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

Abstract

The present application relates to the field of lithium ion batteries, in particular to a multi-element carbon source modified lithium iron phosphate material and its preparation method and application, for solving the problems of poor cycle stability and rate performance of existing lithium iron phosphate positive materials, which limits the application in high-power devices; the preparation method uses siloxane grafted metal organic framework, cobalt nitrate and copper nitrate as modification materials to modify lithium iron phosphate, so that the prepared lithium iron phosphate material has high capacity and excellent cycle stability and rate performance, the overall material has excellent electrochemical performance, in practical application, the energy density and cycle life of lithium ion battery can be significantly improved, which meets the demand of modern portable electronic equipment, electric vehicles and large-scale energy storage system for high-performance lithium ion battery material, and the preparation method is simple, easy to control, suitable for large-scale industrial production, and has high application value.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion batteries, in particular to a multi-element carbon source modified lithium iron phosphate material and a preparation method and application thereof. BACKGROUND

[0002] As an important lithium ion battery positive electrode material, lithium iron phosphate has been widely used in electric vehicles, energy storage and other fields due to its high theoretical specific capacity, good safety and environmental friendliness. However, lithium iron phosphate has inherent defects of low electronic conductivity and ion diffusion rate, which leads to fast capacity decay of the battery during high-current charging and discharging, resulting in poor cycle stability and rate performance, which limits its application in high-power devices.

[0003] Therefore, it is of great practical significance to develop a multi-element carbon source modified lithium iron phosphate material and a preparation method and application thereof. SUMMARY

[0004] In order to overcome the above technical problems, the purpose of the present application is to provide a multi-element carbon source modified lithium iron phosphate material and a preparation method and application thereof, which solves the problem of poor cycle stability and rate performance of the existing lithium iron phosphate positive electrode material, which limits its application in high-power devices.

[0005] The purpose of the present application can be achieved by the following technical solutions:

[0006] In a first aspect, the present application provides a preparation method of a multi-element carbon source modified lithium iron phosphate material, comprising the following steps:

[0007] Lithium iron phosphate, siloxane grafted metal organic framework and ethanol solution are added to a three-necked flask equipped with a stirrer, a thermometer and a gas inlet tube, and nitrogen is introduced for protection. The reaction is stirred at a temperature of 20-25℃ and a stirring rate of 200-300r / min for 10-20min, then adjusted to pH 8-10 with ammonia water, and then continued to stir at a temperature of 80-90℃ for 3-5h. Then, cobalt nitrate and copper nitrate are added and the reaction is continued to stir for 2-3h. After the reaction is completed, the reaction product is cooled to room temperature, then placed in a vacuum drying oven and dried at a temperature of 90-100℃ for 10-12h, and then placed in a tube furnace and calcined at a temperature of 350-400℃ for 4-5h to obtain a multi-element carbon source modified lithium iron phosphate material.

[0008] As a preferred embodiment of the present application, the amount 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.

[0009] As a preferred embodiment of the present application, the volume fraction of the ethanol solution is 40-50%; the mass fraction of the ammonia water is 25-27%.

[0010] As a preferred embodiment of the present application, the lithium carbonate, the iron phosphate and the anhydrous ethanol are added into a ball mill, and ball milling is carried out at a ball-to-material ratio of 8-10:1 and a ball milling speed of 250-350 r / min for 8-10 h. After the ball milling, the obtained ball milling slurry is placed in a vacuum drying box and dried at a temperature of 80-85℃ for 2-3 h. Then, the dried product is placed in a tube furnace, nitrogen is introduced for protection, and calcination is carried out at a temperature of 700-750℃ for 10-12 h. After that, the furnace is cooled down, and the lithium iron phosphate is obtained.

[0011] As a preferred embodiment of the present application, the lithium carbonate, the iron phosphate and the anhydrous ethanol are added into a ball mill, and ball milling is carried out at a ball-to-material ratio of 8-10:1 and a ball milling speed of 250-350 r / min for 8-10 h. After the ball milling, the obtained ball milling slurry is placed in a vacuum drying box and dried at a temperature of 80-85℃ for 2-3 h. Then, the dried product is placed in a tube furnace, nitrogen is introduced for protection, and calcination is carried out at a temperature of 700-750℃ for 10-12 h. After that, the furnace is cooled down, and the lithium iron phosphate is obtained.

