Coated modified nickel cobalt lithium aluminate positive electrode material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of battery materials, and particularly relates to a coated modified nickel cobalt lithium aluminate positive electrode material as well as a preparation method and application thereof. The lithium nickel cobalt aluminate positive electrode material comprises an inner core and a coating layer coated on the inner core, a is greater than or equal to 1.01 and less than or equal to 1.05, x is greater than or equal to 0.75 and less than or equal to 0.90, y is greater than or equal to 0.05 and less than or equal to 0.20, z is greater than or equal to 0.01 and less than or equal to 0.05, and p is greater than or equal to 0 and less than or equal to 0.05; l comprises one of Mg, Zr, Mo, Ti and Zn; and the tap density of the coated and modified nickel cobalt lithium aluminate positive electrode material is 2.7-3.2 g / cm < 3 >. The coated modified nickel cobalt lithium aluminate positive electrode material provided by the invention has relatively good electronic conductivity and rate capability, and can inhibit lattice collapse caused by phase change under high voltage, reduce intergranular gaps, enhance thermal stability of the material, inhibit capacity fading caused by structure looseness in charge and discharge processes, and prolong the cycle life of a battery.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to a coated modified lithium nickel cobalt aluminum oxide cathode material, its preparation method, and its application. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the demand for high-energy-density cathode materials for lithium-ion batteries is becoming increasingly urgent. High-nickel ternary cathode materials are regarded as the core materials for next-generation power batteries due to their high specific capacity. Among them, commercial NCA materials (lithium nickel cobalt aluminum oxide cathode materials) have good capacity performance, but due to the limitations of the sintering process, they usually exhibit random crystal orientation, resulting in tortuous lithium-ion diffusion paths (especially along the c-axis), poor rate performance, low tap density, accelerated capacity decay, shortened cycle life, increased risk of local hot spots, uneven temperature distribution, and poor thermal stability of the material.

[0003] Existing technologies use mechanical ball milling, coating (such as liquid phase coating), and high-temperature annealing to solve the above problems. However, although mechanical ball milling can improve tap density, it will damage the crystal structure; coating will block pores and increase the resistance to lithium-ion transport; high-temperature annealing to reconstruct the crystal surface generally requires temperatures above 900°C, which will cause lithium volatilization and nickel reduction, and consumes a lot of energy. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects of poor rate performance, cycle life and thermal stability of existing lithium nickel cobalt aluminum oxide cathode materials, thereby providing a coated modified lithium nickel cobalt aluminum oxide cathode material, its preparation method and application.

[0005] Therefore, the present invention provides the following technical solution: The first aspect of this invention protects a coated modified lithium nickel cobalt aluminum oxide cathode material, wherein the lithium nickel cobalt aluminum oxide cathode material includes a core and a coating layer covering the core; The general formula of the kernel is Li a Ni x Co y Al z L p O2, wherein 1.01≤a≤1.05, 0.75≤x≤0.90, 0.05≤y≤0.20, 0.01≤z≤0.05, 0≤p≤0.05; L includes one of Mg, Zr, Mo, Ti, and Zn; The tap density of the modified nickel-cobalt-aluminum oxide cathode material is 2.7-3.2 g / cm³. 3 .

[0006] As an example, the tap density of the modified nickel-cobalt-aluminum oxide cathode material can be 2.7 g / cm³. 3 2.8g / cm3 2.9g / cm 3 3.0g / cm 3 3.1g / cm 3 3.2g / cm 3 , or within the range of any of the above values.

[0007] In one alternative implementation, the kernel has the general formula Li. a Ni x Co y Al z L p O2, where 1.01≤a≤1.03, 0.81≤x≤0.88, 0.12≤y≤0.18, 0.01≤z≤0.05, 0.002≤p≤0.02; L includes one of Mg and Zr.

