Preparation method of polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material

Abstract

The present invention discloses a method for preparing a polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material, comprising the steps of preparing Prussian blue polyhedra, pretreating the Prussian blue polyhedra, and preparing the polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material. The composite material is characterized by the gradual formation of FePO4 nanoparticles within the polyhedral framework as a polyhedral Prussian blue precursor is converted. This, accompanied by carbonization of the carbon source, ultimately forms a FePO4 / nitrogen-doped carbon composite material with a polyhedral mesoporous structure (mesoporous polyhedra with a size of less than 1 μm). The FePO4 nanoparticles have a uniform particle size, averaging less than 50 nm, and exhibit no agglomeration, making them suitable for preparing positive electrode materials for lithium-ion batteries. The method is simple, produces a high-purity product, minimizes environmental pollution, and is easily scalable.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy materials and specifically relates to a method for preparing a polyhedral mesoporous FePO4 / nitrogen-doped carbon (FePO4 / NC) composite material. The prepared FePO4 / NC composite material can be used as a positive electrode material for batteries. Background Art

[0002] With the widespread adoption of electric vehicles, the lithium-ion battery industry is developing rapidly to meet the demands of continuous mass production. FePO4 is considered an ideal cathode material for lithium-ion power batteries due to its low price, environmental friendliness, stable structure, and abundant raw materials. However, its low electrical conductivity and tap density result in poor high-rate performance and low energy density. Furthermore, the dramatic volume effect during cyclic lithium insertion / extraction is a significant factor hindering the further application of FePO4. Therefore, designing nanomaterials with different structures and developing carbon composites have become effective approaches to improve electronic conductivity and overcome volume effects. Studies have shown that the morphology and carbon content of FePO4 have a significant impact on the performance of synthesized LiFePO4 materials. Using high-quality FePO4 / carbon composites as precursors can produce high-performance LiFePO4. Therefore, controlling the morphology and carbon content of FePO4 is a key factor in improving the performance of LiFePO4.

[0003] The preparation method of FePO4 is usually the precipitation solution method, that is, adding a phosphate solution to an iron (III) salt solution. The prepared product is mostly hydrated FePO4, which has a low capacity and requires further high-temperature calcination to form a dehydrated product. In addition, due to the 3+ Due to its easy hydrolysis, the reaction must be carried out at a very low pH (1.5). This method is time-consuming and can corrode industrial facilities due to the use of strong acids and bases, posing potential environmental concerns. Therefore, it is highly desirable to use simple and environmentally friendly synthesis methods to prepare FePO4 with improved electrochemical performance.

[0004] Prussian blue is an inexpensive, abundant compound rich in iron, carbon, and nitrogen. Due to its unique coordination structure within the Prussian blue molecule, it readily forms a polyhedral structure. Therefore, using Prussian blue's unique polyhedral shape as a structural template and the iron and nitrogen elements within the molecule as iron and carbon sources, a solid-phase method has been developed to prepare FePO4 / nitrogen-doped carbon (FePO4 / NC) composites with polyhedral mesoporous structures. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a method for preparing a polyhedral mesoporous FePO4 / nitrogen-doped carbon (FePO4 / NC) composite material and its application in the preparation of lithium-ion battery positive electrode materials. The polyhedral mesoporous FePO4 / nitrogen-doped carbon (FePO4 / NC) composite material prepared by the present invention has a polyhedral mesoporous structure.

[0006] The present invention provides a method for preparing a polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material, comprising the steps of preparing a Prussian blue polyhedron, pretreating the Prussian blue polyhedron, and preparing the polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material. The method specifically comprises the following steps:

[0007] 1) Preparation of Prussian Blue Polyhedrons: The pH of the iron salt solution is adjusted to 1-3, and a surfactant is added and stirred evenly. The resulting solution is added to a pre-prepared potassium ferricyanide solution, stirred evenly, and transferred to a hydrothermal reactor for reaction. After the reaction, the Prussian blue polyhedron is obtained through post-treatment.

