COF coated and modified ternary precursor as well as preparation method and application thereof

Abstract

The invention provides a COF coated and modified ternary precursor and a preparation method and application thereof, and the preparation method comprises the following steps: mixing a dispersion liquid containing a COF material with a ternary precursor, and then carrying out heat treatment to obtain the COF coated and modified ternary precursor. According to the preparation method disclosed by the invention, the surface of the ternary precursor is uniformly coated with the COF material with high specific surface area, high stability and adjustable aperture through a solution impregnation method, so that the structural stability and the electron transmission capability of the ternary precursor are improved, and the safety, the cycle performance, the rate capability and the like of the battery can be enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and relates to a COF-coated modified ternary precursor, a preparation method thereof, and an application thereof. Background Art

[0002] Ternary materials (such as lithium nickel cobalt manganese oxide NCM or lithium nickel cobalt aluminate NCA) are important components of the cathode materials for lithium-ion batteries, and have high energy density, high voltage platform, and good cycle performance, and are widely used in the fields of electric vehicles and energy storage. However, ternary materials have the following problems in the prior art: (1) Ternary materials have defects of unstable structure and easy structural collapse during charge and discharge processes, which will lead to capacity attenuation; (2) Side reactions occur between the surface of ternary materials and the electrolyte, generating an unstable solid electrolyte interface (SEI) film, which affects the battery performance; (3) The interfacial binding force between traditional coating materials (such as Al2O3, TiO2, etc.) and ternary materials is weak, and it may hinder the lithium-ion transport.

[0003] The performance of the ternary precursor will affect the performance of the ternary material. Modifying the ternary precursor can improve the above problems of the ternary material; for example, CN112993229A discloses a preparation method for a multi-metal MOF gradient-coated modified ternary precursor. Through one-step surface growth, the ternary precursor is in-situ coated with MOF material to improve the cycle performance of the material. However, the pore size structure of the MOF material is relatively fixed and it is difficult to flexibly adjust to meet the requirements of different precursors, and MOF is prone to decomposition at high temperatures.

[0004] Based on the above research, a preparation method for a ternary precursor is needed. The material obtained by the preparation method has a stable structure and strong electron transport ability, and can enhance the safety, cycle performance, rate performance, etc. of the battery. Summary of the Invention

[0005] The purpose of the present invention is to provide a COF-coated modified ternary precursor, a preparation method thereof, and an application thereof. The preparation method uniformly coats a COF material with a high specific surface area, high stability, and adjustable pore size on the surface of the ternary precursor through a solution impregnation method, improving the structural stability and electron transport ability of the ternary precursor, thereby enhancing the safety, cycle performance, rate performance, etc. of the battery.

[0006] To achieve the purpose of this invention, the following technical solutions are adopted in the present invention:

[0007] In the first aspect, the present invention provides a preparation method for a COF-coated modified ternary precursor, and the preparation method includes the following steps:

[0008] Mix the dispersion containing the COF material with the ternary precursor, and then perform heat treatment to obtain the ternary precursor coated and modified with COF.

[0009] The COF material is a covalent organic framework material, which is a new type of porous material. It has a high specific surface area, adjustable pore size, and excellent chemical stability, making it suitable for surface modification and coating. The porous structure of the COF material can promote lithium ion transport and effectively block the direct contact between the electrolyte and the ternary material. Compared with MOF materials, the synthesis conditions of COF materials are mild, and the pore size structure can be flexibly adjusted. Coating the ternary precursor with COF has more advantages in the field of battery materials.

[0010] In the present invention, the solution impregnation method is used to coat the COF material on the surface of the ternary precursor, and heat treatment can further enhance the binding force between the COF material and the ternary precursor, thereby solving problems such as unstable structure, many surface side reactions, and short cycle life during charge and discharge of the ternary material, and improving its electrochemical performance at the same time. Moreover, due to the high specific surface area and active surface of the precursor, more uniform COF coverage can be achieved, while suppressing sintering defects and reducing bulk cracks. Since the COF coating on the positive electrode surface can only modify the surface and cannot affect the grain boundaries or bulk defects inside the material, the effect of coating the COF material at the precursor end in the present invention is better than that at the positive electrode end.

