Composite positive electrode material and preparation method and application thereof

Abstract

The present application relates to the field of lithium ion batteries, in particular to a composite cathode material and a preparation method and application thereof.The preparation method provided by the present application comprises the following steps: S1, mixing high-nickel NCA precursors, medium-nickel NCM precursors, lithium sources, bulk doping sources and carbon-coated sources to obtain a precursor mixture; the mass ratio of the high-nickel NCA precursors and the medium-nickel NCM precursors is (6.5:3.5) to (7.5:2.5); the bulk doping source comprises at least one of a cation doping source and an anion doping source; S2, performing multi-stage sintering, annealing and crushing on the precursor mixture to obtain a composite cathode material.The present application successfully prepares a cathode material which is superior to traditional NCA in terms of high capacity, long cycle life, excellent rate performance and excellent thermal safety through the synergistic effect of the core-shell gradient structure design, bulk doping and surface carbon coating, and in combination with a multi-stage sintering process.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, specifically to a composite 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 (such as LiNi0.8Co0.) are particularly important. 15 Al0. 05 O2 (NCA) is considered a core material for next-generation power batteries due to its high specific capacity. Currently, commercially available NCA materials are mainly prepared using traditional solid-state methods or co-precipitation-sintering methods, typically yielding dense secondary spherical particles with random crystal orientations. While these materials exhibit certain electrochemical performance in practical applications, further performance improvement still faces numerous challenges.

[0003] Existing high-nickel NCA materials and their preparation methods have significant drawbacks. First, NCA materials prepared by traditional solid-state methods or co-precipitation-sintering methods are mostly dense, secondary spherical particles. The solid-state diffusion path of lithium ions within the particles is relatively long, resulting in high mass transfer resistance and low capacity retention under high-rate (fast charge and discharge) conditions, leading to poor rate performance. Second, the co-precipitation method requires precise control of precursor synthesis conditions (such as pH, concentration, reaction temperature, and stirring rate), resulting in a narrow process window, high reproducibility, and the need for subsequent high-temperature, long-term sintering, which is energy-intensive and prone to lithium volatilization and cation mixing. Third, the high-temperature sintering process easily leads to excessive particle growth and agglomeration, reducing the tap density and processability of the material, and making it difficult to control particle uniformity. Previous studies have attempted to shorten the lithium-ion diffusion path through nano-sizing or the construction of porous structures, but nanoparticles are prone to agglomeration during high-temperature sintering and have low tap density, making it difficult to achieve both high rate capability and high volumetric energy density. Furthermore, while uniform bulk doping can improve cycle stability to some extent, it often comes at the cost of capacity and ionic conductivity. Simple surface coating can only suppress surface side reactions and has limited effect on improving the bulk structural stability of the material. Moreover, the coating layer may increase interfacial impedance, further deteriorating rate performance. At the same time, existing single-temperature long-term holding sintering processes make it difficult to precisely control the crystallinity, primary particle size and distribution of the material, which can easily lead to uneven internal stress and crack formation within the particles, ultimately affecting the cycle life and safety of the material.

[0004] Therefore, how to achieve high capacity, long cycle life, excellent rate performance and superior thermal safety of high-nickel NCA materials without sacrificing capacity remains a pressing technical challenge. Summary of the Invention

[0005] This invention provides a composite cathode material, its preparation method, and its application to solve the above-mentioned problems.

[0006] In a first aspect, the present invention provides a method for preparing a composite cathode material, comprising the following steps: S1, mix high-nickel NCA precursor, medium-nickel NCM precursor, lithium source, bulk doping source and carbon-coated source to obtain precursor mixture; The mass ratio of the high-nickel NCA precursor to the medium-nickel NCM precursor is (6.5:3.5) - (7.5:2.5). The bulk doping source includes at least one of a cation doping source and an anion doping source; S2, the precursor mixture is subjected to multi-stage sintering and annealing to obtain a composite cathode material.

[0007] In one optional embodiment, the multi-segment sintering includes a first sintering, a second sintering, and a third sintering; Optionally, the temperature of the first sintering is 400-600℃, and the holding time is 2-5h; Optionally, the second sintering temperature is 700-800℃, and the holding time is 5-10h; Optionally, the third sintering temperature is 750-850℃, and the holding time is 5-15h; In one optional embodiment, the heating rate of the multi-segment sintering is 2-3°C / min; In one optional embodiment, the atmosphere for the multi-stage sintering is a pure oxygen atmosphere.

[0008] In one alternative embodiment, the high-nickel NCA precursor has the general chemical formula including Ni. x Co y Al z (OH)2, where 0.80≤x≤0.95, 0.02≤y≤0.15, 0.01≤z≤0.05, and x+y+z=1; In one alternative embodiment, the general chemical formula of the medium-nickel NCM precursor includes Ni. a Co b Mn c (OH)2, where 0.50≤a<0.80, 0.05≤b≤0.20, 0.10≤c≤0.30, and a+b+c=1.

[0009] In one optional embodiment, the molar amount of the cation doping source accounts for 0.005 mol%-2.0 mol% of the total transition metal molar amount in the high-nickel NCA precursor and the medium-nickel NCM precursor. In one optional embodiment, the cation doping source includes at least one of Zr-containing oxides and Mg-containing oxides; Further, optionally, the cation doping source includes at least one of ZrO2 and MgO.

