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

Abstract

This invention relates to positive electrode active materials, their preparation methods, and lithium secondary batteries comprising said positive electrode active materials, wherein the positive electrode active materials comprise the formula Li 1+a1 Ni x1 Co y1 M z1 M′ 1‑x1‑y1‑z1 O2 represents polycrystalline particles and Li 1+a2 Ni x2 Co y2 M z2 M′ 1‑x2‑y2‑z2 O2 represents single-crystal particles.

Description

TECHNICAL FIELD

[0001] The present application relates to a positive electrode active material, a method for preparing the same, and a lithium secondary battery comprising the same. BACKGROUND

[0002] In recent years, with the aggravation of energy and environmental crisis, natural energy such as wind energy and solar energy has been developed vigorously, but the use efficiency of these energies is low, which cannot meet the gap of large-scale energy use. Lithium ion battery is a kind of green secondary battery, which has the outstanding advantages of high working voltage, large energy density, good cycle life, small self-discharge and no memory effect, and has developed rapidly.

[0003] In the field of lithium ion batteries, layered ternary materials (NCM) have great development potential due to their high specific capacity and stability. However, with the increase of nickel content in NCM, the stability of the material gradually decreases. The high activity Ni 4+ reacts with the electrolyte to form a NiO-like rock salt phase, which seriously damages the structure of the layered material, leading to the collapse of the positive electrode structure, and further inducing the dissolution of transition metal ions, phase transition and lattice oxygen precipitation. The conventional polycrystalline NCM "secondary particles" are usually composed of many nanoscale "primary particles". During charging and discharging, the change of lattice parameters will cause the formation of microcracks in the secondary particles. The formed microcracks will expose the fresh interface inside the secondary particles, further accelerating the performance decay. It is worth noting that the higher the nickel content, the more obvious the damage effect of the cracks. In summary, the main reason for the decrease of cycle life of NCM, especially high-nickel NCM, is microcracks, which will cause the decrease of thermal stability, structural stability and cycle stability of the positive electrode material.

[0004] At present, in order to improve the generation of microcracks of high-nickel polycrystalline material, most studies use coating and doping technologies to improve the strength of large particles, but in the process of making batteries, the compaction density is difficult to improve. Under the same nickel content, the capacity of polycrystalline small particles is higher than that of large particles, but the cycle and gas production performance are decreased. The morphology of single crystal small particles is different from that of polycrystalline small particles, and the particle strength is relatively high, but the capacity and gas production performance are also difficult to reach the ideal level, and there are also big problems in screening and pulping.

[0005] Patent CN 109962221 B uses agglomerate to mix single crystal materials, the main components are single crystal lithium manganese iron phosphate materials and agglomerated multi-element materials, multi-element and lithium manganese iron phosphate are two different positive electrode materials, their test voltages and use ranges are different, so forcibly mixing the two materials together will inevitably sacrifice their respective advantages and cause resource waste. Patent No. CN 107154491 B mixes two materials with different conductivities together, respectively considers the capacity of the two materials, but does not consider the influence of the Ni content of the two different materials on the final product, mixes the two materials together, and the particle size protection range is also relatively wide, so the effect of the final product is difficult to determine. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings of the prior art and effectively improve the low capacity and poor cycle of the mixed product. The present application effectively improves the capacity of the positive electrode active material by setting the Ni content of the small particles to be higher than that of the large particles. In addition, by preparing polycrystalline large particles and single crystal small particles and controlling their different surface properties, the generation of microcracks in the polycrystalline large particles is effectively inhibited, thereby improving the stability of the positive electrode active material during long-term cycling. The positive electrode active material provided by the present application has the properties of high compaction, high capacity and high stability.

[0007] In one aspect, the present application provides a positive electrode active material for a lithium secondary battery, characterized in that the positive electrode active material comprises polycrystalline particles represented by formula A1 and single crystal particles represented by formula A2

[0008] A1: Li 1+a1 Ni x1 Co y1 M z1 M' 1-x1-y1-z1 O2

[0009] A2: Li 1+a2 Ni x2 Co y2 M z2 M' 1-x2-y2-z2 O2

[0010] wherein,

[0011] M is one or two elements selected from Mn, Al,

[0012] 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, W,

[0013] -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,

[0014] -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,

[0015] with the proviso that: 0 < x2 - x1 < 0.5.

[0016] In another aspect, the present application also provides a method for preparing a positive electrode active material, comprising the following steps:

[0017] i) preparing a polycrystalline particle precursor represented by formula A3 and a single crystal particle precursor represented by formula A4, respectively, using a liquid phase coprecipitation method

[0018] A3: Ni x1 Co y1 M z1 M' 1-x1-y1-z1 (OH)2

[0019] A4: Ni x2 Co y2 M z2 M' 1-x2-y2-z2 (OH)2

[0020] wherein,

[0021] M is one or two elements selected from Mn, Al,

[0022] 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, W,

[0023] 0.30 < x1 < 0.99, 0 < y1 < 0.30, 0 < z1 < 0.30, 0 < 1 - x1 - y1 - z1 < 0.10,

[0024] 0.31 < x2 < 1.00, 0 < y2 < 0.30, 0 < z2 < 0.30, 0 < 1 - x2 - y2 - z2 < 0.10,

[0025] with the proviso that: 0 < x2 - x1 < 0.5;

[0026] ii) mixing a lithium source with the polycrystalline particle precursor in a molar ratio r1, optionally mixing in M' as a doping element, wherein 0.97 < r1 < 1.20; and then primary sintering at a sintering temperature T1 in a sintering atmosphere of air or oxygen, wherein 600 °C < T1 < 1000 °C; and then breaking to obtain polycrystalline particles;

[0027] iii) mixing a lithium source with the single-crystalline particle precursor in a molar ratio r2, optionally mixing in M' as a doping element, wherein 0.97 < r2 < 1.20; and then primary sintering at a sintering temperature T2 in a sintering atmosphere of air or oxygen, wherein 650 °C < T2 < 1050 °C; and then breaking to obtain single-crystalline particles; and

[0028] iv) admixing the polycrystalline particles of step ii) and the single-crystalline particles of step iii) to obtain the positive electrode active material.