[0008] In one optional embodiment, the tap density of the coated modified lithium nickel cobalt aluminum oxide cathode material is 2.8-3.2 g / cm³. 3 As an example, the tap density of the modified nickel-cobalt-aluminum oxide cathode material can be 2.8 g / cm³. 3 2.9g / cm 3 3.0g / cm 3 3.1g / cm 3 3.2g / cm 3 , or within the range of any of the above values.

[0009] In one alternative embodiment, the coating layer comprises fluorine and carbon.

[0010] In this invention, X-ray photoelectron spectroscopy (XPS) is used to characterize the elemental composition of the coating layer.

[0011] A second aspect of this invention protects a method for preparing the aforementioned coated and modified lithium nickel cobalt aluminum oxide cathode material, wherein the preparation method includes the following steps: S1, after mixing lithium nickel cobalt aluminum oxide cathode material and molten salt in a mass ratio of 2-8:1, the mixture is sintered for the first time to obtain a sintered product; S2, wash the calcined product and collect the solid product and liquid product separately; S3. The solid product is dried and then sintered a second time by passing a fluorine- and carbon-containing gas through it to obtain the coated and modified lithium nickel cobalt aluminum oxide cathode material.

[0012] As an example, the mass ratio of the lithium nickel cobalt aluminum oxide cathode material to the molten salt is 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, or within any of the above values.

[0013] In this invention, lithium nickel cobalt aluminum oxide (NCA) cathode material is used, which is a conventional material in the field and can be prepared and synthesized or purchased directly.

[0014] In one alternative implementation, step S1 involves adding a metal dopant during the mixing process.

[0015] In this invention, the lithium nickel cobalt aluminum oxide cathode material and the metal dopant are fed according to the stoichiometric ratio of the target product, as already described in the first aspect of this invention, and will not be repeated here.

[0016] In one optional embodiment, the metal dopant includes at least one of magnesium-containing compounds, zirconium-containing compounds, molybdenum-containing compounds, titanium-containing compounds, and zinc-containing compounds, and is optionally a magnesium-containing compound.

[0017] In one optional implementation, in step S1, the mass ratio of the lithium nickel cobalt aluminum oxide cathode material to the molten salt is 3-5:1. As an example, the mass ratio of the lithium nickel cobalt aluminum oxide cathode material to the molten salt is 3:1, 4:1, 5:1, or within any range of these values.

[0018] In one alternative embodiment, the molten salt comprises LiCl and KCl in a molar ratio of 1:1-3.

[0019] In one optional embodiment, in step S1, the heating rate of the first sintering is 1-5℃ / min, the temperature is 500-600℃, and the time is 1-5h.

[0020] In one optional embodiment, the heating rate of the first sintering is 3-5℃ / min, the temperature is 550-600℃, and the time is 3-5h.

[0021] In this invention, in step S1, by controlling the Ar content and O2 content, the reduction degree of nickel in the lithium nickel cobalt aluminum oxide cathode material can be controlled, thus avoiding over-reduction.

[0022] In step S2 of the present invention, the washing is a conventional washing method in the art. Typically, without limitation, the washing temperature is 60-80°C and the number of washing cycles is 3-5.

[0023] In step S2 of this invention, the liquid product is purified and the molten salt is recovered.

[0024] In one alternative implementation, in step S3, the drying is vacuum drying.

[0025] In one optional embodiment, the vacuum drying temperature is 80-200℃, optionally 80-120℃, and the time is 8-18h, optionally 8-12h. The specific vacuum drying conditions of this invention can effectively remove residual moisture and trace amounts of molten salt ions from the particle surface and pores, while avoiding lithium loss or localized structural degradation on the material surface due to excessively high temperatures.

[0026] In one optional embodiment, the second sintering temperature is 200-400°C and the time is 1-5 hours.

[0027] In step S3 of the present invention, the solid product is dried before coating. The drying is a conventional drying condition in the art, typically and non-limitingly, drying at 100-120°C for 12-18 hours.