[0010] In one optional embodiment, the anion doping source accounts for 0.1 wt%-5.0 wt% of the total mass of the high-nickel NCA precursor and the medium-nickel NCM precursor. In one alternative embodiment, the anion doping source comprises an F-containing compound; Further optionally, the anion doping source includes at least one of NH4F, LiF, and MgF2.

[0011] In one optional embodiment, the amount of carbon-coated source added accounts for 0.1 wt%-3.0 wt% of the total mass of the high-nickel NCA precursor, the medium-nickel NCM precursor, and the lithium source. In one alternative embodiment, the carbon coating source includes at least one of glucose, sucrose, and citric acid.

[0012] In one optional embodiment, the lithium source comprises LiOH·H2O; In one optional embodiment, the molar ratio of the lithium source to the total transition metal in the precursor mixture is (1-1.1):1.

[0013] In an optional embodiment, step S1 further includes the addition of anhydrous ethanol; Optionally, the amount of anhydrous ethanol added is sufficient to ensure uniform mixing of the high-nickel NCA precursor, the medium-nickel NCM precursor, the lithium source, the bulk doped source, and the carbon-coated source.

[0014] In one optional implementation, step S1 further includes drying; Optionally, the drying temperature is 70℃-90℃, and the drying time is sufficient to turn the precursor mixture into a dry powder; In one optional embodiment, in step S1, the mixture includes at least one of high-energy ball milling and high-speed liquid-phase shearing. Optionally, the high-energy ball mill is operated at a speed of 350-450 rpm for 3.5-4.5 hours. It is understood that in S1, mixing includes achieving a uniform mixing of the high-nickel NCA precursor, the medium-nickel NCM precursor, the lithium source, the bulk doped source, and the carbon-coated source at the molecular / nanoscale level.

[0015] In one optional embodiment, in step S2, the annealing temperature is 500-650°C, the holding time is 3-8 hours, and the atmosphere is a mixture of argon and oxygen. Optionally, the volume ratio of argon to oxygen in the mixed gas is (85:15) to (95:5).

[0016] In an alternative implementation, step S2 further includes crushing.

[0017] Secondly, the present invention also provides a composite cathode material prepared by the above-described preparation method.

[0018] In one alternative embodiment, the composite cathode material D 50 It is 8-15μm.

[0019] Thirdly, the present invention also provides a lithium-ion battery comprising the composite cathode material prepared by the above-described preparation method.

[0020] Those skilled in the art will understand that the lithium-ion battery provided by the present invention may include structural components such as an electrolyte, a positive electrode, a negative electrode, a separator, and a casing. During the charging and discharging process, lithium ions repeatedly insert and extract between the positive and negative electrode. The electrolyte acts as a conductor between the positive and negative electrode. The separator is disposed between the positive and negative electrode, primarily to prevent short circuits between the positive and negative electrodes, while simultaneously allowing lithium ions to pass through.

[0021] As an example, the positive electrode sheet includes a positive current collector and a positive active layer. The positive current collector has two opposing surfaces in its own thickness direction, and the positive active layer is disposed on either or both of the opposing surfaces of the positive current collector. The material of the positive electrode sheet used in the lithium-ion battery of the present invention is a composite positive electrode material prepared by the preparation method provided by the present invention.

[0022] As an example, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer. The negative electrode current collector has two opposing surfaces in its own thickness direction, and the negative electrode active layer is disposed on either or both of the opposing surfaces of the negative electrode current collector. The materials, composition, and manufacturing methods of the negative electrode sheet used in the lithium-ion battery of the present invention may include any techniques disclosed in the prior art.

[0023] The material and shape of the separator used in the lithium-ion battery of the present invention are not particularly limited, and may include any technology disclosed in the prior art.

[0024] The electrolyte used in the lithium-ion battery of the present invention may also include any technology disclosed in the prior art.

[0025] This invention does not specifically limit the preparation method of lithium-ion batteries; lithium-ion batteries can be prepared using conventional preparation methods in the art. For example, positive electrode sheets, separators, and negative electrode sheets are stacked sequentially, with the separator located between the positive and negative electrode sheets. A cell is obtained through stacking or winding processes, and then the lithium-ion battery of this invention is obtained through baking, electrolyte injection, formation, and packaging.

[0026] Fourthly, the present invention also provides an electrical device comprising the composite cathode material prepared by the above-described preparation method.

[0027] It is understood that in the electrical equipment provided by the present invention, the lithium-ion battery can be used as a power source for the electrical equipment, or as an energy storage unit for the electrical equipment. The electrical equipment may 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.

