Lithium iron phosphate precursor and preparation method thereof, and lithium iron phosphate and preparation method thereof

Abstract

The invention relates to the technical field of lithium batteries, and relates to a lithium iron phosphate precursor and a preparation method thereof, and lithium iron phosphate and a preparation method thereof, and the preparation method comprises the following steps: preparing mixed slurry containing a phosphorus source, an iron source and a lithium source; controlling the particle size of the mixed slurry to be within a certain range, adding ammonium titanyl oxalate, and performing crushing treatment and sintering treatment to obtain the lithium iron phosphate precursor. According to the method, a stable ferric pyrophosphate phase can be prepared as a transition phase for preparing lithium iron phosphate, so that large-particle lithium iron phosphate can be sintered at a relatively low temperature subsequently, the compaction density of the lithium iron phosphate is greatly improved, formation of an impure phase can be well controlled, the purity of the lithium iron phosphate is improved, and the method is suitable for industrial production. And the lithium battery can have relatively good rate capability when being applied to the lithium battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a lithium iron phosphate precursor and a preparation method thereof, and lithium iron phosphate and a preparation method thereof. Background Art

[0002] Lithium iron phosphate (LiFePO4) is an important cathode material for lithium-ion batteries, which is widely used due to its high energy density, long cycle life and good thermal stability. The high-temperature solid-phase method is widely used in industrial production to prepare lithium iron phosphate due to its advantages such as simple process operation. However, the solid-phase method cannot achieve atomic-level element mixing and the sintering process is difficult to accurately control. Therefore, the particle size of the prepared lithium iron phosphate is difficult to control and the compaction density is difficult to reach the preset value. Therefore, it is necessary to provide a method for improving the compaction density of lithium iron phosphate. Summary of the invention

[0003] The present invention aims to solve one of the technical problems in the related art to at least a certain extent. To this end, the present invention provides a lithium iron phosphate precursor and a preparation method, lithium iron phosphate and a preparation method, which can prepare a stable iron pyrophosphate phase (lithium iron phosphate precursor) as a transition phase for preparing lithium iron phosphate, so that large particles of lithium iron phosphate can be sintered later, greatly improving the compaction density of lithium iron phosphate, and can better control the formation of impurity phases, improve the purity of lithium iron phosphate, and use it in lithium batteries to make lithium batteries have better rate performance.

[0004] To this end, the first aspect of the present invention provides a method for preparing a lithium iron phosphate precursor, comprising the following steps:

[0005] preparing a mixed slurry comprising a phosphorus source, an iron source and a lithium source;

[0006] The particle size of the mixed slurry is controlled within a certain range, ammonium titanium oxalate is added, and crushing and sintering are performed to obtain the lithium iron phosphate precursor.

[0007] Ammonium titanyl oxalate is added to the above preparation process, which can be dissolved in the mixed slurry. Compared with the technical solution of first preparing a lithium iron phosphate precursor and then adding ammonium titanyl oxalate, in the method provided by the present invention, ammonium titanyl oxalate is hydrolyzed to generate nano-scale titanium dioxide, which can improve the dispersibility of titanium. Nano-scale titanium dioxide has the effect of increasing the compaction density of the material, increasing the compaction density of the product, and obtaining a stable iron pyrophosphate phase (lithium iron phosphate precursor), which can be used as a transition phase for preparing the positive electrode material lithium iron phosphate, so that large particles of lithium iron phosphate can be sintered at a lower temperature subsequently, greatly improving the compaction density of lithium iron phosphate, and can better control the formation of impure phases, thereby improving the purity of lithium iron phosphate.

[0008] According to an embodiment of the present invention, the phosphorus source includes at least one of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, iron phosphate, and phosphoric acid.

[0009] According to an embodiment of the present invention, the iron source includes at least one of ferric phosphate, ferric sulfate, ferric chloride, ferrous sulfate, ferrous oxalate, ferrous chloride, and ferric oxide.

