Preparation method of manganese iron ammonium phosphate precursor and lithium manganese iron phosphate

Abstract

The application provides a preparation method of a manganese iron ammonium phosphate precursor and a lithium manganese iron phosphate. The preparation method of the precursor comprises the following steps: preparing an ammonia water solution; preparing a mixed metal salt solution containing manganese and iron; preparing a phosphorus source solution; adding a small amount of the ammonia water solution as a reaction bottom solution, adding the remaining ammonia water solution, the mixed metal salt solution and the phosphorus source solution into a reaction kettle in parallel flow to perform a reaction, maintaining the pH at 5-5.5, then increasing the reaction temperature to 90 DEG C, aging, and obtaining a manganese iron ammonium phosphate monohydrate precipitate; and then performing solid-liquid separation, washing and drying to obtain a manganese iron ammonium phosphate precursor powder. The ammonia water solution is used as the bottom solution, the yield of the manganese iron ammonium phosphate precursor is improved, a secondary phosphorus source is added in an acidic environment, the proportion of P elements in the precursor is increased, the iron-phosphorus ratio is closer to the theoretical value, and the yield is higher. The process is simple, the yield is high, the method is more suitable for large-scale production, and has great market prospects.

Description

Technical Field

[0001] This invention belongs to the field of cathode material synthesis technology for lithium-ion batteries, and particularly relates to a method for preparing a precursor of manganese iron ammonium phosphate and lithium manganese iron phosphate. Background Technology

[0002] Lithium iron phosphate (LFP) batteries possess an ordered and regular olivine structure, in which lithium ions exhibit one-dimensional mobility. LFP technology has a long history of development and is relatively mature. Its core advantages include low cost, environmental friendliness, high safety performance, and good structural stability and cycle performance. The superior structural stability ensures that the battery is less prone to collapse during use, significantly improving battery safety. However, LFP energy density is nearing its limit, resulting in relatively low battery power. Furthermore, LFP exhibits poor low-temperature performance, making it impractical for use in cold regions.

[0003] Lithium iron manganese phosphate (LMP) is a blend of lithium manganese phosphate (LMP) and lithium iron phosphate (LFP). Both LMP and LFP share a uniform and well-ordered olivine structure. Furthermore, LMP and LFP offer the same low cost, high safety, and high thermal stability, effectively combining the advantages of both while maintaining the discharge time of LFP. LMP's high voltage platform contributes to its high energy density. In short, LMP combines the advantages of both LFP and LMP while compensating for LFP's lower energy density. Currently, LMP cathode materials have been successfully applied to two-wheeled vehicles, expanding into the mid-to-low-end electric vehicle market. LMP batteries are expected to penetrate even more application scenarios in the future.

[0004] The production processes of lithium iron manganese phosphate include high-temperature solid-state methods, co-precipitation methods, sol-gel methods, hydrothermal / solvothermal methods, and spray drying methods. Unlike the lithium iron phosphate industry, which has a mature iron phosphate precursor, lithium iron manganese phosphate lacks a standard precursor. Therefore, precursor synthesis should be the main direction for the future synthesis of lithium iron manganese phosphate materials. The co-precipitation method is often used to first synthesize the manganese iron precursor, and then add lithium and phosphorus sources, followed by ball milling and calcination to obtain the finished product. Compared with the traditional solid-state method, the synthesis process is simpler, the materials are more uniformly mixed (Mn and Fe particles are evenly distributed), which is very important for improving energy density. Furthermore, this method makes product quality easier to control, is simple, and can be easily mass-produced.

[0005] Existing precipitation methods for synthesizing iron manganese ammonium phosphate precursors suffer from low yields and significant deviations in the molar ratio of Fe to P from theoretical values. In lithium iron manganese phosphate, a large discrepancy between the iron-phosphorus ratio and the theoretical value can affect the volumetric energy density of the battery, thereby impacting its driving range. Summary of the Invention

[0006] To address the technical problems of low yield and large deviation from the theoretical values ​​of the molar ratio of Fe and P elements in the existing synthesis technology of lithium manganese iron phosphate precursor, this invention provides a method for preparing a precursor of ammonium manganese iron phosphate and lithium manganese iron phosphate.

