Modified iron phosphate, and preparation method therefor and use thereof

Abstract

Modified iron phosphate, and a preparation method therefor and the use thereof. The preparation method comprises the following steps: (1) mixing starch and water to obtain a starch suspension, injecting the starch suspension, an iron source solution and a phosphate solution into a reaction device in a parallel flow manner, controlling the pH value in the system to perform a first-step reaction, and performing solid-liquid separation, so as to obtain a precipitate; (2) mixing the precipitate with an amylase solution, and heating same to perform a second-step reaction, so as to obtain a precursor; and (3) sintering the precursor, so as to obtain modified iron phosphate. By introducing starch during the co-precipitation process of iron phosphate, the starch is continuously and slowly hydrolyzed under acidic conditions and is then thoroughly hydrolyzed by means of amylase, and finally, iron phosphate of a porous hollow structure is spontaneously synthesized after the complete hydrolysis thereof, thereby shortening the diffusion path of lithium ions and improving the electrical properties.

Description

A modified ferric phosphate and its preparation method and application Technical Field

[0001] The present disclosure belongs to the technical field of battery materials and relates to a modified iron phosphate and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries (LIBs) are currently an important rechargeable battery technology, widely used in mobile electronic devices, electric vehicles, and energy storage systems. Compared to other rechargeable battery technologies, lithium-ion batteries have many advantages, such as high energy density, which can store more energy; long cycle life, which allows for multiple charge and discharge cycles; and fast charging speed, which can usually be completed within a few hours. Lithium iron phosphate (LiFePO4), as a leader in lithium-ion battery performance and with low raw material costs, has attracted widespread attention and become a commercial darling in recent years. However, LiFePO4 also has its own shortcomings. Its excellent cycle performance is due to its stable olivine crystal structure, but it is precisely because of this structure that its lithium ions can only diffuse in one-dimensional channels, resulting in slow lithium ion and electron transfer rates. These problems have greatly limited the electrical performance of lithium iron phosphate batteries.

[0003] The most widely used method for synthesizing lithium iron phosphate is to use iron phosphate as the raw material and react it with a lithium source through sintering. This method has the advantages of high purity, stable performance, and simple operation, making it suitable for large-scale industrial production. However, even small changes in the microstructure and chemical composition of iron phosphate can have a significant impact on the performance of LiFePO4 / C. Therefore, the preparation of excellent iron phosphate is crucial for lithium-ion batteries. Most methods for improving lithium-ion transmission rate use the creation of porous structures to shorten the diffusion path of lithium ions.

[0004] CN111362243A introduces a silicon dioxide core and uses it as a carrier and template to prepare iron phosphate, which is then transferred to a hydrofluoric acid solution to etch away the template to obtain a hollow iron phosphate and then synthesize lithium iron phosphate material. This method can improve the electrochemical performance of the battery, but this method introduces additional templates and template removal agents, which increases the preparation cost. In addition, hydrofluoric acid is a strong acid with strong corrosiveness, which limits its operation.

[0005] CN109052358A discloses a method for preparing mesoporous-macroporous ferric phosphate, comprising the following steps: S1, dissolving P123 as a template in an acidic solution and stirring until the solution is clear; S2, preparing a ferrous salt solution, mixing the ferrous salt solution with phosphoric acid in proportion to obtain an iron salt base solution; weighing phosphate according to the molar ratio of total iron to total phosphorus, dissolving the weighed phosphate and adding excess hydrogen peroxide to obtain a phosphate solution; S3, adding the phosphate solution to the iron salt base solution, and simultaneously slowly adding the P123 solution treated in step S1; heating the solution after the addition is completed, reducing the stirring speed after the heating is completed, and maintaining the temperature for reaction under uniform stirring; S4, filtering and washing the product obtained after the reaction in step S3, and then calcining the product to remove the template to obtain anhydrous ferric phosphate.

[0006] The above-mentioned method introduces templates and removes them, which increases process time and cost, and the resulting iron phosphate has poor structural stability. Therefore, finding a simple method to prepare porous iron phosphate is of great significance for the subsequent industrialization and commercialization of lithium-ion batteries.

