Preparation method of manganese iron phosphate and application thereof

Abstract

The application discloses a preparation method of manganese iron phosphate and application thereof, and the preparation method comprises the following steps: S1, mixing an iron-manganese-phosphorus mixed solution, an oxidizing agent and a pH regulator to obtain a mixed slurry; S2, taking 20%-60% of the volume of the mixed slurry at 60-100 DEG C for 2-6 hours, then adding the remaining mixed slurry for heat preservation reaction, impurity removal and calcination to obtain manganese iron phosphate. The monohydrate manganese iron phosphate prepared by the embodiment of the application has olivine-shaped primary particles, the olivine-shaped primary particles are orderly stacked to form secondary particles, the process is simple and stable, and iron and manganese elements are uniformly doped.

Description

Technical Field

[0001] This invention relates to the field of lithium manganese iron phosphate cathode materials, specifically to a method for preparing lithium manganese iron phosphate and its application. Background Technology

[0002] In the field of cathode materials for batteries, olivine-type LiMn x Fe (1-x) PO4 (LMFP) has the advantages of good structural stability and high operating voltage. Its energy density can be increased by 15% to 20% compared with LiFePO4, making it a cathode material with great prospects for industrial application of LIBs.

[0003] Production of LiMn x Fe (1-x) When using PO4 cathode material, Mn, which has trivalent manganese and iron, is employed. x Fe (1-x) PO4, as a precursor, can be directly produced on lithium iron phosphate production lines, offering low replacement costs and rapid industrialization. However, existing processes for producing Mn... x Fe (1-x) When preparing PO4 materials, the disproportionation and common ion effect of trivalent manganese prevent the stable preparation of trivalent manganese products, and iron cannot be uniformly doped into the manganese phosphate lattice during precipitation. Therefore, considering these issues, current methods for preparing divalent manganese products as precursors for lithium manganese iron phosphate cannot be calcined or require inert gas protection. Furthermore, the preparation process involves multiphase material feeding, making it cumbersome and hindering large-scale industrialization.

[0004] Therefore, there is an urgent need to provide a method for preparing a manganese ferrophosphate material in which both manganese and iron are in the trivalent valence state. Summary of the Invention

[0005] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a method for preparing ferromanganese phosphate to obtain olivine-like ferromanganese phosphate material. The process is simple and stable, with uniform doping of iron and manganese elements, and the primary particles exhibiting an olivine-like structure.

[0006] According to a first aspect of the present invention, a method for preparing ferromanganese phosphate includes the following steps:

[0007] S1: Mix the iron-manganese-phosphorus mixed solution, oxidant, and pH adjuster to obtain a mixed slurry;

[0008] S2: Take a portion of the mixed slurry, heat it to 60-100℃, slowly add the remaining mixed slurry, keep it at the temperature for 2-6 hours, remove impurities and calcine to obtain manganese iron phosphate;

[0009] The volume ratio of the partially mixed slurry to the mixed slurry is not greater than 0.75.

[0010] According to some embodiments of the present invention, in step S1, the molar ratio of the oxidant to the metal ions in the iron-manganese-phosphorus mixed solution is (0.2-1):1.

[0011] The above molar ratio range ensures that the amount of oxidant is sufficient to fully oxidize the metal ions in the mixed solution, while avoiding the waste of excessive oxidant.

[0012] According to some embodiments of the present invention, the oxidant includes at least one selected from permanganate, persulfate, ferrate and hypochlorite.

[0013] According to some embodiments of the present invention, in solution state, the solvent of the oxidant solution includes water.

[0014] According to some embodiments of the present invention, the iron source comprises a ferrous salt, wherein the ferrous salt comprises at least one of ferrous sulfate, ferrous chloride and ferrous acetate.

[0015] According to some embodiments of the present invention, the manganese source includes a divalent manganese salt, which includes at least one of manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate.

[0016] According to some embodiments of the present invention, the phosphorus source includes at least one selected from diammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate, potassium hydrogen phosphate, and phosphoric acid.

[0017] According to some embodiments of the present invention, the concentration of metal ions in the iron-manganese-phosphorus mixed solution is 0.6 to 2 mol / L.

[0018] The above concentrations are conducive to the uniform distribution of reactants in the solution, thereby promoting the uniformity of the reaction and reducing the non-uniformity that may be caused by excessively high local concentrations.

[0019] According to some embodiments of the present invention, the molar ratio of manganese ions to iron ions in the iron-manganese-phosphorus mixed solution is 1.4 to 1.8:1.