[0010] According to an embodiment of the present invention, the lithium source includes at least one of lithium carbonate, lithium phosphate, lithium oxalate, lithium acetate, and lithium hydroxide.

[0011] According to an embodiment of the present invention, the molar ratio of elements Fe:P in the mixed slurry is (0.94-0.98):1.

[0012] According to an embodiment of the present invention, the molar ratio of elements Li:Fe in the mixed slurry is (1.01-1.10):1.

[0013] According to an embodiment of the present invention, the particle size of the mixed slurry is controlled within the range of 0.2-0.8 μm.

[0014] According to an embodiment of the present invention, the molar ratio of the ammonium titanium oxalate to the iron element is (1:1000)-(1:200).

[0015] According to an embodiment of the present invention, the pulverization process is performed to a particle size of 200 nm-20 μm.

[0016] According to an embodiment of the present invention, the temperature of the sintering process is 250-500°C.

[0017] According to an embodiment of the present invention, the sintering treatment time is 2-6 hours.

[0018] According to an embodiment of the present invention, the sintering process is performed in an inert atmosphere.

[0019] A second aspect of the present invention provides a lithium iron phosphate precursor, which is obtained according to the preparation method described in the first aspect.

[0020] Thus, a titanium-doped lithium iron phosphate precursor is obtained, which has a stable structure, high purity and high compaction density.

[0021] A third aspect of the present invention provides a method for preparing lithium iron phosphate, comprising:

[0022] Mixing a lithium iron phosphate precursor with a carbon source and performing secondary sintering to obtain the lithium iron phosphate;

[0023] Wherein, the lithium iron phosphate precursor is obtained according to the preparation method described in the first aspect or is the lithium iron phosphate precursor described in the second aspect.

[0024] The preparation method is based on the aforementioned lithium iron phosphate precursor, and can sinter large-particle lithium iron phosphate, improve the compaction density of lithium iron phosphate, and better control the formation of impurity phases.

[0025] According to an embodiment of the present invention, the carbon source includes at least one of sucrose, glucose and chitosan.

[0026] According to an embodiment of the present invention, the mass ratio of the carbon source to the lithium iron phosphate precursor is (1-20):100.

[0027] According to an embodiment of the present invention, the temperature of the secondary sintering is 500-780°C.

[0028] According to an embodiment of the present invention, the secondary sintering time is 4-9 hours.

[0029] According to an embodiment of the present invention, the secondary sintering is performed in an inert atmosphere.

[0030] A fourth aspect of the present invention provides a lithium iron phosphate, which is obtained according to the preparation method described in the third aspect.

[0031] The lithium iron phosphate has good crystallinity, high purity and high compaction density. Using it in lithium batteries can make the lithium batteries have better rate performance.

[0032] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0034] Figure 1 The XRD pattern of the lithium iron phosphate precursor prepared in Example 1 of the present invention is shown;

[0035] Figure 2 The XRD pattern of lithium iron phosphate prepared in Example 1 of the present invention is shown. DETAILED DESCRIPTION

[0036] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be understood as limiting the present invention.

[0037] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. Further, in the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more.

[0038] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0039] In order to make the present invention more easily understood, certain technical and scientific terms are specifically defined below. Unless otherwise clearly defined elsewhere in this document, all other technical and scientific terms used herein have the meanings commonly understood by those skilled in the art to which the present invention belongs.

[0040] In this document, the terms “include” or “comprising” are open expressions, that is, including the contents specified in the present invention but not excluding other contents.

[0041] As used herein, the terms "optionally", "optional" or "optionally" generally mean that the subsequently described event or circumstance may but need not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.

[0042] According to an embodiment of the present invention, the present invention provides a method for preparing a lithium iron phosphate precursor, comprising the following steps:

[0043] (1) A mixed slurry containing a phosphorus source, an iron source and a lithium source is prepared.