[0007] Summary of the Invention

[0008] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0009] The purpose of the present disclosure is to provide a modified ferric phosphate and its preparation method and application. The present disclosure introduces starch during the ferric phosphate co-precipitation process, and the starch is slowly hydrolyzed under acidic conditions. Then, amylase is used to completely hydrolyze the starch, and finally the hydrolysis is completely and spontaneously synthesized into a porous hollow structure of ferric phosphate, thereby shortening the lithium ion diffusion path and improving the electrical performance.

[0010] To achieve this purpose, the present disclosure adopts the following technical solutions:

[0011] In a first aspect, the present disclosure provides a method for preparing modified ferric phosphate, the preparation method comprising the following steps:

[0012] (1) mixing starch and water to obtain a starch suspension, injecting the starch suspension, an iron source solution, and a phosphate solution into a reaction device in parallel, controlling the pH in the system to perform a one-step reaction, and performing solid-liquid separation to obtain a precipitate;

[0013] (2) mixing the precipitate with an amylase solution and heating the mixture to perform a two-step reaction to obtain a precursor;

[0014] (3) Sintering the precursor to obtain the modified iron phosphate.

[0015] The present invention adopts starch as the core structure of the hollow structure of iron phosphate, and then utilizes the hydrolysis property of starch itself to slowly hydrolyze the insoluble matter into glucose and dissolve it in the aqueous solution. During the co-precipitation of iron phosphate, the starch coexists with the iron phosphate from the insoluble state to the gradual hydrolysis process, and the two are in a state of coating each other. As the reaction proceeds, the starch gradually hydrolyzes the iron phosphate into a hollow porous structure. The viscosity of the starch increases in the gelatinized state, which acts as a barrier to inhibit the agglomeration of particles during the pre-synthesis process of the material.

[0016] In one embodiment, the starch in step (1) comprises any one of corn starch, potato starch or tapioca starch, or a combination of at least two of them.

[0017] In one embodiment, the starch has a particle size of 50 to 250 nm, for example, 50 nm, 80 nm, 100 nm, 150 nm or 250 nm.

[0018] In one embodiment, the mass concentration of the starch suspension is 2-15%, for example, 2%, 5%, 8%, 10% or 15%.

[0019] The present invention can control the hydrolysis rate of starch and the pore size of the generated iron phosphate by controlling the particle size and concentration of starch in the starch suspension.

[0020] In one embodiment, the starch suspension is subjected to ultrasonic treatment.

[0021] In one embodiment, the ultrasonic treatment time is 0.5 to 2 h, for example, 0.5 h, 0.8 h, 1 h, 1.5 h or 2 h.

[0022] The present invention pre-ultrasonicates the starch suspension to effectively improve the dispersibility of the starch suspension.

[0023] In one embodiment, the solute of the iron source solution in step (1) includes ferric nitrate and / or ferric chloride.

[0024] In one embodiment, the concentration of the iron source solution is 0.5 to 2.5 mol / L, for example, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, or 2.5 mol / L.

[0025] In one embodiment, the solute of the phosphate solution includes any one of ammonium dihydrogen phosphate, ammonium hydrogen phosphate, phosphoric acid, sodium dihydrogen phosphate or sodium hydrogen phosphate, or a combination of at least two thereof.

[0026] In one embodiment, the concentration of the phosphate solution is 0.5 to 2.5 mol / L, for example, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L or 2.5 mol / L.

[0027] In one embodiment, the molar ratio of the iron element in the iron source solution to the phosphate in the phosphate solution is (0.97-1.02):1, for example: 0.97:1, 0.99:1, 1:1, 1.01:1 or 1.02:1.

[0028] The present invention can produce iron phosphate with a suitable phosphorus-iron ratio by controlling the molar ratio of the iron element in the iron source solution and the phosphate radical in the phosphate solution within the above range, thereby avoiding the generation of impurities.

[0029] In one embodiment, the reaction device in step (1) includes a clearing device, a material receiving device and a reactor.

