Modified ferric phosphate and a preparation method and application thereof

Abstract

The present disclosure provides a modified iron phosphate and a preparation method and application thereof, the preparation method comprising the following steps: (1) preparing NH2-MIL-53(Al) nanoparticles, mixing the nanoparticles with a solvent, adding an acid solution, and obtaining hollow NH2-MIL-53(Al) powder after heating and stirring; (2) preparing a dispersion of the hollow NH2-MIL-53(Al) powder, mixing the dispersion with an iron salt solution, stirring and drying, mixing the obtained powder with a phosphorus source solution, controlling the pH, and performing a reaction; and (3) performing sintering treatment on the material obtained after aging to obtain the modified iron phosphate. The present disclosure provides a small reaction area for the synthesis of iron phosphate by taking hollow metal organic framework nanomaterials as a template, and the micro-morphology of the prepared iron phosphate is constrained and controlled, and a nanoscale iron phosphate with a polyhedral structure is prepared.

Description

Technical Field

[0001] This disclosure belongs to the field of battery materials technology, and relates to a modified iron phosphate, its preparation method and application. Background Technology

[0002] With the escalating global energy crisis, new energy batteries, as a clean and efficient way to store and utilize energy, have experienced rapid development. Among them, lithium-ion batteries are widely used in electric vehicles, smartphones, and other fields due to their advantages such as high energy density, long cycle life, and lightweight design. Currently, among the cathode materials used in the preparation of lithium batteries, olivine-type lithium iron phosphate (LiFePO4) has attracted considerable attention from researchers due to its low cost, environmental friendliness, good cycle performance, and high safety performance. However, some defects caused by the structure of LiFePO4 itself, such as poor conductivity and low lithium-ion diffusion rate, limit its further practical application. To address this issue, carbon coating, doping, and particle size reduction are commonly used to modify lithium iron phosphate to improve its electrical performance. Iron phosphate (FePO4) is an important precursor raw material for the preparation of lithium iron phosphate. Its purity, specific surface area, microstructure, and particle size distribution directly affect the electrochemical performance of the cathode material lithium iron phosphate. Therefore, preparing iron phosphate with excellent structure and performance indicators is of great significance for the synthesis of high-quality lithium iron phosphate.

[0003] In existing technologies for preparing lithium iron phosphate (LFP), the iron phosphate process route uses iron phosphate as a precursor, which is uniformly mixed with a lithium source and a carbon source, followed by grinding, drying, and high-temperature sintering to synthesize LiFePO4 / C cathode materials. The preparation of the iron phosphate precursor often employs a liquid-phase co-precipitation method. However, the precipitation process may encounter problems such as difficulty in controlling particle growth, resulting in products with potentially large particle sizes and small specific surface areas. This hinders the rapid insertion and extraction of lithium ions, thus affecting the electrochemical activity of the cathode material. In recent years, industrial LFP production has placed increasingly stringent requirements on particle size control, as numerous studies have shown that LFP with uniform morphology or smaller particles exhibits better electrochemical performance. Therefore, LFP nanomaterials are becoming the mainstream approach. Summary of the Invention

[0004] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0005] The purpose of this disclosure is to provide a modified iron phosphate, its preparation method and application. This disclosure uses acid-etched hollow metal-organic framework NH2-MIL-53(Al) nanomaterials as templates to provide a small reaction region for the synthesis of iron phosphate, constraining and controlling the microstructure of the prepared iron phosphate, and preparing a nanoscale iron phosphate with a polyhedral structure.

[0006] To achieve this objective, the present disclosure adopts the following technical solution:

[0007] In a first aspect, this disclosure provides a method for preparing modified iron phosphate, the method comprising the following steps:

[0008] (1) Aluminum salt, sodium dodecylbenzenesulfonate and a first solvent are mixed to obtain a first solution. 2-aminoterephthalic acid and a second solvent are mixed to obtain a second solution. The first solution and the second solution are mixed and heated to obtain NH2-MIL-53(Al) nanoparticles. The NH2-MIL-53(Al) nanoparticles are mixed with a third solvent, an acid solution is added, and the mixture is heated and stirred to obtain hollow NH2-MIL-53(Al) powder.

