Composite lithium cobalt oxide positive electrode material, preparation method thereof and battery

Abstract

The invention relates to the technical field of batteries, in particular to a composite lithium cobalt oxide positive electrode material, a preparation method thereof and a battery. The composite lithium cobalt oxide positive electrode material comprises a substrate and a coating layer located on the surface of the substrate, and the substrate comprises a single-crystal doped lithium cobalt oxide material and a polycrystal doped lithium cobalt oxide material; the median particle size of the single-crystal doped lithium cobalt oxide material is greater than that of the polycrystal doped lithium cobalt oxide material; the particle mechanical strength of the composite lithium cobalt oxide positive electrode material is expressed by Euclidean distance ED, and ED is less than or equal to 2.3; the single crystal degree of the composite lithium cobalt oxide positive electrode material is greater than or equal to 50%. The composite lithium cobalt oxide positive electrode material disclosed by the invention has high structural stability, high capacity, long circulation and high rate performance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a composite lithium cobalt oxide cathode material, its preparation method, and a battery. Background Technology

[0002] Lithium-ion batteries are widely used in consumer electronics, energy storage, and electric vehicles due to their high energy density, long cycle life, and good stability. As a core cathode material, lithium cobalt oxide (LiCoO2) has been the mainstream cathode material for 3C batteries due to its high theoretical capacity and excellent volumetric energy density. However, existing lithium cobalt oxide materials still have the following problems: 1) Insufficient single crystallinity: Large particles prepared by conventional solid-state methods are prone to excessive fusion at high temperatures, leading to numerous grain boundary defects, easy microcrack formation, and poor cycle stability. 2) Lack of advantages for small particles: Most existing small particles are single crystals, which can fill pores and improve compaction density, but have limited effect on rate performance improvement. 3) Insufficient performance at high voltages: When the voltage exceeds 4.5V, lithium cobalt oxide undergoes a structural phase transition, Co dissolution, and oxygen release, leading to capacity decay and decreased safety.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] One object of the present invention is to provide a composite lithium cobalt oxide cathode material that combines high capacity, high cycle stability and high rate performance.

[0005] Another objective of this invention is to provide a method for preparing a composite lithium cobalt oxide cathode material, which improves its electrochemical performance through the coordinated operation of each step.

[0006] Another object of the present invention is to provide a battery.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A composite lithium cobalt oxide cathode material includes a matrix and a coating layer located on the surface of the matrix. The matrix includes monocrystalline doped lithium cobalt oxide material and polycrystalline doped lithium cobalt oxide material. The median particle size of the monocrystalline doped lithium cobalt oxide material is larger than that of the polycrystalline doped lithium cobalt oxide material. The particle mechanical strength of the composite lithium cobalt oxide cathode material is expressed as Euclidean distance ED, where ED ≤ 2.30. ED refers to the Euclidean distance between the particle size distribution curves of the composite lithium cobalt oxide cathode material before and after being subjected to a pressure of 300 MPa. The monocrystalline degree of the composite lithium cobalt oxide cathode material is ≥ 50%.

[0008] In some implementations, the ED ≤ 2.00.

[0009] In some embodiments, the monocrystalline degree of the composite lithium cobalt oxide cathode material is ≥52%.

[0010] In some embodiments, the single-crystal doped lithium cobalt oxide material includes a lithium cobalt oxide matrix A, a dopant element A1, and a dopant element A2; the dopant element A1 includes at least one of Al and Mg, and the doping amount of the dopant element A1 is 3000~20000ppm; the dopant element A2 includes at least one of Al, Mg, Ni, Mn, Ti, Zr, Y, La, Nb, Sr, and W, and the doping amount of the dopant element A2 is 1000~5000ppm.

[0011] In some embodiments, the polycrystalline doped lithium cobalt oxide material includes a lithium cobalt oxide matrix B, a dopant element B1, and a dopant element B2; the dopant element B1 includes at least one of Al and Mg, and the doping amount of the dopant element B1 is 3000~20000ppm; the dopant element B2 includes at least one of Al, Mg, Ni, Mn, Ti, Zr, Y, La, Nb, Sr, and W, and the doping amount of the dopant element B2 is 1000~5000ppm.

[0012] In some embodiments, the mass ratio of the single-crystal doped lithium cobalt oxide material to the polycrystalline doped lithium cobalt oxide material is (3~5):1.

[0013] In some embodiments, the ratio x of the median particle size of the single-crystal doped lithium cobalt oxide material to the median particle size of the polycrystalline doped lithium cobalt oxide material satisfies: 2.54 ≤ x ≤ 5.86.

[0014] In some embodiments, the median particle size of the single-crystal doped lithium cobalt oxide material is 16.5~20.5 μm.

[0015] In some embodiments, the median particle size of the polycrystalline doped lithium cobalt oxide material is 3.5~6.5 μm.

[0016] In some embodiments, the coating layer comprises a coating element M, which includes at least one of Mg, Al, Ti, Y, Zr, Nb, La, Ni, Mn, Co, F, and P.

[0017] In some embodiments, the mass of the coating layer is 0.1% to 1% of the composite lithium cobalt oxide cathode material.

[0018] In some embodiments, the median particle size of the composite lithium cobalt oxide cathode material is 15.5~16.5 μm.

[0019] In some embodiments, the specific surface area of ​​the composite lithium cobalt oxide cathode material is 0.19~0.25 m². 2 / g.

[0020] In some embodiments, the tap density of the composite lithium cobalt oxide cathode material is 2.8~3.2 g / cm³. 3 .

[0021] In some embodiments, the compaction density of the composite lithium cobalt oxide cathode material is 4.0~4.4 g / cm³. 3 .

[0022] In some embodiments, the battery prepared from the composite lithium cobalt oxide cathode material has a first-cycle specific capacity ≥200mAh / g. In some embodiments, the battery prepared from the composite lithium cobalt oxide cathode material retains ≥90% of its capacity at 5C.

[0023] In some embodiments, the battery prepared from the composite lithium cobalt oxide cathode material retains ≥92% of its charge after 100 cycles.

[0024] In some embodiments, the impedance of the battery prepared from the composite lithium cobalt oxide cathode material is <50Ω.

[0025] A method for preparing a composite lithium cobalt oxide cathode material includes the following steps: A first cobalt source, a compound of element A2, and a first lithium source are subjected to a first mixing, a first heat treatment, and a first crushing process. Lithium vapor is introduced during the first heat treatment to obtain a single-crystal doped lithium cobalt oxide material. A second cobalt source, a compound of element B2, and a second lithium source are subjected to a second mixing, a second heat treatment, and a second crushing process. The total holding time for the second heat treatment is ≤10 hours to obtain a polycrystalline doped lithium cobalt oxide material. The median particle size of the polycrystalline doped lithium cobalt oxide material is smaller than that of the single-crystal doped lithium cobalt oxide material. The single-crystal doped lithium cobalt oxide material, the polycrystalline doped lithium cobalt oxide material, and a compound of element M are subjected to a third mixing, a third heat treatment, and a third crushing process to obtain a composite lithium cobalt oxide cathode material.

[0026] In some embodiments, the first cobalt source comprises one or more of CoO, Co(OH)2, Co(NO3)2, CoCO3, Co3O4 and CoOOH; preferably, the first cobalt source further comprises Al, wherein the doping amount of Al is 3000~20000ppm.