[0029] In yet another aspect, the present application also provides a lithium secondary battery comprising the positive electrode active material according to the present application or the positive electrode active material prepared by the preparation method according to the present application. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figures 1 to 3 SEM photographs of polycrystalline large particles A1 and single-crystalline small particles A2 in Example 1 and after admixing thereof are shown;

[0031] Figure 4 Charge-discharge curves of Example 1, Comparative Example 1, Comparative Example 2 are shown; and

[0032] Figure 5 Cycle life of Example 1, Comparative Example 1, Comparative Example 2 is shown. DETAILED DESCRIPTION

[0033] All publications, patent applications, patents and other references mentioned herein are expressly incorporated by reference for all purposes as if each were individually incorporated by reference to the extent that they are not inconsistent with the disclosure herein.

[0034] Unless defined otherwise, 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 application belongs. If there is a conflict between usages of terms in the specification and those of the prior art, the definitions as used in the specification shall control.

[0035] If a quantity, concentration, or other numerical value or parameter is given as a range, a preferred range, or a series of preferred upper and lower limits, it should be understood that all ranges formed by any pair of any upper or preferred numerical values ​​and any lower or preferred numerical values ​​are specifically disclosed, regardless of whether these ranges are disclosed separately. When referring to ranges of numerical values ​​herein, unless otherwise stated, it means that the range includes its endpoints and all integers and fractions within that range.

[0036] On one hand, the present invention relates to a positive electrode active material for lithium secondary batteries, characterized in that the positive electrode active material comprises polycrystalline particles represented by formula A1 and single-crystal particles represented by formula A2.

[0037] A1: Li 1+a1 Ni x1 Co y1 M z1 M′ 1-x1-y1-z1 O2

[0038] A2: Li 1+a2 Ni x2 Co y2 M z2 M′ 1-x2-y2-z2 O2

[0039] in,

[0040] M is one or two elements selected from Mn and Al.

[0041] 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.

[0042] –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.

[0043] The x-value is preferably 0.30 ≤ x1 ≤ 0.99, more preferably 0.57 ≤ x1 ≤ 0.99, even more preferably 0.72 ≤ x1 ≤ 0.99, and particularly preferably 0.80 ≤ x1 ≤ 0.99.

[0044] 0 ≤ y1 ≤ 0.30, preferably 0 ≤ y1 ≤ 0.21, more preferably 0 ≤ y1 ≤ 0.15, and particularly preferably 0 ≤ y1 ≤ 0.10.

[0045] 0≤z1≤0.30, preferably 0≤z1≤0.18, more preferably 0≤z1≤0.11, and particularly preferably 0≤z1≤0.06.

[0046] 0 ≤ 1 – x1 – y1 – z1 ≤ 0.10, preferably 0 ≤ 1 – x1 – y1 – z1 ≤ 0.08, more preferably 0 ≤ 1 – x1 – y1 – z1 ≤ 0.05, particularly preferably 0 ≤ 1 – x1 – y1 – z1 ≤ 0.03,

[0047] –0.03 ≤ a2 ≤ 0.20, preferably –0.02 ≤ a2 ≤ 0.16, more preferably –0.01 ≤ a2 ≤ 0.14, particularly preferably 0 ≤ a2 ≤ 0.08,

[0048] 0.31 ≤ x2 ≤ 1.00, preferably 0.59 ≤ x2 ≤ 0.995, more preferably 0.75 ≤ x2 ≤ 0.995, particularly preferably 0.81 ≤ x2 ≤ 0.995,

[0049] 0 ≤ y2 ≤ 0.30, preferably 0 ≤ y2 ≤ 0.21, more preferably 0 ≤ y2 ≤ 0.15, particularly preferably 0 ≤ y2 ≤ 0.10,

[0050] 0 ≤ z2 ≤ 0.30, preferably 0 ≤ z2 ≤ 0.18, more preferably 0 ≤ z2 ≤ 0.11, particularly preferably 0 ≤ z2 ≤ 0.08,

[0051] 0 ≤ 1 – x2 – y2 – z2 ≤ 0.10, preferably 0 ≤ 1 – x2 – y2 – z2 ≤ 0.08, more preferably 0 ≤ 1 – x2 – y2 – z2 ≤ 0.05, particularly preferably 0 ≤ 1 – x2 – y2 – z2 ≤ 0.03,

[0052] with the condition that: 0 < x2 – x1 ≤ 0.5, preferably 0.01 ≤ x2 – x1 ≤ 0.27, more preferably 0.01 ≤ x2 – x1 ≤ 0.20, further preferably 0.015 ≤ x2 – x1 ≤ 0.20, particularly preferably 0.02 ≤ x2 – x1 ≤ 0.15.

[0053] According to one embodiment of the positive electrode active material according to the present invention, a2 > a1, preferably 0.01 ≤ a2 – a1 ≤ 0.20, more preferably 0.01 ≤ a2 – a1 ≤ 0.12, particularly preferably 0.01 ≤ a2 – a1 ≤ 0.07, especially preferably 0.01 ≤ a2 – a1 ≤ 0.04.

[0054] According to another embodiment of the positive electrode active material according to the present invention, the particle size D of the polycrystalline particles 50 is 6 to 30 μm, preferably 8 to 25 μm, more preferably 9 to 20 μm, particularly preferably 10 to 18 μm.

[0055] According to another embodiment of the positive electrode active material according to the present invention, the particle size D of the single crystal particles 50The micrometer size is 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.

[0056] According to another embodiment of the positive electrode active material according to the present invention, based on the weight of the positive electrode active material, the content of the polycrystalline particles is 20 to 90%, preferably 45 to 85%, more preferably 50 to 80%, particularly preferably 60 to 80%, and the content of the single crystal particles is 10 to 80%, preferably 10 to 70%, more preferably 15 to 60%, particularly preferably 20 to 40%.

[0057] According to another embodiment of the positive electrode active material of the present invention, the polycrystalline particles have a coating layer 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, W, wherein the content of the coating element based on the polycrystalline particles is 0.1 to 2 mol%, preferably about 1 mol%; and / or, the single crystal particles have a coating layer 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, W, wherein the content of the coating element based on the single crystal particles is 0.1 to 2 mol%, preferably about 1 mol%; provided that the coating element contained in the coating layer of the polycrystalline particles is different from the coating element contained in the coating layer of the single crystal particles.

[0058] According to another embodiment of the positive electrode active material according to the present invention, the specific surface area BET of the positive electrode active material before and after sintering at 600°C in air atmosphere for 8 hours is... 前 and BET 后 satisfy:

[0059] |BET 后 –BET 前 | / BET 前 ≤50%,

[0060] Preferred |BET 后 –BET 前 | / BET 前 ≤30%.