[0030] In one embodiment, the feed rate and the clearing device are controlled to ensure that the concentration of the starch suspension in the reactor remains constant, and the slurry precipitated at the bottom of the reactor is returned to the reactor through the material receiving port to continue growing, thereby achieving internal circulation of the material and improving the material recovery rate.

[0031] The present disclosure uses the above-mentioned device to improve production efficiency, realize internal circulation of materials and increase material recovery rate.

[0032] In one embodiment, the method of controlling the pH in the system comprises adding an alkaline solution.

[0033] The present invention can generate a precipitate by adjusting the pH by adding an alkaline solution, and then carry out subsequent processes through post-treatment such as filtration and washing.

[0034] In one embodiment, the alkaline solution comprises aqueous ammonia.

[0035] In one embodiment, the pH is 1.4 to 2.2, for example, 1.4, 1.6, 1.8, 2, 2.1 or 2.2.

[0036] In one embodiment, during the one-step reaction, the mass concentration of starch in the system is 2% to 10%, for example, 2%, 4%, 6%, 8% or 10%.

[0037] During the one-step reaction process disclosed herein, the concentration of starch in the reaction system affects its performance. When the starch concentration is controlled at 2-10%, the modified iron phosphate obtained has better performance. If the starch concentration is too low, the starch content in the solution is too little, and the hydrolysis pore-forming effect cannot be achieved, resulting in poor dense packing performance of the iron phosphate obtained. If the starch concentration is too high, the modified iron phosphate obtained has a porous structure of uneven size, the volume increases, and the active substance of the material decreases, affecting the capacity and performance of the battery synthesized in the later stage of lithium iron phosphate.

[0038] In one embodiment, the aging temperature of the one-step reaction is 50-90°C, for example, 50°C, 60°C, 70°C, 80°C or 90°C.

[0039] In one embodiment, the aging time of the one-step reaction is 3 to 12 hours, for example, 3 hours, 5 hours, 8 hours, 10 hours or 12 hours.

[0040] The present disclosure can improve the crystal structure stability of the material through aging.

[0041] In one embodiment, the mass concentration of the amylase solution in step (2) is 0.5-2.5%, for example: 0.5%, 1%, 1.5%, 2% or 2.5%.

[0042] In one embodiment, the mass ratio of the precipitate to the amylase solution is 1:(1-3), for example: 1:1, 1:1.5, 1:2, 1:2.5 or 1:3, etc.

[0043] The present invention controls the mass concentration of the amylase solution and the mass ratio of the precipitate to the amylase solution within the above ranges, thereby controlling the hydrolysis rate of starch and producing iron phosphate having a loose, hollow, porous structure and good stability.

[0044] In one embodiment, the temperature of the second-step reaction is 35-75°C, for example, 35°C, 40°C, 50°C, 60°C or 75°C.

[0045] In one embodiment, ultrasonic treatment is performed during the two-step reaction.

[0046] In one embodiment, the two-step reaction time is 15 to 90 minutes, for example, 15 minutes, 20 minutes, 40 minutes, 50 minutes or 90 minutes.

[0047] In one embodiment, the sintering temperature in step (3) is 500-550°C, for example, 500°C, 510°C, 520°C, 540°C or 550°C.

[0048] The present invention discloses a method of sintering at a relatively low temperature to remove crystal water (the conventional method of sintering to form pores using carbon materials as templates, when the sintering temperature is too high, some pores inside the material will collapse, thereby causing the material structure stability to deteriorate), which can reduce the impact of high temperature on the material structure and avoid problems such as pore collapse caused by high-temperature sintering.

[0049] In one embodiment, the sintering treatment time is 4 to 8 hours, for example, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours.

[0050] In a second aspect, the present disclosure provides a modified ferric phosphate, which is prepared by the method described in the first aspect.

[0051] The iron phosphate prepared by the method disclosed in the present invention has a loose, hollow and porous structure, an increased specific surface area and a more sufficient contact area, a shortened ion diffusion path and an increased diffusion path. The lithium iron phosphate prepared thereby also has a loose, porous, hollow structure. The presence of this structure can significantly shorten the diffusion path of lithium ions, increase the lithium ion transmission speed and thereby enhance the electrochemical performance of the battery.