[0020] Under the above conditions, it is helpful to optimize the crystal structure and electrochemical properties of ferromanganese phosphate, thereby improving the overall performance of the final product.

[0021] According to some embodiments of the present invention, the molar ratio of metal ions to phosphorus in the mixed slurry is (0.4 to 1):1.

[0022] According to some embodiments of the present invention, in step S1, the pH value of the mixed slurry is 0.6 to 4.0.

[0023] Within the aforementioned pH range, the crystallization environment of the slurry is adjusted, and the chemical properties and structure of the product are controlled, thereby achieving the desired characteristics of manganese iron phosphate.

[0024] According to some embodiments of the present invention, the pH adjuster includes at least one selected from sulfuric acid, nitric acid, phosphoric acid, acetic acid, and hydrochloric acid.

[0025] According to some embodiments of the present invention, in step S2, the temperature of the heat preservation reaction is 40 to 100°C.

[0026] According to some embodiments of the present invention, in step S2, the impurity removal step includes pressure filtration, washing, and drying.

[0027] According to some embodiments of the present invention, in step S2, the drying temperature is 100℃~150℃, and the drying time is 2~6h.

[0028] According to some embodiments of the present invention, in step S2, the calcination temperature is 200℃~300℃ and the calcination time is 2~4h.

[0029] According to some embodiments of the present invention, the manganese iron phosphate is Mn x Fe (1-x) PO4·H2O, x is 0.6 to 0.8.

[0030] Application of a preparation method according to a second aspect of the present invention in the preparation of cathode materials for lithium-ion batteries. Attached Figure Description

[0031] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0032] Figure 1 This is a schematic flowchart of a method for preparing ferric manganese phosphate provided in an embodiment of the present invention;

[0033] Figure 2 This is an XRD pattern of a manganese iron phosphate provided in this embodiment.

[0034] Figure 3 This is a SEM image of manganese iron phosphate provided in Example 1 of this specification under a 50,000x electron microscope;

[0035] Figure 4 This is a SEM image of manganese iron phosphate provided in Example 1 of this specification under a 1000x electron microscope;

[0036] Figure 5 This is a SEM image of manganese iron phosphate provided in Example 2 of this specification under a 50,000x electron microscope;

[0037] Figure 6 This is a SEM image of manganese iron phosphate provided in Example 2 of this specification under a 1000x electron microscope;

[0038] Figure 7 This is a cross-sectional SEM image of manganese iron phosphate provided in Example 2 of this specification under a 10,000x electron microscope;

[0039] Figure 8 This is a SEM image of manganese iron phosphate provided in Example 2 of this specification under a 50,000x electron microscope;

[0040] Figure 9 This is a SEM image of manganese iron phosphate provided in Example 2 of this specification under a 1000x electron microscope;

[0041] Figure 10 An XRD pattern of manganese iron phosphate provided for Comparative Example 1 of this application;

[0042] Figure 11 This is a SEM image of manganese iron phosphate provided in Comparative Example 1 of this specification under a 50,000x electron microscope;

[0043] Figure 12 This is a SEM image of manganese iron phosphate provided in Comparative Example 1 of this specification under a 1000x electron microscope;

[0044] Figure 13 This is a SEM image of manganese iron phosphate provided in Comparative Example 1 of this specification under a 50,000x electron microscope;

[0045] Figure 14 This is a SEM image of manganese iron phosphate provided in Comparative Example 2 of this specification under a 1000x electron microscope. Detailed Implementation

[0046] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0047] Example 1

[0048] This embodiment discloses a method for preparing ferric manganese phosphate, which includes the following steps:

[0049] S1: Add 611.5g of manganese sulfate monohydrate crystals (wt% ≥ 99.5%) and 693.5g of ammonium dihydrogen phosphate crystals (wt% ≥ 99.5%) to 4L of 0.6mol / L ferrous sulfate solution, and obtain iron-manganese mixed solution A after dissolution;

[0050] Dissolve 694g of ammonium persulfate crystals (wt% ≥ 98.5%) in water and dilute to 1.5L to prepare oxidant solution B;

[0051] Then, the iron-manganese mixed solution A and the oxidant solution B are mixed to obtain a reaction solution with a total metal ion concentration of 1.0 mol / L. Phosphoric acid is then added to adjust the pH to 1.2 to obtain 6L of reaction slurry.

