A MOF-coated ternary cathode material and its preparation method and application

Abstract

The present invention discloses a MOF-coated ternary cathode material, its preparation method, and application. The method comprises the following steps: 1) mixing the MOF material Fe2(DHBQ)3 and Li2O in an organic solvent, separating, drying, and sieving to obtain a mixed powder, and preheating the mixed powder to obtain a modified MOF material Fe2(DHBQ)3; 2) mixing a mixed salt solution, a lithium salt solution, and a chelating agent solution, and then hydrothermally treating the mixture to obtain a precursor solid solution, wherein the mixed salt solution is a mixed solution of nickel salt, cobalt salt, and manganese salt; sintering the precursor solid solution to obtain the ternary cathode material; 3) saturating the modified MOF material Fe2(DHBQ)3 in a supercritical fluid solvent; and then spraying the saturated Fe2(DHBQ)3 supercritical fluid solution into the dispersed ternary cathode material. After reaction, the MOF-coated ternary cathode material is obtained. The present invention improves the structural stability, electrical conductivity and safety of the ternary positive electrode material by coating Fe2(DHBQ)3, and the preparation method is simple and easy, the coating effect is good, and the performance of the lithium-ion battery can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and in particular relates to a MOF-coated ternary cathode material and a preparation method and application thereof. Background Art

[0002] With the development of new energy, lithium-ion batteries have developed rapidly. Among lithium-ion battery materials, positive electrode materials, as one of the important key materials, are of great significance in determining the performance of batteries.

[0003] Most current ternary cathode materials are composed of large secondary particles formed by the agglomeration of primary particles. These particles are prone to numerous crystal defects, resulting in uneven particle size and poor battery consistency. This results in a small contact area between the ternary cathode material and the electrolyte, hindering lithium ion migration. Furthermore, the agglomerated secondary particles result in a large particle size, with D50 values ​​mostly exceeding 10μm, leading to low compaction and a poor battery energy density. Effectively increasing the contact area between the cathode material and the electrolyte and improving the structural stability of the cathode material are key to extending battery life.

[0004] Currently, the main approach to address the above problems is to prepare coated or doped single crystal positive electrodes, which is a good solution. However, these methods still have great limitations, such as complex steps, uneven doping, or too high annealing temperature, which can easily cause structural lithium to escape and cause excessive residual lithium on the surface of the structure, affecting material performance. Summary of the Invention

[0005] The purpose of the present invention is to provide a MOF-coated ternary positive electrode material, a preparation method and application thereof; the present invention improves the structural stability, electrical conductivity and safety of the ternary positive electrode material by coating the MOF material Fe2(DHBQ)3 on the surface of the ternary positive electrode material, and the preparation method is simple to operate, has strong feasibility, good coating effect, and can effectively improve the performance of lithium-ion batteries.

[0006] The present invention provides a method for preparing a MOF-coated ternary cathode material, comprising the following steps:

[0007] 1) mixing the MOF material Fe2(DHBQ)3 and Li2O in an organic solvent, separating, drying, and sieving to obtain a mixed powder, and preheating the mixed powder to obtain a modified MOF material Fe2(DHBQ)3;

[0008] 2) mixing a mixed salt solution, a lithium salt solution, and a chelating agent solution and then performing a hydrothermal treatment to obtain a precursor solid solution, wherein the mixed salt solution is a mixed solution of nickel salt, cobalt salt, and manganese salt; and sintering the precursor solid solution to obtain a ternary positive electrode material;

[0009] 3) The modified MOF material Fe2(DHBQ)3 is saturated in a supercritical fluid solvent to obtain a saturated Fe2(DHBQ)3 supercritical fluid solution; the saturated Fe2(DHBQ)3 supercritical fluid solution is then sprayed into the spread ternary cathode material through a throttling device, and after the reaction, a MOF-coated ternary cathode material is obtained.

[0010] In the present invention, the ternary cathode material is spread in the reaction chamber;

[0011] The mixed salt solution may also be a nickel salt solution, a cobalt salt solution and a manganese salt solution directly mixed with the lithium salt solution and the chelating agent solution.

[0012] In the above preparation method, the preheating temperature in step 1) can be 130-180° C. and the time can be 2-5 hours;

[0013] The temperature of the hydrothermal treatment in step 2) may be 140-160°C;

[0014] In step 3), the reaction time may be 10 to 15 minutes.

