Lithium iron phosphate precursor, preparation method and application thereof

Abstract

The application belongs to the technical field of lithium ion battery cathode materials, and particularly relates to a lithium iron phosphate precursor, a preparation method and application thereof, and the preparation method of the lithium iron phosphate precursor comprises the following steps: (1) mixing iron oxide red, a phosphorus source and a eutectic solvent, and then grinding to obtain a lithium iron phosphate precursor crude product; (2) washing the lithium iron phosphate precursor crude product obtained in step (1), performing solid-liquid separation and drying to obtain the lithium iron phosphate precursor.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, and specifically relates to a lithium iron phosphate precursor, its preparation method and application. Background Technology

[0002] Lithium iron phosphate (LiFePO4), as a cathode material for lithium-ion batteries, has been widely used in new energy vehicles and energy storage due to its advantages such as high safety, long cycle life, and low cost. Iron phosphate (FePO4), as a key precursor in the synthesis of lithium iron phosphate, directly affects the electrochemical performance and manufacturing cost of the final product. In recent years, the technical route for preparing iron phosphate using alpha-Fe2O3 as the iron source has gradually become a hot research area in the industry due to its wide availability of raw materials and significant cost advantages.

[0003] Currently, the mainstream technical routes for preparing iron phosphate using iron oxide red include wet acidolysis-precipitation process, eutectic solvent ionothermal synthesis process, and mechanical mixing-calcination process, but each has certain technical limitations.

[0004] The wet acidolysis-precipitation process is currently the most widely used industrial route. Its core principle is to completely dissolve iron oxide red in a strong acid (such as phosphoric acid or sulfuric acid) to obtain an iron ion solution. Then, by adjusting the pH and adding a precipitating agent, ferric phosphate is precipitated in the liquid phase. The main drawbacks of the wet acidolysis-precipitation process are: 1. Complex process, involving multiple steps such as acid dissolution, filtration, impurity removal, precipitation, and washing, resulting in a long production cycle; 2. High environmental impact, as the reaction takes place in a large aqueous system, generating a large amount of highly hydrochloric acid wastewater, leading to high treatment costs; 3. High energy consumption, as some steps require high-temperature heating, increasing energy consumption.

[0005] Deep eutectic solvents (DES), as a green solvent, have been introduced into the synthesis of lithium iron phosphate materials in recent years. This technology avoids some of the problems of traditional aqueous systems, but still has the following drawbacks: 1. The amount of DES used is enormous, typically 2-20 times the molar amount of the reactants, making it a costly main solvent; 2. It relies on high temperature and pressure, requiring stringent reaction conditions and sophisticated equipment; 3. The reaction cycle is long.

[0006] The mechanical mixing-calcination process uses mechanical treatment to assist physical mixing, combined with high-temperature calcination to prepare iron phosphate. Its drawbacks are: 1. It still relies on high-temperature calcination, resulting in high energy consumption, and the calcination process may lead to particle agglomeration, affecting product uniformity; 2. The iron source conversion is insufficient; if the iron oxide red is not pre-activated, unreacted residual phases may remain after calcination, affecting product purity.

[0007] In summary, existing technologies for preparing iron phosphate using iron oxide red as the iron source generally suffer from problems such as long process routes, high environmental impact, high energy consumption, and harsh reaction conditions. Summary of the Invention

[0008] This invention aims to at least solve one of the technical problems existing in related technologies. To this end, this invention proposes a lithium iron phosphate precursor, its preparation method, and its application. The preparation method is characterized by a simple process, environmental friendliness, and mild reaction, and the prepared lithium iron phosphate precursor exhibits excellent electrochemical performance when applied in lithium iron phosphate cathode materials.

[0009] The above-mentioned technical objective of the present invention is achieved through the following technical solution: A method for preparing a lithium iron phosphate precursor includes the following steps: (1) After mixing iron oxide red, phosphorus source and eutectic solvent, the mixture is ground to obtain crude lithium iron phosphate precursor; (2) The crude product of lithium iron phosphate precursor obtained in step (1) is washed, solid-liquid separation is performed and dried to obtain the lithium iron phosphate precursor.

[0010] In one embodiment, in step (1), the iron oxide red is battery-grade α-iron oxide red.

[0011] In one embodiment, in step (1), the phosphorus source is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, phosphoric acid, and phosphorus pentoxide.

