element material. The multi-element material and the lithium manganese iron phosphate are two different cathode materials with different test voltages and application ranges. Therefore, forcibly mixing the two materials inevitably sacrifices the advantages of each and results in resource waste. As disclosed in Chinese Patent No. 107154491, two materials with different conductivities are mixed, and the capacity of the two materials is considered separately, but the impact of the Ni content of the two different materials on the final product is not taken into account. Because the two materials are mixed, the particle size tolerance is relatively wide, and the impact on the final product is largely undetermined. Summary of the Invention

[0006] The objective of the present invention is to overcome the shortcomings of the prior art and effectively improve the defects of compounded products, such as low capacity and poor cycle life. The present invention effectively improves the capacity of positive electrode active materials by increasing the Ni content in small particles relative to the Ni content in large particles. Furthermore, by preparing large agglomerated particles and small single-crystal particles and controlling their different surface properties, the occurrence of microcracks in the large agglomerated particles can be effectively suppressed, thereby improving the stability of the positive electrode active material during long-term cycling. The positive electrode active material provided by the present invention has properties such as high compaction density, high capacity, and high stability.

[0007] In one aspect, the present invention provides a positive electrode active material for a lithium secondary battery, the positive electrode active material comprising agglomerated particles represented by Formula A1 and single-crystal particles represented by Formula A2: A1: Li 1+a1 Ni x1 Co y1 M z1 M' 1-x1-y1-z1 O2 A2: Li 1+a2 Ni x2 Co y2 M z2 M' 1-x2-y2-z2 O2

[0008] where: M is one or two elements selected from Mn and Al; M' is one or more elements selected from B, F, Mg, Si, P, Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce, and W; -0.03≦a1≦0.20, 0.30≦x1≦0.99, 0≦y1≦0.30, 0≦z1≦0.30, 0≦1-x1-y1-z1≦0.10, -0.03≦a2≦0.20, 0.31≦x2≦1.00, 0≦y2≦0.30, 0≦z2≦0.30, 0≦1−x2−y2−z2≦0.10, However, 0 <x2-x1≦0.5である。

[0009] In another aspect, the present invention also provides a method for preparing a positive electrode active material, comprising the steps of: i) separately preparing an aggregate particle precursor represented by formula A3 and a single-crystal particle precursor represented by formula A4 by a liquid phase coprecipitation method; A3: Ni x1 Co y1 M z1 M' 1-x1-y1-z1 (OH)2 A4: Ni x2 Co y2 M z2 M' 1-x2-y2-z2 (OH)2

[0010] where: M is one or two elements selected from Mn and Al; M' is one or more elements selected from B, F, Mg, Si, P, Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce, and W; 0.30≦x1≦0.99, 0≦y1≦0.30, 0≦z1≦0.30, 0≦1-x1-y1-z1≦0.10, 0.31≦x2≦1.00, 0≦y2≦0.30, 0≦z2≦0.30, 0≦1−x2−y2−z2≦0.10; However, 0 <x2-x1≦0.5である、

[0011] ii) mixing a lithium source with the agglomerated particle precursor in a molar ratio r1, optionally incorporating M′ as a doping element, wherein 0.97≦r1≦1.20, followed by primary sintering in an air or oxygen sintering atmosphere at a sintering temperature T1, wherein 600° C.≦T1≦1000° C., followed by grinding to obtain agglomerated particles;

[0012] iii) mixing a lithium source with the single crystal particle precursor in a molar ratio r2, optionally incorporating M′ as a doping element, where 0.97≦r2≦1.20, then performing primary sintering under a sintering atmosphere of air or oxygen at a sintering temperature T2, where 650°C≦T2≦1050°C, and then grinding to obtain single crystal particles; and iv) The agglomerated particles of step ii) are mixed with the single crystal particles of step iii) to obtain a positive electrode active material.

[0013] In yet another aspect, the present invention also provides a lithium secondary battery comprising the positive electrode active material according to the present invention or a positive electrode active material prepared by the preparation method according to the present invention. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 shows an SEM photograph of large aggregate particles A1 in Example 1; [Figure 2]FIG. 2 shows an SEM photograph of small single-crystal particles A2 in Example 1; [Figure 3] FIG. 3 shows an SEM photograph of the mixture of the two particles in Example 1; [Figure 4] FIG. 4 shows charge / discharge curves of Example 1, Comparative Example 1, and Comparative Example 2; and [Figure 5] FIG. 5 shows the cycle life of Example 1, Comparative Example 1, and Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0015] Unless otherwise stated, all publications, patent applications, patents, and other references mentioned herein are expressly incorporated by reference in their entirety for all purposes, as if fully set forth.

[0016] 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. In case of conflict, the present specification, including definitions, will control.

[0017] When an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a series of upper and lower preferred values, it is to be understood that all ranges formed by combining any upper or preferred value with a lower or preferred value or preferred value within a range are specifically disclosed, regardless of whether these ranges are disclosed individually. When a range of numerical values ​​is mentioned, unless otherwise indicated, the range includes its endpoints, and all integers and fractions within the range.

[0018] In one aspect, the present invention provides a positive electrode active material for a lithium secondary battery, the positive electrode active material comprising agglomerated particles represented by Formula A1 and single-crystal particles represented by Formula A2: A1: Li 1+a1 Ni x1 Co y1 Mz1 M' 1-x1-y1-z1 O2 A2: Li 1+a2 Ni x2 Co y2 M z2 M' 1-x2-y2-z2 O2

[0019] where: M is one or two elements selected from Mn and Al; M' is one or more elements selected from B, F, Mg, Si, P, Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce, and W;

[0020] -0.03≦a1≦0.20, preferably -0.01≦a1≦0.14, more preferably 0≦a1≦0.10, and particularly preferably 0.01≦a1≦0.08; 0.30≦x1≦0.99, preferably 0.57≦x1≦0.99, more preferably 0.72≦x1≦0.99, and particularly preferably 0.80≦x1≦0.99; 0≦y1≦0.30, preferably 0≦y1≦0.21, more preferably 0≦y1≦0.15, and particularly preferably 0≦y1≦0.10; 0≦z1≦0.30, preferably 0≦z1≦0.18, more preferably 0≦z1≦0.11, and particularly preferably 0≦z1≦0.06; 0≦1−x1−y1−z1≦0.10, preferably 0≦1−x1−y1−z1≦0.08, more preferably 0≦1−x1−y1−z1≦0.05, and particularly preferably 0≦1−x1−y1−z1≦0.03;