[0027] In some embodiments, the compound of element A2 comprises one or more of oxides, hydroxides, carbonates and nitrates of element A2, and element A2 includes one or more of Al, Mg, Ni, Mn, Ti, Zr, Y, La, Nb, Sr and W; the doping amount of the dopant element A2 is 1000~5000ppm.

[0028] In some embodiments, the first lithium source comprises one or more of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium acetate.

[0029] In some embodiments, the molar ratio of the first cobalt source and the first lithium source, respectively, based on cobalt and lithium, is 1:(1.01~1.08).

[0030] In some embodiments, the rotational speed of the first mixing is 900~1000 r / min, and the mixing time is 40~60 min.

[0031] In some embodiments, the first heat treatment includes a first isothermal platform, a second isothermal platform, and a third isothermal platform arranged sequentially, wherein the temperature of the second isothermal platform is greater than the temperature of the first isothermal platform and the temperature of the third isothermal platform.

[0032] In some embodiments, the temperature of the first constant temperature platform is 400~900℃, and the holding time of the first constant temperature platform is 3~10h; the temperature of the second constant temperature platform is 850~1200℃, and the holding time of the second constant temperature platform is 5~12h; the temperature of the third constant temperature platform is 450~950℃, and the holding time of the third constant temperature platform is 2~6h.

[0033] In some embodiments, the first heat treatment is carried out in a heating chamber, with a protective gas as the carrier gas for introducing lithium vapor. After the lithium vapor is introduced, the heating chamber contains lithium vapor, oxygen and the protective gas, and the partial pressure of the lithium vapor is 0.1% to 10%.

[0034] In some implementations, the lithium vapor introduction begins before the first isothermal platform and ends after the second isothermal platform and before the third isothermal platform.

[0035] In some embodiments, the median particle size of the single-crystal doped lithium cobalt oxide material is 16.5~20.5 μm.

[0036] In some embodiments, the second cobalt source comprises one or more of CoO, Co(OH)2, Co(NO3)2, CoCO3, Co3O4 and CoOOH; preferably, the second cobalt source further comprises B1, wherein the doping amount of B1 is 3000~20000ppm.

[0037] In some embodiments, the compound of element B2 comprises one or more of oxides, hydroxides, carbonates and nitrates of element B2, and element B2 includes one or more of Al, Mg, Ni, Mn, Ti, Zr, Y, La, Nb, Sr and W, and the doping amount of the dopant element B2 is 1000~5000ppm.

[0038] In some embodiments, the second lithium source comprises one or more of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium acetate.

[0039] In some embodiments, the molar ratio of the second cobalt source and the second lithium source, respectively, based on cobalt and lithium, is 1:(1.01~1.08).

[0040] In some embodiments, the rotational speed of the second mixing is 900~1000 r / min, and the mixing time is 40~60 min.

[0041] In some embodiments, the second heat treatment includes a fourth constant temperature platform and a fifth constant temperature platform arranged sequentially. The temperature of the fourth constant temperature platform is 400~800℃ and the holding time of the fourth constant temperature platform is 2~4h. The temperature of the fifth constant temperature platform is 750~1000℃ and the holding time of the fifth constant temperature platform is 3~6h.

[0042] In some embodiments, the median particle size of the polycrystalline doped lithium cobalt oxide material is 3.5~6.5 μm.

[0043] In some embodiments, the mass ratio of the single-crystal doped lithium cobalt oxide material to the polycrystalline doped lithium cobalt oxide material is (3~5):1.

[0044] In some embodiments, the element M comprises one or more of Mg, Al, Ti, Y, Zr, Nb, La, Ni, Mn, Co, F, and P.

[0045] In some embodiments, the mass of the element M compound is 0.1% to 1% of the mass of the composite lithium cobalt oxide cathode material.

[0046] In some embodiments, the temperature of the third heat treatment is 750~1000℃, and the holding time of the third heat treatment is 3~6h.

[0047] In some embodiments, after the third crushing, a composite lithium cobalt oxide cathode material with a median particle size of 15.5~16.5μm is obtained.

[0048] A battery comprising the aforementioned composite lithium cobalt oxide cathode material, or the composite lithium cobalt oxide cathode material obtained by the aforementioned method.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The composite lithium cobalt oxide cathode material of the present invention has suitable particle mechanical strength and single crystallinity. The single crystal doped lithium cobalt oxide material significantly reduces the Euclidean distance, indicating that the structure is less fragmented. At the same time, the polycrystalline doped lithium cobalt oxide material does not show fragility in the mixed system, but instead plays the role of dispersing stress and improving ion migration efficiency. Through the coordinated cooperation of large-particle-size single crystal doped lithium cobalt oxide material and small-particle-size polycrystalline doped lithium cobalt oxide material, the rate performance can be improved and the structure can be kept stable during the pressing process. It can achieve the unity of high capacity, high cycle stability and high rate performance, and has high capacity retention and excellent rate performance at high voltage.

[0050] (2) In the preparation method of the composite lithium cobalt oxide cathode material of the present invention, lithium vapor is introduced during the preparation of single-crystal doped lithium cobalt oxide material to adjust the atmosphere of the reaction chamber during the first heat treatment, thereby promoting single crystal growth and obtaining higher single crystallization while avoiding excessive particle fusion. The high single crystallization structure can significantly reduce grain boundary defects, improve the mechanical integrity and electronic continuity of the particles, and make them have stronger structural stability under long cycle and compaction conditions. The polycrystalline doped lithium cobalt oxide material adopts a low-temperature short-time heat treatment method to maintain polycrystalline characteristics and improve the lithium ion diffusion rate; then the single-crystal doped lithium cobalt oxide material and the polycrystalline doped lithium cobalt oxide material are mixed with element M compound, heat treated and crushed to ensure the coating effect of the coating layer; through the coordinated action of each step, the present invention can achieve a balance and breakthrough between the capacity, cycle stability and rate performance of the composite lithium cobalt oxide cathode material.

[0051] (3) The battery of the present invention has high structural stability, high capacity, long cycle performance and high rate performance. Detailed Implementation

[0052] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0053] According to one aspect of the present invention, the present invention relates to a composite lithium cobalt oxide cathode material, comprising a matrix and a coating layer located on the surface of the matrix, wherein the matrix comprises monocrystalline doped lithium cobalt oxide and polycrystalline doped lithium cobalt oxide; the median particle size of the monocrystalline doped lithium cobalt oxide material is larger than the median particle size of the polycrystalline doped lithium cobalt oxide material; the particle mechanical strength of the composite lithium cobalt oxide cathode material is expressed as Euclidean distance ED, wherein ED≤2.30, where ED refers to the Euclidean distance between the particle size distribution curves of the composite lithium cobalt oxide cathode material before and after being subjected to a pressure of 300MPa, for example, 1.45, 1.50, 1.63, 1.76, 1.93, 2.12 or 2.3, etc.; the monocrystalline degree of the composite lithium cobalt oxide cathode material is ≥50%, for example, 50%, 55%, 60%, 65%, etc.