[0044] According to a specific embodiment of the present invention, the type of the phosphorus source is not particularly limited, and those skilled in the art may select it according to actual needs. As some specific examples, the phosphorus source includes but is not limited to lithium dihydrogen phosphate, ammonium dihydrogen phosphate, iron phosphate, and phosphoric acid.

[0045] According to a specific embodiment of the present invention, the type of the iron source is not particularly limited, and those skilled in the art can select it according to actual needs. As some specific examples, the iron source includes but is not limited to ferric phosphate, ferric sulfate, ferric chloride, ferrous sulfate, ferrous oxalate, ferrous chloride, and ferrous oxide.

[0046] According to a specific embodiment of the present invention, the type of the lithium source is not particularly limited, and those skilled in the art may select it according to actual needs. As some specific examples, the lithium source includes but is not limited to lithium carbonate, lithium phosphate, lithium oxalate, lithium acetate, and lithium hydroxide.

[0047] Specifically, the mixed slurry can be obtained by preparing the source solutions in advance and then mixing them, or the sources can be directly dissolved in a solvent to directly obtain the mixed slurry, which will not affect the subsequent steps.

[0048] According to a specific embodiment of the present invention, the element molar ratio Fe:P in the mixed slurry is (0.94-0.98):1. As some specific examples, the iron source and the phosphorus source can be mixed in proportions such as the element molar ratio Fe:P of 0.94:1, 0.95:1, 0.96:1, 0.97:1, and 0.98:1.

[0049] According to a specific embodiment of the present invention, the molar ratio of elements Li:Fe in the mixed slurry is (1.01-1.10):1. As some specific examples, the lithium source and the iron source can be mixed according to the molar ratio of elements Li:Fe of 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1, 1.08:1, 1.09:1, 1.10:1 and the like.

[0050] (2) The particle size of the mixed slurry is controlled within a certain range, and ammonium titanium oxalate is added to perform a crushing process and a sintering process to obtain the lithium iron phosphate precursor.

[0051] According to a specific embodiment of the present invention, the particle size of the mixed slurry is controlled within the range of 0.2-0.8 μm. As some specific examples, the particle size of the mixed slurry is controlled to be 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, etc. The method for controlling the particle size of the mixed slurry is not particularly limited, and the mixed slurry can be controlled to the target particle size by sand grinding or other methods.

[0052] According to a specific embodiment of the present invention, the amount of ammonium titanium oxalate added is not particularly limited, and those skilled in the art can select it according to actual needs. As some specific examples, its molar ratio to the iron element is (1:1000)-(1:200), for example, 1:1000, 1:900, 1:800, 1:700, 1:600, 1:500, 1:400, 1:300, 1:200, etc.

[0053] According to a specific embodiment of the present invention, the pulverization process is performed to a particle size of 200nm-20μm. As some specific examples, the pulverization process is performed to a particle size of 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, etc. The pulverization method is also not particularly limited, and the sample can be pulverized to a target particle size by sand milling or the like.

[0054] According to a specific embodiment of the present invention, the temperature of the sintering treatment is not particularly limited, and those skilled in the art can select it according to actual needs. As some specific examples, the temperature of the sintering treatment is 250-500°C, such as 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, etc. The time of the sintering treatment is not particularly limited, and those skilled in the art can select it according to actual needs. As some specific examples, the time of the sintering treatment is 2-6h, such as 2h, 3h, 4h, 5h, 6h, etc. The sintering treatment is carried out in an inert atmosphere, such as nitrogen, helium, neon, argon, etc., preferably in an inert atmosphere with an oxygen content of less than 50ppm, more preferably, the oxygen content is 10ppm, 15ppm, 20ppm, 25ppm, 30ppm, 35ppm, 40ppm, 45ppm, 50ppm, etc.

[0055] According to a specific embodiment of the present invention, the preparation method further comprises: adding ammonium titanium oxalate and mixing and dispersing uniformly, performing drying treatment, and then performing pulverization treatment and sintering treatment to obtain the lithium iron phosphate precursor.