[0015] In the above-mentioned preparation method, the method for preparing the MOF material Fe2(DHBQ)3 is as follows: the prepared saturated FeCl3 solution is added dropwise into boiling water until the liquid turns reddish brown and heating is stopped to obtain Fe(OH)3 colloid; when the temperature of the Fe(OH)3 colloid drops to 55-75°C, 1.5 times the molar amount of DHBQ ligand is added, and the reaction is carried out in an air atmosphere for 15-35 minutes. After the reaction is completed, it is filtered, dried, and sieved to obtain a dark brown target product powder Fe2(DHBQ)3.

[0016] In the present invention, in the method for preparing the MOF material Fe2(DHBQ)3, the reaction time in the air atmosphere can be specifically 15 minutes, 25 minutes or 35 minutes.

[0017] In the present invention, in the method for preparing the MOF material Fe2(DHBQ)3, the reaction is carried out in an air atmosphere under the action of a dispersing stirrer.

[0018] In the above preparation method, in step 1), the organic solvent is selected from at least one of methanol, ethanol, propanol, isopropanol, polypropylene alcohol, n-butanol, polyethylene glycol, polyvinyl pyrrolidone and acetone;

[0019] The mass ratio of the Fe2(DHBQ)3 to the Li2O may be 200:2.5-15, specifically 200:2.5, 200:10 or 200:2.5-10;

[0020] The total mass of Fe2(DHBQ)3 and Li2O added to every 100 mL of the organic solvent may be 5 to 50 g, specifically 10.5 g / 100 mL, 40.5 g / 100 mL, or 10.5 to 40.5 g / 100 mL.

[0021] In the above preparation method, the molar ratio of the salt in the mixed salt solution to the lithium salt in the lithium salt solution may be 1:1 to 1.25, specifically 1:1.13, 1:1.15, 1:1.18 or 1:1.13 to 1.18;

[0022] The molar ratio of the chelating agent to the second ion may be 1:0.5 to 8, specifically 1:4, 1:5, 1:6, 1:4 to 6, or 1:4 to 8, wherein the second ion is the sum of the amounts of nickel ions, cobalt ions, manganese ions in the nickel salt, cobalt salt, and manganese salt and lithium ions in the lithium salt solution.

[0023] In the above preparation method, the nickel salt is selected from nickel nitrate and / or nickel acetate;

[0024] The cobalt salt is selected from cobalt nitrate and / or cobalt acetate;

[0025] The manganese salt is selected from manganese nitrate and / or manganese acetate;

[0026] The lithium salt is selected from at least one of lithium nitrate, lithium acetate and dilithium oxalate.

[0027] In the above preparation method, the concentration of the chelating agent solution may be 0.5 to 1.2 mol / L;

[0028] The chelating agent is selected from at least one of citric acid, ethylenediaminetetraacetic acid and glycine;

[0029] In the above preparation method, the step of sintering the precursor solid solution is sintering at 800-980°C in an oxygen atmosphere for 10-15 hours; specifically, it can be sintering at 800°C for 12 hours, 850°C for 12 hours or 950°C for 15 hours.

[0030] In the above preparation method, the supercritical fluid solvent is selected from at least one of the following solvents: carbon dioxide, ethane, ethylene and propane;

[0031] The conditions for the solvent to become a supercritical fluid are as follows: the pressure can be 10-25 MPa, and the temperature can be 40-70°C, specifically 25 MPa, 70°C, 15 MPa, 55°C or 10 MPa, 40°C;

[0032] The temperature of the saturated Fe2(DHBQ)3 supercritical fluid solution before being ejected through the throttling device can be 80-110°C, and the ejection pressure can be 0.5-1.5MPa; specifically, it can be 110°C, 1.0MPa, 95°C, 1.5MPa or 8°C, 0.5MPa.

[0033] The present invention also provides the MOF-coated ternary cathode material prepared by the above-mentioned preparation method.

[0034] The MOF-coated ternary cathode material of the present invention is used in the preparation of lithium-ion batteries.