[0009] (2) Hollow NH2-MIL-53(Al) powder is made into NH2-MIL-53(Al) dispersion, the dispersion is mixed with iron salt solution, stirred and dried, the resulting powder is mixed with phosphorus source solution, the pH is controlled and the reaction is carried out;

[0010] (3) The material obtained after aging is sintered to obtain the modified iron phosphate.

[0011] This disclosure uses hollow NH2-MIL-53(Al) nanomaterials as templates to prepare iron phosphate precursors that retain the polyhedral morphology of the template and have fine particle sizes. In the synthesis of iron phosphate, the hollow NH2-MIL-53(Al) template can act as a micro-reaction vessel, constraining the morphology of the internal synthesized materials. This is achieved by utilizing the Fe... 3+ PO4 3- With its adsorption capacity, under suitable reaction conditions, the two ions can be gradually transformed into FePO4 material with uniform morphology inside the NH2-MIL-53(Al) shell, effectively controlling the growth of particles.

[0012] In one embodiment, the aluminum salt in step (1) comprises aluminum nitrate.

[0013] In one embodiment, the first solvent comprises water.

[0014] In one embodiment, the mixing and stirring time of the first solution is 3 to 5 hours, for example: 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours.

[0015] In one embodiment, the molar concentration of aluminum salt in the first solution is 0.05 to 0.1 mol / L, for example: 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L or 0.1 mol / L, etc.

[0016] In one embodiment, the mass concentration of sodium dodecylbenzenesulfonate in the first solution is 10-15%, for example: 10%, 11%, 12%, 14% or 15%, etc.

[0017] In one embodiment, the second solvent comprises DMF.

[0018] In one embodiment, the molar concentration of 2-aminoterephthalic acid in the second solution is 0.025 to 0.05 mol / L, for example: 0.025 mol / L, 0.028 mol / L, 0.03 mol / L, 0.04 mol / L, or 0.05 mol / L, etc.

[0019] In one embodiment, the volume ratio of the first solution to the second solution is 1:(1.5 to 2.5), for example: 1:1.5, 1:1.8, 1:2, 1:2.2 or 1:2.5, etc.

[0020] In one embodiment, the temperature of the heating reaction in step (1) is 150 to 180°C, for example: 150°C, 155°C, 160°C, 170°C or 180°C.

[0021] In one embodiment, the heating reaction time is 24 to 48 hours, for example: 24 hours, 28 hours, 32 hours, 40 hours, or 48 hours.

[0022] In one embodiment, the heating reaction is followed by cooling, washing, and drying.

[0023] In one embodiment, the third solvent in step (1) comprises anhydrous ethanol.

[0024] In one embodiment, the acid solution comprises any one or a combination of at least two of phytic acid, tannic acid, or lauric acid.

[0025] In one embodiment, the concentration of the acid solution is 50 to 100 g / L, for example: 50 g / L, 60 g / L, 80 g / L, 90 g / L or 100 g / L, etc.

[0026] In one embodiment, the mass ratio of the NH2-MIL-53(Al) nanoparticles to the solute in the acid solution is 1:(1.5 to 2.5), for example: 1:1.5, 1:1.8, 1:2, 1:2.2 or 1:2.5, etc.

[0027] In one embodiment, the heating and stirring temperature in step (1) is 90 to 110°C, for example: 90°C, 95°C, 100°C, 105°C or 110°C.

[0028] In one embodiment, the heating and stirring time is 8 to 12 hours, for example: 8 hours, 9 hours, 10 hours, 11 hours or 12 hours.

[0029] In one embodiment, the heating and stirring are followed by centrifugation, washing, and drying.

[0030] In one embodiment, the solvent of the NH2-MIL-53(Al) dispersion in step (2) includes water.

[0031] In one embodiment, the solute in the iron salt solution includes ferric nitrate and / or ferric chloride.

[0032] In one embodiment, the concentration of the iron salt solution is 0.1 to 0.3 mol / L, for example: 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L or 0.3 mol / L, etc.