[0007] This invention discloses a method for preparing a precursor of ferric ammonium manganese phosphate, the method comprising the following steps:

[0008] S1. Prepare an ammonia solution with a pH value of 10;

[0009] S2. Prepare a mixed salt solution containing manganese and iron;

[0010] S3. Prepare the phosphorus source solution;

[0011] S4. Using a small amount of ammonia solution as the reaction base liquid, while stirring, add the remaining ammonia solution, metal mixed salt solution and phosphorus source solution to the reactor in parallel to carry out the reaction. Maintain the pH at 5-5.5 until the metal salt solution and ammonium dihydrogen phosphate solution are finished feeding. Then, continue to adjust the pH to 5.5 with alkaline solution. Then raise the reaction temperature to 90℃ and age it to obtain manganese iron ammonium monohydrate precipitate.

[0012] S5. The manganese iron ammonium phosphate monohydrate precipitate obtained in step S4 is subjected to solid-liquid separation, washing, and drying to obtain manganese iron ammonium phosphate precursor powder.

[0013] Furthermore, the concentration of the metal mixed salt solution in step S2 is 1–3 mol / L.

[0014] Furthermore, in step S2, the iron source is at least one of ferrous sulfate heptahydrate, ferric nitrate, and ferrous chloride.

[0015] Furthermore, in step S2, the manganese source is at least one of manganese sulfate monohydrate, manganese nitrate, manganese acetate tetrahydrate, and manganese chloride tetrahydrate.

[0016] Furthermore, in step S3, the concentration of the phosphorus source solution is 1-2 mol / L; the phosphorus source is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, trisodium phosphate, tripotassium phosphate, and phosphoric acid.

[0017] Furthermore, the reaction conditions for step S4 are: temperature of 50-90℃ and stirring speed of 300-900 rpm.

[0018] Furthermore, in step S4, a second phosphorus supplement is performed before aging. The molar ratio of phosphorus to metal (Mn+Fe) in the second phosphorus supplement is 0.05-0.15, and the phosphorus source for the second phosphorus supplement is phosphoric acid.

[0019] Furthermore, in step S5, the drying temperature is 80–180°C.

[0020] The present invention also provides a lithium manganese iron phosphate, which is prepared by mixing the above-mentioned iron ammonium manganese phosphate precursor with a lithium source and a carbon source, and sintering it at 600°C to 900°C for 6 to 20 hours under a nitrogen atmosphere.

[0021] The working principle and advantages of this invention are as follows:

[0022] In this invention, an ammonia solution is initially used as the base solution and the pH is adjusted to 10 to ensure sufficient ammonium ions at the start of the reaction. A mixture of metal salt solution, phosphorus source solution, and ammonia solution is prepared, and the pH is adjusted to 5-6.5 using an alkaline solution. After the reaction begins, NH4+ is introduced. + After complete dissociation, it complexes with metal ions, and then with OH-. - The formation of a precipitate promotes the forward reaction. Furthermore, adding a secondary phosphorus source under acidic conditions to adjust the pH dissolves the metal ions precipitated as hydroxides, allowing them to dissolve as the target product. This increases the proportion of phosphorus in the precursor, resulting in an iron-phosphorus ratio closer to the theoretical value. The secondary phosphorus supplementation should be controlled so that the molar ratio of phosphorus to metal (Mn+Fe) is 0.05-0.15. Within this range, the iron-phosphorus ratio and yield are both advantageous, and the product quality can be adjusted. Below 0.05, the hydroxide precipitate cannot be completely dissolved, resulting in excessive impurities in the product. Above 0.15, the effect on yield and iron-phosphorus ratio is minimal, leading to phosphorus source waste. A slight excess of the primary phosphorus source is used because the pH is high during the reaction. Excess phosphorus source can shift the equilibrium, forming more manganese iron ammonium phosphate nuclei, providing more growth sites for particles in subsequent aging steps. Once aging begins and particles have already grown, adding too much phosphorus source will prevent it from being replenished and will cause uneven particle growth, affecting the final product quality.

[0023] Meanwhile, this invention has advantages such as strong operability in production and high production capacity, making it suitable for large-scale industrial production. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the preparation process of the manganese iron ammonium phosphate precursor of the present invention.

