Iron phosphate precursor, preparation method thereof, lithium iron phosphate material and preparation method thereof

Abstract

This invention provides an iron phosphate precursor and its preparation method, as well as a lithium iron phosphate material and its preparation method. The iron phosphate precursor, through hydrogen bonding, allows iron phosphate containing a transition metal to be deposited in situ onto a fibrous, polyhydroxyl-containing carbon template. After adding a lithium source and calcining, a porous lithium iron phosphate cathode material is obtained. During the preparation process, an excess of the fibrous, polyhydroxyl-containing carbon material acts not only as a reducing agent but also as a conductive agent, coating the inner and outer walls of the material. The lithium iron phosphate material of this invention exhibits stronger liquid retention, increasing both conductivity and rate performance. The porous interior provides support, preventing morphological damage during compaction.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to an iron phosphate precursor and its preparation method, and lithium iron phosphate materials and their preparation methods. Background Technology

[0002] In recent years, with the rapid development of the lithium-ion battery industry, especially in the power battery sector, lithium iron phosphate materials have gained popularity due to their high capacity, low raw material cost, and good stability and cycle performance. However, due to structural limitations, their electronic and ionic conductivity are relatively low, resulting in poor electrical conductivity and ion mobility, which significantly affects the improvement of their electrochemical performance. Current solutions to these problems mainly involve element doping, coating, and the preparation of nanoparticles.

[0003] Patent CN1785799A discloses a method for preparing transition metal-doped lithium iron phosphate powder. This involves mixing lithium salts (ferrous and phosphates) with elements such as Mn, Co, and Ni in specific proportions, followed by drying, low-temperature pre-calcination, and high-temperature secondary calcination to obtain transition metal-doped lithium iron phosphate powder. Traditional solid-state sintering methods for doping transition metals improve ion migration rates and conductivity, thereby enhancing battery capacity and cycle performance. However, improving the conductivity of lithium iron phosphate materials solely through metal doping has limited effectiveness and cannot significantly improve the material's conductivity.

[0004] Chinese patent CN 110510593 A discloses a method for preparing an iron phosphate precursor and lithium iron phosphate. The method involves adding an iron source and phosphoric acid, and then using a complexing agent and surfactant at specific pH and temperature to obtain an iron phosphate suspension. After aging, pressure filtration, washing, and drying, an iron phosphate dihydrate precursor is obtained. Finally, a lithium source and a carbon source are added, and the mixture is calcined to obtain a lithium iron phosphate cathode material. However, the material obtained by this method, after preparing the precursor, is calcined with an external carbon source, resulting in the carbon source only coating the outside of the material, leading to low conductivity and rate performance.

[0005] Chinese patent CN 113540455 A discloses a hollow carbon-coated lithium iron phosphate particle and its preparation method. The method involves preparing hollow Li3PO4 particles, adding an iron source and a phosphorus source to convert them into a hollow lithium iron phosphate precursor, mixing it with a reducing carbon source, and sintering it under a protective atmosphere to obtain hollow spherical carbon-coated lithium iron phosphate. However, this method only produces a hollow structure of lithium iron phosphate, failing to solve the problems of material and carbon dispersion. Furthermore, the hollow structure has low compaction, making it difficult to maintain its morphology during battery fabrication.

[0006] Chinese patent CN 107507975 A discloses a method for preparing carbon-coated lithium iron phosphate hollow nanospheres. The method involves mixing polyethylene glycol 600 and deionized water, then reacting this mixture with phosphoric acid and lithium hydroxide monohydrate to obtain a lithium phosphate precursor. This precursor is then mixed with ethylene glycol and ferrous chloride tetrahydrate, ultrasonically treated, and heated in a high-pressure reactor to obtain lithium iron phosphate hollow nanospheres. A carbon source is added, and the mixture is calcined under a protective atmosphere. The precursor morphology is used as a template to obtain carbon-coated lithium iron phosphate hollow nanospheres. While this preparation process can solve the problems of conductivity and rate performance, it is complex, unsuitable for industrial production, and the use of organic solvents such as ethylene glycol and the reactor increases the preparation cost.