[0008] 2) Pretreatment of Prussian blue polyhedrons: The Prussian blue polyhedrons obtained in step 1) are mixed with phosphate, a carbon source, and a grinding aid, and then ball-milled and dried to obtain a Prussian blue polyhedron mixture;

[0009] 3) Preparation of polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material The dried Lushi blue polyhedral mixture in step 2) was pretreated in an air atmosphere in a tube furnace, and then inert gas was introduced and directly calcined in an inert atmosphere using a programmed temperature method to obtain a polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material.

[0010] Furthermore, the present invention also defines that the iron salt in step 1) is one of ferric chloride or ferric nitrate, and the dilute acid solution used for adjusting the pH value is a dilute hydrochloric acid solution.

[0011] Furthermore, the present invention further defines that the surfactant in step 1) is one of polyvinyl pyrrolidone, anhydrous sodium citrate or sodium citrate dihydrate, and the molar ratio of the surfactant, potassium ferricyanide and iron salt is 3-10:1:1.

[0012] Furthermore, the present invention also limits the reaction temperature of the hydrothermal reactor in step 1) to 70°C-160°C and the reaction time to 5-13 hours. The post-treatment process is as follows: after the reaction is completed, the reaction is cooled to room temperature, precipitated, and centrifuged. The filter cake is washed with water and anhydrous ethanol respectively, and dried at 60°C for 12 hours to obtain Prussian blue polyhedrons.

[0013] Furthermore, the present invention also defines that the phosphate in step 2) is one of NH4H2PO4, (NH4)2HPO4 or (NH4)3PO4; and the carbon source is one of glucose, urea or ascorbic acid.

[0014] Furthermore, the present invention also limits the grinding aid in step 2) to water or ethanol.

[0015] Furthermore, the present invention also limits the molar ratio of the Prussian blue polyhedron, phosphate and carbon source in step 2) to 1:1:2-10.

[0016] Furthermore, the present invention also limits the pretreatment temperature in step 3) to 300° C. and the pretreatment time to 3 hours.

[0017] Furthermore, the present invention also defines the programmed heating rate in step 3) as 3°C / min-8°C / min, the calcination temperature as 600°C-800°C, and the calcination time as 3-8h.

[0018] Furthermore, the present invention also limits the inert atmosphere in step 3) to nitrogen or argon.

[0019] By adopting the above technology, compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] 1) The Prussian blue polyhedron used in the present invention serves as both an iron source and a nitrogen element, and also as a polyhedral template in the FePO4 synthesis process. Its structure is such that as the polyhedral Prussian blue precursor is converted, FePO4 nanoparticles gradually form within the polyhedral framework, accompanied by the carbonization of the carbon source, ultimately forming a FePO4 / nitrogen-doped carbon composite material with a polyhedral mesoporous structure. The morphology is easily controlled and the size is uniform (the size of the polyhedral structure is less than 1 μm). The FePO4 nanoparticles that make up the mesoporous polyhedron have a uniform particle size of less than 50 nm, and the composite of the carbon material and the FePO4 nanoparticles is also more uniform and free of agglomeration.

[0021] 2) The present invention adopts a limited method to avoid the need for further treatment to remove crystal water from the iron phosphate (FePO4·2H2O) obtained by the precipitation method. The method is simple, has high product purity, has low environmental pollution, and is easy to implement in a process;

[0022] 3) The polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material prepared by the present invention can greatly improve the conductivity of FePO4 and increase the conduction of electrons through the composite of nitrogen-doped carbon; and the unique polyhedral mesoporous structure can shorten the Li + The diffusion path of the positive electrode material is shortened, its diffusion coefficient is increased, and the irreversible phase change of the positive electrode material is suppressed to a certain extent, which greatly improves the electrochemical performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a SEM image of the polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material prepared based on Example 1 of the present invention.

[0024] Figure 2 This is an SEM image of the polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material prepared based on Example 2 of the present invention.

[0025] Figure 3 This is an SEM image of the polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material prepared based on Example 3 of the present invention.

