Preparation method of lithium cobalt oxide positive electrode material, lithium cobalt oxide positive electrode material and lithium battery

Abstract

The invention discloses a preparation method of a lithium cobalt oxide positive electrode material, the lithium cobalt oxide positive electrode material and a lithium battery, and relates to the technical field of lithium ion batteries. The method comprises the following steps: firstly, preparing a polycrystalline lithium cobalt oxide defective product and a single-crystal lithium cobalt oxide defective product, and respectively introducing doping elements in a first additive and a second additive into the polycrystalline lithium cobalt oxide defective product and the single-crystal lithium cobalt oxide defective product; a polycrystalline lithium cobalt oxide defective product, a third additive and a fourth additive are mixed and sintered, a sintering aid (the third additive contains a doping element M1) and a high-valence transition metal compound (the fourth additive contains a doping element M2) are matched, a high-melting-point Li-Co-M1-M2 phase is generated at the grain boundary, the grain boundary binding energy is improved, and therefore the compressive strength of the polycrystalline material is improved. After the grain boundary optimized lithium cobalt oxide defective product and the monocrystal lithium cobalt oxide defective product are graded, the lithium cobalt oxide positive electrode material with high compaction density can be obtained, and meanwhile, the positive electrode material can give consideration to rate performance and cycle performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a method for preparing lithium cobalt oxide cathode material, the lithium cobalt oxide cathode material, and a lithium battery. Background Technology

[0002] Lithium cobalt oxide (LiCoO2, LCO) is a mainstream cathode material in the consumer electronics field. Its volumetric energy density advantage (≥600Wh / L) mainly stems from its high compaction density characteristics (typically ≥3.8g / cm³). 3 With the widespread adoption of fast-charging electronic devices (such as drones, power tools, and high-end mobile phones), the market has placed a dual demand on LCO materials: a synergistic improvement in both high power (>5C discharge) and high energy density. To meet this demand, increasing the primary particle size (D50>15μm) has become an effective way to improve compaction density: larger particles can significantly reduce electrode porosity, increasing the compaction density (5t) to 4.0 g / cm³. 3 The above (traditional small particle materials are approximately 3.6 g / cm³) 3 This increases the battery's volumetric energy density by more than 10%.

[0003] However, single-crystal large-particle LCOs suffer from intrinsic kinetic defects: the lithium-ion diffusion path is prolonged, leading to a sharp capacity decay at high-rate (>5C) discharge (5C discharge capacity retention is often below 90%); internal stress concentration within the particles, lattice distortion accumulation during cycling, and microcracks are induced, accelerating interfacial side reactions and resulting in deterioration of high-temperature cycling performance (capacity retention <75% after 300 cycles at 45℃). While traditional polycrystalline materials shorten the ion diffusion path through grain refinement (5C capacity retention can reach 90%), weak grain boundary bonding leads to insufficient particle mechanical strength. Under high-compaction processes (roller pressure >5t / cm), the particles are easily broken, producing fine powder, which in turn increases the electrode porosity and reduces the compaction density to 3.6 g / cm³. 3 the following.

[0004] Therefore, there is an urgent need to improve the preparation process of lithium cobalt oxide, so as to significantly increase the compaction density of the material while also taking into account rate performance and cycle performance.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing lithium cobalt oxide cathode material, the lithium cobalt oxide cathode material and the lithium battery, which aims to significantly improve the compaction density of the material while also taking into account rate performance and cycle performance.

[0007] This invention is implemented as follows: In a first aspect, the present invention provides a method for preparing a lithium cobalt oxide cathode material, comprising: Large-particle cobalt tetroxide precursor, first lithium salt and first additive are mixed and sintered to obtain polycrystalline lithium cobalt oxide primary product. Small-particle cobalt tetroxide precursor, second lithium salt and second additive are mixed and sintered to obtain single-crystal lithium cobalt oxide primary product. Polycrystalline lithium cobalt oxide primary product, third additive and fourth additive are mixed and sintered to obtain grain boundary optimized lithium cobalt oxide primary product; Grain boundary optimized primary lithium cobalt oxide and monocrystalline primary lithium cobalt oxide are mixed and sintered. Among them, the particle size of the large-particle cobalt tetroxide precursor is 13.5μm≤Dv50≤18.5μm, and the particle size of the small-particle cobalt tetroxide precursor is 1.5μm≤Dv50≤6.5μm; The doping element contained in the first additive is selected from at least one of Al, Mg, Ti, Zr, La, Y, W and B; The doping element contained in the second additive is selected from at least one of Al, Mg, Ti, Zr, La, Y, W and B; The doping element contained in the third additive is selected from at least one of Li, B, Ca, Mg, Cr, Al, La, Y, Mn, Si and V; The doping element contained in the fourth additive is selected from at least one of La, Y, Ti, Zr, W and Nb.

[0008] In an optional embodiment, the third additive is selected from at least one of Li2CO3, LiBO2, Li3BO3, Li2B4O7, CaO, MgO, Cr2O3, Al2O3, La2O3, Y2O3, MnO2, SiO2 and V2O5; And / or, the mass ratio of the dopant element contained in the third additive to the primary polycrystalline lithium cobalt oxide is (0.1-0.5):100; And / or, the fourth additive is selected from at least one of La2O3, Y2O3, TiO2, ZrO2, W2O5 and Nb2O5; And / or, the mass ratio of the dopant element contained in the fourth additive to the primary polycrystalline lithium cobalt oxide is (0.1-0.5):100.

[0009] In an optional embodiment, the third additive is LiBO2 and Li2B4O7, and the mass ratio of LiBO2 to Li2B4O7 is 1:(0.5-1.5); at least B, Ti and Zr are introduced through the third and fourth additives; And / or, during the preparation of grain boundary optimized lithium cobalt oxide primary product, the sintering temperature is controlled at 900℃-1050℃ and the sintering time is 8h-12h; And / or, the process of preparing grain boundary optimized lithium cobalt oxide primary product also includes: coarse crushing and fine crushing after sintering, so that the particle size of the obtained grain boundary optimized lithium cobalt oxide primary product meets the following requirements: 15μm≤Dv50≤20μm.

[0010] In an optional embodiment, the mass ratio of the dopant element contained in the first additive to the large-particle cobalt tetroxide precursor is (0.3-3.5):100; And / or, the first lithium salt is selected from at least one of lithium carbonate and lithium hydroxide; And / or, when preparing primary polycrystalline lithium cobalt oxide, the molar ratio of lithium to cobalt is (1.07-1.09):1.

[0011] In an optional embodiment, when preparing polycrystalline lithium cobalt oxide primary product, the sintering temperature is controlled at 850℃-1000℃ and the sintering time is 7h-11h. And / or, the process of preparing primary polycrystalline lithium cobalt oxide also includes: coarse crushing and fine crushing after sintering, so that the particle size of the obtained primary polycrystalline lithium cobalt oxide meets the following requirements: 15μm≤Dv50≤25μm.

[0012] In an optional embodiment, the mass ratio of the dopant element contained in the second additive to the small-particle cobalt tetroxide precursor is (0.3-3.5):100; And / or, the second lithium salt is selected from at least one of lithium carbonate and lithium hydroxide; And / or, when preparing single-crystal lithium cobalt oxide primary product, the molar ratio of lithium to cobalt is (1.05-1.07):1.