[0028] In an optional embodiment, in step S3, the fluorinated and carbonaceous gas includes at least one of carbon tetrafluoride (CF4), hexafluoroethane (C2F6), difluoromethane (CH2F2), tetrafluoroethylene (C2F4), and trifluoroethylene (C2HF3), and optionally includes CF4 and / or C2F6.

[0029] A third aspect of this invention protects a secondary battery, wherein the secondary battery comprises the aforementioned coated modified lithium nickel cobalt aluminum oxide cathode material.

[0030] The technical solution of this invention has the following advantages: 1. This invention protects a coated modified lithium nickel cobalt aluminum oxide cathode material, wherein the lithium nickel cobalt aluminum oxide cathode material comprises a core and a coating layer covering the core; the core has the general formula Li a Ni x Co y Al z L p O2, wherein 1.01≤a≤1.05, 0.75≤x≤0.90, 0.05≤y≤0.20, 0.01≤z≤0.05, 0≤p≤0.05; L includes one of Mg, Zr, Mo, Ti, and Zn; the tap density of the modified nickel-cobalt-aluminum oxide cathode material is 2.7-3.2 g / cm³. 3 The modified nickel-cobalt-aluminum oxide cathode material provided by this invention employs a specific core-shell structure, enabling the cathode material to maintain high capacity while exhibiting good electronic conductivity and rate performance. The doping with specific elements effectively stabilizes the crystal structure of the nickel-cobalt-aluminum oxide material, suppressing lattice collapse caused by phase transitions under high voltage. The specific tap density avoids obstruction of lithium-ion transport, reduces interparticle voids, lowers the risk of localized hot spots, improves temperature distribution uniformity, enhances material thermal stability, suppresses capacity decay caused by structural loosening during charging and discharging, and extends battery cycle life.

[0031] 2. This invention protects a method for preparing a coated modified lithium nickel cobalt aluminum oxide cathode material, wherein the preparation method includes the following steps: S1, mixing lithium nickel cobalt aluminum oxide cathode material and molten salt in a mass ratio of 2-8:1 and then performing a first sintering to obtain a sintered product; S2, washing the sintered product and collecting the solid product and liquid product respectively; S3, drying the solid product and passing it through a fluorine-containing and carbon-containing gas for a second sintering to obtain a coated modified lithium nickel cobalt aluminum oxide cathode material. The specific amounts of lithium nickel cobalt aluminum oxide cathode material and molten salt can ensure that the molten salt accurately etches the lithium nickel cobalt aluminum oxide cathode material, preferentially exposing the electrochemically stable (104) crystal plane (accounting for >60%), while retaining the (003) plane as a fast lithium-ion channel to obtain a honeycomb densely packed structure; while the coating with fluorine-containing and carbon-containing gas can improve the tap density of the final product, enhance the interface stability, suppress electrolyte side reactions, and retain the capacity advantage of high nickel material. Detailed Implementation

[0032] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having” and any variations thereof in the text of this application are intended to cover non-exclusive inclusion.

[0034] In the description of the embodiments of this application, the technical terms "first", "second", etc. are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0035] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0036] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers from a to b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, and "0-5" is merely a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥ 2, it is equivalent to disclosing that the parameter can be, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] In the description of the embodiments of this application, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0038] In the description of the embodiments of this application, the term "at least one" refers to one or more (including two).

[0039] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0040] X-ray photoelectron spectroscopy (XPS) was used to characterize the elemental composition of the coating layer; NCA-1 material (LiNi) 0.83 Co 0.12 Al 0.05 The particle size distribution (O2), D50 (median particle size) is 5 μm, and the tap density is 2.7 g / cm³. 3 Purchased from GEM Co., Ltd. NCA-2 material (LiNi) 0.88 Co 0.10 Al 0.02 O2), D50 is 5μm, and tap density is 2.9g / cm³. 3 Purchased from GEM Co., Ltd.