[0054] The composite lithium cobalt oxide cathode material of this invention possesses suitable particle mechanical strength and monocrystalline density. The monocrystalline doped lithium cobalt oxide material significantly reduces the Euclidean distance, indicating less structural fragmentation. Meanwhile, the polycrystalline doped lithium cobalt oxide material does not exhibit fragility in the mixed system; instead, it plays a role in dispersing stress and improving ion migration efficiency. Through the coordinated use of large-particle-size monocrystalline doped lithium cobalt oxide material and small-particle-size polycrystalline doped lithium cobalt oxide material, rate performance can be improved while maintaining structural stability during tableting. This achieves a balance between high capacity, high cycle stability, and high rate performance, exhibiting both high capacity retention and excellent rate performance at high voltage.

[0055] Mechanical Strength of Particles (MSP) is a method for characterizing particle strength. It's a test that quantitatively evaluates the resistance to breakage of powder particles by applying external mechanical pressure and analyzing the changes in particle size distribution before and after the stress. Test Principle: In the MSP test, the sample powder is first uniformly loaded under a set pressure (e.g., several hundred MPa), causing some particles to break or expose structural defects. The difference in particle size distribution before and after pressure is then measured using a laser particle size analyzer or other particle size distribution analysis methods. The Euclidean distance is typically used to compare the difference in particle size distribution curves before and after pressure, serving as the MSP index. The smaller the distance value, the stronger the ability of the particles to remain intact after pressure, and the higher their mechanical strength.

[0056] Monocrystalline density: (Number of monocrystalline particles in EBSD test / (Number of monocrystalline particles + Number of polycrystalline particles) * 100%).

[0057] In some embodiments, the ED ≤ 2.00. When ED ≤ 2.00, the composite lithium cobalt oxide cathode material has higher mechanical strength and better structural stability.

[0058] In some embodiments, the composite lithium cobalt oxide cathode material has a single crystallinity of ≥52%, which is a higher proportion of single crystals and can help strengthen the structural framework and provide a longer cycle life.

[0059] In some embodiments, the single-crystal doped lithium cobalt oxide material includes a lithium cobalt oxide matrix A, dopant element A1, and dopant element A2; the dopant element A1 includes at least one of Al and Mg, and the doping amount of the dopant element A1 is 3000~20000ppm (e.g., 3000ppm, 4000ppm, 5000ppm, 8000ppm, 10000ppm, 15000ppm, or 20000ppm); the dopant element A2 includes at least one of Al, Mg, Ni, Mn, Ti, Zr, Y, La, Nb, Sr, and W, and the doping amount of the dopant element A2 is 1000~5000ppm (e.g., 1000ppm, 2000ppm, 3000ppm, 4000ppm, 5000ppm, etc.). The single-crystal doped lithium cobalt oxide material of the present invention has suitable dopant elements A1 and A2, which can better strengthen the crystal lattice and improve its structural stability.

[0060] In some embodiments, the polycrystalline doped lithium cobalt oxide material includes a lithium cobalt oxide matrix B, dopant element B1, and dopant element B2; dopant element B1 includes at least one of Al and Mg, and the doping amount of dopant element B1 is 3000~20000ppm; dopant element B2 includes at least one of Al, Mg, Ni, Mn, Ti, Zr, Y, La, Nb, Sr, and W, and the doping amount of dopant element B2 is 1000~5000ppm. The polycrystalline doped lithium cobalt oxide material of the present invention has suitable dopant elements B1 and B2, which can better strengthen the crystal lattice and improve its structural stability.

[0061] In some embodiments, the mass ratio of the single-crystal doped lithium cobalt oxide material to the polycrystalline doped lithium cobalt oxide material is (3~5):1, for example, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, etc. The single-crystal doped lithium cobalt oxide material of the present invention ensures structural stability and high capacity, while the polycrystalline doped lithium cobalt oxide material provides a fast lithium diffusion channel and improves rate performance. The two materials, through an appropriate mass ratio, exert a good synergistic effect, thereby enabling the material to possess high energy density, long cycle life, and high rate performance.

[0062] In some embodiments, the ratio x of the median particle size of the single-crystal doped lithium cobalt oxide material to the median particle size of the polycrystalline doped lithium cobalt oxide material satisfies: 2.54 ≤ x ≤ 5.86, for example, 2.54, 2.6, 2.7, 2.8, 2.9, 3, 3.5, 4, 4.5, 5, 5.86, etc. The single-crystal doped lithium cobalt oxide material and the polycrystalline doped lithium cobalt oxide material of the present invention have suitable median particle size ratios, which can achieve perfect matching and filling of single-crystal and polycrystalline particles, thereby improving the electrochemical performance of the composite lithium cobalt oxide material.

[0063] In some embodiments, the median particle size of the single-crystal doped lithium cobalt oxide material is 16.5~20.5 μm, for example, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 20 μm, 20.5 μm, etc. In some embodiments, the median particle size of the polycrystalline doped lithium cobalt oxide material is 3.5~6.5 μm, for example, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, etc. The single-crystal doped lithium cobalt oxide material and the polycrystalline doped lithium cobalt oxide material of the present invention have suitable median particle sizes, thereby enabling them to better exert their synergistic effect.

[0064] In some embodiments, the coating layer includes a coating element M, which comprises at least one of Mg, Al, Ti, Y, Zr, Nb, La, Ni, Mn, Co, F, and P, such as a combination of Mg and Al, or a combination of Y, Zr, and Nb. The thickness of the coating layer is 5-50 nm (e.g., 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 40 nm, or 50 nm), and the mass of the coating layer is 0.1%-1% (e.g., 0.1%, 0.2%, 0.5%, 0.8%, 1%, etc.) of the composite lithium cobalt oxide cathode material. By setting the above-mentioned suitable coating layer, the present invention can suppress electrolyte erosion and improve the interfacial stability of the composite material. If the coating layer is too thin (the mass percentage of the coating layer is too low), the coating effect is poor, and the interface improvement performance is inadequate. If the coating layer is too thick (the mass percentage of the coating layer is too high), it will hinder lithium-ion migration and increase impedance.

[0065] In some embodiments, the median particle size of the composite lithium cobalt oxide cathode material is 15.5~16.5 μm, for example, 15.5 μm, 15.8 μm, 16 μm, 16.2 μm, 16.5 μm, etc. In some embodiments, the specific surface area of ​​the composite lithium cobalt oxide cathode material is 0.19~0.25 m². 2 / g, for example 0.19m 2 / g, 0.2m 2 / g, 0.22m 2 / g, 0.23m 2 / g, 0.25m 2 / g, etc. In some embodiments, the tap density of the composite lithium cobalt oxide cathode material is 2.8~3.2 g / cm³. 3 For example, 2.8g / cm 3 2.9g / cm 3 3g / cm 3 3.1g / cm 3 3.2g / cm 3 The compaction density of the composite lithium cobalt oxide cathode material is 4.0~4.4 g / cm³. 3 For example, 4g / cm 3 4.1g / cm 3 4.2g / cm 3 4.4g / cm 3 The composite lithium cobalt oxide cathode material of the present invention has suitable median particle size, specific surface area, tap density and compaction density, which can help reduce side reactions and improve energy density.

[0066] In some embodiments, the battery prepared with the composite lithium cobalt oxide cathode material has an initial cycle specific capacity ≥ 200 mAh / g, such as 200 mAh / g, 210 mAh / g, 220 mAh / g, etc. In some embodiments, the battery prepared with the composite lithium cobalt oxide cathode material has a capacity retention rate ≥ 90% at 5C, such as 90%, 90.5%, 90.8%, 91%, 92%, 93%, etc. In some embodiments, the battery prepared with the composite lithium cobalt oxide cathode material has a cycle retention rate ≥ 92% after 100 cycles, such as 92%, 93%, 94%, etc. In some embodiments, the battery prepared with the composite lithium cobalt oxide cathode material has an impedance < 50 Ω, such as 35 Ω, 40 Ω, 45 Ω, 49 Ω, etc. The battery prepared with the composite lithium cobalt oxide cathode material of the present invention has high initial cycle specific capacity, high rate performance, high cycle retention rate, and low impedance.