[0025] Figure 2 SEM image of the manganese iron ammonium phosphate precursor prepared in Example 1 of this invention;

[0026] Figure 3 SEM image of the manganese iron ammonium phosphate precursor prepared in Example 1 of this invention;

[0027] Figure 4 SEM image of the manganese iron ammonium phosphate precursor prepared in Example 1 of this invention;

[0028] Figure 5The XRD pattern of the manganese iron ammonium phosphate precursor prepared in Example 1 of this invention; Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0030] Example 1

[0031] A method for preparing a precursor of manganese iron ammonium phosphate, the method comprising the following steps:

[0032] S1. Prepare an ammonia solution with a pH value of 10;

[0033] S2. Prepare a mixed metal salt solution containing manganese and iron: Dissolve 36.2g of ferrous sulfate heptahydrate solid (purity 99.5%) and 33.0g of manganese sulfate monohydrate solid (purity 99.5%) in pure water to obtain 325mL of mixed metal salt solution with a concentration of 1mol / L.

[0034] S3. Prepare phosphorus source solution: Dissolve 39.84g of solid ammonium dihydrogen phosphate (98% purity) in pure water to obtain 346.4mL of ammonium dihydrogen phosphate aqueous solution with a concentration of 1mol / L.

[0035] S4. Using 0.5 mL of ammonia solution as the reaction base, while stirring, add the remaining ammonia solution, mixed metal salt solution, and phosphorus source solution to the reactor in parallel flow for reaction. The conditions are: temperature 50℃, stirring speed 900 rpm, and pH maintained at 5-5.5 until the metal salt solution and ammonium dihydrogen phosphate solution are fed in simultaneously. Then, continue to adjust the pH to 5.5 with alkaline solution, and then raise the reaction temperature to 90℃ and age for 4 hours to obtain manganese iron ammonium monohydrate precipitate.

[0036] S5. The manganese iron ammonium phosphate monohydrate precipitate prepared in step S4 is subjected to solid-liquid separation, washing, and drying at 80°C for 12 hours to obtain manganese iron ammonium phosphate precursor powder.

[0037] A lithium manganese iron phosphate, wherein the lithium manganese iron phosphate is prepared by mixing the above-mentioned iron manganese ammonium phosphate precursor with a lithium source and a carbon source, and sintering it at 600°C for 20 hours under a nitrogen atmosphere.

[0038] Example 2

[0039] A method for preparing a precursor of manganese iron ammonium phosphate, the method comprising the following steps:

[0040] S1. Prepare an ammonia solution with a pH value of 10;

[0041] S2. Prepare a mixed metal salt solution containing manganese and iron: Dissolve 31.54g of ferric nitrate and 17.199g of manganese nitrate solid in pure water to obtain 125mL of mixed metal salt solution with a concentration of 1.5mol / L.

[0042] S3. Prepare phosphorus source solution: Dissolve 39.84g of diammonium hydrogen phosphate solid (purity 98%) in pure water to obtain 201mL of diammonium hydrogen phosphate aqueous solution with a concentration of 1.5mol / L.

[0043] S4. Using 1 mL of ammonia solution as the reaction base, while stirring, add the remaining ammonia solution, metal mixed salt solution, and phosphorus source solution to the reactor in parallel flow for reaction. The conditions are: temperature 90℃, stirring speed 300 rpm, and pH maintained at 5-5.5. After the metal salt solution and diammonium hydrogen phosphate solution are fed in simultaneously, continue to adjust the pH to 5.5 with alkaline solution for secondary phosphoric acid supplementation. Add 3.24 g of concentrated phosphoric acid (85% concentration). The amount of phosphoric acid added is such that the molar ratio of P element to metal element (Mn+Fe) is 0.15. Aging for 4 h yields manganese iron ammonium phosphate monohydrate precipitate.

[0044] S5. The manganese iron ammonium phosphate monohydrate precipitate prepared in step S4 is subjected to solid-liquid separation, washing, and drying at 180°C for 8 hours to obtain manganese iron ammonium phosphate precursor powder.

[0045] A lithium manganese iron phosphate, wherein the lithium manganese iron phosphate is prepared by mixing the above-mentioned iron manganese ammonium phosphate precursor with a lithium source and a carbon source, and sintering it at 900°C for 6 hours under a nitrogen atmosphere.

[0046] Example 3

[0047] A method for preparing a precursor of manganese iron ammonium phosphate, the method comprising the following steps:

[0048] S1. Prepare an ammonia solution with a pH value of 10;

[0049] S2. Prepare a mixed metal salt solution containing manganese and iron: Dissolve 16.5282g of ferrous chloride and 33.84g of manganese acetate tetrahydrate solid in pure water to obtain 134mL of mixed metal salt solution with a concentration of 2mol / L.

[0050] S3. Prepare phosphorus source solution: Dissolve 22.71g of trisodium phosphate solid (purity 98%) in pure water to obtain 68mL of trisodium phosphate aqueous solution with a concentration of 2mol / L.