[0011] Preferably, the dispersion containing the COF material includes the COF material and ethanol with a mass ratio of 1:(40 - 60). For example, it can be 1:40, 1:50, or 1:60, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0012] Preferably, the molar ratio of the ternary precursor to the COF material is (6 - 8):(2 - 4). For example, it can be 5:5, 6:4, or 7:3, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0013] The molar ratio of the ternary precursor to the COF material in the present invention will affect the coating amount of the COF material. If the coating amount of the COF material is too small, the coating effect will be reduced, affecting the electrochemical performance of the material. If the coating amount of the COF material is too large, the effective content of the ternary material will be reduced, lowering the energy density of the battery. At the same time, an overly thick coating layer may cause the material to crack or fall off during charge and discharge, affecting the cycle stability.

[0014] Preferably, the time for mixing the dispersion containing the COF material with the ternary precursor is 8 - 12 h. For example, it can be 8 h, 9 h, 10 h, 11 h, or 12 h, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0015] Preferably, the temperature of the heat treatment is 200 - 300 °C. For example, it can be 200 °C, 220 °C, 240 °C, 260 °C, 280 °C or 300 °C, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0016] The temperature of the heat treatment in the present invention also affects the coating effect and the binding force between the COF material and the ternary precursor. If the heat treatment temperature is too low, solvent residues will be caused, affecting the material properties. If the heat treatment temperature is too high, the covalent bonds of the COF material will break, damaging the integrity of its structure.

[0017] Preferably, the time of the heat treatment is 8 - 10 h. For example, it can be 8 h, 8.5 h, 9 h, 9.5 h or 10 h, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0018] Preferably, the heat treatment is carried out in a protective atmosphere, and the protective atmosphere includes any one or a combination of at least two of nitrogen, argon or helium.

[0019] Preferably, the raw materials for preparing the COF material include 1,3,5-triformylbenzene, 1,4-phenylenediamine, 2,5-dimethoxyterephthalaldehyde, 1,3,5-triaminobenzene or 4,4-diaminobiphenyl.

[0020] The present invention selects a specific COF material to coat the ternary precursor. This specific COF material is a highly crystalline COF material formed by connecting 1,3,5-triformylbenzene and 1,4-phenylenediamine through imine bonds. As a coating layer, it has advantages such as high crystallinity, uniform pore structure and good mechanical properties. Moreover, this coating layer can effectively improve the electrochemical performance and cycle stability of the ternary material, and at the same time has the characteristics of low cost and high feasibility, and is suitable for modifying the cathode material of lithium-ion batteries.

[0021] Preferably, the method for preparing the COF material includes the following steps:

[0022] Mix 1,3,5-triformylbenzene, 1,4-phenylenediamine, an organic solvent and a catalyst, and carry out a solvothermal reaction to obtain the COF material.

[0023] Preferably, the temperature of the solvothermal reaction is 80 - 150 °C. For example, it can be 80 °C, 100 °C, 120 °C, 140 °C or 150 °C, and the time is 8 - 15 h. For example, it can be 8 h, 10 h, 12 h, 14 h or 15 h, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0024] Preferably, the molar ratio of the 1,3,5-triformylbenzene to 1,4-phenylenediamine is (1.5 - 2.5):(2.5 - 3.5), for example, it can be 1.5:3.5, 2:3 or 2.5:3.5, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0025] Preferably, the organic solvent includes o-dichlorobenzene and n-butanol.

[0026] Preferably, the volume ratio of the o-dichlorobenzene, n-butanol and the catalyst is (0.8 - 1.2):(0.8 - 1.2):(0.3 - 0.5), for example, it can be 1:1:0.4, 0.8:1.2:0.3 or 1.2:0.8:0.5, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0027] Preferably, the catalyst includes acetic acid.

[0028] Preferably, the method for preparing the ternary precursor includes the following steps:

[0029] Carry out a coprecipitation reaction on the mixed metal salt solution, precipitant solution and complexing agent solution to obtain the ternary precursor.