[0021] -0.03≦a2≦0.20, preferably -0.02≦a2≦0.16, more preferably -0.01≦a2≦0.14, and particularly preferably 0≦a2≦0.08; 0.31≦x2≦1.00, preferably 0.59≦x2≦0.995, more preferably 0.75≦x2≦0.995, and particularly preferably 0.81≦x2≦0.995; 0 ≤ y2 ≤ 0.30, preferably 0 ≤ y2 ≤ 0.21, more preferably 0 ≤ y2 ≤ 0.15, and particularly preferably 0 ≤ y2 ≤ 0.10, and 0 ≤ z2 ≤ 0.30, preferably 0 ≤ z2 ≤ 0.18, more preferably 0 ≤ z2 ≤ 0.11, and particularly preferably 0 ≤ z2 ≤ 0.08, and 0 ≤ 1 - x2 - y2 - z2 ≤ 0.10, preferably 0 ≤ 1 - x2 - y2 - z2 ≤ 0.08, more preferably 0 ≤ 1 - x2 - y2 - z2 ≤ 0.05, and particularly preferably 0 ≤ 1 - x2 - y2 - z2 ≤ 0.03, and

[0022] where 0 < x2 - x1 ≤ 0.5, preferably 0.01 ≤ x2 - x1 ≤ 0.27, more preferably 0.01 ≤ x2 - x1 ≤ 0.2, still more preferably 0.015 ≤ x2 - x1 ≤ 0.20, and particularly preferably 0.02 ≤ x2 - x1 ≤ 0.15.

[0023] According to one aspect of the positive electrode active material of the present invention, a2 > a1, preferably 0.01 ≤ a2 - a1 ≤ 0.20, more preferably 0.01 ≤ a2 - a1 ≤ 0.12, and particularly preferably 0.01 ≤ a2 - a1 ≤ 0.07, and especially preferably 0.01 ≤ a2 - a1 ≤ 0.04.

[0024] According to another aspect of the positive electrode active material of the present invention, the aggregated particles have a particle size D of 6 to 30 μm, preferably 8 to 25 μm, more preferably 9 to 20 μm, and particularly preferably 10 to 18 μm 50 and

[0025] According to another aspect of the positive electrode active material of the present invention, the single crystal particles have a particle size D of 0.1 to 10 μm, preferably 0.5 to 8.0 μm, more preferably 1.0 to 6.0 μm, and particularly preferably 1.5 to 4.5 μm 50 and

[0026] According to another embodiment of the positive electrode active material of the present invention, the aggregate particles are present in an amount of 20 to 90%, preferably 45 to 85%, more preferably 50 to 80%, and particularly preferably 60 to 80%, based on the weight of the positive electrode active material, and the single-crystal particles are present in an amount of 10 to 80%, preferably 10 to 70%, more preferably 15 to 60%, and particularly preferably 20 to 40%.

[0027] According to another embodiment of the positive electrode active material of the present invention, the agglomerated particles have a coating layer containing at least one coating element selected from the group consisting of B, F, Mg, Al, Si, P, Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce, and W, where the coating element is present in an amount of 0.1 to 2 mol %, preferably about 1 mol %, based on the agglomerated particles; and / or the single-crystal particles have a coating layer containing at least one coating element selected from the group consisting of B, F, Mg, Al, Si, P, Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce, and W, where the coating element is present in an amount of 0.1 to 2 mol %, preferably about 1 mol %, based on the single-crystal particles, with the proviso that the coating element contained in the coating layer of the agglomerated particles is different from the coating element contained in the coating layer of the single-crystal particles.

[0028] According to another embodiment of the positive electrode active material of the present invention, the specific surface area BET of the positive electrode active material before and after baking at 600°C for 8 hours in an air atmosphere is before and BET after satisfies the following equation: |BET after -BET before | / BET before ≦50%, Preferably, |BET after -BET before | / BET before ≦30%.

[0029] The present invention uses an optimal blend ratio of single crystal particles with rounded surfaces and agglomerated particles with high particle strength, resulting in a controlled finished material that exhibits a stable crystal structure, thereby suppressing changes in the surface porosity of the finished product during further sintering.

[0030] According to another embodiment of the positive electrode active material of the present invention, the specific surface area BET of the aggregated particles before and after firing at 600° C. for 8 hours in an air atmosphere is before and BET after satisfies the following equation: (BET after -BET before ) / BET before ≧15%, Preferably, 40%≧(BET after -BET before ) / BET before ≧20%.

[0031] Agglomerated particles consist of many nanoscale particles. To maintain good cycle performance, there should be no excessive voids on the surface of the nanoparticles, and the BET of the material must be controlled within a certain range. Under normal circumstances, the BET of the material will further decrease after sintering at high temperatures. However, according to the present invention, the crystallinity and orientation of the nanograins on the surface of the material can be controlled to achieve in situ (in situ) By combining this with an in-situ melt surface treatment, good surface / interface protection effects can be achieved. Furthermore, unexpectedly, it was found that the BET of the material surface did not decrease but rather increased. The inventors further found that mixing agglomerated particles with such surface BET properties with single-crystal particles resulted in a positive electrode material that exhibited relatively excellent compression resistance, better discharge capacity, and cycle performance.

[0032] According to another embodiment of the positive electrode active material of the present invention, the specific surface area BET of the single crystal particles before and after sintering at 600°C for 8 hours in an air atmosphere before and BET after satisfies the following equation: (BET before -BET after ) / BET before ≦15%, Preferably, 0≦(BET before -BET after ) / BET before ≦10%.

[0033] The single crystal particles of the present invention are relatively structurally stable due to their properties such as good crystallinity and rounded surfaces, and the material does not collapse or shrink significantly during high temperature sintering, resulting in a small change in BET compared to that of the unsintered material.

[0034] According to another embodiment of the positive electrode active material of the present invention, the positive electrode active material does not include a nickel-free active material such as lithium manganese iron phosphate. According to another embodiment of the positive electrode active material of the present invention, the positive electrode active material comprises aggregated particles represented by formula A1 and single-crystal particles represented by formula A2.