[0061] This invention uses rounded single-crystal particles and high-strength polycrystalline particles, combined with an optimal mixing ratio, to control the finished material to expose a stable crystal structure, thereby making the surface porosity of the finished product change rate low during further sintering.

[0062] According to another embodiment of the positive electrode active material according to the present invention, the specific surface area BET of the polycrystalline particles before and after sintering at 600°C in air atmosphere for 8 hours is... 前 and BET 后 satisfy:

[0063] (BET 后 –BET 前 ) / BET 前 ≥15%,

[0064] Preferably 40% ≥ (BET) 后 –BET 前 ) / BET 前 ≥20%.

[0065] Polycrystalline particles are composed of multiple nanoscale particles. To maintain good cycle performance, the porosity on the surface of the nanoparticles cannot be excessive, and the BET (Boiler Equivalent Tolerance) of the material needs to be controlled within a certain range. Normally, after high-temperature sintering, the BET of the material further decreases. However, this invention, by controlling the crystallinity and orientation of the nanocrystals on the material surface, combined with in-situ molten surface treatment, achieves excellent surface and interface protection, and unexpectedly, the BET on the material surface increases instead of decreasing. The inventors further discovered that when polycrystalline particles with this surface BET property are blended with single-crystal particles, the cathode material exhibits superior voltage resistance, better discharge capacity, and better cycle performance.

[0066] According to another embodiment of the positive electrode active material according to the present invention, the specific surface area BET of the single crystal particles before and after sintering in air at 600°C for 8 hours is... 前 and BET 后 satisfy:

[0067] (BET 前 –BET 后 ) / BET 前 ≤15%,

[0068] Preferably 0≤(BET) 前 –BET 后 ) / BET 前 ≤10%.

[0069] Due to its good crystallinity and rounded surface, the single crystal particles of the present invention have a relatively stable structure. During the high-temperature sintering process, the material does not collapse or close to a large extent, and its BET changes little compared to the BET of the unsintered material.

[0070] According to another embodiment of the positive electrode active material according to the present invention, the positive electrode active material does not contain nickel-free active materials, such as lithium manganese iron phosphate.

[0071] According to another embodiment of the positive electrode active material according to the present invention, the positive electrode active material is composed of polycrystalline particles represented by formula A1 and single crystal particles represented by formula A2.

[0072] On the other hand, the present invention also relates to a method for preparing a positive electrode active material, which includes the following steps:

[0073] i) Polycrystalline particle precursor represented by formula A3 and single-crystal particle precursor represented by formula A4 were prepared by liquid-phase co-precipitation method.

[0074] A3: Ni x1 Co y1 M z1 M′ 1-x1-y1-z1 (OH)2

[0075] A4: Ni x2 Co y2 M z2 M′ 1-x2-y2-z2 (OH)2

[0076] in,

[0077] M is one or two elements selected from Mn and Al.

[0078] 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.

[0079] The x-value is preferably 0.30 ≤ x1 ≤ 0.99, more preferably 0.57 ≤ x1 ≤ 0.99, even more preferably 0.72 ≤ x1 ≤ 0.99, and particularly preferably 0.80 ≤ x1 ≤ 0.99.

[0080] 0 ≤ y1 ≤ 0.30, preferably 0 ≤ y1 ≤ 0.21, more preferably 0 ≤ y1 ≤ 0.15, and particularly preferably 0 ≤ y1 ≤ 0.10.

[0081] 0≤z1≤0.30, preferably 0≤z1≤0.18, more preferably 0≤z1≤0.11, and particularly preferably 0≤z1≤0.06.

[0082] 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.

[0083] The x² value is preferably 0.31 ≤ x² ≤ 1.00, more preferably 0.59 ≤ x² ≤ 0.995, even more preferably 0.75 ≤ x² ≤ 0.995, and particularly preferably 0.81 ≤ x² ≤ 0.995.

[0084] 0 ≤ y2 ≤ 0.30, preferably 0 ≤ y2 ≤ 0.21, more preferably 0 ≤ y2 ≤ 0.15, and particularly preferably 0 ≤ y2 ≤ 0.10,

[0085] 0 ≤ z2 ≤ 0.30, preferably 0 ≤ z2 ≤ 0.18, more preferably 0 ≤ z2 ≤ 0.11, and particularly preferably 0 ≤ z2 ≤ 0.08,

[0086] 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,

[0087] with the condition that 0 < x2 – x1 ≤ 0.5, preferably 0.01 ≤ x2 – x1 ≤ 0.27, more preferably 0.01 ≤ x2 – x1 ≤ 0.20, further preferably 0.015 ≤ x2 – x1 ≤ 0.20, and particularly preferably 0.02 ≤ x2 – x1 ≤ 0.15;

[0088] ii) Mix the lithium source with the polycrystalline particle precursor in a molar ratio r1, optionally incorporating M′

[0089] as a doping element, where 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; then perform primary sintering in a sintering atmosphere of air or oxygen, preferably oxygen, at a sintering temperature T1, where 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; then obtain polycrystalline particles by crushing;

[0090] iii) Mix the lithium source with the single-crystalline particle precursor in a molar ratio r2, optionally incorporating M′ as a doping element, where 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 perform primary sintering in a sintering atmosphere of air or oxygen, preferably oxygen, at a sintering temperature T2, where 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 obtain single-crystalline particles by crushing; and

[0091] iv) Blend the polycrystalline particles of step ii) with the single-crystalline particles of step iii) to obtain the positive electrode active material.

[0092] According to one embodiment of the method according to the 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.

[0093] According to another embodiment of the method according to the invention, the particle size D of the polycrystalline particle precursor is... 50 The particle size D is 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. 50 The micrometer size is 6 to 30 μm, preferably 8 to 25 μm, more preferably 9 to 20 μm, and particularly preferably 10 to 18 μm.

[0094] According to another embodiment of the method according to the invention, the particle size D of the single-crystal precursor is... 50 The particle size D is 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 micrometer size is 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.

[0095] According to another embodiment of the method according to the invention, based on the weight of the positive electrode active material, the content of the polycrystalline particles is 20 to 90%, preferably 45 to 85%, more preferably 50 to 80%, particularly preferably 60 to 80%, and the content of the single crystal particles is 10 to 80%, preferably 10 to 70%, more preferably 15 to 60%, particularly preferably 20 to 40%.