[0041] Example 1 This embodiment provides a lithium nickel cobalt aluminum oxide cathode material, the preparation method of which includes the following steps: S1, NCA-1 and molten salt (LiCl and KCl in a molar ratio of 1:1) and MgCl2 are mixed, wherein the mass ratio of NCA-1 to molten salt is 3:1, and NCA-1 and MgCl2 are added according to the stoichiometric ratio. The mixture is ball-milled at room temperature for 30 min. The mixture is placed in a corundum crucible and Ar-O2 mixed gas is introduced. The Ar content is 99 vol% and the O2 content is 1 vol% based on the volume of the mixed gas. The temperature is increased to 550℃ at 5℃ / min and held for 3 h to obtain a calcined product. S2, after the calcined product is cooled to room temperature, it is washed three times with deionized water at 60°C. The solid product and liquid product are collected separately. The liquid product is centrifuged to separate and recover the molten salt. S3. The solid product was vacuum dried at 120℃ for 12 h to obtain the dried solid product. The dried solid product was then placed in a tube furnace, evacuated to 0.1 Pa, and N2 was introduced to remove residual moisture. A mixture of CF4 and N2 (CF4 to N2 volume ratio 1:10) was introduced at a flow rate of 10 sccm, and the temperature was increased to 300℃ at a rate of 3℃ / min for 1 h to obtain lithium nickel cobalt aluminum oxide cathode material, wherein the core is LiNi. 0.81 Co 0.12 Al 0.05 Mg 0.02 O2, the coating layer includes fluorine and carbon elements.

[0042] Example 2 This embodiment provides a lithium nickel cobalt aluminum oxide cathode material, the preparation method of which includes the following steps: S1, NCA-2, molten salt (LiCl and KCl in a molar ratio of 1:2), and ZnCl2 are mixed, wherein the mass ratio of NCA-2 to molten salt is 6:1, and NCA-2 and ZnCl2 are added according to the stoichiometric ratio. The mixture is ball-milled at room temperature for 45 min. The mixture is placed in an alumina crucible, and an Ar-O2 mixed gas is introduced. The Ar content is 99 vol% and the O2 content is 1 vol% based on the volume of the mixed gas. The temperature is increased to 580℃ at 3℃ / min and held for 1 h to obtain a calcined product. S2, after the calcined product is cooled to room temperature, it is washed three times with deionized water at 70°C. The solid product and liquid product are collected separately. The liquid product is centrifuged to separate and recover the molten salt. S3. The solid product was vacuum dried at 150℃ for 10h to obtain the dried solid product. The dried solid product was then placed in a tube furnace, evacuated to 0.1Pa, and N2 was introduced to remove residual moisture. A mixture of C2F6 and N2 (C2F6 to N2 volume ratio 1:10) was introduced at a flow rate of 12sccm, and the temperature was increased to 320℃ at a rate of 2℃ / min for 2h to obtain lithium nickel cobalt aluminum oxide cathode material, in which the core is LiNi. 0.86 Co 0.10 Al0.02 Zn 0.02 O2, the coating layer includes fluorine and carbon elements.

[0043] Example 3 This embodiment provides a lithium nickel cobalt aluminum oxide cathode material, the preparation method of which includes the following steps: S1, NCA-1 and molten salt (LiCl and KCl in a molar ratio of 1:1) and MgCl2 are mixed, wherein the mass ratio of NCA-1 to molten salt is 2:1, and NCA-1 and MgCl2 are added according to the stoichiometric ratio. The mixture is ball-milled at room temperature for 30 min. The mixture is placed in a corundum crucible and Ar-O2 mixed gas is introduced. The Ar content is 99 vol% and the O2 content is 1 vol% based on the volume of the mixed gas. The temperature is increased to 550℃ at 5℃ / min and held for 3 h to obtain a calcined product. S2, after the calcined product is cooled to room temperature, it is washed three times with deionized water at 60°C. The solid product and liquid product are collected separately. The liquid product is centrifuged to separate and recover the molten salt. S3. The solid product was vacuum dried at 120℃ for 12 h to obtain the dried solid product. The dried solid product was then placed in a tube furnace, evacuated to 0.1 Pa, and N2 was introduced to remove residual moisture. A mixture of CF4 and N2 (CF4 to N2 volume ratio 1:10) was introduced at a flow rate of 10 sccm, and the temperature was increased to 300℃ at a rate of 3℃ / min for 1 h to obtain lithium nickel cobalt aluminum oxide cathode material, wherein the core is LiNi. 0.81 Co 0.12 Al 0.05 Mg 0.02 O2, the coating layer includes fluorine and carbon elements.

