Multi-element carbon source modified lithium iron phosphate material as well as preparation method and application thereof

Abstract

The invention relates to the field of lithium ion batteries, in particular to a multi-element carbon source modified lithium iron phosphate material as well as a preparation method and application thereof, which are used for solving the problem that the application of an existing lithium iron phosphate positive electrode material in a high-power device is limited due to poor cycling stability and rate capability. According to the preparation method, the siloxane grafted metal organic framework, the cobalt nitrate and the copper nitrate are used as modifying substances to modify the lithium iron phosphate, so that the prepared lithium iron phosphate material has high capacity and excellent cycling stability and rate capability, the electrochemical performance of the whole material is excellent, and in practical application, the lithium iron phosphate material has a good application prospect. According to the present invention, the energy density and the cycle life of the lithium ion battery can be significantly improved, the requirements of modern portable electronic equipment, electric vehicles and large-scale energy storage systems on the high-performance lithium ion battery material can be met, and the preparation method has characteristics of simple process, easy control, suitableness for large-scale industrial production, and high application value.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, specifically to multi-element carbon source modified lithium iron phosphate materials, their preparation methods, and applications. Background Technology

[0002] Lithium iron phosphate (LFP) is an important cathode material for lithium-ion batteries, widely used in electric vehicles and energy storage due to its advantages such as high theoretical specific capacity, good safety, and environmental friendliness. However, LFP has inherent defects such as low electronic conductivity and low ion diffusion rate, which leads to rapid capacity decay during high-current charge and discharge, resulting in poor cycle stability and rate performance, thus limiting its application in high-power devices.

[0003] Therefore, developing a multi-element carbon source modified lithium iron phosphate material, its preparation method, and its application are of great practical significance. Summary of the Invention

[0004] To overcome the aforementioned technical problems, the present invention aims to provide multi-element carbon source modified lithium iron phosphate materials, their preparation methods and applications, which solves the problem that the existing lithium iron phosphate cathode materials have poor cycle stability and rate performance, limiting their application in high-power devices.

[0005] The objective of this invention can be achieved through the following technical solutions: In a first aspect, this application provides a method for preparing multi-element carbon source modified lithium iron phosphate materials, including the following steps: Lithium iron phosphate, siloxane-grafted metal-organic framework, and ethanol solution were added to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Nitrogen gas was introduced for protection, and the mixture was stirred for 10-20 minutes at a temperature of 20-25℃ and a stirring rate of 200-300 r / min. The pH was then adjusted to 8-10 with ammonia water, and the temperature was raised to 80-90℃ and the reaction was continued with stirring for 3-5 hours. Cobalt nitrate and copper nitrate were then added, and the reaction was continued with stirring for 2-3 hours. After the reaction was completed, the reaction product was cooled to room temperature and then placed in a vacuum drying oven at a temperature of 90-100℃ for 10-12 hours. Finally, the product was placed in a tube furnace and calcined at a temperature of 350-400℃ for 4-5 hours to obtain multi-element carbon source modified lithium iron phosphate material.

[0006] In a preferred embodiment of the present invention, the ratio of lithium iron phosphate, siloxane-grafted metal-organic framework, ethanol solution, cobalt nitrate and copper nitrate is 10g:0.9-3.7g:100-120mL:5-15mmol:5-15mmol.

[0007] In a preferred embodiment of the present invention, the volume fraction of the ethanol solution is 40-50%; and the mass fraction of the ammonia solution is 25-27%.

[0008] In a preferred embodiment of the present invention, the lithium iron phosphate is prepared by the following steps: Lithium carbonate, iron phosphate, and anhydrous ethanol are added to a ball mill and ball-milled for 8-10 hours at a ball-to-material ratio of 8-10:1 and a ball-milling rate of 250-350 r / min. After ball milling, the resulting slurry is placed in a vacuum drying oven and dried at 80-85℃ for 2-3 hours. Then, it is placed in a tube furnace and calcined at 700-750℃ for 10-12 hours under nitrogen protection. After calcination, the slurry is cooled with the furnace to obtain lithium iron phosphate.

