A multi-porous iron phosphate precursor, lithium iron phosphate material and preparation method thereof

Abstract

The present invention provides a multi-porous iron phosphate precursor, a lithium iron phosphate material and a preparation method thereof, which belongs to the technical field of positive electrode materials. When the multi-porous iron phosphate material precursor provided by the present invention is applied to a battery, it can increase the infiltration area of ​​the electrolyte and shorten the Li + The ion diffusion path is improved, thereby improving the battery's rate performance and low-temperature performance; and also improving the battery's electronic conductivity. At the same time, the preparation method provided by the present disclosure is simple to operate and is conducive to actual production.

Description

Technical Field

[0001] The present disclosure belongs to the technical field of positive electrode materials, and in particular relates to a multi-porous iron phosphate precursor, a lithium iron phosphate material and a preparation method thereof. Background Art

[0002] Since 1997, the cathode material LiFePO4 (lithium iron phosphate) has attracted widespread attention due to its high theoretical capacity, good safety, long cycle life, and low cost. Compared to other lithium-ion battery cathode materials such as LiMn2O4 (lithium manganese oxide), LiNiO2 (lithium nickel oxide), LiCoO2 (lithium cobalt oxide), and ternary materials (nickel, cobalt, and manganese), lithium manganese oxide has poor cycling stability at low capacities and high temperatures; lithium nickel oxide has poor thermal stability; lithium cobalt oxide has poor overcharge resistance and high cost; and ternary materials have safety issues. Therefore, comprehensive comparisons have made the performance research and development of lithium iron phosphate a current hot topic and priority.

[0003] The iron phosphate process uses iron phosphate as a precursor, which is then uniformly mixed with a lithium source and a carbon source, and then subjected to a high-temperature carbothermal reduction reaction to synthesize lithium iron phosphate cathode materials. The structure, morphology, and reactivity of the iron phosphate precursor significantly influence the performance of the resulting lithium iron phosphate cathode material. Therefore, focusing on the preparation technology of iron phosphate is of great significance for improving the electrochemical performance of lithium iron phosphate cathode materials and promoting their industrial application.

[0004] The morphology, structure and particle size distribution of the precursor iron phosphate are believed to affect the various properties of lithium iron phosphate. Therefore, in order to prepare high-performance lithium iron phosphate materials, it is necessary to prepare a high-performance iron phosphate precursor first. However, due to the inherent characteristics of the lithium iron phosphate olivine structure and other issues, the main problems of current lithium iron phosphate products are: Li + The low ion diffusion rate makes Li + The intercalation and deintercalation hysteresis during the charge and discharge process reduces the rate performance and capacity performance of LiFePO4. Therefore, how to solve this problem has become a research hotspot. Summary of the Invention

[0005] The purpose of the present disclosure is to overcome the deficiencies of the above-mentioned prior art and to provide a multi-porous iron phosphate precursor, a lithium iron phosphate material and a preparation method thereof.

[0006] To achieve the above objectives, in a first aspect of the present disclosure, the present disclosure provides a method for preparing a porous iron phosphate precursor, the preparation method comprising the following steps:

[0007] The soy protein solution and the anionic polysaccharide solution are mixed and the pH value is adjusted to be acidic to obtain a mixed solution;

[0008] The iron source is added to the mixed solution and stirred, followed by adding phosphate and adjusting the pH value for reaction. After the reaction is completed, the mixture is filtered and washed, and the washed residue is collected;

[0009] The filter residue is freeze-dried, calcined and crushed to obtain a multiporous iron phosphate precursor.

[0010] The multi-porous iron phosphate precursor provided by the present invention has pores of different sizes and shapes, that is, a multi-porous structure is formed. The presence of the multi-porous structure can increase the electrolyte infiltration area when it is subsequently prepared as a positive electrode material for use in batteries, shortening the Li + The ion diffusion path is formed, thereby improving the rate performance of the battery and improving the low-temperature performance of the battery; and the nitrogen atoms in the added soy protein can provide carriers for the conductivity of the carbon material, further improving the electronic conductivity of the subsequent material; at the same time, the battery prepared using the multi-porous iron phosphate precursor disclosed in the present invention also has excellent cycle performance.