[0012] As a preferred embodiment of the present application, the lithium carbonate, the iron phosphate and the anhydrous ethanol are added into a ball mill, and ball milling is carried out at a ball-to-material ratio of 8-10:1 and a ball milling speed of 250-350 r / min for 8-10 h. After the ball milling, the obtained ball milling slurry is placed in a vacuum drying box and dried at a temperature of 80-85℃ for 2-3 h. Then, the dried product is placed in a tube furnace, nitrogen is introduced for protection, and calcination is carried out at a temperature of 700-750℃ for 10-12 h. After that, the furnace is cooled down, and the lithium iron phosphate is obtained.

[0013] As a preferred embodiment of the present application, the siloxane-grafted metal organic framework is prepared by the following steps:

[0014] Step a1: 2-amino terephthalic acid, zirconium chloride, glacial acetic acid and N,N-dimethylformamide are added into a three-necked flask equipped with a stirrer and a thermometer, and stirring is carried out at a temperature of 20-25℃ and a stirring speed of 200-300 r / min for 10-20 min. Then, the temperature is raised to 120-130℃, and stirring is continued for 20-30 h. After the reaction, the reaction product is cooled to room temperature, and then centrifuged. The precipitate is soaked in anhydrous methanol for 6-8 h, and then centrifuged. The precipitate is placed in a vacuum drying box and dried at a temperature of 80-90℃ for 3-5 h to obtain an ammonia-grafted metal organic framework.

[0015] Step a2: the ammonia-grafted metal organic framework, 3-chloropropyltriethoxysilane, triethylamine and toluene are added into a three-necked flask equipped with a stirrer, a thermometer and a gas inlet tube, and nitrogen is introduced for protection. Stirring is carried out at a temperature of 0-5℃ and a stirring speed of 200-300 r / min for 10-20 min. Then, the temperature is raised to 80-90℃, and stirring is continued for 6-8 h. After the reaction, the reaction product is cooled to room temperature, and then centrifuged. The precipitate is washed with tetrahydrofuran and anhydrous ethanol for 2-3 times, and then placed in a vacuum drying box and dried at a temperature of 60-70℃ for 3-5 h to obtain a siloxane-grafted metal organic framework.

[0016] As a preferred embodiment of the present application, the amount ratio of the 2-amino terephthalic acid, zirconium chloride, glacial acetic acid and N,N-dimethylformamide in step a1 is 10 mmol: 10 mmol: 5-10 mL: 70-80 mL.

[0017] As a preferred embodiment of the present application, the amount ratio of the amino metal organic framework, 3-chloropropyltriethoxysilane, triethylamine and toluene in step a2 is 5 g: 10-20 mmol: 30-35 mmol: 80-90 mL.

[0018] In a second aspect, the present application provides a multi-element carbon source modified modified lithium iron phosphate material, which is prepared according to the preparation method of the multi-element carbon source modified modified lithium iron phosphate material in the first aspect.

[0019] In a third aspect, the present application provides the application of the multi-element carbon source modified modified lithium iron phosphate material in the second aspect in a lithium ion battery.

[0020] The present application has the following beneficial effects:

[0021] The multi-element carbon source modified modified lithium iron phosphate material and the preparation method and application thereof have the following beneficial effects: the lithium iron phosphate is modified by using siloxane grafted metal organic framework, cobalt nitrate and copper nitrate as modification materials, a carbon layer of multiple elements is realized on the external wrapping of the lithium iron phosphate, and a multi-element carbon source modified modified lithium iron phosphate material is obtained; the multi-element carbon source modified modified lithium iron phosphate material has high capacity and excellent cycle stability and rate performance, and the electrochemical performance of the overall material is excellent; in practical application, the energy density and cycle life of the lithium ion battery can be significantly improved, the demand of modern portable electronic equipment, electric vehicles and large-scale energy storage systems for high-performance lithium ion battery materials can be met, the preparation method is simple and easy to control, is suitable for large-scale industrial production, and has high application value.