[0056] According to an embodiment of the present invention, the present invention also provides a method for preparing lithium iron phosphate, comprising:

[0057] Mixing a lithium iron phosphate precursor with a carbon source and performing secondary sintering to obtain the lithium iron phosphate;

[0058] Wherein, the lithium iron phosphate precursor is obtained according to the aforementioned preparation method.

[0059] The above-mentioned preparation method can obtain a stable iron pyrophosphate phase (lithium iron phosphate precursor) as a transition phase for preparing the positive electrode material lithium iron phosphate. Sintering it with a carbon source can obtain lithium iron phosphate with good crystallinity, low magnetic material content, good purity and high compaction density. Using it in lithium batteries can improve the battery's rate performance.

[0060] According to a specific embodiment of the present invention, the type of carbon source is not particularly limited, and those skilled in the art may select it according to actual needs. Some specific examples include but are not limited to sucrose, glucose, and chitosan.

[0061] According to a specific embodiment of the present invention, the mass ratio of the carbon source to the lithium iron phosphate precursor is (1-20):100. As some specific examples, the mass ratio of the carbon source to the iron source is 1:100, 1.5:100, 2:100, 2.5:100, 3:100, 3.5:100, 4:100, 4.5:100, 5:100, 6:100, 7:100, 8:100, 9:100, 10:100, 11:100, 12:100, 13:100, 14:100, 15:100, 16:100, 17:100, 18:100, 19:100, 20:100, etc.

[0062] According to a specific embodiment of the present invention, the temperature of the secondary sintering is not particularly limited, and those skilled in the art can select it according to actual needs. As some specific examples, the temperature of the secondary sintering is 500-780°C, such as 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 780°C, etc. The time of the secondary sintering is not particularly limited, and those skilled in the art can select it according to actual needs. As some specific examples, the time of the secondary sintering is 4-9h, such as 4h, 5h, 6h, 7h, 8h, 9h, etc. It is preferred to sinter in an inert environment, such as a nitrogen atmosphere, a helium atmosphere, a neon atmosphere, or an argon atmosphere, and more preferably in an inert environment with an oxygen content of less than 50ppm; more preferably, the oxygen content is 10ppm, 15ppm, 20ppm, 25ppm, 30ppm, 35ppm, 40ppm, 45ppm, 50ppm, etc.

[0063] According to a specific embodiment of the present invention, the step further includes: mixing the lithium iron phosphate precursor with a carbon source, performing secondary sintering and secondary crushing to obtain the lithium iron phosphate. The secondary crushing method is not particularly limited, for example, by air flow crushing, etc., thereby obtaining lithium iron phosphate with a target particle size.

[0064] The scheme of the present invention will be explained below in conjunction with the embodiments. It will be appreciated by those skilled in the art that the following embodiments are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Where specific techniques or conditions are not indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used are not indicated by the manufacturer and are all conventional products that can be obtained commercially.

[0065] Example 1

[0066] (1) Weighing iron phosphate and lithium carbonate with an iron-phosphorus molar ratio of 0.97:1 and a lithium-iron molar ratio of 1.02:1, disperse and mix in water, sand-milling in a sand mill to a particle size of 0.35 μm, adding ammonium titanyl oxalate (the molar ratio of ammonium titanyl oxalate to iron element is 1:500), dispersing evenly, drying, and then crushing to a particle size of 0.8 μm, and then sintering at 250° C. under the protection of inert gas in a box furnace with an oxygen content of 45 ppm for 4 hours to obtain a lithium iron phosphate precursor;

[0067] (2) The lithium iron phosphate precursor obtained in step (1) is mixed evenly with glucose (the mass ratio of glucose to lithium iron phosphate precursor is 8:100), and secondary sintering is performed in an inert atmosphere protection box furnace under the condition of an oxygen content of 45 ppm (the secondary sintering temperature is 750°C and the secondary sintering time is 6 h), and the lithium iron phosphate material is obtained by air flow crushing.