[0011] Specifically, by mixing the soy protein solution and the anionic polysaccharide solution and adjusting the pH value to acidic, under acidic conditions, the anionic polysaccharide can be adsorbed to the surface of the soy protein, thereby increasing the steric hindrance effect between the protein molecules and improving the stability of the soy protein; since the anionic polysaccharide is negatively charged, it can continuously adsorb to the surface of the soy protein, or interact with the soy protein through hydrophobic interaction, hydrogen bonding, etc., so that the potential of the soy protein is continuously reduced; and then when the Fe 3+ When the iron source of ions is used, Fe can be adsorbed on the surface of the combination of soybean protein and anionic polysaccharide. 3+ ions, and at the same time, complexation occurs. With the addition of phosphate containing phosphate, free iron ions react with phosphate, and at the same time, soy protein and anionic polysaccharides adsorb and complex Fe 3+ Reacts with phosphate to form iron phosphate; that is, Fe adsorbed and complexed by iron phosphate, protein gel, soy protein and anionic polysaccharide 3+ The reaction is carried out simultaneously with the phosphate reaction, that is, the iron phosphate secondary particles formed contain flocculent protein gel wrapped in iron phosphate; further, the water in the gel is removed by freeze-drying technology, and then the iron phosphate precursor is obtained by high-temperature calcination; that is, iron phosphate precursor particles with carbon layer void channels inside are formed.

[0012] In one embodiment, the separately prepared soy protein solution and anionic polysaccharide solution are mixed and stirred at a rotation speed of 400-800 rpm for 1.5-4 hours until the solutions are uniformly mixed.

[0013] In one embodiment, the solvent of the soy protein solution and the solvent of the anionic polysaccharide solution are both deionized water.

[0014] In one embodiment, in the mixed solution of soy protein and anionic polysaccharide, the mass percentage of soy protein is 2-10%, and the mass percentage of anionic polysaccharide is 0.6-5%.

[0015] The present study found that when the mass percentages of soy protein and anionic polysaccharides are further selected to be 2-10% and 0.6-5% respectively, it is possible to ensure the formation of a certain amount of porous structure to achieve good rate performance of the battery while avoiding the problem of excessive porous structure forming to cause a decrease in battery capacity. When the prepared porous iron phosphate precursor is used in the subsequent preparation of positive electrode materials, the overall performance of the resulting battery is even better.

[0016] In one embodiment, the soy protein solution and the anionic polysaccharide solution are mixed and then the pH value is adjusted to 0.8-1.5.

[0017] In one embodiment, the pH value of the soy protein solution and the anionic polysaccharide solution is adjusted to 0.8-1.5 using hydrochloric acid, sulfuric acid, nitric acid, citric acid, malic acid, etc.

[0018] The present study found that when the soy protein solution and the anionic polysaccharide solution are further mixed and the pH value is adjusted to 0.8-1.5, the low pH condition can allow the soy protein to be suspended rather than precipitated in the solution, and under the acidic condition, the anionic polysaccharide can be better adsorbed to the surface of the soy protein, thereby increasing the steric hindrance effect between protein molecules, thereby improving the stability of the soy protein; and thus achieving a more excellent overall effect.

[0019] In one embodiment, the anionic polysaccharide includes at least one of carboxymethyl cellulose and propylene glycol alginate.

[0020] In one embodiment, the anionic polysaccharide is carboxymethyl cellulose.

[0021] The present study found that when carboxymethyl cellulose is selected as the anionic polysaccharide, its negatively charged carboxyl groups can be better and continuously adsorbed to the surface of soy protein, and can also interact with soy protein through hydrophobic effects, hydrogen bonds, etc., thereby reducing the potential of soy protein, increasing the steric hindrance effect between protein molecules, and improving the stability of soy protein, thereby realizing the formation of a porous structure and achieving good rate performance and cycle performance of the battery.

[0022] In one embodiment, based on the mixed solution, the molar concentration of the iron source is 0.9-2 mol / L.

[0023] The present study found that, based on a mixed solution of soy protein and anionic polysaccharides, when the molar concentration of the iron source is 0.9-2 mol / L, it can facilitate the better adsorption of iron ions in the iron source on the combination of soy protein and anionic polysaccharides, and at the same time produce a good complexation effect, which is conducive to the subsequent addition of sulfate, the reaction between sulfate and iron ions, and then the formation of iron phosphate.

[0024] In one embodiment, the iron source includes at least one of ferric chloride and ferric nitrate.

[0025] In one embodiment, the iron source is added to the mixed solution and stirred for 10-20 minutes.

[0026] In one embodiment, the phosphate includes at least one of ammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid.

[0027] In one embodiment, the molar ratio of the iron ions in the iron source to the phosphate in the phosphate is 1:1.