[0035] The present invention further provides a lithium-ion battery, the positive electrode plate of which is prepared by comprising the MOF-coated ternary positive electrode material.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. The MOF material in the preparation method provided by the present invention first has the advantages of high porosity, large specific surface area, and easy functionalization of the pore surface. The modified Fe2(DHBQ)3, as a new MOF material, has a simple structure, excellent conductivity and stability, and can also be used as a positive electrode material for lithium secondary batteries, showing some unique properties in the storage and conversion of electrical properties. Using the modified Fe2(DHBQ)3 as a coating for the ternary positive electrode material, firstly, effectively improves the structural stability of the ternary positive electrode material and enhances the cycle performance; secondly, the high porosity and large specific surface area of ​​the modified Fe2(DHBQ)3 improve the liquid absorption of the electrode and increase the battery's liquid retention; thirdly, the excellent conductivity of the modified Fe2(DHBQ)3 improves the electronic conductivity of the ternary positive electrode material, reduces the internal resistance, and improves the rate performance; finally, the modified Fe2(DHBQ)3 itself can intercalate and deintercalate lithium ions, improving the theoretical specific capacity and first efficiency of the ternary positive electrode material, and also showing excellent rate and cycle performance.

[0038] 2. In the preparation method provided by the present invention, the expansion and decompression process of the supercritical solution containing the coating material through the nozzle is very fast (10 -8 ~10 -5 ), thus instantly achieving uniform conditions within the expanding solution, resulting in the precipitation of a very small and evenly distributed powder. When the supercritical solution is ejected from the nozzle, it expands dramatically, colliding violently with the ternary cathode material, allowing the coating material to be uniformly and stably coated on the surface of the ternary cathode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a SEM image of the uncoated ternary cathode material prepared in Comparative Example 1;

[0040] Figure 2 This is an SEM image of the coated ternary cathode material prepared in Example 1;

[0041] Figure 3 A comparison chart of the rate discharge performance of batteries made from the ternary cathode materials in Comparative Examples 1 and 2 and Example 1;

[0042] Figure 4 The graph compares the cycle performance of batteries made from the ternary positive electrode materials in Comparative Examples 1 and 2 and Example 1. DETAILED DESCRIPTION

[0043] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0044] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0045] The technical solution of the present invention will be described more clearly and completely below with reference to specific embodiments.

[0046] Example 1

[0047] The preparation method of MOF-coated ternary cathode material specifically comprises the following steps:

[0048] 1) Preparation of the MOF material Fe2(DHBQ)3: First, deionized water was boiled in a reaction vessel and kept boiling. The prepared saturated FeCl3 solution was added dropwise to the boiling water until the liquid turned reddish-brown, and heating was stopped to obtain Fe(OH)3 colloid. When the temperature of the Fe(OH)3 colloid dropped to 65°C, 1.5 equivalents of DHBQ ligand (i.e., the molar ratio of Fe(OH)3 colloid to DHBQ ligand was 1:1.5) was added. The mixture was reacted in an air atmosphere with a disperser for 25 minutes. Finally, the target product Fe2(DHBQ)3 was obtained as a dark brown powder after filtration, drying, and sieving.

[0049] 2) Preparation of modified MOF material Fe2(DHBQ)3: 10 g of Fe2(DHBQ)3 and 0.5 g of Li2O were mixed in 100 mL of anhydrous ethanol, stirred continuously until the mixture was uniformly mixed, separated, dried, and sieved to obtain a mixed powder, and the mixed powder was preheated at 165°C for 4 h to obtain the modified MOF material Fe2(DHBQ)3;

[0050] 3) Preparation of ternary positive electrode material: nickel nitrate, cobalt nitrate and manganese nitrate were weighed respectively according to a Ni:Co:Mn molar ratio of 8:1:1 to prepare a mixed salt solution with a concentration of 1 mol / L, a lithium nitrate solution with a concentration of 1.13 mol / L was prepared, and a citric acid solution was prepared (wherein the molar ratio of citric acid to the metal cations in the mixed salt solution and the lithium salt solution was 1:5), and the mixed salt solution, lithium nitrate solution and citric acid solution were mixed in a reactor at a volume ratio of 1:1:1, and the mixed solution in the reactor was dried at a temperature set to 150°C to obtain a ternary positive electrode material precursor solid solution; the precursor solid solution was sintered at a high temperature in a roller kiln with an oxygen atmosphere at a temperature set to 850°C for 12 hours to obtain the ternary positive electrode material.

[0051] 4) Preparation of coated ternary positive electrode materials: CO2 gas is pressurized at 15 MPa and preheated at 55°C into an extraction kettle in which the above-mentioned modified MOF material Fe2(DHBQ)3 is placed in advance, and the pressure and temperature are maintained for 35 minutes to allow the modified MOF material Fe2(DHBQ)3 to reach a saturated state in the supercritical fluid CO2. Then, it is heated to 95°C through a pipeline and the pressure is adjusted to 1.5 MPa by a throttling device. The saturated Fe2(DHBQ)3 supercritical fluid solution is sprayed into the reaction chamber in which the ternary positive electrode material is spread in advance. After 15 minutes, the product in the reaction chamber is collected, which is the ternary positive electrode material coated with the modified MOF material Fe2(DHBQ)3.