[0028] The technical solution of this invention has the following advantages: 1. The present invention provides a method for preparing a composite cathode material, comprising the following steps: S1, mixing a high-nickel NCA precursor, a medium-nickel NCM precursor, a lithium source, a bulk doping source, and a carbon-coated source to obtain a precursor mixture; the mass ratio of the high-nickel NCA precursor to the medium-nickel NCM precursor is (6.5:3.5)-(7.5:2.5); the bulk doping source includes at least one of a cation doping source and an anion doping source; S2, subjecting the precursor mixture to multi-stage sintering and annealing to obtain the composite cathode material. The selection of a high-nickel NCA precursor as the core material imparts excellent reversible specific capacity, laying a solid foundation for the product's high-capacity characteristics. Maintaining a mass ratio of high-nickel NCA precursor to medium-nickel NCM precursor between (6.5:3.5) and (7.5:2.5) forms a stable concentration gradient transition layer, effectively mitigating internal stress and constructing a robust outer shell structure and a high-strength bulk lattice. This dual protection inhibits structural degradation during cycling, significantly extending the product's cycle life. In the bulk doping stage, at least one of a cation or anion doping source is used to modify and strengthen the material's outer shell, greatly suppressing lattice oxygen release, increasing the battery's thermal runaway initiation temperature, and effectively enhancing the product's thermal safety. Simultaneously, a conductive coating layer is constructed on the material surface using a carbon coating source, which, combined with the bulk doping modification effect, effectively improves lithium-ion diffusion capacity and reduces interfacial impedance, giving the cathode material excellent fast charge / discharge and rate performance. In terms of manufacturing process, this invention abandons the traditional single high-temperature sintering mode and adopts a multi-stage sintering process to precisely control the heating rate and holding time. This breaks down the single sintering process into multiple stages of physical and chemical changes, comprehensively optimizing the material's microstructure, electrochemical performance, and batch production stability. Overall, this invention, through the synergistic application of three major modification technologies—core-shell gradient structure design, bulk doping, and surface carbon coating—combined with a multi-stage sintering process, successfully develops a cathode material with comprehensive performance superior to traditional NCA, possessing multiple advantages such as high capacity, long cycle life, excellent fast-charging rate, and superior thermal safety.

[0029] 2. This invention provides a method for preparing a composite cathode material, wherein the multi-stage sintering includes a first sintering, a second sintering, and a third sintering. The first sintering completely removes free moisture and residual volatile impurities from the material. The sintering temperature is controlled at 400-600℃, and the holding time is 2-5 hours, which efficiently removes water of crystallization. The second sintering promotes significant solid-phase diffusion of cations such as nickel, cobalt, aluminum, and manganese among the precursor particles, constructing an elemental concentration gradient from the core to the shell, while the doping elements gradually embed into the crystal lattice. The second sintering temperature is 700-800℃, and the holding time is 5-10 hours, which induces crystal nucleation and completes preliminary crystallization. The third sintering promotes full crystallization of the material, forming a regular layered crystal structure, while simultaneously controlling the growth of the first-stage particles, resulting in fine and uniform grain morphology and shortening the lithium-ion diffusion path. The third sintering temperature is 750-850℃, and the holding time is 5-15 hours, which enables controllable grain growth and material densification.

[0030] 3. The present invention provides a method for preparing a composite cathode material, wherein the annealing temperature is 500-650℃, the holding time is 3-8h, and the atmosphere is a mixture of argon and oxygen, which can relieve lattice stress, adjust oxygen vacancies, and reduce cation mixing.

[0031] 4. The present invention provides a method for preparing a composite cathode material, wherein the molar amount of the cation doping source accounts for 0.005 mol%-2.0 mol% of the total transition metal molar amount in the precursor mixture, which can suppress phase transition and cation mixing; the molar amount of the anion doping source accounts for 0.1 wt%-5.0 wt% of the mass of the precursor mixture, which can broaden the lithium layer channel; the amount of carbon coating source added accounts for 0.1 wt%-3.0 wt% of the total mass of the high-nickel NCA precursor, the medium-nickel NCM precursor, and the lithium source, which can realize the construction of a three-dimensional conductive network and reduce the generation of electrochemically inert carbon (dead carbon). Detailed Implementation

[0032] The following embodiments are provided to better understand the present invention, but the following embodiments 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 scope of protection 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 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. 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 a particular 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.

[0035] 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.

[0036] In the description of the embodiments of this application, the term "at least one" refers to one or more (including two).

[0037] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0038] Example 1 This embodiment provides a composite cathode material, and the operation steps and specific parameter settings are as follows: S1, high-nickel NCA precursor (Ni 0.88 Co 0.09 Al 0.03 (OH)2), mid-nickel NCM precursor (Ni 0.75 Co 0.10 Mn 0.15(OH)2), lithium source (LiOH·H2O), cation doping source (ZrO2), anion doping source (NH4F), carbon-coated source (glucose) are mixed with an appropriate amount of anhydrous ethanol, and the mixture is dried at 70°C after being mixed by high-speed liquid-phase shearing to obtain a precursor mixture. The mass ratio of the high-nickel NCA precursor to the medium-nickel NCM precursor is 7:3; the molar ratio of the total transition metals in the lithium source to the precursor mixture is 1.05:1; the molar amount of the cation-doped source accounts for 0.05 mol% of the total transition metals in the precursor mixture; the mass of the anion-doped source accounts for 1 wt% of the mass of the precursor mixture; and the amount of the carbon-coated source accounts for 2 wt% of the total mass of the high-nickel NCA precursor, the medium-nickel NCM precursor, and the lithium source. S2, the precursor mixture is placed in a box-type atmosphere furnace. Under a pure oxygen atmosphere, the temperature is first increased to 500℃ at 2℃ / min for the first sintering and held for 3 hours. Then, the temperature is increased to 750℃ at 2℃ / min for the second sintering and held for 8 hours. Next, the temperature is increased to 820℃ at 2℃ / min for the third sintering and held for 10 hours. Finally, the furnace is cooled to 600℃, and the Ar / O2 mixed gas (volume ratio 95:5) is switched. After holding for 5 hours, the furnace is cooled to room temperature. The mixture is then lightly ground and sieved to obtain the composite cathode material with D50=10μm.