[0028] The present disclosure study found that when selecting the above-mentioned iron salt, phosphate and the ratio between the two, costs can be saved while ensuring the preparation effect.

[0029] In one embodiment, the reaction after adjusting the pH value is a reaction after adjusting the pH value to 1.8-2.

[0030] In one embodiment, the pH value is adjusted and then reacted to adjust the pH value to 1.8-2, and then reacted using hydrochloric acid, sulfuric acid, nitric acid, citric acid, or malic acid.

[0031] In one embodiment, the reaction temperature is 60-80° C., and the reaction time is 2-4 hours.

[0032] The present study found that when the reaction is carried out within the pH range of 1.8-2, and the reaction temperature is controlled at 60-80°C and the reaction time is 2-4h, a multi-porous iron phosphate precursor with a better overall effect can be obtained on the basis of improving the reaction efficiency; thereby improving the overall performance of the battery when used in the battery.

[0033] In one embodiment, the freeze-drying temperature is (-80)-(-30)°C, and the freeze-drying time is 12-24 hours.

[0034] The present disclosure research found that the filter residue (ferric phosphate secondary particles) obtained by the preparation method of the present disclosure contains flocculent protein gel wrapped in iron phosphate. Through the freeze-drying technology, the protein gel is freeze-dried to allow water to escape from the gel, forming pores of different sizes and shapes, making the gel structure different, and removing water from the gel; specifically, when the freeze-drying temperature is selected to be (-80)-(-30)°C and the freeze-drying time is 12-24h, the water therein can be better removed to form a multi-porous structure.

[0035] In one embodiment, the calcination temperature is 500-700° C., and the calcination time is 2-6 hours.

[0036] In one embodiment, the calcination is carried out under the protection of an inert gas.

[0037] In one embodiment, the inert gas is nitrogen, argon or helium.

[0038] The present study found that after freeze drying and then calcining at 500-700 ° C for 2-6 hours, an iron phosphate particle precursor with a carbon layer void channel inside can be formed. When it is used in the preparation of batteries, it can increase the electrolyte infiltration area and shorten the Li + Ion diffusion path, thereby improving the battery's rate performance, increasing the battery's capacity, improving the battery's cycle performance and improving the battery's low-temperature performance.

[0039] In a second aspect of the present disclosure, the present disclosure provides a multi-porous iron phosphate precursor, which is prepared by the preparation method described in the present disclosure.

[0040] The multi-porous iron phosphate precursor provided by the present invention has a porous structure. When it is used in the preparation of batteries, it can increase the electrolyte infiltration area and shorten the Li + The ion diffusion path can improve the rate performance of the battery, while also improving the battery's gram capacity, cycle performance and low-temperature performance.

[0041] In a third aspect of the present disclosure, the present disclosure provides a method for preparing a lithium iron phosphate material, the preparation method comprising the following steps:

[0042] The porous iron phosphate precursor of the present disclosure and a lithium source are mixed and wet-milled to obtain a ball-milled product;

[0043] The ball milled product and a carbon source are mixed and calcined to obtain lithium iron phosphate material.

[0044] In one embodiment, the solvent for wet ball milling is anhydrous ethanol, the rotation speed of the wet ball milling is 400-600 rpm, and the time of the wet ball milling is 5-7 hours.

[0045] In one embodiment, the molar ratio of the carbon source, the lithium source, and the porous iron phosphate precursor is 0.1:1.05:1.0.

[0046] In one embodiment, the carbon source includes at least one of glucose, sucrose, starch, graphene, and carbon nanotubes, and the lithium source includes at least one of lithium carbonate and lithium hydroxide.

[0047] In one embodiment, the calcination temperature is 650-750° C., and the calcination time is 5-13 hours.

[0048] In a fourth aspect of the present disclosure, the present disclosure provides a lithium iron phosphate material, which is prepared using the preparation method described in the present disclosure.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] The multi-porous iron phosphate precursor provided by the present invention has pores of different sizes and shapes, that is, a multi-porous structure is formed. The presence of the multi-porous structure can increase the electrolyte infiltration area when it is subsequently prepared as a positive electrode material for use in batteries, shortening the Li + The ion diffusion path improves the battery's rate performance, cycle performance, and low-temperature performance. The added soy protein is not only environmentally friendly and renewable, but its nitrogen atoms also provide charge carriers for the carbon material, further improving the electronic conductivity of subsequent materials and increasing the battery's specific capacity. Furthermore, the preparation method provided by the present disclosure is simple to operate, facilitating practical production. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is the SEM image of the iron phosphate precursor prepared in Example 1. DETAILED DESCRIPTION

[0052] In order to better illustrate the purpose, technical solutions and advantages of the present disclosure, the present disclosure will be further described below in conjunction with specific embodiments.