[0096] According to another embodiment of the method according to the invention, prior to step iv), the polycrystalline 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. Then, a secondary sintering is performed at a sintering temperature T3 in an air or oxygen sintering atmosphere, preferably oxygen, to obtain polycrystalline particles that have undergone secondary sintering, wherein 250°C ≤ T3 ≤ 800°C, preferably 250°C ≤ T3 ≤ 600°C, more preferably 250°C ≤ T3 ≤ 480°C, particularly preferably 250°C ≤ T3 ≤ 400°C, wherein the content of the coating element based on the polycrystalline particles is 0.1 to 2 mol%, preferably about 1 mol%; and / or, the single crystal 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 is mixed and then subjected to a secondary sintering at a sintering temperature T4 in air or oxygen, preferably oxygen, to obtain a second-sintered single crystal particle, wherein 300℃≤T4≤900℃, preferably 460℃≤T4≤800℃, more preferably 550℃≤T4≤750℃, particularly preferably 600℃≤T4≤750℃, wherein the content of the coating element based on the single crystal particle is 0.1 to 2 mol%, preferably about 1 mol%, provided that the coating element contained in the coating precursor of the polycrystalline particle is different from the coating element contained in the coating precursor of the single crystal particle.

[0097] On the other hand, the present invention also relates to lithium secondary batteries comprising positive electrode active materials according to the present invention or positive electrode active materials prepared by the preparation method according to the present invention.

[0098] Example

[0099] Example 1

[0100] First, a Ni composition was prepared separately using a liquid-phase coprecipitation method. 0.83 Co 0.11 Mn 0.06 The 10.5μm polycrystalline cathode precursor of (OH)2 and the Ni composition 0.86 Co 0.08 Mn 0.06 (OH)2 4μm single crystal cathode precursor.

[0101] LiOH and Ni 0.83 Co 0.11 Mn 0.06(OH)₂ was mixed at a molar ratio of 1.08. The mixture was then subjected to a first sintering at 750°C under an oxygen atmosphere. After sintering, the material was crushed, and then boric acid containing 1 mol% B was added to the crushed material for a second sintering at 400°C, yielding D. 50 It is a 10.0μm polycrystalline large particle material, such as Figure 1 As shown, the BET of this polycrystalline material increased after being treated at 600℃ for 8 hours, with a change rate of 35%.

[0102] LiOH and Ni 0.86 Co 0.08 Mn 0.06 (OH)₂ was mixed at a molar ratio of 1.12. The mixture was then subjected to a first sintering in an oxygen atmosphere at a temperature of 812℃. After sintering, the material was crushed, and then Al₂O₃ containing 1 mol% Al was added to the crushed material before a second sintering at a temperature of 620℃, finally yielding D. 50 It is a 3.5μm single-crystal small particle material, such as Figure 2 As shown, the BET of this single-crystal material decreased after being treated at 600℃ for 8 hours, with a change rate of 2%.

[0103] The above-mentioned polycrystalline large particles and single-crystal small particles are mixed at a mass ratio of 7:3 to obtain a positive electrode active material for lithium secondary batteries, such as... Figure 3 As shown, the BET change rate of this positive electrode active material increased by 24% after being treated at 600℃ for 8 hours.

[0104] Example 2

[0105] First, a Ni composition was prepared separately using a liquid-phase coprecipitation method. 0.83 Co 0.11 Mn 0.06 The 10.5μm polycrystalline cathode precursor of (OH)2 and the Ni composition 0.86 Co 0.08 Mn 0.06 (OH)2 4μm single crystal cathode precursor.

[0106] LiOH and Ni 0.83 Co 0.11 Mn 0.06 (OH)₂ was mixed at a molar ratio of 1.06. The mixture was then subjected to a first sintering in an oxygen atmosphere at a temperature of 745°C. After sintering, the material was crushed, and a second sintering was performed with boric acid containing 0.8 mol% B at a temperature of 380°C to obtain D. 50 It is a 10.0 μm polycrystalline material. After being treated at 600℃ for 8 hours, the BET value of this polycrystalline material increased by 24%.

[0107] LiOH and Ni 0.86 Co 0.08 Mn 0.06 (OH)₂ was mixed at a molar ratio of 1.12. The mixture was then subjected to a first sintering in an oxygen atmosphere at a temperature of 812℃. After sintering, the material was crushed, and then Al₂O₃ containing 1.2 mol% Al was added to the crushed material for a second sintering at a temperature of 610℃, ultimately yielding D. 50 It is a 3.5 μm single-crystal particle material. After being treated at 600℃ for 8 hours, the BET value of this single-crystal material decreased by 3%.

[0108] The above-mentioned polycrystalline large particles and single-crystal small particles were mixed at a mass ratio of 8:2 to obtain a positive electrode active material for lithium secondary batteries. After being treated at 600°C for 8 hours, the BET change rate of this positive electrode active material increased by 19%.

[0109] Example 3

[0110] First, a Ni composition was prepared separately using a liquid-phase coprecipitation method. 0.86 Co 0.11 Mn 0.03 The 10.5μm polycrystalline cathode precursor of (OH)2 and the Ni composition 0.88 Co 0.08 Mn 0.04 (OH)2 4μm single crystal cathode precursor.

[0111] LiOH and Ni 0.86 Co 0.11 Mn 0.03 (OH)₂ was mixed at a molar ratio of 1.06. The mixture was then subjected to a first sintering in an oxygen atmosphere at a temperature of 725°C. After sintering, the material was crushed, and then boric acid containing 0.8 mol% B was added to the crushed material for a second sintering at a temperature of 380°C, yielding D. 50 It is a 10.0 μm polycrystalline material. After being treated at 600℃ for 8 hours, the BET value of this polycrystalline material increased by 26%.

[0112] LiOH and Ni 0.88 Co 0.08 Mn 0.04 (OH)₂ was mixed at a molar ratio of 1.11. The mixture was then subjected to a first sintering in an oxygen atmosphere at a temperature of 805℃. After sintering, the material was crushed. The crushed material was then mixed with Al₂O₃ containing 1.0 mol% Al and subjected to a second sintering at a temperature of 610℃, ultimately yielding D. 50It is a 3.5 μm single-crystal particle material. After being treated at 600℃ for 8 hours, the BET value of this single-crystal material decreased by 2%.

[0113] The above-mentioned polycrystalline large particles and single-crystal small particles were mixed at a mass ratio of 7:3 to obtain a positive electrode active material for lithium secondary batteries. After being treated at 600°C for 8 hours, the BET change rate of this positive electrode active material increased by 20%.