[0013] In an optional embodiment, when preparing a single-crystal lithium cobalt oxide primary product, the sintering temperature is controlled at 1000℃-1050℃ and the sintering time is 8h-12h. And / or, the process of preparing single-crystal lithium cobalt oxide primary product also includes: coarse crushing and fine crushing after sintering, so that the particle size of the obtained single-crystal lithium cobalt oxide primary product meets the following requirements: 3.5μm≤Dv50≤8.5μm.

[0014] In an optional embodiment, a primary product of grain boundary optimized lithium cobalt oxide, a primary product of monocrystalline lithium cobalt oxide, and a fifth additive are mixed and sintered, with the sintering temperature controlled at 900℃-1000℃ and the sintering time at 10h-12h. Preferably, the mass percentage of grain boundary optimized lithium cobalt oxide primary product and monocrystalline lithium cobalt oxide primary product is 20%-80% in the total amount. Preferably, the fifth additive is selected from at least one of Co(OH)2, Li2CO3, LiBO2, Li3BO3, LiF, La2O3, Y2O3, Al2O3, TiO2, and ZrO2; Preferably, the mass ratio of the doping element contained in the fifth additive to the total amount of the primary product of grain boundary optimized lithium cobalt oxide and the primary product of monocrystalline lithium cobalt oxide is (0.5-3.5):100; Preferably, after the primary product of grain boundary optimized lithium cobalt oxide, the primary product of single crystal lithium cobalt oxide and the fifth additive are mixed and sintered, mechanical crushing is performed to control the particle size of the finished product to meet the following requirements: 4μm≤Dv50≤20μm.

[0015] In a second aspect, the present invention provides a lithium cobalt oxide cathode material, which is prepared by any of the preparation methods described in the foregoing embodiments; Preferably, the lithium cobalt oxide cathode material simultaneously satisfies the following conditions: a compaction density ≥ 4.0 g / cm³ under a pressure of 180 MPa. 3 Capacity retention rate ≥90% after the first cycle at 5C / 0.1C; Capacity retention rate ≥85% after 100 cycles at 5C 25℃; Capacity retention rate ≥80% after 500 cycles at 1C 45℃.

[0016] Thirdly, the present invention provides a lithium battery comprising the lithium cobalt oxide cathode material of the aforementioned embodiments.

[0017] This invention has the following beneficial effects: First, polycrystalline lithium cobalt oxide primary products and monocrystalline lithium cobalt oxide primary products are prepared. Doping elements from the first and second additives are introduced into the polycrystalline and monocrystalline lithium cobalt oxide primary products, respectively. Bulk doping suppresses phase transitions, improves cycle life, and enhances lithium-ion diffusion rate, thereby improving rate performance. The polycrystalline lithium cobalt oxide primary product is then mixed with the third and fourth additives and sintered. A sintering aid (the third additive contains doping element M1) and a high-valence transition metal compound (the fourth additive contains doping element M2) are used to generate a high-melting-point Li-Co-M1-M2 phase at the grain boundaries, increasing the grain boundary binding energy and thus improving the compressive strength of the polycrystalline material. After grading the grain boundary-optimized lithium cobalt oxide primary product and the monocrystalline lithium cobalt oxide primary product, a high-pump-density lithium cobalt oxide cathode material can be obtained. This cathode material can simultaneously achieve good rate performance and cycle performance to meet market demands. Attached Figure Description

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 The image shows a scanning electron microscope (SEM) image of the optimized large grain boundary LiCoO2 primary product in step (3) of Example 1; (a) and (b) represent different magnification ratios. Figure 2 Scanning electron microscope (SEM) images of the graded LiCoO2 product prepared for Comparative Example 1; (a) and (b) represent different magnification ratios; Figure 3 The XRD pattern of the product prepared in Example 1 and the corresponding XRD standard card for LiCoO2 are shown. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0021] Addressing the core challenge of balancing kinetic performance and compaction density in high-voltage, high-rate applications of lithium cobalt oxide, this invention focuses on synergistically optimizing the design of large particle morphology (particle size distribution and surface structure) with the maintenance of electrochemical activity. Through innovative selection of lithium cobalt oxide sintering aids, sintering processes, and surface modification techniques, the rate performance and high-temperature cycling stability are significantly improved while maintaining high compaction density. This makes the material suitable for high-end consumer electronics, drones, power tools, and other lithium-ion battery applications requiring rapid charge and discharge.

[0022] This invention provides a method for preparing lithium cobalt oxide cathode material. By controlling morphology and optimizing structure, a high-pressure, high-power lithium cobalt oxide cathode material is prepared. The steps are as follows: S1. Preparation of primary polycrystalline lithium cobalt oxide Large-particle cobalt tetroxide precursor, first lithium salt, and first additive are mixed uniformly, followed by high-temperature sintering to prepare primary polycrystalline lithium cobalt oxide. The primary polycrystalline lithium cobalt oxide consists of large polycrystalline particles (small primary particles and large secondary particles). The small primary particles shorten the lithium-ion diffusion path, improving the material's high-rate charge-discharge performance, while the large secondary particles significantly reduce electrode porosity and increase material compaction density.

[0023] It should be noted that the addition of sintering aids in the preparation of lithium cobalt oxide from cobalt tetroxide can act as a flux, which is beneficial for eliminating grain boundaries and improving the degree of single crystallization of the material. The purpose of this embodiment of the invention is to strengthen the grain boundaries of polycrystalline particles, so it is necessary to first synthesize large polycrystalline particles and then add sintering aids in subsequent steps to strengthen the grain boundaries in situ.

[0024] The particle size of the large-particle cobalt tetroxide precursor is 13.5 μm ≤ Dv50 ≤ 18.5 μm, and the particle size Dv50 of the large-particle cobalt tetroxide precursor can be 13.5 μm, 14.0 μm, 15.0 μm, 16.0 μm, 17.0 μm, 18.0 μm, 18.5 μm, etc. If the particle size is too large or too small, it will be detrimental to the rate performance and cycle stability of the material. Specifically, the embodiments of this invention use polycrystalline large particles with reinforced grain boundaries. The particle size mainly affects the final compaction density of the finished product. If the particle size is too large, it will affect the material's processing performance and rate performance; if the particle size is too small, the compaction density will not meet the requirements.

[0025] In some embodiments, the dopant element contained in the first additive is selected from at least one of Al, Mg, Ti, Zr, La, Y, W, and B, and the dopant element contained in the first additive can be any one or more of the above. All of the above dopant elements are suitable for doping primary polycrystalline lithium cobalt oxide, which is beneficial for improving the electrochemical performance of the material. The mass ratio of the dopant element contained in the first additive to the large-particle cobalt tetroxide precursor is (0.3-3.5):100, such as 0.3:100, 0.5:100, 1.0:100, 1.5:100, 2.0:100, 2.5:100, 3.0:100, 3.5:100, etc.

[0026] Specifically, the large-particle cobalt tetroxide precursor is commercially available cobalt tetroxide, as long as the particle size meets the requirements, and the aluminum content in the cobalt tetroxide can be 0.4%-1.4%.