[0052] In a third aspect, the present disclosure provides a lithium iron phosphate, which is prepared by mixing the modified iron phosphate described in the second aspect with a lithium source and a carbon source and subjecting the mixture to a calcination treatment.

[0053] In one embodiment, the lithium source includes any one of lithium carbonate, lithium hydroxide, or lithium acetate, or a combination of at least two thereof.

[0054] In one embodiment, the carbon source comprises any one or a combination of at least two of glucose, sucrose, phenolic resin, starch, dextrin, citric acid, oxalic acid, cellulose or vitamins.

[0055] In one embodiment, the mass of the carbon source is 3% to 15% of the total mass of the iron phosphate and the lithium source, for example, 3%, 5%, 8%, 10% or 15%.

[0056] In one embodiment, the mixing comprises mixing the modified ferric phosphate with the lithium source and grinding the mixture before adding the carbon source.

[0057] In one embodiment, the calcination process includes one-step calcination and two-step calcination.

[0058] The present disclosure uses a two-step calcination method to produce a lithium iron phosphate positive electrode material with both good capacity performance and cycle performance without affecting the material structure.

[0059] In one embodiment, the temperature of the one-step calcination is 300-500°C, for example, 300°C, 350°C, 450°C, 480°C or 500°C.

[0060] In one embodiment, the one-step calcination time is 0.5 to 3 hours, for example, 0.5 hours, 0.85 hours, 1 hour, 2 hours or 3 hours.

[0061] In one embodiment, the temperature of the second-step calcination is 500-850°C, for example, 500°C, 600°C, 700°C, 800°C or 850°C.

[0062] In one embodiment, the second-step calcination time is 6 to 18 hours, for example, 6 hours, 8 hours, 10 hours, 15 hours or 18 hours.

[0063] In a fourth aspect, the present disclosure provides a lithium-ion battery, wherein the lithium-ion battery comprises the lithium iron phosphate as described in the third aspect.

[0064] Compared with the prior art, the present disclosure has the following beneficial effects:

[0065] (1) The method disclosed in the present invention is simple and easy to implement, and avoids the introduction of templates and template removal agents to increase unnecessary component introduction and preparation steps. In addition, by controlling the degree of starch hydrolysis and the number of subsequent washings, part of the hydrolysis product can be retained on the iron phosphate, and after high-temperature calcination, carbon is formed to in situ coat the iron phosphate to improve conductivity.

[0066] (2) The iron phosphate prepared by the method disclosed in the present invention has a loose, hollow, and porous structure, with an increased specific surface area and a more sufficient contact area, and the ion diffusion path is shortened and increased. The lithium iron phosphate prepared therefrom also has a loose, porous, and hollow structure. The presence of this structure can significantly shorten the diffusion path of lithium ions, increase the lithium ion transmission speed, and thereby enhance the electrochemical performance of the battery.

[0067] (3) The battery made of the modified iron phosphate disclosed in the present invention has a 0.1C discharge capacity of more than 156.9 mAh / g, a 0.5C discharge capacity of more than 150.4 mAh / g, a 1C discharge capacity of more than 145.9 mAh / g, and a 2C discharge capacity of more than 141.2 mAh / g.

[0068] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0070] FIG1 is a 5000-fold SEM image of the modified iron phosphate described in Example 1 of the present disclosure. DETAILED DESCRIPTION

[0071] The technical solution of the present disclosure is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present disclosure and should not be regarded as specific limitations of the present disclosure.