[0022] The process for preparing the lithium iron phosphate material first prepares a siloxane grafted metal organic framework. A 2-amino terephthalic acid and zirconium chloride are reacted. The carboxyl group on the 2-amino terephthalic acid forms a complex with zirconium ions to obtain an amino metal organic framework. The amino metal organic framework and 3-chloropropyl triethoxysilane are reacted. The amino group on the amino metal organic framework reacts with the chlorine atom on the 3-chloropropyl triethoxysilane to introduce a large number of siloxane groups to the metal organic framework to obtain the siloxane grafted metal organic framework. The siloxane on the siloxane grafted metal organic framework hydrolyzes to form silanol which can be grafted to the surface of the lithium iron phosphate to form an organic coating layer. Meanwhile, the metal organic framework has a rich pore structure and high specific surface area characteristics and has good adsorption performance to adsorb and load cobalt and copper hydroxide and successfully dope the metal organic framework. After calcination, the metal organic framework forms a carbon layer to wrap the lithium iron phosphate. The hydroxide is converted into an oxide at high temperature. Meanwhile, part of the cobalt and copper ions directly enter the crystal structure of the lithium iron phosphate in the form of a solid solution to form a cationic defect lattice, which improves the conductivity of the lithium iron phosphate. The formed carbon layer has good electronic conductivity and also retains silicon elements, nitrogen, and zirconium elements to enhance the reactive active sites and stabilize the carbon layer structure to improve the cycle stability of the material. Meanwhile, the cobalt and copper oxides and the carbon layer cooperate to form a "carbon-oxide" composite conductive network to effectively reduce the electron transport resistance, further improve the electron transport capacity, effectively improve the overall electronic conductivity of the lithium iron phosphate, and effectively inhibit the volume change of the lithium iron phosphate during the charging and discharging process to further enhance the cycle performance and rate performance of the material. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0024] Embodiment 1

[0025] The present embodiment is a preparation method of a multi-element carbon source modified lithium iron phosphate material, comprising the following steps:

[0026] Step S1: 0.1 mol of lithium carbonate, 0.2 mol of iron phosphate and 80 mL of anhydrous ethanol were added to a ball mill, and ball milling was performed at a ball-to-material ratio of 8:1 and a ball milling speed of 250 r / min for 8 h. After the ball milling, the obtained ball milling slurry was placed in a vacuum drying box and dried at a temperature of 80 °C for 2 h, and then placed in a tube furnace, and calcined at a temperature of 700 °C for 10 h under the protection of nitrogen, and then cooled in the furnace to obtain lithium iron phosphate;

[0027] Step S2: 10 mmol of 2-amino terephthalic 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, and stirred at a temperature of 20 °C and a stirring speed of 200 r / min for 10 min. Then the temperature was increased to 120 °C and the reaction was continued for 20 h. After the reaction, the reaction product was cooled to room temperature, and then centrifuged. The precipitate was soaked in anhydrous methanol for 6 h, and then centrifuged. The precipitate was placed in a vacuum drying box and dried at a temperature of 80 °C for 3 h to obtain an amine metal organic framework;

[0028] Step S3: 5 g of the amine metal organic framework, 10 mmol of 3-chloropropyl triethoxysilane, 30 mmol of triethylamine and 80 mL of toluene were added to a three-necked flask equipped with a stirrer, a thermometer and a gas inlet tube, and stirred at a temperature of 0 °C and a stirring speed of 200 r / min for 10 min. Then the temperature was increased to 80 °C and the reaction was continued for 6 h. After the reaction, the reaction product was cooled to room temperature, and then centrifuged. The precipitate was washed with tetrahydrofuran and anhydrous ethanol for 2 times, and then placed in a vacuum drying box and dried at a temperature of 60 °C for 3 h to obtain a siloxane grafted metal organic framework;

[0029] Step S4: 10 g of lithium iron phosphate, 0.9 g of the siloxane grafted metal organic framework and 100 mL of an ethanol solution with a volume fraction of 40% were added to a three-necked flask equipped with a stirrer, a thermometer and a gas inlet tube, and stirred at a temperature of 20 °C and a stirring speed of 200 r / min for 10 min. Then the pH was adjusted to 8 with 25% ammonia water, and then the temperature was increased to 80 °C and the reaction was continued for 3 h. Then 5 mmol of cobalt nitrate and 5 mmol of copper nitrate were added and the reaction was continued for 2 h. After the reaction, the reaction product was cooled to room temperature, and then placed in a vacuum drying box and dried at a temperature of 90 °C for 10 h. Then it was placed in a tube furnace and calcined at a temperature of 350 °C for 4 h to obtain a multi-element carbon source modified lithium iron phosphate material.