[0030] Preferably, in the mixed metal salt solution, the nickel ions, cobalt ions and manganese ions have a molar ratio of (85 - 95):(2 - 5):(3 - 10), for example, it can be 85:5:10, 90:3:7 or 95:2:3, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0031] Preferably, the total metal ion concentration of the mixed metal salt solution is 1 - 3 mol / L, for example, it can be 1 mol / L, 2 mol / L or 3 mol / L, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0032] Preferably, the flow rate ratio of the mixed metal salt solution, precipitant solution and complexing agent solution is in the range of (5.5 - 6):(2 - 2.5):(1 - 2), for example, it can be 5.5:2:1, 5.8:2.3:1.5 or 6:2.5:2, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0033] Preferably, the pH of the coprecipitation reaction is in the range of 10 - 12, for example, it can be 10, 10.5, 11, 11.5 or 12, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0034] Preferably, the stirring rate of the coprecipitation reaction is 250 - 400 rpm, for example, it can be 250 rpm, 300 rpm, 350 rpm or 400 rpm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0035] Preferably, the temperature of the coprecipitation reaction is 50 - 60 °C, for example, it can be 50 °C, 55 °C or 60 °C, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0036] Preferably, the time of the coprecipitation reaction is 70 - 100 h, for example, it can be 70 h, 80 h, 90 h or 100 h, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0037] Preferably, the particle size D50 of the ternary precursor is 3 - 5 μm, for example, it can be 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0038] In a second aspect, the present invention provides a COF-coated and modified ternary precursor, and the COF-coated and modified ternary precursor is prepared by the preparation method as described in the first aspect.

[0039] In a third aspect, the present invention provides a lithium-ion battery, and the lithium-ion battery includes a positive electrode material prepared from the COF-coated and modified ternary precursor as described in the second aspect.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] By adopting the solution impregnation method combined with heat treatment, the present invention coats the COF material on the ternary precursor. The porous structure of the COF material can effectively block the direct contact between the electrolyte and the ternary material, reducing the occurrence of side reactions. Moreover, the COF material has a stable framework structure, which can effectively inhibit the structural collapse of the ternary material during charge and discharge, improving the strength and chemical stability of the material. At the same time, the porous structure is beneficial to the transmission of lithium ions, improving the conductivity of the material. Description of the Drawings

[0042] Figure 1 It is the SEM image of the ternary precursor obtained in step (1) of Example 1 of the present invention.

[0043] Figure 2 It is the SEM image of the COF-coated and modified ternary precursor obtained in Example 1 of the present invention. Detailed Embodiments

[0044] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0045] Example 1

[0046] This example provides a preparation method of a COF-coated modified ternary precursor. The preparation method includes the following steps:

[0047] (1) Under the protection of a nitrogen atmosphere, nickel sulfate, cobalt sulfate, and manganese sulfate are configured into a mixed salt solution with a total metal ion concentration of 1 mol / L according to the molar ratio of Ni:Co:Mn = 91:3:6. In a 2 m 3 reactor, 1000 L of pure water is added. Among them, the mass concentration ratio of sodium hydroxide to ammonia water is 2:1. According to the set flow rate, the mixed salt solution, sodium hydroxide solution, and ammonia water are fed into the reactor in a flow rate ratio of (5.5 - 6):(2 - 2.5):(1 - 2), so that the pH of the solution during the reaction is within the range of 10 - 12, the stirring rate is 350 rpm, the temperature is maintained at 60 °C, and the reaction continues for 95 h. The machine stops when the particle size D50 reaches 5 μm, and the ternary precursor is obtained. The SEM diagram of the ternary precursor is as Figure 1 shown;

[0048] (2) 1,3,5-Trimethoxybenzene (Tp) and 1,4-phenylenediamine (Pa) are dissolved in a mixed solution of o-dichlorobenzene and n-butanol according to the molar ratio of 2:3, and an acetic acid catalyst is added. The volume ratio of o-dichlorobenzene, n-butanol, and acetic acid = 1:1:0.4, and a solvothermal reaction is carried out. The reaction temperature is controlled at 150 °C, and the reaction time is 15 h to obtain the COF material;