[0033] In one embodiment, the mass concentration ratio of the mixed NH2-MIL-53(Al) to iron ions is (0.8 to 1.2):1, for example: 0.8:1, 0.9:1, 1:1, 1.1:1 or 1.2:1, etc.

[0034] In one embodiment, the stirring time is 3 to 5 hours, for example: 3 hours, 3.5 hours, 4 hours, 4.5 hours, or 5 hours.

[0035] In one embodiment, the solute in the phosphorus source solution in step (2) includes any one or a combination of at least two of ammonium dihydrogen phosphate, ammonium hydrogen phosphate, or sodium hydrogen phosphate.

[0036] In one embodiment, the concentration of phosphorus in the phosphorus source solution is 0.1 to 0.3 mol / L, for example: 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, or 0.3 mol / L.

[0037] In one embodiment, the molar ratio of phosphorus in the phosphorus source solution to iron in the iron salt solution is 1:(0.97-1.05), for example: 1:0.97, 1:0.99, 1:1, 1:1.02 or 1:1.05, etc.

[0038] In one embodiment, the method for controlling pH includes adding an alkaline solution.

[0039] In one embodiment, the alkaline solution comprises ammonia and / or sodium hydroxide solution.

[0040] In one embodiment, the pH is 1.5 to 2.2, for example: 1.5, 1.6, 1.8, 2 or 2.2, etc.

[0041] In one embodiment, heating and stirring are performed during the reaction.

[0042] In one embodiment, the heating and stirring temperature is 70-90°C, for example: 70°C, 75°C, 80°C, 85°C or 90°C.

[0043] In one embodiment, the heating and stirring time is 4 to 10 hours, for example: 4 hours, 5 hours, 7 hours, 8 hours, or 10 hours.

[0044] In one embodiment, the heating and stirring are followed by aging.

[0045] In one embodiment, the aging time is 1 to 2 hours, for example: 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, or 2 hours.

[0046] In one embodiment, the sintering temperature in step (3) is 500 to 750°C, for example: 500°C, 520°C, 550°C, 600°C or 750°C.

[0047] In one embodiment, the sintering treatment time is 4 to 10 hours, for example: 4 hours, 5 hours, 7 hours, 8 hours, or 10 hours.

[0048] In one embodiment, the atmosphere for the sintering process includes a nitrogen atmosphere.

[0049] In the sintering process described in this disclosure, under a nitrogen atmosphere, the nitrogen-containing organic ligands of the NH2-MIL-53(Al) template undergo carbonization at high temperatures, forming a nitrogen-doped carbon thin layer coating the surface of the FePO4 material. Nitrogen doping can improve the electrochemical activity of carbon materials. Compared with only carbon layer coating, the electronic conductivity of materials coated with nitrogen-doped carbon layers can be further enhanced.

[0050] In one embodiment, the sintering process is followed by a washing process.

[0051] In one embodiment, the washing process includes acetic acid washing and water washing.

[0052] In a second aspect, this disclosure provides a modified iron phosphate, which is prepared by the method described in the first aspect.

[0053] The modified iron phosphate particles prepared in this disclosure have a smaller particle size and a larger specific surface area. The lithium iron phosphate prepared from them is also smaller in size, which is beneficial to increasing the contact area between the electrode material and the electrolyte, shortening the diffusion path of lithium ions, increasing the diffusion rate of lithium ions, and thus improving the electrochemical activity of the battery material.

[0054] Thirdly, this disclosure provides a lithium iron phosphate cathode material, which is prepared by sintering a modified iron phosphate and a lithium source as described in the second aspect.

[0055] Compared with the prior art, this disclosure has the following beneficial effects:

[0056] (1) The template NH2-MIL-53(Al) used in this disclosure has the high specific surface area characteristic of MOF materials, so its adsorption capacity is superior. After the material is etched into a hollow structure, its specific surface area will increase, the number of active adsorption sites will increase, and its adsorption capacity will be enhanced accordingly. In this disclosure, the acid-etched hollow NH2-MIL-53(Al) material is first placed in an iron salt solution to adsorb Fe. 3+ The powder was then collected, vacuum dried, and then placed in a phosphate solution. At this point, Fe was adsorbed inside and on the surface of the hollow structure. 3+ The NH2-MIL-53(Al) material will continue to adsorb PO4. 3- At a specific pH value, iron phosphate materials with uniform MOF morphology were synthesized in situ, which could be uniformly dispersed and had small particle size.