[0027] Furthermore, the first lithium salt is selected from at least one of lithium carbonate and lithium hydroxide, and the first lithium salt can be any one or more of the above. When preparing polycrystalline lithium cobalt oxide primary product, the molar ratio of lithium element to cobalt element is (1.07-1.09):1, such as 1.07:1, 1.08:1, 1.09:1, etc. This molar ratio can be adjusted synchronously with the kiln sintering conditions to ensure that the volatilized lithium can be discharged in time; the residual lithium left on the surface of the material after sintering will be eliminated in the coating stage of step S4.

[0028] Furthermore, in the preparation of polycrystalline lithium cobalt oxide primary products, sintering can be carried out under high temperature air, with the sintering temperature controlled at 850℃-1000℃, such as 850℃, 900℃, 950℃, 1000℃, etc., and the sintering time at 7h-11h, such as 7h, 8h, 9h, 10h, 11h, etc.

[0029] In some embodiments, coarse and fine crushing are performed after sintering to obtain a primary polycrystalline lithium cobalt oxide product with a particle size that satisfies the following condition: 15μm ≤ Dv50 ≤ 25μm. That is, the particle size Dv50 of the primary polycrystalline lithium cobalt oxide product can be 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, etc. The method of coarse crushing is not limited; for example, a roller mill can be used. The method of fine crushing is also not limited; for example, an air jet mill can be used.

[0030] S2, Preparation of single-crystal lithium cobalt oxide primary product A primary monocrystalline lithium cobalt oxide product is prepared by uniformly mixing a small-particle cobalt tetroxide precursor, a second lithium salt, and a second additive, followed by high-temperature sintering. The particle size of the small-particle cobalt tetroxide precursor is 1.5 μm ≤ Dv50 ≤ 6.5 μm, and the particle size Dv50 can be 1.5 μm, 2.0 μm, 3.0 μm, 4.0 μm, 5.0 μm, 6.0 μm, or 6.5 μm. If the particle size is too small, the compaction density will be low; if the particle size is too large, the rate performance will decrease.

[0031] In some embodiments, the dopant element contained in the second additive is selected from at least one of Al, Mg, Ti, Zr, La, Y, W, and B, and the dopant element contained in the second additive can be any one or more of the above. All of the above dopant elements are suitable for doping single-crystal lithium cobalt oxide primary products, which is beneficial for improving the electrochemical performance of the material. The mass ratio of the dopant element contained in the second additive to the small-particle cobalt tetroxide precursor is (0.3-3.5):100, such as 0.3:100, 0.5:100, 1.0:100, 1.5:100, 2.0:100, 2.5:100, 3.0:100, 3.5:100, etc.

[0032] Specifically, the small-particle cobalt tetroxide precursor is commercially available cobalt tetroxide, as long as the particle size meets the requirements, and the aluminum content in the cobalt tetroxide can be 0.4%-1.4%.

[0033] In some embodiments, the second lithium salt is selected from at least one of lithium carbonate and lithium hydroxide, and the second lithium salt can be any one or more of the above. When preparing single-crystal lithium cobalt oxide primary product, the molar ratio of lithium to cobalt is (1.05-1.07):1, such as 1.05:1, 1.06:1, 1.07:1, etc., with lithium in slight excess, to allow the cobalt tetroxide precursor to react fully.

[0034] Furthermore, in the preparation of monocrystalline lithium cobalt oxide primary products, sintering can be carried out in high-temperature air, with the sintering temperature controlled at 1000℃-1050℃, such as 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, 1050℃, etc., and the sintering time at 8h-12h, such as 8h, 9h, 10h, 11h, 12h, etc. Compared with the higher sintering temperature in the preparation of polycrystalline lithium cobalt oxide primary products, the sintering temperature in step S1 is lower to first synthesize polycrystalline large particles. In step S2, the lithium content in the material is significantly reduced compared to step S1. Increasing the temperature can be done below the temperature at which grain boundaries fuse, thereby forming optimized grain boundary compounds at the grain boundaries.

[0035] In some embodiments, coarse and fine crushing are performed after sintering to obtain a primary monocrystalline lithium cobalt oxide product with a particle size satisfying: 3.5μm≤Dv50≤8.5μm, that is, the particle size Dv50 of the primary monocrystalline lithium cobalt oxide product can be 3.5μm, 4.0μm, 5.0μm, 6.0μm, 7.0μm, 8.0μm, 8.5μm, etc. The method of coarse crushing is not limited, such as using a roller mill; the method of fine crushing is also not limited, such as using an air jet mill.

[0036] S3, Preparation of grain boundary optimized lithium cobalt oxide primary product Polycrystalline lithium cobalt oxide primary product, third additive, and fourth additive are mixed uniformly and then sintered at high temperature to prepare grain boundary optimized lithium cobalt oxide primary product. The dopant element in the third additive is selected from at least one of Li, B, Ca, Mg, Cr, Al, La, Y, Mn, Si, and V, and can be any one or more of these dopant elements. The dopant element in the fourth additive is selected from at least one of La, Y, Ti, Zr, W, and Nb, and can be any one or more of these dopant elements. By combining a sintering aid (third additive containing dopant element M1) and a high-valence transition metal compound (fourth additive containing dopant element M2) with the polycrystalline lithium cobalt oxide primary product, a high-melting-point Li-Co-M1-M2 phase is generated at the grain boundaries, increasing the grain boundary bonding energy and thus improving the compressive strength of the polycrystalline material.

[0037] In a preferred embodiment, the third additive is selected from at least one of Li₂CO₃, LiBO₂, Li₃BO₃, Li₂B₄O₇, CaO, MgO, Cr₂O₃, Al₂O₃, La₂O₃, Y₂O₃, MnO₂, SiO₂, and V₂O₅. The third additive can be any one or more of these. The mass ratio of the dopant element in the third additive to the primary polycrystalline lithium cobalt oxide is (0.1-0.5):100, such as 0.1:100, 0.2:100, 0.3:100, 0.4:100, 0.5:100, etc. By optimizing the raw materials and dosage of the third additive, the formation of a high-melting-point Li-Co-M₁-M₂ phase at the grain boundaries can be promoted, thereby increasing the grain boundary bonding energy and thus improving the compressive strength of the polycrystalline material.

[0038] In a preferred embodiment, the fourth additive is selected from at least one of La2O3, Y2O3, TiO2, ZrO2, W2O5, and Nb2O5, and can be any one or more of the above. The mass ratio of the dopant element in the fourth additive to the primary polycrystalline lithium cobalt oxide is (0.1-0.5):100, such as 0.1:100, 0.2:100, 0.3:100, 0.4:100, 0.5:100, etc. Optimizing the raw materials and dosage of the fourth additive is beneficial to further improving the compressive strength of the material.

[0039] In a more preferred embodiment, the third additive is LiBO2 and Li2B4O7, and the mass ratio of LiBO2 to Li2B4O7 is 1:(0.5-1.5), such as 1:0.5, 1:0.8, 1:1.0, 1:1.2, 1:1.5, etc. At least B, Ti, and Zr are introduced through the third and fourth additives; that is, the doping elements in the fourth additive contain at least Ti and Zr. Using in-situ sintering aids (such as LiBO2 and Li2B4O7), combined with high-valence transition metals such as Ti and Zr, a high-melting-point Li-Co-B-Ti-Zr-O phase is formed at the grain boundaries. The related compounds readily aggregate at the grain boundaries and react. The formed LiCoBO3 phase inhibits void nucleation and enhances grain boundary bonding energy. Furthermore, the added Ti and Zr-related compounds produce a "pinning effect" at the grain boundaries, synergistically enhancing the grain boundary bonding force with LiCoBO3.

