Preparation method and application of ferromanganese phosphate

Abstract

The invention discloses a preparation method and application of ferromanganese phosphate. The preparation method comprises the following steps: S1, mixing an iron-manganese-phosphorus mixed solution, an oxidant and a pH regulator to obtain mixed slurry; and S2, taking 20-60% of the volume of the mixed slurry according to the volume ratio, reacting at 60-100 DEG C for 2-6 hours, adding the rest of the mixed slurry, carrying out heat preservation reaction, removing impurities, and calcining to obtain the ferromanganese phosphate. The ferromanganese phosphate monohydrate primary particles prepared by the embodiment of the invention are olivine-shaped, 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] The invention relates to the field of lithium manganese iron phosphate positive electrode materials, and in particular to a preparation method of lithium manganese iron phosphate and application thereof. Background Art

[0002] In the field of positive electrode 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. It is a LIBs positive electrode material with great industrial application prospects.

[0003] Making LiMn x Fe (1-x) When using PO4 positive electrode materials, manganese and iron are all trivalent Mn x Fe (1-x) PO4 as its precursor can be directly produced in the lithium iron phosphate production line, with low replacement cost and rapid industrialization. x Fe (1-x) When preparing PO4 materials, due to the disproportionation and common ion effect of trivalent manganese, trivalent manganese products cannot be stably prepared, and the iron element cannot be evenly doped in the manganese phosphate lattice during the precipitation process. Therefore, considering the above problems, there is currently a method of preparing divalent manganese products as lithium manganese iron phosphate precursors, which cannot be calcined or require inert gas protection, and there are multi-phase materials in the preparation process, the process is cumbersome, and it cannot be industrialized on a large scale.

[0004] Based on this, there is an urgent need to provide a method for preparing a ferromanganese phosphate material in which the valence state of manganese and iron is trivalent. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a method for preparing ferromanganese phosphate to prepare an olivine-like ferromanganese phosphate material, which has a simple and stable process, uniform doping of iron and manganese elements, and primary particles presenting an olivine shape.

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

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

[0008] S2: taking part of the mixed slurry and heating it to 60-100°C, then slowly adding the remaining mixed slurry, and keeping the temperature to react for 2-6 hours, removing impurities and calcining to obtain ferromanganese 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 can ensure that the amount of the 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 of permanganate, peroxodisulfate, ferrate and hypochlorite.

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

[0014] According to some embodiments of the present invention, the iron source includes a divalent iron salt, and the divalent iron salt includes 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, and the divalent manganese salt includes at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese acetate, and the like.

[0016] According to some embodiments of the present invention, the phosphorus source includes at least one of 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 0.6-2 mol / L.

[0018] The above concentration is conducive to the uniform distribution of the reactants in the solution, thereby promoting the uniform progress of the reaction and reducing the non-uniformity that may be caused by excessive local concentration.

[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 1.4-1.8:1.

[0020] The above conditions help 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 (0.4-1):1.

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

[0023] The above pH value can adjust the crystallization environment of the slurry, control the chemical properties and structure of the product, and thus obtain the desired ferromanganese phosphate properties.

[0024] According to some embodiments of the present invention, the pH adjuster includes at least one of 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 insulation reaction is 40-100°C.

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

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

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

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

[0030] A preparation method according to an embodiment of the second aspect of the present invention is used in preparing positive electrode materials for lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0032] Figure 1 A schematic flow chart of a method for preparing ferromanganese phosphate provided in an embodiment of the present invention;

[0033] Figure 2 This is an XRD diagram of ferromanganese phosphate provided in this embodiment 1.

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

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

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

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

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

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

[0040] Fig. 9 This is a SEM image of ferromanganese phosphate provided in Example 2 of this specification under a 1000x electron microscope;

[0041] Fig.10 An XRD diagram of ferromanganese phosphate provided in Comparative Example 1 of the present application;

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

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

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

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

[0046] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0047] Example 1

[0048] This embodiment discloses a method for preparing ferromanganese phosphate, which comprises the following steps:

[0049] S1: 611.5 g of manganese sulfate monohydrate crystals (wt% ≥ 99.5%) and 693.5 g of ammonium dihydrogen phosphate crystals (wt% ≥ 99.5%) were added to 4 L of 0.6 mol / L ferrous sulfate solution, and the mixture was dissolved to obtain an iron-manganese mixed solution A;