[0035] In another aspect, the present invention further provides a method for preparing a positive electrode active material, the method comprising the steps of: i) separately preparing an aggregate particle precursor represented by formula A3 and a single-crystal particle precursor represented by formula A4 by a liquid phase coprecipitation method; A3: Ni x1 Co y1 M z1 M' 1-x1-y1-z1 (OH)2 A4: Ni x2 Co y2 M z2 M' 1-x2-y2-z2 (OH)2

[0036] where: M is one or two elements selected from Mn and Al; M' is one or more elements selected from B, F, Mg, Si, P, Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce, and W;

[0037] 0.30≦x1≦0.99, preferably 0.57≦x1≦0.99, more preferably 0.72≦x1≦0.99, and particularly preferably 0.80≦x1≦0.99; 0 ≤ y1 ≤ 0.30, preferably 0 ≤ y1 ≤ 0.21, more preferably 0 ≤ y1 ≤ 0.15, and particularly preferably 0 ≤ y1 ≤ 0.10, and 0 ≤ z1 ≤ 0.30, preferably 0 ≤ z1 ≤ 0.18, more preferably 0 ≤ z1 ≤ 0.11, and particularly preferably 0 ≤ z1 ≤ 0.06, and

[0038] 0 ≤ 1 - x1 - y1 - z1 ≤ 0.10, preferably 0 ≤ 1 - x1 - y1 - z1 ≤ 0.08, more preferably 0 ≤ 1 - x1 - y1 - z1 ≤ 0.05, and particularly preferably 0 ≤ 1 - x1 - y1 - z1 ≤ 0.03, and

[0039] 0.31 ≤ x2 ≤ 1.00, preferably 0.59 ≤ x2 ≤ 0.995, more preferably 0.75 ≤ x2 ≤ 0.995, and particularly preferably 0.81 ≤ x2 ≤ 0.995, and 0 ≤ y2 ≤ 0.30, preferably 0 ≤ y2 ≤ 0.21, more preferably 0 ≤ y2 ≤ 0.15, and particularly preferably 0 ≤ y2 ≤ 0.10, and 0 ≤ z2 ≤ 0.30, preferably 0 ≤ z2 ≤ 0.18, more preferably 0 ≤ z2 ≤ 0.11, and particularly preferably 0 ≤ z2 ≤ 0.08, and

[0040] 0 ≤ 1 - x2 - y2 - z2 ≤ 0.10, preferably 0 ≤ 1 - x2 - y2 - z2 ≤ 0.08, more preferably 0 ≤ 1 - x2 - y2 - z2 ≤ 0.05, and particularly preferably 0 ≤ 1 - x2 - y2 - z2 ≤ 0.03, and

[0041] However, 0 < x2 - x1 ≤ 0.5, preferably 0.01 ≤ x2 - x1 ≤ 0.27, more preferably 0.01 ≤ x2 - x1 ≤ 0.20, still more preferably 0.015 ≤ x2 - x1 ≤ 0.20, and particularly preferably 0.02 ≤ x2 - x1 ≤ 0.15, and

[0042] ii) mixing a lithium source with the agglomerated particle precursor in a molar ratio r1, optionally incorporating M′ as a doping element, wherein 0.97≦r1≦1.20, preferably 0.99≦r1≦1.14, more preferably 1.00≦r1≦1.10, and particularly preferably 1.01≦r1≦1.08, followed by primary sintering in a sintering atmosphere of air or oxygen, preferably oxygen, at a sintering temperature T1, wherein 600°C≦T1≦1000°C, preferably 675°C≦T1≦875°C, more preferably 690°C≦T1≦800°C, and particularly preferably 690°C≦T1≦780°C, followed by grinding to obtain agglomerated particles;

[0043] iii) mixing a lithium source with the single crystal particle precursor in a molar ratio r2, optionally incorporating M′ as a doping element, wherein 0.97≦r2≦1.20, preferably 0.98≦r2≦1.16, more preferably 0.99≦r2≦1.14, and particularly preferably 1.00≦r2≦1.08, then carrying out primary sintering in a sintering atmosphere of air or oxygen, preferably oxygen, at a sintering temperature T2, wherein 650° C.≦T2≦1050° C., preferably 730° C.≦T2≦930° C., more preferably 750° C.≦T2≦930° C., and particularly preferably 750° C.≦T2≦900° C., then obtaining single crystal particles by grinding; and

[0044] iv) The agglomerated particles of step ii) are mixed with the single crystal particles of step iii) to obtain a positive electrode active material.

[0045] According to another embodiment of the method of the present invention, r2>r1, preferably 0.01≦r2−r1≦0.20, more preferably 0.01≦r2−r1≦0.12, particularly preferably 0.01≦r2−r1≦0.07, and especially preferably 0.01≦r2−r1≦0.04.

[0046] According to another aspect of the method of the present invention, the aggregate particle precursor has a particle size D of 6.5 to 30.5 μm, preferably 8.5 to 25.5 μm, more preferably 9.5 to 20.5 μm, and particularly preferably 10.5 to 18.5 μm. 50The agglomerated particles have a particle size D of 6 to 30 μm, preferably 8 to 25 μm, more preferably 9 to 20 μm, and particularly preferably 10 to 18 μm. 50 It has.

[0047] According to another embodiment of the method of the present invention, the single-crystal particle precursor has a particle size D of 0.1 to 30.5 μm, preferably 1.0 to 17.3 μm, more preferably 1.0 to 9.3 μm, and particularly preferably 1.0 to 6.0 μm. 50 The single crystal particles have a particle size D of 0.1 to 10 μm, preferably 0.5 to 8.0 μm, more preferably 1.0 to 6.0 μm, and particularly preferably 1.5 to 4.5 μm. 50 It has.

[0048] According to another embodiment of the method of the present invention, the agglomerated particles are present in an amount of 20 to 90%, preferably 45 to 85%, more preferably 50 to 80%, and particularly preferably 60 to 80%, based on the weight of the positive electrode active material, and the single-crystal particles are present in an amount of 10 to 80%, preferably 10 to 70%, more preferably 15 to 60%, and particularly preferably 20 to 40%.