[0040] It should be added that, under high-compaction processes (roller pressure > 5t / cm), traditional polycrystalline materials are prone to particle breakage, resulting in fine powder and a decrease in compaction density. The embodiments of this invention, through individual grain boundary strengthening of large polycrystalline particles, show that, compared to traditional polycrystalline materials, the grain boundary strengthening increases the compressive strength of the particles by more than 2 times and the Young's modulus by 4 times.

[0041] Furthermore, during the preparation of the primary product of grain boundary-optimized lithium cobalt oxide, the sintering temperature is controlled at 900℃-1050℃, such as 900℃, 950℃, 1000℃, 1050℃, etc.; the sintering time is 8h-12h, such as 8h, 9h, 10h, 12h, etc. By adjusting the sintering temperature and time, the grain boundary strengthening effect is improved.

[0042] In some embodiments, coarse and fine crushing are performed after sintering to ensure that the particle size of the resulting grain boundary optimized lithium cobalt oxide primary product satisfies the following condition: 15μm≤Dv50≤20μm, that is, the particle size Dv50 of the grain boundary optimized lithium cobalt oxide primary product can be 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, etc. The method of coarse crushing is not limited, such as using a roller mill; the method of fine crushing is also not limited, such as using an air jet mill.

[0043] S4, graded Grain boundary optimized lithium cobalt oxide primary product and monocrystalline lithium cobalt oxide primary product were mixed uniformly and then sintered. Gradation of the grain boundary optimized lithium cobalt oxide primary product and monocrystalline lithium cobalt oxide primary product combined the kinetic advantages of polycrystalline structures with the mechanical strength of near-monocrystalline structures, resulting in high-power, high-energy-density lithium cobalt oxide battery materials.

[0044] In some embodiments, the mass percentage of grain boundary optimized lithium cobalt oxide primary product and monocrystalline lithium cobalt oxide primary product is 20%-80%, such as 20%, 30%, 40%, 50%, 60%, 70%, 80%, etc. That is, the mass percentage of monocrystalline lithium cobalt oxide primary product is also 20%-80%.

[0045] In some embodiments, a fifth additive is introduced during the gradation process to uniformly mix the grain boundary optimized lithium cobalt oxide primary product, the monocrystalline lithium cobalt oxide primary product, and the fifth additive, followed by high-temperature sintering. The fifth additive is selected from at least one of Co(OH)2, Li2CO3, LiBO2, Li3BO3, LiF, La2O3, Y2O3, Al2O3, TiO2, and ZrO2, and can be any one or more of the above. The mass ratio of the doping element (at least one of Co, Li, B, F, La, Y, Al, Ti, Zr) contained in the fifth additive to the total amount of the grain boundary optimized lithium cobalt oxide primary product and the monocrystalline lithium cobalt oxide primary product is controlled to be (0.5-3.5):100, such as 0.5:100, 1.0:100, 2.0:100, 3.0:100, 3.5:100, etc.

[0046] Furthermore, high-temperature sintering can be carried out in a high-temperature air atmosphere, with the sintering temperature controlled at 900℃-1000℃, such as 900℃, 950℃, or 1000℃; and the sintering time at 10h-12h, such as 10h, 11h, or 12h. By adjusting the sintering temperature and time, a uniform lithium cobalt oxide cathode material product can be obtained.

[0047] In some embodiments, mechanical crushing is performed after sintering to obtain graded finished products, and the particle size of the finished products is controlled to meet the following requirements: 4μm≤Dv50≤20μm. The particle size Dv50 of the finished products can be 4μm, 10μm, 15μm, 20μm, etc.

[0048] This invention provides a lithium cobalt oxide cathode material prepared by the method described in this invention. This lithium cobalt oxide cathode material exhibits high compaction density, as well as excellent rate performance and cycle performance, meeting market demands. Furthermore, the lithium cobalt oxide cathode material also satisfies the following requirement: compaction density ≥ 4.0 g / cm³ at a pressure of 180 MPa. 3 Capacity retention rate ≥90% after the first cycle at 5C / 0.1C; Capacity retention rate ≥85% after 100 cycles at 5C 25℃; Capacity retention rate ≥80% after 500 cycles at 1C 45℃.

[0049] This invention also provides a positive electrode sheet, including the lithium cobalt oxide positive electrode material provided in this invention, and may further include a positive electrode current collector, with a positive electrode active coating formed on at least one surface of the positive electrode current collector, wherein the lithium cobalt oxide positive electrode material exists as a positive electrode active material in the positive electrode active coating.

[0050] This invention provides a lithium battery, including the above-mentioned positive electrode sheet, and may also include a negative electrode sheet, electrolyte, separator, etc. to form a complete battery structure with good cycle performance.

[0051] Specifically, the types of negative electrode, electrolyte, and separator are not limited and can be any of the commonly used materials for lithium cobalt oxide batteries. During the charging and discharging process of a lithium battery, active ions are inserted and removed back and forth between the positive and negative electrode, while the electrolyte plays the role of conducting ions between the positive and negative electrode.

[0052] In other embodiments, the battery may not be in the form of a lithium battery, but may be in the form of a battery module, battery pack, or the like.

[0053] This invention provides a device including the aforementioned lithium battery. The lithium battery can serve as a power source for the device or as an energy storage unit. This device can be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0054] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0055] Example 1 This embodiment provides a method for preparing lithium cobalt oxide cathode material, including the following steps: (1) A large-particle cobalt tetroxide precursor with a Dv50 of 15.5 μm, lithium carbonate, and a first additive (in molar ratio, zirconium dioxide: magnesium oxide: yttrium oxide = 1:2:2) were mixed evenly. The molar ratio of lithium to cobalt was 1.08:1, and the mass ratio of the dopant element in the first additive to the large-particle cobalt tetroxide precursor was 1.5:100. The mixture was sintered in a high-temperature box furnace at 930℃ in an air atmosphere for 10 h. After cooling, it was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain a primary polycrystalline lithium cobalt oxide product with a Dv50 of 18.5 μm.

[0056] (2) A small-particle cobalt tetroxide precursor with a Dv50 of 3.5 μm, lithium carbonate, and a second additive (in molar ratio, zirconium dioxide: titanium dioxide: magnesium oxide: yttrium oxide = 1:2:3:2) were mixed evenly. The molar ratio of lithium to cobalt was 1.06:1, and the mass ratio of the dopant element in the second additive to the small-particle cobalt tetroxide precursor was 1.2:100. The mixture was sintered in an air atmosphere at a high temperature of 1000℃ for 10 h. After cooling, it was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain a single-crystal lithium cobalt oxide product with a Dv50 of 5.5 μm.

[0057] (3) The polycrystalline lithium cobalt oxide primary product from step (1) is mixed evenly with the third additive (in molar ratio, lithium metaborate: lithium tetraborate = 1:1) and the fourth additive (in molar ratio, titanium dioxide: zirconium oxide = 1:1). The mass ratio of the dopant element in the third additive to the polycrystalline lithium cobalt oxide primary product is 0.3:100, and the mass ratio of the dopant element in the fourth additive to the polycrystalline lithium cobalt oxide primary product is 0.5:100. The mixture is sintered in a high-temperature box furnace at 980℃ in an air atmosphere for 10 hours. After cooling, it is coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain a grain boundary optimized lithium cobalt oxide primary product with a Dv50 of 18.8μm.