[0052] Comparative Example 1

[0053] Compared with Example 1, the MOF material Fe2(DHBQ)3 coating was not modified in this comparative example, and the other steps and raw material compositions were the same as those in Example 1.

[0054] Comparative Example 2

[0055] 1) Providing conventional cladding material alumina;

[0056] 2) Obtaining a precursor solid solution: the steps are the same as those in Example 1 of the present invention;

[0057] 3) Preparation method of coated ternary positive electrode material: A solid solution of alumina and a ternary positive electrode material precursor in a mass ratio of 4:100 is added to ethanol at a rate of 35 g / 100 mL, and the mixture is filtered, dried, and sieved to obtain a mixed powder. The mixed powder is reacted at a temperature of 450°C for 2 hours, and the decomposed nitrogen oxides are cooled to obtain a metal oxide powder, which is then sintered at a high temperature in a roller kiln with an oxygen atmosphere at a temperature of 850°C for 15 hours to obtain an alumina-coated ternary positive electrode material.

[0058] Example 2

[0059] 1) Preparation of the MOF material Fe2(DHBQ)3: First, deionized water was boiled in a reaction vessel and kept boiling. The prepared saturated FeCl3 solution was added dropwise to the boiling water until the liquid turned reddish-brown, and then heating was stopped to obtain Fe(OH)3 colloid. When the temperature of the Fe(OH)3 colloid dropped to 55°C, 1.5 equivalents of DHBQ ligand was added. The mixture was reacted in an air atmosphere with a disperser for 15 minutes. Finally, the target product Fe2(DHBQ)3 was obtained as a dark brown powder after filtration, drying, and sieving.

[0060] 2) Preparation of modified MOF material Fe2(DHBQ)3: 40 g of Fe2(DHBQ)3 and 0.5 g of Li2O were mixed in 100 mL of anhydrous ethanol, stirred continuously until the mixture was uniformly mixed, separated, dried, and sieved to obtain a mixed powder, and the mixed powder was preheated at 130°C for 2 h to obtain the modified MOF material Fe2(DHBQ)3;

[0061] 3) Preparation of ternary positive electrode material: nickel nitrate, cobalt nitrate and manganese nitrate were weighed respectively according to a Ni:Co:Mn molar ratio of 8:1:1 to prepare a mixed salt solution with a concentration of 1 mol / L, a lithium nitrate solution with a concentration of 1.15 mol / L, and a citric acid solution (wherein the molar ratio of citric acid to the total metal cations in the mixed salt solution and the lithium salt solution is 1:4). The mixed salt solution, the lithium nitrate solution and the citric acid solution were mixed in a reactor at a volume ratio of 1:1:1, and the mixed solution in the reactor was dried at a temperature set to 150°C to obtain a ternary positive electrode material precursor solid solution; the precursor solid solution was sintered at a high temperature in a roller kiln with an oxygen atmosphere at a temperature set to 800°C for 12 hours to obtain the ternary positive electrode material.

[0062] 4) Preparation of coated ternary positive electrode materials: CO2 gas is pressurized at 10 MPa and preheated at 40°C into an extraction kettle in which the above-mentioned modified MOF material Fe2(DHBQ)3 is placed in advance, and the pressure and temperature are maintained for 25 minutes to allow the modified MOF material Fe2(DHBQ)3 to reach a saturated state in the supercritical fluid CO2. Then, it is heated to 80°C through a pipeline and the pressure is adjusted to 0.5 MPa by a throttling device. The saturated Fe2(DHBQ)3 supercritical fluid solution is sprayed into the reaction chamber in which the ternary positive electrode material has been spread in advance. After 10 minutes, the product in the reaction chamber is collected, which is the ternary positive electrode material coated with the modified MOF material Fe2(DHBQ)3.

[0063] Example 3

[0064] 1) Preparation of the MOF material Fe2(DHBQ)3: First, deionized water was boiled in a reaction vessel and kept boiling. The prepared saturated FeCl3 solution was added dropwise to the boiling water until the liquid turned reddish-brown, and then heating was stopped to obtain Fe(OH)3 colloid. When the temperature of the Fe(OH)3 colloid dropped to 75°C, 1.5 equivalents of DHBQ ligand was added. The mixture was reacted in an air atmosphere with a disperser for 35 minutes. Finally, the target product Fe2(DHBQ)3 was obtained as a dark brown powder after filtration, drying, and sieving.

