Process for the production of ammonium manganese iron phosphate

Abstract

A process for producing ammonium manganese iron phosphate, comprising the following steps: S1: Mixing a metal salt solution and an ammonium dihydrogen phosphate solution with an organic solution to obtain a mixed metal salt liquid and a mixed phosphate liquid, wherein the metal salt solution is a solution of a manganese salt and a ferrous salt, and the organic solution is obtained by dissolving a surfactant in an organic solvent; and S2: Adding the mixed metal salt liquid, the mixed phosphate liquid, and a first ammonia water under an inert atmosphere in parallel to a base solution for reaction, and when a reaction material reaches a target particle size, performing solid-liquid separation to obtain the ammonium manganese iron phosphate, wherein the base solution is a mixed liquid of the phosphate mixed solution and a second ammonia water, the base solution having a pH of 8-9, and the reaction material is controlled to have a pH of 8-9 upon reaction.

Description

TECHNICAL FIELD

[0001] The present invention belongs to the technical field of cathode materials for lithium batteries and, in particular, relates to a production process for ammonium manganese iron phosphate. BACKGROUND

[0002] Compared with ternary batteries, lithium iron phosphate batteries have the advantages of higher safety and lower cost. They have the advantages of good thermal stability, long cycle life, environmental friendliness, and abundant raw material sources. They are currently the most suitable cathode material for lithium-ion batteries and are favored by more and more automobile manufacturers, with their market share increasing. Lithium iron phosphate has a regular olivine structure, which allows lithium iron phosphate to have the advantages of large discharge capacity, low price, non-toxicity, and less environmental pollution. Therefore, extensive research has been conducted on lithium iron phosphate in recent years.

[0003] Despite these advantages, lithium iron phosphate, when used in batteries, has the disadvantages of low electronic conductivity, low lithium ion diffusion coefficient, and low compaction density due to the limitation of its structure, which greatly limits the application of lithium iron phosphate. To expand the application of lithium iron phosphate, manganese-based compounds are currently being incorporated into lithium iron phosphate to form a lithium manganese iron phosphate solid solution. Since the manganese-based compounds have a high electrochemical reaction voltage and good electrolyte compatibility, the lithium manganese iron phosphate solid solution can achieve good electrical capacity and cycling performance.

[0004] At present, there are many synthesis methods for lithium manganese iron phosphate, which are basically similar to the synthesis of lithium iron phosphate, such as the all-solid-phase method in which a phosphorus source, an iron source, a manganese source, a lithium source and other raw materials are directly sintered to obtain lithium manganese iron phosphate, or a method consisting of first synthesizing manganese phosphate as a manganese source and part of the phosphorus source, then mixing the manganese phosphate, an iron source and a lithium source, and sintering the obtained mixture to obtain lithium manganese iron phosphate.The disadvantage is that manganese and iron cannot be evenly mixed at the atomic level, and the produced lithium manganese iron phosphate has an unsatisfactory charge constant voltage level and poor discharge performance. Furthermore, trivalent manganese is prone to disproportionation reactions in solution to produce divalent manganese and tetravalent manganese, resulting in low product purity. Lithium manganese iron phosphate can also be produced by the hydrothermal method, but the cost is high because the amount of lithium used is three times the theoretical amount. In addition, the investment for high-temperature and high-pressure equipment is high, so the overall cost is significantly higher than that of the solid-phase method.

[0005] CN 1 05 655 584 A describes a process for producing ammonium manganese iron phosphate for preparing a lithium battery cathode material, which comprises dissolving MnSO4 and FeSO4 in distilled water to prepare mixed solution A, dissolving ammonia water and sodium hydroxide in distilled water to prepare mixed solution B, dropwise adding mixed solution A and mixed solution B to distilled water having a pH of 10.0-12.0 0 with the aid of ultrasonic cavitation and dispersion at the same time, and reacting for 2-3 hours to obtain iron manganese hydroxide; then, ammonium dihydrogen phosphate is added dropwise to react with stirring, and the resulting product is washed and dried to obtain ammonium manganese iron phosphate.