[0068] Example 2

[0069] (1) Weighing iron phosphate and lithium carbonate with an iron-phosphorus molar ratio of 0.97:1 and a lithium-iron molar ratio of 1.02:1, disperse and mix in water, sand-milling in a sand mill to a particle size of 0.38 μm, adding ammonium titanyl oxalate (the molar ratio of ammonium titanyl oxalate to iron element is 1:500), dispersing evenly, drying, and then crushing to a particle size of 1.2 μm, and then sintering at 350° C. under the protection of inert gas in a box furnace with an oxygen content of 40 ppm for 4 hours to obtain a lithium iron phosphate precursor;

[0070] (2) The lithium iron phosphate precursor obtained in step (1) is mixed evenly with glucose (the mass ratio of glucose to lithium iron phosphate precursor is 8:100), and secondary sintering is performed in an inert atmosphere protection box furnace under the condition of an oxygen content of 40 ppm (the secondary sintering temperature is 700° C. and the secondary sintering time is 6 h), and the lithium iron phosphate material is obtained by air flow crushing.

[0071] Example 3

[0072] (1) Weighing iron phosphate and lithium carbonate with an iron-phosphorus molar ratio of 0.98:1 and a lithium-iron molar ratio of 1.02:1, disperse and mix in water, sand-milling in a sand mill to a particle size of 0.35 μm, adding ammonium titanyl oxalate (the molar ratio of ammonium titanyl oxalate to iron element is 1:500), dispersing evenly, drying, and then crushing to a particle size of 1.5 μm, and then sintering at 450° C. in a box furnace under inert gas protection and an oxygen content of 45 ppm for 4 hours to obtain a lithium iron phosphate precursor;

[0073] (2) The lithium iron phosphate precursor obtained in step (1) was mixed with glucose (the mass ratio of glucose to lithium iron phosphate precursor was 8:100) and subjected to secondary sintering (secondary sintering temperature was 680° C. and secondary sintering time was 6 h) in an inert atmosphere protection box furnace under the condition of an oxygen content of 45 ppm, and the lithium iron phosphate material was obtained by air flow pulverization.

[0074] Comparative Example 1

[0075] Weigh iron phosphate, lithium carbonate and glucose (iron-phosphorus molar ratio is 0.97:1, lithium-iron molar ratio is 1.03:1, and the amount of glucose added is 8% of the mass of iron phosphate and lithium carbonate) and disperse and mix them in water, and grind them in a sand mill to a particle size of 0.35 μm. Spray dry at 250°C, put them in a box furnace under inert gas protection, sinter them under the condition of 45ppm oxygen content (sintering temperature is 750°C, sintering time is 12h), and finally obtain lithium iron phosphate after air flow pulverization.

[0076] Comparative Example 2

[0077] Weigh iron phosphate, lithium carbonate, glucose (the molar ratio of iron to phosphorus is 0.97:1, the molar ratio of lithium to iron is 1.02:1, and the amount of glucose added is 8% of the sum of the mass of iron phosphate and lithium carbonate), and titanium dioxide (the molar ratio of titanium dioxide to iron element is 1:500), disperse and mix in water, sand grind in a sand mill to a particle size of 0.35 μm, spray dry at 250° C., put into a box furnace under inert gas protection, sinter at an oxygen content of 35 ppm (sintering temperature is 800° C., sintering time is 12 h), and finally air flow pulverize to obtain lithium iron phosphate.

[0078] Test Case

[0079] (1) Phase test: The precursor in Example 1 and the lithium iron phosphate sample prepared according to the precursor in Example 1 were subjected to X-ray diffraction (XRD) analysis to obtain spectra, which were compared with the standard spectra of FeP2O7 PDF#72-1516 and lithium iron phosphate PDF#83-2092, respectively. The results are shown in FIG. Figure 1-2 .