[0057] (2) The modified iron phosphate particles prepared in this disclosure are fine powders. Compared with the iron phosphate agglomerates prepared in most existing technologies, the iron phosphate precursor prepared in this disclosure does not require a crushing process in the subsequent synthesis of lithium iron phosphate, which simplifies the process flow for preparing iron phosphate cathode materials.

[0058] (3) The modified iron phosphate prepared in this disclosure has good performance indicators and regular morphology. The lithium iron phosphate cathode material prepared from it also exhibits excellent electrochemical performance after being assembled into a lithium battery. The first charge-discharge capacity of LiFePO4 / C at room temperature can reach up to 158.6 mAh / g; the first charge-discharge efficiency can reach 99.2%; and the discharge capacity retention rate can still reach 99.5% after 300 cycles at 1C at 45℃.

[0059] After reading and understanding the accompanying diagrams and detailed descriptions, the other aspects can be understood. Attached Figure Description

[0060] The accompanying drawings are provided to further understand the technical solutions herein and form part of the specification. They are used together with the embodiments of this application to explain the technical solutions herein and do not constitute a limitation on the technical solutions herein.

[0061] Figure 1 This is a schematic diagram of the process for preparing modified iron phosphate according to an embodiment of this disclosure.

[0062] Figure 2 This is a SEM image of the modified iron phosphate prepared in Example 1 of this disclosure. Detailed Implementation

[0063] The technical solutions of this disclosure will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of this disclosure and should not be construed as specific limitations thereof.

[0064] Example 1

[0065] This embodiment provides a modified iron phosphate, and the preparation process of the modified iron phosphate is shown in the schematic diagram below. Figure 1 As shown, the modified iron phosphate is prepared by the following method:

[0066] (1) Dissolve 2 mmol Al(NO3)3·9H2O in 20 mL of deionized water, sonicate for 10 min, then add 10 wt% sodium dodecylbenzenesulfonate and stir until homogeneous to obtain solution A; dissolve 2 mmol 2-aminoterephthalic acid (NH2-H2BDC) in 40 mL of DMF and sonicate to obtain solution B; mix the two solutions and transfer them to a 100 mL high-pressure reactor, and heat in an oven at 150 °C for 48 h. After cooling to room temperature, collect the NH2-MIL-53(Al) product by centrifugation, and wash three times with DMF and anhydrous ethanol. Subsequently, the sample was vacuum dried at 120℃ for 12h to obtain NH2-MIL-53(Al) nanoparticles. 0.5g of NH2-MIL-53(Al) nanoparticles were dispersed in 20mL of anhydrous ethanol and sonicated to obtain dispersion A. 13mL of phytic acid solution (80g / L) was added dropwise to dispersion A and stirred evenly at room temperature. The mixture was then placed in a 50mL high-pressure reactor and heated in a 90℃ oven for 8h. After the reaction, the mixture was washed with anhydrous ethanol and deionized water, and dried in a vacuum oven at 120℃ for 12h to obtain hollow NH2-MIL-53(Al) powder.

[0067] (2) 0.5 g of hollow NH2-MIL-53(Al) powder was ultrasonically dispersed in 20 mL of deionized water, and then poured into 100 mL of 0.1 mol / L ferric chloride solution and stirred at room temperature for 3 h (mass ratio of NH2-MIL-53(Al) to Fe was 0.89:1). The product was collected by centrifugation and dried in an oven at 100 °C for 12 h. Subsequently, the dried powder was dispersed in 100 mL of 0.1 mol / L hydrogen phosphate solution, and 25% ammonia water was slowly added dropwise under stirring to control the pH of the solution to 1.8. The mixture was then heated at 70 °C, stirred continuously and kept warm for 6 h (speed was 400 rpm). After the mixture was dried, it was allowed to stand for 1 h. The precipitate was collected and washed several times with deionized water. Then it was dried in a vacuum oven at 100 °C for 12 h to obtain the modified ferric phosphate crude product.

