A lithium iron manganese phosphate positive electrode material prepared by using a mixed manganese source, and a preparation method and application thereof

Abstract

This invention relates to a lithium manganese iron phosphate cathode material prepared using a mixed manganese source, its preparation method, and its application. The preparation method includes: mixing manganese dioxide and manganese acetate to obtain a mixed manganese source; dispersing a lithium source, the mixed manganese source, an iron source, a phosphorus source, and a carbon source in pure water; performing sand milling; and subsequently spray drying and calcination to obtain the final product. By using a mixed manganese source, this invention can significantly reduce the specific surface area of ​​the material, lowering the requirements for the cell's processing performance. Furthermore, the mixed use of manganese sources can significantly increase the material's discharge specific capacity. The resulting lithium manganese iron phosphate cathode material produces a battery with a specific surface area of ​​21.70 m². 2 / g, discharge specific capacity 154.6mAh / g (0.1C), 153.7mAh / g (0.2C), 150.8mAh / g (0.5C), 148.3mAh / g (1C), capacity retention rate of 99.41% at 1C / 20 cycles, with excellent cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of electrode material technology, specifically relating to a lithium iron manganese phosphate cathode material prepared using a mixed manganese source, its preparation method, and its application. Background Technology

[0002] Lithium manganese iron phosphate (LFP) is a novel phosphate-based lithium-ion battery cathode material formed by doping lithium iron phosphate with a certain proportion of manganese. Since manganese and iron are both located in the fourth period of the periodic table and are adjacent to each other, they have similar ionic radii and some chemical properties. Therefore, doping will not significantly affect the original structure. Moreover, by doping with manganese, the performance advantages of both iron and manganese can be effectively combined.

[0003] The theoretical capacity of lithium manganese iron phosphate is the same as that of lithium iron phosphate, at 170 mAh / g. However, compared to Li, lithium manganese iron phosphate has a lower theoretical capacity. + The electrode potential of LiFePO4 is 4.1V, significantly higher than that of LiFePO4 (3.4V), and falls within the stable electrochemical window of organic electrolyte systems. This high potential of 4.1V gives LiFePO4 the potential for high energy density, its greatest advantage over LiFePO4. If the actual capacity of LiFePO4 were to reach the same level as LiFePO4, its energy density would be 35% higher than LiFePO4, and compared to Lithium Manganese Oxide (LiMnO4) at a comparable voltage, its energy density could be more than 20% higher. Furthermore, LiFePO4 has low raw material costs and is environmentally friendly, thus its market prospects for batteries and materials are very broad.

[0004] However, with the increase of manganese content, the low conductivity makes it difficult to realize the capacity, and electrolyte side reactions further hinder the material's capacity utilization, limiting its charge-discharge capability. The introduction of manganese significantly reduces the material's conductivity. Therefore, an improved technical solution is needed to address the shortcomings of the existing technology. Summary of the Invention

[0005] To address the problems of low discharge specific capacity and poor cycle performance of existing lithium manganese iron phosphate cathode materials, the present invention aims to provide a lithium manganese iron phosphate cathode material prepared using a mixed manganese source, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing lithium manganese iron phosphate cathode material using a mixed manganese source, comprising the following steps:

[0008] (1) Mix manganese dioxide and manganese acetate evenly to obtain a mixed manganese source for later use;

[0009] (2) The mixed raw materials: lithium source, mixed manganese source, iron source, phosphorus source and carbon source are dispersed in pure water by ultrasonic treatment to obtain a slurry for later use;

[0010] (3) The slurry is subjected to sand milling treatment;

[0011] (4) Spray dry the slurry after sand milling to obtain precursor powder;

[0012] (5) The precursor powder is calcined to obtain the product.

[0013] Preferably, in step (1), the molar ratio of manganese dioxide to manganese acetate is (3-1):(1-3);

[0014] In step (1), a three-stage processing process is adopted during mixing: first, the mixture is processed at 600-800 r / min for 30-40 min, then at 800-1000 r / min for 30-40 min, and finally at 1000-1200 r / min for 30-40 min.

[0015] Preferably, in step (2), the molar ratio of lithium:manganese:iron:phosphorus in the mixed raw materials is 1.03:(0.6-0.5):(0.4-0.5):1, based on lithium, manganese, iron and phosphorus.