[0052] S2: Take 2L of the above reaction slurry and pump it into the reactor to raise the temperature to 90℃. After reacting for 2 hours, slowly pump the remaining slurry into the reactor for 2 hours. After the mixed solution B turns into a grass-green slurry, keep it at the temperature for another 2 hours and then perform solid-liquid separation. After washing, dry it in an oven at 100℃ for 4 hours to obtain ferromanganese phosphate powder. Then put it into a muffle furnace and calcine it at 250℃ for 4 hours to obtain the ferromanganese phosphate powder.

[0053] The process flow diagram for obtaining ferromanganese phosphate is as follows: Figure 1 As shown, the XRD pattern and electron microscope image are as follows: Figure 2 , Figure 3 and Figure 4 As shown, where, Figure 2 The image shown is an XRD pattern of a manganese iron phosphate provided in this embodiment. Figure 3 This is a SEM image of manganese iron phosphate provided in Example 1 of this specification under a 50,000x electron microscope. Figure 4 This is a SEM image of manganese iron phosphate provided in Example 1 of this specification under a 1000x electron microscope.

[0054] from Figure 2 It can be seen that, compared with the characteristic diffraction peaks in the standard manganese phosphate monohydrate card (PDF-78-1082), the diffraction peak shape and position of the ferromanganese phosphate prepared in Example 1 of this invention are completely consistent with those of the standard card and there are no impurity peaks. Furthermore, the diffraction peaks of the ferromanganese phosphate prepared in this embodiment are sharp and have narrow half-maximum widths (WHM). This indicates that the ferromanganese phosphate prepared in Example 1 of this invention is a pure phase with good crystallinity of manganese phosphate, in which iron is uniformly doped in the MnPO4·H2O lattice in solid solution form, forming a uniform trivalent Mn. x Fe (1-x) PO4 product. From Figure 3 and Figure 4 It can be seen that by adjusting the feeding method, the present invention uses a portion of the reaction liquid to react first to generate seed crystals, and then slowly adds the remaining reaction liquid to promote the slow growth of the crystal nuclei. The primary particles of manganese phosphate monohydrate prepared in Example 1 are olivine-like, and the olivine-like primary particles are stacked in an orderly manner to form secondary particles.

[0055] Example 2

[0056] This embodiment discloses a method for preparing ferromanganese phosphate. The difference between Example 2 and Example 1 is that the added oxidant is potassium permanganate, specifically:

[0057] S1: Add 373.3g of manganese sulfate monohydrate crystals (wt% ≥ 99.5%) and 693.5g of ammonium dihydrogen phosphate crystals (wt% ≥ 99.5%) to 3L of ferrous sulfate solution with a concentration of 0.8mol / L. After dissolution, a mixed iron-manganese solution A is obtained.

[0058] Weigh 191g of potassium permanganate crystals (wt% ≥ 99.3%), dissolve them, and bring the volume to 3L to obtain oxidant solution B. Then mix iron-manganese mixed solution A and oxidant solution B to obtain a reaction solution with a total metal ion concentration of 1.0mol / L. Add phosphoric acid to adjust the pH to 1.2 to obtain 6L of reaction slurry.

[0059] S2: Take 2L of the above reaction slurry and pump it into the reactor to raise the temperature to 90℃. Then slowly pump the remaining slurry into the reactor for 2 hours. After the mixed solution B turns into a grass-green slurry, keep it at the temperature for another 2 hours and then perform solid-liquid separation. After washing, dry it in an oven at 100℃ for 4 hours to obtain manganese iron phosphate powder. Then put it into a muffle furnace and calcine it at 250℃ for 4 hours to obtain the manganese iron phosphate powder.

[0060] The electron micrograph of the obtained manganese iron phosphate is shown below. Figure 5 and Figure 6 As shown. Among them, Figure 5 This is a SEM image of manganese iron phosphate provided in Example 2 of this specification under a 50,000x electron microscope. Figure 6 This is a SEM image of manganese iron phosphate provided in Example 2 of this specification under a 1000x electron microscope. From... Figure 5 It can be seen that by changing the type of oxidant and altering its crystallization environment, the primary particles of manganese ferrophosphate monohydrate prepared in Example 2 of this invention are olivine-like, and these olivine-like primary particles are orderly stacked to form secondary particles. A cross-section of the manganese ferrophosphate prepared in Example 2 of this invention was analyzed using scanning electron microscopy, and its internal morphology was observed. Figure 7 As can be seen, by slowly adding the remaining reaction solution, the manganese iron phosphate prepared in Example 2 of this invention is internally dense and without pores. It is suitable for preparing high-pressure compaction lithium manganese iron phosphate. The different oxidants in the examples resulted in different crystallization environments, thus altering the formation of crystal nuclei.