[0006] WO 2013 / 038516 A1 describes a method for producing a precursor of a cathode active material for lithium secondary batteries, which is a method for producing manganese iron ammonium phosphate, comprising a mixed solution preparation step of preparing a mixed solution of divalent Mn ions, Fe ions, and phosphate ions; and a crystallization step of obtaining a manganese iron ammonium phosphate represented by the general formula NNH4MnFe-PO4HO (where 0 < x < 1) by coprecipitation by adding ammonia to the mixed solution to adjust its pH to a value in the range of 7 to 9.

[0007] CN 1 06 207 164 A describes a manufacturing process for a lithium manganese phosphate composite material, which comprises dissolving a phosphorus-containing compound and a manganese-containing compound in water to form a mixed solution, adding a precipitating agent to the mixed solution, stirring and complete precipitation to form a MnHPO4 hydrate, and calcining the mixture at 550-800 °C for 8-16 hours under a protective gas atmosphere to obtain the lithium manganese iron phosphate composite material.

[0008] CN 1 06 477 545 A describes a process for producing a LiMnPO4 / C composite material with NH4MnPO4 as a precursor, which comprises preparing a divalent manganese starting compound, a phosphorus starting compound, a surfactant and a reducing agent as raw materials into an aqueous mixed solution, reacting the aqueous mixed solution with an ammonia-water solution to produce a flake-shaped NH4MnPO4 precursor and then lithium doping and high-temperature heat treatment to produce the LiMnPO4 / C composite material.

[0009] In addition, lithium manganese iron phosphate typically has a compaction density of 2.1 to 2.2 g / cm 3 and a specific capacity of 135 to 150 mAh / g, which does not meet the requirements of energy battery manufacturers who urgently need higher energy density. SUMMARY

[0010] The present invention aims to solve at least one of the above-mentioned technical problems existing in the prior art. To this end, the present invention provides a process for producing ammonium manganese iron phosphate.

[0011] According to one aspect of the present invention, there is provided a process for producing ammonium manganese iron phosphate comprising the following steps: S1: Mixing a metal salt solution and an ammonium dihydrogen phosphate solution with an organic solution to obtain a mixed metal salt liquid and a mixed phosphate liquid, respectively, wherein the metal salt solution is a solution of a manganese salt and a ferrous salt, and the organic solution is obtained by dissolving a surfactant in an organic solvent; and S2: Adding the mixed metal salt liquid, the mixed phosphate liquid, and a first ammonia water under an inert atmosphere in parallel to a base solution for reaction, and when a reaction material reaches a target particle size, performing solid-liquid separation to obtain the ammonium manganese iron phosphate, wherein the base solution is a mixed solution of the mixed phosphate liquid and a second ammonia water, the base solution has a pH of 8-9, and the reaction material is controlled to have a pH of 8-9 upon reaction.

[0012] In some embodiments of the present invention, in step S1, the iron(II) salt is selected from the group consisting of iron(II) sulfate, iron(II) chloride, and a mixture thereof.

[0013] In some embodiments of the present invention, in step S1, the manganese salt is selected from the group consisting of manganese sulfate, manganese chloride, and a mixture thereof.

[0014] In some embodiments of the present invention, in step S1, the molar ratio of iron element to manganese element in the metal salt solution is 0.25-9:1, the total concentration of metal ions in the metal salt solution is 0.5-1.0 mol / L, and the volume ratio of the metal salt solution to the organic solution in the metal salt solution is 1-5:100.

[0015] In some embodiments of the present invention, in step S1, the concentration of the ammonium dihydrogen phosphate solution is 0.5-1.0 mol / L, and the volume ratio of the ammonium dihydrogen phosphate solution to the organic solution in the mixed phosphate liquid is 1-5:100.

[0016] In some embodiments of the present invention, in step S1, the ratio of the mass of the surfactant to a volume of the organic solvent is 2-8 g: 100 ml.

[0017] In some embodiments of the present invention, the surfactant in step S1 is at least one selected from the group consisting of CTAB, DBS, SDBS, PEG-400, and a mixture thereof.