[0007] Given the aforementioned defects in current lithium iron phosphate materials, it is indeed necessary to provide a technical solution to address these problems. Summary of the Invention

[0008] The purpose of this invention is to provide an iron phosphate precursor, in which iron phosphate containing a transition metal is deposited in situ on a fibrous polyhydroxyl-containing carbon template via hydrogen bonding. After adding a lithium source and calcining, a porous lithium iron phosphate cathode material can be obtained. During the preparation process, the excess fibrous polyhydroxyl-containing carbon material acts not only as a reducing agent but also as a conductive agent, coating the inner and outer walls of the material. The material of this invention has stronger liquid retention properties, increasing not only its conductivity but also its rate performance. The porous interior provides a certain degree of support, and its morphology is not easily damaged during compaction.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A fibrous iron phosphate precursor containing polyhydroxyl carbon material, the chemical structural formula of which is as follows:

[0011]

[0012] Wherein, 0≤x≤1, 100000≤n≤10000000, and M is a transition metal element, which includes at least one of Mn, Ni, V, Mg, Al, and Cu.

[0013] Preferably, the fibrous carbon-containing material includes at least one of polyhydroxy polyethylene resin, polyhydroxy epoxy resin, polyhydroxy polypropylene resin, polyhydroxy phenolic resin, polyvinyl alcohol acrylonitrile copolymer, polyvinyl alcohol, and polyvinyl alcohol vinylpyrrolidone copolymer.

[0014] Preferably, the fibrous polyhydroxy carbon material has a diameter of 2-50 μm and a length of 0.1-5 μm.

[0015] Preferably, the fibrous polyhydroxy carbon material has a carbon content of 30-80%, a hydroxyl content of 30-50%, and a carboxyl content of 10-20%.

[0016] The present invention also provides a method for preparing the above-mentioned fibrous iron phosphate precursor containing polyhydroxy carbon materials, comprising the following steps:

[0017] (1) Under continuous stirring, the fibrous polyhydroxy carbon material is uniformly dispersed in the solution to obtain solution A;

[0018] (2) Add an iron source and a complexing agent to solution A obtained in step (1) and stir continuously. Then add a phosphorus source to make the solution contain iron ions and phosphate ions to obtain solution B.

[0019] (3) Add surfactant to solution B obtained in step (2), stir evenly, adjust pH, and obtain product after reaction;

[0020] (4) The product obtained in step (3) is aged, filtered, washed and dried to obtain a fibrous iron phosphate precursor containing polyhydroxy carbon materials.

[0021] Preferably, the mass ratio of the fibrous polyhydroxy carbon material to the iron phosphate precursor of the fibrous polyhydroxy carbon material is 0.1-5%.

[0022] Preferably, the iron source is at least one of ferric sulfate, ferric acetate, ferric chloride, and ferric nitrate; and the phosphorus source is at least one of ammonium phosphate, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid, sodium phosphate, sodium monohydrogen phosphate, and sodium dihydrogen phosphate.

[0023] Preferably, the complexing agent is at least one of oxalic acid, citric acid, tartaric acid, gluconic acid, or diethanolamine.

[0024] Preferably, the surfactant is at least one of fatty acid polyoxyethylene ester, alkylphenol polyoxyethylene ether, alkylolamide, and sucrose fatty acid ester.

[0025] Preferably, the molar ratio of phosphate to iron ions in solution B is 1.05-1.10:1; and the carbon content in the fibrous iron phosphate precursor containing polyhydroxy carbon material is 0.1-3%.

[0026] Preferably, in step (3), the reaction temperature is 60-90℃; the pH is 1.0-5.0; and the reaction time is 3-5h.

[0027] The present invention also provides a method for preparing lithium iron phosphate using the above-mentioned fibrous iron phosphate precursor containing polyhydroxy carbon material, the steps of which include: mixing carbon source, lithium source and fibrous iron phosphate precursor material containing polyhydroxy carbon material in liquid phase according to the ratio of (0.005-0.05):(1.0-1.05):1.0, drying after uniform mixing, and sintering at high temperature under inert gas protection to obtain lithium iron phosphate material with porous structure.

[0028] Preferably, the carbon source is at least one selected from glucose, sucrose, starch, cellulose, phenolic resin, acetylene black, and carbon black.