[0012] In one embodiment, in step (1), the eutectic solvent is obtained by mixing hydrogen bond acceptors and hydrogen bond donors in a molar ratio of 1:(1-5). The hydrogen bond acceptors include at least one of choline chloride, betaine, quaternary ammonium salt, metal chloride and thymol. The hydrogen bond donors include at least one of oxalic acid, citric acid, urea, ethylene glycol, malonic acid and menthol.

[0013] In one embodiment, the eutectic solvent is obtained by mixing hydrogen bond acceptors and hydrogen bond donors in a molar ratio of 1:1.

[0014] In one embodiment, in step (1), the amount of the eutectic solvent used is 5%-20% of the total mass of the iron oxide red and the phosphorus source.

[0015] In one embodiment, in step (1), the iron oxide red and the phosphorus source are mixed at a Fe to P molar ratio of 1:(1.0-1.2).

[0016] In one embodiment, in step (1), the equipment used for grinding is a ball mill, the rotation speed of the ball mill is 100-800 rpm, the grinding time is 1-10 hours, and the grinding temperature is 20-80℃.

[0017] In one embodiment, the ball mill is a planetary ball mill, a stirred ball mill, a vibratory mill, or a roller mill.

[0018] In one embodiment, in step (2), the solvent used for washing is water, anhydrous ethanol, or an antisolvent of a eutectic solvent. The antisolvent is a polar organic solvent, specifically one or more of C1-C4 alcohols, ketones, ethers, esters, halogenated hydrocarbons, or nitriles.

[0019] In one embodiment, in step (2), the drying temperature is 60-100°C.

[0020] A lithium iron phosphate precursor is prepared by the preparation method described above.

[0021] A method for preparing a lithium iron phosphate cathode material includes the following steps: mixing the lithium iron phosphate precursor as described above with a lithium source and a carbon source, and sintering under a protective atmosphere to obtain the lithium iron phosphate cathode material.

[0022] In one embodiment, the lithium source is at least one of lithium carbonate, lithium hydroxide, and lithium acetate.

[0023] In one embodiment, the carbon source is at least one of citric acid, glucose, sucrose, carbon nanotubes, and acetylene black.

[0024] In one embodiment, the lithium iron phosphate precursor is mixed with a lithium source and a carbon source in a molar ratio of Fe:Li:C = 1:1:(0.1-0.2).

[0025] In one embodiment, the lithium iron phosphate precursor is mixed with a lithium source and a carbon source in a molar ratio of Fe:Li:C = 1:1:0.15.

[0026] In one embodiment, the lithium iron phosphate precursor is mixed with a lithium source and a carbon source, ball-milled for 2-5 hours, and then sintered.

[0027] In one embodiment, the sintering temperature is 650-750°C, and the holding time is 6-12 hours.

[0028] A lithium iron phosphate cathode material is prepared by the preparation method described above.

[0029] A lithium-ion battery comprising the lithium iron phosphate cathode material as described above.

[0030] The beneficial effects of this invention are: (1) The product obtained by the preparation method of the present invention has higher sintering activity, which is due to the lattice defects and higher specific surface area generated by mechanochemical action. This structural feature makes the lithium ion diffusion path shorter and the reaction activity higher when it is mixed with lithium source for sintering, which is beneficial to improving the electrochemical performance of the final lithium iron phosphate product; (2) The preparation method of the present invention can generate lithium iron phosphate precursor in one step without strong acid and high temperature under the synergistic effect of mechanochemical-eutectic solvent, which greatly reduces production energy consumption and equipment requirements.

[0031] (3) The preparation method of the present invention introduces a eutectic solvent (DES) as a small amount of reaction aid (5%-20% of the total mass of the reactants), instead of a large amount of solvent in the traditional sense. DES penetrates to the iron oxide red lattice defects under mechanical force, and at the same time provides H + The dual effects of protic acid and complexation coordination, combined with mechanical force, create a synergistic effect of "simultaneous crushing, reaction, and nucleation." This results in low auxiliary material costs, minimal wastewater treatment pressure, and environmental friendliness. Attached Figure Description

[0032] Figure 1 The XRD diffraction pattern of the lithium iron phosphate precursor in Example 1 of this invention is shown. Figure 2 and 3 These are electron microscope images of the lithium iron phosphate precursor in Example 1 at different magnifications. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments.