[0049] According to another embodiment of the method according to the invention, prior to step iv), the agglomerated particles are mixed with a coating precursor comprising at least one coating element selected from the group consisting of B, F, Mg, Al, Si, P, Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce and W, and then secondary sintering is carried out in a sintering atmosphere of air or oxygen, preferably oxygen, at a sintering temperature T3 to obtain secondary sintered agglomerated particles, wherein 250°C < T3 < 800°C, preferably 250°C < T3 < 600°C, more preferably 250°C < T3 < 480°C, and particularly preferably 250°C < T3 < 450°C, and the coating element is present in an amount of 0.1 to 2 mol%, preferably about 1 mol%, based on the agglomerated particles; and / or additionally, single-crystal particles. with a coating precursor containing at least one coating element selected from the group consisting of B, F, Mg, Al, Si, P, Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce, and W, and then secondary sintering is performed in a sintering atmosphere of air or oxygen, preferably oxygen, at a sintering temperature T4 to obtain secondary sintered single crystal particles, wherein 300°C≦T4≦900°C, preferably 460°C≦T4≦800°C, more preferably 550°C≦T4≦750°C, and particularly preferably 600°C≦T4≦750°C, and the coating element is present in an amount of 0.1 to 2 mol%, preferably about 1 mol%, based on the single crystal particles; provided that the coating element contained in the coating precursor of the agglomerated particles is different from the coating element contained in the coating precursor of the single crystal particles.

[0050] In yet another aspect, the present invention further provides a lithium secondary battery comprising the positive electrode active material according to the present invention or a positive electrode active material prepared by the preparation method according to the present invention. [Example]

[0051] Example 1 First, Ni 0.83 Co 0.11 Mn 0.06 Agglomerated cathode precursor (10.5 μm) with the composition of (OH)2 and Ni 0.86 Co 0.08 Mn 0.06Single-crystal positive electrode precursors (4 μm) with a composition of (OH)2 were separately prepared by liquid-phase coprecipitation method.

[0052] LiOH and Ni 0.83 Co 0.11 Mn 0.06 (OH)2 was mixed at a molar ratio of 1.08. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 750°C. The sintered material was crushed, and boric acid containing 1 mol% of B was added to the crushed material. The second sintering was carried out at a sintering temperature of 400°C, resulting in the D shown in Figure 1. 50 A large agglomerated particle material with a BET of 10.0 μm was obtained. The agglomerated material was treated at 600°C for 8 hours, and had a BET value that increased by 35%.

[0053] LiOH and Ni 0.86 Co 0.08 Mn 0.06 (OH)2 was mixed at a molar ratio of 1.12. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 812°C. The sintered material was crushed, and Al2O3 containing 1 mol% of Al was added to the crushed material. The second sintering was carried out at a sintering temperature of 620°C, resulting in the D shown in Figure 2. 50 The single crystal grain material was obtained with a small particle size of 3.5 μm. The single crystal material was treated at 600°C for 8 hours, and had a BET reduction of 2%.

[0054] The large aggregated particles and small single-crystal particles were mixed in a mass ratio of 7:3 to obtain the positive electrode active material for lithium secondary batteries shown in Figure 3. When the positive electrode active material was treated at 600°C for 8 hours, it had a BET value that increased by 24%.

[0055] Example 2 First, Ni 0.83 Co 0.11 Mn 0.06 Agglomerated cathode precursor (10.5 μm) with the composition of (OH)2 and Ni 0.86 Co 0.08 Mn 0.06 Single-crystal positive electrode precursors (4 μm) with a composition of (OH)2 were separately prepared by liquid-phase coprecipitation method.

[0056] LiOH and Ni 0.83 Co 0.11 Mn 0.06 (OH)2 was mixed at a molar ratio of 1.06. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 745°C. The sintered material was crushed, and boric acid containing 0.8 mol% of B was added to the crushed material. The second sintering was carried out at a sintering temperature of 380°C. 50 A large agglomerated particle material with a BET of 10.0 μm was obtained. The agglomerated material was treated at 600°C for 8 hours, and had a BET increase of 24%.

[0057] LiOH and Ni 0.86 Co 0.08 Mn 0.06 (OH)2 was mixed at a molar ratio of 1.12. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 812°C. The sintered material was crushed, and Al2O3 containing 1.2 mol% of Al was added to the crushed material. The second sintering was carried out at a sintering temperature of 610°C. 50 The single crystal grain material was obtained with a small particle size of 3.5 μm. The single crystal material was treated at 600°C for 8 hours, and had a BET value that decreased by 3%.

[0058] The large aggregated particles and the small single-crystal particles were mixed in a mass ratio of 8:2 to obtain a cathode active material for lithium secondary batteries. After heating at 600°C for 8 hours, the cathode active material showed a 19% increase in BET.

[0059] Example 3 First, Ni 0.86 Co 0.11 Mn 0.03 Agglomerated cathode precursor (10.5 μm) with the composition of (OH)2 and Ni 0.88 Co 0.08 Mn 0.04 Single-crystal positive electrode precursors (4 μm) with a composition of (OH)2 were separately prepared by liquid-phase coprecipitation method.

[0060] LiOH and Ni 0.86 Co 0.11 Mn 0.03(OH)2 was mixed at a molar ratio of 1.06. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 725°C. The sintered material was crushed, and boric acid containing 0.8 mol% of B was added to the crushed material. The second sintering was carried out at a sintering temperature of 380°C. 50 A large agglomerated particle material with a BET of 10.0 μm was obtained. The agglomerated material was treated at 600°C for 8 hours, and had a BET increase of 26%.

[0061] LiOH and Ni 0.88 Co 0.08 Mn 0.04 (OH)2 was mixed at a molar ratio of 1.11. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 805°C. The sintered material was crushed, and Al2O3 containing 1.0 mol% Al was added to the crushed material. The second sintering was carried out at a sintering temperature of 610°C. 50 The single crystal grain material was obtained with a small particle size of 3.5 μm. The single crystal material was treated at 600°C for 8 hours, and had a BET reduction of 2%.

[0062] The large aggregated particles and the small single-crystal particles were mixed in a mass ratio of 7:3 to obtain a cathode active material for lithium secondary batteries. After heating at 600°C for 8 hours, the cathode active material showed a 20% increase in BET.

[0063] Example 4 First, Ni 0.86 Co 0.11 Mn 0.03 Agglomerated cathode precursor (10.5 μm) with the composition of (OH)2 and Ni 0.88 Co 0.08 Mn 0.04 Single-crystal positive electrode precursors (4 μm) with a composition of (OH)2 were separately prepared by liquid-phase coprecipitation method.

[0064] LiOH and Ni 0.86 Co 0.11 Mn 0.03(OH)2 was mixed at a molar ratio of 1.06. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 685°C. The sintered material was crushed, and boric acid containing 0.8 mol% of B was added to the crushed material. The second sintering was carried out at a sintering temperature of 380°C. 50 A large agglomerated particle material with a BET of 10.0 μm was obtained. The agglomerated material was treated at 600°C for 8 hours, and had a BET increase of 26%.