[0016] In step (2), the mass of the carbon source in the mixed raw materials is 6% of the total mass of the lithium source, mixed manganese source, iron source and phosphorus source.

[0017] Preferably, in step (2), the solid content of the slurry is 30-40%;

[0018] In step (2), the ultrasonic treatment power is 35-40Hz, the temperature is 25-30℃, and the time is 1-2h.

[0019] Preferably, in step (2), the lithium source is any one or two or more of lithium carbonate, lithium hydroxide, and lithium phosphate;

[0020] The iron source is any one or two or more of ferric phosphate, ferrous oxalate, and ferrous sulfate.

[0021] The phosphorus source is any one or two or more of the following: ammonium dihydrogen phosphate, diammonium hydrogen phosphate, iron phosphate, and phosphoric acid.

[0022] Preferably, in step (2), the carbon source is polyvinyl alcohol and polyethylene glycol; the mass ratio of polyvinyl alcohol and polyethylene glycol is 1:1.

[0023] In step (3), the rotation speed during sand milling is 800-900 r / min and the time is 4-6 h; the D50 of the slurry after sand milling is 200 nm.

[0024] Preferably, in step (4), the discharge temperature during spray drying is 95-110℃;

[0025] In step (5), the calcination temperature is 660-720℃ and the holding time is 6-10h.

[0026] This invention provides a lithium manganese iron phosphate cathode material, which is prepared by the aforementioned preparation method.

[0027] The present invention provides a lithium-ion battery comprising the aforementioned lithium manganese iron phosphate cathode material.

[0028] This invention provides an application of the lithium manganese iron phosphate cathode material in the preparation of lithium-ion batteries.

[0029] Beneficial effects:

[0030] This invention provides a lithium manganese iron phosphate (LFP) cathode material. By using a mixed manganese source, the specific surface area of ​​the material can be significantly reduced, lowering the requirements for cell processing performance. Furthermore, the mixed use of manganese sources can significantly increase the discharge specific capacity of the material. Compared with existing methods for improving the electrochemical performance of LFP cathode materials through doping, the method of this invention is lower in cost and avoids the problem of insufficient lithium content caused by lithium reacting with dopants to form other compounds on the material surface that cannot penetrate into the internal structure. The specific surface area of ​​the battery assembled from the LFP cathode material obtained by this invention is 21.70 m². 2 / g, with discharge specific capacities of 154.6mAh / g (0.1C), 153.7mAh / g (0.2C), 150.8mAh / g (0.5C), and 148.3mAh / g (1C), and a capacity retention rate of 99.41% at 1C / 20 cycles, demonstrating excellent cycle performance. Attached Figure Description

[0031] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein:

[0032] Figure 1 The charge-discharge curves are of batteries assembled from lithium iron phosphate cathode materials prepared in Examples 4, 1, and 2 of this invention.

[0033] Figure 2 The image shows the 1C cycle results of the battery assembled with the lithium iron phosphate cathode material prepared in Example 4 of this invention.

[0034] Figure 3 This is a SEM image of the lithium manganese iron phosphate cathode material prepared in Example 4 of the present invention. Detailed Implementation

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0036] The present invention will now be described in detail with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0037] To address the existing problems, this invention provides a method for preparing lithium manganese iron phosphate cathode material using a mixed manganese source, comprising the following steps:

[0038] (1) Mix manganese dioxide and manganese acetate evenly to obtain a mixed manganese source for later use;

[0039] (2) The mixed raw materials: lithium source, mixed manganese source, iron source, phosphorus source and carbon source are dispersed in pure water by ultrasonic treatment to obtain a slurry for later use;

[0040] (3) The slurry is subjected to sand milling treatment;

[0041] (4) Spray dry the slurry after sand milling to obtain precursor powder;

[0042] (5) The precursor powder is calcined to obtain the product.