[0018] In some embodiments of the present invention, in step S1, the organic solvent is prepared by mixing cyclohexane and n-butanol in a volume ratio of 8:2 to 9:1.

[0019] In some embodiments of the present invention, in step S2, the concentration of the first ammonia water is 8.0-12.0 mol / L.

[0020] In some embodiments of the present invention, the reaction in step S2 is carried out at a stirring speed of 200-350 rpm.

[0021] In some embodiments of the present invention, in step S2, the temperature of the reaction is controlled to 20-40°C.

[0022] According to a preferred embodiment of the present invention, the present invention has at least the following advantageous effects. 1. By coprecipitating a mixed metal salt solution of an iron source and a manganese source with a phosphorus source in an organic phase, the present disclosure produces an ammonium manganese iron phosphate with a large particle size and high compaction density. After mixing the ammonium manganese iron phosphate with a lithium source and a carbon source and subsequent sintering, the final product, a cathode material made of lithium manganese iron phosphate, can be produced. The reaction equations are as follows: Co-precipitation reaction: NH4 + + x Fe4 2+ + (1-x)Mn 2+ + PO4 3-→ NH4Fe x Mn (1-x) PO4; Calcination reaction: LiOH + NH4Fe x Mn (1-x) PO4 → NH3 + LiFe x Mn (1-x) PO4 + H2O. 2. In the preparation of the precursor ammonium manganese iron phosphate, the present disclosure utilizes the sparingly soluble nature of ammonium manganese iron phosphate in the organic phase to allow the solution to quickly reach supersaturation and rapidly form crystal nuclei. It also controls the pH of the reaction and uses phosphate as a base solution to provide sufficient phosphate ions. As the nucleus grows, it can slowly grow under the influence of surfactants to form a dense particle structure. With the addition of materials, the particles gradually grow to form a large particle morphology. Due to the slow growth of the particles, the larger the particle size, the denser the structure becomes, allowing the cathode material produced by subsequent sintering to inherit the morphology characteristics of the precursor, thereby improving the compaction density of the cathode material. 3. Ammonium manganese iron phosphate is used as a precursor, where iron is divalent iron, so no further reduction is required during sintering, thus reducing the amount of carbon source used. Furthermore, the ammonium in ammonium manganese iron phosphate is released in the form of ammonia gas, which benefits the formation of a porous channel structure in the cathode material. This porous channel structure promotes the infiltration of the cathode material into the electrolyte and improves the deintercalation efficiency of lithium ions. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention is described below in conjunction with the drawings and examples, in which: Fig. 1 is an SEM photograph of the ammonium manganese iron phosphate prepared in Example 1 of the present invention; and Fig.Figure 2 is an SEM image of the lithium manganese iron phosphate prepared in Example 1. DETAILED DESCRIPTION

[0024] The concept of the present invention and the technical effects resulting from the present invention will be clearly and fully described below in conjunction with examples in order to fully understand the purpose, features and effects of the present invention. Example 1