[0053] Unless otherwise specified, the reagents, methods and equipment used in the present disclosure are conventional reagents, methods and equipment in the art.

[0054] Example 1

[0055] The present disclosure provides a lithium iron phosphate material, and a method for preparing the lithium iron phosphate material includes the following steps:

[0056] (1) A soy protein solution and a carboxymethyl cellulose solution were mixed, the pH value was adjusted to 1.3 with hydrochloric acid, and the mixture was stirred at a speed of 600 rpm for 1.5 hours to obtain a mixed solution, in which the mass percentage of soy protein was 8% and the mass percentage of carboxymethyl cellulose was 1%;

[0057] (2) 1 mol / L ferric nitrate was added to the mixed solution and stirred at 600 rpm for 15 min. Then, 1 mol / L ammonium hydrogen phosphate was added and the pH value was adjusted to 2 with hydrochloric acid. The mixture was stirred at 80°C for 3 h.

[0058] (3) After the reaction is completed, filter, wash, and collect the filter residue;

[0059] (4) freeze-drying the filter residue at -80°C for 24 hours, calcining it at 600°C for 3 hours in a nitrogen atmosphere, and crushing it after calcination to obtain a multiporous iron phosphate precursor;

[0060] (5) The porous iron phosphate precursor and Li2CO3 were mixed and loaded into a ball mill, and wet-milled with anhydrous ethanol at a speed of 500 rpm for 6 h. Then, glucose was added and mixed (the molar ratio of glucose, lithium carbonate and porous iron phosphate precursor was 0.1:1.05:1.0) and calcined at 700 °C for 8 h under a nitrogen atmosphere to obtain lithium iron phosphate material.

[0061] Example 2

[0062] The embodiment of the present disclosure provides a lithium iron phosphate material. The only difference between the preparation method of the lithium iron phosphate material and that of Example 1 is that in step (1), the mass percentage of carboxymethyl cellulose is 0.6%.

[0063] Example 3

[0064] The embodiment of the present disclosure provides a lithium iron phosphate material. The only difference between the preparation method of the lithium iron phosphate material and that of Example 1 is that in step (1), the mass percentage of carboxymethyl cellulose is 5%.

[0065] Example 4

[0066] The embodiment of the present disclosure provides a lithium iron phosphate material. The only difference between the preparation method of the lithium iron phosphate material and that of Example 1 is that in step (1), the mass percentage of carboxymethyl cellulose is 0.2%.

[0067] Example 5

[0068] The embodiment of the present disclosure provides a lithium iron phosphate material. The only difference between the preparation method of the lithium iron phosphate material and that of Example 1 is that in step (1), the mass percentage of soy protein is 2%.

[0069] Example 6

[0070] The embodiment of the present disclosure provides a lithium iron phosphate material. The only difference between the preparation method of the lithium iron phosphate material and that of Example 1 is that in step (1), the mass percentage of soy protein is 1%.

[0071] Example 7

[0072] The embodiment of the present disclosure provides a lithium iron phosphate material. The only difference between the preparation method of the lithium iron phosphate material and that of Example 1 is that in step (1), the mass percentage of soy protein is 15%.

[0073] Example 8

[0074] The embodiment of the present disclosure provides a lithium iron phosphate material. The only difference between the preparation method of the lithium iron phosphate material and that of Example 1 is that in step (1), the soy protein solution and the carboxymethyl cellulose solution are mixed and then the pH value is adjusted to 0.8.

[0075] Example 9

[0076] The embodiment of the present disclosure provides a lithium iron phosphate material. The only difference between the preparation method of the lithium iron phosphate material and that of Example 1 is that in step (1), the soy protein solution and the carboxymethyl cellulose solution are mixed and then the pH value is adjusted to 0.5.

[0077] Example 10

[0078] The present embodiment provides a lithium iron phosphate material. The only difference between the preparation method of the lithium iron phosphate material and that of Example 1 is that in step (2), 3 mol / L ferric nitrate is added to the mixed solution and stirred at 600 rpm for 15 minutes, followed by adding 3 mol / L ammonium hydrogen phosphate and adjusting the pH value to 2.

[0079] Comparative Example 1

[0080] The comparative example of the present disclosure provides a lithium iron phosphate material. The only difference between the preparation method of the lithium iron phosphate material and that of Example 1 is that no soy protein solution is added.