[0030] Example 2:

[0031] The embodiment is a preparation method of a multi-element carbon source modified modified lithium iron phosphate material, comprising the following steps:

[0032] Step S1: 0.1 mol of lithium carbonate, 0.2 mol of iron phosphate, and 85 mL of anhydrous ethanol are added to a ball mill, and ball milling is performed at a ball-to-material ratio of 9:1 and a ball milling speed of 300 r / min for 9 h. After the ball milling is completed, the obtained ball milling slurry is placed in a vacuum drying box and dried at a temperature of 82 DEG C for 2.5 h. Then, the dried product is placed in a tube furnace, nitrogen is introduced for protection, and calcination is performed at a temperature of 725 DEG C for 11 h. After that, the furnace is cooled down, and lithium iron phosphate is obtained.

[0033] Step S2: 10 mmol of 2-amino terephthalic acid, 10 mmol of zirconium chloride, 8 mL of glacial acetic acid, and 75 mL of N,N-dimethylformamide are added to a three-necked flask equipped with a stirrer and a thermometer. Stirring is performed at a temperature of 22 DEG C and a stirring speed of 250 r / min for 15 min. Then, the temperature is increased to 125 DEG C, and stirring is continued for 25 h. After the reaction is completed, the reaction product is cooled to room temperature, and then centrifuged. The precipitate is soaked in anhydrous methanol for 7 h, and then centrifuged. The precipitate is placed in a vacuum drying box and dried at a temperature of 85 DEG C for 4 h to obtain an ammine metal organic framework.

[0034] Step S3: 5 g of the ammine metal organic framework, 15 mmol of 3-chloropropyl triethoxysilane, 32 mmol of triethylamine, and 85 mL of toluene are added to a three-necked flask equipped with a stirrer, a thermometer, and a gas inlet tube. Nitrogen is introduced for protection, and stirring is performed at a temperature of 3 DEG C and a stirring speed of 250 r / min for 15 min. Then, the temperature is increased to 85 DEG C, and stirring is continued for 7 h. After the reaction is completed, the reaction product is cooled to room temperature, and then centrifuged. The precipitate is sequentially washed with tetrahydrofuran and anhydrous ethanol for 2 times, and then placed in a vacuum drying box and dried at a temperature of 65 DEG C for 4 h to obtain a siloxane grafted metal organic framework.

[0035] Step S4: 10 g of lithium iron phosphate, 2.3 g of siloxane grafted metal organic framework and 110 mL of ethanol solution with a volume fraction of 45% were added to a three-necked flask equipped with a stirrer, a thermometer and a gas inlet tube, protected by nitrogen, stirred at a temperature of 22°C and a stirring rate of 250 r / min for 15 min, then adjusted to pH 9 with ammonia water with a mass fraction of 26%, and then continued to stir at a temperature of 85°C for 4 h, then added 10 mmol of cobalt nitrate and 10 mmol of copper nitrate, and continued to stir for 2.5 h. After the reaction was completed, the reaction product was cooled to room temperature, and then placed in a vacuum drying oven and dried at a temperature of 95°C for 11 h, and then placed in a tube furnace and calcined at a temperature of 375°C for 4.5 h to obtain a multi-element carbon source modified lithium iron phosphate material.

[0036] Example 3

[0037] The present embodiment is a preparation method of a multi-element carbon source modified lithium iron phosphate material, comprising the following steps:

[0038] Step S1: 0.1 mol of lithium carbonate, 0.2 mol of iron phosphate and 90 mL of anhydrous ethanol were added to a ball mill, ball-milled at a ball-to-material ratio of 10:1 and a ball-milling rate of 350 r / min for 10 h. After ball-milling, the obtained ball-milled slurry was placed in a vacuum drying oven and dried at a temperature of 85°C for 3 h, and then placed in a tube furnace, protected by nitrogen, and calcined at a temperature of 750°C for 12 h. After cooling in the furnace, lithium iron phosphate was obtained.