[0025] In this example, a lithium manganese iron phosphate was prepared. The specific procedure was as follows: A process for producing a large particle size, high compaction density lithium manganese iron phosphate and an ammonium manganese iron phosphate precursor thereof, comprising the following steps: Step 1: A metal salt solution of manganese chloride and ferrous chloride with a total metal ion concentration of 1.0 mol / L was prepared with a molar ratio of iron to manganese of 1:1. Step 2: An ammonium dihydrogen phosphate solution with a concentration of 1.0 mol / L was prepared. Step 3: An organic solvent was prepared using cyclohexane and n-butanol in a volume ratio of 8:1. Step 4: A surfactant was dissolved in an organic solvent in a ratio of 5 g: 100 ml to obtain an organic solution, and the surfactant was CTAB. Step 5: The metal mixed solution and the ammonium dihydrogen phosphate solution were each mixed with the organic solution in a volume ratio of 5 mL: 100 mL to obtain a mixed metal salt liquid and a mixed phosphate liquid. Step 6: The mixed phosphate liquid was added with ammonia water with a concentration of 12.0 mol / L to adjust the pH to 9 and obtain a base solution. Step 7: Under a nitrogen atmosphere, the mixed metal salt liquid, the mixed phosphate liquid, and the ammonia water with a concentration of 12.0 mol / L were added in parallel to a reactor containing the base solution. The temperature in the reactor was set to 20 °C, the pH to 8.5, and the stirring speed to 350 rpm. Step 8: When the D50 value of the material in the reactor was determined to reach 15 µm, the feed was stopped and solid-liquid separation was performed. The resulting material was then washed with deionized water and then with anhydrous ethanol to obtain ammonium manganese iron phosphate. Step 9: The ammonium manganese iron phosphate was pulverized into powder with a particle size of 2-5 µm. Step 10: The powdered ammonium manganese iron phosphate was mixed with lithium hydroxide and glucose in a molar ratio of (Fe+Mn): Li: carbon source of 1: 1.0: 0.3, the resulting mixture was added with deionized water in an amount of 35% of the total mass of ammonium manganese iron phosphate, lithium hydroxide and glucose, mixed well and spray dried. Step 11: Under the protection of an inert gas, the solid obtained after spray drying was calcined at 850 °C for 14 hours and then naturally cooled to room temperature to obtain a finished cathode material of lithium manganese iron phosphate.

[0026] Fig.is an SEM image of the ammonium manganese iron phosphate prepared in this example, and it can be seen from the figure that the precursor particles have a very dense structure. Example 2

[0027] In this example, a lithium manganese iron phosphate was prepared. The specific procedure was as follows: A process for producing a large particle size, high compaction density lithium manganese iron phosphate and a precursor thereof, comprising the following steps: Step 1: A mixed metal salt solution of manganese sulfate and ferrous sulfate with a total metal ion concentration of 0.5 mol / L was prepared in a molar ratio of iron to manganese of 1:1. Step 2: An ammonium dihydrogen phosphate solution with a concentration of 0.5 mol / L was prepared. Step 3: An organic solvent was prepared using cyclohexane and n-butanol in a volume ratio of 8:1. Step 4: A surfactant was dissolved in an organic solvent in a ratio of surfactant to organic solvent of 2 g: 100 ml to obtain an organic solution, and the surfactant was SDBS. Step 5: The metal salt solution and the ammonium dihydrogen phosphate solution were each mixed with the organic solution in a volume ratio of 1 mL: 100 mL to obtain a mixed metal salt liquid and a mixed phosphate liquid. Step 6: The mixed phosphate liquid was added with ammonia water with a concentration of 8.0 mol / L to adjust the pH to 8.5 and obtain a base solution. Step 7: Under a nitrogen atmosphere, the mixed metal salt liquid, the mixed phosphate liquid, and the ammonia water with a concentration of 8.0 mol / L were added in parallel to a reactor containing the base solution. The temperature in the reactor was set to 30 °C, the pH to 8.0, and the stirring speed to 200 rpm. Step 8: When the D50 value of the material in the reactor was determined to reach 5 µm, the feed was stopped and solid-liquid separation was performed. The resulting material was then washed with deionized water and then with anhydrous ethanol to obtain ammonium manganese iron phosphate. Step 9: The ammonium manganese iron phosphate was pulverized into powder with a particle size of 2-5 µm. Step 10: The powdered ammonium manganese iron phosphate was mixed with lithium carbonate and sucrose in a molar ratio of (Fe+Mn): Li: carbon source of 1: 1.0: 0.3, the resulting mixture was added with deionized water in an amount of 20% of the total mass of ammonium manganese iron phosphate, lithium carbonate and sucrose, mixed well and spray dried. Step 11: Under the protection of an inert gas, the solid obtained after spray drying was calcined at 600 °C for 20 hours and then naturally cooled to room temperature to obtain a finished cathode material of lithium manganese iron phosphate. Example 3