[0039] Example 2 This embodiment provides a composite cathode material, and the operation steps and specific parameter settings are as follows: S1, high-nickel NCA precursor (Ni 0.85 Co 0.11 Al 0.04 (OH)2), mid-nickel NCM precursor (Ni 0.65 Co 0.15 Mn 0.20 (OH)2), lithium source (LiOH·H2O), cation doping source (ZrO2), anion doping source (NH4F), carbon-coated source (sucrose) and an appropriate amount of anhydrous ethanol are mixed, ball-milled in a planetary ball mill at 400 rpm for 4 hours and then dried at 70℃ to obtain a precursor mixture; The mass ratio of the high-nickel NCA precursor to the medium-nickel NCM precursor is 6.8:3.2; the molar ratio of the total transition metals in the lithium source to the precursor mixture is 1.05:1; the molar amount of the cation-doped source accounts for 1 mol% of the total transition metals in the precursor mixture; the mass of the anion-doped source accounts for 2 wt% of the mass of the precursor mixture; and the amount of the carbon-coated source accounts for 1.5 wt% of the total mass of the high-nickel NCA precursor, the medium-nickel NCM precursor, and the lithium source. S2. The precursor mixture is placed in a box-type atmosphere furnace. Under a pure oxygen atmosphere, the temperature is first increased to 550℃ at 2.5℃ / min for the first sintering and held for 4 hours. Then, the temperature is increased to 780℃ at 2.5℃ / min for the second sintering and held for 7 hours. Then, the temperature is increased to 800℃ at 2.5℃ / min for the third sintering and held for 12 hours. Finally, the furnace is cooled to 620℃, and the Ar / O2 mixed gas (volume ratio 90:10) is switched. After holding for 6 hours, the furnace is cooled to room temperature. The mixture is then lightly ground and sieved to obtain the composite cathode material with D50=12μm.

[0040] Example 3 This embodiment provides a composite cathode material, and the operation steps and specific parameter settings are as follows: S1, high-nickel NCA precursor (Ni 0.88 Co 0.09 Al 0.03 (OH)2), mid-nickel NCM precursor (Ni 0.75 Co 0.10 Mn 0.15 (OH)2), lithium source (LiOH·H2O), cation doped source (ZrO2), carbon coated source (glucose) are mixed with an appropriate amount of anhydrous ethanol, and the mixture is dried at 70°C after being mixed by high-speed liquid-phase shearing to obtain a precursor mixture. The mass ratio of the high-nickel NCA precursor to the medium-nickel NCM precursor is 7:3; the molar ratio of the total transition metals in the lithium source to the precursor mixture is 1.05:1; the molar amount of the cation-doped source accounts for 0.05 mol% of the total transition metals in the precursor mixture; and the amount of the carbon-coated source accounts for 2 wt% of the total mass of the high-nickel NCA precursor, the medium-nickel NCM precursor, and the lithium source. S2, the precursor mixture is placed in a box-type atmosphere furnace. Under a pure oxygen atmosphere, the temperature is first increased to 500℃ at 2℃ / min for the first sintering and held for 3 hours. Then, the temperature is increased to 750℃ at 2℃ / min for the second sintering and held for 8 hours. Next, the temperature is increased to 820℃ at 2℃ / min for the third sintering and held for 10 hours. Finally, the furnace is cooled to 600℃, and the Ar / O2 mixed gas (volume ratio 95:5) is switched. After holding for 5 hours, the furnace is cooled to room temperature. The mixture is then lightly ground and sieved to obtain the composite cathode material with D50=10μm.

[0041] Example 4 This embodiment provides a composite cathode material, and the operation steps and specific parameter settings are as follows: S1, high-nickel NCA precursor (Ni 0.80 Co 0.15 Al 0.05 (OH)2), mid-nickel NCM precursor (Ni 0.50 Co0.20 Mn 0.30 (OH)2), lithium source (LiOH·H2O), cation doped source (ZrO2), carbon coated source (glucose) are mixed with an appropriate amount of anhydrous ethanol, and the mixture is dried at 70°C after being mixed by high-speed liquid-phase shearing to obtain a precursor mixture. The mass ratio of the high-nickel NCA precursor to the medium-nickel NCM precursor is 7.5:2.5; the molar ratio of the total transition metals in the lithium source to the precursor mixture is 1.05:1; the molar amount of the cation-doped source accounts for 2 mol% of the total transition metals in the precursor mixture; and the amount of the carbon-coated source added accounts for 0.1 wt% of the total mass of the high-nickel NCA precursor, the medium-nickel NCM precursor, and the lithium source. S2. The precursor mixture is placed in a box-type atmosphere furnace. Under a pure oxygen atmosphere, the temperature is first increased to 400℃ at 3℃ / min for the first sintering and held for 5 hours. Then, the temperature is increased to 800℃ at 2℃ / min for the second sintering and held for 5 hours. Next, the temperature is increased to 750℃ at 3℃ / min for the third sintering and held for 15 hours. Finally, the furnace is cooled to 500℃, and the Ar / O2 mixed gas (volume ratio 95:5) is switched. After holding for 8 hours, the furnace is cooled to room temperature. The mixture is then lightly ground and sieved to obtain the composite cathode material with D50=8μm.