[0039] Step S2: 10 mmol of 2-amino terephthalic 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, stirred at a temperature of 25°C and a stirring rate of 300 r / min for 20 min, and then continued to stir at a temperature of 130°C for 30 h. After the reaction was completed, the reaction product was cooled to room temperature, and then centrifuged. The precipitate was added to anhydrous methanol and soaked for 8 h, and then centrifuged. The precipitate was placed in a vacuum drying oven and dried at a temperature of 90°C for 5 h to obtain an ammonia metal organic framework.

[0040] Step S3: 5 g of an ammonia metal organic framework, 20 mmol of 3-chloropropyl triethoxysilane, 35 mmol of triethylamine, and 90 mL of toluene were added to a three-necked flask equipped with a stirrer, a thermometer, and a gas inlet tube, protected by nitrogen, stirred at a temperature of 5 DEG C and a stirring rate of 300 r / min for 20 min, then the temperature was raised to 90 DEG C and the stirring was continued for 8 h. After the reaction was completed, the reaction product was cooled to room temperature, then centrifuged, and the precipitate was washed with tetrahydrofuran and anhydrous ethanol three times in sequence, then placed in a vacuum drying oven, dried at a temperature of 70 DEG C for 5 h, to obtain a siloxane grafted metal organic framework;

[0041] Step S4: 10 g of lithium iron phosphate, 3.7 g of a siloxane grafted metal organic framework, and 120 mL of an ethanol solution with a volume fraction of 50% were added to a three-necked flask equipped with a stirrer, a thermometer, and a gas inlet tube, protected by nitrogen, stirred at a temperature of 25 DEG C and a stirring rate of 300 r / min for 20 min, then adjusted to a pH of 10 with 27% ammonia water, then the temperature was raised to 90 DEG C and the stirring was continued for 5 h. Then 15 mmol of cobalt nitrate and 15 mmol of copper nitrate were added and the stirring was continued for 3 h. After the reaction was completed, the reaction product was cooled to room temperature, then placed in a vacuum drying oven, dried at a temperature of 100 DEG C for 12 h, then placed in a tube furnace, calcined at a temperature of 400 DEG C for 5 h, to obtain a multi-element carbon source modified lithium iron phosphate material.

[0042] Comparative Example 1

[0043] This comparative example is a preparation method of a lithium iron phosphate material, comprising the following steps:

[0044] 0.1 mol of lithium carbonate, 0.2 mol of iron phosphate, and 90 mL of anhydrous ethanol were added to a ball mill, ball milled at a ball-to-material ratio of 10:1 and a ball milling rate of 350 r / min for 10 h. After the ball milling was completed, the obtained ball milling slurry was placed in a vacuum drying oven, dried at a temperature of 85 DEG C for 3 h, then placed in a tube furnace, protected by nitrogen, calcined at a temperature of 750 DEG C for 12 h, and then cooled in the furnace. A lithium iron phosphate material was obtained.

[0045] Comparative Example 2

[0046] This comparative example is a preparation method of a carbon source modified lithium iron phosphate material, comprising the following steps:

[0047] Step S1: 0.1 mol of lithium carbonate, 0.2 mol of iron phosphate and 90 mL of anhydrous ethanol were added to a ball mill, and ball milling was performed at a ball-to-material ratio of 10:1 and a ball milling speed of 350 r / min for 10 h. After the ball milling was completed, the obtained ball milling slurry was placed in a vacuum drying box and dried at a temperature of 85°C for 3 h, and then placed in a tube furnace, and calcined at a temperature of 750°C for 12 h under nitrogen protection, and then cooled in the furnace to obtain lithium iron phosphate;

[0048] Step S2: 10 g of lithium iron phosphate, 3.7 g of glucose and 120 mL of an ethanol solution with a volume fraction of 50% were added to a three-necked flask equipped with a stirrer, a thermometer and a gas inlet tube, and stirred at a temperature of 25°C and a stirring speed of 300 r / min for 20 min under nitrogen protection. Then, the temperature was increased to 90°C, and stirring was continued for 5 h. After the reaction was completed, the reaction product was cooled to room temperature, and then placed in a vacuum drying box and dried at a temperature of 100°C for 12 h. Then, the product was placed in a tube furnace and calcined at a temperature of 400°C for 5 h to obtain a carbon source modified lithium iron phosphate material.