[0009] In a preferred embodiment of the present invention, the ratio of lithium carbonate, iron phosphate and anhydrous ethanol is 0.1 mol: 0.2 mol: 80-90 mL.

[0010] In a preferred embodiment of the present invention, the siloxane-grafted metal-organic framework is prepared by the following steps: Step a1: Add 2-aminoterephthalic acid, zirconium chloride, glacial acetic acid, and N,N-dimethylformamide to a three-necked flask equipped with a stirrer and thermometer. Stir the reaction at 20-25℃ and 200-300 r / min for 10-20 min. Then raise the temperature to 120-130℃ and continue stirring for 20-30 h. After the reaction is complete, cool the reaction product to room temperature, centrifuge, soak the precipitate in anhydrous methanol for 6-8 h, centrifuge again, and place the precipitate in a vacuum drying oven at 80-90℃ for 3-5 h to obtain an amino-metal-organic framework. Step a2: Add the amino-metal-organic framework, 3-chloropropyltriethoxysilane, triethylamine, and toluene to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Purge with nitrogen for protection and stir the reaction at 0-5℃ and a stirring rate of 200-300 r / min for 10-20 min. Then, raise the temperature to 80-90℃ and continue stirring for 6-8 h. After the reaction is complete, cool the reaction product to room temperature, centrifuge, and wash the precipitate 2-3 times with tetrahydrofuran and anhydrous ethanol, respectively. Then, place it in a vacuum drying oven and dry it at 60-70℃ for 3-5 h to obtain the siloxane-grafted metal-organic framework.

[0011] In a preferred embodiment of the present invention, the ratio of 2-aminoterephthalic acid, zirconium chloride, glacial acetic acid and N,N-dimethylformamide in step a1 is 10 mmol: 10 mmol: 5-10 mL: 70-80 mL.

[0012] In a preferred embodiment of the present invention, the ratio of the amino-metal-organic framework, 3-chloropropyltriethoxysilane, triethylamine and toluene in step a2 is 5g:10-20mmol:30-35mmol:80-90mL.

[0013] Secondly, this application provides a multi-element carbon source modified lithium iron phosphate material, which is prepared according to the preparation method of the multi-element carbon source modified lithium iron phosphate material described in the first aspect.

[0014] Thirdly, this application provides the application of multi-element carbon source modified lithium iron phosphate materials as described in the second aspect in lithium-ion batteries.

[0015] The beneficial effects of this invention are: This invention relates to a multi-element carbon source modified lithium iron phosphate material, its preparation method, and its application. By using siloxane-grafted metal-organic frameworks, cobalt nitrate, and copper nitrate as modifiers to modify lithium iron phosphate, a multi-element carbon layer is formed on the outside of the lithium iron phosphate, resulting in a multi-element carbon source modified lithium iron phosphate material. This multi-element carbon source modified lithium iron phosphate material exhibits high capacity, excellent cycle stability, and rate performance. The overall electrochemical performance of the material is excellent. In practical applications, it can significantly improve the energy density and cycle life of lithium-ion batteries, meeting the demands of modern portable electronic devices, electric vehicles, and large-scale energy storage systems for high-performance lithium-ion battery materials. Moreover, the preparation method is simple, easy to control, suitable for large-scale industrial production, and has high application value.