[0044] Example 4 This embodiment provides a lithium nickel cobalt aluminum oxide cathode material, the preparation method of which includes the following steps: S1, NCA-1 and molten salt (LiCl and KCl in a molar ratio of 1:1) and MgCl2 are mixed, wherein the mass ratio of NCA-1 to molten salt is 3:1, and NCA-1 and MgCl2 are added according to the stoichiometric ratio. The mixture is ball-milled at room temperature for 30 min. The mixture is placed in a corundum crucible and Ar-O2 mixed gas is introduced. The Ar content is 99 vol% and the O2 content is 1 vol% based on the volume of the mixed gas. The temperature is increased to 550℃ at 5℃ / min and held for 3 h to obtain a calcined product. S2, after the calcined product is cooled to room temperature, it is washed three times with deionized water at 60°C. The solid product and liquid product are collected separately. The liquid product is centrifuged to separate and recover the molten salt. S3. The solid product was vacuum dried at 120℃ for 12 h to obtain the dried solid product. The dried solid product was then placed in a tube furnace, evacuated to 0.1 Pa, and N2 was introduced to remove residual moisture. A mixture of CF4 and N2 (CF4 to N2 volume ratio 1:10) was introduced at a flow rate of 10 sccm, and the temperature was increased to 300℃ at a rate of 3℃ / min for 1 h to obtain lithium nickel cobalt aluminum oxide cathode material, wherein the core is LiNi. 0.79 Co 0.11 Al 0.05 Mg 0.05 O2, the coating layer includes fluorine and carbon elements.

[0045] Example 5 This embodiment provides a lithium nickel cobalt aluminum oxide cathode material, the preparation method of which includes the following steps: S1, NCA-1 and molten salt (LiCl and KCl in a molar ratio of 1:1) and MgCl2 are mixed, wherein the mass ratio of NCA-1 to molten salt is 3:1, and NCA-1 and MgCl2 are added according to the stoichiometric ratio. The mixture is ball-milled at room temperature for 30 min, and the mixture is placed in an alumina crucible. An Ar-O2 mixed gas is introduced, and the Ar content is 99 vol% and the O2 content is 1 vol% based on the volume of the mixed gas. The temperature is increased to 550℃ at 5℃ / min and held for 3 h to obtain a calcined product. S2, after the calcined product is cooled to room temperature, it is washed three times with deionized water at 60°C. The solid product and liquid product are collected separately. The liquid product is centrifuged to separate and recover the molten salt. S3. The solid product was vacuum dried at 200℃ for 12 hours to obtain the dried solid product. The dried solid product was then placed in a tube furnace, evacuated to 0.1 Pa, and N2 was introduced to remove residual moisture. A mixture of CF4 and N2 (CF4 to N2 volume ratio 1:10) was introduced at a flow rate of 10 sccm, and the temperature was increased to 300℃ at a rate of 3℃ / min for 1 hour to obtain lithium nickel cobalt aluminum oxide cathode material, wherein the core is LiNi. 0.81 Co 0.12 Al 0.05 Mg 0.02 O2, the coating layer includes fluorine and carbon elements.