[0051] S4. Using 0.3 mL of ammonia solution as the reaction base, while stirring, the remaining ammonia solution, metal mixed salt solution, and phosphorus source solution are added to the reactor in parallel flow for reaction. The conditions are: temperature 70℃, stirring speed 600 rpm, and pH maintained at 5-5.5 until the metal salt solution and trisodium phosphate solution are fed in simultaneously. Then, the pH is adjusted to 5.5 using an alkaline solution. The reaction temperature is then raised to 90℃ for a second phosphorus supplementation. 3.09 g of concentrated phosphoric acid (85% concentration) is added, with the amount of phosphoric acid added being 0.1 molar ratio of P to metal (Mn+Fe). After aging for 4 h, manganese iron ammonium phosphate monohydrate precipitate is obtained.

[0052] S5. The manganese ferric ammonium phosphate monohydrate precipitate obtained in step S4 is subjected to solid-liquid separation, washing, and drying at 130℃ for 10 h to obtain manganese ferric ammonium phosphate precursor powder.

[0053] A lithium manganese iron phosphate, wherein the lithium manganese iron phosphate is prepared by mixing the above-mentioned iron manganese ammonium phosphate precursor with a lithium source and a carbon source, and sintering it at 750°C for 13 hours under a nitrogen atmosphere.

[0054] Example 4

[0055] A method for preparing a precursor of manganese iron ammonium phosphate, the method comprising the following steps:

[0056] S1. Prepare an ammonia solution with a pH value of 10;

[0057] S2. Prepare a mixed metal salt solution containing manganese and iron: Dissolve 36.2g of ferrous sulfate heptahydrate solid (purity 99.5%) and 24.61g of manganese chloride tetrahydrate solid in pure water to obtain 101.7mL of mixed metal salt solution with a concentration of 2.5mol / L.

[0058] S3. Prepare phosphorus source solution: Dissolve 29.411g of tripotassium phosphate solid (purity 98%) in pure water to obtain 75.4mL of tripotassium phosphate aqueous solution with a concentration of 1.8mol / L.

[0059] S4. Using 1.5 mL of ammonia solution as the reaction base, while stirring, the remaining ammonia solution, metal mixed salt solution, and phosphorus source solution are added to the reactor in parallel flow for reaction. The conditions are: temperature 60℃, stirring speed 800 rpm, pH maintained at 5-6.5. After the metal salt solution and tripotassium phosphate solution are fed in simultaneously, the pH is adjusted to 5.5 with alkaline solution. Then the reaction temperature is raised to 90℃ for secondary phosphorus supplementation. 1.46 g of concentrated phosphoric acid (85% concentration) is added. The amount of phosphoric acid added is such that the molar ratio of P to metal (Mn+Fe) is 0.05. After aging for 4 h, manganese iron ammonium phosphate monohydrate precipitate is obtained.

[0060] S5. The manganese ferric ammonium phosphate monohydrate precipitate obtained in step S4 is subjected to solid-liquid separation, washing, and drying at 100°C for 15 hours to obtain manganese ferric ammonium phosphate precursor powder.

[0061] A lithium manganese iron phosphate, wherein the lithium manganese iron phosphate is prepared by mixing the above-mentioned iron ammonium manganese phosphate precursor with a lithium source and a carbon source, and sintering it at 700°C for 15 hours under a nitrogen atmosphere.

[0062] Example 5

[0063] A method for preparing a precursor of manganese iron ammonium phosphate, the method comprising the following steps:

[0064] S1. Prepare an ammonia solution with a pH value of 10;

[0065] S2. Prepare a mixed metal salt solution containing manganese and iron: Dissolve 36.2g of ferrous sulfate heptahydrate solid (purity 99.5%) and 29.5356g of manganese sulfate monohydrate solid in pure water to obtain 101.5mL of mixed metal salt solution with a concentration of 3mol / L.

[0066] S3. Prepare phosphorus source solution: Dissolve 13.577g of concentrated phosphoric acid (concentration of 85%) in pure water to obtain 98.1mL of phosphoric acid aqueous solution with a concentration of 1.2mol / L.