[0068] (3) The modified iron phosphate crude product was placed in a muffle furnace and heated to 650°C at a rate of 5°C / min under a nitrogen atmosphere and held for 8 hours to obtain anhydrous FePO4 crude product coated with a nitrogen-doped carbon layer. Subsequently, the crude product was washed with acetic acid for 3 hours and deionized water for 1 hour to remove residual alumina impurities. After drying in a vacuum oven, the modified iron phosphate was obtained.

[0069] SEM images of the modified iron phosphate are shown below. Figure 2 As shown.

[0070] Example 2

[0071] This embodiment provides a modified iron phosphate, and the preparation process of the modified iron phosphate is shown in the schematic diagram below. Figure 1 As shown, the modified iron phosphate is prepared by the following method:

[0072] (1) Dissolve 1 mmol Al(NO3)3·9H2O in 20 mL of deionized water, sonicate for 10 min, then add 10 wt% sodium dodecylbenzenesulfonate and stir until homogeneous to obtain solution A; dissolve 1 mmol NH2-H2BDC in 40 mL of DMF and sonicate to obtain solution B; mix the two solutions and transfer them to a 100 mL high-pressure reactor, and heat in an oven at 170 °C for 36 h. After cooling to room temperature, collect the NH2-MIL-53(Al) product by centrifugation, and wash three times with DMF and anhydrous ethanol. Subsequently, the sample was vacuum dried at 120℃ for 12h to obtain NH2-MIL-53(Al) nanoparticles. 0.8g of NH2-MIL-53(Al) nanoparticles were dispersed in 30mL of anhydrous ethanol and sonicated to obtain dispersion A. 15mL of tannic acid solution (80g / L) was added dropwise to dispersion A and stirred evenly at room temperature. The mixture was then placed in a 100mL high-pressure reactor and heated in an oven at 90℃ for 12h. After the reaction, the mixture was washed with anhydrous ethanol and deionized water, and dried in a vacuum oven at 120℃ for 12h to obtain hollow NH2-MIL-53(Al) powder.

[0073] (3) 0.8 g of hollow NH2-MIL-53(Al) powder was ultrasonically dispersed in 20 mL of deionized water, and then poured into 100 mL of 0.15 mol / L ferric chloride solution and stirred at room temperature for 3 h (mass ratio of NH2-MIL-53(Al) to Fe was 0.95:1). The product was collected by centrifugation and dried in an oven at 100 °C for 12 h. Subsequently, the dried powder was dispersed in 100 mL of 0.15 mol / L ammonium hydrogen phosphate solution and poured into the above mixture. 25% sodium hydroxide solution was slowly added dropwise under stirring to control the pH of the solution to 1.5. The mixture was then heated at 70 °C, stirred continuously and kept warm for 10 h (speed was 400 rpm). After the mixture was finished, it was allowed to stand for 1 h to age. The precipitate was collected and washed several times with deionized water. Then it was placed in a vacuum oven at 100 °C and dried for 12 h to obtain the modified ferric phosphate crude product.

[0074] (3) The modified iron phosphate crude product prepared above is then placed in a muffle furnace and heated to 500°C at a rate of 5°C / min under a nitrogen atmosphere and held for 10 hours to obtain anhydrous FePO4 crude product coated with a nitrogen-doped carbon layer. Subsequently, the crude product is washed with acetic acid for 3 hours and deionized water for 1 hour to remove residual alumina impurities. After drying in a vacuum oven, the modified iron phosphate is obtained.

[0075] Example 3

[0076] This embodiment provides a modified iron phosphate, and the preparation process of the modified iron phosphate is shown in the schematic diagram below. Figure 1 As shown, the modified iron phosphate is prepared by the following method:

[0077] (1) Dissolve 1.5 mmol Al(NO3)3·9H2O in 20 mL of deionized water, sonicate for 10 min, then add 12 wt% sodium dodecylbenzenesulfonate and stir until homogeneous to obtain solution A; dissolve 1.5 mmol NH2-H2BDC in 40 mL of DMF and sonicate to obtain solution B; mix the two solutions and transfer them to a 100 mL high-pressure reactor, and heat in an oven at 180 °C for 24 h. After cooling to room temperature, collect the NH2-MIL-53(Al) product by centrifugation, and wash three times with DMF and anhydrous ethanol. Subsequently, the sample was vacuum dried at 120℃ for 12h to obtain NH2-MIL-53(Al) nanoparticles. 0.8g of NH2-MIL-53(Al) nanoparticles were dispersed in 30mL of anhydrous ethanol and sonicated to obtain dispersion A. 25mL of lauric acid solution (80g / L) was added dropwise to dispersion A and stirred evenly at room temperature. The mixture was then placed in a 100mL high-pressure reactor and heated in an oven at 110℃ for 8h. After the reaction, the mixture was washed with anhydrous ethanol and deionized water, and dried in a vacuum oven at 120℃ for 12h to obtain hollow NH2-MIL-53(Al) powder.

[0078] (3) 0.8 g of hollow NH2-MIL-53(Al) powder was ultrasonically dispersed in 20 mL of deionized water, and then poured into 50 mL of 0.3 mol / L ferric chloride solution and stirred at room temperature for 3 h (mass ratio of NH2-MIL-53(Al) to Fe was 0.95:1). The product was collected by centrifugation and dried in an oven at 100 °C for 12 h. Subsequently, the dried powder was dispersed in 50 mL of 0.3 mol / L ammonium hydrogen phosphate solution and poured into the above mixture. 20% sodium hydroxide solution was slowly added dropwise under stirring to control the pH of the solution to 2.2. The mixture was then heated at 90 °C, stirred continuously and kept warm for 4 h (speed was 400 rpm). After the mixture was finished, it was allowed to stand for 1 h to age. The precipitate was collected and washed several times with deionized water. Then it was placed in a vacuum oven at 100 °C and dried for 12 h to obtain the modified ferric phosphate crude product.

[0079] (3) The modified iron phosphate crude product prepared above is then placed in a muffle furnace and heated to 750°C at a rate of 5°C / min under a nitrogen atmosphere and held for 4 hours to obtain anhydrous FePO4 crude product coated with a nitrogen-doped carbon layer. Subsequently, the crude product is washed with acetic acid for 3 hours and deionized water for 1 hour to remove residual alumina impurities. After drying in a vacuum oven, the modified iron phosphate is obtained.

[0080] Example 4

[0081] The only difference between this embodiment and Example 1 is that the volume of the phytic acid solution is 6.25 mL (the mass ratio of NH2-MIL-53(Al) nanoparticles to the solute in the acid solution is 1:1), while the other conditions and parameters are exactly the same as in Example 1.

[0082] Example 5

[0083] The only difference between this embodiment and Example 1 is that the volume of the phytic acid solution is 18.75 mL (the mass ratio of NH2-MIL-53(Al) nanoparticles to the solute in the acid solution is 1:3), while the other conditions and parameters are exactly the same as in Example 1.

[0084] Example 6

[0085] The only difference between this embodiment and Example 1 is that the mass of NH2-MIL-53(Al) powder is 0.28g (the mass concentration ratio of NH2-MIL-53(Al) to iron ions is 0.5:1), and all other conditions and parameters are exactly the same as in Example 1.

[0086] Example 7

[0087] The only difference between this embodiment and Example 1 is that the mass of NH2-MIL-53(Al) powder is 0.84g (the mass concentration ratio of NH2-MIL-53(Al) to iron ions is 1.5:1), and the other conditions and parameters are exactly the same as in Example 1.

[0088] Comparative Example 1

[0089] The only difference between this comparative example and Example 2 is that NH2-MIL-53(Al) is not added; all other conditions and parameters are exactly the same as in Example 1.

[0090] Comparative Example 2

[0091] The only difference between this comparative example and Example 2 is that hollow NH2-MIL-53(Al) was directly placed in a mixed precursor solution of iron salt and phosphate. All other conditions and parameters were exactly the same as in Example 1.