[0026] Figure 4 This is an SEM image of the polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material prepared based on Example 4 of the present invention. DETAILED DESCRIPTION

[0027] The present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

[0028] Example 1:

[0029] (1) Dissolve 0.02 mol of ferric chloride in 100 ml of deionized water under stirring, adjust the pH value to 1 with 0.1 M hydrochloric acid solution, then add 0.06 mol of polyvinyl pyrrolidone and continue stirring for 20 minutes. In addition, dissolve 0.02 mol of potassium ferrocyanide in 60 ml of deionized water to prepare a uniform solution. After the ferric chloride solution and polyvinyl pyrrolidone are stirred evenly, slowly add the prepared potassium ferrocyanide solution. After stirring evenly, transfer the mixed solution into a hydrothermal reactor, control the temperature at 80 ° C, and the time is 10 hours. Finally, cool to room temperature, precipitate, centrifuge, wash with water and anhydrous ethanol respectively, and dry (60 ° C, 12 hours) to obtain Prussian blue polyhedron;

[0030] (2) 0.015 mol of the Prussian blue polyhedron prepared in the first step was mixed with an equal molar amount of NH4H2PO4. 0.03 mol of glucose and 3 ml of deionized water were placed in a steel grinding jar and ball milled on a ball mill (milling rate of 300 r / min, milling time of 1 h). The treated mixture was further dried at 80°C for 12 h to obtain a Prussian blue polyhedron mixture.

[0031] (3) The dried Russi blue polyhedron mixture in the second step was first pretreated in a tube furnace at 300°C for 3 hours under air atmosphere. Then nitrogen was introduced and the temperature was directly raised to 600°C using a programmed temperature increase method (heating rate 3°C / min) and kept constant at that temperature for 8 hours to obtain the desired polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material. Figure 1The following is an SEM image of the polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material prepared according to this example. The image clearly shows the product's polyhedral porous structure, with the polyhedrons less than 1 μm in size. Furthermore, the image shows that the FePO4 nanoparticles are relatively uniform in size, with an average particle size of less than 50 nm. This confirms that the prepared composite material is indeed a polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material.

[0032] Example 2:

[0033] (1) Dissolve 0.02 mol of ferric nitrate in 100 ml of deionized water under stirring, adjust the pH value to 3 with 0.1 M hydrochloric acid solution, then add 0.2 mol of anhydrous sodium citrate and continue stirring for 20 minutes. In addition, dissolve 0.02 mol of potassium ferrocyanide in 60 ml of deionized water to prepare a uniform solution. After the ferric nitrate solution and anhydrous sodium citrate are stirred evenly, slowly add the prepared potassium ferrocyanide solution. After stirring evenly, transfer the mixed solution into a hydrothermal reactor, control the temperature at 160 ° C, and the time is 5 hours. Finally, cool to room temperature, precipitate, centrifuge, wash with water and anhydrous ethanol respectively, and dry (60 ° C, 12 hours) to obtain Prussian blue polyhedrons;

[0034] (2) Take 0.01 mol of the Prussian blue polyhedron prepared in the first step and mix it with an equal mole of (NH4)2HPO4; take 0.1 mol of ascorbic acid and 2 ml of anhydrous ethanol and put them into a steel grinding jar. Mill them on a ball mill (milling speed of 300 r / min, milling time of 1 h). The treated mixture is further dried at 80 ° C for 12 h to obtain a Prussian blue polyhedron mixture;

[0035] (3) The dried Russi blue polyhedron mixture in the second step was first pretreated in a tube furnace at 300°C for 3 hours under air atmosphere. Then, argon was introduced and the temperature was directly raised to 800°C using a programmed temperature increase method (heating rate 8°C / min) and kept constant at that temperature for 3 hours to obtain the desired polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material. Figure 2 The SEM image of the polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material prepared according to this embodiment is shown. It can be clearly seen from the image that the product has a polyhedral porous structure, and the size of the polyhedron is less than 1μm. In addition, it can be observed from the image that the size of the FePO4 nanoparticles is relatively uniform, with an average particle size of less than 50nm. This proves that the prepared composite material is indeed a polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material.