[0114] Example 4

[0115] First, a Ni composition was prepared separately using a liquid-phase coprecipitation method. 0.86 Co 0.11 Mn 0.03 The 10.5μm polycrystalline cathode precursor of (OH)2 and the Ni composition 0.88 Co 0.08 Mn 0.04 (OH)2 4μm single crystal cathode precursor.

[0116] LiOH and Ni 0.86 Co 0.11 Mn 0.03 (OH)₂ was mixed at a molar ratio of 1.06. The mixture was then subjected to a first sintering in an oxygen atmosphere at a temperature of 685°C. After sintering, the material was crushed, and then boric acid containing 0.8 mol% B was added to the crushed material for a second sintering at a temperature of 380°C, yielding D. 50 It is a 10.0 μm polycrystalline material. After being treated at 600℃ for 8 hours, the BET value of this polycrystalline material increased by 26%.

[0117] LiOH and Ni 0.88 Co 0.08 Mn 0.04 (OH)₂ was mixed at a molar ratio of 1.11. The mixture was then subjected to a first sintering in an oxygen atmosphere at a temperature of 805℃. After sintering, the material was crushed. The crushed material was then mixed with Al₂O₃ containing 1.0 mol% Al and subjected to a second sintering at a temperature of 610℃, ultimately yielding D. 50 It is a 3.5 μm single-crystal particle material. After being treated at 600℃ for 8 hours, the BET value of this single-crystal material decreased by 2%.

[0118] The above-mentioned polycrystalline large particles and single-crystal small particles were mixed at a mass ratio of 3:7 to obtain a positive electrode active material for lithium secondary batteries. After being treated at 600°C for 8 hours, the BET change rate of this positive electrode active material increased by 6%.

[0119] Example 5

[0120] First, a Ni composition was prepared separately using a liquid-phase coprecipitation method. 0.88 Co 0.10 Mn 0.02 The 10.5μm polycrystalline cathode precursor of (OH)2 and the Ni composition 0.90 Co 0.08 Mn 0.02 (OH)2 4μm single crystal cathode precursor.

[0121] LiOH and Ni 0.88 Co 0.10 Mn 0.02 (OH)₂ was mixed at a molar ratio of 1.08. The mixture was then subjected to a first sintering in an oxygen atmosphere at a temperature of 780°C. After sintering, the material was crushed, and then boric acid containing 1 mol% B was added to the crushed material for a second sintering at a temperature of 400°C, yielding D. 50 It is a 10.0 μm polycrystalline material. After being treated at 600℃ for 8 hours, the BET value of this polycrystalline material increased by 32%.

[0122] LiOH and Ni 0.90 Co 0.08 Mn 0.02 (OH)₂ was mixed at a molar ratio of 1.12. The mixture was then subjected to a first sintering in an oxygen atmosphere at a temperature of 812℃. After sintering, the material was crushed, and then Al₂O₃ containing 1 mol% Al was added to the crushed material before a second sintering at a temperature of 620℃, finally yielding D. 50 It is a 3.5 μm single-crystal particle material. After being treated at 600℃ for 8 hours, the BET value of this single-crystal material decreased by 2%.

[0123] The above-mentioned polycrystalline large particles and single-crystal small particles were mixed at a mass ratio of 7:3 to obtain a positive electrode active material for lithium secondary batteries. After being treated at 600°C for 8 hours, the BET change rate of this positive electrode active material increased by 22%.

[0124] Example 6

[0125] First, a Ni composition was prepared separately using a liquid-phase coprecipitation method. 0.83 Co 0.11 Mn 0.06 The 10.5μm polycrystalline cathode precursor of (OH)2 and the Ni composition 0.86 Co 0.08 Mn 0.06 (OH)2 4μm single crystal cathode precursor.

[0126] LiOH and Ni 0.83 Co 0.11 Mn0.06 (OH)₂ was mixed at a molar ratio of 1.08. The mixture was then subjected to a first sintering at 750°C under an oxygen atmosphere. After sintering, the material was crushed, and then boric acid containing 1 mol% B was added to the crushed material for a second sintering at 400°C, yielding D. 50 It is a 10.0 μm polycrystalline material. After being treated at 600℃ for 8 hours, the BET value of this polycrystalline material increased by 35%.

[0127] LiOH and Ni 0.86 Co 0.08 Mn 0.06 (OH)₂ was mixed at a molar ratio of 1.12. The mixture was then subjected to a first sintering in an oxygen atmosphere at a temperature of 812℃. After sintering, the material was crushed, and the crushed material, containing 0.4 mol% boric acid (B), underwent a second sintering at a temperature of 400℃, ultimately yielding D. 50 It is a 3.5 μm single-crystal particle material. After being treated at 600℃ for 8 hours, the BET of this single-crystal material increased by 9%.

[0128] The above-mentioned polycrystalline large particles and single-crystal small particles were mixed at a mass ratio of 7:3 to obtain a positive electrode active material for lithium secondary batteries. After being treated at 600°C for 8 hours, the BET change rate of this positive electrode active material increased by 27%.

[0129] Example 7

[0130] First, a Ni composition was prepared separately using a liquid-phase coprecipitation method. 0.83 Co 0.11 Mn 0.06 The 10.5μm polycrystalline cathode precursor of (OH)2 and the Ni composition 0.86 Co 0.08 Mn 0.06 (OH)2 4μm single crystal cathode precursor.

[0131] LiOH and Ni 0.83 Co 0.11 Mn 0.06 (OH)₂ was mixed at a molar ratio of 1.08. The mixture was then subjected to a first sintering in an oxygen atmosphere at a temperature of 750°C. After sintering, the material was crushed. The crushed material was then mixed with boric acid containing 0.5 mol% B for a second sintering at a temperature of 400°C, yielding D. 50 It is a 10.0 μm polycrystalline material. After being treated at 600℃ for 8 hours, the BET value of this polycrystalline material increased by 11%.

[0132] LiOH and Ni 0.86 Co0.08 Mn 0.06 (OH)₂ was mixed at a molar ratio of 1.12. The mixture was then subjected to a first sintering in an oxygen atmosphere at a temperature of 812℃. After sintering, the material was crushed, and then Al₂O₃ containing 1 mol% Al was added to the crushed material before a second sintering at a temperature of 620℃, finally yielding D. 50 It is a 3.5 μm single-crystal particle material. After being treated at 600℃ for 8 hours, the BET value of this single-crystal material decreased by 2%.