[0067] According to another aspect of the present invention, the present invention also relates to a method for preparing a composite lithium cobalt oxide cathode material, comprising the following steps: A first cobalt source, a compound of element A2, and a first lithium source are subjected to a first mixing, a first heat treatment, and a first crushing process. Lithium vapor is introduced during the first heat treatment to obtain a single-crystal doped lithium cobalt oxide material. A second cobalt source, a compound of element B2, and a second lithium source are subjected to a second mixing, a second heat treatment, and a second crushing process. The total holding time for the second heat treatment is ≤10 hours to obtain a polycrystalline doped lithium cobalt oxide material. The median particle size of the polycrystalline doped lithium cobalt oxide material is smaller than that of the single-crystal doped lithium cobalt oxide material. The single-crystal doped lithium cobalt oxide material, the polycrystalline doped lithium cobalt oxide material, and a compound of element M are subjected to a third mixing, a third heat treatment, and a third crushing process to obtain a composite lithium cobalt oxide cathode material.

[0068] The preparation method of the composite lithium cobalt oxide cathode material of the present invention involves introducing lithium vapor during the first heat treatment process of preparing the single-crystal doped lithium cobalt oxide material to regulate the atmosphere of the reaction chamber. This promotes single-crystal growth while avoiding excessive particle fusion, resulting in higher single-crystal density. The high single-crystal density structure significantly reduces grain boundary defects, improves the mechanical integrity and electronic continuity of the particles, and enhances their structural stability under long-cycle and compaction conditions. The polycrystalline doped lithium cobalt oxide material is treated with a low-temperature, short-time heat treatment method to maintain polycrystalline characteristics and improve the lithium-ion diffusion rate. Then, the single-crystal doped lithium cobalt oxide material and the polycrystalline doped lithium cobalt oxide material are mixed with element M compound, heat-treated, and crushed to ensure the coating effect of the coating layer. Through the coordinated action of each step, the present invention achieves a balance and breakthrough in the capacity, cycle stability, and rate performance of the composite lithium cobalt oxide cathode material.

[0069] In some embodiments, the first cobalt source comprises one or more of CoO, Co(OH)2, Co(NO3)2, CoCO3, Co3O4, and CoOOH, such as a combination of CoO and Co(OH)2, or a combination of Co3O4 and CoOOH. In some embodiments, the first cobalt source further comprises element Al, which includes at least one of Al and Mg, and the doping amount of element Al is 3000~20000 ppm, such as 3000 ppm, 5000 ppm, 10000 ppm, or 20000 ppm. The median particle size of the first cobalt source is 15~18 μm, such as 15 μm, 16 μm, 17 μm, or 18 μm. This invention ensures the performance of the obtained single-crystal lithium cobalt oxide material by employing a first cobalt source containing suitable Al.

[0070] In some embodiments, the compound of element A2 comprises one or more of oxides, hydroxides, carbonates, and nitrates of element A2. Element A2 includes one or more of Al, Mg, Ni, Mn, Ti, Zr, Y, La, Nb, Sr, and W, such as combinations of Y and La, combinations of Y, La, and Nb, and combinations of Mn, Ti, and Zr. The doping amount of element A2 is 1000~5000 ppm, for example, 1000 ppm, 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm, etc. This invention adds a suitable compound of element A2 to improve the structural stability of single-crystal lithium cobalt oxide materials through doping.

[0071] In some embodiments, the present invention employs a suitable lithium source, the first lithium source comprising one or more of lithium carbonate, lithium hydroxide, lithium nitrate and lithium acetate, such as a combination of lithium carbonate and lithium hydroxide, a combination of lithium nitrate and lithium acetate, etc.

[0072] In some embodiments, the molar ratio of the first cobalt source and the first lithium source, respectively, based on cobalt and lithium, is 1:(1.01~1.08), such as 1:1.01, 1:1.02, 1:1.03, 1:1.05, 1:1.06 or 1:1.08.

[0073] In some embodiments, the rotational speed of the first mixing is 900~1000 r / min, such as 900 r / min, 920 r / min, 950 r / min, 980 r / min, 1000 r / min, etc.; the first mixing time is 40~60 min, such as 40 min, 45 min, 50 min, 55 min, or 60 min, etc. This invention ensures the mixing effect of each material by using appropriate first mixing speed and time, which is beneficial for subsequent heat treatment.

[0074] In some embodiments, the first heat treatment includes a first isothermal platform, a second isothermal platform, and a third isothermal platform arranged sequentially, wherein the temperature of the second isothermal platform is higher than the temperatures of the first and third isothermal platforms. In some embodiments, the temperature of the first isothermal platform is 400~900℃, for example, 400℃, 450℃, 500℃, 600℃, 700℃, 800℃, or 900℃, etc., and the holding time of the first isothermal platform is 3~10h, for example, 3h, 4h, 5h, 6h, 7h, 8h, or 10h, etc., with a heating rate of 3~9℃ / min; the temperature of the second isothermal platform is 850~1200℃, for example, 850℃, 900℃, 950℃, 1000℃, 1100℃, or 12... The first heat treatment of the present invention has a suitable three-stage isothermal platform, with a holding time of 5-12 hours (e.g., 5h, 6h, 7h, 8h, 9h, 10h, 11h, or 12h) and a heating rate of 3-8℃ / min. The third isothermal platform has a temperature of 450-950℃ (e.g., 450℃, 500℃, 600℃, 700℃, 800℃, 900℃, or 950℃) and a holding time of 2-6 hours (e.g., 2h, 3h, 4h, 5h, or 6h) and a heating rate of 1-3℃ / min. The first heat treatment of the present invention has a suitable three-stage isothermal platform, thereby ensuring the electrochemical performance of the obtained single-crystal lithium cobalt oxide material.

[0075] In some embodiments, the first heat treatment is performed in a heating chamber, with lithium vapor introduced using a protective gas as a carrier gas. After the lithium vapor is introduced, the heating chamber contains lithium vapor, oxygen, and the protective gas, wherein the partial pressure of the lithium vapor is 0.1%~10% (e.g., 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 10%, etc.). Air is used as the base atmosphere, with an oxygen volume fraction of 21%. The protective gas includes nitrogen, and the flow rate of the protective gas is 3~5 L / min. In some embodiments, the lithium vapor introduction begins before the first isothermal plateau and ends after the second isothermal plateau and before the third isothermal plateau. The appropriate timing of lithium vapor introduction in this invention can better regulate the atmosphere of the reaction chamber, promote single crystal growth while avoiding excessive particle fusion, obtain higher single crystallinity, reduce grain boundary defects, improve the mechanical integrity and electronic continuity of the particles, and enhance the structural stability of the material under long-term cycling and compaction conditions.

[0076] In some embodiments, the median particle size of the single-crystal doped lithium cobalt oxide material is 16.5~20.5 μm, for example, 16.5 μm, 17 μm, 18 μm, 19 μm, 20 μm, or 20.5 μm. The single-crystal doped lithium cobalt oxide material of the present invention has a suitable particle size, which can form a good combination with the polycrystalline doped lithium cobalt oxide material, thus benefiting the coating effect of the first coating layer.