[0049] (3) The COF material is dispersed in ethanol (where the mass ratio of the COF material to ethanol is 1:50) to form a uniform dispersion. The prepared ternary precursor is immersed in the COF dispersion. The molar ratio of the ternary precursor to the COF material is 7:3. After stirring for 8 h, it is heat-treated at 200 °C for 8 h under a nitrogen atmosphere to obtain the COF-coated modified ternary precursor. The SEM of the COF-coated modified ternary precursor is as Figure 2 shown.

[0050] Example 2

[0051] This example provides a preparation method of a COF-coated modified ternary precursor. The preparation method includes the following steps:

[0052] (1) Under the protection of a nitrogen atmosphere, nickel sulfate, cobalt sulfate, and manganese sulfate were configured into a mixed salt solution with a total metal ion concentration of 3 mol / L according to the molar ratio of Ni:Co:Mn = 86:5:9. In a 2 m 3 reactor, 1000 L of pure water was added. Among them, the mass concentration ratio of sodium hydroxide to ammonia water was 2:1. According to the set flow rate, the mixed salt solution, sodium hydroxide solution, and ammonia water were fed into the reactor in a flow rate ratio within the range of (5.5 - 6):(2 - 2.5):(1 - 2), so that the pH of the solution during the reaction was within the range of 11 - 12, the stirring rate was 250 rpm, the temperature was maintained at 50 °C, and the reaction continued for 70 h. The machine was stopped when the particle size D50 reached 3 μm to obtain the ternary precursor;

[0053] (2) 1,3,5-triformylbenzene (Tp) and 1,4-phenylenediamine (Pa) were dissolved in a mixed solution of ortho-dichlorobenzene and n-butanol according to the molar ratio of 1.5:3.5, and an acetic acid catalyst was added. Among them, the volume ratio of ortho-dichlorobenzene, n-butanol, and acetic acid = 0.8:1.2:0.5. A solvothermal reaction was carried out, and the reaction temperature was controlled at 100 °C and the reaction time was 10 h to obtain the COF material;

[0054] (3) The COF material was dispersed in ethanol (where the mass ratio of the COF material to ethanol was 1:40) to form a uniform dispersion. The prepared ternary precursor was immersed in the COF dispersion. Among them, the molar ratio of the ternary precursor to the COF material was 6:4. After stirring for 9 h, it was heat-treated at a temperature of 250 °C for 9 h under a nitrogen atmosphere to obtain the COF-coated and modified ternary precursor,

[0055] Example 3

[0056] This example provides a method for preparing a COF-coated and modified ternary precursor, and the preparation method includes the following steps:

[0057] (1) Under the protection of a nitrogen atmosphere, nickel sulfate, cobalt sulfate, and manganese sulfate were configured into a mixed salt solution with a total metal ion concentration of 1 mol / L according to the molar ratio of Ni:Co:Mn = 91:3:6. In a 2 m 3 reactor, 1000 L of pure water was added. Among them, the mass concentration ratio of sodium hydroxide to ammonia water was 2:1. According to the set flow rate, the mixed salt solution, sodium hydroxide solution, and ammonia water were fed into the reactor in a flow rate ratio within the range of (5.5 - 6):(2 - 2.5):(1 - 2), so that the pH of the solution during the reaction was within the range of 10 - 12, the stirring rate was 400 rpm, the temperature was maintained at 60 °C, and the reaction continued for 100 h. The machine was stopped when the particle size D50 reached 5 μm to obtain the ternary precursor;

[0058] (2) Dissolve 1,3,5-triformylbenzene (Tp) and 1,4-phenylenediamine (Pa) in a mixed solution of o-dichlorobenzene and n-butanol according to a molar ratio of 2.5:2.5, add an acetic acid catalyst, where the volume ratio of o-dichlorobenzene, n-butanol, and acetic acid = 1.2:0.8:0.3, and carry out a solvothermal reaction. Control the reaction temperature at 150 °C and the reaction time at 8 h to obtain a COF material;

[0059] (3) Disperse the COF material in ethanol (where the mass ratio of the COF material to ethanol is 1:60) to form a uniform dispersion. Immerse the prepared ternary precursor into the COF dispersion, where the molar ratio of the ternary precursor to the COF material is 8:2. After stirring for 10 h, heat-treat at a temperature of 300 °C for 10 h under a nitrogen atmosphere to obtain the ternary precursor modified by COF coating.