[0072] Example 1

[0073] This embodiment provides a modified ferric phosphate, and the preparation method of the modified ferric phosphate is as follows:

[0074] (1) Under ultrasonic conditions, potato starch with a particle size of 150 nm was uniformly dispersed in deionized water to prepare an 8% starch suspension. Ferric chloride and ammonium dihydrogen phosphate were weighed to prepare 1 mol / L ferric chloride and 1 mol / L ammonium dihydrogen phosphate solutions, respectively. The ferric chloride solution and the ammonium dihydrogen phosphate solution were slowly injected into a stirred tank at a molar ratio of 1:1, and stirred at a stirring speed of 1200 rpm until the mixture was uniformly mixed. At the same time, the starch suspension was injected at a controlled flow rate so that the starch concentration in the reactor was always maintained at 3%. At the same time, 25% ammonia water was slowly added dropwise to adjust the solution to pH = 1.6. The mixture was heated to 55°C with stirring for 8 h to obtain a precipitate.

[0075] (2) placing the precipitate in a 1% amylase solution, controlling the pH to 5, heating to 60° C. and maintaining the temperature for 30 min, and using ultrasound to promote the final hydrolysis of starch into glucose to obtain a precursor;

[0076] (3) The precursor was washed four times with deionized water, dried in a vacuum drying oven at 85°C for 8 h, placed in a muffle furnace, and heated to 520°C at a heating rate of 5°C / min and kept warm for 6 h to obtain the modified iron phosphate. The SEM image of the modified iron phosphate is shown in Figure 1.

[0077] Example 2

[0078] This embodiment provides a modified ferric phosphate, and the preparation method of the modified ferric phosphate is as follows:

[0079] (1) Under ultrasonic conditions, corn starch with a particle size of 50 nm was uniformly dispersed in deionized water to prepare a 5% starch suspension. Ferric nitrate and ammonium hydrogen phosphate were weighed to prepare 1 mol / L ferric nitrate and 1 mol / L ammonium hydrogen phosphate solutions, respectively. The ferric nitrate solution and the ammonium hydrogen phosphate solution were slowly injected into a stirred tank at a molar ratio of 1:1, and stirred at a stirring speed of 1200 rpm until the mixture was uniformly mixed. At the same time, the starch suspension was injected at a controlled flow rate so that the starch concentration in the reactor was always maintained at 5%. At the same time, 25% ammonia water was slowly added dropwise to adjust the solution to pH = 2.0. The mixture was heated to 90°C with stirring for 3 h to obtain a precipitate.

[0080] (2) placing the precipitate in a 2% amylase solution, controlling the pH to 5, heating to 40° C. and maintaining the temperature for 80 min, and using ultrasound to promote the final hydrolysis of starch into glucose to obtain a precursor;

[0081] (3) The precursor was washed four times with deionized water, dried in a vacuum drying oven at 85° C. for 8 h, placed in a muffle furnace, and heated to 500° C. at a heating rate of 5° C. / min and kept warm for 8 h to obtain the modified iron phosphate.

[0082] Example 3

[0083] This embodiment provides a modified ferric phosphate, and the preparation method of the modified ferric phosphate is as follows:

[0084] (1) Under ultrasonic conditions, cassava starch is uniformly dispersed in deionized water to prepare a starch suspension with a concentration of 15%. Ferric chloride and ammonium dihydrogen phosphate are weighed to prepare 1 mol / L ferric chloride and 1 mol / L ammonium dihydrogen phosphate solutions, respectively. The ferric chloride solution and the ammonium dihydrogen phosphate solution are slowly injected into a stirred tank at a molar ratio of 1:1, and stirred at a stirring speed of 1200 rpm until the mixture is uniformly mixed. At the same time, the starch suspension is injected at a controlled flow rate so that the starch concentration in the reactor is always maintained at 8%. At the same time, 25% ammonia water is slowly added dropwise to adjust the solution to pH = 1.4, and the mixture is heated to 50°C with stirring for 12 hours to obtain a precipitate;

[0085] (2) placing the precipitate in a 2.5% amylase solution, controlling the pH to 5, heating to 75° C. and maintaining the temperature for 25 min, and using ultrasound to promote the final hydrolysis of starch into glucose to obtain a precursor;

[0086] (3) The precursor was washed four times with deionized water, dried in a vacuum drying oven at 85° C. for 8 h, placed in a muffle furnace, and heated to 550° C. at a heating rate of 5° C. / min and kept warm for 4 h to obtain the modified iron phosphate.