[0065] 2) Preparation of modified MOF material Fe2(DHBQ)3: 40 g of Fe2(DHBQ)3 and 0.5 g of Li2O were mixed in 100 mL of anhydrous ethanol, and the mixture was stirred continuously until uniformly mixed. The mixture was separated, dried, and sieved to obtain a mixed powder. The mixed powder was preheated at 180°C for 5 h to obtain the modified MOF material Fe2(DHBQ)3;

[0066] 3) Preparation of ternary positive electrode material: nickel nitrate, cobalt nitrate and manganese nitrate were weighed respectively according to a Ni:Co:Mn molar ratio of 8:1:1 to prepare a mixed salt solution with a concentration of 1 mol / L, a lithium nitrate solution with a concentration of 1.18 mol / L was prepared, and a citric acid solution was prepared (wherein the molar ratio of citric acid to the metal cations in the mixed salt solution and the lithium salt solution was 1:6), and the mixed salt solution, lithium nitrate solution and citric acid solution were mixed in a reactor at a volume ratio of 1:1:1, and the mixed solution in the reactor was dried at a temperature set to 150°C to obtain a ternary positive electrode material precursor solid solution; the precursor solid solution was sintered at a high temperature in a roller kiln with an oxygen atmosphere at a temperature set to 950°C for 15 hours to obtain the ternary positive electrode material.

[0067] 4) Preparation of coated ternary positive electrode materials: CO2 gas is pressurized at 25 MPa and preheated at 70°C into an extraction kettle in which the above-mentioned modified MOF material Fe2(DHBQ)3 is placed in advance, and the pressure and temperature are maintained for 50 minutes to allow the modified MOF material Fe2(DHBQ)3 to reach a saturated state in the supercritical fluid CO2. Then, it is heated to 110°C through a pipeline and the pressure is adjusted to 1.0 MPa by a throttling device. The saturated Fe2(DHBQ)3 supercritical fluid solution is sprayed into the reaction chamber in which the ternary positive electrode material is spread in advance. After 10 minutes, the product in the reaction chamber is collected, which is the ternary positive electrode material coated with the modified MOF material Fe2(DHBQ)3.

[0068] Test Case

[0069] The ternary cathode materials obtained in Example 1 and Comparative Example 1 were characterized by SEM. Figure 1 and Figure 2From the comparison, it can be seen that the surface of the ternary positive electrode material in Example 1 is uniformly coated with the modified MOF material Fe2(DHBQ)3.

[0070] The ternary cathode materials in Example 1 and Comparative Examples 1-2 were made into 3Ah wound soft-pack batteries, and 1C / 2C / 3C rate discharge tests and 45° high temperature cycle tests were performed at a test voltage of 3.0-4.35V. The test results are shown in Table 1 and Figure 3 、 Figure 4 As shown in .

[0071] Depend on Figure 3 、 Figure 4 It can be seen from the test results that the ternary positive electrode material coated with the modified MOF material Fe2(DHBQ)3 in the present invention has significantly improved 2C, 3C rate discharge performance and high temperature cycle performance at high voltage.

[0072] Table 1 3Ah soft pack battery rate discharge and 45° high temperature cycle test results

[0073]

[0074] The test results in Table 1 show that the high-temperature cycle performance of the coated ternary cathode materials in Example 1 and Comparative Example 2 is significantly better than that of the uncoated ternary cathode materials. This is because the uncoated ternary cathode materials are relatively unstable and their structure slowly deteriorates during the cycle, resulting in poor cycle performance. The rate discharge performance of the ternary cathode material coated with the modified MOF material Fe2(DHBQ)3 in Example 1 is significantly better than that of the uncoated ternary cathode material. This is because the high porosity and high conductivity of the modified MOF material Fe2(DHBQ)3 improve the diffusion of lithium ions and reduce impedance. Compared with the conventional coating material alumina and conventional coating method used in Comparative Example 2, the modified MOF material Fe2(DHBQ)3 of the present invention can itself deintercalate and deintercalate lithium ions, thereby improving the theoretical specific capacity and initial efficiency of the ternary positive electrode material, and the coating effect is also better. This is mainly because the present invention utilizes the characteristics of supercritical fluid, which expands violently at the moment of ejection, causing a violent collision with the ternary positive electrode material to be coated, and can quickly coat the surface of the ternary positive electrode material, thereby significantly improving the coating efficiency and effect. The ejection time can also be controlled to control the coating amount. Specifically, using the traditional coating method, an overly thick coating layer will hinder the escape of lithium ions and the contact between the electrolyte and the material, reduce the electrical conductivity, and thus affect the battery capacity and cycle to a certain extent.