[0034] Example 1: A method for preparing a lithium iron phosphate precursor includes the following steps: (1) Take 80g of battery-grade α-Fe2O3 (iron oxide red) and 138g of ammonium dihydrogen phosphate (Fe:P molar ratio = 1:1.2) and mix them evenly; (2) Preparation of eutectic solvent: Mix choline chloride and oxalic acid in a molar ratio of 1:1, stir at 80°C until a colorless and transparent liquid is formed, and cool for later use; (3) Add the above solid mixture and 21.8g of eutectic solvent (10% of the solid mass) into a planetary ball mill, use zirconia grinding balls, ball-to-material ratio of 10:1, speed of 400rpm, and ball mill for 4 hours at room temperature of 25℃; (4) After the reaction was completed, the product was washed three times with anhydrous ethanol, centrifuged, and dried under vacuum at 80°C to obtain lithium iron phosphate precursor powder. X-ray diffraction (XRD) analysis was performed, as shown... Figure 1As shown, the obtained product is FePO4·2H2O, with no residual characteristic peak of α-Fe2O3 (iron oxide red). The specific surface area of ​​the product was measured to be 31.5 m² / g. The electron micrograph of the product is shown below. Figure 2 and Figure 3 As shown, by Figure 2 and Figure 3 The product, as observed under SEM, exhibits a rice-grain shape, narrow particle size distribution, and good dispersion, revealing that the product of this invention possesses an amorphous-nanocrystalline mixed structure and abundant lattice defects. These morphological and structural characteristics collectively endow the product of this invention with higher sintering activity and lithium-ion diffusion efficiency, while avoiding the hard agglomeration problem and subsequent pulverization process associated with traditional wet-process products.

[0035] A method for preparing a lithium iron phosphate cathode material includes the following steps: The prepared lithium iron phosphate precursor (iron phosphate dihydrate) was mixed with Li2CO3 (lithium carbonate) and glucose at a molar ratio of Fe:Li:C = 1:1:0.15, ball-milled for 4 hours with anhydrous ethanol as the medium, and sintered at 700℃ for 10 hours under a nitrogen atmosphere to obtain lithium iron phosphate cathode material.

[0036] The above-mentioned lithium iron phosphate cathode material is formulated into a coin cell. The specific steps include: uniformly mixing the lithium iron phosphate cathode material, conductive agent acetylene black and adhesive polyvinylidene fluoride in N-methylpyrrolidone at a mass ratio of 94:3:3 to form a slurry, then coating it onto aluminum foil, and placing it in a vacuum drying oven at 100°C for 15 hours. Then, it is pressed into a positive electrode sheet using a tablet press, the negative electrode sheet is a lithium metal sheet, the electrolyte is 1 mol / L LiPF6-EC:DMC (volume ratio of 1:1), and a polypropylene porous membrane is used as the separator. The battery assembly is carried out in an argon glove box.

[0037] Electrochemical performance tests were conducted on the above-mentioned battery. At a 0.1C rate, the initial discharge specific capacity of the obtained cathode material was 162.4 mAh / g; after 100 cycles at a 1C rate, the capacity retention rate was 92.0%.

[0038] Example 2: A method for preparing a lithium iron phosphate precursor includes the following steps: (1) Take 80g of battery-grade α-Fe2O3 (iron oxide red) and 138g of ammonium dihydrogen phosphate (Fe:P molar ratio = 1:1.2) and mix them evenly; (2) Preparation of eutectic solvent: Mix choline chloride and urea in a molar ratio of 1:1, stir at 80°C until a colorless and transparent liquid is formed, and cool for later use; (3) Add the above solid mixture and 10.9g of eutectic solvent (about 5% of the solid mass) into a planetary ball mill, use zirconia grinding balls, ball-to-material ratio of 10:1, speed of 400rpm, and ball mill for 4 hours at room temperature of 25℃; (4) After the reaction was completed, the product was washed three times with anhydrous ethanol, centrifuged, and dried under vacuum at 80°C to obtain lithium iron phosphate precursor product powder. The specific surface area of ​​the product was determined to be 27.8 m² / g.

[0039] A method for preparing a lithium iron phosphate cathode material includes the following steps: The prepared lithium iron phosphate precursor (iron phosphate dihydrate) was mixed with Li2CO3 (lithium carbonate) and glucose at a molar ratio of Fe:Li:C = 1:1:0.15, ball-milled for 4 hours with anhydrous ethanol as the medium, and sintered at 700℃ for 10 hours under a nitrogen atmosphere to obtain lithium iron phosphate cathode material.

[0040] The lithium iron phosphate cathode material described above was used to prepare a coin cell according to the preparation method in Example 1. The electrochemical performance of the cell was tested. At a rate of 0.1C, the initial discharge specific capacity of the cathode material was 157.6 mAh / g. After 100 cycles at a rate of 1C, the capacity retention rate was 89.4%.