[0058] (4) The primary product of grain boundary optimized lithium cobalt oxide in step (3) and the primary product of single crystal lithium cobalt oxide in step (2) are graded at a mass ratio of 4:6, and mixed with the fifth additive (in molar ratio, cobalt hydroxide: (alumina + lanthanum oxide + yttrium oxide + zirconium dioxide + titanium dioxide + lithium carbonate) = 5:1, and the molar ratio of alumina, lanthanum oxide, yttrium oxide, zirconium dioxide, titanium dioxide and lithium carbonate is 1:2:1:2:1:5). The mass ratio of the doping element contained in the fifth additive to the graded sample is 2.3:100. The mixture is sintered in a high-temperature box furnace at 910℃ in an air atmosphere for 10h. After cooling, it is mechanically crushed to obtain graded finished product LiCoO2 with a Dv50 of 7.6μm.

[0059] Example 2 This embodiment provides a method for preparing lithium cobalt oxide cathode material. The difference between the preparation method and that in embodiment 1 is that the sintering temperature of the box furnace in step (1) is 880℃.

[0060] Example 3 This embodiment provides a method for preparing lithium cobalt oxide cathode material. The difference between this method and that in Example 1 is that the sintering temperature in step (1) is 980°C using a box furnace.

[0061] Example 4 This embodiment provides a method for preparing lithium cobalt oxide cathode material. The difference between the preparation method and that in embodiment 1 is that the third additive in step (3) is (calcium oxide: silicon dioxide: aluminum oxide = 1:1:1 in molar ratio).

[0062] Example 5 This embodiment provides a method for preparing lithium cobalt oxide cathode material. The difference between the preparation method and that in Example 1 is that the third additive in step (3) is lanthanum oxide: magnesium oxide = 1:1 in molar ratio.

[0063] Example 6 This embodiment provides a method for preparing lithium cobalt oxide cathode material. The difference between the preparation method and that in Example 1 is that the fourth additive in step (3) is lanthanum oxide: yttrium oxide = 1:1 in molar ratio.

[0064] Example 7 This embodiment provides a method for preparing lithium cobalt oxide cathode material. The difference between the preparation method and that in Example 1 is that the fourth additive in step (3) is tungsten oxide (W2O5): niobium oxide (Nb2O5) = 1:1 in molar ratio.

[0065] Example 8 This embodiment provides a method for preparing lithium cobalt oxide cathode material. The difference between the preparation method and that in embodiment 1 is that the sintering temperature of the box furnace in step (3) is 930°C.

[0066] Example 9 This embodiment provides a method for preparing lithium cobalt oxide cathode material. The difference between the preparation method and that in embodiment 1 is that the sintering temperature of the box furnace in step (3) is 1030℃.

[0067] Example 10 This embodiment provides a method for preparing lithium cobalt oxide cathode material. The difference between the preparation method and that in Example 1 is that the particle size distribution ratio in step (4) is 3:7.

[0068] Example 11 This embodiment provides a method for preparing lithium cobalt oxide cathode material. The difference between the preparation method and that in embodiment 1 is that the particle size distribution ratio in step (4) is 5:5.

[0069] Example 12 This embodiment provides a method for preparing lithium cobalt oxide cathode material, including the following steps: (1) A large-particle cobalt tetroxide precursor with a Dv50 of 13.5 μm, lithium carbonate and a first additive (in molar ratio, zirconium dioxide: magnesium oxide: yttrium oxide = 1:2:2) were mixed evenly. The molar ratio of lithium to cobalt was 1.07:1. The mass ratio of the dopant element in the first additive to the large-particle cobalt tetroxide precursor was 0.3:100. The mixture was sintered in a high-temperature box furnace at 900℃ in an air atmosphere for 7 h. After cooling, it was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain a primary polycrystalline lithium cobalt oxide product with a Dv50 of 16.5 μm.

[0070] (2) A small-particle cobalt tetroxide precursor with a Dv50 of 1.5 μm, lithium carbonate, and a second additive (in molar ratio, zirconium dioxide: titanium dioxide: magnesium oxide: yttrium oxide = 1:2:3:2) were mixed evenly. The molar ratio of lithium to cobalt was 1.05:1, and the mass ratio of the dopant element in the second additive to the small-particle cobalt tetroxide precursor was 0.3:100. The mixture was sintered in an air atmosphere at a high temperature of 1000℃ for 8 hours. After cooling, it was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain a single-crystal lithium cobalt oxide product with a Dv50 of 3.5 μm.

[0071] (3) The polycrystalline lithium cobalt oxide primary product from step (1) is mixed evenly with the third additive (in molar ratio, lithium metaborate: lithium tetraborate = 1:1) and the fourth additive (in molar ratio, titanium dioxide: zirconium oxide = 1:1). The mass ratio of the dopant element in the third additive to the polycrystalline lithium cobalt oxide primary product is 0.1:100, and the mass ratio of the dopant element in the fourth additive to the polycrystalline lithium cobalt oxide primary product is 0.1:100. The mixture is sintered in a high-temperature box furnace at 900℃ in an air atmosphere for 8 hours. After cooling, it is coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain a grain boundary optimized lithium cobalt oxide primary product with a Dv50 of 18.8μm.

[0072] (4) The primary product of grain boundary optimized lithium cobalt oxide in step (3) and the primary product of single crystal lithium cobalt oxide in step (2) are graded at a mass ratio of 2:8 and mixed evenly with the fifth additive (same as in Example 1). The mass ratio of the doping element contained in the fifth additive to the graded sample is 0.5:100. The mixture is sintered in an air atmosphere in a high-temperature box furnace at 900℃ for 10 hours. After cooling, it is mechanically crushed to obtain graded finished product LiCoO2 with a Dv50 of 4.5μm.

[0073] Example 13 This embodiment provides a method for preparing lithium cobalt oxide cathode material, including the following steps: (1) A large-particle cobalt tetroxide precursor with a Dv50 of 18.5 μm, lithium carbonate, and a first additive (in molar ratio, zirconium dioxide: magnesium oxide: yttrium oxide = 1:2:2) were mixed evenly. The molar ratio of lithium to cobalt was 1.09:1, and the mass ratio of the dopant element in the first additive to the large-particle cobalt tetroxide precursor was 3.5:100. The mixture was sintered in an air atmosphere at a high temperature of 1000℃ for 11 h. After cooling, it was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain a primary polycrystalline lithium cobalt oxide product with a Dv50 of 21.5 μm.

[0074] (2) A small-particle cobalt tetroxide precursor with a Dv50 of 6.5 μm, lithium carbonate, and a second additive (in molar ratio, zirconium dioxide: titanium dioxide: magnesium oxide: yttrium oxide = 1:2:3:2) were mixed evenly. The molar ratio of lithium to cobalt was 1.07:1, and the mass ratio of the dopant element in the second additive to the small-particle cobalt tetroxide precursor was 3.5:100. The mixture was sintered in an air atmosphere at a high temperature of 1050℃ for 12 h. After cooling, it was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain a single-crystal lithium cobalt oxide primary product with a Dv50 of 8.5 μm.