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

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

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

[0053] The process flow chart of the obtained ferromanganese phosphate is as follows: Figure 1 As shown, the XRD pattern and electron microscope picture are as follows Figure 2 , Figure 3 and Figure 4 As shown, Figure 2 This is an XRD diagram of ferromanganese phosphate provided in this embodiment. Figure 3 This is a SEM image of a ferromanganese phosphate provided in Example 1 of this specification under a 50,000x electron microscope. Figure 4 This is a SEM image of ferromanganese 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 peak in the standard manganese phosphate monohydrate card (PDF-78-1082), the diffraction peak shape and peak position of the ferromanganese phosphate prepared in Example 1 of the present invention are completely consistent with it and there is no impurity peak. At the same time, the diffraction peak of the ferromanganese phosphate prepared in the embodiment of the present invention is sharp and the half-height width is narrow, which shows that the ferromanganese phosphate prepared in Example 1 of the present invention is a pure phase and a manganese phosphate phase with good crystallinity, and its iron element is uniformly doped in the MnPO4·H2O lattice in the form of a solid solution to form a uniform trivalent Mn x Fe (1-x) PO4 product. Figure 3 and Figure 4 It can be seen that the present invention adjusts its feeding method, uses part 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 its crystal nucleus. The primary particles of manganese ferrophosphate monohydrate prepared in Example 1 are olivine-shaped, and the olivine-shaped 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 Embodiment 2 and Embodiment 1 is that the added oxidant is potassium permanganate, specifically:

[0057] S1: 373.3 g of manganese sulfate monohydrate crystals (wt% ≥ 99.5%) and 693.5 g of ammonium dihydrogen phosphate crystals (wt% ≥ 99.5%) were added to 3 L of 0.8 mol / L ferrous sulfate solution, and the mixture was dissolved to obtain an iron-manganese mixed solution A;

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

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

[0060] The electron microscope image of the obtained ferromanganese phosphate is as follows: Figure 5 and Figure 6 As shown. Among them, Figure 5 This is a SEM image of a manganese iron phosphate provided in Example 2 of this specification under a 50,000x electron microscope. Figure 6 This is a SEM image of a manganese iron phosphate provided in Example 2 of this specification under a 1000x electron microscope. Figure 5 It can be seen that by changing the type of oxidant and its crystallization environment, the primary particles of manganese ferrophosphate monohydrate prepared in Example 2 of the present invention are olivine-like, and the olivine-like primary particles are stacked in an orderly manner to form secondary particles. The cross section of the manganese ferrophosphate prepared in Example 2 of the present invention was analyzed by scanning electron microscopy, and its internal morphology was observed. Figure 7 It can be seen that by slowly adding the remaining reaction solution, the ferromanganese phosphate prepared in Example 2 of the present invention is dense and has no holes. It is suitable for preparing high-density lithium ferromanganese phosphate. The different oxidants in the embodiments achieve different crystallization environments, thereby changing the generation of crystal nuclei.

[0061] Example 3

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

[0063] S1: 611.5 g of manganese sulfate monohydrate crystals (wt% ≥ 99.5%) and 693.5 g of ammonium dihydrogen phosphate crystals (wt% ≥ 99.5%) were added to 4 L of 0.6 mol / L ferrous sulfate solution, and the mixture was dissolved to obtain an iron-manganese mixed solution A;

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

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

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

[0067] The electron microscope image of the obtained ferromanganese phosphate is as follows: Figure 8 and Fig. 9 As shown, Figure 8 This is a SEM image of a manganese iron phosphate provided in Example 3 of this specification under a 50,000x electron microscope. Fig. 9 This is a SEM image of ferromanganese 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 temperature is directly raised to react after the mixed slurry is obtained, specifically:

[0070] S1: 611.5 g of manganese sulfate monohydrate crystals (wt% ≥ 99.5%) and 796 g of monoammonium phosphate crystals (wt% ≥ 99.5%) were added to 4 L of 0.6 mol / L ferrous sulfate solution, and the mixture was dissolved to obtain an iron-manganese mixed solution A;

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

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

[0073] S2: The reaction slurry is pumped into a reactor to heat up. After the temperature reaches 90°C, the mixture is kept warm for reaction 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. The mixture is then 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 in Figure 10 to Figure 11 As shown, Fig.10 This is a SEM image of the product provided in Comparative Example 1 of the present application under a 50,000x electron microscope; Fig.11 This is a SEM image of the product provided in Comparative Example 1 of this specification under a 1000x electron microscope. Fig.10 It can be seen that the direct heating iron and manganese oxidation process is faster and the supersaturation is higher, resulting in the primary particles of the prepared manganese iron phosphate monohydrate being in the form of broken crystals, and the broken crystal primary particles are stacked in an orderly manner to form secondary particles. The main difference between it and the embodiment is that the feeding method is controlled to change the morphology of the primary particles.