[0016] In the preparation of lithium iron phosphate materials, a siloxane-grafted metal-organic framework (MOF) was first prepared. Utilizing the reaction of 2-aminoterephthalic acid and zirconium chloride, the carboxyl group on 2-aminoterephthalic acid formed a complex with zirconium ions, yielding an amino-MOF. Then, the amino-MOF reacted with 3-chloropropyltriethoxysilane, where the amino group on the amino-MOF reacted with the chlorine atom on the 3-chloropropyltriethoxysilane, introducing a large number of siloxane groups onto the MOF, resulting in a siloxane-grafted MOF. The siloxanes on this siloxane-grafted MOF hydrolyzed to form silanols, which can be grafted onto the surface of lithium iron phosphate, forming an organic coating layer. Simultaneously, the MOF possesses a rich porous structure and high specific surface area, exhibiting excellent adsorption performance, thus successfully adsorbing and loading cobalt and copper hydroxides, achieving doping. Within the metal-organic framework (MOF), after calcination, a carbon layer forms within the MOF, encapsulating lithium iron phosphate (LFP). Hydroxides are converted into oxides at high temperatures, while some cobalt and copper ions directly enter the LFP crystal structure in solid solution form, creating a cationic defect lattice that improves LFP conductivity. The resulting carbon layer possesses excellent electronic conductivity and retains silicon, nitrogen, and zirconium elements, enhancing its reactive sites and stabilizing the carbon layer structure, thus improving the material's cycle stability. Furthermore, the cobalt and copper oxides interact with the carbon layer to form a carbon-oxide composite conductive network, effectively reducing electron transport resistance and further enhancing electron transport capability. This effectively improves the overall electronic conductivity of LFP and suppresses volume changes during charge and discharge, further enhancing the material's cycle performance and rate capability. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1: This embodiment describes a method for preparing a multi-element carbon source modified lithium iron phosphate material, including the following steps: Step S1: Add 0.1 mol lithium carbonate, 0.2 mol iron phosphate and 80 mL anhydrous ethanol to a ball mill and ball mill for 8 h at a ball-to-material ratio of 8:1 and a ball milling rate of 250 r / min. After ball milling, place the resulting ball mill slurry in a vacuum drying oven and dry it at 80 °C for 2 h. Then place it in a tube furnace, purge it with nitrogen for protection, and calcine it at 700 °C for 10 h. After that, cool it with the furnace to obtain lithium iron phosphate. Step S2: 10 mmol of 2-aminoterephthalic acid, 10 mmol of zirconium chloride, 5 mL of glacial acetic acid and 70 mL of N,N-dimethylformamide were added to a three-necked flask equipped with a stirrer and a thermometer. The mixture was stirred at 20 °C and 200 r / min for 10 min. The temperature was then raised to 120 °C and the mixture was stirred for another 20 h. After the reaction was completed, the product was cooled to room temperature and centrifuged. The precipitate was soaked in anhydrous methanol for 6 h and then centrifuged again. The precipitate was placed in a vacuum drying oven and dried at 80 °C for 3 h to obtain an amino-metal-organic framework. Step S3: Add 5g of amino-metal-organic framework, 10mmol of 3-chloropropyltriethoxysilane, 30mmol of triethylamine and 80mL of toluene to a three-necked flask equipped with a stirrer, thermometer and gas delivery tube. Purge with nitrogen for protection and stir at 0℃ and 200r / min for 10min. Then raise the temperature to 80℃ and continue stirring for 6h. After the reaction is completed, cool the reaction product to room temperature and centrifuge. Wash the precipitate twice with tetrahydrofuran and anhydrous ethanol, then place it in a vacuum drying oven and dry at 60℃ for 3h to obtain siloxane-grafted metal-organic framework. Step S4: 10g of lithium iron phosphate, 0.9g of siloxane-grafted metal-organic framework, and 100mL of 40% ethanol solution were added to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Nitrogen gas was introduced for protection, and the mixture was stirred at 20℃ and 200r / min for 10min. The pH was then adjusted to 8 with 25% ammonia. The mixture was then heated to 80℃ and stirred for 3h. 5mmol of cobalt nitrate and 5mmol of copper nitrate were added, and the mixture was stirred for another 2h. After the reaction was completed, the product was cooled to room temperature and then placed in a vacuum drying oven at 90℃ for 10h. Finally, it was placed in a tube furnace and calcined at 350℃ for 4h to obtain multi-element carbon source modified lithium iron phosphate material.