[0133] The above-mentioned polycrystalline large particles and single-crystal small particles were mixed at a mass ratio of 7:3 to obtain a positive electrode active material for lithium secondary batteries. After being treated at 600°C for 8 hours, the BET change rate of this positive electrode active material increased by 7%.

[0134] Example 8

[0135] First, a Ni composition was prepared separately using a liquid-phase coprecipitation method. 0.83 Co 0.11 Mn 0.06 The 10.5μm polycrystalline cathode precursor of (OH)2 and the Ni composition 0.86 Co 0.08 Mn 0.06 (OH)2 4μm single crystal cathode precursor.

[0136] LiOH and Ni 0.83 Co 0.11 Mn 0.06 (OH)₂ was mixed at a molar ratio of 1.08. The mixture was then subjected to a first sintering at 750°C under an oxygen atmosphere. After sintering, the material was crushed, and a second sintering was performed with Al₂O₃ containing 1 mol% Al at 620°C to obtain D. 50 It is a 10.0 μm polycrystalline material. After being treated at 600℃ for 8 hours, the BET value of this polycrystalline material decreased by 3%.

[0137] LiOH and Ni 0.86 Co 0.08 Mn 0.06 (OH)₂ was mixed at a molar ratio of 1.12. The mixture was then subjected to a first sintering in an oxygen atmosphere at a temperature of 812℃. After sintering, the material was crushed, and then Al₂O₃ containing 1 mol% Al was added to the crushed material before a second sintering at a temperature of 620℃, finally yielding D. 50 It is a 3.5 μm single-crystal particle material. After being treated at 600℃ for 8 hours, the BET value of this single-crystal material decreased by 2%.

[0138] The above-mentioned polycrystalline large particles and single-crystal small particles were mixed at a mass ratio of 7:3 to obtain a positive electrode active material for lithium secondary batteries. After being treated at 600°C for 8 hours, the BET change rate of this positive electrode active material decreased by 3%.

[0139] Example 9

[0140] First, a Ni composition was prepared separately using a liquid-phase coprecipitation method. 0.83 Co 0.11 Mn 0.06 The 10.5μm polycrystalline cathode precursor of (OH)2 and the Ni composition 0.86 Co 0.08 Mn 0.06 (OH)2 4μm single crystal cathode precursor.

[0141] LiOH and Ni 0.83 Co 0.11 Mn 0.06 (OH)₂ was mixed at a molar ratio of 1.08. The mixture was then subjected to a first sintering in an oxygen atmosphere at a temperature of 750°C. After sintering, the material was crushed. The crushed material was then mixed with boric acid containing 0.5 mol% B for a second sintering at a temperature of 400°C, yielding D. 50 It is a 10.0 μm polycrystalline material. After being treated at 600℃ for 8 hours, the BET value of this polycrystalline material increased by 11%.

[0142] LiOH and Ni 0.86 Co 0.08 Mn 0.06 (OH)₂ was mixed at a molar ratio of 1.12. The mixture was then subjected to a first sintering in an oxygen atmosphere at a temperature of 812℃. After sintering, the material was crushed, and the crushed material, containing 0.4 mol% boric acid (B), underwent a second sintering at a temperature of 400℃, ultimately yielding D. 50 It is a 3.5 μm single-crystal particle material. After being treated at 600℃ for 8 hours, the BET of this single-crystal material increased by 9%.

[0143] The above-mentioned polycrystalline large particles and single-crystal small particles were mixed at a mass ratio of 7:3 to obtain a positive electrode active material for lithium secondary batteries. After being treated at 600°C for 8 hours, the BET change rate of this positive electrode active material increased by 10%.

[0144] Example 10

[0145] First, a Ni composition was prepared separately using a liquid-phase coprecipitation method. 0.83 Co 0.11 Mn 0.06 The 10.5μm polycrystalline cathode precursor of (OH)2 and the Ni composition0.84 Co 0.08 Mn 0.08 (OH)2 4μm single crystal cathode precursor.

[0146] LiOH and Ni 0.83 Co 0.11 Mn 0.06 (OH)₂ was mixed at a molar ratio of 1.08. The mixture was then subjected to a first sintering in an oxygen atmosphere at a temperature of 750°C. After sintering, the material was crushed. The crushed material was then mixed with boric acid containing 0.5 mol% B for a second sintering at a temperature of 400°C, yielding D. 50 It is a 10.0 μm polycrystalline material. After being treated at 600℃ for 8 hours, the BET value of this polycrystalline material increased by 35%.

[0147] LiOH and Ni 0.84 Co 0.08 Mn 0.08 (OH)₂ was mixed at a molar ratio of 1.12. The mixture was then subjected to a first sintering in an oxygen atmosphere at a temperature of 812℃. After sintering, the material was crushed, and the crushed material, containing 0.4 mol% boric acid (B), underwent a second sintering at a temperature of 400℃, ultimately yielding D. 50 It is a 3.5 μm single-crystal particle material. After being treated at 600℃ for 8 hours, the BET value of this single-crystal material decreased by 2%.

[0148] The above-mentioned polycrystalline large particles and single-crystal small particles were mixed at a mass ratio of 7:3 to obtain a positive electrode active material for lithium secondary batteries. After being treated at 600°C for 8 hours, the BET change rate of this positive electrode active material increased by 24%.

[0149] Comparative Example 1

[0150] First, a Ni composition was prepared separately using a liquid-phase coprecipitation method. 0.83 Co 0.11 Mn 0.06 The 10.5μm polycrystalline cathode precursor of (OH)2 and the Ni composition 0.80 Co 0.11 Mn 0.09 (OH)2 4μm single crystal cathode precursor.

[0151] LiOH and Ni 0.83 Co 0.11 Mn 0.06(OH)₂ was mixed at a molar ratio of 1.08. The mixture was then subjected to a first sintering at 750°C under an oxygen atmosphere. After sintering, the material was crushed, and then boric acid containing 1 mol% B was added to the crushed material for a second sintering at 400°C, yielding D. 50 It is a 10.0 μm polycrystalline material. After being treated at 600℃ for 8 hours, the BET value of this polycrystalline material increased by 35%.