[0065] LiOH and Ni 0.88 Co 0.08 Mn 0.04 (OH)2 was mixed at a molar ratio of 1.11. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 805°C. The sintered material was crushed, and Al2O3 containing 1.0 mol% Al was added to the crushed material. The second sintering was carried out at a sintering temperature of 610°C. 50 The single crystal grain material was obtained with a small particle size of 3.5 μm. The single crystal material was treated at 600°C for 8 hours, and had a BET reduction of 2%.

[0066] The large aggregated particles and the small single-crystal particles were mixed in a mass ratio of 3:7 to obtain a cathode active material for lithium secondary batteries. After heating at 600°C for 8 hours, the cathode active material showed a 6% increase in BET.

[0067] Example 5 First, Ni 0.88 Co 0.10 Mn 0.02 Agglomerated cathode precursor (10.5 μm) with the composition of (OH)2 and Ni 0.90 Co 0.08 Mn 0.02 Single-crystal positive electrode precursors (4 μm) with a composition of (OH)2 were separately prepared by liquid-phase coprecipitation method.

[0068] LiOH and Ni 0.88 Co 0.10 Mn 0.02(OH)2 was mixed at a molar ratio of 1.08. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 780°C. The sintered material was crushed, and boric acid containing 1 mol% of B was added to the crushed material. The second sintering was carried out at a sintering temperature of 400°C. 50 A large agglomerated particle material with a BET of 10.0 μm was obtained. The agglomerated material was treated at 600°C for 8 hours, and had a BET increase of 32%.

[0069] LiOH and Ni 0.90 Co 0.08 Mn 0.02 (OH)2 was mixed at a molar ratio of 1.12. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 812°C. The sintered material was crushed, and Al2O3 containing 1 mol% of Al was added to the crushed material. The second sintering was carried out at a sintering temperature of 620°C. 50 The single crystal grain material was obtained with a small particle size of 3.5 μm. The single crystal material was treated at 600°C for 8 hours, and had a BET reduction of 2%.

[0070] The large aggregated particles and the small single-crystal particles were mixed in a mass ratio of 7:3 to obtain a cathode active material for lithium secondary batteries. After heating at 600°C for 8 hours, the cathode active material showed a 22% increase in BET.

[0071] Example 6 First, Ni 0.83 Co 0.11 Mn 0.06 Agglomerated cathode precursor (10.5 μm) with the composition of (OH)2 and Ni 0.86 Co 0.08 Mn 0.06 Single-crystal positive electrode precursors (4 μm) with a composition of (OH)2 were separately prepared by liquid-phase coprecipitation method.

[0072] LiOH and Ni 0.83 Co 0.11 Mn 0.06(OH)2 was mixed at a molar ratio of 1.08. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 750°C. The sintered material was crushed, and boric acid containing 1 mol% of B was added to the crushed material. The second sintering was carried out at a sintering temperature of 400°C. 50 A large agglomerated particle material with a BET of 10.0 μm was obtained. The agglomerated material was treated at 600°C for 8 hours, and had a BET value that increased by 35%.

[0073] LiOH and Ni 0.86 Co 0.08 Mn 0.06 (OH)2 was mixed at a molar ratio of 1.12. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 812°C. The sintered material was crushed, and boric acid containing 0.4 mol% of B was added to the crushed material. The second sintering was carried out at a sintering temperature of 400°C. 50 The single crystal grain material was obtained with a small particle size of 3.5 μm. The single crystal material was treated at 600°C for 8 hours, and had a BET value that increased by 9%.

[0074] The large aggregated particles and the small single-crystal particles were mixed in a mass ratio of 7:3 to obtain a cathode active material for lithium secondary batteries. After heating at 600°C for 8 hours, the cathode active material showed a 27% increase in BET.

[0075] Example 7 First, Ni 0.83 Co 0.11 Mn 0.06 Agglomerated cathode precursor (10.5 μm) with the composition of (OH)2 and Ni 0.86 Co 0.08 Mn 0.06 Single-crystal positive electrode precursors (4 μm) with a composition of (OH)2 were separately prepared by liquid-phase coprecipitation method.

[0076] LiOH and Ni 0.83 Co 0.11 Mn 0.06(OH)2 was mixed at a molar ratio of 1.08. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 750°C. The sintered material was crushed, and boric acid containing 0.5 mol% of B was added to the crushed material. The second sintering was carried out at a sintering temperature of 400°C. 50 A large agglomerated particle material with a BET of 10.0 μm was obtained. The agglomerated material was treated at 600°C for 8 hours, and had an increased BET of 11%.

[0077] LiOH and Ni 0.86 Co 0.08 Mn 0.06 (OH)2 was mixed at a molar ratio of 1.12. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 812°C. The sintered material was crushed, and Al2O3 containing 1 mol% of Al was added to the crushed material. The second sintering was carried out at a sintering temperature of 620°C. 50 The single crystal grain material was obtained with a small particle size of 3.5 μm. The single crystal material was treated at 600°C for 8 hours, and had a BET reduction of 2%.

[0078] The large aggregated particles and the small single-crystal particles were mixed in a mass ratio of 7:3 to obtain a cathode active material for lithium secondary batteries. After heating at 600°C for 8 hours, the cathode active material showed a 7% increase in BET.

[0079] Example 8 First, Ni 0.83 Co 0.11 Mn 0.06 Agglomerated cathode precursor (10.5 μm) with the composition of (OH)2 and Ni 0.86 Co 0.08 Mn 0.06 Single-crystal positive electrode precursors (4 μm) with a composition of (OH)2 were separately prepared by liquid-phase coprecipitation method.

[0080] LiOH and Ni 0.83 Co 0.11 Mn 0.06(OH)2 was mixed at a molar ratio of 1.08. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 750°C. The sintered material was crushed, and Al2O3 containing 1 mol% of Al was added to the crushed material. The second sintering was carried out at a sintering temperature of 620°C. 50 A large agglomerated particle material with a BET of 10.0 μm was obtained. The agglomerated material was treated at 600°C for 8 hours, and had a BET reduction of 3%.

[0081] LiOH and Ni 0.86 Co 0.08 Mn 0.06 (OH)2 was mixed at a molar ratio of 1.12. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 812°C. The sintered material was crushed, and Al2O3 containing 1 mol% of Al was added to the crushed material. The second sintering was carried out at a sintering temperature of 620°C. 50 The single crystal grain material was obtained with a small particle size of 3.5 μm. The single crystal material was treated at 600°C for 8 hours, and had a BET reduction of 2%.