[0019] Example 2: This embodiment describes a method for preparing a multi-element carbon source modified lithium iron phosphate material, including the following steps: Step S1: Add 0.1 mol lithium carbonate, 0.2 mol iron phosphate and 85 mL anhydrous ethanol to a ball mill and ball mill for 9 h at a ball-to-material ratio of 9:1 and a ball milling rate of 300 r / min. After ball milling, place the resulting ball mill slurry in a vacuum drying oven and dry it at 82℃ for 2.5 h. Then place it in a tube furnace, purge it with nitrogen, and calcine it at 725℃ for 11 h. After that, cool it with the furnace to obtain lithium iron phosphate. Step S2: 10 mmol of 2-aminoterephthalic acid, 10 mmol of zirconium chloride, 8 mL of glacial acetic acid and 75 mL of N,N-dimethylformamide were added to a three-necked flask equipped with a stirrer and a thermometer. The mixture was stirred at 22 °C and 250 r / min for 15 min. The temperature was then raised to 125 °C and the mixture was stirred for 25 h. After the reaction was completed, the reaction product was cooled to room temperature and centrifuged. The precipitate was soaked in anhydrous methanol for 7 h and then centrifuged again. The precipitate was placed in a vacuum drying oven and dried at 85 °C for 4 h to obtain an amino-metal-organic framework. Step S3: Add 5g of amino-metal-organic framework, 15mmol of 3-chloropropyltriethoxysilane, 32mmol of triethylamine and 85mL of toluene to a three-necked flask equipped with a stirrer, thermometer and gas delivery tube. Purge with nitrogen for protection and stir at 3℃ and 250r / min for 15min. Then raise the temperature to 85℃ and continue stirring for 7h. After the reaction is completed, cool the reaction product to room temperature and centrifuge. Wash the precipitate twice with tetrahydrofuran and anhydrous ethanol, then place it in a vacuum drying oven and dry at 65℃ for 4h to obtain siloxane-grafted metal-organic framework. Step S4: 10g of lithium iron phosphate, 2.3g of siloxane-grafted metal-organic framework, and 110mL of 45% ethanol solution were added to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Nitrogen gas was introduced for protection, and the mixture was stirred at 22℃ and 250r / min for 15min. The pH was then adjusted to 9 with 26% ammonia solution, and the mixture was heated to 85℃ and stirred for 4h. Then, 10mmol of cobalt nitrate and 10mmol of copper nitrate were added, and the mixture was stirred for another 2.5h. After the reaction was completed, the product was cooled to room temperature and then placed in a vacuum drying oven at 95℃ for 11h. Finally, it was placed in a tube furnace and calcined at 375℃ for 4.5h to obtain multi-element carbon source modified lithium iron phosphate material.