[0067] S4. Using 0.8 mL of ammonia solution as the reaction base, while stirring, the remaining ammonia solution, metal mixed salt solution, and phosphorus source solution are added to the reactor in parallel flow for reaction. The conditions are: temperature 80℃, stirring speed 500 rpm, and pH maintained at 5-5.5 until the metal salt solution and phosphoric acid solution are fed in simultaneously. Then, the pH is adjusted to 5.5 using an alkaline solution. The reaction temperature is then raised to 90℃ for a second phosphorus supplementation. 4.21 g of concentrated phosphoric acid (85% concentration) is added, with the amount of phosphoric acid added being 0.12 molar ratio of P to metal (Mn+Fe). After aging for 4 h, manganese iron ammonium phosphate monohydrate precipitate is obtained.

[0068] S5. The manganese iron ammonium phosphate monohydrate precipitate prepared in step S4 is subjected to solid-liquid separation, washing, and drying at 150°C for 10 hours to obtain manganese iron ammonium phosphate precursor powder.

[0069] A lithium manganese iron phosphate, wherein the lithium manganese iron phosphate is prepared by mixing the above-mentioned iron manganese ammonium phosphate precursor with a lithium source and a carbon source, and sintering it at 800°C for 10 hours under a nitrogen atmosphere.

[0070] Comparative Example 1

[0071] A method for preparing a precursor of manganese iron ammonium phosphate, the method comprising the following steps:

[0072] S1. Prepare a mixed metal salt solution containing manganese and iron: Dissolve 36.2g of ferrous sulfate heptahydrate solid (purity 99.5%) and 33.0g of manganese sulfate monohydrate solid (purity 99.5%) in pure water to obtain 325mL of mixed metal salt solution with a concentration of 1mol / L.

[0073] S2. Preparation of phosphorus source solution: Dissolve 39.84g of ammonium dihydrogen phosphate solid (purity 98%) in pure water to obtain 346.4mL of ammonium dihydrogen phosphate aqueous solution with a concentration of 1mol / L.

[0074] S3. Using a mixed metal salt solution as the base liquid, ammonium dihydrogen phosphate and ammonia solution are added simultaneously at different feed rates under stirring. The reaction conditions are: temperature 50℃, stirring speed 900 rpm, pH 5-5.5. After the ammonium dihydrogen phosphate solution is finished feeding, the pH is adjusted to 5.5 with ammonia solution. Then the reaction temperature is raised to 90℃ and aged for 4 hours to obtain manganese iron ammonium monohydrate precipitate.

[0075] S4. The manganese iron ammonium phosphate monohydrate precipitate prepared in step S3 is subjected to solid-liquid separation, washing, and drying at 80°C for 12 hours to obtain manganese iron ammonium phosphate precursor powder.

[0076] A lithium manganese iron phosphate, wherein the lithium manganese iron phosphate is prepared by mixing the above-mentioned iron manganese ammonium phosphate precursor with a lithium source and a carbon source, and sintering it at 600°C for 20 hours under a nitrogen atmosphere.

[0077] Comparative Example 2

[0078] A method for preparing a precursor of manganese iron ammonium phosphate, the method comprising the following steps:

[0079] S1. Prepare a mixed metal salt solution containing manganese and iron: Dissolve 36.2g of ferrous sulfate heptahydrate solid (purity 99.5%) and 33.0g of manganese sulfate monohydrate solid (purity 99.5%) in pure water to obtain 325mL of mixed metal salt solution with a concentration of 1mol / L.

[0080] S2. Preparation of phosphorus source solution: Dissolve 39.84g of ammonium dihydrogen phosphate solid (purity 98%) in pure water to obtain 346.4mL of ammonium dihydrogen phosphate aqueous solution with a concentration of 1mol / L.

[0081] S3. The metal mixed salt solution, phosphorus source solution and ammonia solution are simultaneously added to the reactor in parallel to carry out the reaction. While stirring, the ammonia solution is added to the reactor to maintain the pH. The conditions are: temperature 50℃, stirring speed 900 rpm, and the reaction pH is maintained at 5-5.5. After the metal salt solution and ammonium dihydrogen phosphate solution are fed in simultaneously, the pH is adjusted to 5.5 with alkaline solution. Then the reaction temperature is raised to 90℃ and aged for 4 hours to obtain manganese iron ammonium monohydrate precipitate.

[0082] S4. The manganese iron ammonium phosphate monohydrate precipitate prepared in step S3 is subjected to solid-liquid separation, washing, and drying at 80°C for 12 hours to obtain manganese iron ammonium phosphate precursor powder.