[0046] Comparative Example 1 This comparative example provides a lithium nickel cobalt aluminum oxide cathode material, the preparation method of which includes the following steps: S1, NCA-1 and molten salt (LiCl and KCl in a molar ratio of 1:1) and MgCl2 are mixed, wherein the mass ratio of NCA-1 to molten salt is 3:1, and NCA-1 and MgCl2 are added according to the stoichiometric ratio. The mixture is ball-milled at room temperature for 30 min. The mixture is placed in a corundum crucible and Ar-O2 mixed gas is introduced. The Ar content is 99 vol% and the O2 content is 1 vol% based on the volume of the mixed gas. The temperature is increased to 550℃ at 5℃ / min and held for 3 h to obtain a calcined product. S2, after the calcined product is cooled to room temperature, it is washed three times with deionized water at 60°C. The solid product and liquid product are collected separately. The liquid product is centrifuged to separate and recover the molten salt. S3. The solid product was vacuum dried at 120℃ for 12 hours to obtain the dried solid product. The dried solid product was then placed in a tube furnace, evacuated to 0.1 Pa, and N2 was introduced to remove residual moisture. The temperature was increased to 300℃ at a rate of 3℃ / min and reacted for 1 hour to obtain lithium nickel cobalt aluminum oxide cathode material, wherein the core is LiNi. 0.81 Co 0.12 Al 0.05 Mg 0.02 O2, the coating layer includes fluorine and carbon elements.

[0047] Comparative Example 2 This comparative example provides a lithium nickel cobalt aluminum oxide cathode material, the preparation method of which includes the following steps: S1, NCA-1 and molten salt (LiCl and KCl in a molar ratio of 1:1) and MgCl2 are mixed, wherein the mass ratio of NCA-1 to molten salt is 1:1, and NCA-1 and MgCl2 are added according to the stoichiometric ratio. The mixture is ball-milled at room temperature for 30 min. The mixture is placed in a corundum crucible and Ar-O2 mixed gas is introduced. The Ar content is 99 vol% and the O2 content is 1 vol% based on the volume of the mixed gas. The temperature is increased to 550℃ at 5℃ / min and held for 3 h to obtain a calcined product. S2, after the calcined product is cooled to room temperature, it is washed three times with deionized water at 60°C. The solid product and liquid product are collected separately. The liquid product is centrifuged to separate and recover the molten salt. S3. The solid product was vacuum dried at 120℃ for 12 h to obtain the dried solid product. The dried solid product was then placed in a tube furnace, evacuated to 0.1 Pa, and N2 was introduced to remove residual moisture. A mixture of CF4 and N2 (CF4 to N2 volume ratio 1:10) was introduced at a flow rate of 10 sccm, and the temperature was increased to 300℃ at a rate of 3℃ / min for 1 h to obtain lithium nickel cobalt aluminum oxide cathode material, wherein the core is LiNi. 0.81 Co 0.12 Al 0.05 Mg 0.02O2, the coating layer includes fluorine and carbon elements.

[0048] Test case Tap density: using Baxter's BT... The test was conducted using a Model 30 tap density tester; The test results are shown in Table 1; Table 1

[0049] Preparation method of CR2032 button cell: The materials obtained in the examples and comparative examples are used as positive electrode active materials, and polyvinylidene fluoride and carbon black are added in a mass ratio of 90:5:5. N-methylpyrrolidone (NMP) is added to obtain a positive electrode slurry. The solid content of the positive electrode slurry is 52%. The slurry is then homogenized and coated, and the compaction density of the electrode sheet is 3.3 g / cm³. 3 The electrode was fabricated using a lithium metal sheet as the counter electrode and a glass fiber separator. A 1 mol / L lithium hexafluorophosphate solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC to DMC volume ratio of 1:1) was used as the electrolyte. The CR2032 coin cell was assembled in an argon-filled glove box and then placed in the Blue Electric Test System for electrical performance testing.