[0020] Example 3: This embodiment describes a method for preparing a multi-element carbon source modified lithium iron phosphate material, including the following steps: Step S1: Add 0.1 mol lithium carbonate, 0.2 mol iron phosphate and 90 mL anhydrous ethanol to a ball mill and ball mill for 10 h at a ball-to-material ratio of 10:1 and a ball milling rate of 350 r / min. After ball milling, place the resulting ball mill slurry in a vacuum drying oven and dry it at 85 °C for 3 h. Then place it in a tube furnace, purge it with nitrogen for protection, and calcine it at 750 °C for 12 h. After that, cool it with the furnace to obtain lithium iron phosphate. Step S2: 10 mmol of 2-aminoterephthalic acid, 10 mmol of zirconium chloride, 10 mL of glacial acetic acid and 80 mL of N,N-dimethylformamide were added to a three-necked flask equipped with a stirrer and a thermometer. The mixture was stirred at 25 °C and a stirring rate of 300 r / min for 20 min. Then, the temperature was raised to 130 °C and the mixture was stirred for another 30 h. After the reaction was completed, the reaction product was cooled to room temperature and centrifuged. The precipitate was soaked in anhydrous methanol for 8 h and then centrifuged again. The precipitate was placed in a vacuum drying oven and dried at 90 °C for 5 h to obtain an amino-metal-organic framework. Step S3: Add 5g of amino-metal-organic framework, 20mmol of 3-chloropropyltriethoxysilane, 35mmol of triethylamine and 90mL of toluene to a three-necked flask equipped with a stirrer, thermometer and gas delivery tube. Purge with nitrogen for protection and stir at 5℃ and 300r / min for 20min. Then raise the temperature to 90℃ and continue stirring for 8h. After the reaction is completed, cool the reaction product to room temperature and centrifuge. Wash the precipitate three times with tetrahydrofuran and anhydrous ethanol, and then place it in a vacuum drying oven and dry at 70℃ for 5h to obtain siloxane-grafted metal-organic framework. Step S4: 10g of lithium iron phosphate, 3.7g of siloxane-grafted metal-organic framework, and 120mL of 50% ethanol solution were added to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Nitrogen gas was introduced for protection, and the mixture was stirred at 25℃ and 300r / min for 20min. The pH was then adjusted to 10 with 27% ammonia. The mixture was then heated to 90℃ and stirred for 5h. 15mmol of cobalt nitrate and 15mmol of copper nitrate were added, and the mixture was stirred for another 3h. After the reaction was completed, the product was cooled to room temperature and then placed in a vacuum drying oven at 100℃ for 12h. Finally, it was placed in a tube furnace and calcined at 400℃ for 5h to obtain multi-element carbon source modified lithium iron phosphate material.

[0021] Comparative Example 1: This comparative example illustrates a method for preparing a lithium iron phosphate material, comprising the following steps: 0.1 mol lithium carbonate, 0.2 mol iron phosphate, and 90 mL anhydrous ethanol were added to a ball mill and ball-milled for 10 h at a ball-to-material ratio of 10:1 and a ball-milling rate of 350 r / min. After ball milling, the resulting slurry was placed in a vacuum drying oven and dried at 85 °C for 3 h. Then, it was placed in a tube furnace, protected by nitrogen, and calcined at 750 °C for 12 h. After that, it was cooled with the furnace to obtain lithium iron phosphate material.

[0022] Comparative Example 2: This comparative example illustrates a method for preparing a carbon-source modified lithium iron phosphate material, comprising the following steps: Step S1: Add 0.1 mol lithium carbonate, 0.2 mol iron phosphate and 90 mL anhydrous ethanol to a ball mill and ball mill for 10 h at a ball-to-material ratio of 10:1 and a ball milling rate of 350 r / min. After ball milling, place the resulting ball mill slurry in a vacuum drying oven and dry it at 85 °C for 3 h. Then place it in a tube furnace, purge it with nitrogen for protection, and calcine it at 750 °C for 12 h. After that, cool it with the furnace to obtain lithium iron phosphate. Step S2: Add 10g of lithium iron phosphate, 3.7g of glucose, and 120mL of 50% ethanol solution to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Purge with nitrogen for protection and stir at 25℃ and 300r / min for 20min. Then raise the temperature to 90℃ and continue stirring for 5h. After the reaction is complete, cool the reaction product to room temperature and place it in a vacuum drying oven at 100℃ for 12h. Then place it in a tube furnace and calcine at 400℃ for 5h to obtain carbon source modified lithium iron phosphate material.