[0075] (3) The polycrystalline lithium cobalt oxide primary product from step (1) is mixed evenly with the third additive (in molar ratio, lithium metaborate: lithium tetraborate = 1:1) and the fourth additive (in molar ratio, titanium dioxide: zirconium oxide = 1:1). The mass ratio of the dopant element in the third additive to the polycrystalline lithium cobalt oxide primary product is 0.5:100, and the mass ratio of the dopant element in the fourth additive to the polycrystalline lithium cobalt oxide primary product is 0.5:100. The mixture is sintered in an air atmosphere at a high temperature of 1050℃ for 11 hours. After cooling, it is coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain a grain boundary optimized lithium cobalt oxide primary product with a Dv50 of 18.8μm.

[0076] (4) The primary product of grain boundary optimized lithium cobalt oxide in step (3) and the primary product of single crystal lithium cobalt oxide in step (2) are graded at a mass ratio of 8:2 and mixed evenly with the fifth additive (same as in Example 1). The mass ratio of the doping element contained in the fifth additive to the graded sample is 3.5:100. The mixture is sintered in an air atmosphere in a high-temperature box furnace at 1000℃ for 12 hours. After cooling, it is mechanically crushed to obtain graded finished product LiCoO2 with a Dv50 of 19.5μm.

[0077] Comparative Example 1 This comparative example provides a method for preparing a lithium cobalt oxide cathode material, including the following steps: (1) A large-particle cobalt tetroxide precursor with a Dv50 of 15.5 μm, lithium carbonate and the first additive (in molar ratio, zirconium dioxide: magnesium oxide: yttrium oxide = 1:2:2) were mixed evenly. The molar ratio of lithium to cobalt was 1.08:1. The mass ratio of the doped elements in the first additive to the large-particle cobalt tetroxide precursor was 1.5:100. The mixture was sintered in an air atmosphere at a high temperature of 1050℃ for 10 h. After cooling, it was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain a single-crystal large-particle LiCoO2 primary product with a Dv50 of 19.5 μm. (2) A small-particle cobalt tetroxide precursor with a Dv50 of 3.5 μm, lithium carbonate, and a second additive (in molar ratio, zirconium dioxide: titanium dioxide: magnesium oxide: yttrium oxide = 1:2:3:2) were mixed evenly. The molar ratio of lithium to cobalt was 1.06:1, and the mass ratio of the dopant element in the second additive to the small-particle cobalt tetroxide was 1.2:100. The mixture was sintered in an air atmosphere at a high temperature of 1000℃ for 10 h. After cooling, it was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain a primary product of single-crystal lithium cobalt oxide with a Dv50 of 5.5 μm.

[0078] (3) The primary single-crystal large-particle LiCoO2 product from step (1) is mixed evenly with the third additive (in molar ratio, lithium metaborate: lithium tetraborate = 1:1) and the fourth additive (in molar ratio, titanium dioxide: zirconium oxide = 1:1). The mass ratio of the doping element in the third additive to the primary single-crystal large-particle LiCoO2 product is 0.3:100, and the mass ratio of the doping element in the fourth additive to the primary single-crystal large-particle LiCoO2 product is 0.5:100. The mixture is sintered in an air atmosphere at a high temperature of 980℃ for 10 hours. After cooling, it is coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain a primary grain boundary optimized lithium cobalt oxide product with a Dv50 of 18.8μm.

[0079] (4) The primary product of grain boundary optimized lithium cobalt oxide in step (3) and the primary product of single crystal lithium cobalt oxide in step (2) are graded at a mass ratio of 4:6, and mixed evenly with the fifth additive (same as in Example 1). The mass ratio of the doping element contained in the fifth additive to the graded sample is 2.3:100. The mixture is sintered in an air atmosphere in a high-temperature box furnace at 910℃ for 10 hours. After cooling, it is crushed by mechanical grinding to obtain graded finished product LiCoO2 with Dv50 of 8.0μm. The difference between Comparative Example 1 and Example 1 is that this sample uses single-crystal large particles for gradation.

[0080] Comparative Example 2 The only difference from Example 1 is that no third additive was used in step (3).

[0081] Comparative Example 3 This comparative example provides a method for preparing a lithium cobalt oxide cathode material, including the following steps: (1) A large-particle cobalt tetroxide precursor with a Dv50 of 15.5 μm, lithium carbonate, and a first additive (in molar ratio, zirconium dioxide: magnesium oxide: yttrium oxide = 1:2:2) and a third additive (in molar ratio, lithium metaborate: lithium tetraborate = 1:1) were mixed evenly. The molar ratio of lithium to cobalt was 1.08. The mass ratio of the dopant element in the first additive to the large-particle cobalt tetroxide precursor was 1.5:100, and the mass ratio of the dopant element in the third additive to the large-particle cobalt tetroxide precursor was 0.3:100. The mixture was sintered in a high-temperature box furnace at 930℃ in an air atmosphere for 10 h. After cooling, it was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain a primary polycrystalline lithium cobalt oxide product with a Dv50 of 18.5 μm.

[0082] (2) A small-particle cobalt tetroxide precursor with a Dv50 of 3.5 μm, lithium carbonate, and a second additive (in molar ratio, zirconium dioxide: titanium dioxide: magnesium oxide: yttrium oxide = 1:2:3:2) were mixed evenly. The molar ratio of lithium to cobalt was 1.06:1, and the mass ratio of the dopant element in the second additive to the small-particle cobalt tetroxide precursor was 1.2:100. The mixture was sintered in an air atmosphere at a high temperature of 1000℃ for 10 h. After cooling, it was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain a single-crystal lithium cobalt oxide product with a Dv50 of 5.5 μm.

[0083] (3) The polycrystalline lithium cobalt oxide primary product from step (1) is mixed with the fourth additive (in molar ratio, titanium dioxide:zirconia = 1:1). The mass ratio of the doping element contained in the fourth additive to the polycrystalline lithium cobalt oxide primary product is 0.5:100. The mixture is sintered in an air atmosphere at a high temperature of 980℃ for 10 hours. After cooling, it is coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain a grain boundary optimized lithium cobalt oxide primary product with a Dv50 of 18.8μm.

[0084] (4) The primary product of grain boundary optimized lithium cobalt oxide in step (3) and the primary product of single crystal lithium cobalt oxide in step (2) are graded according to a mass ratio of 4:6, and mixed with the fifth additive (in molar ratio, cobalt hydroxide: (alumina + lanthanum oxide + yttrium oxide + zirconium dioxide + titanium dioxide + lithium carbonate) = 5:1, and the molar ratio of alumina, lanthanum oxide, yttrium oxide, zirconium dioxide, titanium dioxide and lithium carbonate is 1:2:1:2:1:5). The mass ratio of the doping element contained in the fifth additive to the graded sample is 2.3:100. The mixture is sintered in a high-temperature box furnace at 910℃ in an air atmosphere for 10h. After cooling, it is crushed by mechanical grinding to obtain graded finished product LiCoO2 with Dv50 of 7.6μm. The only difference between Comparative Example 3 and Example 1 is that the third additive is used in the cobalt tetroxide sintering lithium cobalt oxide stage.