[0036] Example 3:

[0037] (1) Dissolve 0.03 mol of ferric chloride in 150 ml of deionized water under stirring, adjust the pH value to 2 with 0.1 M hydrochloric acid solution, then add 0.15 mol of sodium citrate dihydrate and continue stirring for 20 minutes. In addition, dissolve 0.03 mol of potassium ferrocyanide in 60 ml of deionized water to prepare a uniform solution. After the ferric chloride solution and sodium citrate dihydrate are stirred evenly, slowly add the prepared potassium ferrocyanide solution. After stirring evenly, transfer the mixed solution into a hydrothermal reactor, control the temperature at 100 ° C, and the time is 8 hours. Finally, cool to room temperature, precipitate, centrifuge, wash with water and anhydrous ethanol respectively, and dry (60 ° C, 12 hours) to obtain Prussian blue polyhedron;

[0038] (2) Mix 0.02 mol of the Prussian blue polyhedron prepared in the first step with an equal molar amount of (NH4)3PO4. Also, place 0.16 mol of urea and 2.5 ml of deionized water in a steel grinding jar and ball mill them (milling speed: 300 r / min, milling time: 1 h). The treated mixture is then dried at 80°C for 12 h to obtain a Prussian blue polyhedron mixture.

[0039] (3) The dried Russi blue polyhedron mixture in the second step was first pretreated in a tube furnace at 300°C for 3 hours under air atmosphere. Then, argon was introduced and the temperature was directly raised to 700°C using a programmed temperature increase method (heating rate 5°C / min) and kept constant at that temperature for 5 hours to obtain the desired polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material. Figure 3 The SEM image of the polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material prepared according to this embodiment is shown. It can be clearly seen from the image that the product has a polyhedral porous structure, and the size of the polyhedron is less than 1μm. In addition, it can be observed from the image that the size of the FePO4 nanoparticles is relatively uniform, with an average particle size of less than 50nm. This proves that the prepared composite material is indeed a polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material.

[0040] Example 4:

[0041] (1) Dissolve 0.025 mol of ferric chloride in 100 ml of deionized water under stirring, adjust the pH value to 1 with 0.1 M hydrochloric acid solution, then add 0.1 mol of anhydrous sodium citrate and continue stirring for 20 minutes. In addition, dissolve 0.025 mol of potassium ferrocyanide in 60 ml of deionized water to prepare a uniform solution. After the ferric chloride solution and anhydrous sodium citrate are stirred evenly, slowly add the prepared potassium ferrocyanide solution. After stirring evenly, transfer the mixed solution into a hydrothermal reactor, control the temperature at 90 ° C, and the time is 10 hours. Finally, cool to room temperature, precipitate, centrifuge, wash with water and anhydrous ethanol respectively, and dry (60 ° C, 12 hours) to obtain Prussian blue polyhedrons;

[0042] (2) Mix 0.02 mol of the Prussian blue polyhedron prepared in the first step with an equal molar amount of (NH4)2HPO4. Also, place 0.14 mol of glucose and 3 ml of deionized water in a steel grinding jar and ball mill them (milling speed: 300 r / min, milling time: 1 h). The treated mixture is then dried at 80°C for 12 h to obtain a Prussian blue polyhedron mixture.

[0043] (3) The dried Russi blue polyhedron mixture in the second step was first pretreated in a tube furnace at 300°C for 3 hours under air atmosphere. Then, nitrogen was introduced and the temperature was directly raised to 600°C using a programmed temperature increase method (heating rate 6°C / min) and kept constant at that temperature for 7 hours to obtain the desired polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material. Figure 4 The SEM image of the polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material prepared according to this embodiment is shown. It can be clearly seen from the image that the product has a polyhedral porous structure, and the size of the polyhedron is less than 1μm. In addition, it can be observed from the image that the size of the FePO4 nanoparticles is relatively uniform, with an average particle size of less than 50nm. This proves that the prepared composite material is indeed a polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material.

[0044] Example 5:

[0045] (1) Dissolve 0.015 mol of ferric nitrate in 80 ml of deionized water under stirring, adjust the pH value to 2 with 0.1 M hydrochloric acid solution, then add 0.1 mol of polyvinyl pyrrolidone and continue stirring for 20 minutes. In addition, dissolve 0.015 mol of potassium ferrocyanide in 50 ml of deionized water to prepare a uniform solution. After the ferric nitrate solution and polyvinyl pyrrolidone are stirred evenly, slowly add the prepared potassium ferrocyanide solution. After stirring evenly, transfer the mixed solution into a hydrothermal reactor, control the temperature at 110 ° C, and the time is 7 hours. Finally, cool to room temperature, precipitate, centrifuge, wash with water and anhydrous ethanol respectively, and dry (60 ° C, 12 hours) to obtain Prussian blue polyhedron;

[0046] (2) Mix 0.01 mol of the Prussian blue polyhedron prepared in the first step with an equal molar amount of NH4H2PO4. Separately, place 0.07 mol of glucose and 1 ml of anhydrous ethanol in a steel grinding jar and ball mill them (milling speed: 300 r / min, milling time: 1 h). The treated mixture is then dried at 80°C for 12 h to obtain a Prussian blue polyhedron mixture.