[0029] Preferably, the lithium source is at least one of lithium carbonate, lithium hydroxide, lithium acetate, and lithium sulfate; and the inert gas is at least one of nitrogen, argon, helium, neon, and xenon.

[0030] Preferably, the high-temperature sintering temperature is 550-850℃.

[0031] The present invention also provides a lithium iron phosphate material prepared by the above-described method for preparing lithium iron phosphate.

[0032] The present invention also provides a positive electrode sheet comprising the above-mentioned lithium iron phosphate material.

[0033] The present invention also provides a lithium-ion battery, comprising a positive electrode, a negative electrode, and a separator spaced between the positive electrode and the negative electrode, wherein the positive electrode is the aforementioned positive electrode.

[0034] Compared with the prior art, the present invention has at least the following beneficial effects:

[0035] (1) The present invention provides an iron phosphate precursor, which allows iron phosphate containing transition metal to be deposited in situ on a fibrous carbon material template containing polyhydroxyl through hydrogen bonding. After adding a lithium source and calcining, a lithium iron phosphate cathode material with a porous structure can be obtained.

[0036] (2) The present invention uses liquid phase to prepare precursors, which makes the mixing of phosphorus and iron elements more uniform and increases the mass transfer efficiency in the later stage.

[0037] (3) In this invention, lithium source is added to the precursor and mixed evenly before calcination. As the fibrous polyhydroxy carbon material decomposes at high temperature to produce water and carbon dioxide, it also acts as a reducing agent and is consumed. The generated gas and the consumed carbon source will form a three-dimensional network-like void structure. This lithium iron phosphate cathode material with a three-dimensional network-like void structure has stronger liquid retention and improved rate performance. Moreover, the porous interior has a certain support, and the morphology is not easily destroyed during the compaction process. At the same time, the excessive fibrous polyhydroxy carbon material will act as a conductive agent to coat the inner and outer walls of the material, increasing the conductivity of the material. Attached Figure Description

[0038] Figure 1 This is a SEM cross-sectional view of lithium iron phosphate material in one embodiment of the present invention. Detailed Implementation

[0039] To make the technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] According to a first aspect of the present invention, the present invention provides a fibrous iron phosphate precursor containing a polyhydroxy carbon material, the chemical structural formula of which is as follows:

[0041]

[0042] Wherein, 0≤x≤1, 100000≤n≤10000000, and M is a transition metal element, which includes at least one of Mn, Ni, V, Mg, Al, and Cu.

[0043] This invention enables the in-situ deposition of iron phosphate containing transition metals onto a fibrous carbon material template containing polyhydroxyl groups through hydrogen bonding. At the same time, the preparation of the precursor in the liquid phase makes the mixing of phosphorus and iron elements more uniform, thereby increasing the mass transfer efficiency in the later stage.

[0044] In one embodiment of the present invention, the fibrous carbon-containing material includes at least one of polyhydroxy polyethylene resin, polyhydroxy epoxy resin, polyhydroxy polypropylene resin, polyhydroxy phenolic resin, polyvinyl alcohol acrylonitrile copolymer, polyester polyol, polyvinyl alcohol, and polyvinyl alcohol vinylpyrrolidone copolymer.

[0045] In one embodiment of the present invention, the diameter of the fibrous polyhydroxy carbon-containing material is 2-50 μm, specifically 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, and the length is 0.1-5 μm, specifically 0.1 μm, 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm.

[0046] In one embodiment of the present invention, the carbon content of the fibrous polyhydroxy carbon material is 30-80%, specifically 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%; the hydroxyl content is 30-50%, specifically 30%, 35%, 40%, 45%, 50%; and the carboxyl content is 10-20%, specifically 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%.

[0047] According to a second aspect of the present invention, the present invention also provides a method for preparing the above-mentioned fibrous iron phosphate precursor containing polyhydroxy carbon materials, comprising the following steps:

[0048] (1) Under continuous stirring, the fibrous polyhydroxy carbon material is uniformly dispersed in the solution to obtain solution A;

[0049] (2) Add an iron source and a complexing agent to solution A obtained in step (1) and stir continuously. Then add a phosphorus source to make the solution contain iron ions and phosphate ions to obtain solution B.