[0061] Example 3

[0062] This embodiment discloses a method for preparing ferromanganese phosphate. The difference between Example 3 and Example 1 is that the added oxidant is a combination of sodium persulfate and hydrogen peroxide, specifically:

[0063] S1: Add 611.5g of manganese sulfate monohydrate crystals (wt% ≥ 99.5%) and 693.5g of ammonium dihydrogen phosphate crystals (wt% ≥ 99.5%) to 4L of 0.6mol / L ferrous sulfate solution, and obtain iron-manganese mixed solution A after dissolution;

[0064] Dissolve 416.4g of sodium persulfate crystals (wt% ≥ 98.5%) in water, then add 178g of hydrogen peroxide (wt = 27.5%) and bring the volume to 1.5L to prepare oxidant solution B;

[0065] Then, the iron-manganese mixed solution A and the oxidant solution B are mixed to obtain a reaction solution with a total metal ion concentration of 1.0 mol / L. Phosphoric acid is then added to adjust the pH to 1.2 to obtain 6L of reaction slurry.

[0066] S2: Take 2L of the above reaction slurry and pump it into the reactor to raise the temperature to 90℃. Then slowly pump the remaining slurry into the reactor for 2 hours. After the mixed solution B turns into a grass-green slurry, keep it at the temperature for another 2 hours and then perform solid-liquid separation. After washing, dry it in an oven at 100℃ for 4 hours to obtain manganese iron phosphate powder. Then put it into a muffle furnace and calcine it at 250℃ for 4 hours to obtain the manganese iron phosphate powder.

[0067] The electron micrograph of the obtained manganese iron phosphate is shown below. Figure 8 and Figure 9 As shown, where, Figure 8 This is a SEM image of manganese iron phosphate provided in Example 3 of this specification under a 50,000x electron microscope. Figure 9 This is a SEM image of manganese iron phosphate provided in Example 3 of this specification under a 1000x electron microscope.

[0068] Comparative Example 1

[0069] The difference between Comparative Example 1 and Example 1 is that the mixture slurry is directly heated for reaction after being obtained, specifically:

[0070] S1: Add 611.5g of manganese sulfate monohydrate crystals (wt% ≥ 99.5%) and 796g of monoammonium phosphate crystals (wt% ≥ 99.5%) to 4L of 0.6mol / L ferrous sulfate solution, and obtain iron-manganese mixed solution A after dissolution;

[0071] Dissolve 694g of ammonium persulfate crystals (wt% ≥ 98.5%) and dilute to 1.5L to prepare oxidant solution B;

[0072] Then, the iron-manganese mixed solution A and the oxidant solution B are mixed to obtain a reaction solution with a total metal ion concentration of 1.0 mol / L. Phosphoric acid is then added to adjust the pH to 1.2 to obtain 6L of reaction slurry.

[0073] S2: The above reaction slurry is pumped into the reactor and heated. After the temperature reaches 90°C, the reaction is maintained at this temperature and then solid-liquid separation is performed. After washing, the mixture is dried in an oven at 100°C for 4 hours to obtain ferromanganese phosphate powder. Then, it is placed in a muffle furnace and calcined at 250°C for 4 hours to obtain the ferromanganese phosphate powder.

[0074] The electron micrograph of the obtained product is shown below. Figures 10 to 11 As shown, where, Figure 10 SEM image of the product provided in Comparative Example 1 of this application under a 50,000x electron microscope; Figure 11 This is a SEM image of the product provided in Comparative Example 1 of this specification under a 1000x electron microscope. From... Figure 10 It can be seen that the direct heating oxidation process of iron and manganese is relatively fast, and its supersaturation is relatively high, resulting in the formation of fragmented crystalline primary particles of manganese phosphate monohydrate. These fragmented primary particles are then stacked in an orderly manner to form secondary particles. The main difference between this and the previous example lies in controlling the feeding method, thereby changing the morphology of the primary particles.

[0075] Comparative Example 2

[0076] The difference between Comparative Example 2 and Example 1 is that the oxidant added is hydrogen peroxide, which is widely used in the industry. All other conditions are the same.