[0085] Comparative Example 4 The only difference between Comparative Example 4 and Example 1 is that no fourth additive was added in step (3).

[0086] Comparative Example 5 This comparative example provides a method for preparing a lithium cobalt oxide cathode material, including the following steps: (1) A small-particle cobalt tetroxide precursor with a Dv50 of 3.5 μm, lithium carbonate, and a second additive (in molar ratio, zirconium dioxide: titanium dioxide: magnesium oxide: yttrium oxide = 1:2:3:2) were mixed evenly. The molar ratio of lithium to cobalt was 1.06:1, and the mass ratio of the dopant element in the second additive to the small-particle cobalt tetroxide precursor was 1.2:100. The mixture was sintered in an air atmosphere at a high temperature of 1000℃ for 10 h. After cooling, it was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain a single-crystal lithium cobalt oxide product with a Dv50 of 5.5 μm.

[0087] (2) The single-crystal lithium cobalt oxide primary product in step (1) is mixed with the fifth additive (in molar ratio, cobalt hydroxide: (alumina + lanthanum oxide + yttrium oxide + zirconium dioxide + titanium dioxide + lithium carbonate) = 5:1, and the molar ratio of alumina, lanthanum oxide, yttrium oxide, zirconium dioxide, titanium dioxide and lithium carbonate is 1:2:1:2:1:5). The mass ratio of the doping element contained in the fifth additive to the single-crystal lithium cobalt oxide primary product is 2.3:100. The mixture is sintered in a high-temperature box furnace at 910℃ in an air atmosphere for 10h. After cooling, it is mechanically crushed to obtain the finished product LiCoO2 with a Dv50 of 5.8μm. The only difference between Comparative Example 5 and Example 1 is that only single-crystal small particles are used to make the finished lithium cobalt oxide product.

[0088] Comparative Example 6 This comparative example provides a method for preparing a lithium cobalt oxide cathode material, including the following steps: (1) A large-particle cobalt tetroxide precursor with a Dv50 of 15.5 μm, lithium carbonate, and a first additive (in molar ratio, zirconium dioxide: magnesium oxide: yttrium oxide = 1:2:2) were mixed evenly. The molar ratio of lithium to cobalt was 1.08:1, and the mass ratio of the dopant element in the first additive to the large-particle cobalt tetroxide precursor was 1.5:100. The mixture was sintered in a high-temperature box furnace at 930℃ in an air atmosphere for 10 h. After cooling, it was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain a primary polycrystalline lithium cobalt oxide product with a Dv50 of 18.5 μm.

[0089] (2) The polycrystalline lithium cobalt oxide primary product from step (1) is mixed evenly with the third additive (in molar ratio, lithium metaborate: lithium tetraborate = 1:1) and the fourth additive (in molar ratio, titanium dioxide: zirconium oxide = 1:1). The mass ratio of the dopant element in the third additive to the polycrystalline lithium cobalt oxide primary product is 0.3:100, and the mass ratio of the dopant element in the fourth additive to the polycrystalline lithium cobalt oxide primary product is 0.5:100. The mixture is sintered in a high-temperature box furnace at 980℃ in an air atmosphere for 10 hours. After cooling, it is coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain a grain boundary optimized lithium cobalt oxide primary product with a Dv50 of 18.8μm.

[0090] (3) The primary product of grain boundary optimized lithium cobalt oxide in step (2) is mixed evenly with the fifth additive (same as in Example 1). The mass ratio of the doping element contained in the fifth additive to the primary product of grain boundary optimized lithium cobalt oxide is 2.3:100. The mixture is sintered in an air atmosphere at a high temperature of 910℃ for 10 hours. After cooling, it is crushed by mechanical grinding to obtain the finished product LiCoO2 with a Dv50 of 19.1μm. The only difference between Comparative Example 6 and Example 1 is that the lithium cobalt oxide product was made using only large polycrystalline particles with optimized grain boundaries.

[0091] Experimental Example 1 Electron micrograph of the primary product of grain boundary optimized lithium cobalt oxide obtained in step (3) of test example 1, as shown in the figure. Figure 1 As shown. Figure 1 As shown, the primary product of grain boundary optimized lithium cobalt oxide prepared in Example 1 still retains a large number of grain boundaries after sintering in step (3), which ensures the rate performance of the subsequent finished product.

[0092] Scanning electron microscope (SEM) images of the graded LiCoO2 product prepared in Comparative Example 1 are shown below. Figure 2 As shown, the finished sample using single-crystal particle size gradation has virtually no obvious grain boundaries.

[0093] The XRD pattern of the product prepared in Example 1 is shown below. Figure 3 As shown, the XRD test results of the grain boundary optimized lithium cobalt oxide primary product prepared in Example 1 correspond well with the lithium cobalt oxide standard card. At the same time, the peak intensity ratio 003 / 104≈1.4 indicates that the material has a good layered structure and can perform well in electrochemical performance.

[0094] Experimental Example 2 The electrochemical performance of the lithium cobalt oxide cathode materials prepared in the examples and comparative examples was tested, and the results are shown in Table 1. Table 1 includes the initial discharge specific capacity and initial coulombic efficiency of the examples and comparative examples; the cycling performance at 45°C of the examples and comparative examples; the 5C cycling performance at 25°C of the examples and comparative examples; and the compaction density at 180 MPa of the examples and comparative examples.

[0095] Test Method: The working electrode was prepared by coating an aluminum foil with a mixture of active material, conductive carbon, and polyvinylidene fluoride in deionized water at a mass ratio of 95:2:3. The initial discharge specific capacity test used a coin cell half-cell with a lithium electrode as the counter electrode, and the test temperature was 25℃. The 45℃ 1C cycle performance and 25℃ 5C rate discharge tests used coin cells full-cells with a graphite electrode as the counter electrode (active material: conductive carbon: binder = 95:2:3). The electrolyte was 1 mol / L LiPF6 dissolved in an EC / DEC (volume ratio 1:1) mixed solvent with 3 wt% FEC added. The separator was a PP / PE / PP composite membrane. Coin cell assembly was performed in a glove box with oxygen and water content below 1 ppm. Electrochemical performance tests were conducted on an electrochemical workstation. The test voltage for coin cell half-cells was 2.3-4.55V, and the test voltage for coin cell full-cells was 3.0-4.50V.

[0096] Table 1. Performance test results of lithium cobalt oxide cathode materials prepared in the examples and comparative examples.

[0097] Through Examples 1-3, 8, and 9, higher sintering temperatures reduce grain boundaries, thus lowering the subsequent rate performance of the samples. Lower sintering temperatures increase grain boundaries, thus reducing the cycle performance of the samples. Insufficient grain boundary strength enhancement due to lower temperatures reduces the compressive strength of the samples during rolling, resulting in a decrease in compaction density.

[0098] Through Examples 1, 4, and 5, the formation of a high-melting-point Li-Co-B-Ti-Zr-O phase at the grain boundaries can enhance the grain boundary bonding energy, thereby improving the compressive strength of the polycrystalline material. The CaO+SiO2+Al2O3 sintering aid combination, due to its low ionic conductivity, reduces the rate performance of the samples. The La2O3+MgO sintering aid combination, after solid solution treatment with additives, has a weak strengthening effect on grain boundaries, reducing the cycle performance of the samples.