[0081] Comparative Example 2

[0082] The comparative example of the present disclosure provides a lithium iron phosphate material. The only difference between the preparation method of the lithium iron phosphate material and that of Example 1 is that no carboxymethyl cellulose solution is added.

[0083] Comparative Example 3

[0084] The comparative example of the present disclosure provides a lithium iron phosphate material. The only difference between the preparation method of the lithium iron phosphate material and that of Example 1 is that chitosan solution is used instead of carboxymethyl cellulose solution.

[0085] Comparative Example 4

[0086] The comparative example of the present disclosure provides a lithium iron phosphate material. The only difference between the preparation method of the lithium iron phosphate material and that of Example 1 is that in step (4), the filter residue is placed in a nitrogen atmosphere and calcined at 600° C. for 3 hours to obtain a multiporous iron phosphate precursor.

[0087] Effect Examples

[0088] The present disclosure verifies the performance of the lithium iron phosphate materials prepared in Examples 1-10 and Comparative Examples 1-4, wherein the SEM image of the iron phosphate precursor prepared in Example 1 is as follows: Figure 1 As stated, Figure 1 It can be seen that the surface of the prepared iron phosphate precursor has a porous structure.

[0089] The prepared lithium iron phosphate material was mixed with a cyclohexane solution of acetylene black and polyvinylidene fluoride (PVDF) at room temperature and pressure to form a slurry (the weight ratio of positive electrode material: acetylene black: PVDF was 75:15:10). The slurry was evenly coated on an aluminum foil substrate to serve as the positive electrode of a simulated battery. The negative electrode of the simulated battery used a lithium sheet, and the electrolyte was 1 mol LiPF6 dissolved in a mixed solvent of 1 mol LEC and DMC (volume ratio 1:1). The separator was a composite film of polypropylene and polyethylene. The positive electrode, negative electrode, electrolyte, and separator were assembled into a simulated battery in an argon-protected glove box. The performance of the simulated battery was tested.

[0090] 1. Rate performance: First, charge to 4.2V at 30mA / g, then discharge to 2.0V at the rate current. The capacity released is the discharge capacity at that rate. After discharge, discharge again at 30mA / g to 2.0V, and then test at the next rate. The test results are shown in Table 1.

[0091] 2. Initial charge and discharge and coulombic efficiency performance: First, charge to 3.7V at a constant current of 0.1C, which is the charge specific capacity, and discharge to 2V at a constant current of 0.1C, which is the discharge specific capacity. The initial coulombic efficiency is: discharge rate / charge specific capacity. The test results are shown in Table 1.

[0092] Table 1

[0093]

[0094]

[0095] As can be seen from Table 1, when the lithium iron phosphate material prepared by the preparation method disclosed herein is used in the preparation of a battery, the resulting battery has excellent rate performance, high charge capacity, and excellent first coulombic efficiency. Specifically, the resulting battery has a rate performance of more than 120 mAh / g at 10C, a charge capacity of more than 146 mAh / g, and a first coulombic efficiency of more than 95.5%.

[0096] It can be seen from Example 1 and Comparative Examples 1-2 that when soy protein is not added in Comparative Example 1, a pore structure cannot be formed, so that the rate performance, charge capacity and first coulomb efficiency of the prepared battery are significantly reduced. Compared with Example 1, the 10C rate performance of the battery in Comparative Example 1 decreased by 20.55%, the charge capacity decreased by 17.61%, and the first coulomb efficiency decreased by 6.78%; when carboxymethyl cellulose is not added in Comparative Example 2, the soy protein will precipitate and become a precipitated protein gel with iron ions, and will not affect each other with iron phosphate, resulting in the inability to form a pore structure. Therefore, the rate performance and charge capacity of the prepared battery are reduced. The rate performance, charge capacity and first coulombic efficiency of the battery in Comparative Example 2 decreased significantly compared with Example 1. Compared with Example 1, the 10C rate performance of the battery in Comparative Example 2 decreased by 23.29%, the charge capacity decreased by 15.57%, and the first coulombic efficiency decreased by 5.67%. It can be seen from Example 1 and Comparative Example 3 that when the carboxymethyl cellulose solution is replaced by the chitosan solution, the rate performance, charge capacity and first coulombic efficiency of the prepared battery are also significantly reduced, which is similar to the effect of not adding carboxymethyl cellulose, that is, the pore structure cannot be formed. It can be seen from Example 1 and Comparative Example 4 that if the filter residue is not freeze-dried after filtration, the rate performance of the prepared battery is reduced.