[0082] The large aggregated particles and the small single-crystal particles were mixed in a mass ratio of 7:3 to obtain a cathode active material for lithium secondary batteries. After heating at 600°C for 8 hours, the BET decreased by 3%.

[0083] Example 9 First, Ni 0.83 Co 0.11 Mn 0.06 Agglomerated cathode precursor (10.5 μm) with the composition of (OH)2 and Ni 0.86 Co 0.08 Mn 0.06 Single-crystal positive electrode precursors (4 μm) with a composition of (OH)2 were separately prepared by liquid-phase coprecipitation method.

[0084] LiOH and Ni 0.83 Co 0.11 Mn 0.06(OH)2 was mixed at a molar ratio of 1.08. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 750°C. The sintered material was crushed, and boric acid containing 0.5 mol% of B was added to the crushed material. The second sintering was carried out at a sintering temperature of 400°C. 50 A large agglomerated particle material with a BET of 10.0 μm was obtained. The agglomerated material was treated at 600°C for 8 hours, and had an increased BET of 11%.

[0085] LiOH and Ni 0.86 Co 0.08 Mn 0.06 (OH)2 was mixed at a molar ratio of 1.12. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 812°C. The sintered material was crushed, and boric acid containing 0.4 mol% of B was added to the crushed material. The second sintering was carried out at a sintering temperature of 400°C. 50 The single crystal grain material was obtained with a small particle size of 3.5 μm. The single crystal material was treated at 600°C for 8 hours, and had a BET value that increased by 9%.

[0086] The large aggregated particles and the small single-crystal particles were mixed in a mass ratio of 7:3 to obtain a cathode active material for lithium secondary batteries. After heating at 600°C for 8 hours, the cathode active material showed a 10% increase in BET.

[0087] Example 10 First, Ni 0.83 Co 0.11 Mn 0.06 Agglomerated cathode precursor (10.5 μm) with the composition of (OH)2 and Ni 0.84 Co 0.08 Mn 0.08 Single-crystal positive electrode precursors (4 μm) with a composition of (OH)2 were separately prepared by liquid-phase coprecipitation method.

[0088] LiOH and Ni 0.83 Co 0.11 Mn 0.06(OH)2 was mixed at a molar ratio of 1.08. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 750°C. The sintered material was crushed, and boric acid containing 0.5 mol% of B was added to the crushed material. The second sintering was carried out at a sintering temperature of 400°C. 50 A large agglomerated particle material with a BET of 10.0 μm was obtained. The agglomerated material was treated at 600°C for 8 hours, and had a BET value that increased by 35%.

[0089] LiOH and Ni 0.84 Co 0.08 Mn 0.08 (OH)2 was mixed at a molar ratio of 1.12. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 812°C. The sintered material was crushed, and boric acid containing 0.4 mol% of B was added to the crushed material. The second sintering was carried out at a sintering temperature of 400°C. 50 The single crystal grain material was obtained with a small particle size of 3.5 μm. The single crystal material was treated at 600°C for 8 hours, and had a BET reduction of 2%.

[0090] The large aggregated particles and the small single-crystal particles were mixed in a mass ratio of 7:3 to obtain a cathode active material for lithium secondary batteries. After heating at 600°C for 8 hours, the cathode active material showed a BET increase of 24%.

[0091] Comparative Example 1 First, Ni 0.83 Co 0.11 Mn 0.06 Agglomerated cathode precursor (10.5 μm) with the composition of (OH)2 and Ni 0.80 Co 0.11 Mn 0.09 Single-crystal positive electrode precursors (4 μm) with a composition of (OH)2 were separately prepared by liquid-phase coprecipitation method.

[0092] LiOH and Ni 0.83 Co 0.11 Mn 0.06(OH)2 was mixed at a molar ratio of 1.08. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 750°C. The sintered material was crushed, and boric acid containing 1 mol% of B was added to the crushed material. The second sintering was carried out at a sintering temperature of 400°C. 50 A large agglomerated particle material with a BET of 10.0 μm was obtained. The agglomerated material was treated at 600°C for 8 hours, and had a BET value that increased by 35%.

[0093] LiOH and Ni 0.80 Co 0.11 Mn 0.09 (OH)2 was mixed at a molar ratio of 1.12. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 820°C. The sintered material was crushed, and Al2O3 containing 1 mol% of Al was added to the crushed material. The second sintering was carried out at a sintering temperature of 620°C. 50 The single crystal grain material was obtained with a small particle size of 3.5 μm. The single crystal material was treated at 600°C for 8 hours, and had a BET reduction of 2%.

[0094] The large aggregated particles and the small single-crystal particles were mixed in a mass ratio of 7:3 to obtain a cathode active material for lithium secondary batteries. When the cathode active material was heated at 600°C for 8 hours, the BET increased by 25%.

[0095] Comparative Example 2 First, Ni 0.83 Co 0.11 Mn 0.06 Agglomerated cathode precursor (10.5 μm) with the composition of (OH)2 and Ni 0.83 Co 0.11 Mn 0.06 Single-crystal positive electrode precursors (4 μm) with a composition of (OH)2 were separately prepared by liquid-phase coprecipitation method.

[0096] LiOH and Ni 0.83 Co 0.11 Mn 0.06(OH)2 was mixed at a molar ratio of 1.08. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 750°C. The sintered material was crushed, and boric acid containing 1 mol% of B was added to the crushed material. The second sintering was carried out at a sintering temperature of 400°C. 50 A large agglomerated particle material with a BET of 10.0 μm was obtained. The agglomerated material was treated at 600°C for 8 hours, and had a BET value that increased by 35%.

[0097] LiOH and Ni 0.83 Co 0.11 Mn 0.06 (OH)2 was mixed at a molar ratio of 1.12. The mixed material was sintered for the first time in an oxygen atmosphere at a sintering temperature of 816°C. The sintered material was crushed, and Al2O3 containing 1 mol% of Al was added to the crushed material. The second sintering was carried out at a sintering temperature of 620°C. 50 The single crystal grain material was obtained with a small particle size of 3.5 μm. The single crystal material was treated at 600°C for 8 hours, and had a BET reduction of 2%.

[0098] The large aggregated particles and the small single-crystal particles were mixed in a mass ratio of 7:3 to obtain a cathode active material for lithium secondary batteries. When the cathode active material was heated at 600°C for 8 hours, the BET increased by 25%.