[0042] Example 5 This embodiment provides a composite cathode material, and the operation steps and specific parameter settings are as follows: S1, high-nickel NCA precursor (Ni 0.95 Co 0.01 Al 0.04 (OH)2), mid-nickel NCM precursor (Ni 0.79 Co 0.05 Mn 0.16 (OH)2), lithium source (LiOH·H2O), cation doped source (ZrO2), carbon coated source (glucose) are mixed with an appropriate amount of anhydrous ethanol, and the mixture is dried at 70°C after being mixed by high-speed liquid-phase shearing to obtain a precursor mixture. The mass ratio of the high-nickel NCA precursor to the medium-nickel NCM precursor is 6.5:3.5; the molar ratio of the total transition metals in the lithium source to the precursor mixture is 1.05:1; the molar amount of the cation-doped source accounts for 0.005 mol% of the total transition metals in the precursor mixture; and the amount of the carbon-coated source accounts for 3 wt% of the total mass of the high-nickel NCA precursor, the medium-nickel NCM precursor, and the lithium source. S2, the precursor mixture is placed in a box-type atmosphere furnace. Under a pure oxygen atmosphere, the temperature is first increased to 600℃ at 2℃ / min for the first sintering and held for 2 hours. Then, the temperature is increased to 700℃ at 3℃ / min for the second sintering and held for 10 hours. Next, the temperature is increased to 850℃ at 2℃ / min for the third sintering and held for 5 hours. Finally, the temperature is cooled to 650℃ with the furnace, and the Ar / O2 mixed gas (volume ratio 85:15) is switched. After holding for 3 hours, the temperature is cooled to room temperature with the furnace. The mixture is then lightly ground and sieved to obtain the composite cathode material with D50=15μm.

[0043] Example 6 This embodiment provides a composite cathode material, which differs from Embodiment 1 only in that the cation doping source is MgO and the anion doping source is MgF2. The rest is the same as in Example 1.

[0044] Comparative Example 1 This comparative example provides a composite cathode material, and the operating steps and specific parameter settings are as follows: S1, high-nickel NCA precursor (Ni 0.95 Co 0.01 Al 0.04 (OH)2), lithium source (LiOH·H2O), cation doped source (ZrO2), carbon coated source (glucose) are mixed with an appropriate amount of anhydrous ethanol, and the mixture is dried at 70°C after being mixed by high-speed liquid-phase shearing to obtain a precursor mixture. The molar ratio of the lithium source to the total transition metals in the precursor is 1.05:1; the molar amount of the cation-doped source accounts for 0.005 mol% of the total transition metals in the precursor; the amount of the carbon-coated source added accounts for 0.5 wt% of the total mass of the high-nickel NCA precursor, the medium-nickel NCM precursor, and the lithium source. S2, the precursor mixture is placed in a box-type atmosphere furnace. Under a pure oxygen atmosphere, the temperature is first increased to 600℃ at 2℃ / min for the first sintering and held for 2 hours. Then, the temperature is increased to 700℃ at 3℃ / min for the second sintering and held for 10 hours. Next, the temperature is increased to 850℃ at 2℃ / min for the third sintering and held for 5 hours. Finally, the temperature is cooled to 650℃ with the furnace, and the Ar / O2 mixed gas (volume ratio 85:15) is switched. After holding for 3 hours, the temperature is cooled to room temperature with the furnace. The mixture is then lightly ground and sieved to obtain the composite cathode material with D50=15μm.

[0045] Comparative Example 2 This comparative example provides a composite cathode material, and the operating steps and specific parameter settings are as follows: S1, the mid-nickel NCM precursor (Ni 0.79 Co 0.05 Mn 0.16(OH)2), lithium source (LiOH·H2O), cation doped source (ZrO2), carbon coated source (glucose) are mixed with an appropriate amount of anhydrous ethanol, and the mixture is dried at 70°C after being mixed by high-speed liquid-phase shearing to obtain a precursor mixture. The molar ratio of the lithium source to the total transition metals in the precursor is 1.05:1; the molar amount of the cation-doped source accounts for 0.005 mol% of the total transition metals in the precursor; the amount of the carbon-coated source added accounts for 3 wt% of the total mass of the high-nickel NCA precursor, the medium-nickel NCM precursor, and the lithium source. S2, the precursor mixture is placed in a box-type atmosphere furnace. Under a pure oxygen atmosphere, the temperature is first increased to 600℃ at 2℃ / min for the first sintering and held for 2 hours. Then, the temperature is increased to 700℃ at 3℃ / min for the second sintering and held for 10 hours. Next, the temperature is increased to 850℃ at 2℃ / min for the third sintering and held for 5 hours. Finally, the temperature is cooled to 650℃ with the furnace, and the Ar / O2 mixed gas (volume ratio 85:15) is switched. After holding for 3 hours, the temperature is cooled to room temperature with the furnace. The mixture is then lightly ground and sieved to obtain the composite cathode material with D50=15μm.