[0043] Among manganese-based cathode materials, manganese dioxide and manganese tetroxide are commonly used. While manganese dioxide-based materials offer more stable performance, calcination of manganese dioxide alone is detrimental to redox reactions, leading to low capacity. This invention selects manganese dioxide and manganese acetate as a mixed manganese source. Since manganese acetate reacts with acetate ions to generate carbon dioxide during calcination, it possesses reducing properties and removes oxygen. Therefore, combining the high capacity of manganese acetate with the low specific surface area of ​​manganese dioxide results in a mixed lithium manganese iron phosphate material with superior performance. Furthermore, milling the mixture after mixing, due to the differences in hardness and particle size between the two materials, leads to a more reasonable particle size distribution and better capacity performance.

[0044] In a preferred embodiment of the present invention, in step (1), the molar ratio of manganese dioxide to manganese acetate is (3-1):(1-3);

[0045] In a preferred embodiment of the present invention, in step (1), the molar ratio of manganese dioxide to manganese acetate is 1:2;

[0046] In a preferred embodiment of the present invention, in step (1), a high-speed mixer is used for uniform mixing; the mixing process is carried out in three stages: first, the mixture is processed at 600-800 r / min for 30-40 min, then at 800-1000 r / min for 30-40 min, and finally at 1000-1200 r / min for 30-40 min.

[0047] In this method, the mixture is first mixed at a low speed to prevent any material from flying away due to its lightness, which would result in insufficient material usage. After mixing at a low speed, the mixture is then rotated at a high speed to reduce the occurrence of incorrect proportions.

[0048] In a preferred embodiment of the present invention, in step (2), the molar ratio of lithium:manganese:iron:phosphorus in the mixed raw materials is 1.03:(0.6-0.5):(0.4-0.5):1, based on lithium, manganese, iron and phosphorus.

[0049] In a preferred embodiment of the present invention, in step (2), the mass of the carbon source in the mixed raw materials is 6% of the total mass of the lithium source, mixed manganese source, iron source and phosphorus source;

[0050] In a preferred embodiment of the present invention, in step (2), the amount of pure water added is adjusted according to the total mass of the mixed raw materials so that the solid content of the resulting slurry is 30-40%.

[0051] In a preferred embodiment of the present invention, in step (2), the solid content of the slurry is 35%;

[0052] In a preferred embodiment of the present invention, in step (2), the ultrasonic treatment power is 35-40Hz, the temperature is 25-30℃, and the time is 1-2h;

[0053] In a preferred embodiment of the present invention, in step (2), the lithium source is any one or two or more of lithium carbonate, lithium hydroxide, and lithium phosphate; the iron source is any one or two or more of ferric phosphate, ferrous oxalate, and ferrous sulfate; and the phosphorus source is any one or two or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ferric phosphate, and phosphoric acid.

[0054] In a preferred embodiment of the present invention, in step (2), the carbon source is polyvinyl alcohol and polyethylene glycol; the mass ratio of polyvinyl alcohol and polyethylene glycol is 1:1.

[0055] In a preferred embodiment of the present invention, in step (3), a sand mill is used for sand milling; the rotation speed during sand milling is 800-900 r / min, and the time is 4-6 h; the D50 of the slurry after sand milling is 200 nm.

[0056] In a preferred embodiment of the present invention, in step (4), the discharge temperature during spray drying is 95-110°C;

[0057] In a preferred embodiment of the present invention, in step (5), calcination is performed in a graphite sagger under an inert atmosphere; the calcination temperature is 660-720℃ and the holding time is 6-10h.

[0058] In a preferred embodiment of the present invention, in step (5), the calcination temperature is 680°C and the holding time is 9 hours.

[0059] This invention provides a lithium manganese iron phosphate cathode material, which is prepared using the method described herein.

[0060] The present invention provides a lithium-ion battery comprising the aforementioned lithium manganese iron phosphate cathode material.

[0061] This invention provides an application of the lithium manganese iron phosphate cathode material in the preparation of lithium-ion batteries.

[0062] The following detailed description, through specific embodiments, illustrates the present invention of a lithium iron phosphate cathode material prepared using a mixed manganese source, its preparation method, and its application.

[0063] Example 1

[0064] This embodiment relates to a method for preparing lithium iron phosphate cathode material using a mixed manganese source, including the following steps:

[0065] (1) Manganese dioxide and manganese acetate with a molar ratio of 3:1 were placed in a high-speed mixer and processed in three stages: first at 700 r / min for 30 min, then at 900 r / min for 30 min, and finally at 1100 r / min for 30 min; after mixing evenly, a mixed manganese source was obtained for later use.