[0099] Specific surface area test: A Tri-star 3020 specific surface area analyzer was used for the test. 3 g of sample was weighed. The sample tube was placed in the vacuum joint of the degassing station port. The heating temperature was set to 300°C, and the degassing time was set to 120 minutes. After degassing, the sample tube was cooled. The mass of the empty sample tube and the mass of the sample and sample tube after degassing were entered through the software interface of the analyzer. The specific surface area data (BET method) calculated and output by the software was recorded, completing the specific surface area test of the positive electrode material sample.

[0100] Particle size testing: A Mastersizer 2000 laser particle size analyzer was used for the test. The following changes were made to the software's "Measurement" section: In the "Measurement Time" section, both the "Sample Measurement Time" and "Background Measurement Time" were set to 6 seconds. In the "Repeat Measurement" section, the "Number of Repeats" was set to 3, and the "Delay Time" was set to 5 seconds. "Generate Average Results from Measurements" was clicked. Next, "Start" was clicked to automatically measure the background. After the automatic measurement was completed, 40 ml of sodium pyrophosphate was first added, followed by a small amount of sample using a spatula. When obscuration reached half of the visually recognizable range of 10-20%, "Start" was clicked. Finally, three results and their average values ​​were recorded.

[0101] Preparation of button cell batteries: First, a nickel-cobalt-manganese composite multi-element cathode active material for non-aqueous electrolyte secondary batteries, acetylene black, and polyvinylidene fluoride (PVDF) were mixed, coated onto aluminum foil, and dried in an oven. The dried cathode sheet, separator, anode sheet, and electrolyte were assembled into a 2025-type button cell in an Ar-filled glove box with a moisture and oxygen content of less than 5 ppm.

[0102] Initial discharge capacity measurement method: The button cell batteries were left for 2 hours after fabrication. After the open circuit voltage stabilized, the positive electrode was charged at a current density of 0.1 C to a cutoff voltage of 4.3 V, then charged at a constant voltage for 30 minutes, and subsequently discharged at the same current density to a cutoff voltage of 3.0 V. This process was repeated in the same manner, and the resulting discharge capacity was considered the initial discharge capacity. Figure 4 shows the charge / discharge curves of the button cell batteries fabricated from the positive electrode materials of Example 1 and Comparative Examples 1 and 2. It can be seen that the positive electrode material of Example 1 has a higher initial discharge capacity than the positive electrode material of the Comparative Examples.

[0103] Full battery preparation and gas generation test: The cathode material, lithium nickel cobalt manganese oxide, anode material, graphite, conductive agent, carbon black, and binder, PVDF, were dried in a vacuum oven at 120°C for 12 hours. The oven-dried cathode material, conductive agent, carbon black, PVDF, and NMP were uniformly mixed to prepare a cathode slurry. This slurry was applied to aluminum foil using a lithium battery coater and allowed to dry. The electrode sheet was cut using an electrode sheet cutter and wound around an electrode sheet roller.

[0104] Anode slurry was prepared by uniformly mixing 950g of dried artificial graphite, 13g of Super-P, 14g of CMC, 46g of SBR solution, and 1200g of deionized water. This slurry was applied to copper foil using a lithium battery coater and allowed to dry. The resulting anode sheet was dried in a vacuum oven, cut with an electrode sheet cutter, and wound around an electrode sheet roller.

[0105] The above-mentioned positive and negative electrode sheets were wound using a conventional manufacturing method, and electrolyte was injected to fabricate a full battery. The initial thickness of the formed full battery was measured, and after storing it in a constant temperature bath at 45°C for 7 days, the thickness of the full battery was measured again. The thickness increase rate was used to indicate the gas generation characteristics of the positive electrode material in the full battery. Figure 5 shows the change in cycle life of full batteries fabricated from the positive electrode materials of Example 1 and Comparative Examples 1 and 2. It can be seen that the full battery fabricated from the positive electrode material of Example 1 exhibits better stability and longer cycle life.

[0106] [Table 1]

[0107] [Table 2]

[0108] The positive electrode active material and its lithium ion battery provided by the present invention achieve the following beneficial effects:

[0109] 1) Compared with agglomerated materials, single crystal materials with the same nickel content have a longer cycle life and lower gas generation capacity. Therefore, the introduction of single crystal materials can effectively improve the properties of mixed materials, such as cycle life and gas generation.

[0110] 2) Due to its unique single-crystal morphology, single-crystal materials have a lower capacity per gram than agglomerated materials with the same nickel content. Therefore, the present invention employs single-crystal materials with a slightly higher nickel content to compensate for the drawback of lower capacity per gram, while maintaining properties such as cycle life and gas generation at similar levels to agglomerated materials with a lower nickel content.

[0111] 3) The blended small particle single crystal material can penetrate into the gaps between the large agglomerates, exerting a synergistic effect of mutual support and co-packing with the large agglomerates, thereby effectively improving the compaction density of the material.

[0112] 4) The problems of single crystal materials, such as poor flowability and difficulty in screening and pulping, can be effectively overcome by adding a small amount of large agglomerated spherical particles to a system consisting mainly of small single crystal particles.

[0113] While specific embodiments have been described, these embodiments are presented for illustrative purposes only and are not intended to limit the scope of the present invention. The appended claims and their equivalents are intended to cover all modifications, substitutions, and alterations that fall within the scope and spirit of the present invention.

Claims

1. A positive electrode active material for a lithium secondary battery, the positive electrode active material comprising aggregated particles represented by Formula A1 and single-crystal particles represented by Formula A2, A1: Li １＋ａ１ Ni ｘ１ Co ｙ１ M ｚ１ M' １－ｘ１－ｙ１－ｚ１ O ２ A2: Li １＋ａ２ Ni ｘ２ Co ｙ２ M ｚ２ M' １－ｘ２－ｙ２－ｚ２ O ２ where: M is one or two elements selected from Mn and Al; M' is one or more elements selected from B, F, Mg, Si, P, Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce, and W; -0.03≦a1≦0.20, 0.80≦x1≦0.99, 0≦y1≦0.30, 0≦z1≦0.30, 0≦1−x1−y1−z1≦0.10, -0.03≦a2≦0.20, 0.81≦x2≦0.995, 0≦y2≦0.30, 0≦z2≦0.30, 0≦1−x2−y2−z2≦0.10, However, 0<x2-x1≦0.5, and a2>a1, The specific surface areas BET before and BET after of the positive electrode active material before and after firing at 600° C. for 8 hours in an air atmosphere satisfy the following formula: |BET after -BET before | / BET before ≦50%, The specific surface areas BET before and BET after of the agglomerated particles before and after firing at 600°C for 8 hours in an air atmosphere satisfy the following formula: (BET after - BET before) / BET before ≧15%, The specific surface areas BET before and BET after of the single crystal particles before and after firing at 600°C for 8 hours in an air atmosphere satisfy the following formula: (BET before - BET after) / BET before ≦15%, The positive electrode active material for a lithium secondary battery,

2. 0≦y1≦0.15, 0≦z1≦0.18, and 2. The positive electrode active material according to claim 1, wherein 0≦z2≦0.