[0028] In this example, a lithium manganese iron phosphate was prepared. The specific procedure was as follows: A process for producing a large particle size, high compaction density lithium manganese iron phosphate and a precursor thereof, comprising the following steps: Step 1: A metal salt solution of manganese chloride and iron(II) chloride with a total metal ion concentration of 0.8 mol / L was prepared in a molar ratio of iron to manganese of 1:1. Step 2: An ammonium dihydrogen phosphate solution with a concentration of 0.8 mol / L was prepared. Step 3: An organic solvent was prepared using cyclohexane and n-butanol in a volume ratio of 8:1. Step 4: A surfactant was dissolved in an organic solvent in a ratio of 5 g: 100 ml to obtain an organic solution, and the surfactant was PEG-400. Step 5: The metal salt solution and the ammonium dihydrogen phosphate solution were each mixed with the organic solution in a volume ratio of 2.5 mL: 100 mL to obtain a mixed metal salt liquid and a mixed phosphate liquid. Step 6: The mixed phosphate solution was added with ammonia water with a concentration of 10.0 mol / L to adjust the pH to 8.0 and obtain a base solution. Step 7: Under a nitrogen atmosphere, the mixed metal salt solution, the mixed phosphate solution, and the ammonia water with a concentration of 10.0 mol / L were added in parallel to a reactor containing the base solution. The temperature in the reactor was set to 40 °C, the pH to 8.0, and the stirring speed to 300 rpm. Step 8: When the D50 value of the material in the reactor was determined to reach 10 µm, the feed was stopped and solid-liquid separation was performed. The resulting material was then washed with deionized water and then with anhydrous ethanol to obtain ammonium manganese iron phosphate. Step 9: The ammonium manganese iron phosphate was pulverized into powder with a particle size of 2-5 µm. Step 10: The powdered ammonium manganese iron phosphate was mixed with lithium hydroxide and glucose in a molar ratio of (Fe+Mn): Li: carbon source of 1: 1.1: 0.4, the resulting mixture was added with deionized water in an amount of 25% of the total mass of ammonium manganese iron phosphate, lithium hydroxide and glucose, mixed well and spray dried. Step 11: Under the protection of an inert gas, the solid obtained after spray drying was calcined at 750 °C for 16 hours and then naturally cooled to room temperature to obtain a finished cathode material of lithium manganese iron phosphate. Comparative Example 1

[0029] In this comparative example, a lithium manganese iron phosphate was prepared. The specific procedure was as follows and differed from Example 1 in that no organic solution was added: Step 1: A metal salt solution of manganese chloride and ferrous chloride with a total metal ion concentration of 0.05 mol / L was prepared in a molar ratio of iron to manganese of 1:1. Step 2: An ammonium dihydrogen phosphate solution with a concentration of 0.05 mol / L was prepared. Step 3: Ammonia water with a concentration of 12.0 mol / L was prepared. Step 4: The ammonium dihydrogen phosphate solution was added with ammonia water with a concentration of 12.0 mol / L to adjust the pH to 9 and obtain a base solution. Step 5: Under a nitrogen atmosphere, the metal salt solution, the ammonium dihydrogen phosphate solution, and the ammonia water with a concentration of 12.0 mol / L were added in parallel to a reactor containing the base solution. The temperature in the reactor was set to 20 °C, the pH to 8.5, and the stirring speed to 350 rpm. Step 6: When the D50 value of the material in the reactor was determined to reach 15 µm, the feed was stopped and solid-liquid separation was performed. The resulting material was then washed with deionized water and then with anhydrous ethanol to obtain ammonium manganese iron phosphate. Step 7: The ammonium manganese iron phosphate was pulverized into powder with a particle size of 2-5 µm. Step 8: The powdered ammonium manganese iron phosphate was mixed with lithium hydroxide and glucose in a molar ratio of (Fe+Mn): Li: carbon source of 1: 1.1: 0.3, the resulting mixture was added with deionized water in an amount of 35% of the total mass of ammonium manganese iron phosphate, lithium hydroxide and glucose, mixed well and spray dried. Step 9: Under the protection of an inert gas, the solid obtained after spray drying was calcined at 850 °C for 14 hours and then naturally cooled to room temperature to obtain a finished cathode material of lithium manganese iron phosphate. Comparative Example 2