[0066] (2) The mixed raw materials: lithium hydroxide, iron phosphate, mixed manganese source, diammonium hydrogen phosphate, and carbon source (the mass ratio of polyvinyl alcohol and polyethylene glycol is 1:1) are ultrasonically dispersed in pure water to obtain a slurry for later use.

[0067] The molar ratio of lithium to manganese to iron to phosphorus in the mixed raw materials is 1.03:0.6:0.4:1, calculated by lithium, manganese, iron, and phosphorus.

[0068] The mass of the carbon source in the mixed raw materials is 6% of the total mass of the lithium source, mixed manganese source, iron source, and phosphorus source;

[0069] The ultrasonic treatment was performed at a power of 35 Hz, a temperature of 25 ℃, and a time of 1 h; the solid content of the resulting slurry was 35%.

[0070] (3) The slurry is subjected to sand milling treatment;

[0071] The milling speed was 800 r / min and the time was 4 h; the D50 of the slurry after milling was 200 nm.

[0072] (4) Spray dry the slurry after sand milling to obtain precursor powder;

[0073] The discharge temperature during spray drying is 110℃ to reduce the moisture content.

[0074] (5) The dried precursor powder was placed into a graphite crucible and kept at 680°C for 9 hours under an inert atmosphere to obtain lithium manganese iron phosphate cathode material.

[0075] Example 2

[0076] This embodiment provides a method for preparing lithium manganese iron phosphate cathode material. The difference from Embodiment 1 is that the molar ratio of manganese dioxide to manganese acetate in step (1) of this embodiment is 2:1, and the other steps and parameters are the same as in Embodiment 1.

[0077] Example 3

[0078] This embodiment provides a method for preparing lithium manganese iron phosphate cathode material. The difference from Embodiment 1 is that the molar ratio of manganese dioxide to manganese acetate in step (1) of this embodiment is 1:1, and the other steps and parameters are the same as in Embodiment 1.

[0079] Example 4

[0080] This embodiment provides a method for preparing lithium manganese iron phosphate cathode material. The difference from Embodiment 1 is that the molar ratio of manganese dioxide to manganese acetate in step (1) of this embodiment is 1:2, and the other steps and parameters are the same as in Embodiment 1.

[0081] Example 5

[0082] This embodiment provides a method for preparing lithium manganese iron phosphate cathode material. The difference from Embodiment 1 is that the molar ratio of manganese dioxide to manganese acetate in step (1) of this embodiment is 1:3, and the other steps and parameters are the same as in Embodiment 1.

[0083] Example 6

[0084] This embodiment provides a method for preparing lithium manganese iron phosphate cathode material. The difference between this embodiment and embodiment 4 is that the molar ratio of lithium:manganese:iron:phosphorus in step (2) is 1.03:0.5:0.5:1. Other steps and parameters are the same as in embodiment 4.

[0085] Example 7

[0086] This embodiment provides a method for preparing lithium manganese iron phosphate cathode material. The difference from embodiment 4 is that the solid content of the slurry in step (2) of this embodiment is 30%, while the other steps and parameters are the same as those in embodiment 4.

[0087] Example 8

[0088] This embodiment provides a method for preparing lithium manganese iron phosphate cathode material. The difference from embodiment 4 is that the solid content of the slurry in step (2) of this embodiment is 40%, while the other steps and parameters are the same as those in embodiment 4.

[0089] Example 9

[0090] This embodiment provides a method for preparing lithium manganese iron phosphate cathode material. The difference between this embodiment and embodiment 4 is that polyvinyl alcohol is the only C source in step (2) of this embodiment, while the other steps and parameters are the same as in embodiment 4.

[0091] Example 10

[0092] This embodiment provides a method for preparing lithium manganese iron phosphate cathode material. The difference between this embodiment and embodiment 4 is that polyethylene glycol is the only C source in step (2), while the other steps and parameters are the same as in embodiment 4.

[0093] Example 11

[0094] This embodiment provides a method for preparing lithium manganese iron phosphate cathode material. The difference between this embodiment and embodiment 4 is that the calcination condition in step (5) is 660℃ for 9 hours, while the other steps and parameters are the same as in embodiment 4.