[0087] Example 4

[0088] The only difference between this embodiment and embodiment 1 is that the concentration of starch in the reactor is 1%, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0089] Example 5

[0090] The only difference between this embodiment and embodiment 1 is that the concentration of starch in the reactor is 15%, and other conditions and parameters are exactly the same as those in embodiment 1.

[0091] Comparative Example 1

[0092] The only difference between this comparative example and Example 1 is that no amylase is added, and other conditions and parameters are exactly the same as those in Example 1.

[0093] Comparative Example 2

[0094] This comparative example provides a kind of iron phosphate, and the preparation method of the iron phosphate is as follows:

[0095] (1) Weighing ferric chloride and ammonium dihydrogen phosphate to prepare 1 mol / L ferric chloride and 1 mol / L ammonium dihydrogen phosphate solutions, respectively, the ferric chloride solution and the ammonium dihydrogen phosphate solution were mixed at a molar ratio of 1:1, and stirred at a stirring speed of 1200 rpm until the mixture was uniformly mixed;

[0096] (2) Slowly add 25% ammonia water to adjust the solution to pH = 1.8, stir and heat to 60 ° C for 8 hours to obtain a precipitate, and filter the precipitate;

[0097] (3) The filtered precipitate was washed three times with deionized water, and dried in a vacuum drying oven at 85°C for 8 h to obtain a precursor. The precursor prepared above was then placed in a muffle furnace, heated to 550°C at a heating rate of 5°C / min, and kept warm for 8 h to obtain the iron phosphate.

[0098] Performance testing:

[0099] The modified iron phosphate and lithium carbonate and glucose were prepared in the embodiment and comparative example according to the stoichiometric ratio of lithium, iron and carbon elements of 1:1.03:0.07 and uniformly dispersed in water. The mixture was ball-milled at a speed of 4000 rpm for 5 h until uniformly mixed, and then spray-dried to obtain a precursor powder. The precursor powder was kept at 400 ° C for 1.5 h at a heating rate of 5 ° C / min under a nitrogen atmosphere, and then heated to 750 ° C and calcined at a high temperature for 10 h to obtain lithium iron phosphate. The lithium iron phosphate was uniformly mixed with the conductive agent acetylene black and the adhesive polyvinylidene fluoride in N-methyl pyrrolidone at a ratio of 92:4:4, and then coated on aluminum foil and placed in a vacuum drying oven for drying. After drying, the battery was assembled in an argon glove box and pressed into a positive electrode sheet with a tablet press. The negative electrode was a metal lithium sheet. The electrolyte was 1M LiPF6-EC:DMC (volume ratio 1:1) and a polypropylene porous membrane was used as a diaphragm. The charge and discharge voltage was controlled between 2.5-4.5V to test its electrochemical performance. The test results are shown in Table 1:

[0100] Table 1

[0101] As can be seen from Table 1, from Examples 1-3, the battery prepared by the modified iron phosphate disclosed in the present invention has a 0.1C discharge capacity of more than 156.9 mAh / g, a 0.5C discharge capacity of more than 150.4 mAh / g, a 1C discharge capacity of more than 145.9 mAh / g, and a 2C discharge capacity of more than 141.2 mAh / g.

[0102] By comparing Example 1 with Examples 4-5, it can be seen that in the preparation process of the modified iron phosphate described in the present disclosure, the concentration of starch in the reaction system will affect its performance. When the starch concentration is controlled at 2-10%, the performance of the modified iron phosphate obtained is better. If the starch concentration is too low and the starch content in the solution is too little, the hydrolysis pore-forming effect cannot be achieved, and the dense stacking performance of the obtained iron phosphate is poor. If the starch concentration is too high, the modified iron phosphate obtained has a porous structure of uneven size, the volume becomes larger, and the active substance of the material becomes less, which affects the battery capacity and performance of the later synthesized lithium iron phosphate.

[0103] By comparing Example 1 and Comparative Example 1, it can be seen that when amylase is not added, starch is not completely hydrolyzed and will remain inside the iron phosphate. It will be removed by high-temperature dehydration later, but it will affect the crystallinity of the iron phosphate. Compared with iron phosphate with residual starch, iron phosphate without starch has better crystallinity after high-temperature dehydration.