[0030] In this example, a lithium manganese iron phosphate was prepared. The specific procedure was as follows and differs from Example 2 in that no organic solution was added: Step 1: A metal salt solution of manganese sulfate and iron(II) sulfate with a total metal ion concentration of 0.005 mol / L was prepared at a molar ratio of iron to manganese of 1:1. Step 2: An ammonium dihydrogen phosphate solution with a concentration of 0.005 mol / L was prepared. Step 3: Ammonia water with a concentration of 8.0 mol / L was prepared. Step 4: The ammonium dihydrogen phosphate solution was added with ammonia water with a concentration of 8.0 mol / L to adjust the pH to 8.5 and obtain a base solution. Step 5: Under a nitrogen atmosphere, the metal salt solution, the ammonium dihydrogen phosphate solution, and the ammonia water with a concentration of 8.0 mol / L were added in parallel to a reactor containing the base solution. The temperature in the reactor was set to 30 °C, the pH to 8.0, and the stirring speed to 200 rpm. Step 6: When the D50 value of the material in the reactor was determined to reach 5 µm, the feed was stopped and solid-liquid separation was performed. The resulting material was then washed with deionized water and then with anhydrous ethanol to obtain ammonium manganese iron phosphate. Step 7: The ammonium manganese iron phosphate was pulverized into powder with a particle size of 2-5 µm. Step 8: The powdered ammonium manganese iron phosphate was mixed with lithium carbonate and sucrose in a molar ratio of (Fe+Mn): Li: carbon source of 1: 1.0: 0.3, the resulting mixture was added with deionized water in an amount of 20% of the total mass of ammonium manganese iron phosphate, lithium carbonate and sucrose, mixed well and spray dried. Step 9: Under the protection of an inert gas, the solid obtained after spray drying was calcined at 600 °C for 20 hours and then naturally cooled to room temperature to obtain a finished cathode material of lithium manganese iron phosphate. Comparative Example 3

[0031] In this example, a lithium manganese iron phosphate was prepared. The specific procedure was as follows and differs from Example 3 in that no organic solution was added: Step 1: A metal salt solution of manganese chloride and ferrous chloride with a total metal ion concentration of 0.02 mol / L was prepared with a molar ratio of iron to manganese of 1:1. Step 2: An ammonium dihydrogen phosphate solution with a concentration of 0.02 mol / L was prepared. Step 3: Ammonia water with a concentration of 10.0 mol / L was prepared. Step 4: The ammonium dihydrogen phosphate solution was added with ammonia water at a concentration of 10.0 mol / L to adjust the pH to 8.0 and obtain a base solution. Step 5: Under a nitrogen atmosphere, the metal salt solution, the ammonium dihydrogen phosphate solution, and the ammonia water at a concentration of 10.0 mol / L were added in parallel to a reactor containing the base solution. The temperature in the reactor was set to 40 °C, the pH to 8.0, and the stirring speed to 300 rpm. Step 6: When the D50 value of the material in the reactor was determined to reach 10 µm, the feed was stopped and solid-liquid separation was performed. The resulting material was then washed with deionized water and then with anhydrous ethanol to obtain ammonium manganese iron phosphate. Step 7: The ammonium manganese iron phosphate was pulverized into powder with a particle size of 2-5 µm. Step 8: The powdered ammonium manganese iron phosphate was mixed with lithium hydroxide and glucose in a molar ratio of (Fe+Mn): Li: carbon source of 1: 1.1: 0.4, the resulting mixture was added with deionized water in an amount of 25% of the total mass of ammonium manganese iron phosphate, lithium hydroxide and glucose, mixed well and spray dried. Step 9: Under the protection of an inert gas, the solid obtained after spray drying was calcined at 750 °C for 16 hours and then naturally cooled to room temperature to obtain a finished cathode material of lithium manganese iron phosphate. Table 1 Compaction density of the examples and comparative examples Compaction density [g / cm 3 ] Example 1 2,68 Example 2 2,66 Example 3 2,66 Comparative example1 2,14 Comparative example2 2,13 Comparative example3 2,16 Example of a test