[0041] Example 3: A method for preparing a lithium iron phosphate precursor includes the following steps: (1) Take 80g of α-Fe2O3 (iron oxide red) and 138g of ammonium dihydrogen phosphate (Fe:P molar ratio = 1:1.2), and mix them evenly; (2) Preparation of eutectic solvent: Mix choline chloride and oxalic acid in a molar ratio of 1:1, stir at 80°C until a colorless and transparent liquid is formed, and cool for later use; (3) Add the above solid mixture and 43.6g of eutectic solvent (about 20% of the solid mass) into a planetary ball mill, use zirconia grinding balls, ball-to-material ratio of 10:1, speed of 400rpm, and ball mill for 4 hours at room temperature of 25℃; (4) After the reaction was completed, the product was washed three times with anhydrous ethanol, centrifuged, and dried under vacuum at 80°C to obtain lithium iron phosphate precursor product powder. The specific surface area of ​​the product was measured to be 32.7 m² / g.

[0042] A method for preparing a lithium iron phosphate cathode material includes the following steps: The prepared lithium iron phosphate precursor (iron phosphate dihydrate) was mixed with Li2CO3 (lithium carbonate) and glucose at a molar ratio of Fe:Li:C = 1:1:0.15, ball-milled for 4 hours with anhydrous ethanol as the medium, and sintered at 700℃ for 10 hours under a nitrogen atmosphere to obtain lithium iron phosphate cathode material.

[0043] The above-mentioned lithium iron phosphate cathode material was used to prepare a coin cell according to the preparation method of Example 1, and the electrochemical performance of the cell was tested. At 0.1C rate, the initial discharge specific capacity of the obtained cathode material was 161.7 mAh / g; after 100 cycles at 1C rate, the capacity retention rate was 91.5%.

[0044] Comparative Example 1: (Preparation of ferric phosphate by conventional wet acid hydrolysis-precipitation method) This comparative example provides a method for preparing lithium iron phosphate precursor using a traditional wet acid hydrolysis process, including the following steps: (1) Take 100g of α-Fe2O3 (iron oxide red) and H3PO4 (phosphoric acid diluted to 40%) according to the Fe:P molar ratio of 1:2; (2) Acid hydrolysis reaction: Heat the diluted phosphoric acid solution to 70±2℃ and start stirring. Slowly add iron oxide red and keep the temperature for 5 hours. (3) Precipitation aging reaction: After the acid hydrolysis reaction is completed, the reaction solution is heated to 90±2℃ and stirred for 2 hours to allow the precipitate to grow fully; (4) The precipitated product was filtered and washed with deionized water 5 times until the conductivity of the filtrate was ≤200μS / cm. The washed filter cake was dried in a vacuum drying oven at 80℃ for 12 hours to obtain lithium iron phosphate precursor product powder. The specific surface area of ​​the product was measured to be 12.5m² / g.

[0045] A method for preparing a lithium iron phosphate cathode material includes the following steps: The prepared lithium iron phosphate precursor (iron phosphate dihydrate) was mixed with Li2CO3 (lithium carbonate) and glucose in a molar ratio of Fe:Li:C = 1:1:0.15, ball-milled for 4 hours with anhydrous ethanol as the medium, dried, and sintered at 700℃ for 10 hours under a nitrogen atmosphere to obtain the lithium iron phosphate cathode material.

[0046] The above-mentioned lithium iron phosphate cathode material was used to prepare a coin cell according to the preparation method of Example 1, and the electrochemical performance of the cell was tested. At 0.1C rate, the initial discharge specific capacity of the obtained cathode material was 156.8 mAh / g; after 100 cycles at 1C rate, the capacity retention rate was 87.2%.

[0047] The comparative process flow has the following obvious shortcomings: 1. The process is lengthy: it involves multiple steps such as acid hydrolysis, precipitation, washing, and drying, with a production cycle exceeding 12 hours; 2. Large wastewater generation: The acidolysis and precipitation processes generate a large amount of acidic wastewater containing phosphorus and nitrogen. Approximately 15-20L of wastewater is generated for every 1kg of ferric phosphate produced, resulting in high environmental treatment costs. 3. High energy consumption: The acid hydrolysis process requires heating to 95°C, and the precipitation process requires temperature-controlled aging, resulting in significantly higher energy consumption than the present invention; 4. Lower electrochemical performance: Under the same test conditions, its capacity and cycle retention are lower than those of the embodiments of the present invention.