[0077] The XRD pattern and electron micrograph of the obtained product are as follows: Figure 12 , Figure 13 As shown, where, Figure 12 The XRD pattern of the product provided in Comparative Example 2 of this specification. Figure 13 The image shows the product described in this specification under a 50,000x electron microscope (SEM). Figure 14 This is a SEM image of the product provided in Comparative Example 2 of this specification under a 1000x electron microscope. From... Figure 12 and Figure 14 It can be seen that the product obtained in Comparative Example 2 has an impure crystalline phase and is a mixture of various manganese iron phosphates. This proves that hydrogen peroxide cannot oxidize the divalent manganese salt under these conditions. Its primary particles are in blocky form. The difference between Comparative Example 2 and the example is that the oxidation of manganese salt is controlled. The inability of hydrogen peroxide to oxidize manganese salt in Comparative Example 2 results in a non-pure phase product.

[0078] Test Example 1

[0079] In this test, the manganese ferric phosphate prepared in the above-mentioned examples and comparative examples was used for performance testing, and the corresponding properties are shown in Table 1 below.

[0080] Table 1. Index testing of each embodiment and comparative example.

[0081]

[0082] As shown in Table 1, the olivine-like manganese iron phosphate (Mn) prepared by this invention...x Fe (1-x) In MnPO4·H2O, the x value is generally between 0.6 and 0.7. The manganese-iron ratio is 6:4, with iron uniformly doped into the MnPO4·H2O lattice in solid solution form, forming a uniform trivalent Mn. x Fe (1-x) The product is PO4·H2O, and the manganese-iron ratio can be controlled by changing the ratio of manganese and iron elements added.

[0083] Furthermore, to verify the performance of lithium manganese iron phosphate prepared from ferromanganese phosphate in this application, lithium source, carbon source, deionized water and additives were added to the ferromanganese phosphate obtained in Example 1, and the mixture was then subjected to sand milling. After being ground to a certain particle size, it was spray-dried and finally calcined at 750°C under a protective atmosphere to obtain lithium manganese iron phosphate.

[0084] Table 2 Comparison of Lithium Manganese Iron Phosphate Performance in Example 1 and Comparative Example 1

[0085]

[0086] Table 2 shows that the manganese iron phosphate (Mn) prepared by this invention... x Fe (1-x) The lithium iron phosphate prepared by PO4·H2O, compared with the lithium iron phosphate prepared by direct heating, shows improved compaction density and discharge performance of the lithium iron phosphate prepared by olivine-like ferrophosphate. This indicates that the preparation method provided in this application can effectively prepare battery-grade lithium iron phosphate with good discharge performance.

[0087] The foregoing has described specific embodiments of this specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims may be performed in a different order than that shown in the embodiments and may still achieve the desired result. Furthermore, the processes depicted in the drawings do not necessarily require the specific or sequential order shown to achieve the desired result. In some embodiments, multitasking and parallel processing are possible or may be advantageous.

[0088] The above description is merely one or more embodiments of this specification and is not intended to limit this specification. Various modifications and variations can be made to the one or more embodiments of this specification by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of one or more embodiments of this specification should be included within the scope of the claims of this specification.

Claims

1. A method for producing manganese iron phosphate, characterized by, The preparation method includes the following steps: S1: Mix the iron-manganese-phosphorus mixed solution, oxidant, and pH adjuster to obtain a mixed slurry; S2: By volume ratio, take 20% to 60% of the mixed slurry volume and react at 60 to 100℃ for 2 to 6 hours. Then add the remaining mixed slurry, keep it at the temperature for reaction, remove impurities and calcine to obtain manganese iron phosphate. The iron source of the iron-manganese-phosphorus mixed solution is a ferrous salt, which is selected from at least one of ferrous sulfate, ferrous chloride and ferrous acetate. The manganese source of the iron-manganese-phosphorus mixed solution is a divalent manganese salt, which is selected from at least one of manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate. The concentration of metal ions in the iron-manganese-phosphorus mixed solution is 0.6–2 mol / L, and the molar ratio of manganese ions to iron ions in the iron-manganese-phosphorus mixed solution is 1.4–1.8:

1. The oxidant is at least one of permanganate, persulfate, ferrate, hypochlorite, and hydrogen peroxide; In step S1, the molar ratio of the oxidant to the metal ions in the iron-manganese-phosphorus mixed solution is (0.2-1):1, the pH adjuster includes at least one of sulfuric acid, nitric acid, phosphoric acid, acetic acid and hydrochloric acid, the pH value of the mixed slurry is 0.6-4.0, and the molar ratio of metal ions to phosphorus in the mixed slurry is (0.4-1):

1. The primary particles of manganese iron phosphate are olivine-like, and the olivine-like primary particles are stacked in an orderly manner to form secondary particles.

2. The application of the preparation method as described in claim 1 in the preparation of lithium-ion battery cathode materials.

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