[0032] The lithium manganese iron phosphate obtained in the examples and comparative examples as the cathode material, acetylene black as the conductive agent, and PVDF as the binder were mixed in a mass ratio of 8:1:1. A certain amount of the organic solvent NMP was added to the resulting mixture, stirred, and then coated on an aluminum foil to prepare the cathode sheet. The lithium metal sheet served as the negative electrode, and the Celgard2400 porous polypropylene film served as the separator. A solution of EC, DMC, and EMC in a mass ratio of 1:1:1 served as the electrolyte, and the solute was LiPF6 with a concentration of 1.0 mol / L. A 2023 button battery was assembled in a glove box. The battery was tested for charge-discharge cycle performance to measure the specific discharge capacity at 0.2 C and 1 C in the cutoff voltage range of 2.2 to 4.3 V.The electrochemical performance results are presented in Table 2. Table 2 Discharge capacity at 0.2 C, [mAh / cm 3 ] Discharge capacity at 1 C, [mAh / cm 3 ] Capacity retention rate for 600 cycles at 1C Example 1 382,56 300,24 95,3% Example 2 380,88 300,22 94,9% Example 3 381,36 299,28 94,8% Comparative Example 1 284,83 219,78 83,6% Comparative Example 2 279,88 222,16 86,7% Comparative Example 3 285,55 222,70 84,3%

[0033] From Tables 1 and 2 it can be seen that the compaction density of the examples is significantly higher than that of the comparative examples and is 2.6 g / cm 3or more. By increasing the compaction density, the discharge capacity is improved. The reason for this change is that in Comparative Examples, the production method was the traditional water-phase method, and the primary particles in the obtained secondary particles had a relatively loose structure and tended to be separated upon carbonization of the carbon source during subsequent sintering when combined with the carbon source, making it difficult for them to agglomerate and crystallize, resulting in a loose particle structure and a low compaction density after sintering. By the method of the present invention, a high-density particle structure can be formed, thereby improving the compaction density.

Claims

[1] A process for producing ammonium manganese iron phosphate, comprising the following steps: S1: Mixing a metal salt solution and an ammonium dihydrogen phosphate solution with an organic solution to obtain a mixed metal salt liquid and a mixed phosphate liquid, wherein the metal salt solution is a solution of a manganese salt and a ferrous salt, and the organic solution is obtained by dissolving a surfactant in an organic solvent; and S2: Adding the mixed metal salt liquid, the mixed phosphate liquid, and a first ammonia water under an inert atmosphere in parallel to a base solution for reaction, and when a reaction material reaches a target particle size, performing solid-liquid separation to obtain the ammonium manganese iron phosphate, wherein the base solution is a mixed liquid of the phosphate mixed solution and a second ammonia water, the base solution having a pH of 8-9, and the reaction material is controlled to have a pH of 8-9 upon reaction. [2] The method according to claim 1, wherein in step S1 in the metal salt solution the molar ratio of iron element to manganese element is 0.25-9:

1. [3] The method according to claim 1, wherein in step S1 the concentration of the ammonium dihydrogen phosphate solution is 0.5-1.0 mol / l and in the mixed phosphate liquid the volume ratio of the ammonium dihydrogen phosphate solution to the organic solution is 1-5:

100. [4] The process according to claim 1, wherein in step S1 the ratio of the mass of the surfactant to the volume of the organic solvent is 2-8 g : 100 ml. [5] The method according to claim 1, wherein in step S1, the surfactant is at least one selected from the group consisting of CTAB, DBS, SDBS, and PEG-400. [6] The process according to claim 1, wherein in step S1 the organic solvent is prepared by mixing cyclohexane and n-butanol in a volume ratio of 8:2-9:

1. [7] The method according to claim 1, wherein in step S2 the target particle size of the reaction material is 5-15 µm.

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