[0104] By comparing Example 1 and Comparative Example 2, it can be seen that the present invention introduces starch during the co-precipitation of iron phosphate, the starch is slowly hydrolyzed under acidic conditions, and then the starch is completely hydrolyzed using amylase, and finally the hydrolysis is completely and spontaneously synthesized to form a porous hollow structure of iron phosphate, thereby shortening the lithium ion diffusion path and improving the electrical performance.

Claims

1. A method for preparing modified ferric phosphate, comprising the following steps: (1) mixing starch and water to obtain a starch suspension, injecting the starch suspension, an iron source solution and a phosphate solution into a reaction device in parallel, controlling the pH in the system to perform a one-step reaction, and performing solid-liquid separation to obtain a precipitate; (2) mixing the precipitate with an amylase solution and heating the mixture to perform a two-step reaction to obtain a precursor; (3) Sintering the precursor to obtain the modified iron phosphate.

2. The preparation method according to claim 1, wherein The particle size of the starch in step (1) is 50 to 250 nm.

3. The preparation method according to claim 1 or 2, wherein: The mass concentration of the starch suspension is 2-15%.

4. The preparation method according to any one of claims 1 to 3, wherein Step (1) subjecting the starch suspension to ultrasonic treatment; And / or, the ultrasonic treatment time is 0.5 to 2 hours.

5. The preparation method according to any one of claims 1 to 4, wherein: The molar ratio of the iron element in the iron source solution and the phosphate in the phosphate solution in step (1) is (0.97-1.02):

1.

6. The preparation method according to any one of claims 1 to 5, wherein: The reaction device in step (1) includes a clearing device, a material receiving device and a reaction kettle; And / or, the feed rate and the clearing device are controlled to ensure that the concentration of the starch suspension in the reactor remains constant, and the slurry precipitated at the bottom of the reactor is returned to the reactor through the feed inlet to continue growing, thereby achieving internal circulation of the material and improving the material recovery rate.

7. The preparation method according to any one of claims 1 to 6, wherein: The method for controlling the pH in the system in step (1) comprises adding an alkaline solution; And / or, the pH is 1.4 to 2.

2.

8. The preparation method according to any one of claims 1 to 7, wherein: During the one-step reaction in step (1), the mass concentration of starch in the system is 2-10%.

9. The preparation method according to any one of claims 1 to 8, wherein: The aging temperature of the one-step reaction in step (12) is 50 to 90° C. And / or, the aging time of the one-step reaction is 3 to 12 hours.

10. The preparation method according to any one of claims 1 to 9, wherein: The mass concentration of the amylase solution in step (2) is 0.5-2.5%.

11. The preparation method according to any one of claims 1 to 9, wherein: The mass ratio of the precipitate to the amylase solution in step (2) is 1:(1-3).

12. The preparation method according to any one of claims 1 to 11, wherein: The temperature of the second step reaction in step (2) is 35-75°C; And / or, ultrasonic treatment is performed during the two-step reaction; And / or, the time of the two-step reaction is 15 to 90 minutes.

13. The preparation method according to any one of claims 1 to 12, wherein: The sintering temperature in step (3) is 500-550° C. And / or, the sintering treatment time is 4 to 8 hours.

14. A modified iron phosphate obtained by the method according to any one of claims 1 to 13.

15. A lithium iron phosphate, wherein the lithium iron phosphate is prepared by mixing the modified iron phosphate according to claim 14 with a lithium source and a carbon source and subjecting the mixture to a calcination treatment.

16. The lithium iron phosphate according to claim 15, wherein: The calcination treatment includes one-step calcination and two-step calcination; And / or, the temperature of the one-step calcination is 300-500°C; And / or, the one-step calcination time is 0.5 to 3 hours; And / or, the temperature of the second-step calcination is 500-850°C; And / or, the time of the second-step calcination is 6 to 18 hours.

17. A lithium ion battery comprising the lithium iron phosphate according to claim 15 or 16.

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