[0050] At 25℃, the device was first charged at a constant current of 1C to 4.3V, then charged at a constant voltage of 4.3V until the current dropped to 20mA, yielding the 1C charging capacity. Then, it was first discharged at 1C to 3V, yielding the 1C discharging capacity. The initial charging efficiency was calculated as: (initial 1C discharging capacity / initial 1C charging capacity) × 100%. At 25℃, the capacitor was charged at a constant current of 0.2C to 4.3V, then charged at a constant voltage of 4.3V until the current dropped to 20mA. After resting for 10 minutes, it was discharged at a constant current of 0.2C until the cutoff voltage was 3V, and then rested for 10 minutes. This process was repeated three times. Then, the capacitor was charged at a constant current of 1C to 4.3V, then charged at a constant voltage of 4.3V until the current dropped to 20mA. After resting for 10 minutes, it was discharged at a constant current of 1C until the cutoff voltage was 3.0V, and then rested for 10 minutes. This process was repeated three times, and the specific capacity of the 1C discharge at the third cycle was recorded. Finally, the capacitor was charged at a constant current of 5C to 4.3V, then charged at a constant voltage of 4.3V until the current dropped to 20mA. After resting for 10 minutes, it was discharged at a constant current of 5C until the cutoff voltage was 3.0V, and then rested for 10 minutes. This process was repeated three times, and the specific capacity of the 5C discharge at the third cycle was recorded. Rate performance = 5C discharge specific capacity / 1C discharge specific capacity × 100%; The capacity retention rate test method is as follows: At 25℃, the battery is charged to 4.3V at a rate of 1C, and then discharged to 2.0V at a rate of 1C, and this cycle is repeated 500 times. The capacity retention rate on the 500th cycle is calculated as (discharge capacity on the 500th cycle / discharge capacity on the 1st cycle) × 100%. Test method for thermal runaway initiation temperature: Electrode sheets were prepared using the materials obtained in the examples and comparative examples, and the temperature was measured at a 1C rate from 3.0V to 4.3V (relative to Li). + Constant current charging was performed within the / Li voltage range until a fully charged state of 4.3V was reached. In an argon-protected glove box, 3.0 mg of charged positive electrode material was scraped off from the electrode sheet. The scraped positive electrode material was mixed with commercial electrolyte (specifically, ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1) at a mass ratio of 1:1 in a sealed crucible (high-pressure sealed DSC crucible) to simulate the internal environment of the battery. The sealed crucible was placed in a differential scanning calorimeter for DSC testing. Under a high-purity nitrogen atmosphere, the temperature was increased from 50℃ to 400℃ at a constant heating rate of 5℃ / min. The heat flow curve of the sample was recorded during the entire heating process. The starting temperature of the first obvious exothermic peak on the DSC curve (determined by the tangent method, i.e., the temperature value corresponding to the intersection of the tangent line at the inflection point of the starting edge of the exothermic peak and the extended baseline) was recorded as the thermal runaway initiation temperature. The test results are shown in Table 2; Table 2

[0051] The modified nickel-cobalt-aluminum oxide cathode material of this invention adopts a specific core-shell structure, which maintains high capacity while ensuring electronic conductivity and rate performance. The doping of specific elements can effectively stabilize the crystal structure of the nickel-cobalt-aluminum oxide material and suppress lattice collapse caused by phase transition under high voltage. The use of a specific tap density can avoid the obstruction of lithium-ion transport, reduce interparticle voids, reduce the risk of local hot spots, improve temperature distribution uniformity, enhance the thermal stability of the material, suppress capacity decay caused by structural loosening during charging and discharging, and extend battery cycle life.

[0052] A comparison of Examples 1 and 3 shows that vacuum drying under specific conditions can effectively remove residual moisture and trace amounts of molten salt ions from the particle surface and pores, while avoiding lithium loss or local structural degradation on the material surface due to excessively high temperatures. A comparison of Examples 1 and 4 shows that the Mg doping concentration in Example 4 is too high. 2+ Ion-substituted Ni 2+ The position of ions in the crystal lattice determines the Ni content that can participate in redox reactions. 2+ A reduction in ions decreases electrochemical performance. Comparing Example 1 and Comparative Example 1, it can be seen that Example 1 has a coating layer, while Comparative Example 1 does not. The initial efficiency of Example 1 is improved to 92.3%, while that of Comparative Example 1 is only 89.2%. The Example 1 has better electrical performance. Comparing Example 1 and Comparative Example 2, the mass ratio of NCA-1 to molten salt in Example 1 was 3:1, which was able to fully melt and fill the gaps between particles, resulting in the highest tap density (2.92 g / cm³). 3 In Comparative Example 2, due to excessive molten salt, the tap density was only 2.71 g / cm³. 3 .