[0077] In some embodiments, the second cobalt source comprises one or more of CoO, Co(OH)2, Co(NO3)2, CoCO3, Co3O4, and CoOOH, such as CoO and Co(OH)2, Co(OH)2 and Co(NO3)2, etc. In some embodiments, the second cobalt source further comprises element B1, which includes at least one of Al and Mg, and the doping amount of element B1 is 3000~20000 ppm, such as 3000 ppm, 5000 ppm, 6000 ppm, 7000 ppm, 10000 ppm, 15000 ppm, or 20000 ppm. The median particle size of the second cobalt source is 3~6 μm, such as 3 μm, 4 μm, 5 μm, 6 μm, etc. This invention ensures the performance of the obtained single-crystal lithium cobalt oxide material by employing a second cobalt source containing suitable B1.

[0078] In some embodiments, the compound of element B2 comprises one or more of oxides, hydroxides, carbonates, and nitrates of element B2, wherein element B2 includes one or more of Al, Mg, Ni, Mn, Ti, Zr, Y, La, Nb, Sr, and W, such as Ti, Zr, and Y, and La and Nb. The doping amount of the dopant element B2 is 1000~5000 ppm, for example 1000 ppm, 1500 ppm, 2000 ppm, 3000 ppm, 5000 ppm, etc. This invention adds a suitable compound of element B2 to improve the structural stability of polycrystalline lithium cobalt oxide materials through doping.

[0079] In some embodiments, the present invention employs a suitable second lithium source, which comprises one or more of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium acetate, such as a combination of lithium hydroxide and lithium nitrate.

[0080] In some embodiments, the molar ratio of the second cobalt source and the second lithium source, respectively, based on cobalt and lithium, is 1:(1.01~1.08), such as 1:1.01, 1:1.02, 1:1.03, 1:1.05, 1:1.06 or 1:1.08.

[0081] In some embodiments, the rotational speed of the second mixing is 900~1000 r / min, such as 900 r / min, 950 r / min, 1000 r / min, etc., and the mixing time is 40~60 min, such as 40 min, 50 min, 60 min, etc. The second mixing of the present invention has suitable rotational speed and time, thereby ensuring the mixing effect of each material.

[0082] In some embodiments, the second heat treatment includes a fourth isothermal platform and a fifth isothermal platform arranged sequentially. The temperature of the fourth isothermal platform is 400~800℃, for example, 400℃, 500℃, 600℃, 700℃, 800℃, etc., and the holding time of the fourth isothermal platform is 2~4h, for example, 2h, 3h, or 4h, etc., with a heating rate of 3~8℃ / min, for example, 3℃ / min, 5℃ / min, 8℃ / min, etc.; the temperature of the fifth isothermal platform is 750~1000℃, for example, 750℃, 800℃, 900℃, 1000℃, etc., and the holding time of the fifth isothermal platform is 3~6h, for example, 3h, 4h, 5h, 6h, etc., with a heating rate of 1~3℃ / min. The atmosphere of the second heat treatment includes an oxygen-containing atmosphere, such as air. The second heat treatment of the present invention has a suitable two-stage isothermal platform, thereby ensuring the heat treatment effect on the material and improving the electrochemical performance of polycrystalline lithium cobalt oxide materials.

[0083] In some embodiments, the median particle size of the polycrystalline doped lithium cobalt oxide material is 3.5~6.5 μm, for example, 3.5 μm, 4 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, etc. The polycrystalline doped lithium cobalt oxide material of the present invention has a suitable median particle size, which can synergize with single-crystal doped lithium cobalt oxide materials and is beneficial to the coating effect of the second coating layer.

[0084] In some embodiments, the mass ratio of the monocrystalline doped lithium cobalt oxide material to the polycrystalline doped lithium cobalt oxide material is (3~5):1, for example, 3:1, 3.5:1, 4:1, 4.5:1, or 5:1. The monocrystalline doped lithium cobalt oxide material of the present invention ensures structural stability and high capacity, while the polycrystalline doped lithium cobalt oxide material provides a fast lithium diffusion channel and improves rate performance. The suitable mass ratio of the two materials allows for excellent synergy, resulting in a material that combines high energy density, cycle life, and rate performance.

[0085] In some embodiments, the element M comprises one or more of Mg, Al, Ti, Y, Zr, Nb, La, Ni, Mn, Co, F, and P, such as combinations of Mg and Al, combinations of Y, Zr, and Nb, and combinations of Mn, Co, and F. The coating layer of the present invention, having the aforementioned suitable coating elements, is beneficial for improving the interfacial properties of the final composite lithium cobalt oxide material.

[0086] In some embodiments, the mass of the element M compound is 0.1% to 1% of the mass of the composite lithium cobalt oxide cathode material, for example, 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 1%, etc. The element M compound of the present invention has a suitable addition amount, thereby ensuring a suitable thickness of the coating layer and ensuring the coating effect on the core substrate.

[0087] In some embodiments, the temperature of the third heat treatment is 750~1000℃, for example, 750℃, 800℃, 900℃, 1000℃, etc.; the holding time of the third heat treatment is 3~6h, for example, 3h, 3.5h, 4h, 4.5h, 5h, 6h, etc., and it is carried out under low oxygen atmosphere (O2<5%) conditions. The third heat treatment of the present invention has a suitable treatment temperature and time to ensure that the element M compound forms a uniform and stable coating layer on the particle surface, thereby improving the electrochemical performance of the composite material.

[0088] In some embodiments, after the third crushing, a composite lithium cobalt oxide cathode material with a median particle size of 15.5~16.5μm (e.g., 15.5μm, 16μm, 16.5μm, etc.) is obtained.

[0089] In some embodiments, the first heat treatment, the second heat treatment, and the third heat treatment of the present invention employ calcination equipment, including a box furnace, a rotary kiln, or a tube furnace.

[0090] According to another aspect of the present invention, the present invention also relates to a battery comprising the aforementioned composite lithium cobalt oxide cathode material, or the composite lithium cobalt oxide cathode material obtained by the method.

[0091] The battery of this invention has high structural stability, high capacity, long cycle performance, and high rate performance.

[0092] The following explanation, combined with specific embodiments and comparative examples, further illustrates the point.

[0093] Example 1 A method for preparing a composite lithium cobalt oxide cathode material includes the following steps: (1) Preparation of single-crystal doped lithium cobalt oxide material: Weigh 3kg Co3O4 (D50=16.5μm, Al content 8000ppm) and mix with 1.55kg Li2CO3 and additives MgO 1000ppm and Y2O3 800ppm. Mix for 50min at 950r / min in a high-speed mixer. After the materials are mixed evenly, they are placed in a box furnace for the first heat treatment. The temperature is increased to 850℃ at 5℃ / min and held for 5 hours, then increased to 1080℃ at 3℃ / min and held for 8 hours. Subsequently, the temperature is decreased to 850℃ at 2℃ / min and held for 3 hours. During the first heat treatment, the temperature starts at 680℃, and lithium vapor generated in the independent heating chamber is introduced through nitrogen carrier gas to form an oxygen-nitrogen mixed atmosphere containing lithium vapor in the furnace. Air is used as the base atmosphere with an oxygen volume fraction of 21%, nitrogen is used as the carrier gas with a flow rate of 4L / min, the partial pressure of lithium vapor is maintained at 1.5% of the total pressure, and the remainder is nitrogen. When the temperature drops to 849℃, the gas introduction is stopped. After the first heat treatment, high monocrystalline large-particle lithium cobalt oxide is obtained, with a D50 of 18.8μm after crushing.