[0092] Performance testing:

[0093] Lithium carbonate, modified iron phosphate, and glucose were dispersed in anhydrous ethanol at a stoichiometric ratio of lithium source, iron source, and carbon source of 1:1.03:0.07. The mixture was ball-milled for 3 h at 4000 rpm until homogeneous, followed by spray drying to obtain precursor powder. The precursor powder was then calcined at 400℃ for 1.5 h under a nitrogen atmosphere at a heating rate of 5℃ / min to obtain LiFePO4 / C cathode material. The obtained lithium iron phosphate cathode material was then used to construct coin cells for lithium-ion battery electrochemical performance testing. The test results are shown in Table 1.

[0094] Table 1

[0095]

[0096] As can be seen from Table 1, and from Examples 1-7, the modified iron phosphate battery described in this disclosure has a first charge-discharge specific capacity of over 150.7 mAh / g, a first charge-discharge efficiency of over 96.5%, and a capacity retention rate of over 97.3% after 300 1C cycles.

[0097] A comparison of Examples 1 and 4-5 shows that the mass ratio of NH2-MIL-53(Al) nanoparticles to the solute in the acid solution affects the performance of the modified ferric phosphate as disclosed in this disclosure. Controlling the mass ratio of NH2-MIL-53(Al) nanoparticles to the solute in the acid solution to 1:(1.5-2.5) yields better performance of the modified ferric phosphate. Excessive acid content can damage the structure of NH2-MIL-53(Al), potentially causing agglomeration of the ferric phosphate product. Insufficient acid content results in a smaller hollow volume inside the etched NH2-MIL-53(Al), leading to a smaller specific surface area and fewer active adsorption sites, thus affecting the synthesis of the ferric phosphate product.

[0098] A comparison of Examples 1 and 6-7 shows that the mass concentration ratio of NH2-MIL-53(Al) to iron ions affects the performance of the modified iron phosphate described in this disclosure. Controlling the mass concentration ratio of NH2-MIL-53(Al) to iron ions at (0.8–1.2):1 yields modified iron phosphate with better performance. Excessive or insufficient addition of NH2-MIL-53(Al) will affect its resistance to Fe. 3+ and PO4 3- The adsorption of ferric phosphate can affect the purity of the product.

[0099] Comparing Example 1 and Comparative Example 1, it can be seen that, compared with the large-sized irregular iron phosphate agglomerates prepared directly by co-precipitation method in Comparative Example 1, the iron phosphate particles prepared by the present disclosure using hollow template NH2-MIL-53(Al) are smaller in size and more uniformly dispersed, and the lithium battery made from its cathode material also has better electrochemical performance.

[0100] A comparison of Example 1 and Comparative Example 2 shows that if the hollow NH2-MIL-53(Al) template is directly placed in a mixed precursor solution of iron salt and phosphate, some Fe2+ that has not yet been adsorbed and is in a free state will be released. 3+ PO4 3- It may generate more iron phosphate with irregular morphology and easy agglomeration, which will reduce the electrochemical performance of lithium iron phosphate cathode materials prepared from it.

Claims

1. A method for preparing modified iron phosphate, comprising the following steps: (1) Aluminum salt, sodium dodecylbenzenesulfonate and a first solvent are mixed to obtain a first solution. 2-aminoterephthalic acid and a second solvent are mixed to obtain a second solution. The first solution and the second solution are mixed and heated to obtain NH2-MIL-53(Al) nanoparticles. The NH2-MIL-53(Al) nanoparticles are mixed with a third solvent, an acid solution is added, and the mixture is heated and stirred to obtain hollow NH2-MIL-53(Al) powder. The acid solution includes any one or a combination of at least two of phytic acid, tannic acid, or lauric acid. (2) Prepare an NH2-MIL-53(Al) dispersion by hollow NH2-MIL-53(Al) powder, mix the dispersion with an iron salt solution, stir and dry, mix the obtained powder with a phosphorus source solution, control the pH and carry out the reaction; (3) The material obtained after aging is sintered to obtain the modified iron phosphate.

2. The preparation method according to claim 1, wherein, The aluminum salt in step (1) includes aluminum nitrate.

3. The preparation method according to claim 1, wherein, The first solvent includes water.

4. The preparation method according to claim 1, wherein, The mixing and stirring time for the first solution is 3 to 5 hours.