[0095] Example 12

[0096] This embodiment provides a method for preparing lithium manganese iron phosphate cathode material. The difference from embodiment 4 is that the calcination condition in step (5) of this embodiment is 700℃ for 9 hours, and the other steps and parameters are the same as in embodiment 4.

[0097] Comparative Example 1

[0098] This comparative example provides a method for preparing lithium manganese iron phosphate cathode material. The difference between this example and Example 4 is that manganese dioxide is used as the only manganese source in step (1) of this example, while the other steps and parameters are the same as in Example 4.

[0099] Comparative Example 2

[0100] This comparative example provides a method for preparing lithium manganese iron phosphate cathode material. The difference between this example and Example 4 is that manganese acetate is used as the only manganese source in step (1) of this example, while the other steps and parameters are the same as in Example 4.

[0101] Application examples

[0102] (1) Preparation of the battery to be tested

[0103] Using the lithium manganese iron phosphate cathode materials prepared in the examples and comparative examples as raw materials, they were mixed with conductive graphite and polyvinylidene fluoride in N-methylpyrrolidone (NMP) at a mass ratio of 8:1:1 to form the cathode sheet. The battery was assembled in the following order: negative electrode shell, lithium sheet, electrolyte, separator, electrolyte, cathode sheet, and cathode shell, and then sealed in a manual button battery sealing machine.

[0104] (2) Electrochemical performance testing

[0105] The constant current charge-discharge test was used to evaluate the cycle stability of the sample under different current densities. The test was conducted using the Blue Electric test system. Under the test conditions of 2.5V-4.2V, the electrochemical performance at 0.1C, 0.2C, 0.5C and 1C was measured respectively. The discharge specific capacity data are shown in Table 1.

[0106] The charge-discharge curves of the batteries assembled from the materials obtained in Example 4, Comparative Example 1, and Comparative Example 2 under 0.1C conditions are shown below. Figure 1 As shown.

[0107] Based on the discharge specific capacity of 0.1C-1C, the rate performance data for 0.2C / 0.1C, 0.5C / 0.1C, and 1C / 0.1C were calculated and are shown in Table 1.

[0108] Under the test conditions of 1C charge / discharge rate, the coin cell was subjected to multiple charge tests to determine the cycle performance at 1C. The capacity retention rate at 1C / 20 cycles is shown in Table 1.

[0109] The 1C cycle results of the battery assembled from the materials obtained in Example 4 are as follows: Figure 2 As shown.

[0110] (3) Specific surface area measurement

[0111] The specific surface area of ​​the lithium manganese iron phosphate cathode materials obtained in the examples and comparative examples was determined according to the standard GB / T 19587-2017 Gas Adsorption BET Method for Determination of Specific Surface Area of ​​Solid Materials. The results are shown in Table 1.

[0112] (4) SEM analysis

[0113] Figure 3 This is a SEM image of the lithium manganese iron phosphate cathode material prepared in Example 4 of this invention. As shown in the image, the lithium manganese iron phosphate cathode material prepared in Example 4 has a spherical morphology formed by primary particle stacking. The milling process can change the primary particle size of the material, which is approximately 15 μm in size. The particle size has a significant impact on the Li... + This has a significant impact on transmission.

[0114] Table 1. Performance test results of lithium manganese iron phosphate cathode materials prepared in different embodiments and comparative examples.

[0115]

[0116] As can be seen from the comparison of Examples 1-5, adjusting the molar ratio of manganese dioxide to manganese acetate can not only change the specific capacity of the material, but also control the specific surface area of ​​the finished product, which facilitates the subsequent preparation of battery cells and reduces the difficulty of the preparation process.

[0117] According to the comparison of Examples 4, 7 and 8, adjusting the solid content of the slurry will affect the reaction rate of the precursor materials in the slurry. Moreover, when the solid content is 40%, the slurry will expand in volume as the particle size becomes finer. The slurry becomes more viscous in the later stage of sand milling, which is not conducive to long-term cyclic sand milling. When spraying in the later stage, if the slurry is too thick, it is easy to clump and dry on the nozzle when passing through the atomizing nozzle, clogging the nozzle and causing obvious particles to appear after spraying.