[0050] (3) Add surfactant to solution B obtained in step (2), stir evenly, adjust pH, and obtain product after reaction;

[0051] (4) The product obtained in step (3) is aged, filtered, washed and dried to obtain a fibrous iron phosphate precursor containing polyhydroxy carbon materials.

[0052] In one embodiment of the present invention, the mass ratio of the fibrous polyhydroxy carbon-containing material to the fibrous polyhydroxy carbon-containing iron phosphate precursor is 0.1-5%, specifically 0.1%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.5%, 2.8%, 3.0%, 3.5%, 4.0%, 4.5%, and 5.0%. When the content of the fibrous polyhydroxy carbon-containing material is controlled within the above range, a precursor with good performance can be obtained. If too much is added, it will increase the carbon content in the subsequent material and affect the material performance.

[0053] In one embodiment of the present invention, the iron source is at least one of ferric sulfate, ferric acetate, ferric chloride, and ferric nitrate, preferably ferric sulfate; the phosphorus source is at least one of ammonium phosphate, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid, sodium phosphate, sodium monohydrogen phosphate, and sodium dihydrogen phosphate, preferably ammonium monohydrogen phosphate.

[0054] In one embodiment of the present invention, the complexing agent is at least one of oxalic acid, citric acid, tartaric acid, gluconic acid, or diethanolamine.

[0055] In one embodiment of the present invention, the surfactant is at least one selected from fatty acid polyoxyethylene ester, alkylphenol polyoxyethylene ether, alkylolamide, and sucrose fatty acid ester.

[0056] In one embodiment of the present invention, the molar ratio of phosphate to iron ions in solution B is 1.05-1.10:1, specifically 1.05:1, 1.06:1, 1.07:1, 1.08:1, 1.09:1, or 1.10:1. Controlling the molar ratio of phosphate to iron ions within the above range yields a precursor with good performance. The carbon content in the fibrous iron phosphate precursor containing polyhydroxy carbon material is 0.1-3%, specifically 0.1%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.5%, 2.8%, or 3.0%.

[0057] In one embodiment of the present invention, in step (3), the reaction temperature is 60-90℃, specifically 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, or 90℃. The reaction temperature is controlled within the above range because temperature controls the reaction. If the temperature is too low, the reaction time is too long; if the temperature is too high, the reaction is too fast, affecting the material quality. The pH is 1.0-5.0, specifically 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.2, 4.8, or 5.0. The reaction time is 3-5h, specifically 3h, 3.2h, 3.5h, 4.0h, 4.2h, 4.5h, 4.8h, or 5.0h.

[0058] According to a third aspect of the present invention, the present invention also provides a method for preparing lithium iron phosphate using the above-mentioned fibrous iron phosphate precursor containing polyhydroxy carbon material, the method comprising the steps of: mixing a carbon source, a lithium source, and the fibrous iron phosphate precursor material containing polyhydroxy carbon material in a liquid phase according to a ratio of (0.005-0.05):(1.0-1.05):1.0; drying the mixture after uniform mixing; and sintering it at high temperature under inert gas protection to obtain a lithium iron phosphate material with a porous structure.

[0059] In one embodiment of the present invention, the carbon source is at least one selected from glucose, sucrose, starch, cellulose, phenolic resin, acetylene black, and carbon black.

[0060] In one embodiment of the present invention, the lithium source is at least one selected from lithium carbonate, lithium hydroxide, lithium acetate, and lithium sulfate; the inert gas is at least one selected from nitrogen, argon, helium, neon, and xenon.

[0061] In one embodiment of the present invention, the high-temperature sintering temperature is 550-850°C, specifically 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, or 850°C. If the sintering temperature is too low, the crystalline phase of the material will not be formed, and if the temperature is too high, more impurity phases will be formed in the material.

[0062] According to a fourth aspect of the present invention, the present invention also provides a lithium iron phosphate material prepared by the above-described method for preparing lithium iron phosphate.

[0063] The present invention will be further described below through specific embodiments.

[0064] Example 1

[0065] S1: The target synthetic fibrous ferric phosphate precursor containing polyhydroxy carbon material is weighed out as follows: 1g of glycerol alkyd resin with a weight ratio of 1% is weighed out and uniformly dispersed in 100g of water under strong shearing to form a dispersion.