[0152] LiOH and Ni 0.80 Co 0.11 Mn 0.09 (OH)₂ was mixed at a molar ratio of 1.12. The mixture was then subjected to a first sintering at 820℃ under an oxygen atmosphere. After sintering, the material was crushed, and then Al₂O₃ containing 1 mol% Al was added to the crushed material for a second sintering at 620℃, ultimately yielding D. 50 It is a 3.5 μm single-crystal particle material. After being treated at 600℃ for 8 hours, the BET value of this single-crystal material decreased by 2%.

[0153] The above-mentioned polycrystalline large particles and single-crystal small particles were mixed at a mass ratio of 7:3 to obtain a positive electrode active material for lithium secondary batteries. This positive electrode active material, after being treated at 600°C for 8 hours, showed a 25% increase in its BET (Benefit Equivalent).

[0154] Comparative Example 2

[0155] First, a Ni composition was prepared separately using a liquid-phase coprecipitation method. 0.83 Co 0.11 Mn 0.06 The 10.5μm polycrystalline cathode precursor of (OH)2 and the Ni composition 0.83 Co 0.11 Mn 0.06 (OH)2 4μm single crystal cathode precursor.

[0156] LiOH and Ni 0.83 Co 0.11 Mn 0.06 (OH)₂ was mixed at a molar ratio of 1.08. The mixture was then subjected to a first sintering at 750°C under an oxygen atmosphere. After sintering, the material was crushed, and then boric acid containing 1 mol% B was added to the crushed material for a second sintering at 400°C, yielding D. 50 It is a 10.0 μm polycrystalline material. After being treated at 600℃ for 8 hours, the BET value of this polycrystalline material increased by 35%.

[0157] LiOH and Ni 0.83 Co 0.11 Mn0.06 (OH)₂ was mixed at a molar ratio of 1.12. The mixture was then subjected to a first sintering in an oxygen atmosphere at a temperature of 816℃. After sintering, the material was crushed, and then Al₂O₃ containing 1 mol% Al was added to the crushed material for a second sintering at a temperature of 620℃, ultimately yielding D. 50 It is a 3.5 μm single-crystal particle material. After being treated at 600℃ for 8 hours, the BET value of this single-crystal material decreased by 2%.

[0158] The above-mentioned polycrystalline large particles and single-crystal small particles were mixed at a mass ratio of 7:3 to obtain a positive electrode active material for lithium secondary batteries. This positive electrode active material, after being treated at 600°C for 8 hours, showed a 25% increase in its BET (Benefit Equivalent).

[0159] Specific surface area measurement:

[0160] The specific surface area was tested using a Tri-star 3020 surface area analyzer. A 3-gram sample was weighed and the sample tube was attached to the vacuum connector at the degassing station. The heating temperature was set to 300℃, and the degassing time to 120 minutes. After degassing, the sample tube was cooled. The mass of the empty sample tube and the mass of the degassed sample and sample tube were entered into the testing instrument software interface. The specific surface area data (BET method) calculated by the software was recorded to complete the test of the specific surface area of ​​the cathode material sample.

[0161] Particle size measurement:

[0162] Tests were performed using a Mastersizer 2000 laser particle size analyzer. In the software, the "Sample Test Time" and "Background Test Time" in the "Measurement" section were modified to 6 seconds; the number of cycles in the measurement cycle section was set to 3, with a delay time of 5 seconds. An average result record was then created from the measurements. Next, "Start" was clicked to automatically measure the background. After the automatic measurement was completed, 40 mL of sodium pyrophosphate was added, followed by a small amount of sample using a reagent spoon, until the occlusion reached halfway through the visually obscured area (10-20%). "Start" was then clicked, and the results were recorded three times and the average value was recorded. Button cell preparation:

[0163] First, a non-aqueous electrolyte secondary battery using a composite nickel-cobalt-manganese multi-electrode positive electrode active material, acetylene black, and polyvinylidene fluoride (PVDF) is mixed, coated onto aluminum foil, and then dried. The dried positive electrode, separator, negative electrode, and electrolyte are then assembled into a 2025-type coin cell in an Ar gas glove box with a water and oxygen content of less than 5 ppm.

[0164] First discharge capacity test method: After the button cell is made, it is placed for 2 hours. After the open circuit voltage stabilizes, the positive electrode is charged to the cutoff voltage of 4.3V with a current density of 0.1C. Then it is charged at a constant voltage for 30 minutes. Then it is discharged to the cutoff voltage of 3.0V with the same current density. Repeat the same process once more, and the discharge capacity is taken as the first discharge capacity. Figure 4 The charge-discharge curves of coin cells prepared from the cathode materials in Examples 1, 1, and 2 are shown. It can be seen that the cathode material in Example 1 has a higher initial discharge capacity compared to the comparative example.

[0165] Full cell fabrication and gas generation testing:

[0166] Lithium nickel cobalt manganese oxide cathode material, graphite anode material, carbon black conductive agent, and PVDF binder were dried in a vacuum oven at 120°C for 12 hours. The dried cathode material, carbon black conductive agent, PVDF, and NMP were then mixed evenly to prepare a cathode slurry. This slurry was coated onto aluminum foil using a lithium battery coating machine and dried. The electrode sheets were then cut using an electrode slitting machine and rolled using an electrode rolling press.

[0167] 950g of dried artificial graphite, 13g of Super-P, 14g of CMC, 46g of SBR solution, and 1200g of deionized water were mixed evenly to prepare a negative electrode slurry. This slurry was then coated onto copper foil using a lithium battery coating machine and dried. The resulting negative electrode sheet was dried in a vacuum oven, cut using an electrode slitting machine, and rolled using an electrode rolling press.

[0168] The aforementioned positive and negative electrode sheets were wound using conventional manufacturing methods and then injected with electrolyte to form a full cell. The initial thickness of the full cell after formation was measured. After being placed in a 45°C constant temperature chamber for 7 days, the thickness of the full cell was measured again. The rate of increase in thickness was used to characterize the gas production of the positive electrode material in the full cell. Figure 5 The cycle life changes of full cells made with cathode materials in Examples 1, 1, and 2 are shown. It can be seen that the full cell made with cathode material in Example 1 has better stability and a longer cycle life.

[0169]

[0170]

[0171] The positive electrode active material and its lithium-ion battery provided by this invention have the following beneficial effects:

[0172] 1) Compared with polycrystalline materials, single crystals with the same nickel content have better cycle life and lower gas production performance. Therefore, the addition of single crystals can effectively improve the cycle and gas production performance of the blended material.