[0097] It can be seen from Example 1 and Examples 2-4 that, within a certain range, as the mass percentage of carboxymethyl cellulose increases, the chemical properties of the battery tend to become better, but when the mass percentage of carboxymethyl cellulose is further increased, the chemical properties of the battery do not change much. When the mass percentage of carboxymethyl cellulose is further selected to be 0.6-5%, the protein gel can be stably formed, thereby ensuring that there are sufficient pores in the iron phosphate, thereby significantly improving the chemical properties of the battery. It can be seen from Example 1 and Examples 5-7 that with the increase of the mass percentage of soy protein, the performance of the battery first becomes better and then deteriorates. When the mass percentage of soy protein is further selected to be 2-10%, it can be ensured that there will not be too many cavities formed on the basis of a certain amount of protein gel, that is, the balance between gram capacity and rate performance is maintained, so that the overall performance of the obtained battery is better. It can be seen from Example 1 and Examples 8-9 that too low pH will lead to a decrease in the stability of the protein gel, thereby causing the stability of the formed pore structure to also decrease, and ultimately affecting the electrochemical performance of the obtained battery.

[0098] 3. Low temperature performance test

[0099] The lithium iron phosphate cathode materials prepared in Example 1 and Comparative Examples 1-4 were assembled into button-type batteries, and their low-temperature performance was tested. At a 1C discharge rate at -20°C, the discharge capacity retention rates obtained by the test are shown in Table 2.

[0100] Table 2

[0101] Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Discharge capacity retention rate / % 69.2 38.1 36.5 37.4 47.5

[0102] As can be seen from Table 2, the battery obtained by using the lithium iron phosphate positive electrode material prepared by the technical solution disclosed in the present invention has excellent low-temperature resistance, and the discharge capacity retention rate at low temperature is above 69%.

Claims

1. A method for preparing a porous iron phosphate precursor, characterized in that: The preparation method comprises the following steps: The soy protein solution and the anionic polysaccharide solution are mixed and the pH value is adjusted to be acidic to obtain a mixed solution; The iron source is added to the mixed solution and stirred, followed by adding phosphate and adjusting the pH value for reaction. After the reaction is completed, the mixture is filtered and washed, and the washed residue is collected; The filter residue is freeze-dried, calcined and crushed to obtain a multiporous iron phosphate precursor.

2. The preparation method according to claim 1, characterized in that In the mixed solution of soybean protein and anionic polysaccharide, the mass percentage of soybean protein is 2-10%, and the mass percentage of anionic polysaccharide is 0.6-5%.

3. The preparation method according to claim 1, characterized in that The soy protein solution and the anionic polysaccharide solution are mixed and the pH value is adjusted to 0.8-1.

5.

4. The preparation method according to claim 1, characterized in that The anionic polysaccharide includes at least one of carboxymethyl cellulose and propylene glycol alginate.

5. The preparation method according to claim 1, characterized in that Based on the mixed solution, the molar concentration of the iron source is 0.9-2 mol / L.

6. The preparation method according to claim 1, characterized in that The iron source includes at least one of ferric chloride and ferric nitrate.

7. The preparation method according to claim 1, characterized in that The phosphate includes at least one of ammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid.

8. The preparation method according to claim 1, characterized in that The molar ratio of the iron ions in the iron source to the phosphate radicals in the phosphate is 1:

1.

9. The preparation method according to claim 1, characterized in that The reaction after adjusting the pH value is to adjust the pH value to 1.8-2 and then react.

10. The preparation method according to claim 1, characterized in that The reaction temperature is 60-80°C, and the reaction time is 2-4 hours.

11. The preparation method according to claim 1, characterized in that The freeze-drying temperature is (-80)-(-30)°C, and the freeze-drying time is 12-24 hours.

12. The preparation method according to claim 1, characterized in that The calcination temperature is 500-700° C., and the calcination time is 2-6 hours.

13. A porous iron phosphate precursor, characterized in that: The multi-porous iron phosphate precursor is prepared by the preparation method according to any one of claims 1 to 12.

14. A method for preparing a lithium iron phosphate material, characterized in that: The preparation method comprises the following steps: mixing the porous iron phosphate precursor according to claim 13 and a lithium source and then wet-ball milling the mixture to obtain a ball-milled product; The ball milled product and a carbon source are mixed and calcined to obtain lithium iron phosphate material.

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