[0048] Comparative Example 2: (The difference from Example 1 is that no eutectic solvent is added) A method for producing a lithium iron phosphate precursor includes the following steps: (1) Take 80g of α-Fe2O3 (iron oxide red) and 138g of ammonium dihydrogen phosphate (Fe:P molar ratio = 1:1.2), and mix them evenly; (2) Add the above solid mixture into a planetary ball mill, use zirconia grinding balls, ball-to-material ratio of 10:1, speed of 400 rpm, and ball mill for 4 hours at room temperature of 25℃; (3) After the reaction was completed, the product was washed three times with anhydrous ethanol, centrifuged, and dried under vacuum at 80°C to obtain lithium iron phosphate precursor product powder. The specific surface area of ​​the product was determined to be 8.1 m² / g.

[0049] A method for preparing a lithium iron phosphate cathode material includes the following steps: The prepared lithium iron phosphate precursor (iron phosphate dihydrate) was mixed with Li2CO3 (lithium carbonate) and glucose in a molar ratio of Fe:Li:C = 1:1:0.15, ball-milled for 4 hours with anhydrous ethanol as the medium, dried, and sintered at 700℃ for 10 hours under a nitrogen atmosphere to obtain the lithium iron phosphate cathode material.

[0050] The above-mentioned lithium iron phosphate cathode material was used to prepare a coin cell according to the preparation method of Example 1, and the electrochemical performance of the cell was tested. At 0.1C rate, the initial discharge specific capacity of the obtained cathode material was 118.6 mAh / g; after 100 cycles at 1C rate, the capacity retention rate was 76.9%.

[0051] Comparative Example 3: (The difference from Example 1 is that the mass of the eutectic solvent added is 1% of the mass of the solid mixture) A method for producing a lithium iron phosphate precursor includes the following steps: (1) Take 80g of α-Fe2O3 (iron oxide red) and 138g of ammonium dihydrogen phosphate (Fe:P molar ratio = 1:1.2), and mix them evenly; (2) Preparation of eutectic solvent: Mix choline chloride and oxalic acid in a molar ratio of 1:1, stir at 80°C until a colorless and transparent liquid is formed, and cool for later use; (3) Add the above solid mixture and 2.18g of eutectic solvent (1% of the mass of the solid mixture) into a planetary ball mill, use zirconia grinding balls, ball-to-material ratio of 10:1, speed of 400rpm, and ball mill for 4 hours at room temperature of 25℃; (4) After the reaction was completed, the product was washed three times with anhydrous ethanol, centrifuged, and dried under vacuum at 80°C to obtain lithium iron phosphate precursor product powder. The specific surface area of ​​the product was determined to be 18.3 m² / g.

[0052] A method for preparing a lithium iron phosphate cathode material includes the following steps: The prepared lithium iron phosphate precursor (iron phosphate dihydrate) was mixed with Li2CO3 (lithium carbonate) and glucose in a molar ratio of Fe:Li:C = 1:1:0.15, ball-milled for 4 hours with anhydrous ethanol as the medium, dried, and sintered at 700℃ for 10 hours under a nitrogen atmosphere to obtain the lithium iron phosphate cathode material.

[0053] The above-mentioned lithium iron phosphate cathode material was used to prepare a coin cell according to the preparation method of Example 1, and the electrochemical performance of the cell was tested. At 0.1C rate, the initial discharge specific capacity of the obtained cathode material was 135.2 mAh / g; after 100 cycles at 1C rate, the capacity retention rate was 83.5%.

[0054] Comparative Example 4: (The difference from Example 1 is that the mass of the eutectic solvent added is 50% of the mass of the solid mixture) A method for producing a lithium iron phosphate precursor includes the following steps: (1) Take 80g of α-Fe2O3 (iron oxide red) and 138g of ammonium dihydrogen phosphate (Fe:P molar ratio = 1:1.2), and mix them evenly; (2) Preparation of eutectic solvent: Mix choline chloride and oxalic acid in a molar ratio of 1:1, stir at 80°C until a colorless and transparent liquid is formed, and cool for later use; (3) The above solid mixture and 109g of eutectic solvent (50% of the mass of the solid mixture) were added to a planetary ball mill. Zirconia grinding balls were used, the ball-to-material ratio was 10:1, the rotation speed was 400rpm, and the ball milling was carried out at room temperature of 25℃ for 4 hours. During the ball milling process, the material was observed to be in slurry form, and a lot of material adhered to the inner wall of the ball mill jar. (4) After the reaction is complete, the product is washed 5 times with anhydrous ethanol (increasing the number of washing times ensures that a large amount of eutectic solvent is washed away), centrifuged, and vacuum dried at 80°C to obtain lithium iron phosphate precursor product powder. The specific surface area of ​​the product is 22.6 m² / g.