[0094] (2) Preparation of polycrystalline doped lithium cobalt oxide material: Weigh 3 kg Co3O4 (D50=4μm, Al content 7000ppm) and mix it with 1.35 kg Li2CO3 and additives ZrO2 1200ppm and MgO 500ppm evenly, and then carry out a second heat treatment: heat up to 700℃ at 5℃ / min in air atmosphere and hold for 3h, then heat up to 930℃ at 2℃ / min and hold for 4h. After cooling, polycrystalline small-particle lithium cobalt oxide is obtained. After crushing and grading, D50=4.8μm.

[0095] (3) Coating treatment: 1.6 kg of single-crystal doped lithium cobalt oxide material and 0.4 kg of polycrystalline doped lithium cobalt oxide material were mixed at a mass ratio of 4:1. 0.5 wt% lithium phosphate and 1000 ppm TiO2 were added as coating agents. After ball milling for 4 h to mix evenly, a third heat treatment was performed: the temperature was increased to 900 °C at 3 °C / min under a low-oxygen atmosphere (O2=4%) and held for 6 h. After cooling, crushing, and demagnetizing, lithium cobalt oxide cathode material with D50=16 μm was obtained.

[0096] Example 2 A method for preparing a composite lithium cobalt oxide cathode material includes the following steps: (1) Preparation of single-crystal doped lithium cobalt oxide material: Weigh 3 kg Co3O4 (D50=17μm, Al content 9000ppm) and mix it with 1.6 kg Li2CO3, Nb2O3 1000ppm and MgO 800ppm. Mix at 1000r / min for 45min in a high-speed mixer. After the materials are mixed evenly, they are placed in a box furnace and heated to 820℃ at a rate of 4℃ / min and held for 4 hours. Then, the temperature is increased to 1070℃ at a rate of 2℃ / min and held for 7 hours. The temperature is then reduced to 900℃ and held for 3 hours. In the first heat treatment, the temperature starts at 680℃, and lithium vapor generated in the independent heating chamber is introduced through nitrogen carrier gas to form an oxygen-nitrogen mixed atmosphere containing lithium vapor in the furnace. Air is used as the base atmosphere with an oxygen volume fraction of 21%, nitrogen is used as the carrier gas with a flow rate of 4L / min, the partial pressure of lithium vapor is maintained at 1.5% of the total pressure, and the remainder is nitrogen. When the temperature drops to 849℃, the gas introduction is stopped. After the first heat treatment, high monocrystalline large-particle lithium cobalt oxide with D50=19μm is obtained.

[0097] (2) Preparation of polycrystalline doped lithium cobalt oxide material: 3 kg Co3O4 (D50=4.5μm, Al content 7500ppm) was mixed with 1.32 kg Li2CO3, Y2O3 1000ppm and MgO 500ppm, and then subjected to a second heat treatment: the temperature was raised to 720℃ at 5℃ / min and held for 3h in air atmosphere, and then raised to 950℃ at 2℃ / min and held for 4h to obtain polycrystalline small particles with D50=5μm.

[0098] (3) Coating treatment: 1.4 kg of single crystal doped lithium cobalt oxide material and 0.35 kg of polycrystalline doped lithium cobalt oxide material were mixed, and 0.4 wt% magnesium hydrogen phosphate and 1500 ppm ZrO2 were added. After ball milling, the mixture was subjected to a third heat treatment: the mixture was kept at 880℃ for 7 h, cooled, crushed, and demagnetized to obtain a composite lithium cobalt oxide cathode material with D50 = 15.9 μm.

[0099] Example 3 A method for preparing a composite lithium cobalt oxide cathode material includes the following steps: (1) Preparation of single-crystal doped lithium cobalt oxide material: Weigh 3 kg Co3O4 (D50=16.8μm, Al content 8500ppm, Mg content 500ppm), add 1.55 kg Li2CO3 and In2O3 800ppm, dry mix for 45 min, and after the material is homogeneous, place it into a tube furnace and heat at 4℃ / min The temperature was raised to 850℃ and held for 5 hours, then raised to 1080℃ and held for 8 hours, and then lowered to 900℃ and held for 3 hours. During the first heat treatment, the temperature started at 680℃, and lithium vapor generated in the independent heating chamber was introduced through nitrogen carrier gas to form an oxygen-nitrogen mixed atmosphere containing lithium vapor in the furnace. Air was used as the base atmosphere with an oxygen volume fraction of 21%, nitrogen was used as the carrier gas with a flow rate of 4 L / min, the partial pressure of lithium vapor was maintained at 1.5% of the total pressure, and the remainder was nitrogen. When the temperature dropped to 849℃, the gas introduction was stopped. After the first heat treatment, high monocrystalline large-particle lithium cobalt oxide with D50=18.6μm was obtained.

[0100] (2) Preparation of polycrystalline doped lithium cobalt oxide material: 3 kg Co3O4 (D50=3.8μm, Al content 6500ppm) was mixed with 1.33 kg Li2CO3 and TiO2 1000ppm evenly, and then subjected to a second heat treatment: the temperature was raised to 680℃ at 4℃ / min and held for 3h, and then raised to 900℃ at 2℃ / min and held for 4h to obtain small particles with D50=4.2μm.

[0101] (3) Coating treatment: 1.5 kg of single crystal doped lithium cobalt oxide material and 0.37 kg of polycrystalline doped lithium cobalt oxide material were mixed, and 0.5 wt% magnesium phosphate and 1000 ppm La2O3 were added for coating. After ball milling, a third heat treatment was performed: the temperature was kept at 910℃ for 6 h, and after cooling, crushing and demagnetizing, lithium cobalt oxide cathode material with D50=16.1 μm was obtained.

[0102] Example 4 A method for preparing a composite lithium cobalt oxide cathode material differs from Example 1 in that: In step (1), the partial pressure of lithium vapor is maintained at 2% of the total pressure.

[0103] Comparative Example 1 A method for preparing a lithium cobalt oxide cathode material includes the following steps: (1) Preparation of large particles: Weigh 3 kg Co3O4 (D50=16.5μm, Al content 8000ppm), mix it with 1.55 kg Li2CO3 and additives Y2O3 1000ppm and MgO 500ppm, heat it to 600℃ at 5℃ / min in air atmosphere and hold for 4h, then heat it to 1070℃ at 3℃ / min and hold for 9h, cool and crush it to obtain large particles of lithium cobalt oxide single crystals with D50=18.6μm.

[0104] (2) Preparation of small particles: Weigh 3 kg of Co3O4 (D50=4.5μm, Al content 7000ppm), mix with 1.32 kg of Li2CO3 and ZrO2 1000ppm, heat to 650℃ at 4℃ / min and hold for 3h in air atmosphere, then heat to 980℃ at 2.5℃ / min and hold for 8h, cool and crush to obtain small particles of lithium cobalt oxide single crystals with D50=5μm.