[0066] S2: Weigh 169.7g of ferric sulfate and prepare 1L of aqueous solution, wherein the concentration of metal ions is 0.63mol / L;

[0067] S3: The dispersion in S1 and the aqueous solution in S2 are mixed evenly by mechanical stirring to obtain a mixture;

[0068] S4: Weigh 73.6g of monoammonium phosphate (NH4H2PO4) and prepare 0.5L of monoammonium phosphate aqueous solution with a concentration of 1.27mol / L;

[0069] S5: Add 0.1L of deionized water, complexing agent and surfactant to the reactor, stir at 500rpm, and simultaneously pump the mixture in S3 and the monoammonium phosphate aqueous solution in S5 into the reactor using a metering pump. The feed rate of the mixture in S3 is 3mL / min, and the feed rate of the monoammonium phosphate aqueous solution is 1.5mL / min.

[0070] S6: After feeding, adjust the pH to 4.2, age for 4 hours, and then transfer the slurry to a centrifuge for washing and filtration;

[0071] S7: Place the washed slurry in an oven and dry it at 80°C for 5 hours to obtain a fibrous iron phosphate precursor containing polyhydroxy carbon materials.

[0072] This embodiment also provides a method for preparing lithium iron phosphate material, the steps of which include:

[0073] A carbon source, a lithium source, and a fibrous, polyhydroxyl-containing carbon material iron phosphate precursor were mixed in a liquid phase at a ratio of 0.05:1.05:1.0. After being mixed evenly, the mixture was dried and then sintered at 600°C under inert gas protection to obtain a porous lithium iron phosphate material.

[0074] Example 2

[0075] The difference between this embodiment and Embodiment 1 is that in step S2, 164.3 g of ferric sulfate and 5.4 g of manganese sulfate are weighed according to the molar ratio of (Fe + Mn) = (0.95 + 0.05) and prepared into a 1 L aqueous solution with a metal ion concentration of 0.63 mol / L. The rest is the same as in Embodiment 1 and will not be repeated here.

[0076] Example 3

[0077] The difference between this embodiment and Embodiment 2 is that the molar ratio of Fe to Ni is 0.95:0.05. Everything else is the same as in Embodiment 2 and will not be repeated here.

[0078] Example 4

[0079] The difference between this embodiment and Embodiment 2 is that the molar ratio of Fe to V is 0.95:0.05. Everything else is the same as in Embodiment 2 and will not be repeated here.

[0080] Example 5

[0081] The difference between this embodiment and Embodiment 2 is that the molar ratio of Fe to Mg is 0.95:0.05. Everything else is the same as in Embodiment 2 and will not be repeated here.

[0082] Example 6

[0083] The difference between this embodiment and Embodiment 2 is that the molar ratio of Fe to Al is 0.95:0.05. Everything else is the same as in Embodiment 2 and will not be repeated here.

[0084] Example 7

[0085] The difference between this embodiment and Embodiment 2 is that the molar ratio of Fe to Cu is 0.95:0.05. Everything else is the same as in Embodiment 2 and will not be repeated here.

[0086] Comparative Example 1

[0087] The difference between this comparative example and Example 1 is that ferrous sulfate and monoammonium phosphate were directly used as raw materials to prepare the ferric phosphate precursor. Everything else is the same as in Example 1, and will not be repeated here.

[0088] Performance testing

[0089] The lithium iron phosphate materials obtained in Examples 1-7 were subjected to SEM testing, and the cross-sectional images of the lithium iron phosphate materials are shown below. Figure 1 As shown.

[0090] Results Analysis

[0091] As can be seen from the figure, lithium iron phosphate materials have a large number of pores inside. This is because after adding lithium source to the precursor and mixing it evenly, it is calcined. Since the insoluble fibrous polyhydroxy carbon material decomposes at high temperature to produce water and carbon dioxide, it also acts as a reducing agent and is consumed. The generated gas and the consumed carbon source form a three-dimensional network-like void structure. This lithium iron phosphate cathode material with a three-dimensional network-like void structure enhances liquid retention, improves rate performance, and the porous interior provides a certain degree of support, making the morphology less likely to be destroyed during the compaction process.