[0046] Comparative Example 3 This comparative example provides a composite cathode material, and the operating steps and specific parameter settings are as follows: S1, high-nickel NCA precursor (Ni 0.95 Co 0.01 Al 0.04 (OH)2), mid-nickel NCM precursor (Ni 0.79 Co 0.05 Mn 0.16 (OH)2), lithium source (LiOH·H2O), carbon-coated source (glucose) and an appropriate amount of anhydrous ethanol are mixed, and the mixture is dried at 70°C after being mixed by high-speed liquid-phase shearing to obtain a precursor mixture; The mass ratio of the high-nickel NCA precursor to the medium-nickel NCM precursor is 6.5:3.5; the molar ratio of the total transition metals in the lithium source and precursor mixture is 1.05:1; and the amount of carbon-coated source added accounts for 3 wt% of the total mass of the high-nickel NCA precursor, the medium-nickel NCM precursor, and the lithium source. S2, the precursor mixture is placed in a box-type atmosphere furnace. Under a pure oxygen atmosphere, the temperature is first increased to 600℃ at 2℃ / min for the first sintering and held for 2 hours. Then, the temperature is increased to 700℃ at 3℃ / min for the second sintering and held for 10 hours. Next, the temperature is increased to 850℃ at 2℃ / min for the third sintering and held for 5 hours. Finally, the temperature is cooled to 650℃ with the furnace, and the Ar / O2 mixed gas (volume ratio 85:15) is switched. After holding for 3 hours, the temperature is cooled to room temperature with the furnace. The mixture is then lightly ground and sieved to obtain the composite cathode material with D50=15μm.

[0047] Comparative Example 4 This comparative example provides a composite cathode material, and the operating steps and specific parameter settings are as follows: S1, high-nickel NCA precursor (Ni 0.95 Co 0.01 Al 0.04 (OH)2), mid-nickel NCM precursor (Ni 0.79 Co 0.05 Mn 0.16 (OH)2), lithium source (LiOH·H2O), cation doping source (ZrO2) and appropriate amount of anhydrous ethanol are mixed, and the mixture is dried at 70°C after high-speed liquid-phase shearing to obtain precursor mixture; The mass ratio of the high-nickel NCA precursor to the medium-nickel NCM precursor is 6.5:3.5; the molar ratio of the total transition metals in the lithium source to the precursor mixture is 1.05:1; and the molar amount of the cation-doped source accounts for 0.005 mol% of the total transition metal molar amount in the precursor mixture. S2, the precursor mixture is placed in a box-type atmosphere furnace. Under a pure oxygen atmosphere, the temperature is first increased to 600℃ at 2℃ / min for the first sintering and held for 2 hours. Then, the temperature is increased to 700℃ at 3℃ / min for the second sintering and held for 10 hours. Next, the temperature is increased to 850℃ at 2℃ / min for the third sintering and held for 5 hours. Finally, the temperature is cooled to 650℃ with the furnace, and the Ar / O2 mixed gas (volume ratio 85:15) is switched. After holding for 3 hours, the temperature is cooled to room temperature with the furnace. The mixture is then lightly ground and sieved to obtain the composite cathode material with D50=15μm.

[0048] Comparative Example 5 This comparative example provides a composite cathode material, and the operating steps and specific parameter settings are as follows: S1, high-nickel NCA precursor (Ni 0.95 Co 0.01 Al 0.04 (OH)2), mid-nickel NCM precursor (Ni 0.79 Co 0.05 Mn 0.16 (OH)2), lithium source (LiOH·H2O), cation doped source (ZrO2), carbon coated source (glucose) are mixed with an appropriate amount of anhydrous ethanol and dried at 70°C. The mixture is then subjected to high-speed liquid-phase shear mixing to obtain a precursor mixture. The mass ratio of the high-nickel NCA precursor to the medium-nickel NCM precursor is 8.5:1.5; the molar ratio of the total transition metals in the lithium source to the precursor mixture is 1.05:1; the molar amount of the cation-doped source accounts for 0.005 mol% of the total transition metals in the precursor mixture; and the amount of the carbon-coated source accounts for 3 wt% of the total mass of the high-nickel NCA precursor, the medium-nickel NCM precursor, and the lithium source. S2, the precursor mixture is placed in a box-type atmosphere furnace. Under a pure oxygen atmosphere, the temperature is first increased to 600℃ at 2℃ / min for the first sintering and held for 2 hours. Then, the temperature is increased to 700℃ at 3℃ / min for the second sintering and held for 10 hours. Next, the temperature is increased to 850℃ at 2℃ / min for the third sintering and held for 5 hours. Finally, the temperature is cooled to 650℃ with the furnace, and the Ar / O2 mixed gas (volume ratio 85:15) is switched. After holding for 3 hours, the temperature is cooled to room temperature with the furnace. The mixture is then lightly ground and sieved to obtain the composite cathode material with D50=15μm.

[0049] Comparative Example 6 This comparative example provides a composite cathode material, and the operating steps and specific parameter settings are as follows: S1, high-nickel NCA precursor (Ni 0.95 Co 0.01 Al 0.04 (OH)2), mid-nickel NCM precursor (Ni 0.79 Co 0.05 Mn 0.16 (OH)2), lithium source (LiOH·H2O), cation doped source (ZrO2), carbon coated source (glucose) are mixed with an appropriate amount of anhydrous ethanol and dried at 70°C. The mixture is then subjected to high-speed liquid-phase shear mixing to obtain a precursor mixture. The mass ratio of the high-nickel NCA precursor to the medium-nickel NCM precursor is 3.5:6.5; the molar ratio of the total transition metals in the lithium source to the precursor mixture is 1.05:1; the molar amount of the cation-doped source accounts for 0.005 mol% of the total transition metals in the precursor mixture; and the amount of the carbon-coated source accounts for 3 wt% of the total mass of the high-nickel NCA precursor, the medium-nickel NCM precursor, and the lithium source. S2, the precursor mixture is placed in a box-type atmosphere furnace. Under a pure oxygen atmosphere, the temperature is first increased to 600℃ at 2℃ / min for the first sintering and held for 2 hours. Then, the temperature is increased to 700℃ at 3℃ / min for the second sintering and held for 10 hours. Next, the temperature is increased to 850℃ at 2℃ / min for the third sintering and held for 5 hours. Finally, the temperature is cooled to 650℃ with the furnace, and the Ar / O2 mixed gas (volume ratio 85:15) is switched. After holding for 3 hours, the temperature is cooled to room temperature with the furnace. The mixture is then lightly ground and sieved to obtain the composite cathode material with D50=15μm.