[0083] A lithium manganese iron phosphate, wherein the lithium manganese iron phosphate is prepared by mixing the above-mentioned iron manganese ammonium phosphate precursor with a lithium source and a carbon source, and sintering it at 600°C for 20 hours under a nitrogen atmosphere.

[0084] Comparative Example 1 and Comparative Example 2 are both based on Example 1 with certain adjustments. Comparative Example 1 is the metal salt bottom solution method, and Comparative Example 2 is the bottom solution-free method.

[0085] The yield and Fe:P ratio of the manganese ferric ammonium phosphate precursors prepared in Examples 1-5 were compared with those prepared by conventional methods and primary phosphorus supplementation methods in Comparative Examples 1 and 2. The results are shown in Table 1.

[0086] Table 1 Comparison of the effects of the secondary phosphorus supplementation proposed in this invention and the traditional primary phosphorus source.

[0087] Yield (%) Fe:P (theoretical value 0.4) Example 1 98％ 0.421 Example 2 98.2 0.406 Example 3 98.5 0.404 Example 4 98.3 0.407 Example 5 98.3 0.411 Comparative Example 1 95.6 0.417 Comparative Example 2 94.1 0.487 Existing technology CN117303342 95.2 0.45

[0088] The test data in Table 1 show that, under the initial conditions of this invention, ammonia solution was used as the base solution and the pH was adjusted to 10 to ensure sufficient ammonium ions at the beginning of the reaction. A mixture of metal salt solution, phosphorus source solution, and ammonia solution was prepared, and the pH was adjusted to 5-5.5 using an alkaline solution. After the reaction started and the solution was introduced, NH4+... + After complete dissociation, it complexes with metal ions, and then with OH-. - The formation of a precipitate promotes the forward reaction; that is, the ammonia solution-based bottom solution method can significantly improve the yield of the manganese iron ammonium phosphate precursor. Furthermore, the addition of a secondary phosphorus source under acidic conditions dissolves the metal ions precipitated in hydroxide form, which are then dissolved as the target product, thereby increasing the proportion of phosphorus in the precursor. This results in an iron-phosphorus ratio closer to the theoretical value and a higher yield. This invention boasts advantages such as a simple process and high yield, making it more suitable for large-scale production and possessing significant market potential.

[0089] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For 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 protection scope of the present invention.

Claims

1. A method for preparing a precursor of manganese iron ammonium phosphate, the method comprising the following steps: S1. Prepare an ammonia solution with a pH value of 10; S2. Prepare a mixed salt solution containing manganese and iron; S3. Prepare the phosphorus source solution; S4. A small amount of ammonia solution is used as the reaction base liquid. The remaining ammonia solution, metal mixed salt solution and phosphorus source solution are added to the reactor in parallel to carry out the reaction. The reaction temperature is 50-90℃, the stirring speed is 300-900rpm, and the pH is maintained at 5-5.

5. After the metal salt solution and ammonium dihydrogen phosphate solution are fed, the pH is adjusted to 5.5 with alkaline solution. Then the reaction temperature is raised to 90℃ and aged to obtain manganese iron ammonium monohydrate precipitate. S5. The manganese iron ammonium phosphate monohydrate precipitate obtained in step S4 is subjected to solid-liquid separation, washing, and drying to obtain manganese iron ammonium phosphate precursor powder. Before aging in step S4, a second phosphorus supplement is performed. The molar ratio of phosphorus to metal (Mn+Fe) in the second phosphorus supplement is 0.05-0.15, and the phosphorus source for the second phosphorus supplement is phosphoric acid.

2. The method for preparing the manganese iron ammonium phosphate precursor according to claim 1, characterized in that, The concentration of the metal mixed salt solution in step S2 is 1–3 mol / L.

3. The method for preparing the manganese iron ammonium phosphate precursor according to claim 1, characterized in that, In step S2, the iron source is at least one of ferrous sulfate heptahydrate, ferric nitrate, and ferrous chloride.

4. The method for preparing the manganese iron ammonium phosphate precursor according to claim 1, characterized in that, In step S2, the manganese source is at least one of manganese sulfate monohydrate, manganese nitrate, manganese acetate tetrahydrate, and manganese chloride tetrahydrate.

5. The method for preparing the manganese iron ammonium phosphate precursor according to claim 1, characterized in that, The concentration of the phosphorus source solution in step S3 is 1~2 mol / L.

6. The method for preparing the manganese iron ammonium phosphate precursor according to claim 1, characterized in that, The drying temperature in step S5 is 80–180°C.

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