[0023] Comparative Example 3: This comparative example illustrates a method for preparing a multi-element carbon source-modified lithium iron phosphate material, comprising the following steps: Step S1: Add 0.1 mol lithium carbonate, 0.2 mol iron phosphate and 90 mL anhydrous ethanol to a ball mill and ball mill for 10 h at a ball-to-material ratio of 10:1 and a ball milling rate of 350 r / min. After ball milling, place the resulting ball mill slurry in a vacuum drying oven and dry it at 85 °C for 3 h. Then place it in a tube furnace, purge it with nitrogen for protection, and calcine it at 750 °C for 12 h. After that, cool it with the furnace to obtain lithium iron phosphate. Step S2: 10g of lithium iron phosphate, 3.7g of glucose, and 120mL of 50% ethanol solution were added to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Nitrogen gas was introduced for protection, and the mixture was stirred at 25℃ and 300r / min for 20min. The pH was then adjusted to 10 with 27% ammonia solution. The mixture was then heated to 90℃ and stirred for 5h. 15mmol of cobalt nitrate and 15mmol of copper nitrate were added, and the mixture was stirred for another 3h. After the reaction was completed, the product was cooled to room temperature and then placed in a vacuum drying oven at 100℃ for 12h. Finally, it was placed in a tube furnace and calcined at 400℃ for 5h to obtain multi-element carbon source modified lithium iron phosphate material.

[0024] Comparative Example 4: This comparative example illustrates a method for preparing a multi-element carbon source-modified lithium iron phosphate material, comprising the following steps: Step S1: Add 0.1 mol lithium carbonate, 0.2 mol iron phosphate and 90 mL anhydrous ethanol to a ball mill and ball mill for 10 h at a ball-to-material ratio of 10:1 and a ball milling rate of 350 r / min. After ball milling, place the resulting ball mill slurry in a vacuum drying oven and dry it at 85 °C for 3 h. Then place it in a tube furnace, purge it with nitrogen for protection, and calcine it at 750 °C for 12 h. After that, cool it with the furnace to obtain lithium iron phosphate. Step S2: 10 mmol of 2-aminoterephthalic acid, 10 mmol of zirconium chloride, 10 mL of glacial acetic acid and 80 mL of N,N-dimethylformamide were added to a three-necked flask equipped with a stirrer and a thermometer. The mixture was stirred at 25 °C and a stirring rate of 300 r / min for 20 min. Then, the temperature was raised to 130 °C and the mixture was stirred for another 30 h. After the reaction was completed, the reaction product was cooled to room temperature and centrifuged. The precipitate was soaked in anhydrous methanol for 8 h and then centrifuged again. The precipitate was placed in a vacuum drying oven and dried at 90 °C for 5 h to obtain an amino-metal-organic framework. Step S3: Add 5g of amino-metal-organic framework, 20mmol of 3-chloropropyltriethoxysilane, 35mmol of triethylamine and 90mL of toluene to a three-necked flask equipped with a stirrer, thermometer and gas delivery tube. Purge with nitrogen for protection and stir at 5℃ and 300r / min for 20min. Then raise the temperature to 90℃ and continue stirring for 8h. After the reaction is completed, cool the reaction product to room temperature and centrifuge. Wash the precipitate three times with tetrahydrofuran and anhydrous ethanol, and then place it in a vacuum drying oven and dry at 70℃ for 5h to obtain siloxane-grafted metal-organic framework. Step S4: Add 10g of lithium iron phosphate, 3.7g of siloxane-grafted metal-organic framework, and 120mL of 50% ethanol solution to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Purge with nitrogen for protection and stir at 25℃ and 300r / min for 20min. Then adjust the pH to 10 with 27% ammonia solution. Continue stirring at 90℃ for 5h. After the reaction, cool the product to room temperature and place it in a vacuum drying oven at 100℃ for 12h. Then place it in a tube furnace and calcine at 400℃ for 5h to obtain multi-element carbon source modified lithium iron phosphate material.