[0075] Comparative Example 2

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

[0077] The XRD patterns and electron microscopy images of the obtained products are shown in Fig.12 , Fig.13 As shown, Fig.12 This is the XRD diagram of the product provided in Comparative Example 2 of this specification, Fig.13 This is a SEM image of the product provided in this specification under a 50,000x electron microscope; Fig.14 This is a SEM image of the product provided in Comparative Example 2 of this specification under a 1000x electron microscope. Fig.12 and Fig.14 It can be seen that the product obtained in Comparative Example 2 is impure in crystal phase and is a mixed product of multiple manganese iron phosphates, proving that hydrogen peroxide cannot oxidize the divalent manganese salt under this condition, and its primary particles are in block form. The difference from the embodiment is that the oxidation of its manganese salt is controlled, and its hydrogen peroxide cannot oxidize the manganese salt, resulting in its product being a non-pure phase.

[0078] Test Example 1

[0079] In this test example, the ferromanganese phosphate prepared in the above-mentioned embodiment and comparative example was tested for performance, and the corresponding properties were shown in Table 1 below.

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

[0081]

[0082] As shown in Table 1, the olivine-like manganese iron phosphate Mn prepared by the present inventionx Fe (1-x) PO4·H2O, the x value is basically between 0.6 and 0.7. Among them, the ratio of manganese to iron is 6:4, and the iron element is uniformly doped in the MnPO4·H2O lattice in the form of solid solution, forming a uniform trivalent Mn x Fe (1-x) PO4·H2O products, and the manganese-iron ratio can be adjusted by changing the ratio of manganese and iron elements added.

[0083] Furthermore, in order to verify the performance of lithium iron manganese phosphate prepared from the ferromanganese phosphate of the present application, lithium source, carbon source, deionized water and additives were added to the ferromanganese phosphate obtained in Example 1, mixed, sand milled, ground to a certain particle size, spray dried, and finally calcined at 750°C in a protective gas to obtain lithium iron manganese phosphate.

[0084] Table 2 Performance comparison of lithium manganese iron phosphate of Example 1 and Comparative Example 1

[0085]

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

[0087] The above is a description of a specific embodiment of the specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in an order different from that in the embodiments and still achieve the desired results. In addition, the processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0088] The above description is only one or more embodiments of this specification and is not intended to limit this specification. For those skilled in the art, one or more embodiments of this specification may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of one or more embodiments of this specification shall be included in the scope of the claims of this specification.

Claims

1. A method for preparing ferromanganese phosphate, characterized in that: The preparation method comprises the following steps: S1: mixing an iron-manganese-phosphorus mixed solution, an oxidant, and a pH adjuster to obtain a mixed slurry; S2: Based on the volume ratio, 20% to 60% of the mixed slurry is taken to react at 60 to 100° C. for 2 to 6 hours, and then the remaining mixed slurry is added to keep warm for reaction, remove impurities and calcine to obtain ferromanganese phosphate.

2. The preparation method according to claim 1, characterized in that: 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.

3. The preparation method according to claim 1, characterized in that: The oxidant includes at least one of permanganate, peroxodisulfate, ferrate, hypochlorite and hydrogen peroxide.

4. The preparation method according to claim 1, characterized in that: The iron source of the iron-manganese-phosphorus mixed solution includes a divalent iron salt, and the divalent iron salt includes at least one of ferrous sulfate, ferrous chloride and ferrous acetate.

5. The preparation method according to claim 1, characterized in that: The manganese source of the iron-manganese-phosphorus mixed solution includes a divalent manganese salt, and the divalent manganese salt includes at least one of manganese sulfate, manganese nitrate, manganese chloride and manganese acetate.

6. The preparation method according to claim 1, characterized in that: The concentration of metal ions in the iron, manganese and phosphorus mixed solution is 0.6-2 mol / L.

7. The preparation method according to claim 1, characterized in that: The molar ratio of manganese ions to iron ions in the iron-manganese-phosphorus mixed solution is 1.4-1.8:1; and / or the molar ratio of metal ions to phosphorus in the mixed slurry is (0.4-1):

1.

8. The preparation method according to claim 1, characterized in that: In step S1, the pH value of the mixed slurry is 0.6-4.

0.

9. The preparation method according to claim 1, characterized in that: In step S1, the pH adjuster includes at least one of sulfuric acid, nitric acid, phosphoric acid, acetic acid and hydrochloric acid.

10. Use of the preparation method according to any one of claims 1 to 9 in preparing positive electrode materials for lithium-ion batteries.

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