[0092] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A method for preparing lithium iron phosphate using a fibrous iron phosphate precursor containing polyhydroxy carbon materials, characterized in that, The method for preparing lithium iron phosphate includes the following steps: mixing a carbon source, a lithium source, and a fibrous polyhydroxy carbon material-containing iron phosphate precursor in a liquid phase at a ratio of (0.005 - 0.05):(1.0 - 1.05):1.0, drying the mixture evenly after mixing, and performing high-temperature sintering under the protection of an inert gas to obtain a lithium iron phosphate material with a porous structure; The method for preparing the fibrous polyhydroxy carbon material-containing iron phosphate precursor includes the following steps: (1) Under continuous stirring, uniformly disperse the fibrous polyhydroxy carbon material in a solution to obtain solution A; (2) Add an iron source and a complexing agent to solution A obtained in step (1), continuously stir, and then add a phosphorus source to make the solution contain iron ions and phosphate ions to obtain solution B; (3) Add a surfactant to solution B obtained in step (2), stir evenly, adjust the pH, and obtain a product after reaction; (4) Subject the product obtained in step (3) to aging, pressure filtration, washing, and drying treatments to obtain a fibrous polyhydroxy carbon material-containing iron phosphate precursor; The mass of the fibrous polyhydroxy carbon material is 0.1 - 5% of the mass of the fibrous polyhydroxy carbon material-containing iron phosphate precursor; The fibrous polyhydroxy carbon material includes at least one of polyhydroxy polyvinyl resin, polyhydroxy epoxy resin, polyhydroxy polypropylene resin, polyhydroxy phenolic resin, polyvinyl alcohol acrylonitrile copolymer, polyvinyl alcohol, and polyvinyl alcohol vinyl pyrrolidone copolymer; The chemical structural formula of the fibrous polyhydroxy carbon material-containing iron phosphate precursor is as follows: where 0 ≤ x ≤ 1, 100000 ≤ n <1000000>0, M is a transition metal element, and the transition metal element includes at least one of Mn, Ni, V, and Cu.

2. The method for preparing lithium iron phosphate according to claim 1, characterized in that, The diameter of the fibrous polyhydroxy carbon material is 0.1 - 5 μm, and the length is 2 - 50 μm.

3. The method for preparing lithium iron phosphate according to claim 1, characterized in that, The carbon content of the fibrous polyhydroxy carbon material is 30 - 80%, the hydroxyl content is 30 - 50%, and the carboxyl content is 10 - 20%.

4. The method for preparing lithium iron phosphate according to claim 1, characterized in that, The iron source is at least one of ferric sulfate, ferric acetate, ferric chloride, and ferric nitrate; the phosphorus source is at least one of ammonium phosphate, monoammonium phosphate, diammonium phosphate, phosphoric acid, sodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate; the complexing agent is at least one of oxalic acid, citric acid, tartaric acid, gluconic acid, or diethanolamine; the surfactant is at least one of fatty acid polyoxyethylene ester, alkylphenol polyoxyethylene ether, alkylolamide, and sucrose fatty acid ester.

5. The method for preparing lithium iron phosphate according to claim 1, characterized in that, The molar ratio of phosphate to iron ions in solution B is 1.05 - 1.10:1; the carbon content in the fibrous polyhydroxy carbon material-containing iron phosphate precursor is 0.1 - 3%.

6. The method for preparing lithium iron phosphate according to claim 1, characterized in that, In step (3), the reaction temperature is 60 - 90 °C; the pH = 1.0 - 5.0; the reaction time is 3 - 5 h.

7. The method for preparing lithium iron phosphate according to claim 1, characterized in that, The carbon source is at least one of glucose, sucrose, starch, cellulose, phenolic resin, and carbon black; the lithium source is at least one of lithium carbonate, lithium hydroxide, lithium acetate, and lithium sulfate; the inert gas is at least one of nitrogen, argon, helium, neon, and xenon.

8. The method for preparing lithium iron phosphate according to claim 1, characterized in that, The high-temperature sintering temperature is 550-850℃.

9. A lithium iron phosphate material, characterized in that: It is prepared by the method for preparing lithium iron phosphate according to any one of claims 1-8.

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