5. The preparation method according to claim 1, wherein, The molar concentration of aluminum salt in the first solution is 0.05~0.1 mol / L.

6. The preparation method according to claim 1, wherein, The mass concentration of sodium dodecylbenzenesulfonate in the first solution is 10-15%.

7. The preparation method according to claim 1, wherein, The second solvent includes DMF.

8. The preparation method according to claim 1, wherein, The molar concentration of 2-aminoterephthalic acid in the second solution is 0.025~0.05 mol / L.

9. The preparation method according to claim 1, wherein, The volume ratio of the first solution to the second solution is 1:(1.5~2.5).

10. The preparation method according to claim 1, wherein, The heating reaction in step (1) is carried out at a temperature of 150~180℃.

11. The preparation method according to claim 1, wherein, The heating reaction takes 24 to 48 hours.

12. The preparation method according to claim 1, wherein, The heating reaction is followed by cooling, washing, and drying.

13. The preparation method according to claim 1, wherein, The third solvent in step (1) includes anhydrous ethanol.

14. The preparation method according to claim 1, wherein, The concentration of the acid solution is 50~100g / L.

15. The preparation method according to claim 1, wherein, The mass ratio of the NH2-MIL-53(Al) nanoparticles to the solute in the acid solution is 1:(1.5~2.5).

16. The preparation method according to claim 1, wherein, The heating and stirring temperature in step (1) is 90~110℃.

17. The preparation method according to claim 1, wherein, The heating and stirring time is 8-12 hours.

18. The preparation method according to claim 1, wherein, The mixture is heated and stirred before being centrifuged, washed, and dried.

19. The preparation method according to claim 1, wherein, The solvent for the NH2-MIL-53(Al) dispersion in step (2) includes water.

20. The preparation method according to claim 1, wherein, The solutes in the iron salt solution include ferric nitrate and / or ferric chloride.

21. The preparation method according to claim 1, wherein, The concentration of the iron salt solution is 0.1~0.3 mol / L.

22. The preparation method according to claim 1, wherein, The mass concentration ratio of NH2-MIL-53(Al) to iron ions after mixing is (0.8~1.2):

1.

23. The preparation method according to claim 1, wherein, The stirring time is 3-5 hours.

24. The preparation method according to claim 1, wherein, The solute in the phosphorus source solution in step (2) includes any one or a combination of at least two of the following: ammonium dihydrogen phosphate, ammonium hydrogen phosphate, or sodium hydrogen phosphate.

25. The preparation method according to claim 1, wherein, The concentration of phosphorus in the phosphorus source solution is 0.1~0.3 mol / L.

26. The preparation method according to claim 1, wherein, The molar ratio of phosphorus in the phosphorus source solution to iron in the iron salt solution is 1:(0.97~1.05).

27. The preparation method according to claim 1, wherein, The method for controlling pH includes adding an alkaline solution.

28. The preparation method according to claim 27, wherein, The alkaline solution includes ammonia and / or sodium hydroxide solution.

29. The preparation method according to claim 1, wherein, The pH is 1.5 to 2.

2.

30. The preparation method according to claim 1, wherein, Heating and stirring are performed during the reaction.

31. The preparation method according to claim 30, wherein, The heating and stirring temperature is 70~90℃.

32. The preparation method according to claim 30, wherein, The heating and stirring time is 4 to 10 hours.

33. The preparation method according to claim 30, wherein, The process involves heating and stirring followed by aging.

34. The preparation method according to claim 33, wherein, The aging time is 1 to 2 hours.

35. The preparation method according to claim 1, wherein, The sintering temperature in step (3) is 500~750℃.

36. The preparation method according to claim 1, wherein, The sintering process takes 4 to 10 hours.

37. The preparation method according to claim 1, wherein, The atmosphere for the sintering process includes a nitrogen atmosphere.

38. The preparation method according to claim 1, wherein, The sintering process is followed by a washing process.

39. The preparation method according to claim 38, wherein, The washing process includes acetic acid washing and water washing.

40. A modified iron phosphate prepared by the method according to any one of claims 1-39.

41. A lithium iron phosphate cathode material prepared by sintering modified iron phosphate and lithium source as described in claim 40.

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