[0173] 2) Due to its special single-crystal morphology, the specific capacity of single-crystal materials is lower than that of polycrystals with the same nickel content. Therefore, this invention uses single crystals with a slightly higher nickel content to make up for its low specific capacity, while maintaining the same level of performance in terms of circulation and gas production as polycrystals with low nickel content.

[0174] 3) After mixing, small single-crystal materials can enter the gaps between large polycrystalline particles, forming a synergistic effect of mutual support and gap filling with the large polycrystalline particles, effectively improving the compaction density of the material.

[0175] 4) Adding a small amount of large-diameter polycrystalline spherical particles to a system mainly composed of single-crystal small particles can effectively improve the problems of poor fluidity of single-crystal materials, making them difficult to screen and pulp.

[0176] While specific embodiments have been described, these embodiments are given by way of example only and are not intended to limit the scope of the 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 invention.

Claims

1. A positive electrode active material for lithium secondary batteries, characterized in that, The positive electrode active material comprises polycrystalline 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 in, 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, The conditions are: 0 < x2 – x1 ≤ 0.5, and a2 > a1. The specific surface area (BET) of the positive electrode active material before and after sintering at 600°C in air for 8 hours. 前 and BET 后 satisfy: |BET 后 – BET 前 | / BET 前 ≤ 50%, The specific surface area (BET) of the polycrystalline particles before and after sintering in air at 600°C for 8 hours. 前 and BET 后 satisfy: (BET 后 – BET 前 ) / BET 前 ≥ 15%, The specific surface area (BET) of the single crystal particles before and after sintering in air at 600°C for 8 hours. 前 and BET 后 satisfy: (BET 前 – BET 后 ) / BET 前 ≤ 15%。 2. The positive electrode active material according to claim 1, characterized in that, 0 ≤ y1 ≤ 0.15, 0 ≤ z1 ≤ 0.18, 0 ≤ z2 ≤ 0.

08.

3. The positive electrode active material according to claim 1, characterized in that, The particle size D of the polycrystalline particles 50 It ranges from 6 to 30 μm, and The particle size D of the single crystal particles 50 The range is from 0.1 to 10 μm.

4. The positive electrode active material according to claim 1, characterized in that, Based on the weight of the positive electrode active material, the content of the polycrystalline particles is 20% to 90%, and Based on the weight of the positive electrode active material, the content of the single crystal particles is 10% to 80%.

5. The positive electrode active material according to claim 1, characterized in that, The polycrystalline particles have a coating layer 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, W, wherein the content of the coating element is 0.1 to 2 mol% based on the polycrystalline particles, and / or The single-crystal particle has a coating layer 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, W, wherein the content of the coating element based on the single-crystal particle is from 0.1 to 2 mol%. The coating elements contained in the coating layer of the polycrystalline particles are different from those contained in the coating layer of the single-crystal particles.

6. The positive electrode active material according to claim 1, characterized in that, The specific surface area (BET) of the positive electrode active material before and after sintering in air at 600°C for 8 hours. 前 and BET 后 satisfy: |BET 后 – BET 前 | / BET 前 ≤ 30%, The specific surface area (BET) of the polycrystalline particles before and after sintering in air at 600°C for 8 hours. 前 and BET 后 satisfy: 40% ≥ (BET 后 – BET 前 ) / BET 前 ≥ 20%, The specific surface area (BET) of the single crystal particles before and after sintering in air at 600°C for 8 hours. 前 and BET 后 satisfy: 0 ≤ (BET 前 – BET 后 ) / BET 前 ≤ 10%。 7. A method for preparing a positive electrode active material, comprising the following steps: i) Polycrystalline particle precursor represented by formula A3 and single-crystal particle precursor represented by formula A4 were prepared by liquid-phase co-precipitation method. A3: Ni x1 What y1 M z1 M′ 1-x1-y1-z1 (OH)2 A4: Ni x2 What y2 M z2 M′ 1-x2-y2-z2 (OH)2 in, 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, The condition is: 0 < x2 – x1 ≤ 0.5; ii) The lithium source and the polycrystalline particle precursor are mixed at a molar ratio r1, and M′ is optionally mixed in as a dopant element, wherein 0.97 ≤ r1 ≤ 1.20; then, the primary sintering is carried out at a sintering temperature T1 in an air or oxygen sintering atmosphere, wherein 600℃ ≤ T1 ≤ 1000℃; then, the polycrystalline particles are obtained by crushing. iii) The lithium source and the single-crystal particle precursor are mixed at a molar ratio r2, and M′ is optionally added as a dopant element, wherein 0.97 ≤ r2 ≤ 1.20; then, a primary sintering is performed at a sintering temperature T2 in an air or oxygen sintering atmosphere, wherein 650℃ ≤ T2 ≤ 1050℃; then, the particles are crushed to obtain single-crystal particles; and iv) The polycrystalline particles from step ii) are blended with the single-crystal particles from step iii) to obtain the positive electrode active material. Where r2 > r1.

8. The method according to claim 7, characterized in that, In step i), 0 ≤ y1 ≤ 0.15, 0 ≤ z1 ≤ 0.18, and 0 ≤ z2 ≤ 0.

08.

9. The method according to claim 7, characterized in that, The particle size D of the polycrystalline precursor 50 The thickness ranges from 6.5 to 30.5 μm. The particle size D of the polycrystalline particles 50 The size ranges from 6 to 30 μm. The particle size D of the single crystal precursor 50 The range is from 0.1 to 30.5 μm, and The particle size D of the single crystal particles 50 The range is from 0.1 to 10 μm.

10. The method according to claim 7, characterized in that, Based on the weight of the positive electrode active material, the content of the polycrystalline particles is 20% to 90%, and Based on the weight of the positive electrode active material, the content of the single crystal particles is 10% to 80%.

11. The method according to claim 7, characterized in that, Before step iv), The polycrystalline 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. The mixture is then subjected to a second sintering at a sintering temperature T3 in an air or oxygen atmosphere to obtain second-sintered polycrystalline particles, wherein 250°C ≤ T3 ≤ 800°C, and wherein the content of the coating element, based on the polycrystalline particles, is 0.1 to 2 mol%, 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. The mixture is then subjected to a second sintering at a sintering temperature T4 in an air or oxygen atmosphere to obtain second-sintered single crystal particles, wherein 300℃ ≤ T4 ≤ 900℃, and the content of the coating element based on the single crystal particles is 0.1 to 2 mol%. The coating elements contained in the polycrystalline particle coating precursor are different from those contained in the single-crystal particle coating precursor.

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