[0049] Comparative Example 3:

[0050] The present comparative example is a preparation method of a multi-element carbon source modified lithium iron phosphate material, which comprises the following steps:

[0051] Step S1: 0.1 mol of lithium carbonate, 0.2 mol of iron phosphate and 90 mL of anhydrous ethanol were added to a ball mill, and ball milling was performed at a ball-to-material ratio of 10:1 and a ball milling speed of 350 r / min for 10 h. After the ball milling was completed, the obtained ball milling slurry was placed in a vacuum drying box and dried at a temperature of 85°C for 3 h, and then placed in a tube furnace, and calcined at a temperature of 750°C for 12 h under nitrogen protection, and then cooled in the furnace to obtain lithium iron phosphate;

[0052] Step S2: 10 g of lithium iron phosphate, 3.7 g of glucose and 120 mL of an ethanol solution with a volume fraction of 50% were added to a three-necked flask equipped with a stirrer, a thermometer and a gas inlet tube, and stirred at a temperature of 25°C and a stirring speed of 300 r / min for 20 min under nitrogen protection. Then, the temperature was increased to 90°C, and stirring was continued for 5 h. After the reaction was completed, the reaction product was cooled to room temperature, and then placed in a vacuum drying box and dried at a temperature of 100°C for 12 h. Then, the product was placed in a tube furnace and calcined at a temperature of 400°C for 5 h to obtain a carbon source modified lithium iron phosphate material.

[0053] Comparative Example 4:

[0054] The present comparative example is a preparation method of a multi-element carbon source modified lithium iron phosphate material, comprising the following steps:

[0055] Step S1: 0.1 mol of lithium carbonate, 0.2 mol of iron phosphate, and 90 mL of anhydrous ethanol were added to a ball mill, and ball milling was performed at a ball-to-material ratio of 10:1 and a ball milling speed of 350 r / min for 10 h. After the ball milling, the obtained ball milling slurry was placed in a vacuum drying box and dried at a temperature of 85°C for 3 h. Then, the dried product was placed in a tube furnace, nitrogen was introduced for protection, and calcination was performed at a temperature of 750°C for 12 h. After that, the furnace was cooled down, and lithium iron phosphate was obtained.

[0056] Step S2: 10 mmol of 2-amino terephthalic 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 reaction was stirred at a temperature of 25°C and a stirring speed of 300 r / min for 20 min. Then, the temperature was increased to 130°C, and the reaction was continued for 30 h. After the reaction, the reaction product was cooled to room temperature, and then centrifuged. The precipitate was soaked in anhydrous methanol for 8 h, and then centrifuged. The precipitate was placed in a vacuum drying box and dried at a temperature of 90°C for 5 h to obtain an ammine metal organic framework.

[0057] Step S3: 5 g of the ammine metal organic framework, 20 mmol of 3-chloropropyl triethoxysilane, 35 mmol of triethylamine, and 90 mL of toluene were added to a three-necked flask equipped with a stirrer, a thermometer, and a gas inlet tube. Nitrogen was introduced for protection, and the reaction was stirred at a temperature of 5°C and a stirring speed of 300 r / min for 20 min. Then, the temperature was increased to 90°C, and the reaction was continued for 8 h. After the reaction, the reaction product was cooled to room temperature, and then centrifuged. The precipitate was washed with tetrahydrofuran and anhydrous ethanol three times, respectively. Then, the precipitate was placed in a vacuum drying box and dried at a temperature of 70°C for 5 h to obtain a siloxane grafted metal organic framework.

[0058] Step S4: 10 g of lithium iron phosphate, 3.7 g of siloxane grafted metal organic framework, and 120 mL of an ethanol solution with a volume fraction of 50% were added to a three-necked flask equipped with a stirrer, a thermometer, and a gas inlet tube, and nitrogen was introduced for protection. The mixture was stirred at a temperature of 25°C and a stirring rate of 300 r / min for 20 min, and then adjusted to a pH of 10 with 27% ammonia water. The mixture was then heated to 90°C and continuously stirred for 5 h. After the reaction was completed, the reaction product was cooled to room temperature, and then placed in a vacuum drying oven and dried at a temperature of 100°C for 12 h. Then, the mixture was placed in a tube furnace and calcined at a temperature of 400°C for 5 h to obtain the multi-element carbon source modified lithium iron phosphate material.