08.

3. The aggregated particles have a particle size D of 6 to 30 μm. ５０ and The single crystal particles have a particle size D of 0.1 to 10 μm. ５０ The positive electrode active material according to claim 1 , wherein

4. The agglomerated particles are present in an amount of 20 to 90% based on the weight of the positive electrode active material, and 2. The positive electrode active material according to claim 1, wherein the single-crystal particles are present in an amount of 10 to 80% based on the weight of the positive electrode active material.

5. the agglomerate particles have a coating layer containing at least one coating element selected from the group consisting of B, F, Mg, Al, Si, P, Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce, and W, wherein the coating element is present in an amount of 0.1 to 2 mol %, based on the agglomerate particles; and / or the single crystal particles have a coating layer containing at least one coating element selected from the group consisting of B, F, Mg, Al, Si, P, Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce, and W, wherein the coating element is present in an amount of 0.1 to 2 mol % based on the single crystal particles; 2. The positive electrode active material according to claim 1, wherein a coating element contained in the coating layer of the agglomerated particles is different from a coating element contained in the coating layer of the single-crystal particles.

6. The specific surface area BET of the positive electrode active material before and after baking at 600°C for 8 hours in an air atmosphere ｂｅｆｏｒｅ and BET ａｆｔｅｒ satisfies the following equation, |BET ａｆｔｅｒ -BET ｂｅｆｏｒｅ | / BET ｂｅｆｏｒｅ ≦30%、 The specific surface area BET of the agglomerated particles before and after firing at 600°C for 8 hours in an air atmosphere ｂｅｆｏｒｅ and BET ａｆｔｅｒ satisfies the following equation, 40%≧(BET ａｆｔｅｒ -BET ｂｅｆｏｒｅ ) / BET ｂｅｆｏｒｅ ≧20%、 The specific surface area BET of the single crystal particles before and after firing at 600°C for 8 hours in an air atmosphere ｂｅｆｏｒｅ and BET ａｆｔｅｒ satisfies the following equation: 0≦(BET ｂｅｆｏｒｅ -BET ａｆｔｅｒ ) / BET ｂｅｆｏｒｅ ≦10%、 The positive electrode active material according to claim 1 .

7. Steps below: i) separately preparing an aggregate particle precursor represented by formula A3 and a single-crystal particle precursor represented by formula A4 by a liquid phase coprecipitation method; A3: Ni ｘ１ Co ｙ１ M ｚ１ M' １－ｘ１－ｙ１－ｚ１ (OH) ２ A4: No ｘ２ Co ｙ２ M ｚ２ M' １－ｘ２－ｙ２－ｚ２ (OH) ２ where: M is one or two elements selected from Mn and Al; M' is one or more elements selected from B, F, Mg, Si, P, Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce, and W; 0.80≦x1≦0.99, 0≦y1≦0.30, 0≦z1≦0.30, 0≦1−x1−y1−z1≦0.10, 0.81≦x2≦0.995, 0≦y2≦0.30, 0≦z2≦0.30, 0≦1−x2−y2−z2≦0.10, However, 0<x2-x1≦0.5, ii) mixing a lithium source with the agglomerated particle precursor in a molar ratio r1, optionally incorporating M′ as a doping element, wherein 0.97≦r1≦1.20, followed by primary sintering under a sintering atmosphere of air or oxygen at a sintering temperature T1, wherein 600° C.≦T1≦1000° C., followed by grinding to obtain agglomerated particles; iii) mixing a lithium source with the single crystal particle precursor in a molar ratio r2, optionally incorporating M′ as a doping element, where 0.97≦r2≦1.20, then carrying out primary sintering under a sintering atmosphere of air or oxygen at a sintering temperature T2, where 650° C.≦T2≦1050° C., and then obtaining single crystal particles by grinding; and iv) combining the agglomerated particles of step ii) with the single-crystal particles of step iii) to obtain a cathode active material; Including, A method for preparing a positive electrode active material, wherein r2>r1.

8. In step i), 0≦y1≦0.15, 0≦z1≦0.18, and 8. The method of claim 7, wherein 0≦z2≦0.

08.

9. The aggregate particle precursor has a particle diameter D of 6.5 to 30.5 μm. ５０ and The aggregated particles have a particle size D of 6 to 30 μm. ５０ and The single crystal particle precursor has a particle size D of 0.1 to 30.5 μm. ５０ and The single crystal particles have a particle size D of 0.1 to 10 μm. ５０ 8. The method of claim 7, comprising:

10. The agglomerated particles are present in an amount of 20 to 90% based on the weight of the positive electrode active material, 8. The method of claim 7, wherein the single-crystal particles are present in an amount of 10 to 80% based on the weight of the positive electrode active material.

11. Before step iv), mixing the agglomerate particles with a coating precursor comprising at least one coating element selected from the group consisting of B, F, Mg, Al, Si, P, Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce, and W, and then secondary sintering at a sintering temperature T3 in a sintering atmosphere of air or oxygen to obtain secondary sintered agglomerate particles, wherein 250°C≦T3≦800°C, and the coating element is present in an amount of 0.1 to 2 mol % based on the agglomerate particles; and / or the single crystal particles are mixed with a coating precursor containing at least one coating element selected from the group consisting of B, F, Mg, Al, Si, P, Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce, and W, and then secondary sintering is performed in an air or oxygen sintering atmosphere at a sintering temperature T4 to obtain secondary sintered single crystal particles, wherein 300°C≦T4≦900°C, and the coating element is present in an amount of 0.1 to 2 mol% based on the single crystal particles; 8. The method of claim 7, wherein the coating element contained in the coating precursor of the agglomerated particles is different from the coating element contained in the coating precursor of the single crystal particles.

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