[0075] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0076] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for preparing a MOF-coated ternary cathode material, comprising the following steps: 1) Mixing the MOF material Fe2(DHBQ)3 and Li2O in an organic solvent, separating, drying, and sieving to obtain a mixed powder, and preheating the mixed powder to obtain a modified MOF material Fe2(DHBQ)3; The method for preparing the MOF material Fe2(DHBQ)3 is as follows: adding a prepared saturated FeCl3 solution dropwise to boiling water until the liquid turns reddish brown and stopping heating to obtain Fe(OH)3 colloid; when the temperature of the Fe(OH)3 colloid drops to 55-75°C, adding 1.5 times the molar amount of DHBQ ligand, reacting in an air atmosphere for 15-35 minutes, filtering, drying, and sieving after the reaction to obtain a dark brown target product powder Fe2(DHBQ)3; The preheating temperature is 130-180°C and the time is 2-5 hours; 2) mixing a mixed salt solution, a lithium salt solution, and a chelating agent solution and then performing a hydrothermal treatment to obtain a precursor solid solution, wherein the mixed salt solution is a mixed solution of nickel salt, cobalt salt, and manganese salt; and sintering the precursor solid solution to obtain a ternary cathode material; 3) The modified MOF material Fe2(DHBQ)3 is saturated in a supercritical fluid solvent to obtain a saturated Fe2(DHBQ)3 supercritical fluid solution; the saturated Fe2(DHBQ)3 supercritical fluid solution is then sprayed into the spread ternary cathode material through a throttling device, and after reaction, a MOF-coated ternary cathode material is obtained; The supercritical fluid solvent is selected from at least one of the following solvents: carbon dioxide, ethane, ethylene and propane; The conditions for the solvent to become a supercritical fluid are as follows: pressure of 10-25 MPa, temperature of 40-70°C; The temperature of the saturated Fe2(DHBQ)3 supercritical fluid solution before being ejected through the throttling device is 80-110°C, and the ejection pressure is 0.5-1.5 MPa.

2. The preparation method according to claim 1, characterized in that The temperature of the hydrothermal treatment in step 2) is 140-160°C; In step 3), the reaction time is 10 to 15 minutes.

3. The preparation method according to claim 1 or 2, characterized in that In step 1), the organic solvent is selected from at least one of methanol, ethanol, propanol, polypropylene alcohol, n-butanol, polyethylene glycol, polyvinyl pyrrolidone and acetone; The mass ratio of the Fe2(DHBQ)3 to the Li2O is 200:2.5-15; The total mass of Fe2(DHBQ)3 and Li2O is added to every 100 mL of the organic solvent in a quantity of 5 to 50 g.

4. The preparation method according to claim 1, characterized in that The molar ratio of the salt in the mixed salt solution to the lithium salt in the lithium salt solution is 1:1 to 1.25; The molar ratio of the chelating agent to the second ion is 1:0.5-8, and the second ion is the sum of the amount of nickel ions, cobalt ions, manganese ions in the nickel salt, cobalt salt and manganese salt and the lithium ions in the lithium salt solution.

5. The preparation method according to claim 1 or 4, characterized in that The nickel salt is selected from nickel nitrate and / or nickel acetate; The cobalt salt is selected from cobalt nitrate and / or cobalt acetate; The manganese salt is selected from manganese nitrate and / or manganese acetate; The lithium salt is selected from at least one of lithium nitrate, lithium acetate and dilithium oxalate.

6. The preparation method according to claim 1 or 4, characterized in that The concentration of the chelating agent solution is 0.5-1.2 mol / L; The chelating agent is selected from at least one of citric acid, ethylenediaminetetraacetic acid and glycine.

7. The preparation method according to claim 1, characterized in that The step of sintering the precursor solid solution is to sinter the precursor at 800-980° C. for 10-15 hours in an oxygen atmosphere.

8. The MOF-coated ternary cathode material prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the MOF-coated ternary cathode material according to claim 8 in the preparation of lithium-ion batteries.

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