[0105] (3) Mixed coating: The obtained large-particle lithium cobalt oxide single crystals and small-particle lithium cobalt oxide single crystals are mixed at a mass ratio of 4:1, and 0.5wt% lithium phosphate and 1000ppm Al2O3 coating agent are added. After ball milling for 4 hours, the mixture is kept at 880℃ for 6 hours in air atmosphere to obtain lithium cobalt oxide cathode material.

[0106] Comparative Example 2 A method for preparing a lithium cobalt oxide cathode material includes the following steps: (1) Preparation of large particles: Weigh 3 kg Co3O4 (D50=16.5μm, Al content 8500ppm), mix with 1.55 kg Li2CO3 and additive TiO2 1000ppm, heat to 650 ℃ at 5℃ / min and hold for 4h under lithium vapor-assisted atmosphere, then heat to 1080 ℃ at 3℃ / min and hold for 10h, cool and crush to obtain large particle single crystal lithium cobalt oxide with D50=19μm.

[0107] (2) Preparation of small particles: Weigh 3 kg Co3O4 (D50=4.0μm, Al content 7000ppm), mix with 1.3 kg Li2CO3 and Y2O3 1500ppm, heat to 650℃ at 4℃ / min and hold for 4h in air atmosphere, then heat to 995℃ at 3℃ / min and hold for 8h to obtain small particle single crystal lithium cobalt oxide with D50=4.8μm.

[0108] (3) Mixed coating: Large particles and small particles are mixed at a mass ratio of 4:1, and 0.5wt% magnesium hydrogen phosphate and 1000ppm ZrO2 coating agent are added. After ball milling for 4 hours, the temperature is raised to 870℃ at 3℃ / min under an oxygen atmosphere and held for 7 hours. The final product is obtained by cooling.

[0109] Experimental Example I. Particle mechanical strength and monocrystalline density of cathode materials The cathode materials of each embodiment and comparative example were subjected to particle mechanical strength (MSP) and monocrystalline density tests, and the results are shown in Table 1. The test methods are as follows: 1. Particle mechanical strength (MSP): In the MSP test, the sample powder was first subjected to uniform loading at a pressure of 300 MPa, causing some particles to break or expose structural defects. The difference in particle size distribution before and after compression was then measured using a laser particle size analyzer. The Euclidean distance (ED) was used to compare the difference in particle size distribution curves before and after compression, serving as the MSP index. A smaller ED value indicates a stronger ability of the particles to maintain their integrity under pressure, and thus higher mechanical strength.

[0110] 2. Monocrystallineity test EBSD was used for analysis.

[0111] Table 1. Particle mechanical strength and monocrystalline density

[0112] II. Battery Performance Testing The cathode materials of each embodiment and comparative example were used to prepare coin cells and their performance was tested.

[0113] A method for preparing a coin cell includes: mixing a positive electrode material with a conductive agent and a binder at a mass ratio of 96:2:2, wherein the conductive agent is conductive carbon black (Super P) and the binder is polyvinylidene fluoride (PVDF); adding an appropriate amount of N-methylpyrrolidone (NMP) solvent; and stirring to obtain a uniform slurry. The slurry is then coated onto an aluminum foil current collector (15 μm thick), dried at 100°C to remove the solvent, and then rolled to achieve a compaction density of 4.0~4.4 g / cm³ for the positive electrode sheet. 3 The material was then punched into positive electrode sheets with a diameter of 14 mm, and the areal density of the active material was controlled at 14~16 mg / cm². In an argon-atmosphere glove box (H₂O and O₂ contents both less than 1 ppm), lithium metal sheets were used as the negative electrode, a polypropylene microporous membrane (e.g., Celgard 2400) as the separator, and 1 mol / L LiPF₆ as the electrolyte. The solvents were EC, DEC, and EMC, with an EC:DEC:EMC ratio of 1:1:1 (volume ratio), and 1.5 wt% VC additive was added. CR2032 coin cells were assembled. All electrochemical tests were performed at 25°C.

[0114] The test results are shown in Table 2.

[0115] Table 2 Battery performance test results

[0116] As shown in Tables 1 and 2, the cathode materials obtained by the methods of the various embodiments of the present invention have low ED, i.e., higher mechanical strength and higher single crystallinity. The batteries prepared from the cathode materials obtained in the various embodiments of the present invention have high initial specific capacity, high cycle performance and rate performance, and low impedance. Specifically, the batteries prepared from the composite lithium cobalt oxide cathode materials of the various embodiments have an initial specific capacity ≥ 200 mAh / g, a capacity retention rate ≥ 90% at 5C, a capacity retention rate ≥ 92% after 100 cycles, and an impedance < 50Ω.

[0117] In Comparative Example 1, the lithium cobalt oxide materials all exhibited conventional single-crystal structures. Small particles were prone to breakage during compaction, and MSP testing showed a significant increase in Euclidean distance, resulting in noticeable capacity decay during cycling and insufficient performance at high rates. In Comparative Example 2, while the large lithium cobalt oxide particles were single-crystal materials, the small particles remained single-crystals, exhibiting low mechanical strength, low crystallinity, and a lack of grain boundary diffusion channels. Consequently, rate performance was not significantly improved, and discharge capacity decay was severe at high rates. The batteries in Comparative Examples 1 and 2 exhibited low initial specific capacity, low cycle performance, low rate performance, and high impedance.

[0118] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite lithium cobalt oxide cathode material, characterized in that, It includes a substrate and a coating layer located on the surface of the substrate, wherein the substrate includes monocrystalline doped lithium cobalt oxide material and polycrystalline doped lithium cobalt oxide material; The median particle size of the single-crystal doped lithium cobalt oxide material is larger than that of the polycrystalline doped lithium cobalt oxide material; The particle mechanical strength of the composite lithium cobalt oxide cathode material is expressed by the Euclidean distance ED, where ED≤2.

30. ED refers to the Euclidean distance between the particle size distribution curves of the composite lithium cobalt oxide cathode material before and after being subjected to a pressure of 300MPa. The monocrystalline degree of the composite lithium cobalt oxide cathode material is ≥50%.

2. The composite lithium cobalt oxide cathode material according to claim 1, characterized in that, It includes at least one of the following features (1) to (2): (1) The ED ≤ 2.00; (2) The single crystallinity of the composite lithium cobalt oxide cathode material is ≥52%.

3. The composite lithium cobalt oxide cathode material according to claim 1, characterized in that, It includes at least one of the following features (1) to (6): (1) The single-crystal doped lithium cobalt oxide material includes a lithium cobalt oxide matrix A, a doping element A1 and a doping element A2; the doping element A1 includes at least one of Al and Mg, and the doping amount of the doping element A1 is 3000~20000ppm; the doping element A2 includes at least one of Al, Mg, Ni, Mn, Ti, Zr, Y, La, Nb, Sr and W, and the doping amount of the doping element A2 is 1000~5000ppm; (2) The polycrystalline doped lithium cobalt oxide material includes a lithium cobalt oxide matrix B, a dopant element B1 and a dopant element B2; the dopant element B1 includes at least one of Al and Mg, and the doping amount of the dopant element B1 is 3000~20000ppm; the dopant element B2 includes at least one of Al, Mg, Ni, Mn, Ti, Zr, Y, La, Nb, Sr and W, and the doping amount of the dopant element B2 is 1000~5000ppm; (3) The mass ratio of the single-crystal doped lithium cobalt oxide material to the polycrystalline doped lithium cobalt oxide material is (3~5):1; (4) The ratio x of the median particle size of the single-crystal doped lithium cobalt oxide material to the median particle size of the polycrystalline doped lithium cobalt oxide material satisfies: 2.54≤x≤5.86; (5) The median particle size of the single-crystal doped lithium cobalt oxide material is 16.5~20.5 μm; (6) The median particle size of the polycrystalline doped lithium cobalt oxide material is 3.5~6.5μm.