[0055] A method for preparing a lithium iron phosphate cathode material includes the following steps: The prepared lithium iron phosphate precursor (iron phosphate dihydrate) was mixed with Li2CO3 (lithium carbonate) and glucose in a molar ratio of Fe:Li:C = 1:1:0.15, ball-milled for 4 hours with anhydrous ethanol as the medium, dried, and sintered at 700℃ for 10 hours under a nitrogen atmosphere to obtain the lithium iron phosphate cathode material.

[0056] The above-mentioned lithium iron phosphate cathode material was used to prepare a coin cell according to the preparation method of Example 1, and the electrochemical performance of the cell was tested. At 0.1C rate, the initial discharge specific capacity of the obtained cathode material was 142.8 mAh / g; after 100 cycles at 1C rate, the capacity retention rate was 86.1%.

[0057] The comparative examples 2, 3, and 4 and the embodiments above show that the amount of DES (eutectic solvent) has a significant impact on the solid-phase coordination conversion reaction of the present invention. When no DES is added, the reaction degree of the solid mixture is low, and the lithium iron phosphate cathode material obtained by sintering is not usable. When the amount of DES is too low, the activation effect is not significant, the specific surface area of ​​the product is low, and the specific capacity and cycle capacity of the cathode material are significantly lower than those of the embodiments. When the amount of DES is too high, the mechanical energy transfer efficiency decreases significantly, the specific surface area of ​​the product is still lower than that of the embodiments, and the electrical performance of the cathode material is not as good as that of the present solution. Therefore, only when the amount of DES is controlled between 5% and 30% can the synergistic effect of mechanical force and DES (eutectic solvent) be fully exerted, so as to achieve the complete reaction and conversion of iron oxide red at room temperature and obtain a product with a high specific surface area.

Claims

1. A method for preparing a lithium iron phosphate precursor, characterized in that: Includes the following steps: (1) After mixing iron oxide red, phosphorus source and eutectic solvent, the mixture is ground to obtain crude lithium iron phosphate precursor; (2) The crude product of lithium iron phosphate precursor obtained in step (1) is washed, solid-liquid separation is performed and dried to obtain the lithium iron phosphate precursor.

2. The method for preparing a lithium iron phosphate precursor according to claim 1, characterized in that: In step (1), the iron oxide red is battery-grade α-iron oxide red.

3. The method for preparing a lithium iron phosphate precursor according to claim 1, characterized in that: In step (1), the eutectic solvent is obtained by mixing hydrogen bond acceptors and hydrogen bond donors in a molar ratio of 1:(1-5). The hydrogen bond acceptors include at least one of choline chloride, betaine, quaternary ammonium salt, metal chloride and thymol. The hydrogen bond donors include at least one of oxalic acid, citric acid, urea, ethylene glycol, malonic acid and menthol.

4. The method for preparing a lithium iron phosphate precursor according to claim 1, characterized in that: In step (1), the amount of the eutectic solvent used is 5%-20% of the total mass of the iron oxide red and the phosphorus source.

5. The method for preparing a lithium iron phosphate precursor according to claim 1, characterized in that: In step (1), the iron oxide red and the phosphorus source are mixed at a Fe to P molar ratio of 1:(1.0-1.2).

6. The method for preparing a lithium iron phosphate precursor according to claim 1, characterized in that: In step (1), the equipment used for grinding is a ball mill. The speed of the ball mill during grinding is 100-800 rpm, the grinding time is 1-10 hours, and the grinding temperature is 20-80℃.

7. A lithium iron phosphate precursor, characterized in that: It is prepared by the preparation method according to any one of claims 1-6.

8. A method for preparing a lithium iron phosphate cathode material, characterized in that: Includes the following steps: The lithium iron phosphate precursor of claim 7 is mixed with a lithium source and a carbon source, and sintered under a protective atmosphere to obtain the lithium iron phosphate cathode material.

9. A lithium iron phosphate cathode material, characterized in that: It is prepared by the preparation method described in claim 8.

10. A lithium-ion battery, characterized in that: Including the lithium iron phosphate cathode material as described in claim 9.

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