[0053] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A coated and modified lithium nickel cobalt aluminum oxide cathode material, characterized in that, The lithium nickel cobalt aluminum oxide cathode material includes a core and a coating layer covering the core; The general formula of the kernel is Li a Ni x Co y Al z L p O2, wherein 1.01≤a≤1.05, 0.75≤x≤0.90, 0.05≤y≤0.20, 0.01≤z≤0.05, 0≤p≤0.05; L includes one of Mg, Zr, Mo, Ti, and Zn; The tap density of the modified nickel-cobalt-aluminum oxide cathode material is 2.7-3.2 g / cm³. 3 .

2. The coated and modified lithium nickel cobalt aluminum oxide cathode material according to claim 1, characterized in that, The general formula of the kernel is Li a Ni x Co y Al z L p O2, where 1.01≤a≤1.03, 0.81≤x≤0.88, 0.12≤y≤0.18, 0.01≤z≤0.05, 0.002≤p≤0.02; L includes one of Mg and Zr; And / or, the tap density of the coated modified lithium nickel cobalt aluminum oxide cathode material is 2.8-3.2 g / cm³. 3 .

3. The coated modified lithium nickel cobalt aluminum oxide cathode material according to claim 1 or 2, characterized in that, The coating layer includes fluorine and carbon elements.

4. A method for preparing the coated modified lithium nickel cobalt aluminum oxide cathode material according to any one of claims 1-3, characterized in that, The preparation method includes the following steps: S1, after mixing lithium nickel cobalt aluminum oxide cathode material and molten salt in a mass ratio of 2-8:1, the mixture is sintered for the first time to obtain a sintered product; S2, wash the calcined product and collect the solid product and liquid product separately; S3. The solid product is dried and then sintered a second time by passing a fluorine- and carbon-containing gas through it to obtain the coated and modified lithium nickel cobalt aluminum oxide cathode material.

5. The preparation method according to claim 4, characterized in that, Step S1, during the mixing process, a metal dopant is also added; Optionally, the metal dopant includes at least one of magnesium-containing compounds, zirconium-containing compounds, molybdenum-containing compounds, titanium-containing compounds, and zinc-containing compounds, and may be a magnesium-containing compound.

6. The preparation method according to claim 4 or 5, characterized in that, In step S1, the mass ratio of the lithium nickel cobalt aluminum oxide cathode material to the molten salt is 3-5:1; And / or, the molten salt comprises LiCl and KCl in a molar ratio of 1:1-3.

7. The preparation method according to any one of claims 4-6, characterized in that, In step S1, the heating rate of the first sintering is 1-5℃ / min, the temperature is 500-600℃, and the time is 1-5h. Optionally, the heating rate for the first sintering is 3-5℃ / min, the temperature is 550-600℃, and the time is 3-5h.

8. The preparation method according to any one of claims 4-7, characterized in that, In step S3, the drying is vacuum drying; Optionally, the vacuum drying temperature is 80-200℃, optionally 80-120℃, and the time is 8-18h, optionally 8-12h; Optionally, the second sintering temperature is 200-400℃ and the time is 1-5h.

9. The preparation method according to any one of claims 4-8, characterized in that, In step S3, the fluorine-containing and carbon-containing gas includes at least one of CF4, C2F6, CH2F2, C2F4, and C2HF3, and optionally includes CF4 and / or C2F6.

10. A secondary battery, characterized in that, The secondary battery includes the coated modified lithium nickel cobalt aluminum oxide cathode material as described in any one of claims 1-3.

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