4. The composite lithium cobalt oxide cathode material according to claim 1, characterized in that, It includes at least one of the following features (1) to (2): (1) The coating layer contains a coating element M, which contains at least one of Mg, Al, Ti, Y, Zr, Nb, La, Ni, Mn, Co, F and P; (2) The mass of the coating layer is 0.1% to 1% of the composite lithium cobalt oxide cathode material.

5. The composite lithium cobalt oxide cathode material according to claim 1, characterized in that, It includes at least one of the following features (1) to (8): (1) The median particle size of the composite lithium cobalt oxide cathode material is 15.5~16.5 μm; (2) The specific surface area of ​​the composite lithium cobalt oxide cathode material is 0.19~0.25m². 2 / g; (3) The tap density of the composite lithium cobalt oxide cathode material is 2.8~3.2 g / cm³. 3 ; (4) The compaction density of the composite lithium cobalt oxide cathode material is 4.0~4.4 g / cm³. 3 ; (5) The battery prepared by the composite lithium cobalt oxide cathode material has a first-cycle specific capacity ≥200mAh / g; (6) The battery prepared from the composite lithium cobalt oxide cathode material retains ≥90% of its capacity at 5C. (7) The battery prepared from the composite lithium cobalt oxide cathode material retains a rate of ≥92% after 100 cycles; (8) The impedance of the battery prepared by the composite lithium cobalt oxide cathode material is <50Ω.

6. A method for preparing a composite lithium cobalt oxide cathode material, characterized in that, Includes the following steps: The first cobalt source, the compound of element A2 and the first lithium source are mixed, heat-treated and crushed. Lithium vapor is introduced during the first heat treatment to obtain a single-crystal doped lithium cobalt oxide material. The second cobalt source, the compound of element B2, and the second lithium source are subjected to a second mixing, a second heat treatment, and a second crushing. The total holding time of the second heat treatment is ≤10h to obtain a polycrystalline doped lithium cobalt oxide material. The median particle size of the polycrystalline doped lithium cobalt oxide material is smaller than that of the single-crystal doped lithium cobalt oxide material. The single-crystal doped lithium cobalt oxide material, the polycrystalline doped lithium cobalt oxide material, and the element M compound are subjected to a third mixing, a third heat treatment, and a third crushing to obtain a composite lithium cobalt oxide cathode material.

7. The method for preparing the composite lithium cobalt oxide cathode material according to claim 6, characterized in that, It includes at least one of the following features (1) to (7): (1) The first cobalt source contains one or more of CoO, Co(OH)2, Co(NO3)2, CoCO3, Co3O4 and CoOOH; preferably, the first cobalt source also contains element Al, wherein element Al contains at least one of Al and Mg, and the doping amount of element Al is 3000~20000ppm. (2) The compound of element A2 includes one or more of the oxides, hydroxides, carbonates and nitrates of element A2, and element A2 includes one or more of Al, Mg, Ni, Mn, Ti, Zr, Y, La, Nb, Sr and W; the doping amount of the doping element A2 is 1000~5000ppm; (3) The first lithium source comprises one or more of lithium carbonate, lithium hydroxide, lithium nitrate and lithium acetate; (4) The molar ratio of the first cobalt source and the first lithium source, respectively, based on cobalt and lithium, is 1:(1.02~1.08). (5) The rotation speed of the first mixing is 900~1000 r / min, and the mixing time is 40~60 min; (6) The first heat treatment includes a first constant temperature platform, a second constant temperature platform and a third constant temperature platform arranged in sequence, wherein the temperature of the second constant temperature platform is greater than the temperature of the first constant temperature platform and the temperature of the third constant temperature platform; preferably, the temperature of the first constant temperature platform is 400~900℃ and the holding time of the first constant temperature platform is 3~10h; the temperature of the second constant temperature platform is 850~1200℃ and the holding time of the second constant temperature platform is 5~12h; the temperature of the third constant temperature platform is 450~950℃ and the holding time of the third constant temperature platform is 2~6h. Preferably, the first heat treatment is carried out in a heating chamber, with a protective gas as the carrier gas for introducing lithium vapor. After the lithium vapor is introduced, the heating chamber contains lithium vapor, oxygen, and the protective gas, and the partial pressure of the lithium vapor is 0.1% to 10%. Preferably, the lithium vapor is introduced at a time before the first isothermal platform and at a time after the second isothermal platform and before the third isothermal platform. (7) The median particle size of the single-crystal doped lithium cobalt oxide material is 16.5~20.5μm.

8. The method for preparing the composite lithium cobalt oxide cathode material according to claim 6, characterized in that, It includes at least one of the following features (1) to (7): (1) The second cobalt source contains one or more of CoO, Co(OH)2, Co(NO3)2, CoCO3, Co3O4 and CoOOH; preferably, the second cobalt source also contains element B1, wherein element B1 contains at least one of Al and Mg, and the doping amount of element B1 is 3000~20000ppm; (2) The compound of element B2 includes one or more of the oxides, hydroxides, carbonates and nitrates of element B2, and element B2 includes one or more of Al, Mg, Ni, Mn, Ti, Zr, Y, La, Nb, Sr and W, and the doping amount of the doping element B2 is 1000~5000ppm; (3) The second lithium source comprises one or more of lithium carbonate, lithium hydroxide, lithium nitrate and lithium acetate; (4) The molar ratio of the second cobalt source and the second lithium source, respectively, based on cobalt and lithium, is 1:(1.01~1.08). (5) The rotation speed of the second mixing is 900~1000 r / min, and the mixing time is 40~60 min; (6) The second heat treatment includes a fourth constant temperature platform and a fifth constant temperature platform arranged in sequence. The temperature of the fourth constant temperature platform is 400~800℃ and the holding time of the fourth constant temperature platform is 2~4h. The temperature of the fifth constant temperature platform is 750~1000℃ and the holding time of the fifth constant temperature platform is 3~6h. (7) The median particle size of the polycrystalline doped lithium cobalt oxide material is 3.5~6.5μm.

9. The method for preparing the composite lithium cobalt oxide cathode material according to claim 6, characterized in that, It includes at least one of the following features (1) to (5): (1) The mass ratio of the single-crystal doped lithium cobalt oxide material to the polycrystalline doped lithium cobalt oxide material is (3~5):1; (2) The element M includes one or more of Mg, Al, Ti, Y, Zr, Nb, La, Ni, Mn, Co, F and P; (3) The mass of the element M compound is 0.1% to 1% of the mass of the composite lithium cobalt oxide cathode material; (4) The temperature of the third heat treatment is 750~1000℃, and the holding time of the third heat treatment is 3~6h; (5) After the third crushing, a composite lithium cobalt oxide cathode material with a median particle size of 15.5~16.5μm is obtained.

10. A battery, characterized in that, The composite lithium cobalt oxide cathode material comprising any one of claims 1 to 5, or the composite lithium cobalt oxide cathode material obtained by the method of any one of claims 6 to 9.

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