[0025] Comparative Example 5: This comparative example illustrates a method for preparing a multi-element carbon source-modified lithium iron phosphate material, comprising the following steps: Step S1: Add 0.1 mol lithium carbonate, 0.2 mol iron phosphate and 90 mL anhydrous ethanol to a ball mill and ball mill for 10 h at a ball-to-material ratio of 10:1 and a ball milling rate of 350 r / min. After ball milling, place the resulting ball mill slurry in a vacuum drying oven and dry it at 85 °C for 3 h. Then place it in a tube furnace, purge it with nitrogen for protection, and calcine it at 750 °C for 12 h. After that, cool it with the furnace to obtain lithium iron phosphate. Step S2: 10 mmol of 2-aminoterephthalic acid, 10 mmol of zirconium chloride, 10 mL of glacial acetic acid and 80 mL of N,N-dimethylformamide were added to a three-necked flask equipped with a stirrer and a thermometer. The mixture was stirred at 25 °C and a stirring rate of 300 r / min for 20 min. Then, the temperature was raised to 130 °C and the mixture was stirred for another 30 h. After the reaction was completed, the reaction product was cooled to room temperature and centrifuged. The precipitate was soaked in anhydrous methanol for 8 h and then centrifuged again. The precipitate was placed in a vacuum drying oven and dried at 90 °C for 5 h to obtain an amino-metal-organic framework. Step S3: 10g of lithium iron phosphate, 3.7g of amino-metal-organic framework, and 120mL of 50% ethanol solution were added to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Nitrogen gas was introduced for protection, and the mixture was stirred at 25℃ and 300r / min for 20min. The pH was then adjusted to 10 with 27% ammonia solution, and the mixture was stirred at 90℃ for 5h. 15mmol of cobalt nitrate and 15mmol of copper nitrate were added, and the mixture was stirred for another 3h. After the reaction was completed, the product was cooled to room temperature and then placed in a vacuum drying oven at 100℃ for 12h. Finally, it was placed in a tube furnace and calcined at 400℃ for 5h to obtain multi-element carbon source modified lithium iron phosphate material.

[0026] Performance testing The lithium iron phosphate materials from Examples 1-3 and Comparative Examples 1-5 were coated onto aluminum foil and then placed in a vacuum drying oven at 120°C for 12 hours. After drying, they were cut into 16mm diameter discs to obtain positive electrode sheets. CR2025 coin cells were then assembled using lithium foil as the negative electrode sheet, Celgard 2400 as the separator, and 1M LiPF6 (EC:DMC:DEC=1:1:1, v / v / v) as the electrolyte. The cells were allowed to stand for 12 hours before performance testing. The test results are shown in Table 1 below.

[0027] Table 1: Electrochemical Performance Test Results of Lithium Iron Phosphate Materials

[0028] Referring to the data in the table above, based on the data from Examples 1-3, it can be seen that the lithium iron phosphate material of this application has excellent electrochemical performance. Specifically, a comparison between Example 3 and Comparative Example 1 shows that coating with a multi-element carbon source can significantly improve the discharge specific capacity and capacity retention of the lithium iron phosphate material; a comparison between Example 3 and Comparative Example 2 shows that doping the carbon source with multiple elements can significantly improve the discharge specific capacity and capacity retention of the lithium iron phosphate material; a comparison between Example 3 and Comparative Example 3 shows that using siloxane-grafted metal-organic frameworks as a carbon source has a better performance improvement effect than using glucose as a carbon source; a comparison between Example 3 and Comparative Example 4 shows that doping with cobalt and copper can significantly improve the discharge specific capacity of the lithium iron phosphate material; and a comparison between Example 3 and Comparative Example 5 shows that grafting with siloxane groups can significantly improve the capacity retention of the lithium iron phosphate material.

[0029] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0030] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in this application, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing multi-element carbon source modified lithium iron phosphate materials, characterized in that, Includes the following steps: Lithium iron phosphate, siloxane-grafted metal-organic framework, and ethanol solution were added to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Nitrogen gas was introduced for protection, and the mixture was stirred for 10-20 minutes at a temperature of 20-25℃ and a stirring rate of 200-300 r / min. The pH was then adjusted to 8-10 with ammonia water, and the temperature was raised to 80-90℃ and the reaction was continued with stirring for 3-5 hours. Cobalt nitrate and copper nitrate were then added, and the reaction was continued with stirring for 2-3 hours. After the reaction was completed, the reaction product was cooled to room temperature and then placed in a vacuum drying oven at a temperature of 90-100℃ for 10-12 hours. Finally, the product was placed in a tube furnace and calcined at a temperature of 350-400℃ for 4-5 hours to obtain multi-element carbon source modified lithium iron phosphate material.