[0118] According to the comparison of Examples 4, 9 and 10, adjusting the type of carbon source has a significant impact on both capacity and specific surface area, because different carbon sources will leave different residues on the surface of the material when calcined. After using a mixed carbon source, the present invention can not only retain a smaller specific surface area, but also achieve a material capacity of 154.6 mAh / g.

[0119] A comparison of Examples 4, 11, and 12 shows that adjusting the calcination temperature affects the crystallinity of the finished product, thus impacting the material's capacity and cycle life. Excessively high temperatures may lead to larger grains and a smaller specific surface area, hindering the extraction and insertion of lithium ions. Furthermore, it may generate oxygen-deficient compounds, promoting secondary recrystallization and negatively affecting the material's electrochemical performance. Therefore, selecting an appropriate calcination temperature is crucial for obtaining lithium manganese iron phosphate with excellent electrochemical performance.

[0120] A comparison of Example 4 and Comparative Examples 1-2 shows that if the mixed manganese source is replaced with a single manganese source, the calcination of manganese dioxide is not conducive to redox reactions, resulting in a low capacity of the finished product. However, during the calcination of manganese acetate, the decomposition of acetate ions generates gas, forming micropores on the material surface, which is beneficial for Li... +While traditional methods exist for transporting materials, manganese acetate, due to its low hardness, easily forms fine powder, resulting in poor particle size distribution. This invention, however, uses a mixture of manganese acetate and manganese acetate followed by sand milling. Because of the difference in hardness, this results in a more reasonable particle size distribution and better capacity performance.

[0121] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing lithium manganese iron phosphate cathode material using a mixed manganese source, characterized in that, Includes the following steps: (1) Mix manganese dioxide and manganese acetate evenly to obtain a mixed manganese source for later use; (2) The mixed raw materials: lithium source, mixed manganese source, iron source, phosphorus source and carbon source are dispersed in pure water by ultrasonic treatment to obtain a slurry for later use; (3) The slurry is subjected to sand milling treatment; (4) Spray dry the slurry after sand milling to obtain precursor powder; (5) The precursor powder is calcined to obtain the product; In step (1), the molar ratio of manganese dioxide to manganese acetate is (3-1):(1-3); In step (2), the carbon source is polyvinyl alcohol and polyethylene glycol; the mass ratio of polyvinyl alcohol and polyethylene glycol is 1:1; in step (2), the solid content of the slurry is 30-40%; In step (5), the calcination temperature is 660-720℃ and the holding time is 6-10h.

2. The preparation method according to claim 1, characterized in that, In step (1), a three-stage processing process is adopted during mixing: first, the mixture is processed at 600-800 r / min for 30-40 min, then at 800-1000 r / min for 30-40 min, and finally at 1000-1200 r / min for 30-40 min.

3. The preparation method according to claim 1, characterized in that, In step (2), the molar ratio of lithium:manganese:iron:phosphorus in the mixed raw materials is 1.03:(0.6-0.5):(0.4-0.5):1, based on lithium, manganese, iron and phosphorus. In step (2), the mass of the carbon source in the mixed raw materials is 6% of the total mass of the lithium source, mixed manganese source, iron source and phosphorus source.

4. The preparation method according to claim 1, characterized in that, In step (2), the lithium source is any one or two or more of lithium carbonate, lithium hydroxide, and lithium phosphate. The iron source is any one or two or more of ferric phosphate, ferrous oxalate, and ferrous sulfate. The phosphorus source is any one or two or more of the following: ammonium dihydrogen phosphate, diammonium hydrogen phosphate, iron phosphate, and phosphoric acid.

5. The preparation method according to claim 1, characterized in that, In step (3), the rotation speed during sand milling is 800-900 r / min and the time is 4-6 h; the D50 of the slurry after sand milling is 200 nm.

6. The preparation method according to claim 1, characterized in that, In step (4), the discharge temperature during spray drying is 95-110℃.

7. A lithium manganese iron phosphate cathode material, characterized in that, The lithium manganese iron phosphate cathode material is prepared using the preparation method described in any one of claims 1-6.

8. A lithium-ion battery, characterized in that, Including the lithium manganese iron phosphate cathode material as described in claim 7.

9. The application of the lithium manganese iron phosphate cathode material as described in claim 7 in the preparation of lithium-ion batteries.

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