[0060] Example 4

[0061] This example provides a method for preparing a ternary precursor modified by COF coating. Except that the molar ratio of the ternary precursor to the COF material in step (3) is 1:1, the rest are the same as in Example 1.

[0062] Example 5

[0063] This example provides a method for preparing a ternary precursor modified by COF coating. Except that the molar ratio of the ternary precursor to the COF material in step (3) is 9:1, the rest are the same as in Example 1.

[0064] Example 6

[0065] This example provides a method for preparing a ternary precursor modified by COF coating. Except that the heat-treatment temperature in step (3) is 150 °C, the rest are the same as in Example 1.

[0066] Example 7

[0067] This example provides a method for preparing a ternary precursor modified by COF coating. Except that the heat-treatment temperature in step (3) is 350 °C, the rest are the same as in Example 1.

[0068] Comparative Example 1

[0069] This comparative example provides a method for preparing a ternary precursor. Except that steps (2) and (3) are not carried out, the rest are the same as in Example 1.

[0070] Comparative Example 2

[0071] This comparative example provides a method for preparing a ternary positive electrode material, wherein the ternary precursor obtained in step (1) of Example 1 is mixed with LiOH at a metal ratio of 1:1.05, and sintered at 450°C for 5h, and then sintered at 850°C for 14h to obtain a positive electrode sintered material;

[0072] The positive electrode sintered material was mixed with the COF material obtained in step (2) of Example 1 at a molar ratio of 7:3, and then sintered at 450° C. for 8 h in a nitrogen atmosphere to obtain the ternary positive electrode material.

[0073] The COF-coated modified ternary precursor obtained in the above Examples 1-7 and Comparative Example 1 was mixed with LiOH in a molar ratio of 1:1.05 of metal ratio, and sintered at 450°C for 5 hours, and then sintered at 850°C for 14 hours to obtain a positive electrode active material. The obtained positive electrode active material and the ternary positive electrode material obtained in Comparative Example 2 were fully ground with polyvinylidene fluoride and conductive carbon black in a mass ratio of 8:1:1, and then N-methylpyrrolidone was added and continued to grind to a thick and suitable uniform slurry. The slurry was then evenly coated on a flat metal aluminum foil, and then placed in a vacuum oven and dried at 90°C for 10 hours. After completion, the positive electrode coated peak aluminum foil was cut into positive electrode sheets.

[0074] The positive electrode obtained above was prepared into a CR2032 type button half-cell, in which a polypropylene film was used as a separator, lithium metal was used as a negative electrode, and a mixed solution of LiPF6 (1M) and EC:DMC:EMC (volume ratio 1:1:1) was used as an electrolyte for battery assembly. The entire assembly process was completed in a glove box filled with argon gas. The glove box strictly controlled the water and oxygen content, and the water and oxygen content was less than 0.01ppm. After the battery was assembled, it was allowed to stand at room temperature for 10 hours until the voltage stabilized before testing. Specifically, the test was carried out on an Autolab electrochemical workstation, and it was charged to 4.3V (relative to the potential of Li) at a rate of 0.1C (1C = 200mAh / g), allowed to stand, and then discharged to 2.5V, and also allowed to stand. Subsequent cycles were repeated as needed, and the cycle performance was tested at room temperature 1.9V-4.3V and 0.1C rate. The test results are shown in Table 1:

[0075] Table 1

[0076]

[0077]

[0078] From Table 1 we can see that:

[0079] As can be seen from Example 1 and Comparative Example 1, coating the surface of the ternary precursor material with the COF material according to the present invention can solve problems such as unstable structure, many surface side reactions, and short cycle life during charge and discharge of the ternary material, thereby improving the cycle and rate performance of the battery; as can be seen from Example 1 and Comparative Example 2, when the present invention coats the precursor material, the high specific surface area and active surface of the precursor can achieve more uniform COF coverage, while suppressing sintering defects and reducing bulk cracks. When the COF is coated on the surface of the positive electrode, it can only modify the surface and cannot affect the grain boundaries or bulk defects inside the material. Therefore, the coating effect of Example 1 of the present invention at the precursor end is better than that at the positive electrode end; as can be seen from Example 1 and Examples 4-5, the coating amount of the COF material of the present invention will affect the coating effect, thereby affecting the cycle and rate performance of the battery; as can be seen from Example 1 and Examples 6-7, the heat treatment temperature of the present invention will also affect the coating effect, thereby affecting the performance of the battery.

[0080] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of within the technical scope disclosed by the present invention by those skilled in the art all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A preparation method of a COF-coated modified ternary precursor, characterized in that, The preparation method includes the following steps: Mix the dispersion containing the COF material with the ternary precursor, and then perform heat treatment to obtain the COF-coated and modified ternary precursor.

2. The preparation method according to claim 1, characterized in that, The dispersion containing the COF material includes the COF material and ethanol; Preferably, the molar ratio of the ternary precursor to the COF material is (6 - 8):(2 - 4); Preferably, the time for mixing the dispersion containing the COF material with the ternary precursor is 8 - 12 h.

3. The preparation method according to claim 1 or 2, characterized in that, The temperature of the heat treatment is 200 - 300 °C; Preferably, the time of the heat treatment is 8 - 10 h; Preferably, the heat treatment is carried out in a protective atmosphere, and the protective atmosphere includes any one or a combination of at least two of nitrogen, argon or helium.

4. The preparation method according to any one of claims 1-3, characterized in that, The method for preparing the COF material includes the following steps: Mix 1,3,5-triformylbenzene, 1,4-phenylenediamine, an organic solvent and a catalyst, and perform a solvothermal reaction to obtain the COF material; Preferably, the temperature of the solvothermal reaction is 80 - 150 °C, and the time is 8 - 15 h.

5. The preparation method according to claim 4, characterized in that, The molar ratio of 1,3,5-triformylbenzene to 1,4-phenylenediamine is (1.5 - 2.5):(2.5 - 3.5); Preferably, the organic solvent includes o-dichlorobenzene and n-butanol; Preferably, the volume ratio of o-dichlorobenzene, n-butanol and the catalyst is (0.8 - 1.2):(0.8 - 1.2):(0.3 - 0.5); Preferably, the catalyst includes acetic acid.

6. The preparation method according to any one of claims 1-5, characterized in that, The method for preparing the ternary precursor includes the following steps: Perform a coprecipitation reaction on the mixed metal salt solution, the precipitant solution and the complexing agent solution to obtain the ternary precursor; Preferably, in the mixed metal salt solution, the molar ratio of nickel ions, cobalt ions and manganese ions is (85 - 95):(2 - 5):(3 - 10); Preferably, the total metal ion concentration of the mixed metal salt solution is 1 - 3 mol / L.

7. The preparation method according to claim 6, characterized in that, The flow rate ratio of the mixed metal salt solution, the precipitant solution and the complexing agent solution is in the range of (5.5 - 6):(2 - 2.5):(1 - 2); Preferably, the pH of the coprecipitation reaction is in the range of 10 - 12.

8. The preparation method according to claim 6 or 7, characterized in that, The stirring rate of the coprecipitation reaction is 250 - 400 rpm; Preferably, the temperature of the coprecipitation reaction is 50 - 60 °C; Preferably, the time of the coprecipitation reaction is 70 - 100 h; Preferably, the particle size D50 of the ternary precursor is 3 - 5 μm.

9. A ternary precursor modified by COF coating, characterized in that, The COF-coated and modified ternary precursor is prepared by the preparation method described in any one of claims 1 - 8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode material prepared from the COF-coated and modified ternary precursor described in claim 9.

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