2. The preparation method of the multi-element carbon source modified lithium iron phosphate material according to claim 1, characterized in that, The ratio of lithium iron phosphate, siloxane-grafted metal-organic framework, ethanol solution, cobalt nitrate, and copper nitrate is 10g:0.9-3.7g:100-120mL:5-15mmol:5-15mmol.

3. The preparation method of the multi-element carbon source modified lithium iron phosphate material according to claim 1, characterized in that, The volume fraction of the ethanol solution is 40-50%; the mass fraction of the ammonia solution is 25-27%.

4. The preparation method of the multi-element carbon source modified lithium iron phosphate material according to claim 1, characterized in that, The lithium iron phosphate is prepared by the following steps: Lithium carbonate, iron phosphate, and anhydrous ethanol are added to a ball mill and ball-milled for 8-10 hours at a ball-to-material ratio of 8-10:1 and a ball-milling rate of 250-350 r / min. After ball milling, the resulting slurry is placed in a vacuum drying oven and dried at 80-85℃ for 2-3 hours. Then, it is placed in a tube furnace and calcined at 700-750℃ for 10-12 hours under nitrogen protection. After calcination, the slurry is cooled with the furnace to obtain lithium iron phosphate.

5. The preparation method of the multi-element carbon source modified lithium iron phosphate material according to claim 4, characterized in that, The ratio of lithium carbonate, iron phosphate, and anhydrous ethanol is 0.1 mol: 0.2 mol: 80-90 mL.

6. The method for preparing multi-element carbon source modified lithium iron phosphate material according to claim 1, characterized in that, The siloxane-grafted metal-organic framework was prepared by the following steps: Step a1: Add 2-aminoterephthalic acid, zirconium chloride, glacial acetic acid, and N,N-dimethylformamide to a three-necked flask equipped with a stirrer and thermometer. Stir the reaction at 20-25℃ and 200-300 r / min for 10-20 min. Then raise the temperature to 120-130℃ and continue stirring for 20-30 h. After the reaction is complete, cool the reaction product to room temperature, centrifuge, soak the precipitate in anhydrous methanol for 6-8 h, centrifuge again, and place the precipitate in a vacuum drying oven at 80-90℃ for 3-5 h to obtain an amino-metal-organic framework. Step a2: Add the amino-metal-organic framework, 3-chloropropyltriethoxysilane, triethylamine, and toluene to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Purge with nitrogen for protection and stir the reaction at 0-5℃ and a stirring rate of 200-300 r / min for 10-20 min. Then, raise the temperature to 80-90℃ and continue stirring for 6-8 h. After the reaction is complete, cool the reaction product to room temperature, centrifuge, and wash the precipitate 2-3 times with tetrahydrofuran and anhydrous ethanol, respectively. Then, place it in a vacuum drying oven and dry it at 60-70℃ for 3-5 h to obtain the siloxane-grafted metal-organic framework.

7. The preparation method of the multi-element carbon source modified lithium iron phosphate material according to claim 6, characterized in that, The ratio of 2-aminoterephthalic acid, zirconium chloride, glacial acetic acid, and N,N-dimethylformamide in step a1 is 10 mmol: 10 mmol: 5-10 mL: 70-80 mL.

8. The method for preparing multi-element carbon source modified lithium iron phosphate material according to claim 6, characterized in that, The ratio of the amino-metal-organic framework, 3-chloropropyltriethoxysilane, triethylamine and toluene in step a2 is 5g:10-20mmol:30-35mmol:80-90mL.

9. A multi-element carbon source modified lithium iron phosphate material, characterized in that, The multi-element carbon source modified lithium iron phosphate material is prepared by the preparation method of the multi-element carbon source modified lithium iron phosphate material according to any one of claims 1-8.

10. The application of the multi-element carbon source modified lithium iron phosphate material according to claim 9 in lithium-ion batteries.

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