[0099] Through Examples 1, 6, 7 and Comparative Example 4, it was found that the absence of solid solution elements would reduce grain boundary strength. The solid solution coating of tetravalent element oxides was better than that of trivalent element oxides in strengthening grain boundaries and improving rate performance. The examples also showed that the solid solution coating of pentavalent element oxides was not effective. Therefore, selecting more suitable sintering aids is the future improvement point. Through Examples 10-11 and Comparative Examples 5-6, single-crystal small particles have excellent rate performance due to their small size and shortened lithium-ion diffusion path, but their compaction density is significantly lower. Although optimized grain boundary large particles have higher compaction density through grain boundary strengthening, their rate performance is still inferior to that of single-crystal small particles. By adjusting the ratio of the two particle sizes, a finished product with better performance can be obtained. Further comparison of Example 1 and Comparative Example 1 shows that, due to the larger primary particle size of the single crystal large particle, the lithium ion diffusion path is longer, resulting in poorer rate performance.

[0100] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium cobalt oxide cathode material, characterized in that, include: Large-particle cobalt tetroxide precursor, first lithium salt and first additive are mixed and sintered to obtain polycrystalline lithium cobalt oxide primary product. Small-particle cobalt tetroxide precursor, second lithium salt and second additive are mixed and sintered to obtain single-crystal lithium cobalt oxide primary product. The primary polycrystalline lithium cobalt oxide, the third additive, and the fourth additive are mixed and sintered to obtain a primary grain boundary optimized lithium cobalt oxide. The grain boundary optimized lithium cobalt oxide primary product and the monocrystalline lithium cobalt oxide primary product are mixed and sintered. The particle size of the large-particle cobalt tetroxide precursor is 13.5 μm ≤ Dv50 ≤ 18.5 μm, and the particle size of the small-particle cobalt tetroxide precursor is 1.5 μm ≤ Dv50 ≤ 6.5 μm. The doping element contained in the first additive is selected from at least one of Al, Mg, Ti, Zr, La, Y, W and B; The doping element contained in the second additive is selected from at least one of Al, Mg, Ti, Zr, La, Y, W and B; The doping element contained in the third additive is selected from at least one of Li, B, Ca, Mg, Cr, Al, La, Y, Mn, Si and V; The dopant element contained in the fourth additive is selected from at least one of La, Y, Ti, Zr, W and Nb.

2. The preparation method according to claim 1, characterized in that, The third additive is selected from at least one of Li2CO3, LiBO2, Li3BO3, Li2B4O7, CaO, MgO, Cr2O3, Al2O3, La2O3, Y2O3, MnO2, SiO2 and V2O5; And / or, the mass ratio of the dopant element contained in the third additive to the primary polycrystalline lithium cobalt oxide is (0.1-0.5):100; And / or, the fourth additive is selected from at least one of La2O3, Y2O3, TiO2, ZrO2, W2O5 and Nb2O5; And / or, the mass ratio of the dopant element contained in the fourth additive to the primary polycrystalline lithium cobalt oxide is (0.1-0.5):

100.

3. The preparation method according to claim 2, characterized in that The third additive is LiBO2 and Li2B4O7, and the mass ratio of LiBO2 to Li2B4O7 is 1:(0.5-1.5); at least B, Ti and Zr are introduced through the third additive and the fourth additive; And / or, during the preparation of the grain boundary optimized lithium cobalt oxide primary product, the sintering temperature is controlled at 900℃-1050℃ and the sintering time is 8h-12h; And / or, the process of preparing the grain boundary optimized lithium cobalt oxide primary product further includes: coarse crushing and fine crushing after sintering, so that the particle size of the obtained grain boundary optimized lithium cobalt oxide primary product meets the following requirements: 15μm≤Dv50≤20μm.

4. The preparation method according to claim 1, characterized in that, The mass ratio of the dopant element in the first additive to the large-particle cobalt tetroxide precursor is (0.3-3.5):100; And / or, the first lithium salt is selected from at least one of lithium carbonate and lithium hydroxide; And / or, when preparing the primary polycrystalline lithium cobalt oxide, the molar ratio of lithium to cobalt is (1.07-1.09):

1.

5. The preparation method according to claim 1 or 4, characterized in that, When preparing the polycrystalline lithium cobalt oxide primary product, the sintering temperature is controlled at 850℃-1000℃ and the sintering time is 7h-11h. And / or, the process of preparing the primary polycrystalline lithium cobalt oxide product further includes: coarse crushing and fine crushing after sintering, so that the particle size of the obtained primary polycrystalline lithium cobalt oxide product satisfies: 15μm≤Dv50≤25μm.

6. The preparation method according to claim 1, characterized in that, The mass ratio of the dopant element in the second additive to the small-particle cobalt tetroxide precursor is (0.3-3.5):100; And / or, the second lithium salt is selected from at least one of lithium carbonate and lithium hydroxide; And / or, when preparing the single-crystal lithium cobalt oxide primary product, the molar ratio of lithium to cobalt is (1.05-1.07):

1.

7. The preparation method according to claim 1 or 6, characterized in that, When preparing the single-crystal lithium cobalt oxide primary product, the sintering temperature is controlled at 1000℃-1050℃ and the sintering time is 8h-12h. And / or, the process of preparing the single-crystal lithium cobalt oxide primary product further includes: coarse crushing and fine crushing after sintering, so that the particle size of the obtained single-crystal lithium cobalt oxide primary product satisfies: 3.5μm≤Dv50≤8.5μm.

8. The preparation method according to claim 1, characterized in that, The grain boundary optimized lithium cobalt oxide primary product, the single crystal lithium cobalt oxide primary product, and the fifth additive are mixed and sintered, with the sintering temperature controlled at 900℃-1000℃ and the sintering time at 10h-12h. Preferably, the grain boundary optimized lithium cobalt oxide primary product accounts for 20%-80% of the total amount of the grain boundary optimized lithium cobalt oxide primary product and the monocrystalline lithium cobalt oxide primary product; Preferably, the fifth additive is selected from at least one of Co(OH)2, Li2CO3, LiBO2, Li3BO3, LiF, La2O3, Y2O3, Al2O3, TiO2, and ZrO2; Preferably, the mass ratio of the dopant element contained in the fifth additive to the total amount of the grain boundary optimized lithium cobalt oxide primary product and the single crystal lithium cobalt oxide primary product is (0.5-3.5):100; Preferably, after the primary product of grain boundary optimized lithium cobalt oxide, the primary product of single crystal lithium cobalt oxide, and the fifth additive are mixed and sintered, mechanical crushing is performed to control the particle size of the finished product to meet the following requirements: 4μm≤Dv50≤20μm.

9. A lithium cobalt oxide cathode material, characterized in that, Prepared by the preparation method according to any one of claims 1-8; Preferably, the lithium cobalt oxide cathode material simultaneously satisfies the following condition: a compaction density ≥ 4.0 g / cm³ under a pressure of 180 MPa. 3 Capacity retention rate ≥90% after the first cycle at 5C / 0.1C; Capacity retention rate ≥85% after 100 cycles at 5C 25℃; Capacity retention rate ≥80% after 500 cycles at 1C 45℃.

10. A lithium battery, characterized in that, Including the lithium cobalt oxide cathode material as described in claim 9.

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