[0050] Comparative Example 7 This comparative example provides a composite cathode material, which differs from Example 5 only in that: in S2, multi-stage sintering is not performed, but the precursor mixture is placed in a box-type atmosphere furnace and sintered at 850°C at a rate of 2°C / min under a pure oxygen atmosphere, and held for 17 hours. The rest is the same as in Example 5.

[0051] Comparative Example 8 This comparative example provides a composite cathode material, which differs from Example 5 only in that: in S1, the medium-nickel NCM precursor (Ni 0.79 Co 0.05 Mn 0.16 (OH)2) was replaced with a high-nickel NCM precursor (Ni 0.95 Co 0.01 Mn 0.04 (OH)2); The rest is the same as in Example 5.

[0052] Experimental Example 1 The composite cathode materials prepared in each embodiment and comparative example were applied to lithium-ion batteries, and then their electrical performance was tested.

[0053] The method for preparing the lithium-ion battery includes the following steps: In an argon atmosphere within a glove box, a Celgard 2500 separator is used, with lithium metal sheets as the negative electrode and LBC3021C011 electrolyte. The positive electrode is prepared by coating an aluminum foil current collector with a mixture of the composite positive electrode material, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) in a weight ratio of 90:5:5, with an active material surface loading of 10 mg / cm³. 2 The CR2032 button cell is assembled in the following order: negative electrode, electrolyte, separator, electrolyte, and positive electrode.

[0054] The specific methods for electrical performance testing are as follows: (1) First-cycle charge and discharge efficiency test The assembled coin cells were subjected to their first charge and discharge at a rate of 0.1C within a voltage range of 2.0V to 4.0V. The first charge capacity and the first discharge capacity were recorded, and the first coulombic efficiency (first efficiency) was calculated.

[0055] The Coulomb efficiency for the first lap is calculated as follows: ; Where: ICE is the initial Coulomb efficiency; D1 is the initial discharge capacity at a specified rate (e.g., 0.1C); C1 represents the initial charging capacity at the same rate.

[0056] (2) Ratio performance test The assembled button cells were charged and discharged at constant currents of 0.1 C and 5 C within a voltage range of 2.0V to 4.0V. The rate capacity was calculated as follows: magnification .

[0057] (3) Cyclic stability test The assembled button cells were subjected to 100 charge-discharge cycle tests at a constant current of 1C within a voltage range of 2.0V to 4.0V.

[0058] (4) Thermal safety performance test Experiment 1 was assembled into a CR2032 type button half-cell for thermal safety performance testing. The specific testing method is as follows: ① Charge and discharge cycles The assembled battery was subjected to charge-discharge cycles at 25±1 ℃. Perform two charge-discharge cycles at a rate of 0.1 C within a voltage range of 2.0 V to 4 V, then charge at a constant current of 0.1 C to 4.6 V, and then switch to constant voltage (4.6 V) charging until the current drops to 0.05 C and stops.

[0059] ② Sample collection and processing Disassemble the battery in the glove box and remove the positive electrode. Soak and clean it three times (2 minutes each time) with anhydrous dimethyl carbonate (DMC). Let it air dry at room temperature until constant weight. Scrape off 4 mg of the positive electrode material, weigh it accurately (accuracy 0.01 mg), and put it into a high-pressure sealed crucible.

[0060] ③ Electrolyte addition Fresh electrolyte (1 MLiPF6 in EC / DMC / EMC) was added to the crucible at a ratio of 1 μL: 1.5 mg electrolyte to positive electrode material.

[0061] ④ Test parameters Under a nitrogen atmosphere with a flow rate of 45 mL / min, a differential scanning calorimeter (Netzsch 214, TA Q20) was used to scan the above-mentioned positive electrode material with added electrolyte from 30 °C to 400 °C at a heating rate of 5 °C / min, and the onset temperature of the exothermic peak (T) was recorded. onset ).

[0062] The specific test results are as follows: Table 1 Performance Test Data

[0063] The data in Table 1 show that Examples 1 and 6 both use co-doping modification with anions and cations, and the ratio of high and low nickel is reasonable. Both have the best overall discharge capacity and first-cycle coulombic efficiency, higher thermal onset temperature, and outstanding thermal stability. Compared with Examples 1 and 6, Example 2 slightly reduced the capacity and first-cycle efficiency by adjusting the doping amount and preparation process, but improved long-cycle stability and slightly decreased thermal safety performance. Example 3 lacked anion doping protection, and compared with the other examples, the lattice stability effect was weakened, the first-cycle efficiency was reduced, the cycle decay was accelerated, and the thermal stability also declined significantly. In Example 4, the nickel content in the high-nickel NCA precursor and the medium-nickel NCM precursor was low, resulting in a lower inherent capacity, but strong structural stability, the best cycle life among all groups, and moderate thermal safety performance. Example 5 used an ultra-high nickel precursor, which was more prone to cation mixing and interfacial side reactions compared with all other examples. It had the worst first-cycle efficiency and cycle performance, was prone to structural instability at high temperatures, and had the lowest thermal stability among the examples. Overall, it is evident that appropriate nickel content ratios, doping with anions and cations, reasonable modification methods, and sintering processes can synergistically balance the material's capacity, initial efficiency, cycle life, and thermal safety performance.