[0059] Comparative Example 5:

[0060] The present comparative example is a method for preparing a multi-element carbon source modified lithium iron phosphate material, comprising the following steps:

[0061] Step S1: 0.1 mol of lithium carbonate, 0.2 mol of iron phosphate, and 90 mL of anhydrous ethanol were added to a ball mill, and ball milled at a ball-to-material ratio of 10:1 and a ball milling rate of 350 r / min for 10 h. After the ball milling was completed, the obtained ball milling slurry was placed in a vacuum drying oven and dried at a temperature of 85°C for 3 h. Then, the mixture was placed in a tube furnace, nitrogen was introduced for protection, and calcined at a temperature of 750°C for 12 h. After the calcination, the mixture was cooled in the furnace to obtain lithium iron phosphate.

[0062] Step S2: 10 mmol of 2-amino terephthalic 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 a temperature of 25°C and a stirring rate of 300 r / min for 20 min, and then heated to 130°C and continuously stirred for 30 h. After the reaction was completed, the reaction product was cooled to room temperature, and then centrifuged. The precipitate was added to anhydrous methanol and soaked for 8 h, and then centrifuged. The precipitate was placed in a vacuum drying oven and dried at a temperature of 90°C for 5 h to obtain the ammonia metal organic framework.

[0063] Step S3: 10 g of lithium iron phosphate, 3.7 g of ammonia metal organic framework and 120 mL of ethanol solution with a volume fraction of 50% were added into a three-necked flask equipped with a stirrer, a thermometer and a gas inlet pipe, and nitrogen was introduced for protection. The reaction was stirred at a temperature of 25°C and a stirring speed of 300 r / min for 20 min, then adjusted to pH 10 with ammonia water with a mass fraction of 27%, and then continued to be stirred at a temperature of 90°C for 5 h. Then 15 mmol of cobalt nitrate and 15 mmol of copper nitrate were added and the reaction was continued to be stirred for 3 h. After the reaction was completed, the reaction product was cooled to room temperature, and then placed in a vacuum drying oven and dried at a temperature of 100°C for 12 h. Then it was placed in a tube furnace and calcined at a temperature of 400°C for 5 h to obtain a multi-element carbon source modified lithium iron phosphate material.

[0064] Performance test

[0065] The lithium iron phosphate materials of Examples 1-3 and Comparative Examples 1-5 were respectively coated on aluminum foil, and then placed in a vacuum drying oven and dried at a temperature of 120°C for 12 h. Then they were cut into round pieces with a diameter of 16 mm to obtain positive electrode sheets. Then CR2025 button cells were assembled with lithium sheets as negative electrode sheets, Celgard 2400 as separators and 1M LiPF6 (EC:DMC:DEC=1:1:1, v / v / v) as electrolyte, and left to stand for 12 h to test their performance. The test results are shown in Table 1 below.

[0066] Table 1: Test results of the electrochemical performance of lithium iron phosphate materials

[0067]

[0068] Referring to the data in the above table, according to the data of Examples 1-3, it can be seen that the lithium iron phosphate material of the present application has excellent electrochemical performance. Among them, according to the comparison between Example 3 and Comparative Example 1, it can be seen that coating a multi-element carbon source can significantly improve the specific discharge capacity and capacity retention rate of the lithium iron phosphate material. According to the comparison between Example 3 and Comparative Example 2, it can be seen that doping multiple elements in the carbon source can significantly improve the specific discharge capacity and capacity retention rate of the lithium iron phosphate material. According to the comparison between Example 3 and Comparative Example 3, it can be seen that using siloxane grafted metal organic framework as the carbon source has a better performance improvement effect than using glucose as the carbon source. According to the comparison between Example 3 and Comparative Example 4, it can be seen that doping cobalt and copper can significantly improve the specific discharge capacity of the lithium iron phosphate material. According to the comparison between Example 3 and Comparative Example 5, it can be seen that grafting siloxane groups can significantly improve the capacity retention rate of the lithium iron phosphate material.

[0069] In the description of the specification, reference to terms "one embodiment", "an example", "a specific example" and so on is intended to indicate that a particular feature, structure, material or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the application. Descriptive expressions of the above terms in the specification do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0070] The above is only an example and illustration of the application, and those skilled in the art can make various modifications or supplements to the described specific embodiments or replace them with similar ways, as long as they do not deviate from the application or exceed the scope defined in the application.

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.

Images