[0080] Depend on Figure 1 By comparing the standard XRD spectra of the precursor prepared in Example 1 with iron pyrophosphate, it can be seen that the prepared precursor is FeP2O7 and has good crystallinity; Figure 2 By comparing the sample prepared according to the precursor with the standard XRD spectrum of lithium iron phosphate, it can be seen that the synthesized sample is LiFePO4 and has good crystallinity.

[0081] (2) The lithium iron phosphate obtained in the above-mentioned embodiments and comparative examples was taken to test the powder compaction density, and was mixed and stirred evenly with SP carbon powder, PVDF, and NMP in a mass ratio of 92:4:0.1:3.9, and then the prepared slurry was coated on a 20 μm aluminum foil, dried at 100°C and vacuum dried at 120°C, and then the prototype pole pieces with a diameter of 150 mm were cut out for button battery assembly, and finally placed in a button battery performance test cabinet for testing at different magnifications. The results are shown in Table 1. It can be seen that the compaction density of lithium iron phosphate in the embodiments is basically higher than that in the comparative examples, and the specific capacity of the button battery test is slightly different.

[0082] Table 1

[0083]

[0084] (3) The above examples and comparative examples were tested for magnetic foreign matter content, and the results are shown in Table 2. It can be seen that the magnetic matter content of lithium iron phosphate in the examples is lower and the sample purity is higher.

[0085] Table 2

[0086]

[0087]

[0088] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0089] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a lithium iron phosphate precursor, characterized in that: The following steps are involved: preparing a mixed slurry comprising a phosphorus source, an iron source and a lithium source; The particle size of the mixed slurry is controlled within a certain range, ammonium titanium oxalate is added, and crushing and sintering are performed to obtain the lithium iron phosphate precursor.

2. The preparation method according to claim 1, characterized in that: The phosphorus source includes at least one of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, iron phosphate, and phosphoric acid; Optionally, the iron source includes at least one of ferric phosphate, ferric sulfate, ferric chloride, ferrous sulfate, ferrous oxalate, ferrous chloride, and ferric oxide; Optionally, the lithium source includes at least one of lithium carbonate, lithium phosphate, lithium oxalate, lithium acetate, and lithium hydroxide; Optionally, the molar ratio of elements Fe:P in the mixed slurry is (0.94-0.98):1; Optionally, the molar ratio of elements Li:Fe in the mixed slurry is (1.01-1.10):

1.

3. The preparation method according to claim 1, characterized in that: The particle size of the mixed slurry is controlled within the range of 0.2-0.8 μm.

4. The preparation method according to claim 1, characterized in that: The molar ratio of the ammonium titanium oxalate to the iron element is (1:1000)-(1:200).

5. The preparation method according to claim 1, characterized in that: The powder is crushed to a particle size of 200nm-20μm.

6. The preparation method according to claim 1, characterized in that: The sintering temperature is 250-500°C; Optionally, the sintering treatment time is 2-6h; Optionally, the sintering process is performed in an inert atmosphere.

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

8. A method for preparing lithium iron phosphate, characterized in that: include: Mixing a lithium iron phosphate precursor with a carbon source and performing secondary sintering to obtain the lithium iron phosphate; Wherein, the lithium iron phosphate precursor is obtained according to the preparation method according to any one of claims 1 to 6 or is the lithium iron phosphate precursor according to claim 7.

9. The preparation method according to claim 8, characterized in that: The carbon source includes at least one of sucrose, glucose and chitosan; Optionally, the mass ratio of the carbon source to the lithium iron phosphate precursor is (1-20):100; Optionally, the secondary sintering temperature is 500-780°C; Optionally, the secondary sintering time is 4-9h; Optionally, the secondary sintering is performed in an inert atmosphere.

10. A lithium iron phosphate, characterized in that: The lithium iron phosphate is obtained according to the preparation method of claim 8 or 9.

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