[0047] (3) The dried Russi blue polyhedron mixture was first pretreated in a tube furnace at 300°C for 3 h under air atmosphere. Then, nitrogen was introduced and the temperature was directly raised to 600°C using a programmed temperature ramp (heating rate 4°C / min) and maintained at that temperature for 7 h to obtain the desired polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material.

[0048] The above embodiments are not limitations of the present invention, and the present invention is not limited to the above embodiments. As long as the requirements of the present invention are met, they belong to the protection scope of the present invention.

Claims

1. A method for preparing a polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material, comprising preparing a Prussian blue polyhedron, pretreating the Prussian blue polyhedron, and preparing a polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material, characterized in that The specific steps include: 1) Preparation of Prussian Blue Polyhedrons: The pH of the iron salt solution is adjusted to 1-3, and a surfactant is added and stirred evenly. The resulting solution is added to a pre-prepared potassium ferricyanide solution, stirred evenly, and transferred to a hydrothermal reactor for reaction. After the reaction, the Prussian blue polyhedron is obtained through post-treatment. 2) Pretreatment of Prussian blue polyhedrons: The Prussian blue polyhedrons obtained in step 1) are mixed with phosphate, a carbon source, and a grinding aid, and then ball-milled and dried to obtain a Prussian blue polyhedron mixture; 3) Preparation of polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material The dried Lushi blue polyhedral mixture in step 2) was pretreated in an air atmosphere in a tube furnace, and then inert gas was introduced and directly calcined in an inert atmosphere using a programmed temperature method to obtain a polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material.

2. The method for preparing a polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material according to claim 1, characterized in that The iron salt in step 1) is one of ferric chloride or ferric nitrate, and the dilute acid solution used for adjusting the pH value is dilute hydrochloric acid solution.

3. The method for preparing a polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material according to claim 1, characterized in that The surfactant in step 1) is one of polyvinyl pyrrolidone, anhydrous sodium citrate or sodium citrate dihydrate, and the molar ratio of the surfactant, potassium ferricyanide and iron salt is 3-10:1:

1.

4. The method for preparing a polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material according to claim 1, characterized in that The reaction temperature of the hydrothermal reactor in step 1) is 70°C to 160°C for 5-13 hours. The post-treatment process is as follows: after the reaction is completed, the reaction is cooled to room temperature, precipitated, and centrifuged. The filter cake is washed with water and anhydrous ethanol respectively, and dried at 60°C for 12 hours to obtain Prussian blue polyhedrons.

5. The method for preparing a polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material according to claim 1, characterized in that The phosphate in step 2) is one of NH4H2PO4, (NH4)2HPO4 or (NH4)3PO4; the carbon source is one of glucose, urea or ascorbic acid.

6. The method for preparing a polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material according to claim 1, characterized in that The grinding aid in step 2) is water or ethanol.

7. The method for preparing a polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material according to claim 1, characterized in that The molar ratio of the Prussian blue polyhedron, phosphate, and carbon source in step 2) is 1:1:2-10.

8. The method for preparing a polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material according to claim 1, characterized in that The pretreatment temperature in step 3) is 300°C and the pretreatment time is 3 hours.

9. The method for preparing a polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material according to claim 1, characterized in that In step 3), the programmed heating rate is 3°C / min to 8°C / min, the calcination temperature is 600°C to 800°C, and the calcination time is 3 to 8 hours.

10. A method for preparing a polyhedral mesoporous FePO4 / nitrogen-doped carbon composite material according to any one of claims 1 to 9, characterized in that The inert atmosphere in step 3) is nitrogen or argon.

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