[0064] Compared to Example 5, Comparative Examples 1 and 2 used only a single high-nickel NCA precursor or medium-nickel NCM precursor, lacking the synergistic effect of two-phase composite, resulting in insufficient capacity utilization and thermal stability; Comparative Example 3 did not undergo doping modification, which affected the capacity to some extent, but the crystal structure lacked stabilizing effect, leading to severe phase transitions during charge and discharge, faster cycle decay, and decreased heat resistance; Comparative Example 4 omitted carbon coating modification, resulting in a lack of conductive network and comprehensive deterioration in rate capability, cycle performance, and thermal safety performance; Comparative Example 5 had an excessively high proportion of high-nickel NCA precursor and an insufficient proportion of medium-nickel NCM precursor, making it difficult to form effective grain boundary anchoring during sintering, failing to suppress excessive growth of high-nickel particles and cation mixing, causing a decrease in structural stability, and ultimately a significant deterioration in cycle stability and thermal safety performance; Comparative Example 6 significantly... While reducing the proportion of high-nickel NCA precursors and excessively increasing the proportion of medium-nickel NCM precursors improves structural stability, it significantly weakens the core advantage of high-capacity high-nickel NCA precursors, rendering the synergistic design of high- and medium-nickel composites meaningless. This indicates that when the proportion of high-nickel NCA precursors is too low, its "high capacity" advantage is almost lost, and the composite material degenerates into a "high-cost medium-nickel material," losing its composite significance. Comparative Example 7 abandons the multi-stage gradient sintering process and replaces it with a one-time high-temperature long-time sintering process. The unreasonable heating regime easily causes uneven grain development, an increase in internal defects, and damages the consistency of the material's microstructure. Comparative Example 8 uses high-nickel NCM precursors to replace medium-nickel NCM precursors. Although it has higher capacity, the corresponding cycle stability and thermal stability deteriorate sharply.

[0065] 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 method for preparing a composite cathode material, characterized in that, Includes the following steps: S1, mix high-nickel NCA precursor, medium-nickel NCM precursor, lithium source, bulk doping source and carbon-coated source to obtain precursor mixture; The mass ratio of the high-nickel NCA precursor to the medium-nickel NCM precursor is (6.5:3.5) - (7.5:2.5). The bulk doping source includes at least one of a cation doping source and an anion doping source; S2, the precursor mixture is subjected to multi-stage sintering and annealing to obtain a composite cathode material.

2. The preparation method according to claim 1, characterized in that, The multi-stage sintering includes a first sintering, a second sintering, and a third sintering; Optionally, the temperature of the first sintering is 400-600℃, and the holding time is 2-5h; Optionally, the second sintering temperature is 700-800℃, and the holding time is 5-10h; Optionally, the temperature of the third sintering is 750-850℃, and the holding time is 5-15h; And / or, the heating rate of the multi-segment sintering is 2-3℃ / min.

3. The preparation method according to claim 1 or 2, characterized in that, The general chemical formula of the high-nickel NCA precursor includes Ni x Co y Al z (OH)2, where 0.80≤x≤0.95, 0.02≤y≤0.15, 0.01≤z≤0.05, and x+y+z=1; And / or, the general chemical formula of the nickel NCM precursor includes Ni a Co b Mn c (OH)2, where 0.50≤a<0.80, 0.05≤b≤0.20, 0.10≤c≤0.30, and a+b+c=1.

4. The preparation method according to any one of claims 1-3, characterized in that, The molar amount of the cation dopant source accounts for 0.005 mol%-2.0 mol% of the total transition metal molar amount in the high-nickel NCA precursor and the medium-nickel NCM precursor. And / or, the mass of the anion doping source accounts for 0.1 wt%-5.0 wt% of the total mass of the high-nickel NCA precursor and the medium-nickel NCM precursor; And / or, the cation doping source includes at least one of Zr-containing oxides and Mg-containing oxides; Optionally, the cation doping source includes at least one of ZrO2 and MgO; And / or, the anion doping source includes an F-containing compound; Optionally, the anion doping source includes at least one of NH4F, LiF, and MgF2.

5. The preparation method according to any one of claims 1-4, characterized in that, The amount of carbon-coated source added accounts for 0.1 wt%-3.0 wt% of the total mass of the high-nickel NCA precursor, medium-nickel NCM precursor, and lithium source. And / or, the carbon coating source includes at least one of glucose, sucrose, and citric acid.

6. The preparation method according to any one of claims 1-5, characterized in that, The annealing temperature is 500-650℃, the holding time is 3-8h, and the atmosphere is a mixture of argon and oxygen. Optionally, the volume ratio of argon to oxygen in the mixed gas is (85:15) to (95:5).

7. A composite cathode material prepared by the preparation method according to any one of claims 1-6.

8. The composite cathode material according to claim 7, characterized in that, The composite cathode material D 50 It is 8-15μm.

9. A lithium-ion battery, characterized in that, Includes the composite cathode material as described in claim 7 or 8.

10. An electrical appliance, characterized in that, Including the lithium-ion battery as described in claim 9.

Images